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Lignin. Properties and Materials
 9780841216310, 9780841212480, 0-8412-1631-2

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.fw001

Lignin

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.fw001

ACS

SYMPOSIUM

SERIES

397

Lignin

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.fw001

Properties and Materials Wolfgang G . Glasser, EDITOR Virginia Polytechnic Institute and State University

Simo Sarkanen, EDITOR University of Minnesota

Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division of the American Chemical Society at the Third Chemical Congress of North America (195th National Meeting of the American Chemical Society), Toronto, Ontario, Canada, June 5-11, 1988

American Chemical Society, Washington, DC 1989

Library of Congress Cataloging-in-Publication Data

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.fw001

Lignin: properties and materials. (ACS symposium series, ISSN 0097-6156; 397) "Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division of the American Chemical Society at the Third Chemical Congress of North America (195th National Meeting of the American Chemical Society), Toronto, Ontario, Canada, June 5-11, 1988." Includes bibliographies and indexes. 1. Lignin—Congresses. 2. Polymers—Congresses. I. Glasser, Wolfgang, G., 1941- . II. Sarkanen, Simo, 1946— . III. American Chemical Society. Cellulose, Paper, and Textile Division. IV. Chemical Congress of North America (3rd: 1988: Toronto, Ont.) V . American Chemical Society. Meeting (195th: 1988: Toronto, Ont.) VI. Series. TS933.L5L54 1989 ISBN 0-8412-1631-2

661'.802

89-15069

Copyright ©1989 American Chemical Society All Rights Reserved. The appearance o f the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per-copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, MA 01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN T H E UNITED STATES O F A M E R I C A

ACS Symposium Series M . Joan Comstock, Series Editor 1989 ACS Books Advisory Board Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.fw001

Paul S. Anderson

Mary A . Kaiser

Merck Sharp & Dohme Research Laboratories

Ε. I. du Pont de Nemours and Company

Alexis T. Bell

Michael R. Ladisch

University of California—Berkeley

Harvey W. Blanch University of California—Berkeley

Malcolm H. Chisholm Indiana University

Purdue University

John L. Massingill Dow Chemical Company

Daniel M . Quinn University of Iowa

James C . Randall Alan Elzerman

Exxon Chemical Company

Clemson University

Elsa Reichmanis

John W. Finley Nabisco Brands, Inc.

Natalie Foster Lehigh University

Marye Anne Fox The University of Texas—Austin

A T & T Bell Laboratories

C. M . Roland U.S. Naval Research Laboratory

Stephen A . Szabo Conoco Inc.

Wendy A . Warr Imperial Chemical Industries

G. Wayne Ivie U.S. Department of Agriculture, Agricultural Research Service

Robert A . Weiss

University of Connecticut

Foreword Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.fw001

The A C S S Y M P O S I U M S E R I E S was founded in 1974

to provide a

medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing A D V A N C E S IN C H E M I S T R Y S E R I E S except that, in order to save time, the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable, because symposia may embrace both types of presentation.

Preface

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.pr001

T H E

INTRIGUING

MACROMOLECULAR

BEHAVIOR

of

lignin

and

its

derivatives has yielded to ever greater measures of explicability; the properties of lignin-based polymeric materials have become amenable to modification over a considerable range, even in a predicatable fashion. Significant developments in both macromolecular behavior and property modification owe a great deal to the application of physico-chemical techniques that have been made accessible through profound improvements in commercially available instrumentation and related supplies. The flexibility achieved in both open-column and highperformance size-exclusion chromatography during the past 20 years has been invaluable to progress in documenting the macromolecular properties of lignin preparations. N o less important have been the contributions from methods for absolute molecular weight determinations, such as low-angle laser light scattering, vapor pressure osmometry, and differential viscometry. It is curious that analytical ultracentrifugation occupies a more pivotal position in lignin chemistry now than before production of the classical Beckman model E instrument was discontinued more than half a decade ago. Twenty-three years have elapsed since the American Chemical Society published a book devoted to papers from a symposium exclusively about lignin. In the preface to Lignin Structure and Reactions (Advances in Chemistry Series 59, 1966), the symposium chairperson remarked that "the current presentation of lignin structure is oversimplified. . . . more ingenious work is needed to establish the sequence of units—the most prominent singular task of future lignin research." Presumably, the author of these words had in mind the sequence of intermonomer linkages rather than the units themselves (which differ only in their aromatic methoxyl substitution pattern), and from this perspective his observation could be as true in 1989 as it was in 1966. Lignin: Properties and Materials is illuminated by two keynote chapters: " T h e Lignin Paradigm" reminds readers that inadequacies still punctuate our understanding of lignin in both its native and its derivative configurations; on the other hand, "Specialty Polymers from

xiii

L i g n i n " draws attention to the spectacular vistas of new polymeric materials derived from this important biopolymer.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.pr001

The advent of lignin-based polymeric materials as putative engineering plastics represents one of several technological advancements in the field during the past 10 years. T h e characterization of polymeric materials has relied heavily upon differential scanning calorimetry and dynamic mechanical thermal analysis, and scanning electron microscopy has provided invaluable confirmatory evidence about blend morphology. Successful incorporation as integral components, rather than as mere fillers or extenders, in useful polymeric materials clearly represents a potential for adding high value to industrial byproduct lignins. What "the most prominent singular task of future lignin research" would be in this context asks for speculation beyond the scope of a preface, but the answer may unfold in the productive developments that are destined to appear during the coming decade. The book itself is divided into six sections. Collectively, the chapters provide a perspective that anticipates the future. T h e book's usefulness should extend to academic research groups and industrial organizations alike. Acknowledgments We acknowledge with gratitude the individual authors; Kathryn Hollandsworth, who has so skillfully and patiently prepared the final copy for this book; and Cheryl Shanks, A C S Books Acquisitions Editor. Particular thanks are due to Daishowa Chemicals, the Department of Energy, Empresa Nacional de Celulosas S A , Georgia-Pacific Corporation, I T T Rayonier, Westvaco Corporation, and Weyerhaeuser Corporation, whose generous support contributed so much in very real terms to ensuring the success of the symposium. It has been for us a distinct privilege to have been associated with such an interesting and absorbing enterprise. W O L F G A N G G. G L A S S E R Department of W o o d Science and Forest Products Virginia Polytechnic Institute and State University Blacksburg, VA 24061 SIMO S A R K A N E N Department of Forest Products University of Minnesota St. Paul, MN 55108 February 21, 1989 xiv

Chapter 1

The Lignin Paradigm D . A. I. Goring

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch001

Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario M5S 1A4, Canada

Evidence supp o r t i n g the o r i g i n a l p a r a d i g m of l i g n i n i n w o o d as a r a n d o m , t h r e e - d i m e n s i o n a l network p o l y m e r is r e v i e w e d . M o r e recent results w h i c h do not fit t h i s s i m p l e p i c t u r e are discussed. A m o d i f i e d p a r a d i g m is proposed i n w h i c h l i g n i n in w o o d is c o m p r i s e d of several types of network w h i c h differ f r o m each other b o t h u l t r a s t r u c t u r a l l y a n d chemically. W h e n w o o d is d e l i g n i fied, the properties of the macromolecules m a d e soluble reflect the properties of the network f r o m w h i c h they are derived. L i g n i n i n w o o d m a y be considered to be a r a n d o m t h r e e - d i m e n s i o n a l netw o r k p o l y m e r c o m p r i s e d of p h e n y l p r o p a n e u n i t s l i n k e d together i n different ways. W h e n w o o d is delignified the properties of the macromolecules m a d e soluble reflect the properties of the network f r o m w h i c h they are d e r i v e d . F o r several decades, the above has been the generally accepted p a r a d i g m for the s t r u c t u r e of l i g n i n i n w o o d (1,2). I n the present paper, some of the evidence i n favor of t h i s p a r a d i g m is reviewed. H o w e v e r , c e r t a i n recently discovered aspects of the b e h a v i o r of l i g n i n do not fit easily i n t o the s i m p l e concept of a r a n d o m t h r e e - d i m e n s i o n a l network p o l y m e r . These are discussed a n d a n a t t e m p t is m a d e to m o d i f y the o r i g i n a l p a r a d i g m so t h a t i t agrees more closely w i t h e x p e r i m e n t a l o b s e r v a t i o n . Behavior of L i g n i n C o m p a t i b l e w i t h the P a r a d i g m of a R a n d o m , Three-Dimensional Network Polymer Non-Crystalliniiy. L i g n i n seems t o be a m o r p h o u s (3). N o one has ever r e p o r t e d a n y evidence of c r y s t a l l i n e order i n l i g n i n . A n d the molecule does not appear to be o p t i c a l l y active (3), u n u s u a l for a b i o p o l y m e r . S u c h b e h a v ior is w h a t m i g h t be expected f r o m a r a n d o m , t h r e e - d i m e n s i o n a l n e t w o r k . However, w i t h the m o r e sensitive m e t h o d s of a n a l y s i s available today, i t 0097-6156/89/0397-0002$06.00A) © 1989 American Chemical Society

1.

GORING

The Lignin Paradigm

3

m i g h t be a g o o d i d e a t o check whether t h i s lack of c r y s t a l l i n i t y a n d o p t i c a l a c t i v i t y is, i n d e e d , absolute.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch001

Insolubility. T h e n we have the n o t o r i o u s i n s o l u b i l i t y o f l i g n i n i n v i r t u a l l y a l l s i m p l e solvents. A s s h o w n b y B r a u n s (4), a s m a l l p r o p o r t i o n (2-3%) of the l i g n i n i n w o o d can be dissolved i n e t h a n o l . If the w o o d is e x t e n s i v e l y m i l l e d , B j o r k m a n f o u n d t h a t 5 0 % or more o f the l i g n i n f r o m spruce c a n be e x t r a c t e d w i t h aqueous dioxane (5). However, the m i l l i n g is so severe t h a t i t is l i k e l y t h a t c h e m i c a l b o n d s are b r o k e n (6). T h u s , some t y p e o f covalent b o n d r u p t u r e seems to be necessary to m a k e the l i g n i n s o l u b l e . T h i s w o u l d be expected o f a t h r e e - d i m e n s i o n a l network. N o t e t h a t , once the n e t w o r k has been degraded, there is n o t h i n g u n u s u a l about the s o l u b i l i t y o f the fragments, as s h o w n b y Schuerch (7) a n d b y L i n d b e r g (8). Molecular Weight. B y reversing F l o r y ' s theory of t r i f u n c t i o n a l p o l y m e r i z a t i o n , i t c a n be s h o w n t h a t , w h e n a r a n d o m crosslinked t h r e e - d i m e n s i o n a l gel is degraded, there is a t r e n d i n the m o l e c u l a r weight o f the fragments p r o d u c e d (9). S m a l l molecules become soluble e a r l y i n the d e g r a d a t i o n , w h i l e larger molecules are released later i n the process. T h i s u s u a l l y h a p pens w h e n l i g n i n i n w o o d is m a d e soluble b y c h e m i c a l t r e a t m e n t (10-12). T h e theory also predicts t h a t the fractions m a d e soluble w i l l c o n t a i n a s u b s t a n t i a l p r o p o r t i o n of low m o l e c u l a r weight m a t e r i a l w i t h a p o l y d i s p e r s e , h i g h m o l e c u l a r weight t a i l (9). F r a c t i o n a t i o n o f k r a f t l i g n i n s m a d e soluble i n a continuous flow process has confirmed t h i s b e h a v i o r (12). T h e d e g r a d a t i o n of a gel has been a n a l y z e d i n more d e t a i l b y B o l k e r a n d his coworkers (13-15) a n d b y Y a n a n d his coworkers (16-18). T h e results, i n general, s u p p o r t the concept o f l i g n i n i n w o o d as a r a n d o m , t h r e e - d i m e n s i o n a l network polymer. Conformation of the Macromolecule. I n s o l u t i o n , macromolecules c a n have a w i d e v a r i e t y o f shapes or conformations. T h e s i m p l e s t is the s o l i d sphere or E i n s t e i n sphere. It is a r o u n d b a l l , i m p e r m e a b l e t o solvent. T h e b a l l m a y be stretched i n t o a p r o l a t e e l l i p s o i d like a f o o t b a l l or flattened i n t o a n o b l a t e e l l i p s o i d like a flying saucer. M a n y soluble proteins have c o n f o r m a t i o n s t h a t a p p r o x i m a t e ellipsoids. If a p r o l a t e e l l i p s o i d is stretched e n o u g h , i t becomes a r o d . C e r t a i n v i r u s macromolecules are r o d l i k e . T h e n there are flexible linear p o l y m e r s w h i c h c u r l u p i n s o l u t i o n to give a r a n d o m cell. If the c h a i n is stiff, such as i n cellulose or i n D N A , the c o i l becomes h i g h l y e x p a n d e d . C o n f o r m a t i o n i n s o l u t i o n is i n d i c a t e d b y the way i n w h i c h the h y d r o d y n a m i c properties of the macromolecules change w i t h change i n m o l e c u l a r weight. F r o m trends i n the i n t r i n s i c viscosity, the s e d i m e n t a t i o n coefficient, or the diffusion constant w i t h m o l e c u l a r weight we c a n l e a r n s o m e t h i n g a b o u t the c o n f o r m a t i o n o f the molecule i n s o l u t i o n (19,20). W h e r e do soluble l i g n i n s fit w i t h respect to c o n f o r m a t i o n ? T h e y seem t o be r a t h e r c o m p a c t molecules i n s o l u t i o n — t h e opposite o f the h i g h l y e x p a n d e d cellulose molecule. T h e y are not as c o m p a c t as a s i m p l e s o l i d sphere. Y e t , the chains o f the l i g n i n macromolecules i n s o l u t i o n are more densely packed t h a n those o f a linear flexible p o l y m e r s u c h as p o l y s t y r e n e

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch001

4

LIGNIN: PROPERTIES AND MATERIALS

(19,20). S u c h b e h a v i o r is w h a t w o u l d be e x p e c t e d for s o l u b l e fragments o f a r a n d o m t h r e e - d i m e n s i o n a l network p o l y m e r . Before l e a v i n g the t o p i c o f c o n f o r m a t i o n , i t s h o u l d be n o t e d t h a t there do not a p p e a r t o be m u c h interest i n t h i s p r o p e r t y t o d a y . I n earlier t i m e s , several schools i n c l u d e d c o n f o r m a t i o n a l studies i n t h e i r c h a r a c t e r i z a t i o n o f soluble l i g n i n s (19). R e c e n t l y , o n l y P l a a n d his g r o u p (20) s e e m t o be t a k i n g t h i s p r o p e r t y seriously. Y e t i t is i m p o r t a n t , b o t h t o the u n d e r s t a n d i n g o f d e l i g n i f i c a t i o n a n d t o the use o f l i g n i n s as colloids a n d d i s p e r s a n t s . C o n f o r m a t i o n is also i m p o r t a n t i n the use o f size-exclusion c h r o m a t o g raphy. I n the m a n y papers w h i c h have been g r a c i o u s l y d e d i c a t e d t o the a u t h o r (21-23), there are t e n or m o r e i n w h i c h G P C or H P L C has been used t o determine the m o l e c u l a r weight a n d i t s d i s t r i b u t i o n . It s h o u l d be r e m e m b e r e d , however, t h a t the e x c l u s i o n p h e n o m e n o n depends n o t so m u c h o n m o l e c u l a r weight b u t r a t h e r o n h y d r o d y n a m i c v o l u m e . T h u s , t o give r e l i a b l e m o l e c u l a r weights, the c o l u m n s h o u l d be c a l i b r a t e d , n o t w i t h p o l y s t y r e n e , b u t w i t h a m o r e c o m p a c t l i g n i n - l i k e molecule, preferably w i t h n a r r o w fractions o f the soluble l i g n i n derivative under s t u d y . T h e f r a c t i o n s used for c a l i b r a t i o n s h o u l d be characterized i n d e p e n d e n t l y by a n absolute m e t h o d such as u l t r a c e n t r i f u g e s e d i m e n t a t i o n e q u i l i b r i u m or low angle l i g h t s c a t t e r i n g . H o w e v e r , these absolute methods are t i m e - c o n s u m i n g a n d expensive. P e r h a p s i n t r i n s i c v i s c o s i t y s h o u l d be l o o k e d at a g a i n . T h i s p a r a m e t e r gives the effective h y d r o d y n a m i c specific v o l u m e o f the m o l e c u l e . B e n o i t et al. (24) have s h o w n t h a t the p r o d u c t [rj\ M is u n i q u e l y r e l a t e d t o the e l u t i o n v o l u m e . T h u s , b y measurement o f i n t r i n s i c v i s c o s i t y o n selected f r a c t i o n s , a p o l y s t y r e n e c a l i b r a t i o n can be converted t o a l i g n i n c a l i b r a t i o n w i t h l i t t l e effort a n d s i m p l e e q u i p m e n t . It is i n t e r e s t i n g t o note t h a t t w o rep o r t s o f the use o f a n o n - l i n e differential viscometer w i t h G P C are i n c l u d e d i n the present s y m p o s i u m v o l u m e (25-26). Behavior of Lignin Incompatible with the P a r a d i g m of a R a n d o m , Three-Dimensional Network Polymer F r o m the discussion i n the previous sections we see t h a t the b e h a v i o r o f the p r o t o l i g n i n i n w o o d a n d the p a t t e r n o f i t s subsequent d e g r a d a t i o n a n d s o l u t i o n are c o m p a t i b l e , i n a b r o a d sense, w i t h the p a r a d i g m o f a r a n d o m t h r e e - d i m e n s i o n a l network p o l y m e r . T h e r e emerge, however, several aspects o f the p r o b l e m w h i c h do not fit easily w i t h the s i m p l e p a r a d i g m given above. I n the f o l l o w i n g sections some o f these anomalies are discussed. Molecular Weight Distribution. T h e gel d e g r a d a t i o n t h e o r y a p p l i e d t o a single network predicts t h a t the sol f r a c t i o n w i l l be polydisperse b u t u n i m o d a l (9). T h u s , there s h o u l d be o n l y one peak i n the m o l e c u l a r weight d i s t r i b u t i o n c u r v e — e x c e p t at low molecular weights w h e n a s u b s t a n t i a l p r o p o r t i o n o f oligomers are present. Y e t m a n y a u t h o r s have r e p o r t e d b i m o d a l d i s t r i b u t i o n s o f m o l e c u l a r weight i n soluble l i g n i n s . S u c h b i m o d a l b e h a v i o r t u r n s u p not o n l y i n organosolv l i g n i n s (27-29) b u t also i n l i g n i n s m a d e soluble i n the c h e m i c a l p u l p i n g o f w o o d (12,30). A s the r e s o l u t i o n o f the c h r o m a t o g r a p h i c techniques are i m p r o v e d , the b r o a d b i m o d a l p a t t e r n s

1.

GORING

The Lignin Paradigm

5

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch001

are b e i n g resolved i n t o d i s t r i b u t i o n s w i t h several m a x i m a (31-38). S o m e o f these c o m p o n e n t s are well-defined low m o l e c u l a r weight oligomers o f the l i g n i n m a c r o m o l e c u l e . O t h e r s seem to be o f higher m o l e c u l a r weight a n d m o r e i n d e t e r m i n a t e . S u c h paucidisperse b e h a v i o r is not r e a l l y c o m p a t i b l e w i t h a r a n d o m n e t w o r k . It suggests a r e p e t i t i v e p a t t e r n o f weak l i n k s w h i c h allows the p o l y m e r t o be degraded i n t o separate families o f molecules, each w i t h a c h a r a c t e r i s t i c m o l e c u l a r weight a n d , p e r h a p s , c h e m i c a l c o m p o s i t i o n . Association. S e v e r a l a u t h o r s have p o s t u l a t e d t h a t some l i g n i n s i n s o l u t i o n are n o t covalent p o l y m e r s i n the n o r m a l sense, b u t r a t h e r a n a s s o c i a t i o n o f s m a l l e r molecules h e l d together b y v a r i o u s types o f non-covalent l i n k ages (30,34,36,39,40,41). S. S a r k a n e n a n d his coworkers have presented s t r o n g evidence t h a t low m o l e c u l a r weight l i g n i n f r a c t i o n s show considera b l y h i g h e r m o l e c u l a r weights i n c e r t a i n solvents (34,41). A n d the effect appears t o be reversible. T h e association p h e n o m e n o n raises the p o s s i b i l i t y t h a t l i g n i n i n w o o d is c o m p o s e d o f low m o l e c u l a r weight molecules. W h e n these are m a d e s o l u b l e they associate i n t o complexes o f higher m o l e c u l a r weight. T h i s p i c t u r e is not r e a l l y i n accord w i t h the i d e a o f a r a n d o m , t h r e e - d i m e n s i o n a l n e t w o r k p o l y m e r . It s h o u l d be n o t e d , however, t h a t a h i g h m o l e c u l a r weight lignosulfonate gave constant m o l e c u l a r weight i n solvents as different as 0.1 M aqueous s o d i u m c h l o r i d e a n d d i m e t h y l sulfoxide, w h i c h i n d i c a t e s a covalent s t r u c t u r e for the m a c r o m o l e c u l e (42). N o n - c o v a l e n t association m a y not be the o n l y w a y i n w h i c h h i g h m o l e c u l a r weight l i g n i n is p r o d u c e d f r o m smaller molecules. T h e c o n j u g a t e d , p h e n o l i c n a t u r e o f the l i g n i n m o n o m e r s makes t h e m prone t o " c o n d e n s a t i o n " reactions b o t h i n a c i d a n d alkaline m e d i a (44-46). T h u s , d e l i g n i f i c a t i o n m a y b e i n v a r i a b l y a c c o m p a n i e d b y p o l y m e r i z a t i o n . A g a i n , such b e h a v i o r goes b e y o n d the s i m p l e p a r a d i g m of the d e g r a d a t i o n o f a t h r e e - d i m e n s i o n a l network p o l y m e r . However, i t s h o u l d be r e m e m b e r e d t h a t very few e x a m ples have been r e p o r t e d i n w h i c h the m o l e c u l a r weights o f soluble l i g n i n s have been increased b y f u r t h e r t r e a t m e n t i n the m e d i u m used for d e l i g n i fication (47). I f condensation does o c c u r , perhaps i t takes place r a p i d l y , t h u s p r o d u c i n g a network p o l y m e r w h i c h m u s t t h e n be degraded b y the d e l i g n i f i c a t i o n reactions. Topochemistry. M a n y a u t h o r s have sought to characterize the c h e m i c a l n a t u r e o f l i g n i n . T h i s work has been extended i n t o a s t u d y o f the c h e m i c a l s t r u c t u r e of l i g n i n i n the v a r i o u s m o r p h o l o g i c a l regions o f the cell w a l l . It n o w seems c e r t a i n t h a t i n b o t h h a r d w o o d s a n d softwoods there are differences between the chemical s t r u c t u r e o f l i g n i n i n the m i d d l e l a m e l l a a n d the secondary w a l l (48-56), a l t h o u g h there are s t i l l m a n y questions t o be resolved (57-59). T h e r e are also c h e m i c a l differences between the l i g n i n s i n the fiber a n d vessel walls o f b i r c h w o o d (48,49,52,56,60). T e r a s h i m a et al (61) a n d B e a t s o n (62) have suggested t h a t these t o p o c h e m i c a l differences are r e l a t e d t o the b i o s y n t h e t i c sequence o f l i g n i f i c a t i o n i n p l a n t tissue. T h e p a r a d i g m of a n infinite r a n d o m t h r e e - d i m e n s i o n a l network p o l y mer implies a u n i f o r m chemistry throughout. T h e topochemical behavior

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of lignin indicates that, from a structural chemical point of view, more t h a n one t y p e o f network exists i n w o o d . S u c h t o p o c h e m i c a l differences i n c h e m i c a l s t r u c t u r e w i l l have a n i m p o r t a n t b e a r i n g o n the course of d e l i g n i f i c a t i o n reactions a n d the properties of the r e s u l t i n g p u l p s (62-70). Utirastructure. P e r h a p s the most c o m p e l l i n g reason for seeking a n a l t e r n a tive p a r a d i g m for the n a t u r e o f l i g n i n is the u l t r a s t r u c t u r e o f the p o l y s a c c h a rides i n the cell w a l l . T h e i r arrangement is a n y t h i n g b u t r a n d o m . M i c r o f i b rils are p r o b a b l y single crystals of cellulose chains (71,72). A l t h o u g h the a r r a n g e m e n t o f the hemicelluloses is not k n o w n for c e r t a i n , i t seems l i k e l y t h a t the molecules l i n e u p i n the d i r e c t i o n o f the cellulose m i c r o f i b r i l s (7375). T h e m i c r o f i b r i l s themselves are l a i d d o w n i n c o m p l e x p a t t e r n s (76,77). I n the S2 layer, there is evidence o f a l a m e l l a r u l t r a s t r u c t u r e w i t h the i n t e r l a m e l l a r distance b e i n g e q u a l t o about t w i c e the w i d t h o f the m i c r o f i b r i l , i.e., 7-10 n m (78-82). I n viev: of the fact t h a t most o f i t is i n the secondary w a l l (83-85), h o w can l i g n i n be regarded as a r a n d o m network w h e n i t is the m i r r o r i m a g e on a molecular scale of the h i g h l y o r g a n i z e d p o l y s a c c h a ride u l t r a s t r u c t u r e ? T h e l i g n i n lamellae are p r o b a b l y a b o u t 2 n m t h i c k , enough r o o m for 2 t o 4 p h e n y l p r o p a n e m o n o m e r s . It seems a l m o s t c e r t a i n t h a t c o n s t r a i n t s o f space w i l l impose n o n - r a n d o m n e s s o n the crosslinked n e t w o r k . Here i t is i n t e r e s t i n g to note t h a t A t a l l a has f o u n d evidence i n d i c a t i n g t h a t the a r o m a t i c rings i n l i g n i n are aligned p r e f e r e n t i a l l y i n the d i r e c t i o n t a n g e n t i a l to the secondary w a l l (86). W e s h o u l d note, also, t h a t the l i g n i n i n the S2 layers is c h e m i c a l l y b o n d e d t o the p o l y s a c c h a r i d e m o i e t y (87-92). S u c h b o n d s occur not o n l y i n w o o d b u t m a y be f o r m e d d u r i n g c h e m i c a l p u l p i n g (93,94). E v e n i f the l i g n i n - c a r b o h y d r a t e b o n d s are r e s t r i c t e d t o the hemicelluloses (95), the regu l a r i t y o f these c h a i n molecules w i l l p r o b a b l y impose some n o n - r a n d o m n e s s o n the l i g n i n s t r u c t u r e . T h e l a m e l l a r s t r u c t u r e o f the cell w a l l w i l l p r o b a b l y affect the c o n f o r m a t i o n of the l i g n i n macromolecules dissolved w h e n w o o d is d e l i g n i f i e d . T h i s is p a r t i c u l a r l y t r u e w h e n h i g h m o l e c u l a r weight l i g n i n s diffuse out of the fibers d u r i n g the w a s h i n g of k r a f t p u l p (96,97). T h e m o l e c u l a r weights o f the fractions o f l i g n i n leached out o f the cell w a l l are of the order of h u n d r e d s o f t h o u s a n d s (98). S p h e r i c a l l i g n i n macromolecules of t h i s mass w o u l d be too large to pass t h r o u g h the porous s t r u c t u r e o f the cell w a l l . It is possible t h a t i n the w a l l they are flatish covalently free fragments o f the l i g n i n l a m e l l a e , w h i c h diffuse t h r o u g h the i n t e r l a m e l l a r spaces i n t o s o l u t i o n . Because the c h a i n s are flexible, these l a m e l l a r fragments f o l d i n s o l u t i o n t o a n a p p r o x i m a t e l y s p h e r i c a l c o n f o r m a t i o n . S u c h a c o n f o r m a t i o n w o u l d be expected to be more c o m p a c t t h a n t h a t o f a r a n d o m c o i l b u t m o r e exp a n d e d t h a n t h a t of a n E i n s t e i n sphere, i n accord w i t h the h y d r o d y n a m i c b e h a v i o r n o t e d earlier i n the paper. I n s u p p o r t o f t h i s concept, we find t h a t l i g n i n macromolecules, i f spread o n the surface of a non-solvent (99,100) or deposited o n a carbon-coated g r i d for electron m i c r o s c o p y (101), assume a flat c o n f o r m a t i o n w i t h a thickness of a b o u t 2 n m . It seems t h a t the c o n f o r m a t i o n of the macromolecules m a d e soluble, reflects the u l t r a s t r u c t u r e o f the cell w a l l f r o m w h i c h they have been e x t r a c t e d .

1.

GORING

The Lignin Paradigm

7

O f course, t h e p i c t u r e given i n t h e p r e c e d i n g p a r a g r a p h cannot a p p l y t o t h e almost pure l i g n i n i n t h e t r u e m i d d l e l a m e l l a . Here t h e l a m e l l a r thickness i s u s u a l l y more t h a n 100 n m (83,84). T h e concept o f a r a n d o m t h r e e - d i m e n s i o n a l network p o l y m e r w o u l d seem t o be a p p r o p r i a t e for s u c h a t h i c k layer. However, t h e t r u e m i d d l e l a m e l l a p r o b a b l y c o n t a i n s less t h a n 2 0 % o f t h e t o t a l l i g n i n (83,84,102). T h u s , l i g n i n f r o m t h e s e c o n d a r y w a l l w i l l be the dominant fraction i n most preparations f r o m whole wood.

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A Modified Paradigm F r o m the foregoing, i t seems t h a t we need a b e t t e r p a r a d i g m for l i g n i n . T h e o l d , c o m f o r t a b l e concept o f a n infinite r a n d o m , t h r e e - d i m e n s i o n a l network p o l y m e r i s t o o s i m p l e t o encompass e v e r y t h i n g we k n o w a b o u t l i g n i n a n d its soluble derivatives. T o give a b e t t e r fit w i t h the e x p e r i m e n t a l l y observed b e h a v i o r o f l i g n i n , t h e o r i g i n a l p a r a d i g m m a y be m o d i f i e d as follows: L i g n i n i n t h e t r u e m i d d l e l a m e l l a o f w o o d is a r a n d o m threed i m e n s i o n a l network p o l y m e r c o m p r i s e d o f p h e n y l p r o p a n e m o n ­ omers l i n k e d together i n different ways. L i g n i n i n t h e secondary w a l l is a n o n r a n d o m t w o - d i m e n s i o n a l network p o l y m e r . T h e c h e m ­ i c a l s t r u c t u r e o f the m o n o m e r s a n d linkages w h i c h c o n s t i t u t e these networks differ i n different m o r p h o l o g i c a l regions ( m i d d l e l a m e l l a vs. secondary w a l l ) , different types o f cell (vessels v s . fibers), a n d different types o f w o o d (softwoods v s . h a r d w o o d s ) . W h e n w o o d is delignified, t h e properties o f the macromolecules m a d e soluble reflect t h e properties o f the network f r o m w h i c h they are d e r i v e d . O f course, t h e m o d i f i e d p a r a d i g m given above is n o t e n t i r e l y satisfac­ tory. I t is silent o n t h e question o f the association o f l i g n i n molecules. A l s o , it does n o t take i n t o account t h e p o s s i b i l i t y o f c o n d e n s a t i o n reactions. T h e t e r m " n o n r a n d o m " begs for a clearer d e f i n i t i o n w h i c h t h e p a r a d i g m does not p r o v i d e . P e r h a p s t h e clearest concept i n i t is t h e t w o - d i m e n s i o n a l n e t ­ w o r k . A f t e r a l l , most nets are t w o - d i m e n s i o n a l ! I n spite o f its f a i l i n g s , t h e m o d i f i e d p a r a d i g m is p r o b a b l y t h e best we c a n d o at t h e present t i m e . W e s h o u l d n o t b e s u r p r i s e d , however, t h a t , as t h e b e h a v i o r o f the p r o t o l i g n i n i n w o o d is f u r t h e r e l u c i d a t e d , a n e n t i r e l y n e w p a r a d i g m w i l l emerge.

Literature Cited 1. Nokihara, E . ; Tuttle, M . J.; Felicetta, V . F.; McCarthy, J . L. J. Am. Chem. Soc. 1957, 79, 4495. 2. Goring, D. A. I. In Lignins; Sarkanen, Κ. V.; Ludwig, C. H., Eds.; Wiley-Interscience: New York, 1971; p. 698. 3. Sarkanen, Κ. V . In The Chemistry of Wood; Browning, B. L . , Ed.; Interscience: New York, 1963; p. 278. 4. Brauns, F. E . J. Am. Chem. Soc. 1939, 6 1 , 2120. 5. Björkman, A. Svensk Papperstidn. 1956, 59, 477. 6. Chang, H.-M.; Cowling, Ε. B.; Brown, W.; Adler, E.; Miksche, G . Holzforschung 1975, 29, 153.

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7. 8. 9. 10. 11. 12.

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13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

26.

27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

LIGNIN: PROPERTIES AND MATERIALS

Schuerch, C . J. Am. Chem. Soc. 1952, 74, 5061. Lindberg, J . J. Suomen Kemistilehti 1967, B40, 225. Szabo, A.; Goring, D. A . I. Tappi 1968, 51, 440. Rezanowich, A.; Yean, W. Q.; Goring, D. A . I. Svensk Papperstidn. 1963, 66, 141. Yean, W. Q.; Goring, D. A. I. Pulp Paper Mag. Can. 1964, 65, T-127. McNaughton, J . G.; Yean, W. Q.; Goring, D. A . I. Tappi 1967, 50, 548. Bolker, H. I.; Brenner, H. S. Science 1970, 170, 173. Berry, R. M.; Bolker, H. I. J. Pulp Paper Sci. 1986, 12, J16. Argyropoulos, D. S.; Bolker, H. I. J. Wood Chem. Technol. 1987, 7, 499. Yan, J . F. Macromolecules 1981, 14, 1438. Yan, J . F.; Johnson, D. C. J. Appl. Polym. Sci. 1981, 26, 1623. Yan, J . F.; Pla, F.; Kondo, R.; Dolk, M . ; McCarthy, J . L. Macromolecules 1984, 17, 2137. Goring, D. A . I. In Lignins; Sarkanen, K. V.; Ludwig, C. H., Eds.; Wiley-Interscience: New York, 1971; p. 705. Pla, F.; Robert, A. Holzforschung 1984, 38, 37. Holzforschung 1986, Suppl., 40, 5-157; 1986, 40, 325-338. J. Wood Chem. Technol. 1987, 7, 1-131. J. Cell. Chem. Technol. 1987, 21, 215-327, 371-395. Grubisic, Z.; Rempp, P.; Benoit, H. Polym. Lett. 1967, 5, 753. Siochi, E . J . ; Haney, M . A.; Mahn, W.; Ward, T . C . In Lignin: Properties and Materials; Glasser, W. G.; Sarkanen, S., Eds.; American Chemical Society: Washington, DC, 1989. Himmel, M . E.; Tatsumoto, K.; Oh, K. K.; Grohmann, K.; Johnson, D. K.; Chum, H. L. In Lignin: Properties and Materials; Glasser, W. G.; Sarkanen, S., Eds.; American Chemical Society: Washington, D C , 1989. Brown, W.; Cowling, E . B.; Falkehag, S. I. Svensk Papperstidn. 1968, 71, 811. Wayman, M.; Obiaga, T . I. Tappi 1974, 57, 123. Wegener, G.; Fengel, D. Wood Sci. Technol. 1977, 11, 133. Lindström, T . Colloid Polym. Sci. 1979, 257, 277. Shaw, A. C.; Dignam, M . Can. J. Chem. 1957, 35, 322. Forss, K.; Fremer, K. E . Pap. Puu 1965, 47, 443. Gupta, P. R.; McCarthy, J . L. Macromolecules 1968, 1, 495. Connors, W. J.; Sarkanen, S.; McCarthy, J . L. Holzforschung 1980, 34, 80. Lewis, N. G.; Goring, D. A. I.; Wong, A. Can. J. Chem. 1983, 61, 416. Chum, H. L.; Johnson, D. K.; Tucker, M . P.; Himmel, M . E . Holzforschung 1987, 41, 97. Woerner, D.; McCarthy, J . L. Tappi 1987, 70, 126. Lewis, N. G.; Eberhardt, T . L.; Luthe, C. E . Tappi 1988, 71, 141. Gross, S. K.; Sarkanen, K. V.; Schuerch, C. Anal. Chem. 1958, 30, 518. Benko, J . Tappi 1964, 47, 508.

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1.

GORING

The Lignin Paradigm

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41. Sarkanen, S.; Teller, D. C . ; Hall, J.; McCarthy, J. L . Macromolecules 1981, 14, 426. 42. Yean, W . Q.; Goring, D. A . I. J. Appl. Polym. Sci. 1970, 14, 1115. 43. Lai, Y. Z.; Sarkanen, K . V . In Lignins; Sarkanen, K . V . ; Ludwig, C . H . , Eds.; Wiley-Interscience: New York, 1971; p. 182. 44. Marton, J. In Lignins; Sarkanen, K . V . ; Ludwig, C . H . , Eds.; Wiley-Interscience:New York, 1971; p. 658. 45. Gierer, J. Holzforschung 1982, 36, 43. 46. Gellerstedt, G . ; Lindfors, E . - L . Nordic Pulp Paper J. 1987, 2, 71. 47. Argyropoulos, D . S.; Bolker, H . I. J. Wood Chem. Technol. 1987, 7, 1. 48. Fergus, B. J.; Goring, D. A . I. Holzforschung 1970, 24, 113. 49. Musha, Y . ; Goring, D. A . I. Wood Sci. Technol. 1975, 9, 45. 50. Yang, J.-M.; Goring, D. A . I. Can. J. Chem. 1980, 58, 2411. 51. Hardell, H.-L.; Leary, G . J.; Stoll, M . ; Westermark, U . Svensk Papperstidn. 1980, 83, 44. 52. Hardell, H.-L.; Leary, G . J.; Stoll, M . ; Westermark, U . Svensk Papperstidn. 1980, 83, 71. 53. Cho, N. S.; Lee, J. Y . ; Meshitsuka, G . ; Nakano, J. Mokuzai Gakkaishi 1980, 26, 527. 54. Whiting, P.; Goring, D. A . I. Pap. Puu 1982, 64, 592. 55. Whiting, P.; Goring, D. A . I. Wood Sci. Technol. 1982, 16, 261. 56. Saka, S.; Goring, D. A . I. In Biosynthesis and Biodegradation of Wood Components; Higuchi, T . , Ed.; Academic: New York, 1985; p. 51. 57. Kolar, J. J.; Lindgren, B. O.; Roy, T . K . Cell. Chem. Technol. 1979, 13, 491. 58. Obst, J. R.; Ralph, J. Holzforschung 1983, 37, 297. 59. Westermark, U . Wood Sci. Technol. 1985, 19, 223. 60. Wolter, K. E . ; Harkin, J. M . ; Kirk, T . K . Physiol. Plant 1974, 31, 140. 61. Terashima, N.; Fukushima, K . ; Takabe, K . Holzforschung 1986, 40 Suppl., 101. 62. Beatson, R. P. Holzforschung 1986, 40 Suppl., 11. 63. Procter, A . R.; Yean, W . Q.; Goring, D . A . I. Pulp Paper Mag. Can. 1967, 68, T445. 64. Fergus, B. J.; Goring, D . A . I. Pulp Paper Mag. Can. 1969, 70, T314. 65. Wood, J. R.; Ahlgren, P. A . ; Goring, D. A . I. Svensk Papperstidn. 1972, 75, 1. 66. Saka, S.; Thomas, R. J.; Gratzl, J. S.; Abson, D. Wood Sci. Technol. 1982, 16, 139. 67. Beatson, R. P.; Gancet, C . ; Heitner, C . Tappi J. 1984, 67(3), 82. 68. Berry, R. M . ; Bolker, H . I. J. Wood Sci. Technol. 1987, 7, 25. 69. Westermark, U . ; Samuelsson, B. Holzforschung 1986, 40 Suppl., 139. 70. Heazel, T . E . ; McDonough, T . J. Tappi J. 1988, 86(3), 129. 71. Manley, R. St.J. J. Polym. Sci. A-2 1971, 9, 1025. 72. Revol, J.-F.; Goring, D. A . I. Polymer 1983, 24, 1547. 73. Preston, R. D. In The Formation of Wood in Forest Trees; Zimmerman, M . H . , Ed.; Academic: New York, 1964; p. 169.

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10

LIGNIN: PROPERTIES AND MATERIALS

74. Marchessault, R. H. In Chimie et Biochimie de la Lignine, de la Cellulose et des Hémicellulose; Les Imprimeries Réunies de Chambéry: E d . Grenoble, 1964; p. 287. 75. Fengel, D . Tappi 1970, 53, 497. 76. Dunning, C . E. Tappi 1969, 52, 1326. 77. Kishi, K.; Harada, H.; Saiki, H . Mokuzai Gakkaishi 1979, 25, 521. 78. Scallan, A . M . Wood Sci. 1974, 6, 266. 79. Kerr, A . J.; Goring, D . A . I. Cell. Chem. Technol. 1975, 9, 563. 80. Ruel, K.; Barnoud, F.; Goring, D . A . I. Wood Sci. Technol. 1978, 12, 287. 81. Ruel, K.; Barnoud, F.; Goring, D. A . I. Cell. Chem. Technol. 1979, 13, 429. 82. Fengel, D.; Shao, X . Wood Sci. Technol. 1984, 18, 103. 83. Fergus, B. J.; Procter, A . R.; Scott, J. A . N.; Goring, D . A . I. Wood Sci. Technol. 1969, 3, 117. 84. Wood, J. R.; Goring, D . A . I. Pulp Paper Mag. Can. 1971, 72, T95. 85. Saka, S.; Goring, D . A . I. Holzforschung 1988, 42, 149. 86. Atalla, R. H . J. Wood Chem. Technol. 1987, 7, 115. 87. Fengel, D.; Wegner, G . Wood: Chemistry, Structure, Reactions; de Gruyter: Berlin, 1984; p. 167. 88. Meshitsuka, G.; Lee, Z. Z.; Nakano, J.; Eda, S. J. Wood Chem. Technol. 1982, 2, 251. 89. Iversen, T . Wood Sci. Technol. 1985, 19, 243. 90. Papadopoulos, J.; Defaye, J. J. Wood Chem. Technol. 1986, 6, 203. 91. Joseleau, J.-P.; Kesraoui, R. Holzforschung 1986, 40, 163. 92. Minor, J. L . J. Wood Chem. Technol. 1986, 6, 185. 93. Glasser, W . G.; Barnett, C . A . Tappi 1979, 62(8), 101. 94. Gierer, J.; Wännström, S. Holzforschung 1986, 40, 347. 95. Eriksson, Ö.; Goring, D . A . I.; Lindgren, B. O . Wood Sci. Technol. 1980, 14, 267. 96. Favis, B. D.; Choi, P. M . K . ; Adler, P. M . ; Goring, D . A . I. Trans. Tech. Sect. Can. Pulp Pap. Assoc. 1981, 7, TR35. 97. Favis, B. D.; Goring, D . A . I. J. Pulp Paper Sci. 1984, 10, J139. 98. Favis, B. D.; Yean, W . Q.; Goring, D . A . I. J. Wood Chem. Technol. 1984, 4, 313. 99. Luner, P.; Kempf, U . Tappi 1970, 53, 2069. 100. Goring, D . A . I. In Cellulose Chemistry and Technology; Arthur, J. C., Jr., Ed.; ACS Symp. Ser. No. 48; American Chemical Society: Washington, D C , 1977; p. 273. 101. Goring, D . A . I.; Vuong, R.; Gancet, C.; Chanzy, H . J. Appl. Polym. Sci. 1979, 24, 931. 102. Fergus, B. J.; Goring, D . A . I. Holzforschung 1970, 24, 118. RECEIVED February 27,1989

Chapter 2

Structure and Properties of the Lignin-Carbohydrate Complex Polymer as an Amphipathic Substance T . Koshijima , T . Watanabe , and F . Y a k u 1

1

1

2

Wood Research Institute, Kyoto University, Gokasho, U j i , Kyoto 611, Japan

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

2

Government Industrial Research Institute, Osaka 563, Japan

It has been f o u n d t h a t l i g n i n - c a r b o h y d r a t e complexes (LCC's) consist o f sugar chains a n d r e l a t i v e l y s m a l l l i g n i n fragments a t t a c h e d as p e n d a n t side chains; they have number-average m o l e c u l a r weights of ca. 6000-8000. T h e linkage between sugar a n d l i g n i n was d e t e r m i n e d t o be m a i n l y o f the b e n z y l ether t y p e by a n e w l y developed m e t h o d u s i n g DDQ o x i d a t i o n . Some of the LCC's exh i b i t a s t r o n g tendency to f o r m micelles or aggregates in aqueous s o l u t i o n due t o h y d r o p h o b i c a n d also electrostatic interactions. Since B j o r k m a n first proposed the existence o f l i g n i n - c a r b o h y d r a t e c o m plexes ( L C C ' s ) as species i n c a p a b l e of s e p a r a t i o n i n t o the respective c o m ponents b y selective c h e m i c a l t r e a t m e n t s or s p e c i a l p u r i f i c a t i o n techniques, e x p e r i m e n t a l results s u p p o r t i n g the presence o f L C C ' s i n w o o d have been r e p o r t e d b y M e r e w e t h e r (1), K o s h i j i m a (2), Wegener (3), a n d Y a k u (4). T h e r e a f t e r , a lot of experiments designed to isolate fractions c o n t a i n i n g L C C ' s f r o m p a r t l y degraded w o o d preserving the n a t i v e c o n f i g u r a t i o n t o different extents have been c o n d u c t e d . A m o n g t h e m , B j o r k m a n (5), B r o w n e l l (6), K o s h i j i m a (7), Y a k u (8,9), E r i k s s o n (10) a n d W a t a n a b e (11) have ext r a c t e d L C C ' s f r o m finely d i v i d e d w o o d powder f r o m w h i c h m i l l e d w o o d l i g n i n h a d been e x t r a c t e d previously. B y c o n t r a s t , L u n d q u i s t (12), A z u m a (13), M u k o y o s h i (14), T a k a h a s h i (15) a n d K a t o (16) have separated the L C C ' s c o n t a i n e d i n a m i l l e d w o o d l i g n i n f r a c t i o n e x t r a c t e d w i t h 8 0 % aqueous dioxane f r o m v e r y fine w o o d powder. M e a n w h i l e , F r e u d e n b e r g (17) was the first person w h o d e m o n s t r a t e d the f o r m a t i o n o f a n a d d i t i o n c o m p o u n d f r o m a q u i n o n e m e t h i d e a n d s u crose d u r i n g e n z y m a t i c d e h y d r o g e n a t i o n o f c o n i f e r y l a l c o h o l i n a concent r a t e d sucrose s o l u t i o n . T h e r e a f t e r , T a n a k a (18) observed the f o r m a t i o n of a b e n z y l ester between the q u i n o n e m e t h i d e o f a d i l i g n o l a n d a u r o n i c 0097-6156/89/0397-0011$06.00A> © 1989 American Chemical Society

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

12

a c i d . K a t a y a m a (19) isolated a c o m p o u n d i n w h i c h glucose is l i n k e d t o c o n i f e r y l a l c o h o l t h r o u g h a b e n z y l ether b o n d . A n a l o g o u s c o m p o u n d s were also o b t a i n e d b y Feckel (20). Since those e x p e r i m e n t s were c a r r i e d o u t i n the presence of 20 t o 500 t i m e s the a m o u n t of c o n i f e r y l a l c o h o l i n r e l a t i o n to sugar, those results i n d i c a t e d o n l y the p o s s i b i l i t y o f c h e m i c a l l i n k a g e f o r m a t i o n between l i g n i n precursors a n d sugars. N o t e w o r t h y results have been o b t a i n e d f r o m electron m i c r o s c o p i c o b servations of L C C ' s b y Fengel (21) a n d K o s i k o v a (22). W h e n c o m p a r i n g these t w o schematic i l l u s t r a t i o n s , coiled a n d w o u n d fibrils of p o l y s a c c h a rides are b u r i e d i n the l i g n i n m a t r i x i n b o t h cases, b u t the p o l y s a c c h a r i d e fibril i n FengePs scheme is m u l t i p l y connected t o a b i g l i g n i n p a r t i c l e . I n K o s i k o v a ' s scheme, a fibril is a t t a c h e d to a r e l a t i v e l y s m a l l l i g n i n p a r t i c l e at o n l y one p o s i t i o n . D e s p i t e so m a n y investigations of L C C ' s , no c h e m i c a l p r o o f has been advanced so far a b o u t the k i n d of linkage c o n n e c t i n g the sugar t o the l i g n i n moiety. A l s o , no d i s t i n c t m a c r o m o l e c u l a r c o n f i r m a t i o n has yet been p r o v i d e d for the s c h e m a t i c m o l e c u l a r forms t h a t have been proposed o n the basis of electron microscopic observations. I n t h i s p a p e r , the molecular shape a n d micelle or aggregate f o r m a t i o n of L C C molecules, the n a t u r e of the s u g a r - l i g n i n linkage, a n d the m o l e c u l a r weights of L C C ' s w i l l be d o c u m e n t e d o n c h e m i c a l or p h y s i c o c h e m i c a l grounds. New Methods Oligomers

for

Extraction of L C C ' s

and Isolation of

L C C

T h e use of h i g h - b o i l i n g p o i n t solvents, such as d i m e t h y l f o r m a m i d e or d i m e t h y l s u l f o x i d e used b y B j o r k m a n for e x t r a c t i o n of L C C ' s f r o m spruce w o o d , m a y lead to d e n a t u r a t i o n or p a r t i a l d e g r a d a t i o n o f L C C ' s i n the course of solvent r e m o v a l or c o n c e n t r a t i o n . W e have developed the f o l l o w i n g two m e t h o d s for easily o b t a i n i n g L C C ' s . O n e involves i s o l a t i o n o f L C C ' s f r o m a n aqueous 8 0 % dioxane e x t r a c t o b t a i n e d f r o m finely d i v i d e d w o o d p o w d e r . A f t e r s e p a r a t i n g the p r e c i p i t a t e of m i l l e d w o o d l i g n i n f r o m the aqueous s o l u t i o n r e m a i n i n g after dioxane r e m o v a l , the L C C ' s i n the s u p e r n a t a n t are t a k e n out a n d purified b y u s i n g a p y r i d i n e - a c e t i c a c i d w a t e r - c h l o r o f o r m solvent s y s t e m t o remove sugar-free l i g n i n . T h e L C C - W t h u s o b t a i n e d is analogous t o B j o r k m a n L C C i n respect t o c h e m i c a l c o m p o s i t i o n a n d m o l e c u l a r weight, b u t differs i n y i e l d w h i c h ranges f r o m 0.75 to 1.1% of w o o d (13). T h e second way consists o f hot-water e x t r a c t i o n o f finely d i v i d e d w o o d p o w d e r , p r e v i o u s l y e x t r a c t e d w i t h aqueous dioxane for r e m o v i n g m i l l e d w o o d l i g n i n . T h e r e s u l t a n t L C C - W E is o b t a i n e d i n 9.3-10.0% y i e l d a n d does not differ f r o m B j o r k m a n L C C i n r e l a t i o n to c h e m i c a l c o m p o s i t i o n a n d m o l e c u l a r weight (11) (see T a b l e I). T h i s fact is v e r y significant i n d e m o n s t r a t i n g t h a t L C C ' s c o n t a i n i n g u p t o 1 8 % l i g n i n are able t o be ext r a c t e d w i t h hot w a t e r alone f r o m w o o d powder. I n order t o estimate the frequency of l i g n i n - s u g a r linkages i n p i n e L C C ' s , L C C oligomers were a t t e m p t e d t o be prepared f r o m L C C - W E of p i n e w o o d . T h e greatest p r o b l e m s to be solved were the s e p a r a t i o n o f

KOSHIJIMA ETAL.

2.

Complex Polymer as an Amphipathic Substance

13

T a b l e I. C h e m i c a l C o m p o s i t i o n a n d P r o p e r t i e s o f P i n e L C C - W Lignin-Carbohydrate Complexes Components

LCC-WE

R e c o v e r y (%) C a r b o h y d r a t e content N e u t r a l sugar Uronic acid L i g n i n content (%)

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

A c e t y l content Mi? S(S) M M w

n

a

6

c

(%)

C-l-A

C-l-M 43.4*

9.3°

C-l-R 2.1*

48.7*

(%) 80.0 4.2 17.9

95.5 N.D. 3.7

76.0 6.4 26.6

41.5 1.9 43.6

3.3 -15.5° N.D.

7.6 -28.2° 0.9

N.D. -11.4° 0.8

N.D. -8.0° N.D.

1.2 x 1 0 7.6 x 1 0

1.2 x 1 0 7.5 x 1 0

1.1 x 1 0 6.7 x 1 0

C

C

4

3

e

e

4

3

C

4

3

N.D. N.D.

C

C

V a l u e s are expressed as weight percentages o f the w o o d m e a l e x t r a c t e d w i t h 8 0 % aqueous dioxane. V a l u e s are expressed as weight percentages o f L C C - W E . Not determined.

L C C oligomers f r o m oligosaccharides a n d the p r e v e n t i o n o f reaggregation o f L C C oligomers t h r o u g h h y d r o p h o b i c i n t e r a c t i o n s . C h r o m a t o g r a p h y o f a n e n z y m e - d e g r a d e d C - l - A f r a c t i o n was successful o n a T o y o p e a r l H W - 4 0 S c o l u m n w h i c h h a d been a l r e a d y d e m o n s t r a t e d t o adsorb o n l y l i g n i n - c o n t a i n i n g oligosaccharides (23). T h e m i x t u r e o f L C C oligomers a n d oligosaccharides was p r e p a r e d b y h y d r o l y z i n g the f r a c t i o n C - l - A t h a t h a d been f r a c t i o n a t e d f r o m L C C - W E w i t h purified C e l l u l o s i n A C ( p r o t e i n 93.7%) a n d t h e n w i t h a m i x t u r e o f purified Meicelase ( p r o t e i n 92.2%) a n d C e l l u l o s i n A C at 40° C for 72 h o u r s . T h e e n z y m e - d e g r a d e d p r o d u c t s were i n t r o d u c e d o n t o the T o y o p e a r l H W - 4 0 S c o l u m n , w h i c h was e l u t e d w i t h water t o remove the oligosaccharide components ( A - E S W ) a n d subsequently w i t h 5 0 % aqueous d i o x a n e t o recover the adsorbed L C C oligomers ( A - E S D ) , w h i c h c o n t a i n e d n o c o n t a m i n a t i n g l i g n i n or oligosaccharide (see ref. 23 a n d T a b l e II). Estimation of Lignin-Sugar Linkages i n L C C ' s In 1982, O i k a w a et al. r e p o r t e d t h a t 2,3-dichloro-5,6-dicyanobenzoquinone ( D D Q ) reacts w i t h 4 - m e t h o x y b e n z y l ether t o give the a l c o h o l q u a n t i t a t i v e l y (24). P r o v i d e d t h a t D D Q a t t a c k s specifically at the p - a l k o x y b e n z y l ether l i n k a g e , direct evidence c a n be o b t a i n e d for the occurrence o f b e n z y l i c l i g n i n - c a r b o h y d r a t e linkages w h i c h m a y be present i n L C C molecules. N i n e m o d e l c o m p o u n d analogs of L C C ' s were synthesized a n d s u b j e c t e d to r e a c t i o n w i t h D D Q at 5 0 ° C for 1 h r or 40° C for 24 hrs i n 5 0 % d i o x a n e s o l u t i o n (25). F u r t h e r , m o d e l c o m p o u n d s ( I - I V ) were also s y n t h e s i z e d t o check the effect o f s u b s t i t u e n t s at the para p o s i t i o n s o f the g u a i a c y l moieties u p o n the release o f sugar residues b y D D Q o x i d a t i o n ( F i g . 1). A t w o - h o u r r e a c t i o n o f the m o d e l c o m p o u n d s w i t h D D Q at the b o i l i n g t e m p e r a t u r e

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

LIGNIN: PROPERTIES AND MATERIALS

F i g u r e 1. S y n t h e s i z e d m o d e l

compounds.

K O S H U I M A ET AL.

2.

Complex Polymer as an Amphipathic Substance

15

T a b l e I I . N e u t r a l S u g a r C o m p o s i t i o n of L C C S u b f r act ions Lignin-Carbohydrate Complexes

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

Components

C-l-A

A-ESD

C a r b o h y d r a t e content, %

76.0

8.3

Carbohydrate composition": L-Arabinose D-Xylose D-Mannose D-Galactose D-Glucose

7.3 49.5 27.0 7.2 9.1

7.5 17.6 48.7 7.7 18.6

a

V a l u e s are expressed as m o l e percentages o f the t o t a l n e u t r a l sugars.

o f the d i c h l o r o m e t h a n e - w a t e r (18:1) m i x t u r e e m p l o y e d was o p t i m u m (26). T h e L C C models 3 - m e t h o x y - 4 - h y d r o x y (I) a n d 3 - m e t h o x y - 4 - b e n z y l o x y b e n z y l ether ( I V ) were o x i d a t i v e l y decomposed b y D D Q , w h i l e the p - a c e t o x y L C C m o d e l c o m p o u n d II was inert to the o x i d a t i o n process because o f the electron w i t h d r a w i n g i n d u c t i v e effect of the acetoxy g r o u p , as r e p o r t e d b y B e c k e r . F u r t h e r m o r e , a l l o f the /?-ether linkages i n the L C C models I - I V were stable d u r i n g the D D Q o x i d a t i o n . However, the L C C m o d e l c o m p o u n d III h a v i n g the 3 , 4 - d i m e t h o x y p h e n y l m o i e t y was stable d u r i n g D D Q o x i d a t i o n under these c o n d i t i o n s . P r o b a b l y , t h i s is because the o x i d a t i o n p o t e n t i a l of the L C C m o d e l III is not low enough t o f o r m a charge t r a n s fer c o m p l e x w i t h D D Q . In fact, w h e n the para p o s i t i o n was s u b s t i t u t e d w i t h the more electron d o n a t i n g b e n z y l o x y g r o u p , q u a n t i t a t i v e o x i d a t i v e cleavage was observed i n the L C C m o d e l I V . M o s t o f the p a m - s u b s t i t u e n t s i n l i g n i n s are far more electron d o n a t i n g t h a n the m e t h o x y l g r o u p a n d , i n m a n y cases, t h a n the b e n z y l o x y group i n their effects. T h u s , i t m a y be c o n c l u d e d t h a t D D Q effectively decomposes n o n p h e n o l i c b e n z y l ether linkages i n l i g n i n s . G l y c o s i d i c b o n d s between sugar residues, however, were i n e r t to D D Q o x i d a t i o n (24,25). T o identify w h i c h sugar h y d r o x y Is p a r t i c i p a t e i n b e n z y l ether linkages t o l i g n i n , W a t a n a b e a n d K o s h i j i m a (23) developed a new m e t h o d w h i c h i n volves a c e t y l a t i o n o f L C C ' s or L C C oligomers followed b y D D Q o x i d a t i o n a n d P r e h m ' s m e t h y l a t i o n . Before a p p l i c a t i o n o f t h i s m e t h o d t o L C C ' s , i t was confirmed b y u s i n g 1,2,3,4-tetraacetyl- a n d 1 , 2 , 3 , 6 - t e t r a a c e t y l - D glucose t h a t D D Q does not cause a c e t y l group r e m o v a l f r o m or m i g r a t i o n i n the sugar a n d t h a t P r e h m ' s m e t h y l a t i o n does not i n d u c e a c e t y l m i g r a t i o n . A c c o r d i n g to t h i s m e t h o d (Scheme 1), the L C C oligomers A - E S D were s u b j e c t e d to a n a l y s i s of the t y p e of linkage present a n d the c o r r e s p o n d i n g m o n o m e t h y l a t e d sugars are s u m m a r i z e d i n T a b l e I I I . T h e sites o f b e n z y l ether linkages t o the sugar moieties of the L C C ' s are p r e d o m i n a n t l y at C - 6 i n hexoses a n d m o s t l y at C - 3 a n d somewhat less so at C - 2 i n pentoses. T h e sugars l i b e r a t e d by t h i s r e a c t i o n are the ones located at the a - c a r b o n s of l i g n i n p h e n y l p r o p a n e u n i t s etherified at the p - h y d r o x y l p o s i t i o n . M o s t o f

16

LIGNIN: PROPERTIES AND MATERIALS

the n o n - p h e n o l i c b e n z y l ether linkages are easily b r o k e n b y the a c t i o n o f D D Q due t o the enhanced e l e c t r o n - d o n a t i n g properties o f para s u b s t i t u t e d p h e n y l p r o p a n e u n i t s . H o w e v e r , phenolic h y d r o x y l s are a c e t y l a t e d d u r i n g the first step o f t h i s m e t h o d i n p h e n o l i c b e n z y l ethers a n d the enhanced electron w i t h d r a w i n g properties o f the a c e t o x y groups m a k e cleavage o f the b e n z y l ether l i n k e d sugar residues (as s h o w n i n Scheme 1) d i f f i c u l t . T a b l e I I I . M e t h y l E t h e r s o f M o n o s a c c h a r i d e s f r o m the H y d r o l y z a t e o f Methylated L C C Oligomers ( A - E S D )

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

M e t h y l a t e d Sugars

a

Mol %

a

2- 0 - m e t h y l - D - x y l o s e 3- 0 - m e t h y l - D - x y l o s e T o t a l xylose

9.2 24.2 33.4

2- O - m e t h y l - D - m a n n o s e 6- O m e t h y l - D - m a n n o s e T o t a l mannose

2.8 41.6 44.4

2- 0 - m e t h y l - D - g l u c o s e 6- O - m e t h y l - D - g l u c o s e T o t a l glucose

2.0 20.3 22.3

B a s e d o n t o t a l m e t h y l a t e d sugar c o m p o n e n t s i d e n t i f i e d .

Molecular Shape of L C C ' s T h e m o l e c u l a r sizes o f L C C ' s e x t r a c t e d f r o m finely d i v i d e d w o o d p o w d e r o f 10 t o 30 n a n o m e t e r d i a m e t e r p a r t i c l e size m a y be s o m e w h a t s m a l l e r t h a n o r i g i n a l l y the case o w i n g t o vigorous m e c h a n i c a l a c t i o n d u r i n g the course o f m i l l i n g . H o w e v e r , t h i s a c t i o n affects b o t h l i g n i n a n d p o l y s a c c h a r i d e molecules evenly (2), a n d so i t does not seem to be the case t h a t o n l y specific linkages are cleaved b y m i l l i n g . F i r s t , f r a c t i o n a t i o n of the L C C ' s e x t r a c t e d f r o m p i n e (Pinus densiflora) w o o d was a t t e m p t e d a c c o r d i n g t o the m e t h o d o f B j o r k m a n (5) i n t o three f r a c t i o n s b y means o f a d s o r p t i o n c h r o m a t o g r a p h y w i t h a D E A E S e p h a d e x c o l u m n . I n the case o f pine L C C ' s , the f r a c t i o n C - l - M e l u t i n g first w i t h w a t e r was composed o f n e u t r a l L C C ' s (fraction C - l - M - 1 , 5 % y i e l d ) consisti n g o f mannose, glucose, arabinose, xylose a n d l i g n i n , as well as lignin-free a c e t y l g l u c o m a n n a n ( 4 5 % y i e l d ) . Subsequent e l u t i o n w i t h one m o l a r a m m o n i u m carbonate solution liberated acidic L C C ' s (fraction C - l - A , 25-30% y i e l d ) w h i c h c o n s t i t u t e d the m a j o r p o r t i o n o f the p i n e L C C ' s c o n s i s t i n g o f 1 2 - 1 3 % l i g n i n , a b o u t 6% u r o n i c a c i d a n d 7 6 % n e u t r a l sugars. T h e last e l u t i o n ( f r a c t i o n C - l - R , 2 - 5 % y i e l d ) was effected b y u s i n g 10 m o l a r acetic a c i d , w h i c h released a f r a c t i o n c o n t a i n i n g a r o u n d 4 4 % l i g n i n a n d 4 3 % sugars. T h e f o l l o w i n g e x p e r i m e n t s were c o n d u c t e d u s i n g f r a c t i o n C - l - A , w h i c h was t h o u g h t t o be representative of the L C C ' s (17). T h e a c i d i c L C C f r a c t i o n , C - l - A , was p a r t i a l l y h y d r o l y z e d w i t h a cellulase p r e p a r a t i o n , C e l l u l o s i n A C , a n d changes i n the l i g n i n a n d sugar d i s t r i b u t i o n s were a n a l y z e d

2.

KOSHIJIMA ETAL.

Complex Polymer as an Amphipathic Substance

CH OH 2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002



O-CH

WOAc —0—CH fc-0

D-Glucose 4

I

Hydrolysis

Scheme 1. E s t i m a t i o n of linkage sites i n l i g n i n - c a r b o h y d r a t e moieities.

17

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

18

LIGNIN: PROPERTIES AND MATERIALS

b y means of Sephadex c o l u m n c h r o m a t o g r a p h y . F i g u r e 1, where the l i g n i n c o m p o n e n t is m a r k e d b y a d o t t e d l i n e , shows t h a t not o n l y the p o l y s a c c h a r i d e b u t also even the l i g n i n component was b r o k e n d o w n to s m a l l e r molecules b y the a c t i o n of the cellulase p r e p a r a t i o n . T h i s was q u i t e u n e x p e c t e d , since the C e l l u l o s i n A C has been confirmed t o have intense carb o x y met hylcellulase, hemicellulase a n d /?-glucosidase as w e l l as avicelase a c t i v i t i e s b u t no ligninase or peroxidase a c t i v i t i e s . F i g u r e 2 a shows the p r o file of f r a c t i o n C - l - A f r o m a Sephadex G - 1 5 c o l u m n . T h e m a j o r f r a c t i o n i n F i g u r e 2 A was secured, p a r t i a l l y h y d r o l y z e d w i t h C e l l u l o s i n A C a n d rechrom a t o g r a p h e d ( F i g . 2b). W h e n peaks I a n d I I i n F i g u r e 2b were i s o l a t e d a n d a g a i n h y d r o l y z e d w i t h the same cellulase p r e p a r a t i o n , the l i g n i n c o m ponents a g a i n separated i n t o four fractions i n the lower m o l e c u l a r weight region of the profile as s h o w n i n F i g u r e 2c (4). T h i s p h e n o m e n o n is easily u n d e r s t a n d a b l e b y a s s u m i n g the l i g n i n component of the L C C ' s t o consist of low m o l e c u l a r weight p e n d a n t - l i k e fragments a t t a c h e d to a sugar c h a i n ( F i g . 3). I n other words, C e l l u l o s i n A C c o u l d break d o w n o n l y the i n t e r c o n n e c t i n g sugar c h a i n between l i g n i n moieties, w i t h the result t h a t the l i g n i n components a p p e a r e d t o be cleaved by the cellulases a n d separated i n t o several peaks c o r r e s p o n d i n g t o different m o l e c u l a r sizes o n the g e l - f i l t r a t i o n c h r o m a t o g r a m s (4). T h i s v i e w was s u p p o r t e d b y the v i s c o s i m e t r i c b e h a v i o r of the n e u t r a l L C C ( C - l - M - 1 ) s o l u t i o n i n water (9). Micelle or Aggregate F o r m a t i o n a n d H y d r o p h o b i c Interactions of L C C Molecules in Aqueous Solution W h e n h y d r o p h i l i c a n d h y d r o p h o b i c groups are present i n a single molecule a n d t h e i r r a t i o a n d d i s t r i b u t i o n over the molecule are s u i t a b l e , the molecules associate w i t h each other a n d f o r m micelles or aggregates i n aqueous s o l u t i o n . A s L C C molecules have b o t h h y d r o p h o b i c l i g n i n a n d h y d r o p h i l i c sugar moieties, i t is reasonable t o consider t h a t they s h o u l d associate t o f o r m a g gregates or micelles. F i g u r e 4 displays the r e l a t i o n s h i p between e l e c t r i c a l c o n d u c t i v i t y of the L C C s o l u t i o n a n d c o n c e n t r a t i o n , w h i c h changes s h a r p l y at the p o i n t where the micelles or aggregates are f o r m e d , c o n f i r m i n g indeed t h a t s u c h entities do occur. T h e c r i t i c a l micelle c o n c e n t r a t i o n (c.m.c.) was 0 . 0 3 5 % i n t h i s case (8). M e a n w h i l e , p i n a c y a n o l c h l o r i d e , a k i n d of p i g m e n t , has two v i s i b l e a b s o r p t i o n m a x i m a , the a - b a n d ( A 6 0 5 n m ) a n d /?-band ( A 5 5 0 nm). These \ ' s shift to longer wavelengths w i t h increasing m o l a r e x t i n c t i o n coefficient as the L C C c o n c e n t r a t i o n increases. F i g u r e 5 i l l u s t r a t e s p l o t s of the m o l a r e x t i n c t i o n coefficients of the L C C - p i n a c y a n o l c h l o r i d e s o l u t i o n against the c o n c e n t r a t i o n of C - l - A - 1 , the purified a c i d i c L C C f r a c t i o n . T h e d i s c o n t i n u i t y (corresponding to the c.m.c.) i n F i g u r e 5 confirms t h a t m i c e l l e f o r m a t i o n occurs. F i g u r e 5 shows the same c.m.c. value, 0.035%, as F i g u r e 4, i n d i c a t i n g t h a t m i c e l l e or aggregate f o r m a t i o n takes place i n L C C s o l u t i o n s (8). F i g u r e 6 provides another instance d e m o n s t r a t i n g m i celle f o r m a t i o n or aggregation of L C C ' s i n s o l u t i o n as a result of c a t i o n i c d e t e r g e n t - L C C i n t e r a c t i o n s . T h e L C C ' s used here were isolated together w i t h m i l l e d w o o d l i g n i n f r o m finely d i v i d e d p i n e w o o d w i t h a n aqueous d i o x m a r

m a x

m a r

Figure 2. Gel-filtration patterns of enzyme-hydrolyzates of L C C ' s (fraction C - l - A ) on Sephadex G-15 column. (Reprinted with permission from réf. 4. Copyright 1976 Walter de Gruyter & Co.)

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

so

h*

J

s-

î

8

f

f

η

20

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

LIGNIN: PROPERTIES AND MATERIALS

|

: Attack

points

of

carbohydrolase

F i g u r e 3. D e g r a d a t i o n p a t t e r n o f L C C molecule b y carbohydrolases.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

2.

KOSHIJIMA ET AL.

Complex Polymer as an Amphipathic Substance

Concentration, %

F i g u r e 4. P l o t of c o n d u c t i v i t y a g a i n s t LCC ( f r a c t i o n C-l-A-1) c o n c e n t r a t i o n . ( R e p r i n t e d w i t h p e r m i s s i o n from r e f . 8, C o p y r i g h t 1979 Walter de G r u y t e r & Co.)

21

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

22

LIGNIN: PROPERTIES AND MATERIALS

Concentration

of C - l - A - 1 , %

F i g u r e 5. P l o t of molar e x t i n c t i o n c o e f f i c i e n t a g a i n s t LCC ( f r a c t i o n C-l-A-1) c o n c e n t r a t i o n . ( R e p r i n t e d w i t h p e r m i s s i o n from r e f . 8. C o p y r i g h t 1979 Walter de Gruyt e r & Co.)

Fraction

1

volume,

1

ml

1

1

T

Figure 6. Gel-filtration o f pine L C C - W with the addition of a variety of detergents on Sepharose 4 B column. (Reprinted with permission from ref. 27. Copyright 1981.)

o oo

AAA • • •

without detergent c a t i o n i c detergent anionic detergent non-ionic detergent amphionic detergent

T

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

24

LIGNIN: PROPERTIES AND MATERIALS

ane s o l u t i o n ; the f r a c t i o n is denoted b y L C C - W i n t h i s c h a p t e r . L C C - W was f r a c t i o n a t e d i n t o three f r a c t i o n s , n a m e l y W - l , W - 2 a n d W - 3 , t h r o u g h a Sepharose 4 B c o l u m n (13). W - l is the one e l u t e d at the v o i d v o l u m e , W - 2 (M = 2 x 10 ) c o n t a i n e d 5 1 % l i g n i n a n d 3 8 % n e u t r a l sugar moieties, a n d W - 3 ( M = 3 x 10 ) i n c l u d e d 2 1 % l i g n i n a n d 7 3 % sugars. 5

n

n

3

T h e a d d i t i o n o f 0 . 1 % o f a v a r i e t y o f detergents t o the eluents i n g e l filtration c h r o m a t o g r a p h y u s i n g a Sepharose 4 B c o l u m n resulted i n the decrease or disappearance o f the higher m o l e c u l a r weight f r a c t i o n W - 2 , w h i l e the lower molecular weight f r a c t i o n W - 3 r e m a i n e d at its i n i t i a l p o s i t i o n i n the c h r o m a t o g r a m . W - 3 a p p e a r e d i n the c h r o m a t o g r a m alone w h e n c a t i o n i c or a m p h i o n i c detergents were used as a d d i t i v e s (27). A s the f r a c t i o n W - 2 h a d a number-average m o l e c u l a r weight i n the region o f 1 0 a n d the r e m a i n i n g W - 3 is o f the order o f 1 0 , W - 2 corresponds to micelles or aggregates o f pine L C C ' s w h i c h are decomposed b y i n t e r a c t i o n s w i t h c a t i o n i c detergents. F u r t h e r , i t became evident f r o m t h i s e x p e r i m e n t t h a t electrostatic i n t e r a c t i o n s c o n t r i b u t e as d r i v i n g forces for m i c e l l e or aggregate f o r m a t i o n i n a d d i t i o n to h y d r o p h o b i c interactions (27). 5

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

3

T h e L C C molecules e x h i b i t i n g a tendency to f o r m micelles or aggregates are t h o u g h t to be confined t o those w i t h l i g n i n rsugar r a t i o s a r o u n d 1:1. T h i s is e x e m p l i f i e d b y f r a c t i o n W - 2 here. O n the other h a n d , L C C molecules c o n t a i n i n g a larger a m o u n t o f c a r b o h y d r a t e a n d less l i g n i n w o u l d l a c k the a b i l i t y to f o r m micelles as i n the case of those L C C molecules i n f r a c t i o n W - 3 w h i c h c o n t a i n e d 7 0 % sugar a n d 2 0 % l i g n i n o n average ( F i g . 7 b ) . F i g ure 7 depicts the s t r u c t u r a l d e t e r m i n a n t s of the L C C molecules a n d t h e i r micelles or aggregates proposed o n the basis o f the s u m m a r i z e d r e s u l t s . T h e L C C molecules proposed here f u r n i s h a c h e m i c a l a n d p h y s i c o c h e m i c a l basis to the images o b t a i n e d b y K o s i k o v a a n d Fengel f r o m elect r o n m i c r o s c o p i c observations. A s s h o w n i n F i g u r e 7, some o f the sugar c h a i n t e r m i n a l s are e x p e c t e d to l i n k g l y c o s i d i c a l l y t o l i g n i n moieties since sugar-free l i g n i n fragments have been isolated b y e n z y m a t i c d e g r a d a t i o n o f C - l - A u s i n g C e l l u l o s i n A C (4). H o w e v e r , there is no direct evidence c o n c e r n i n g the occurrence of g l y c o s i d i c linkages, so t h i s p r o b l e m r e m a i n s a n open q u e s t i o n . It is expected f r o m the m o l e c u l a r shapes of L C C ' s t h a t s t r o n g h y d r o p h o b i c i n t e r a c t i o n s due to the l i g n i n moieties act between the L C C molecules i n aqueous s o l u t i o n . W h e n the c h r o m a t o g r a p h y o f L C C ' s was carried o u t w i t h h y d r o p h o b i c s t a t i o n a r y phases u s i n g c o l u m n s o f p h e n y l a n d o c t y l Sepharose, 8 0 . 4 % a n d 7 7 . 6 % of the charged L C C ' s were a d s o r b e d o n t o the c o l u m n , w h i c h were b e i n g eluted w i t h a solvent m i x t u r e c o m p o s e d o f a n i n c r e a s i n g c o n c e n t r a t i o n o f e t h y l cellosolve (0, 15, 30, 45 a n d 50%) a n d decreasing c o n c e n t r a t i o n of a m m o n i u m sulfate (0.8, 0.6, 0.4, 0.2 a n d 0 . 0 M ) , respectively, adjusted t o p H 6.8. T h e c h e m i c a l c o m p o s i t i o n s o f the five components hereby o b t a i n e d i n d i c a t e d t h a t the fractions w i t h higher l i g n i n content are e l u t e d at the higher c o n c e n t r a t i o n o f e t h y l cellosolve ( T a ble I V ; ref. 15). E v e n t h o u g h one p h e n y l g r o u p is a p p r o x i m a t e l y equivalent t o a threec a r b o n a l k y l c h a i n i n h y d r o p h o b i c i t y , p h e n y l Sepharose adsorbs a larger

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

2.

KOSHIJIMA ETAL.

a

e

Complex Polymer as an Amphipathic Substance

F r . W-2

b.

Lignin

W-3

fragment

Carbohydrate

moiety

glycosidically Carbohydrate to

Fr.

25

lignin

to

linking

lignin

moiety

non-

fragment

linking

glycosidically

fragment

Figure 7. Structural determinants of L C C molecules and their micelle (or aggregate) formation. (Reprinted with permission from ref. 27. Copyright 1981.)

(X)

0

3

(%)

(X)

13.9 37.4 13.9 20.5 14.3 12.7

7.8

17 .5

34.0

P-III

19.0 22.6 28.8 19.3 10.4

22.6

P-II

.4 .5 .8 .0 .3

23 24 25 15 11

8 .0

40,.5

22, 5 15. 2 29. 2 19..1 11..0

P -I

LCC- •W

29.7

17.0 22.3 28.6 23.0 9.2

43.5

P-IV

30. 6 17. 8 18.,5 10.,2 23.,4 12.,7

32 .3

8. 8

0-•I

.4 .7 .5 .0 .4

13 13 32 18 22

50 .5

P -V

D e t a i l s of the procedure are given i n the Experimental S e c t i o n . ^Percentage of the dry weight of each l i g n i n - c a r b o h y d r a t e complex. P e r c e n t a g e of the t o t a l n e u t r a l sugar. ^Percentage of the e l u t e d l i g n i n - c a r b o h y d r a t e complex. Source: Reprinted w i t h permission from r e f . 15. Copyright 1982 Elsevier.

a

Recovery**

Neutral sugar L-Arabinose D-Xylose D-Mannose D-Galactose D-Glucose

L i g n i n content*

Component

Phenyl-Sepharose

25.3

24.0 15.6 32.2 21.3 7.9 10.9

15.4 22.7 18.0 23.1 20.7 14.6

15.0 12.4 27.7 32.1 12.6 36.5

60.5

44.9

38.8

28.4

14.7 16.0 31.5 25.3 12.5

0-V

0-IV

0-III

O-II

,0c tvl-Sepharose

Table IV. P r o p e r t i e s of F r a c t i o n s Obtained from Hydrophobic Chromatography of Pine LCC's

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

2.

KOSHIJIMA ETAL.

Complex Polymer as an Amphipathic Substance

27

a m o u n t o f L C C ' s t h a n o c t y l Sepharose, i n d i c a t i n g t h a t 7T-7T i n t e r a c t i o n s due t o the l i g n i n a r o m a t i c r i n g moieties o f the L C C ' s act i n a d d i t i o n to h y d r o p h o b i c i n t e r a c t i o n s i n v o l v i n g the c a r b o n a t o m s o f l i g n i n side chains. T h e number-average m o l e c u l a r weights were 6 x 1 0 for p i n e L C C ' s , and 6 x 1 0 a n d 2 x 1 0 for the species (present i n a 1:1 r a t i o ) c o m p r i s i n g beech L C C ' s (28). T h e beech L C C molecules seem t o consist o f very few b u t bigger l i g n i n moieties c o m p a r e d w i t h those of pine L C C ' s . T h e progress o f l i g n i n biosynthesis i n the presence o f oligo- or p o l y s a c charides i n the p r i m a r y cell w a l l w o u l d necessarily engender the f o r m a t i o n o f s u g a r - l i n k e d l i g n i n s or l i g n i n - i n t e r c o n n e c t i n g sugar c h a i n s , p r o v i d e d t h a t l i g n i n biosynthesis involves q u i n o n e m e t h i d e i n t e r m e d i a t e s . T h e r e s u l t i n g p r o d u c t s are a l l l i g n i n - c a r b o h y d r a t e complexes i n a b r o a d sense, b u t the L C C ' s w h i c h c a n be e x t r a c t e d by the u s u a l m e t h o d s w i l l be l i m i t e d t o those w i t h less t h a n a 5 0 % l i g n i n content. A p a r t o f the c h e m i c a l s t r u c t u r e s o f the i n t e r u n i t linkages i n p i n e L C C ' s is presented i n F i g u r e 8. T h e role o f L C C ' s i n l i v i n g p l a n t tissues is p r e s u m e d t o be r e l a t e d t o the p r e v e n t i o n o f water-soluble hemicelluloses f r o m d i s s o l v i n g o u t o f the cell w a l l b y the f o r m a t i o n o f micelles or aggregates t h a t i m m o b i l i z e sugar c h a i n s , a n d the s o l u b i l i z a t i o n o f w a t e r - i n s o l u b l e m a t e r i a l s u c h as l i g n i n , thereby e n a b l i n g i t to move t o a n y place i n the c e l l . 3

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

3

5

F i g u r e 8. S t r u c t u r a l features o f the i n t e r u n i t linkages i n the c a r b o h y d r a t e moieties i n p i n e L C C ' s .

lignin-

28

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch002

Literature Cited 1. Merewether, J . W. T . Holzforschung 1957, 11, 65-80. 2. Koshijima, T.; Taniguchi, T.; Tanaka, R. Holzforschung 1972, 26, 21117. 3. Wegener, G . Ph.D. Thesis, Universitat München, 1975. 4. Yaku, F.; Yamada, Y.; Koshijima, T . Holzforschung 1976, 30, 148-56. 5. Björkman, A . Svensk Papperstidn. 1957, 60, 243-51. 6. Brownell, H. H. Tappi 1971, 54, 66-71. 7. Koshijima, T.; Yaku, F.; Tanaka, R. Appl. Polym. Symp. 1976, 28, 1025-39. 8. Yaku, F.; Tsuji, S.; Koshijima, T . Holzforschung 1979, 33, 54-9. 9. Yaku, F.; Tanaka, R.; Koshijima, T . Holzforschung 1981, 35, 177-81. 10. Eriksson, O.; Lindgren, B. O. Svensk Papperstidn. 1977, 80, 59-63. 11. Watanabe, T.; Azuma, J.; Koshijima, T . Mokuzai Gakkaishi 1987, 33, 798-803. 12. Lundquist, K.; Simonson, R.; Tingsvik, K. Svensk Papperstidn. 1980, 83, 452-4. 13. Azuma, J.; Takahashi, N.; Koshijima, T . Carbohydr. Res. 1981, 93, 91-104. 14. Mukoyoshi, S.; Azuma, J.; Koshijima, T . Holzforschung 1981, 35, 23340. 15. Takahashi, N.; Azuma, J.; Koshijima, T . Carbohydr. Res. 1982, 107, 161-8. 16. Kato, A.; Azuma, J.; Koshijima, T . Chem. Lett. 1983, 137-40. 17. Freudenberg, K.; Harkin, J . M . Chem. Ber. 1960, 93, 2814-9. 18. Tanaka, K.; Nakatsubo, F.; Higuchi, T . Mokuzai Gakkaishi 1979, 25, 653-9. 19. Katayama, Y.; Morohoshi, N.; Haraguchi, T . Mokuzai Gakkaishi 1980, 26, 358-62. 20. Feckel, J . Ph.D. Thesis, Universitat München, 1982. 21. Fengel, D. Svensk Papperstidn. 1976, 79, 24-8. 22. Kosíková, B.; Zakutna, L.; Joniak, D. Holzforschung 1978, 32, 15-8. 23. Watanabe, T.; Kaizu, S.; Koshijima, T . Chem. Lett. 1986, 1871-4. 24. Oikawa, Y.; Yoshida, T.; Yonemitsu, O. Tet. Lett. 1982, 23, 885-8; Yonemitsu, O. Yuki-Goseikagaku 1985, 43, 691-6. 25. Koshijima, T.; Watanabe, T.; Azuma, J . Chem. Lett. 1984, 1737-40. 26. Watanabe, T.; Koshijima, T . Mokuzai Gakkaishi 1989, 35, in press. 27. Koshijima, T.; Azuma, J.; Takahashi, N. The Ekman Days 1981, I, 67. 28. Takahashi, N.; Koshijima, T . Wood Sci. Technol. 1988, 22, 177-89. RECEIVED May 29,1989

Chapter 3

Heterogeneity of Lignin Dissolution and Properties of Low-Molar-Mass Components Kaj Forss, Raimo Kokkonen, and Pehr-Erik Sågfors The Finnish Pulp and Paper Research Institute, P.O. Box 136, 00101 Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

Helsinki, Finland

On heating pre-extracted spruce wood meal for 48 h with a 60:40 v/v mixture of dioxane and 0.5 M phosphate buffer pH 6.8, low molar mass lignins (i.e., hemilignins and breakdown products of high molar mass glycolignin) amounting to 24 percent of total lignin are dissolved. By extraction of the solution with n-hexane the dioxane is transferred to the hexane phase together with hexane-dioxane soluble lignins. Removal of dioxane results in precipitation of dark brown hydrophobic lignin. Water soluble lignins remain in solution. When wood is heated first with the buffer solution alone and then with the mixture of dioxane and buffer solution, only small amounts of the hydrophobic lignin dissolve. It seems that during heating with the aqueous buffer solution the hydrophobic lignin, which may form the residual lignin in kraft pulp, becomes irreversibly bound to the fibers. It has earlier been shown that spruce wood (Picea abies) lignin is a group of compounds, consisting of 80-85% polymeric carbohydrate-bound lignin, which we are designating glycolignin and 15-20% of a group of low molar mass lignins, monomers, dimers and oligomers, which we are collectively designating hemilignins (1). The purpose of this work is to elucidate the role of hemilignins and glycolignin in the formation of color in pulp. The aim of the present part of the work was to develop a selective method for dissolution of low molar mass lignins without dissolving the glycolignin. Heating wood with an acid bisulfite solution causes sulfonation of both the hemilignins and the glycolignin. The hemilignins are sulfonated and dissolved before the glycolignin. In all probability, due to its bonding with carbohydrates, the dissolution of glycolignin is strongly affected by the pH 0097-6156y89/0397-0029$06.00A) © 1989 American Chemical Society

30

LIGNIN: PROPERTIES A N D MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

of the c o o k i n g l i q u o r . F o r instance, o n h e a t i n g w o o d w i t h a bisulfite s o l u t i o n of p H 5.5 at 130°C, b o t h h e m i l i g n i n s a n d g l y c o l i g n i n are sulfonated b u t d i s s o l u t i o n is l i m i t e d almost entirely to the h e m i l i g n i n sulfonates. However, b y s u b j e c t i n g the w o o d m a t e r i a l to a subsequent a c i d - c a t a l y z e d h y d r o l y s i s , the g l y c o l i g n i n - c a r b o h y d r a t e bonds are broken a n d the g l y c o l i g n i n sulfonic acids dissolve (1). T h e conclusion t h a t a l l low m o l a r mass lignins are h e m i l i g n i n s is, h o w ever, a n o v e r s i m p l i f i c a t i o n since i t has been s h o w n t h a t , o n h e a t i n g a n aqueous s o l u t i o n of g l y c o l i g n i n sulfonic a c i d acidified w i t h h y d r o c h l o r i c a c i d or sulfur dioxide a n d bisulfite, a m o n o m e r i c sulfonated h y d r o l y s i s p r o d u c t is f o r m e d (2). A c o m p a r i s o n of the rates of d i s s o l u t i o n shows t h a t g l y c o l i g n i n is d i s solved m u c h faster i n the k r a f t process t h a n i n the a c i d bisulfite process (3). I n spite of t h i s , k r a f t p u l p contains more r e s i d u a l l i g n i n t h a n sulfite p u l p a n d is more difficult t o bleach. T h i s observation leads to the view t h a t the so-called r e s i d u a l l i g n i n m a y not originate f r o m undissolved g l y c o l i g n i n b u t f r o m low m o l a r mass l i g n i n s , i.e., h e m i l i g n i n s or b r e a k d o w n p r o d u c t s f r o m g l y c o l i g n i n deposited o n the fibers at a n early stage of the cook. In order to investigate t h i s possibility, a series of k r a f t cooks was p e r f o r m e d . C o t t o n w o o l was placed i n each digester. T h e chlorine n u m b e r , ( I S O 3260), of the c o t t o n wool i n F i g u r e 1 shows t h a t the d e p o s i t i o n of lignins takes place at a n early stage of the cook. These colored l i g n i n s c o u l d not be removed b y w a s h i n g the c o t t o n w o o l w i t h s o d i u m h y d r o x i d e solution. T h i s result s u p p o r t s the hypothesis t h a t the r e s i d u a l l i g n i n i n k r a f t p u l p is formed f r o m some h e m i l i g n i n s or the d e g r a d a t i o n p r o d u c t s of g l y c o l i g n i n . I n sulfite p u l p i n g , s u l f o n a t i o n of the h e m i l i g n i n s a n d the h y d r o l y s i s p r o d u c t of g l y c o l i g n i n m a y prevent these c o m p o u n d s f r o m r e a c t i n g f u r t h e r a n d f r o m b e c o m i n g deposited o n the fibers. In m e c h a n i c a l w o o d p u l p i n g , the g l y c o l i g n i n r e m a i n s u n d i s s o l v e d , whereas some of the h e m i l i g n i n s are dissolved, their s o l u b i l i t i e s i n water bei n g the m a i n l i m i t i n g factor. It is thus possible t h a t some of the h e m i l i g n i n s are also responsible for the y e l l o w i n g of m e c h a n i c a l p u l p . Delignification of Spruce W o o d M e a l on H e a t i n g w i t h W a t e r In order to show the a m o u n t a n d m o l a r masses of lignins t h a t can be d i s solved o n h e a t i n g w o o d w i t h w a t e r , 5 g p o r t i o n s of w o o d m e a l e x t r a c t e d w i t h cyclohexane-ethanol (4) were heated w i t h 100 m L water at 150°C. F i g u r e 2 shows t h a t d e l i g n i f i c a t i o n reaches a m a x i m u m of 8% after 4 h of h e a t i n g . P r o l o n g e d h e a t i n g caused a redeposition of lignins o n the w o o d material. D u r i n g h e a t i n g the p H d r o p p e d below 4 due to the f o r m a t i o n of acetic a c i d . T h e a c i d caused h y d r o l y s i s of hemicelluloses a n d f o r m a t i o n of f u r f u r a l . It is thus possible t h a t the d e l i g n i f i c a t i o n was caused by h y d r o l y t i c cleavage of i n t e r u n i t linkages. F i g u r e 3 shows t h a t the dissolved l i g n i n s

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

3. FORSS ET AL. Heterogeneity of Lignin 31

32

LIGNIN: PROPERTIES A N D MATERIALS

were m o n o m e r s a n d oligomers w i t h m o l a r masses of less t h a n 1000 g / m o l (7).

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

Delignification of Spruce W o o d Phosphate Buffer Solution

Meal on Heating with

Neutral

T o test the a s s u m p t i o n t h a t the d e l i g n i f i c a t i o n t a k i n g place w h e n spruce w o o d m e a l is heated w i t h water is a result of a c i d c a t a l y z e d h y d r o l y s i s , w o o d m e a l samples were heated w i t h 0.5 M phosphate buffer s o l u t i o n at p H 6.8 ( F i g . 4). F i g u r e 4 shows t h a t 8% d e l i g n i f i c a t i o n was reached b y h e a t i n g w i t h buffer s o l u t i o n b u t t h a t the rate was slower t h a n w h e n h e a t i n g w i t h w a t e r . F i g u r e 5 shows t h a t , o n h e a t i n g w i t h buffer s o l u t i o n , the l i g n i n s dissolved are also of low m o l a r mass. N o furfural was formed i n t h i s e x p e r i m e n t . It can be concluded t h a t the d i s s o l u t i o n of lignins w i t h water a n d w i t h buffer s o l u t i o n is not the result of a n a c i d - c a t a l y z e d h y d r o l y t i c cleavage of c h e m i c a l bonds. However, as s h o w n b y S a k a k i b a r a et al. (5), a - O - 4 bonds i n m o d e l c o m p o u n d s dissolved i n water-dioxane (1:1) are r e a d i l y cleaved o n h e a t i n g . Delignification of Spruce W o o d M e a l on H e a t i n g w i t h M i x t u r e s of Phosphate Buffer a n d Dioxane Since the reason for the l i m i t e d degree of delignification reached o n h e a t i n g w o o d w i t h water or w i t h buffer s o l u t i o n m a y be the low s o l u b i l i t y of l i g n i n s i n w a t e r , w o o d m e a l was heated w i t h m i x t u r e s of phosphate buffer a n d dioxane ( F i g . 6). F i g u r e 6 shows t h a t , o n h e a t i n g w o o d m e a l w i t h buffer s o l u t i o n for 6 h at 150°C, 6% of the t o t a l l i g n i n was dissolved, b u t o n h e a t i n g w i t h dioxane o n l y 4 % dissolved. However, o n h e a t i n g w i t h a m i x t u r e of buffer a n d dioxane 1 4 % of the l i g n i n dissolved. U s i n g reversed-phase c h r o m a t o g r a p h y ( F i g . 7), i t was possible to show t h a t , o n h e a t i n g w i t h buffer s o l u t i o n , most of the l i g n i n s dissolved were of a h y d r o p h i l i c n a t u r e , e l u t i n g between 0 a n d 30 m i n u t e s , whereas dioxane preferentially dissolved h y d r o p h o b i c l i g n i n s , w h i c h eluted between 30 a n d 80 m i n u t e s . A s h e a t i n g w i t h buffer s o l u t i o n was f o u n d preferentially to dissolve h y d r o p h i l i c molecules, an a t t e m p t was m a d e to delignify b y h e a t i n g w o o d m e a l successively w i t h buffer a n d w i t h a buffer-dioxane m i x t u r e . F i g u r e 8 shows t h a t h e a t i n g w i t h buffer resulted i n a m a x i m u m d e l i g n i f i c a t i o n of about 8% after 8 h , at w h i c h p o i n t some of the dissolved l i g n i n was redeposited o n the w o o d m a t e r i a l . A f t e r 48 h of h e a t i n g w i t h buffer, 5 % of the l i g n i n was i n s o l u t i o n . W h e n the w o o d residue was subsequently heated i n dioxane-buffer, a n a d d i t i o n a l 3 % of the t o t a l l i g n i n dissolved instantaneously. Thereafter almost no l i g n i n was dissolved. However, b y h e a t i n g w o o d m e a l w i t h buffer-dioxane s o l u t i o n , 2 4 % of the l i g n i n was dissolved after 48 h . It c a n be concluded t h a t h e a t i n g w i t h buffer alone i r r e v e r s i b l y b o u n d l i g n i n to the w o o d m a t e r i a l .

FORSS ETAL.

3.

Heterogeneity of Lignin

33

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

i — ^ 280 nm 1.2n



i 10000

RELATIVE RETENTION VOLUME i 1 1500 1000 MOLAR M A S S

i i 5000 3000

F i g u r e 3. L i g n i n s dissolved a n d f u r f u r a l f o r m e d o n h e a t i n g spruce w o o d m e a l w i t h w a t e r for 6 h at 150°C. C o l u m n : Sephadex G - 5 0 . E l u e n t : 0.5 M NaOH.

DELIGNIFICATION,%

1 01

I 0

I 1

I 2

I 3

I 4

I

5

I I 1—I 6 7 8 HEATING TIME AT 1 5 0 C , h o

F i g u r e 4. D e l i g n i f i c a t i o n o n h e a t i n g spruce w o o d m e a l w i t h p h o s p h a t e buffer, p H 6.8, at 150°C.

LIGNIN: PROPERTIES A N D MATERIALS

34

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

280nm

i 10000

» » 5000 3000

RELATIVE RETENTION i i 1500 1000 MOLAR M A S S

VOLUME

F i g u r e 5. L i g n i n s dissolved o n h e a t i n g spruce wood m e a l w i t h p h o s p h a t e buffer, p H 6.8, for 6 h at 150°C. C o l u m n : Sephadex G - 5 0 . E l u e n t : 0.5 M NaOH.

F i g u r e 6. D e l i g n i f i c a t i o n o n h e a t i n g spruce w o o d m e a l for 6 h at 150°C w i t h 0.5 M phosphate buffer ( p H 6.8) a n d dioxane i n various v o l u m e p r o p o r t i o n s .

FORSS ETAL.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch003

3.

35

Heterogeneity ofLignin

F i g u r e 7. L i g n i n s dissolved o n h e a t i n g spruce w o o d m e a l w i t h p h o s phate buffer 0.5 M ( p H 6.8) a n d w i t h d i o x a n e for 6 h at 150°C. C o l u m n : Spherisorb O D S . E l u t i o n : G r a d i e n t e l u t i o n w i t h p h o s p h a t e buffermethanol.

DELIGNIFICATION,% 251B: DIOXANE/BUFFER 20 15 C: DIOXANE/BUFFER 10 5

u

k-S-x-x—x - S — TTTV — -

^

-.x x

A

xx — — xx *

"Er—

x

x

x to B


2

dt

(i)

where s is t h e s e d i m e n t a t i o n coefficient, u = 2TT(RPM)/6Q, r is t h e r a d i u s measured f r o m the center o f r o t a t i o n , a n d t is the t i m e . T h e s e d i m e n t a t i o n coefficient has u n i t s o f t i m e (sec) a n d is measured i n u n i t s o f svedbergs (s) where 1 s = 1 0 ~ sec. T h e s e d i m e n t a t i o n coefficient is c a l c u l a t e d f r o m t h e slope o f a plot o f the l o g a r i t h m o f b o u n d a r y p o s i t i o n versus t i m e . U s u a l l y the b o u n d a r y p o s i t i o n is assumed to be t h e p o s i t i o n o f the m a x i m u m o r d i n a t e o f the peak t h a t is o b t a i n e d w i t h a n o p t i c a l s y s t e m w h i c h records the derivative p a t t e r n o f the refractive i n d e x . U s i n g a m o r e s o p h i s t i c a t e d t r e a t m e n t o f p o i n t s a l o n g the b o u n d a r y , one can o b t a i n t h e weight-average s e d i m e n t a t i o n coefficient for t h e solute at t h e c o n c e n t r a t i o n c o r r e s p o n d i n g to the p l a t e a u region. 1 3

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62

LIGNIN: PROPERTIES A N D MATERIALS

DISTANCE DOWN CELL F i g u r e 1. A d i a g r a m of several R a y l e i g h fringes placed o n a n image of the c e n t r i f t ^ t i o n cell. D i s t o r t i o n of the fringe f r o m a s t r a i g h t line is caused b y a c o n c e n t r a t i o n gradient p r o d u c e d by s p i n n i n g the cell about the p o i n t r = 0.

5.

MEISTER & RICIIARDS

MWDistribution by Ultracentrifugation

63

Since the theories for the i n t e r p r e t a t i o n o f s e d i m e n t a t i o n v e l o c i t y exp e r i m e n t s require the s e d i m e n t a t i o n coefficient at zero c o n c e n t r a t i o n , a series of e x p e r i m e n t s is performed at different concentrations. T h e value at zero c o n c e n t r a t i o n (or " l i m i t i n g s e d i m e n t a t i o n coefficient"), $o> is o b t a i n e d f r o m plots u s i n g either of these equations, l / « = ( l + *,c)/*o s - s (l 0

(2) (3)

- k c) s

where k is a p o s i t i v e t e r m t h a t represents the given s y s t e m . G e n e r a l l y , t h e former e q u a t i o n covers a wider c o n c e n t r a t i o n range. T h e molecular weight M o f a macromolecule c a n be c a l c u l a t e d f r o m the s e d i m e n t a t i o n coefficient u s i n g the Svedberg e q u a t i o n , s

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

r

M

r

(4)

= Nsf/(l-vp)

where N is A v o g a d r o ' s n u m b e r , / is the f r i c t i o n a l coefficient, v is the p a r t i a l specific volume o f the solute, a n d p is the density o f the s o l u t i o n . I f the values of a l l the parameters are k n o w n , one c a n calculate the m o l e c u l a r weight for a homogeneous m a t e r i a l . If the m a c r o m o l e c u l e is heterogeneous, an i n d e t e r m i n a t e average is o b t a i n e d . D u r i n g the 1950's, a n u m b e r of theoretical m e t h o d s were p u t f o r t h for the d e t e r m i n a t i o n o f s e d i m e n t a t i o n d i s t r i b u t i o n s of heterogeneous m a c r o molecules, neglecting or i n c l u d i n g the effect of diffusion. For macromolecules of sufficient size t h a t diffusion is negligible, i t is sufficient t o p e r f o r m several velocity e x p e r i m e n t s at different concentrations a n d s o m e h o w e x t r a p o l a t e " c o r r e s p o n d i n g " p o i n t s o n the p a t t e r n t o zero c o n c e n t r a t i o n . Several approaches made use of parameters more easily o b t a i n a b l e w i t h the Schlieren o p t i c a l s y s t e m generally used at t h a t t i m e , b u t they are o f u n certain v a l i d i t y (2-4). W i t h c o n c e n t r a t i o n d a t a o b t a i n e d f r o m the R a y l e i g h o p t i c a l s y s t e m , the e x t r a p o l a t i o n procedure based u p o n r e l a t i v e concent r a t i o n is reasonable a n d the necessary d a t a m a n i p u l a t i o n s are "easy" t o p e r f o r m . R e l a t i v e concentrations c a n be determined because the R a y l e i g h o p t i c a l system corrects for solvent component gradients or pressure g r a d i e n t effects because i t records i n d e x of refraction differences between s e d i m e n t i n g solvent a n d s o l u t i o n . Before c o n t i n u i n g , i t is i m p o r t a n t t o u n d e r s t a n d the c o m p l e x i t y o f the processes t h a t warp the shape of the b o u n d a r y , even i f diffusion is negligible. T h e J o h n s t o n - O g s t o n effect w i l l be described w i t h t h e a i d o f F i g u r e 1. I n the figure, the p a t t e r n at t = t has been d i v i d e d i n t o three components i n the lower c o n c e n t r a t i o n zone. T h e first component (between r a n d r\) starts at C = 0, rises t o C i as a step a n d continues t o the cell b o t t o m . T h e second component starts at a c o n c e n t r a t i o n o f zero a n d rises at the second step t o C 2 , w i t h the t o t a l c o n c e n t r a t i o n b e y o n d the step b e i n g C\ - f C 2 . Since the m a t e r i a l i n the first step s e d i m e n t i n g b e y o n d t h e second step moves at a slower rate (because of the higher c o n c e n t r a t i o n ) , more m a t e r i a l enters t h e second step t h a n leaves i t . T h u s , the m a g n i t u d e of the 2

a

64

LIGNIN: PROPERTIES A N D MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

first step increases; i n other w o r d s , its apparent c o n c e n t r a t i o n is h i g h e r . T h e effect moves a l o n g the b o u n d a r y , the net effect b e i n g a n u p w a r d shift of the p a t t e r n . However, the t o t a l c o n c e n t r a t i o n r e m a i n s u n c h a n g e d (4). T h e c o n c e n t r a t i o n dependence of s e d i m e n t a t i o n causes a n a d d i t i o n a l r e s h a p i n g of the b o u n d a r y , called b o u n d a r y s h a r p e n i n g . T h e faster m o v i n g m a t e r i a l is at a higher c o n c e n t r a t i o n t h a n the slower m a t e r i a l , w i t h the result t h a t the b o u n d a r y is progressively sharpened as the c o n c e n t r a t i o n increases; t h a t is, i t shifts to the left. T h e dependence of s e d i m e n t a t i o n c o n s t a n t o n c o n c e n t r a t i o n a n d o n the c o n c e n t r a t i o n of other molecules a r o u n d the s e d i m e n t i n g molecule, w h i c h causes the above effects, are too difficult to measure. I n some systems w i t h s p h e r i c a l macromolecules, a p p r o x i m a t e corrections have been m a d e (5). T h e e x t r a p o l a t i o n of s t o zero p o l y m e r c o n c e n t r a t i o n s h o u l d e l i m i n a t e the m a j o r p a r t of these effects.

Conversion of Sedimentation Patterns to Distribution Patterns T h e most c o m m o n s y m b o l i s m for c h a r a c t e r i z i n g s e d i m e n t a t i o n d i s t r i b u t i o n patterns is the use of G ( s ) (where G ( s ) represents the weight f r a c t i o n of m a t e r i a l h a v i n g a s e d i m e n t a t i o n coefficient less t h a n or e q u a l to the given value) for the i n t e g r a l d i s t r i b u t i o n , a n d g(s) for the differential d i s t r i b u t i o n , where g(s) = d G ( s ) d s . T h e integral d i s t r i b u t i o n is s i m p l e to o b t a i n f r o m R a y l e i g h - f r i n g e d a t a . W e w i l l assume t h a t the c o n c e n t r a t i o n of p o l y m e r is p r o p o r t i o n a l to refractive i n d e x , w h i c h the o p t i c a l s y s t e m records. F i r s t the r a d i a l p o s i t i o n is converted to u n i t s of s e d i m e n t a t i o n coefficient. T h i s is a c c o m p l i s h e d b y u s i n g the integrated f o r m of E q u a t i o n 1.

(5) where r is the p o s i t i o n of the meniscus at the top ( l o w r ) of the s o l u t i o n . E q u a t i o n 5 relates s e d i m e n t a t i o n coefficients to a r a t i o of r a d i a l distance a l o n g the cell, r / r , a n d t i m e , t, at a n g u l a r velocity, u>. T h i s e q u a t i o n allows p o s i t i o n along the cell t o be p l o t t e d as s instead of r . T h e n u m b e r of fringes, J , seen i n the interference p a t t e r n is a f u n c t i o n of solute c o n c e n t r a t i o n , C2, specific refractive i n d e x increment, dnjdci, cell thickness a l o n g the o p t i c a l p a t h , a, a n d wavelength of the incident l i g h t , A: a

a

J =

a(dn/dc2)c2

(6)

X

E q u a t i o n 6 allows the n u m b e r of fringes to be converted to s t a n d a r d c o n c e n t r a t i o n u n i t s . T h e c o n c e n t r a t i o n values i n fringes must be corrected for r a d i a l d i l u t i o n . T h e number of d a t a p o i n t s n serves t o d i v i d e the profile i n t o zones. E a c h zone, A C , - = C,- — is m u l t i p l i e d b y x\jx\ where %i = (%i + # t - i ) / 2 a n d each x is the distance d o w n the fringe p a t t e r n recorded o n film t h a t corresponds to a given r p o s i t i o n i n the s p i n n i n g cell. T h e n o t a t i o n x thus denotes the p o s i t i o n of the meniscus. T h e corrected y

a

5.

MEISTER & RICHARDS

MW Distribution by Ultracentrij"ligation

65

relative c o n c e n t r a t i o n CRi is

Cft = ^ A C , ( ^ ) / C „

where C

(7)

is the corrected c o n c e n t r a t i o n i n the p l a t e a u region, n a m e l y

n

c„ = X;ac*(«J/«2)

(8)

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

Jb=l A t a n y i , CRi i s , o f course, a weight f r a c t i o n c o n c e n t r a t i o n o f solute based o n or referenced t o the c o n c e n t r a t i o n of the p l a t e a u region. W h e n c o n s i d ered as a weight f r a c t i o n c o n c e n t r a t i o n , CRi w i l l be denoted as Wi. A p l o t of Wi versus s is the i n t e g r a l m o l e c u l a r weight d i s t r i b u t i o n for a s a m p l e . T o o b t a i n the d i s t r i b u t i o n e x t r a p o l a t e d t o zero c o n c e n t r a t i o n , the d i s t r i b u t i o n at each c o n c e n t r a t i o n is d i v i d e d i n t o a n u m b e r o f zones w i t h i n the weight f r a c t i o n zone 0 t o 1. T h e n for each zone a p l o t o f s or 1/s versus the sample c o n c e n t r a t i o n is m a d e a n d e x t r a p o l a t e d t o o b t a i n e d t h e sedim e n t a t i o n coefficient at zero c o n c e n t r a t i o n , SQ . A p l o t o f weight f r a c t i o n versus so is the corrected i n t e g r a l d i s t r i b u t i o n at zero c o n c e n t r a t i o n . T h e differential d i s t r i b u t i o n , dc/ds, c a n be o b t a i n e d b y f i t t i n g groups o f p o i n t s w i t h a s l i d i n g least m e a n squares cubic fit. T h e conversion of the s e d i m e n t a t i o n d i s t r i b u t i o n to a m o l e c u l a r weight d i s t r i b u t i o n u s i n g the Svedberg equation requires knowledge o f t h e f r i c t i o n a l coefficient a n d p a r t i a l specific volume of each weight f r a c t i o n . F o r a s y n t h e t i c linear p o l y m e r , the p a r t i a l specific volumes of a l l species s h o u l d be the same, w h i c h leaves the f r i c t i o n a l coefficient t o be e s t i m a t e d f r o m a r a n d o m - c o i l m o d e l . O n e a p p r o a c h is to use the r e l a t i o n c o n t a i n i n g t h e s e d i m e n t a t i o n coefficient, l i m i t i n g viscosity a n d m o l e c u l a r weight (2,6), £ ^ 2/3

i / 3 p - i i l z M ~ r

4

9

M

n

N

( ) W 9

where [rj] is the l i m i t i n g viscosity, n is the viscosity of the solvent a n d $i/3p-i t a n t of value 2.5 x 1 0 . C o m b i n i n g E q u a t i o n 9 w i t h the M a r k - H o u w i n k e q u a t i o n ( 7 , 8 ) , i s

a

6

c o n s

(10)

[n] = K'M

Q

gives M

x

= (ib) /( -«) 3

2

(11)

where M is a m o l e c u l a r weight average determined b y the s t a n d a r d molecular weights used t o determine K' a n d a i n E q u a t i o n 10 a n d x

66

LIGNIN: PROPERTIES A N D MATERIALS

N o t e the difference between K\ the M a r k - H o u w i n k constant, a n d k defined i n E q u a t i o n 12. T h e differential s e d i m e n t a t i o n d i s t r i b u t i o n can be t r a n s f o r m e d to the differential m o l e c u l a r weight d i s t r i b u t i o n by t a k i n g the derivative of E q u a t i o n 11 w i t h respect to 5, to get

ds w i t h the result t h a t

~

(2-a)

dc_

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

dM

=

S

'

{

(dc/ds) (dM/ds)

K

}

N o t e the i m p l i c a t i o n s of E q u a t i o n 14. If the change i n a m o u n t of p o l y m e r w i t h respect to the m o l e c u l a r weight of t h a t p o l y m e r , dc/dM), is needed, it can be f o u n d i n a two step process. F i r s t determine (dc/ds) a n d t h e n determine (dM/ds). T h e f u n c t i o n (dc/dM) is often desired since i t is the p l o t of the n u m b e r of molecules of a given molecular weight versus m o l e c u l a r weight, or the differential molecular weight distribution. F u r t h e r , (dc/ds) is the slope of the R a y l e i g h interference p a t t e r n i n a s e d i m e n t a t i o n v e l o c i t y e x p e r i m e n t . If t h i s slope is quantified a n d the value of (dM/ds) is o b t a i n e d f r o m E q u a t i o n 13, t h e n the differential m o l e c u l a r weight d i s t r i b u t i o n can be f o u n d for a given s a m p l e . D e t a i l s of this procedure are given here.

Experimental Viscometry. Viscosities of aqueous p o l y m e r solutions were measured u s i n g a C a n n o n - F e n s k e # 5 0 viscometer i m m e r s e d i n a 2 0 ° C water b a t h . T h e l i m i t i n g viscosity n u m b e r was d e t e r m i n e d f r o m 5 viscosity measurements using the H u g g i n s e q u a t i o n (9). T h e l i m i t i n g viscosity n u m b e r of aged p o l y ( l - a m i d o e t h y l e n e ) i n 0.01 M aqueous N a S 0 4 was 2.45 d L / g . 2

Materials and Solution Preparation. T h e p o l y ( l - a m i d o e t h y l e n e ) used i n a l l e x p e r i m e n t s was a " m o l e c u l a r weight s t a n d a r d " s u p p l i e d by Polysciences, Inc., as m a t e r i a l 8249, b a t c h 93-5. T h e p o l y m e r was d r i e d for 3 h r . u n der a v a c u u m of < 10 P a at a t e m p e r a t u r e of 2 5 ° C . T h e p o l y m e r was dispersed o n a v o r t e x of 0.01 M N a S 0 4 s o l u t i o n a n d stirred for 1 day. T h e s o l u t i o n was t h e n centrifuged to remove undissolved p o l y m e r particles a n d the preweighed centrifuge tube was d r i e d a n d reweighed. T h e p o l y m e r c o n c e n t r a t i o n of the master s a m p l e was c a l c u l a t e d f r o m the weight of p o l y mer r e t a i n e d i n the s o l u t i o n . T h e c o n c e n t r a t i o n of the master s a m p l e was 2,115 p p m or 0.2115 g / d L . A l l solutions were stored for 60 days before use. T h i s delay was necessary for accurate results since N a r k i s (10) h a d already s h o w n t h a t p o l y ( l amidoethylene) solutions are not m o l e c u l a r l y disperse u n t i l 54 days after p r e p a r a t i o n . These solutions age b y losing i n t e r m o l e c u l a r entanglements a n d b e c o m i n g m o n o m o l e c u l a r solutions (10). P o l y ( l - a m i d o e t h y l e n e ) sol u t i o n s are k n o w n to lose viscosity w i t h t i m e (11). Several authors have a t t r i b u t e d this viscosity loss to oxygen or r a d i c a l d e g r a d a t i o n of the p o l y mer (11), b u t F r a n c o i s (12) has s h o w n t h a t changes i n viscosity o n l y 2

5.

MEISTER & RICIIARDS

MWDistribution

by Ultracentrifugation

67

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

o c c u r i n solutions made f r o m b r o a d - m o l e c u l a r - w e i g h t - d i s t r i b u t i o n p o l y ( l a m i d o e t h y l e n e ) . Since very n a r r o w - m o l e c u l a r - w e i g h t - d i s t r i b u t i o n p o l y ( l amidoethylene) produces a stable s o l u t i o n viscosity a n d since N a r k i s (10) has s h o w n t h a t the o r i g i n a l s o l u t i o n viscosity can be o b t a i n e d b y p r e c i p i t a t i n g a n d r e d i s s o l v i n g the p o l y m e r , i t w o u l d appear t h a t s o l u t i o n v i s c o s i t y loss is caused b y slow d i s e n t a n g l i n g o f a b r o a d - m o l e c u l a r - w e i g h t p o l y m e r m i x t u r e . A l l solutions used here were aged t o insure complete d i s s o l u t i o n and u n i f o r m i t y i n s a m p l i n g the a c t u a l d i s t r i b u t i o n o f the p o l y m e r . Sedimentation Velocity Experiments. T h e sedimentation velocity experiments were c a r r i e d o u t i n a B e c k m a n M o d e l E u l t r a c e n t r i f u g e e q u i p p e d w i t h R a y l e i g h interference optics a n d a d i g i t a l electronic s y s t e m t h a t m e a sures the rotor t e m p e r a t u r e t o 0.01° w i t h c o n t r o l t o ± 0 . 0 3 ° C (13). T h e o p t i c a l s y s t e m was aligned a c c o r d i n g t o the procedure o f R i c h a r d s et al. (14). A R a y l e i g h m a s k w i t h 0.4 m m slit w i d t h (instead o f 0.8 m m ) i m p r o v e d the accuracy of fringe measurement b y increasing the n u m b e r of fringes i n the p a t t e r n . T h e two sectors o f the charcoal-filled E p o n centerpiece were filled w i t h a m i c r o l i t e r syringe w i t h the solvent side filled sufficiently higher t o p e r m i t r e s o l u t i o n of the s o l u t i o n meniscus o n the fringe p a t t e r n . T h e r o tor w i t h cell a n d counterbalance was controlled at 20.0°C i n the centrifuge chamber (no v a c u u m ) for at least 10 m i n . T h e rotor was accelerated t o 5200 r p m , where a baseline p h o t o g r a p h ( K o d a k M e t a l l o g r a p h plates) was o b t a i n e d d u r i n g a 30 second pause. T h e rotor was t h e n accelerated at c o n s t a n t amperage t o the o p e r a t i n g speed of 44,000 r p m , w h e r e u p o n another baseline p i c t u r e was t a k e n . D u r i n g acceleration, a d d i t i o n a l h e a t i n g was used t o m a i n t a i n the t e m p e r a t u r e constant at 20.0°C a n d the clock m e a s u r i n g the t i m e of s e d i m e n t a t i o n was s t a r t e d when the rotor reached 2 / 3 of the final speed. S e d i m e n t a t i o n pictures were taken s t a r t i n g at 20 t o 40 m i n . after clock start a n d were taken at 20 m i n . intervals u n t i l 160 m i n . h a d elapsed. T h e e x p e r i m e n t s w i t h the p o l y ( l - a m i d o e t h y l e n e ) samples were c a r r i e d o u t under i d e n t i c a l c o n d i t i o n s , insofar as possible. Reading of Rayleigh Fringe Patterns. Fringe p a t t e r n s were read w i t h a N i k o n Profile P r o j e c t o r m o d e l 6 C equipped w i t h d i g i t a l m i c r o m e t e r s (accurate t o 1.25 fim) a n d a d u a l - p h o t o c e l l light-difference detector m o u n t e d o n the screen t h a t locates fringe centers (15). T h e r e a d i n g of p a t t e r n s is s e m i - a u t o m a t i c , b e i n g controlled b y a n A l t a i r 8080 microprocessor c o m puter w i t h the d a t a recorded o n a floppy disc. A f t e r a l i g n m e n t o f the p a t tern o n the projector stage, the positions of the counterbalance reference edges a n d solutions m e n i s c i are located a n d recorded. T h e R a y l e i g h fringe p a t t e r n t h a t is o b t a i n e d f r o m the u l t r a c e n t r i f u g e u s i n g a R a y l e i g h mask w i t h 0.4 m m slit w i d t h has o n l y about nine r e a d able fringes i n the y d i r e c t i o n . T h e fringes are e q u a l l y spaced, except for progressive warpage i n the p o s i t i o n of fringe centers away f r o m t h e center of the diffraction envelope; hence, i t is necessary t o confine readings t o the central region of the envelope. However, i m p r o v e d accuracy is achieved b y averaging as m a n y fringes as possible, i n t h i s case three.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

68

LIGNIN: PROPERTIES A N D MATERIALS

F o r the r e a d i n g of the fringe profile ( u s u a l l y the l i g h t fringes o n the negative p h o t o g r a p h ) i n the s o l u t i o n region of the p a t t e r n , the a p p r o x i m a t e center of the fringe envelope i n the y d i r e c t i o n is l o c a t e d . T h e r e a d i n g of fringes i n the y d i r e c t i o n is t h e n confined t o the c e n t r a l distance corres p o n d i n g to three fringe spacings (the distance between fringes b e i n g a b o u t 280 ^ m ) . T h e r e a d i n g of fringes is begun near the meniscus ( F i g u r e 2). T h e x - a x i s of the p a t t e r n is the l o n g axis i n the interference p a t t e r n . T h e d i s tance across the fringe image is the y - a x i s . A t each x p o s i t i o n , the p o s i t i o n of the fringe centers is transferred to the c o m p u t e r b y a s i g n a l f r o m the l i g h t detector as the stage is m o v e d i n the y d i r e c t i o n , across the light p a t h . T h e x a n d average y values a n d the fringe spacings are stored b y the c o m p u t e r . A b o u t 150 p o i n t s across the b o u n d a r y a n d i n t o the p l a t e a u are read at e q u a l x increments. A s the lower of the three fringes b e i n g measured rises to w i t h i n 1/2 fringe of the center of the envelope ( m i d d l e of the fringe p a t tern i n the y d i r e c t i o n ) , one drops d o w n one fringe i n order to s t a y i n the c e n t r a l region. T h i s need t o d r o p " d o w n " a fringe i n order t o stay i n the y - m i d d l e of the fringe p a t t e r n is caused b y the s i g m o d a l d i s t o r t i o n of the R a y l e i g h fringe p a t t e r n caused b y the s e d i m e n t i n g b o u n d a r y . T h e profile t h a t results f r o m t h i s procedure is discontinuous, b u t a s i m p l e statement i n the subsequent c o m p u t e r p r o g r a m converts the d a t a to the correct profile. B y m e a s u r i n g the fringe p a t t e r n i n this way, three h i g h - a c c u r a c y fringes are converted to a set of (x, y) d a t a points w h i c h are the n u m e r i c a l equivalent of the p l o t of three fringes f r o m the low r p o i n t to the h i g h r p o i n t i n the s p i n n i n g cell. T h i s d a t a set can then be smoothed a n d averaged t o give a complete p l o t of the fringe profile (and the s e d i m e n t i n g b o u n d a r y w h i c h represents c as a f u n c t i o n of r) f r o m the meniscus of the centrifuged s o l u t i o n to the b o t t o m of the cell. T h e low- a n d high-speed baseline patterns a n d the 80 a n d 100 m i n . s e d i m e n t a t i o n patterns for each s o l u t i o n were read i n the same m a n n e r . T h e d a t a were transferred to a R a d i o Shack M o d e l III c o m p u t e r for f u r t h e r treatment.

Calculations A c o m p u t e r p r o g r a m converted the fringe d a t a i n t o c o n c e n t r a t i o n i n u n i t s of fringes b y d i v i s i o n of the y values b y the average fringe s e p a r a t i o n . T h e sedi m e n t a t i o n patterns were corrected for differences i n o p t i c a l p a t h t h r o u g h the two cell c o m p a r t m e n t s b y s u b t r a c t i n g the h i g h speed baseline, u s i n g a n i n t e r p o l a t i v e procedure. T h e h i g h or l o w speed baseline c o u l d be used i n t h i s correction step. B o t h baselines were tested a n d f o u n d t o give the same results for the higher c o n c e n t r a t i o n samples b u t to differ s l i g h t l y i n the effect o n the low c o n c e n t r a t i o n sample's p a t t e r n s . T h e h i g h speed baseline a d j u s t m e n t was chosen for c o r r e c t i n g a l l d a t a sets to avoid b i a s i n g the d a t a . T h e x values of the corrected patterns were then t r a n s f o r m e d i n t o distance r f r o m the center of r o t a t i o n a c c o r d i n g to the r e l a t i o n r = r + (x c

x )/MF ave

(15)

Figure 2. A print of a photograph of the Rayleigh fringe pattern produced by sedimentation of a graft copolymer of starch from aqueous brine. (For more information see ref. 17.)

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

SO

î ί

I

ï

I

SO

fi»

Ά

Ξ

s

70

LIGNIN: PROPERTIES AND MATERIALS

where r is the distance of the center of the cell f r o m the axis of r o t a t i o n (6.5 c m ) , x is the fringe p o s i t i o n i n m i c r o m e t e r u n i t s , x is the average of the inner a n d outer reference p o s i t i o n s i n m i c r o m e t e r u n i t s , a n d MF is the o p t i c a l m a g n i f i c a t i o n factor. T h e fringe values are corrected for r a d i a l d i l u t i o n a n d the r a d i a l p o s i t i o n s are t r a n s f o r m e d i n t o s e d i m e n t a t i o n u n i t s as described earlier. c

a v e

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch005

T h e same p r o g r a m fits the d a t a w i t h a s l i d i n g 15 p o i n t least m e a n squares cubic fit, using two passes to s m o o t h the d a t a . T h e use of f o u r t h or fifth power fits for a v a r i a t i o n of the n u m b e r of p o i n t s fitted (13 to 21 points) d i d not significantly i m p r o v e the results. T h e average d e v i a t i o n for the fringe value (after averaging three fringes) was about 0.005 fringes a n d 0.001 fringes for the s m o o t h e d values. O t h e r c o m p u t e r p r o g r a m s were used to p l o t the d i s t r i b u t i o n profiles, i n t e r p o l a t e these curves for e x t r a p o l a t i o n to zero c o n c e n t r a t i o n , generate the m o l e c u l a r weight d i s t r i b u t i o n profiles, a n d to plot t h e m .

Results F i v e solutions of a p o l y ( l - a m i d o e t h y l e n e ) sample at concentrations r a n g i n g f r o m 0.0422 to 0.2111 g / d L were sedimented i n the a n a l y t i c a l u l t r a c e n trifuge. E x a m i n a t i o n of the patterns at different times revealed t h a t the 80 m i n . patterns h a d a definite p l a t e a u region, b u t there was s t i l l a s m a l l a m o u n t of m a t e r i a l near the meniscus. F o r the 100 m i n . p a t t e r n s , the p l a t e a u was n e a r i n g the cell b o t t o m , a n d the meniscus region was almost clear of solute. L a t e r patterns e x h i b i t e d a definite region near the meniscus w i t h no solute, b u t no p l a t e a u near the b o t t o m . It is possible to splice the d i s t r i b u t i o n patterns o b t a i n e d at different times, b u t errors can lead to a d i s c o n t i n u i t y i n the overlap region. Because the d i s t r i b u t i o n p a t t e r n s o b t a i n e d at 80 a n d 100 m i n . were nearly the same, i t was decided to treat o n l y those a n d ignore any s m a l l a m o u n t of m a t e r i a l t h a t m a y not have sedimented: i t s c o n t r i b u t i o n to the average viscosity a n d m o l e c u l a r weight s h o u l d be negligible. A f t e r i n t e g r a t i o n of these p a t t e r n s , the m o l e c u l a r weight d i s t r i b u t i o n curve showed t h a t the m a t e r i a l at the b o u n d a r y h a d m o l e c u l a r weights of less t h a n 9,000 a n d the m a t e r i a l already sedimented h a d a m o l e c u l a r weight of 5,000,000 or more. T h e s t a r t i n g a n d e n d i n g regions of the integral d i s t r i b u t i o n p a t t e r n s were e x a m i n e d to determine the fringe values at these levels. T h e s t a r t i n g value for each p a t t e r n was s u b t r a c t e d f r o m the fringe values for the rest of the p a t t e r n . T h e p l a t e a u values for the 80 a n d 100 m i n . p a t t e r n s for each s o l u t i o n agreed to w i t h i n 0.02 fringes. W i t h the zero a n d p l a t e a u concentrations d e t e r m i n e d , the patterns were converted to weight f r a c t i o n distributions. Since the i n t e g r a l d i s t r i b u t i o n patterns for the 80 a n d 100 m i n . p a t terns were n e a r l y the same, o n l y the results f r o m the former are s h o w n i n F i g u r e 3. T h e differential patterns (not shown) o b t a i n e d f r o m the s l i d i n g 15 p o i n t least m e a n squares cubic fit were also n e a r l y the same, w i t h considerable noise for the two solutions of lowest c o n c e n t r a t i o n .

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PR4R50

5 20,u

F i g u r e 3. C o n c e n t r a t i o n of p o l y ( l - a m i d o e t h y l e n e ) i n a centrifuged s a m p l e p l o t t e d as a f u n c t i o n o f s e d i m e n t a t i o n coefficient.

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T h e five i n t e g r a l patterns were i n t e r p o l a t e d to o b t a i n 49 values o f the b o u n d a r y r a n g i n g f r o m 0.02 to 0.98 weight f r a c t i o n of the p o l y m e r s a m p l e . T h e e x t r a p o l a t i o n s of 1/s versus c to zero c o n c e n t r a t i o n for the nine w e i g h t f r a c t i o n c o n c e n t r a t i o n levels r a n g i n g f r o m 0.1 to 0.9 are s h o w n i n F i g u r e 4. T h e noise i n the p o s i t i o n of the d a t a p o i n t s relative to the l i n e are r a n d o m . F o r the c o r r e s p o n d i n g plot for s versus c (not shown) there was definite c u r v a t u r e i n the p o s i t i o n of the p o i n t s . T h e i n t e g r a l p l o t for the 80 m i n . p a t t e r n is the r i g h t - h a n d lowest line o n F i g u r e 3. T h e results of the s l i d i n g 7 p o i n t least m e a n squares fit are s h o w n i n F i g u r e 5. T h e accuracy of the d a t a is i n d i c a t e d b y the closeness o f the a c t u a l d a t a p o i n t s (squares) t o the s m o o t h e d p o i n t s (continuous line) for the differential d i s t r i b u t i o n curve given i n F i g u r e 6. O n e cannot tell whether the s m a l l convolutions w h i c h are revealed i n the c o r r e s p o n d i n g differential d i s t r i b u t i o n p a t t e r n are r e a l , or represent artifacts or errors i n the d a t a . F i n a l l y , the i n t e g r a l molecular weight d i s t r i b u t i o n is s h o w n i n F i g ure 7 a n d differential m o l e c u l a r weight d i s t r i b u t i o n is s h o w n i n F i g u r e 8. These transforms were m a d e u s i n g E q u a t i o n s 11 a n d 14 w i t h the M a r k H o u w i n k constants K' = 6.31 x 1 0 ~ a n d a = 0.8 for weight-average, m o l e c u l a r weight samples as measured b y S h a w k i a n d H a m i e l e c (16). T h e shape o f these curves are w h a t one w o u l d expect for a f r a c t i o n o f p o l y ( l a m i d o e t h y l e n e ) o b t a i n e d f r o m a free-radical p o l y m e r i z e d p o l y m e r . T h e h i g h molecular weight t a i l of the d i s t r i b u t i o n is a c o m m o n a n d c h a r a c t e r istic aspect of t h i s p o l y m e r . It s h o u l d be noted t h a t the t r a n s f o r m a t i o n of s e d i m e n t a t i o n coefficient as given i n F i g u r e s 5 a n d 6 to m o l e c u l a r weight as given i n F i g u r e s 7 a n d 8 generates a profile w i t h shifted p o s i t i o n a n d relative m a g n i t u d e . T h e peak at 4s seen i n F i g u r e 6 shifts to a m o l e c u l a r weight peak of 220,000 i n the m o l e c u l a r weight d i s t r i b u t i o n g i v e n i n F i g u r e 8. T h e one s u n i t displacement to the shoulder at 5s seen i n F i g ure 6, w h i c h i m p l i e s a significant weight f r a c t i o n of s a m p l e s e d i m e n t i n g w i t h coefficients between 4s a n d 5s, truncates to a m i n o r inflection i n the differential m o l e c u l a r weight curve given i n F i g u r e 8, w h i l e the m o n o t o n i c t a i l f r o m 5.5s to 14s i n F i g u r e 6 expands to the l o n g 1,000,000 to 4,500,000 m o l e c u l a r weight t a i l o f F i g u r e 8. 5

T h e average l i m i t i n g v i s c o s i t y number a n d weight-average m o l e c u l a r weight were c a l c u l a t e d by u s i n g E q u a t i o n s 10 a n d 11. These values increase w i t h a n increase i n the n u m b e r of zones i n t o w h i c h the s e d i m e n t a t i o n fringe curve is b r o k e n , because increasing the zones leads to greater i n c l u s i o n o f a region t h a t is m u c h higher i n m o l e c u l a r weight. T h e values o b t a i n e d for 10, 20, a n d 50 zones are s h o w n i n T a b l e I for b o t h the 80 a n d 100 m i n . p a t t e r n s . T h e values for the 80 m i n . p a t t e r n s rise more s h a r p l y w i t h the n u m b e r of zones. T h e sharper rise is due to the fact the earlier p a t t e r n s reveal the existence of larger molecules t h a t are sedimented past the p l a t e a u at a later t i m e . F r o m the d a t a i n the table one can estimate a n average m o l e c u l a r weight of about 5.5 to 6.5 x 1 0 a n d a l i m i t i n g viscosity of 2.2-2.5. 5

Since increasing the n u m b e r of zones used to measure the above averages incorporates more of the h i g h m o l e c u l a r weight t a i l of the p o l y m e r s a m p l e , the measurement w i t h the highest n u m b e r of zones s h o u l d be the

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Figure 4. Determination of limiting sedimentation coefficient for 9 weight fractions of the poly(l-amidoethylene) standard based on equation 2.

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0

10

5

15

5

F i g u r e 5. A plot of G ( s ) , the i n t e g r a l s e d i m e n t a t i o n w i t h s s h o w n i n svedbergs.

distribution pattern

w i t h s s h o w n i n svedbergs.

F i g u r e 6. A p l o t of g(s), the differential s e d i m e n t a t i o n d i s t r i b u t i o n p a t t e r n

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(SI

ι

i

ι

I

η

S

ι

Ξ

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MOL WT

F i g u r e 7. A plot of the integral molecular weight d i s t r i b u t i o n for the p o l y ( l amidoethylene) standard.

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F i g u r e 8. A plot o f the differential molecular weight d i s t r i b u t i o n for the poly(l-amidoethylene) standard.

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78

T a b l e I. A v e r a g e L i m i t i n g V i s c o s i t y N u m b e r a n d Weight-average, M o l e c u l a r W e i g h t for the P o l y ( l - a m i d o e t h y l e n e ) S a m p l e M

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w

x 10"

5

N u m b e r of Zones

80 m i n .

100 m i n .

80 m i n .

100 m i n .

10 20 50

5.14 6.31 6.42

4.90 5.61 5.61

2.18 2.39 2.52

2.11 2.22 2.29

better measure of the a c t u a l properties of the p o l y m e r s a m p l e . F u r t h e r more, the fringe p a t t e r n w i t h the largest p l a t e a u region a n d a clear meniscus w i l l a g a i n i n c l u d e the largest f r a c t i o n of the sample's m o l e c u l a r weight d i s t r i b u t i o n . T h e best d a t a p o i n t s s h o u l d then come f r o m the 80 m i n . p a t t e r n a n a l y z e d w i t h 50 zones. T h e sample was s u p p l i e d as a 500,000 m o l e c u l a r weight s t a n d a r d w i t h M = 476,000 as d e t e r m i n e d b y light s c a t t e r i n g . T h e value f o u n d f r o m the d i s t r i b u t i o n curve i n t e g r a t i o n is 642,000, signifi c a n t l y higher t h a n the l a b e l r a t i n g for the s t a n d a r d a n d 3 5 % higher t h a n the m o l e c u l a r weight f o u n d b y light s c a t t e r i n g . T h e several averages for the m o l e c u l a r weight d i s t r i b u t i o n of the 80 m i n . p a t t e r n a n a l y z e d w i t h 50 zones are M = 127,000, M = 642,000, a n d M = 2 , 0 1 1 , 0 0 0 . T h e loss of the h i g h m o l e c u l a r weight end of the d i s t r i b u t i o n w i t h longer s p i n n i n g times is verified by a detailed analysis of the d a t a . T h e s e d i m e n t a t i o n coefficients of the two b o t t o m zones of the 80 m i n . r u n were 4 9 t h = 12.69 and 5 0 t h = 14.50. T h e sedimentation coefficient of the b o t t o m zone of the 100 m i n . r u n was 5 0 t h = 12.24. T h u s , i n 20 minutes of s p i n n i n g , m a t e r i a l w i t h s between 12.24 a n d 14.5 was s p u n out of s o l u t i o n . T h e M at 80 m i n . , based o n o n l y the first 49 p o i n t s , was 551,000 or 9 8 . 3 % of the M f r o m a l l zones of the 100 m i n . r u n . T h e m e t h o d allows a l l m o l e c u lar weight fractions of a sample to be observed when the fringe p a t t e r n is p h o t o g r a p h e d after s p i n n i n g times of 40 m i n . or less. F u r t h e r , t h i s m e t h o d w i l l allow a clearer a n d more q u a n t i t a t i v e d i s t i n c t i o n t o be m a d e between c o n t a m i n a n t s a n d s a m p l e . In light s c a t t e r i n g , i f the s a m p l e scatters too m u c h l i g h t , it is filtered or s p u n to remove " d u s t . " If the s a m p l e were c o n t a m i n a t e d b y macroscopic p a r t i c u l a t e s , u l t r a c e n t r i f u g a t i o n w o u l d show a discontinuous h i g h m o l e c u l a r weight t a i l . T h i s c o n t a m i n a n t c o u l d t h e n be excluded f r o m c a l c u l a t i o n of molecular weight averages. If the " d u s t " to be removed for a light s c a t t e r i n g e x p e r i m e n t is the h i g h m o l e c u l a r weight t a i l of the m o l e c u l a r weight d i s t r i b u t i o n , this m e t h o d w o u l d q u a n t i t a t i v e l y demonstrate t h a t . A light scattering experiment w o u l d not show t h a t the results h a d been biased b y removal of some of the s a m p l e . w

n

w

2

w

w

T h e l i m i t i n g viscosity n u m b e r for the 80 m i n . p a t t e r n w i t h 50 zones is 2.50 d L / g as compared to an e x p e r i m e n t a l value of 2.45 d L / g . T h e e x p e r i m e n t a l l i m i t i n g viscosity n u m b e r was d e t e r m i n e d f r o m the d a t a of T a b l e II. T h e r a t i o of c a l c u l a t e d [rj\ to e x p e r i m e n t a l [77] is 1.020. T h i s result is i n s t r o n g contrast to the molecular weight values d e t e r m i n e d f r o m the

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T a b l e II. V i s c o s i t y of the S a m p l e s S p u n i n the U l t r a c e n t r i f u g e

Sample Number

Concentration (ppm)

Relative Viscosity (dimensionless)

1 2 3 4 5 Solvent*

2120 1690 1250 849 412 0

1.497 1.400 1.302 1.205 1.102 1.000

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* V i s c o s i t y of solvent was 1.005 x 1 0

- 3

Pas.s at 2 0 ° C .

d i s t r i b u t i o n since the [rj\ values m a t c h to w i t h i n 2.0%. Since the rheological properties of any p o l y m e r are controlled b y the h i g h m o l e c u l a r weight t a i l of the m o l e c u l a r weight d i s t r i b u t i o n , the [rj\ values provide very s t r o n g s u p p o r t for the v a l i d i t y of the m e t h o d . A l s o , the [rj\ value o b t a i n e d f r o m e x p e r i m e n t was determined o n the p o l y m e r solutions tested for M. w

Errors T h e r e are a n u m b e r of factors to be considered i n the e v a l u a t i o n of the m e a surements. F i r s t , the average d e v i a t i o n of the fringe p o s i t i o n s as c a l c u l a t e d f r o m the averaging of three fringes is about 0.004 fringes. T h u s , c o r r e c t i o n of the s e d i m e n t a t i o n patterns w i t h a baseline p a t t e r n doubles the d e v i a t i o n to about 0.01 fringes. A f t e r the s l i d i n g least m e a n squares cubic fit, the average d e v i a t i o n is reduced to 0.001 fringes. However, there is a persistent variable p r o b l e m i n u l t r a c e n t r i f u g e m e a surements, n a m e l y the i n s t a b i l i t y of the cell at h i g h centrifugal fields a r i s i n g f r o m d i s t o r t i o n of plastic centerpieces a n d w i n d o w gaskets. T h e u s u a l test for cell s t a b i l i t y is e x a m i n a t i o n of baselines at low speed a n d j u s t after a t t a i n i n g the o p e r a t i n g speed. (Sometimes a d d i t i o n a l baselines are o b t a i n e d after r e m o v i n g the rotor, s h a k i n g the rotor w i t h o u t r e m o v i n g the cell to red i s t r i b u t e the sedimented m a t e r i a l , a n d o b t a i n i n g new baseline patterns.) If the low a n d h i g h speed patterns are the same, one is more confident t h a t the baseline is correct. If they differ, one assumes t h a t the high-speed baseline is the better of the two, b u t there is always the p o s s i b i l i t y t h a t the p a t t e r n continued to change further w i t h t i m e . Moreover, after disassembly a n d reassembly of a cell, the baseline p a t t e r n u s u a l l y changes; hence, it m u s t be measured for every experiment. F o r these e x p e r i m e n t s , the baseline patterns deviate f r o m one another by, at m o s t , 0.05 fringes. Baseline error leads to warpage of the interference fringe p a t t e r n ; the m a g n i t u d e of this cannot be d e t e r m i n e d . A n a l t e r n a t i v e m e t h o d , s e d i m e n t a t i o n e q u i l i b r i u m u l t r a c e n t r i f u g a t i o n , does not require the h i g h rotor speeds t h a t p r o d u c e warpage. In these experiments, the lack of a well-defined s u p e r n a t a n t region leads to a n u n c e r t a i n t y i n the weight-fraction values for each s o l u t i o n , w i t h the error b e i n g less i n the steeper parts of the curves. T h e p l a t e a u region

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was sufficiently free o f r a n d o m noise t h a t t h e fringes values are accurate to p r o b a b l y better t h a n ± 0 . 0 2 fringes. T h e m a g n i t u d e o f t h i s fringe error i n molecular weight u n i t s depends o n the c o n c e n t r a t i o n o f p o l y m e r i n t h e s a m p l e a n d p o s i t i o n w i t h respect t o the p l a t e a u region o f the s p u n s o l u t i o n . A s a n e x a m p l e o f the effect o f t h i s u n c e r t a i n t y , however, a n error o f .02 fringes w o u l d b e a m o l e c u l a r weight error o f 0 . 3 % for measurements o n s a m p l e 2 i n the p l a t e a u region.

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Conclusions A m e t h o d has been developed for the c a l c u l a t i o n o f detailed a n d absolute m o l e c u l a r weight d i s t r i b u t i o n s for complex p o l y m e r samples. T h e m e t h o d enjoys the advantages o f speed a n d c o m p a r a t i v e convenience w i t h respect to e q u i l i b r i u m u l t r a c e n t r i f u g a t i o n a n d the m u c h needed features o f absolute measurement a n d c o n d i t i o n independence w i t h respect t o gel p e r m e a t i o n chromatography. T h e m e t h o d requires t h a t a s e d i m e n t a t i o n v e l o c i t y e x p e r iment be performed o n at least three different concentrations o f the p o l y m e r i n solvent. T h e solutions m u s t be d i l u t e a n d the R a y l e i g h interference p a t tern photos o f the s e d i m e n t i n g samples must be t a k e n at e q u a l times d u r i n g the e x p e r i m e n t . T h r e e fringes o f the interference p a t t e r n are d i g i t i z e d , a v eraged, a n d fitted w i t h a p o l y n o m i a l . T h e p o l y n o m i a l c a n b e differentiated to give a curve w h i c h , when c o m b i n e d w i t h a f u n c t i o n o b t a i n e d f r o m t h e M a r k - H o u w i n k e q u a t i o n , produces a differential molecular weight d i s t r i b u t i o n . T h e differential f o r m o f the d i s t r i b u t i o n c a n be integrated t o give a n integral m o l e c u l a r weight d i s t r i b u t i o n . E i t h e r d i s t r i b u t i o n c a n be used t o calculate molecular weight averages or moments o f the d i s t r i b u t i o n . A p p l i c a t i o n o f the m e t h o d t o a c o m m e r c i a l p o l y ( l - a m i d o e t h y l e n e ) s t a n d a r d gave a l i m i t i n g viscosity number t h a t m a t c h e d the e x p e r i m e n t a l value t o w i t h i n 3 % a n d weight average molecular weight t h a t bracketed the value c l a i m e d by the s u p p l i e r . Acknowledgments T h i s work was p a r t i a l l y s u p p o r t e d b y t h e N a t i o n a l Science F o u n d a t i o n under grants C P E - 8 2 6 0 7 6 6 a n d C B T - 8 4 1 7 8 7 6 . Literature C i t e d 1. Mark, J . E . ; Eisenberg, A.; Graessley, W . W.; Mandelkern, L . ; Koenig, J. L . Physical Properties of Polymers; A m . Chem. Soc.: Washington, D C , 1984; pp. 111-137. 2. Schachman, H . K . Ultracentrifugation in Biochemistry; Academic Press: New York, 1959. 3. Fujita, H . Mathematical Theory of Sedimentation Analysis; Academic Press: New York, 1962. 4. Fujita, H.Foundations of UltracentrifugalAnalysis (Chemical Analysis Series Monographs, Vol. 42); Wiley: New York, 1975. 5. Gralen, N.; Lagermalm, G . J. Phys. Chem. 1952, 56, 514.

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6. Mandelkern, L.; Krigbaum, W.R.; Scheraga, H.A.; Flory, P.J. J. Phys. Chem. 1952, 20, 1392. 7. Mark, H . Z. Elektrochem 1934, 40, 499. 8. Houwink, R. J. Prakt, Chem. 1940, 157, 15. 9. Huggins, M . L . J. Amer. Chem. Soc. 1942, 64, 2716-18. 10. Narkis, N.; Rebhun, M . Polymer 1966, 7, 507-12. 11. MacWilliams, D. C . ; Rogers, J. H.; West, T . J . In Water Soluble Polymers; Bikales, N. M . , Ed.; Plenum: New York, 1973; 106-24. 12. Francois, J . ; Sarazin, D.; Schwarts, T . ; Weill, G . Polymer 1979, 20, 969-75. 13. Richards, E . G . ; Rockholt, D . L . ; Richards, J . H . Fed. Proc. 1977, 36, 854. 14. Richards, E . G . ; Richards, J . H . Anal. Biochem. 1974, 62, 523. 15. Richards, E . G . ; Teller, D . C . ; Hoagland, V . C . Jr.; Haschemeyer, R . H . ; Schachman, H . K . Anal. Biochem. 1971, 41, 214. 16. Shawki, S. M . ; Hamielec, A . E . J. Appl. Polym. Sci. 1979, 23, 3323. 17. Meister, J . J.; Sha, M . - L . ; Richards, E . G . J. Appl. Sci. 1987, 33, 187385. RECEIVED March 17,1989

Chapter 6

Molecular Weight Distribution of Aspen Lignins Estimated by Universal Calibration M . E . Himmel , K. Tatsumoto , K. K. Oh , K. Grohmann , D. K. Johnson , and Helena L i Chum 1

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Applied Biological Sciences Section, Biotechnology Research Branch, Solar Fuels Research Division, Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401 Chemical Conversion Branch, Solar Fuels Research Division, Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401 2

This study describes the application of differential viscometry as a G P C detector to the problem of determining molecular weight distributions of acetylated hardwood lignins in tetrahydrofuran. Molecular weight distributions of ball-milled, organosolv, alkali-extracted/mild acid hydrolyzed, and alkali-extracted/steam exploded aspen lignins were estimated using universal calibration. Low molecular weight lignin model compounds (synthetic phenyl-tetramers and Igepals™) were found to fit universal calibration. Fractions from preparative G P C , when analyzed by universal calibration, yield molecular weight distributions which add to a similar value to that found for the unfractionated parent sample. Lignins are irregular phenylpropane polymers that represent approximately 20-30% by weight of the available polymeric content of hardwood tree stems (1-3). This material offers, therefore, a valuable resource that must be utilized as fully as possible if the full value of harvested tree crops is to be attained. The understanding of the macromolecular properties of lignins requires a reliable method for estimating the molecular weights (MW or M) and distribution of molecular weights (MWD) in a suitable solvent. Suitable solvents must be defined here as those that minimize interactions of solutesolute (aggregation), solute-solvent, and solute-column packing material. Although important contributions have been made to this field historically through packed-bed and high performance size exclusion chromatography (HPSEC) (4-17), the design of a chromatography system (solvent and stationary phase) that performs optimally has not been reported. Indeed, the more hydrophobic solvents such as dioxane and tetrahydrofuran ( T H F ) , which work well to minimize solute-column and solute-solute interactions, 0097-6156/89/0397-0082$06.00/0 © 1989 American Chemical Society

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p e r f o r m p o o r l y at t h e task o f s o l u b i l i z i n g l i g n i n s over a w i d e range o f M W . However, these solvents work very w e l l w i t h p o l y s t y r e n e - d i v i n y l b e n z e n e (e.g., / / - S t y r a g e l ) c o l u m n p a c k i n g m a t e r i a l s , causing n o p e r c e p t i b l e c o l u m n d e t e r i o r a t i o n (18). A p a r t f r o m these i m p o r t a n t l i m i t a t i o n s presented b y c o n v e n t i o n a l " G P C " m e t h o d o l o g y t o t h e s t u d y of l i g n i n M W D is t h e issue of the c o m p l e x i t y of these p o l y m e r s even i n i d e a l solvents. C o n v e n t i o n a l G P C is effective i n e s t i m a t i n g M W of u n k n o w n p o l y m e r s o f s i m i l a r or i d e n t i c a l c h e m i c a l s t r u c t u r e s t o those used t o c a l i b r a t e c o l u m n s . T h e e l u t i o n of p o l y m e r s of u n k n o w n (or i m p r e c i s e l y k n o w n ) chemistry, degree o f b r a n c h i n g , shape, degree o f s o l v a t i o n , a n d degree o f r e p e a t i n g u n i t s (as i n c h e m i c a l c o p o l y m e r s ) c a n be t r e a t e d o n l y " p h e n o m e n o l o g i c a l l y " w i t h c o n v e n t i o n a l S E C . T h e result o f the size e x c l u s i o n m e t h o d ( i f c h e m i c a l i n t e r a c t i o n s c a n be assumed t o be negligible) is t h e s e p a r a t i o n of solutes o n t h e basis of their respective h y d r o d y n a m i c r a d i i , T h i s i n f o r m a t i o n , alone, is n o t o f great u t i l i t y . Size e x c l u s i o n c h r o m a t o g r a p h y has been g r e a t l y e n r i c h e d recently b y the advent of two c o m m e r c i a l detectors, t h e r e a l - t i m e differential viscometer ( D V ) a n d the low angle laser l i g h t s c a t t e r i n g ( L A L L S ) p h o t o m e t e r . T h e o n l y D V detector c u r r e n t l y available is offered b y V i s c o t e k i n P o r t e r , T X , as the m o d e l 100. T h i s s t u d y reports the first a p p l i c a t i o n of u n i v e r s a l c a l i b r a t i o n v i a H P S E C - D V t o four a c e t y l a t e d h a r d w o o d l i g n i n s o b t a i n e d f r o m aspen (Populus tremuloides) w o o d m e a l b y b a l l m i l l i n g a n d solvent e x t r a c t i o n ; s t e a m e x p l o s i o n followed b y alkaline e x t r a c t i o n ; organosolv p u l p i n g followed b y water e x t r a c t i o n of the associated sugars; a n d d i l u t e s u l f u r i c a c i d h y d r o l y sis followed b y s o d i u m h y d r o x i d e e x t r a c t i o n .

Materials and Methods Chemicals and Standards. A l l chemicals a n d H P S E C eluants used i n this s t u d y were o b t a i n e d f r o m m a j o r c h e m i c a l suppliers ( J . T . B a k e r , F i s h e r Scientific, a n d A l d r i c h ) . T h e T H F used was F i s h e r H P L C grade. T h e M W s t a n d a r d s used t o c a l i b r a t e the three c o l u m n s y s t e m were o b t a i n e d f r o m A m e r i c a n P o l y m e r L a b s , M e n t o r , O h i o [polybutadienes (narrow M W D ) : P B 9 0 0 , P B 1 K , P B 3 K , P B 5 K , P B 2 3 K , P B 4 3 K ; p o l y - a methylstyrenes ( n a r r o w M W D ) : P A M S 6 K , P A M S 2 3 K , P A M S 6 6 K ; p o l y methylmethacrylates (broad M W D ) : P M M A 1 7 K , P M M A 3 5 K , P M M A 7 5 K , P M M A 1 0 0 K ] a n d f r o m P o l y m e r L a b s , E n g l a n d [polystyrenes ( n a r r o w M W D ) : PS1250, PS1700, PS2450, PS3250, PS5050, PS7000, PS9200, PS11600, P S 2 2 K , P S 3 4 K , a n d P S 6 8 K ; a n d polymethylmethacrylates (narrow M W D ) : P M M A 3 0 0 0 , P M M A 1 0 K , P M M A 2 7 K , P M M A 6 0 K , a n d P M M A 1 0 7 K ] . T h r e e s y n t h e t i c p o l y s t y r e n e s t a r - p o l y m e r s f r o m Polysciences, W a r r i n g t o n , P e n n s y l v a n i a , were also used [ M n = 7000, l o t # 55687; M n = 5 9 , 2 0 0 , l o t # 71520; M n = 126,900, l o t # 55690; a n d M n = 116,700, l o t # 55689]. O t h e r M W s t a n d a r d s e x a m i n e d i n c l u d e d four p h e n y l - t e t r a m e r s w h i c h were s u p p l i e d as generous gifts f r o m D r . J . A . H y a t t at E a s t m a n K o dak L a b s . These m o d e l c o m p o u n d s were prepared b y a m o d i f i e d enolate a d d i t i o n m e t h o d (19) a n d i n c l u d e b i p h e n y l t e t r a m e r hexaacetate (C54H6602o>

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M W = 1034), b i p h e n y l t e t r a m e r h e x a o l ( M W = 782), / ? - 0 - 4 t e t r a m e r heptaacetate (C55H66O22, M W = 1078) a n d / ? - 0 - 4 t e t r a m e r h e p t a o l ( M W = 784). T h e I g e p a l ™ ( G A F C o r p . , sold t h r o u g h A l d r i c h ) s t a n d a r d s F . W . = 749 a n d 1982 were also e x a m i n e d . T w o s y n t h e t i c p o l y m e r s p r e p a r e d b y a n i o n - i n i t i a t e d p o l y m e r i z a t i o n s of a q u i n o n e m e t h i d e a c c o r d i n g t o the p r o cedure o f C h u m et al. (20) were treated as i n t e r m e d i a t e M W l i g n i n m o d e l polymers. Lignin Samples. B a l l - m i l l e d ( B M ) aspen l i g n i n was p r e p a r e d f o l l o w i n g the procedure of L u n d q u i s t et al. (21). T h e y i e l d of p u r i f i e d m i l l e d w o o d l i g n i n o b t a i n e d was u s u a l l y a b o u t 1 0 % w / w t h a t of e t h a n o l / b e n z e n e - e x t r a c t e d aspen w o o d . A l k a l i n e - e x t r a c t e d / s t e a m - e x p l o d e d ( A E S E ) aspen l i g n i n samples were p r e p a r e d f r o m s t e a m e x p l o d e d w o o d samples (55 s residence t i m e at 2 4 0 ° C ) o b t a i n e d f r o m Iotech C o r p . E x p l o d e d w o o d p u l p was treated w i t h a series o f c a r b o n t e t r a c h l o r i d e a n d alkaline e x t r a c t i o n s (12). A l k a l i n e - e x t r a c t e d / a c i d h y d r o l y s i s ( A H / N a O H ) l i g n i n samples were p r e p a r e d by s u b j e c t i n g aspen w o o d flour t o a one h o u r cook at 120°C i n 0 . 0 5 N s u l f u r i c a c i d (22), followed b y m i x i n g the clarified s u p e r n a t a n t w i t h 1% w / w N a O H at 25°C w i t h a W a r i n g blender. T h e i n s o l u b l e l i g n i n s were p r e c i p i t a t e d b y a d d i t i o n of a c i d a n d water washes ( 3 2 % y i e l d ) . T h e organosolv ( O S ) l i g n i n was prepared f r o m the l i q u o r o b t a i n e d b y t r e a t i n g aspen w o o d flour w i t h a 7 0 : 3 0 M e O H : w a t e r ( v / v ) e x t r a c t i o n at 165°C for 2.5 hours i n a r o c k i n g autoclave as described i n ref. 23. L i g n i n samples were a c e t y l a t e d f o l l o w i n g a m e t h o d developed b y G i e r e r a n d L i n d e b e r g (24) w h i c h allows q u a n t i t a t i v e recovery of l i g n i n s . L i g n i n samples were stored frozen d u r i n g the course of the s t u d y . T h r o u g h o u t the s t u d y , freshly prepared solutions were i n v e s t i g a t e d . However, no t i m e dependence of M W d a t a was observed i n any of the techniques e m p l o y e d w h e n samples were o c c a s i o n a l l y r e e x a m i n e d after i n i t i a l p r e p a r a t i o n . Chromatography System. T h e H P S E C - D V s y s t e m used i n t h i s s t u d y c o n sisted o f a B e c k m a n M o d e l 1 0 0 A d u a l - p i s t o n H P L C p u m p fitted w i t h extern a l pulse d a m p e n i n g , a B e c k m a n M o d e l 210 i n j e c t i o n valve fitted w i t h a 250 fiL l o o p , an S S I i n j e c t i o n valve filter, a H e w l e t t - P a c k a r d M o d e l 1 0 3 7 A h i g h s e n s i t i v i t y R I detector, a n d a V i s c o t e k M o d e l 1 0 0 L C differential v i s c o m e ter. F o r studies of l i g n i n c o n c e n t r a t i o n effects, a K n a u e r U V detector set at 280 n m was used as w e l l . T h e c h r o m a t o g r a p h y c o l u m n s y s t e m was c o m posed of three 7.8 x 30 m m c o l u m n s ( B e c k m a n ^ - S p h e r o g e l , 10,000, 1,000, a n d 5 0 0 A ) connected i n series i n order of increasing pore size. C a l c u l a t i o n s were p e r f o r m e d u s i n g the V i s c o t e k U n i c a l 2.71 software. A l l injections o n the H P S E C - D V s y s t e m were m a d e b y o v e r f i l l i n g the 2 5 0 / / L l o o p , thereby p r o v i d i n g a true 250 fiL i n j e c t i o n . N a r r o w a n d b r o a d M W s t a n d a r d s were injected o n t o the H P S E C - D V s y s t e m at concentrations near 1 m g / m L a n d 2 m g / m L , respectively. I n i t i a l l y , i n order to o b t a i n a usable differential pressure c h r o m a t o g r a m , the l i g n i n samples were injected at concentrations near 20 m g / m L , w i t h a n i n s t r u m e n t ( A - D amplifier) g a i n s e t t i n g o f 1 (0-1.0 volt F u l l Scale). A s the

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w o r k proceeded, a g a i n s e t t i n g o f 2 (0-0.1 v o l t F S ) a l l o w e d e x a m i n a t i o n of l i g n i n samples at concentrations o f 4 a n d 8 m g / m L . A s a test for l i g n i n a s s o c i a t i o n i n T H F at these concentrations, the organosolv l i g n i n was c h r o m a t o g r a p h e d at i n i t i a l i n j e c t i o n concentrations of 0.5 a n d 1 m g / m L as well. C o n c e n t r a t i o n s o f a l l s t a n d a r d a n d s a m p l e s o l u t i o n s s t u d i e d were precisely d e t e r m i n e d by w e i g h i n g the d r y m a t e r i a l s to the nearest 0.0005 m g u s i n g a S a r t o r i u s U l t r a m i c r o balance M o d e l 4504 M P 8 . L i g n i n samples e x a m i n e d b y H P S E C - D V were m a d e t o c o n c e n t r a t i o n i m m e d i a t e l y before i n j e c t i o n . T h e organosolv l i g n i n samples were s u b j e c t e d t o p r e p a r a t i v e c o l u m n c h r o m a t o g r a p h y i n T H F u s i n g a t w o c o l u m n , μ-Styragel s y s t e m f r o m Y M C , J a p a n (5 c m x 2 0 0 c m , 500 a n d 1000Â). A B e c k m a n M o d e l H O B p u m p , M o d e l 210 i n j e c t i o n valve w i t h a 2 m L l o o p , a n d a M o d e l 153 U V detect o r w i t h s e m i - p r e p a r a t i v e flow cell were used w i t h these c o l u m n s . S a m p l e l o a d i n g s were u s u a l l y 60 m g . F r a c t i o n s were collected w i t h a n Isco F o x y f r a c t i o n collector w i t h p r e p a r a t i v e c a p a b i l i t y a n d stored i n K i m a x screwt o p p e d glass tubes (25 x 150 m m ) w i t h T e f l o n - l i n e d caps. Before c h r o m a t o g r a p h i c a n a l y s i s these fractions were p o o l e d i n t o five m a s t e r f r a c t i o n s a n d c o n c e n t r a t e d b y r o t o - e v a p o r a t i o n at 25°C. V a l u e s f o u n d for the e x t i n c t i o n coefficient of organosolv a n d b a l l m i l l e d l i g n i n b y c o n v e n t i o n a l g r a v i m e t r i c a n a l y s i s , e 70nm (g m L ~ c m " " ) = 15,300 a n d 10,100, respectively, were used to estimate the dried-weight equivalent of the concentrated fractions recovered f r o m p r e p a r a t i v e c h r o m a t o g r a p h y . These c o n c e n t r a t i o n values are c r i t i c a l for m e a n i n g f u l e s t i m a t i o n o f M W u s i n g the U n i c a l software. 2

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Calculation of Results from Differential Viscometry and SEC. T h e f a m i l i a r r e l a t i o n s h i p first expressed b y M a r k (25) a n d H o u w i n k (26) i n the 1940's is c e n t r a l to the concept of u n i v e r s a l c a l i b r a t i o n first suggested by B e n o i t et al. (27). I n t h i s r e l a t i o n s h i p , [η] = K'M

a

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[η] is the i n t r i n s i c viscosity, a n d K' a n d a are k n o w n as the M a r k - H o u w i n k constants a n d are specific t o a p o l y m e r - s o l v e n t - t e m p e r a t u r e s y s t e m . F o r flexible, linear p o l y m e r s , values of α are l i m i t e d t o the range 0.50 t o 0.80. C o n s i d e r i n g the derivations of e q u a t i o n (1), i t can be p r e d i c t e d t h a t a l l molecules h a v i n g the same value o f [η]Μ w o u l d have the same v a l u e of v/», the h y d r o d y n a m i c v o l u m e . A l s o , i f ν Λ is the p a r a m e t e r t h a t u n i q u e l y determines the e l u t i o n v o l u m e , V , these molecules s h o u l d have the same e l u t i o n v o l u m e . T h e arguments presented b y these a u t h o r s d o n o t p r e d i c t t h a t the r e l a t i o n s h i p between these parameters s h o u l d necessarily be l i n e a r . M o s t u n i v e r s a l c a l i b r a t i o n curves s h o w n i n the l i t e r a t u r e t h a t cover 4 to 6 decades o f M show a definite u p w a r d c u r v a t u r e at h i g h values o f M (28). Sources o f error i n t h i s a p p r o a c h arise f r o m b o t h e x p e r i m e n t a l a n d the­ o r e t i c a l grounds. M o d e r n theories of S E C r e t e n t i o n m e c h a n i s m are based o n the a s s u m p t i o n t h a t the size e x c l u s i o n process u n i q u e l y determines the e l u t i o n v o l u m e , a n d yet the p o s s i b i l i t y of reversible a d s o r p t i o n is difficult to dismiss a n d , where i t occurs, errors i n the i n t e r p r e t a t i o n m a y easily result. A s a w a r n i n g for the a p p l i c a t i o n o f universal c a l i b r a t i o n m e t h o d o l o g y , C a s sassa (29) i n d i c a t e s i n a l a t e r paper t h a t the q u a n t i t y [η]Μ is not a t r u l y e

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u n i v e r s a l e l u t i o n p a r a m e t e r for S E C , b u t t h a t b o t h t h e o r y a n d experience i n d i c a t e t h a t g o o d results can be o b t a i n e d for e l u t i n g species of s i m i l a r t y p e (e.g., r o d - l i k e macromolecules of s i m i l a r cross-sectional d i m e n s i o n i n a r e s t r i c t e d size range or l i n e a r flexible p o l y m e r c h a i n s ) . C a s s a s s a predicts f r o m theory, however, t h a t over r e s t r i c t e d ranges of M, a c o m m o n [η]M dependence between r a n d o m c o i l p o l y m e r s a n d r o d - l i k e s t r u c t u r e s s h o u l d exist. Divergence often increases, however, w h e n considering fit u s i n g d a t a over three orders of m a g n i t u d e i n M (30). A p p l i c a t i o n of u n i v e r s a l c a l i b r a t i o n to u n k n o w n p o l y m e r s u s i n g the V i s c o t e k U n i c a l software, once the c o l u m n s y s t e m has been c a l i b r a t e d w i t h n a r r o w M W D s t a n d a r d s , is q u i t e s t r a i g h t f o r w a r d . A m a s t e r c a l i b r a t i o n file of n a r r o w M W D s t a n d a r d s was developed w h i c h i n c o r p o r a t e s the "peak p a r a m e t e r " values c a l c u l a t e d f r o m one (or averaged f r o m several) w e l l be­ haved n a r r o w M W D s t a n d a r d . These values correct for c h r o m a t o g r a p h i c m i s m a t c h of the two detectors ( R I a n d differential pressure) used i n the s y s t e m a n d l e a d t o the c a l c u l a t i o n of values t h a t a p p r o x i m a t e a correc­ t i o n for peak b r o a d e n i n g ( r ) a n d peak t a i l i n g ( σ ) . T h e s e peak parameters represent effects specific t o the c h r o m a t o g r a p h i c s y s t e m used i n each l a b ­ o r a t o r y , a n d were d e t e r m i n e d for t h i s s t u d y to be 0.256 m L , 0.280 a n d 0.256 for σ, τ ( V ) , a n d r ( C ) , respectively. T h e c o n c e n t r a t i o n value for each s a m p l e processed b y t h i s procedure m u s t be k n o w n accurately, as t h i s t e r m enters i n t o c a l c u l a t i o n s of reduced viscosity, measured here d i r e c t l y as specific viscosity, a n d the M W averages. A n a s s u m p t i o n c e n t r a l t o the d a t a processing is t h a t under c h r o m a t o g r a p h i c c o n d i t i o n s s a m p l e d i l u t i o n is sufficient to assume t h a t the reduced v i s c o s i t y a p p r o x i m a t e s the i n t r i n s i c v i s c o s i t y (or l i m i t i n g v i s c o s i t y n u m b e r ) . T h e software c a n be used t o c a l ­ culate the M a r k - H o u w i n k plots ([η] versus M) for each s t a n d a r d p o l y m e r series. A l l p o l y m e r s t a n d a r d s are t h e n used t o c o n s t r u c t a u n i v e r s a l c a l i ­ b r a t i o n p l o t of [η]M versus e l u t i o n v o l u m e . T h e software can also be used t o recalculate the values of M , M , M a n d M * + i for the n a r r o w M W D s t a n d a r d s used to construct the curve ( a p p r o x i m a t e l y ± 1 0 % d e v i a t i o n for M is observed i n these r e c a l c u l a t e d values w h e n c o m p a r e d w i t h the v a l ­ ues entered i n i t i a l l y ) . M o l e c u l a r weight averages are f o u n d for u n k n o w n p o l y m e r s (accepting the l i m i t i n g a s s u m p t i o n s discussed above) i n a s i m i l a r way. A p p l i c a t i o n of U n i c a l software also requires the selection of c h r o m a t o ­ g r a p h i c baselines, thus selecting the specific d a t a t a k e n for further a n a l y s i s . In the studies r e p o r t e d here, we choose to analyze o n l y the p o l y disperse en­ velope f r o m l i g n i n e l u t i o n , so t h a t the d i s t i n c t c o m p o n e n t w h i c h often elutes near Y (the t o t a l c o l u m n v o l u m e ) was not i n c l u d e d i n the a n a l y s i s . n

w

Z1

w

t

Results and Discussion Universal Calibration. T h e aspen w o o d l i g n i n samples chosen for t h i s s t u d y were prepared b y organosolv, s t e a m e x p l o s i o n , d i l u t e a c i d h y d r o l y s i s , a n d b a l l - m i l l i n g procedures. C a l i b r a t i o n curves were developed for H P S E C - D V u s i n g p o l y m e r s t a n ­ d a r d s i n c l u d i n g n a r r o w M W D polystyrenes, p o l y butadienes, p o l y m e t h y l -

6.

HIMMEL ET A L

MWDistribution

by Universal Calibration

87

m e t h a c r y l a t e s , a n d p o l y - a - m e t h y l s t y r e n e s . A set of b r o a d M W D p o l y ­ m e t h y l m e t h a c r y l a t e s was also e x a m i n e d . A l l five s t a n d a r d curves i n d i c a t e d very g o o d fit to a l i n e a r f u n c t i o n over the range of M W tested. T h e M a r k H o u w i n k parameters for a a n d —K were f o u n d to be 0.73 a n d 4.35, 0.60 a n d 3.76, 0.72 a n d 3.87, 0.69 a n d 4.26, 0.73 a n d 4.55 for the P S , P A M S , P B , P M M A , a n d P M M A - 6 s t a n d a r d s , respectively. A l l M a r k - H o u w i n k p a ­ rameters, a a n d K\ w i t h the exception of α for the p o l y - a - m e t h y l s t y r e n e s , c o m p a r e closely w i t h those p u b l i s h e d b y H a n e y a n d A r m o n a s (31) u s i n g identical conditions and instrumentation. A u n i v e r s a l c a l i b r a t i o n p l o t (log [η]Μ vs. e l u t i o n v o l u m e ) u s i n g these five s t a n d a r d s series was c o n s t r u c t e d ( F i g . 1). Several other s t a n d a r d M W p o l y m e r s a p p r o p r i a t e t o l i g n i n m o d e l studies were also e x a m i n e d . T h e s e i n c l u d e d two Igepals, four p o l y s t y r e n e star p o l y m e r s , a n d four s y n t h e t i c p h e n y l t e t r a m e r s (two b i p h e n y l s a n d two β-Ο-4 l i n k e d t e t r a m e r s ) . O f a l l the s t a n d a r d s e x a m i n e d , o n l y the p o l y s t y r e n e star p o l y m e r p r e p a r a t i o n i n d i c a t e d p a u c i d i s p e r s i t y . H e r e , the e l u t i o n o f the lower M W c o m p o n e n t ( u s u a l l y i n preponderance) was considered i n the c a l c u l a t i o n s . W i t h the e x c e p t i o n o f one h i g h M W s t a r p o l y m e r , a l l these c o m p o u n d s were f o u n d t o fit u n i v e r s a l c a l i b r a t i o n at least as w e l l as the c o m m e r c i a l p o l y m e r s t a n d a r d s ( F i g . 1). Indeed, the fit o f the low M W p h e n y l t e t r a m e r s ( M W « 800-1000) was i m p o r t a n t . T h e c a l i b r a t i o n curve c o n s t r u c t e d for use i n t h i s s t u d y shows l i t t l e or not c u r v a t u r e over the five decade range o f log[?;]M. T h i s o b s e r v a t i o n is consistent w i t h t h a t of other workers ( 2 8 , 3 1 ) , where the lowermost p o r t i o n o f such curves approaches l i n e a r i t y , w h i l e over a w i d e r range o f l o g [η] M some u p w a r d c u r v a t u r e is e v i d e n t . U n i c a l 2.71 software allowed the c a l c u l a t i o n of a u n i v e r s a l c a l i b r a t i o n curve f r o m a b r o a d M W D s t a n d a r d , P M M A 1 7 K - 6 . T h i s curve appears i n F i g u r e 1 as a dashed l i n e . A l t h o u g h some d e v i a t i o n at d a t a extremes is a p p a r e n t , the fit near the l i g n i n e l u t i o n region is n e a r l y i d e n t i c a l to the curve f r o m n a r r o w c a l i b r a t i o n .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

1

MWD of Acttylated Lignins. T h e first a t t e m p t s at l i g n i n c h r o m a t o g r a p h y e m p l o y e d 250 / i L injections of samples m a d e to 20 m g / m L . T h i s p r o c e ­ dure p r o d u c e d acceptable differential pressure signals; however, the very h i g h c o n c e n t r a t i o n was undesirable as i t is k n o w n t o i n d u c e solute-solute i n t e r a c t i o n . A f t e r r e s e t t i n g the amplifier g a i n t o 2 ( a s e t t i n g o f 1 be­ i n g the s t a n d a r d " d e f a u l t " value for the i n s t r u m e n t ) , differential pressure c h r o m a t o g r a m s w i t h l i g n i n s at loadings o f 2 m g (250 μΐι injections f r o m 8 m g / m L stock solutions) were very w e l l behaved ( F i g s . 2-4). I n s p e c t i o n of F i g u r e s 2 a n d 3 reveals t h a t the r e l a t i v e m a g n i t u d e of the differential pressure s i g n a l at higher M W is greater t h a n t h a t f r o m the differential refractive i n d e x detector. T h e four l i g n i n s were also injected o n the c h r o ­ m a t o g r a p h y s y s t e m at a l o a d i n g of 1 m g (250 / i L f r o m a 4 m g / m L stock s o l u t i o n ) . These d u a l c h r o m a t o g r a m s proved t o i n d i c a t e the l i m i t i n g sen­ s i t i v i t y for the b r o a d l y p o l y disperse l i g n i n samples s t u d i e d here. A l t h o u g h the " s m o o t h i n g " routines i n U n i c a l were capable of r e n d e r i n g these noisy differential c h r o m a t o g r a m s usable, i t was clear t h a t a m o r e d i l u t e injec­ t i o n s a m p l e w o u l d not be m e a n i n g f u l . A n e x a m p l e o f the best d u a l c h r o m a t o g r a m f r o m a 1 m g l o a d i n g (before s m o o t h i n g ) is s h o w n i n F i g u r e 4 U .

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

88

F i g u r e 1. M a s t e r u n i v e r s a l c a l i b r a t i o n curve o b t a i n e d w i t h a B e c k m a n μ-Spherogel c o l u m n s y s t e m i n T H F . T h e fit of n a r r o w M W D s t a n d a r d s , p o l y s t y r e n e star p o l y m e r s , a n d a single b r o a d M W D s t a n d a r d ( c a l c u l a t e d w i t h U n i c a l 2.71 software) are s h o w n .

R I M M E L ET AL.

6.

MW Distribution by Universal Calibration

89

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

DUAL CHROMATOGRAM

25.0 RET

30.0 VOL (ml)

35.0 CONC CHROMATOGRAM ?

MOLECULAR HEIGHT DISTRIBUTION

S

6.00

LOG M

Figure 2 A . Dual chromatograms showing the elution of aspen A E S E lignin from the H P S E C - D V system. A 250 /zL sample was injected from a freshly prepared 8 mg / m L stock solution. Viscotek A / D amplifier gain setting of 2 and R I detector setting o f l x . Calculated molecular weights are also shown.

90

LIGNIN: PROPERTIES AND MATERIALS

8.00 y

DUAL CHROMATOGRAM

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

5.00

2.00

V l.oo

25.0

RET VOL

CJ

θ.00

30.0

(ml)

35.0

40.0

CONC CHROMATOGRAM ?

HEIGHT DISTRIBUTION

7.00

5.00

1.00

Figure 2 B . D u a l chromatograms showing the elution of ball-milled lignin from the H P S E C - D V system. Sample loading was the same as in Figure 2 A .

6.

H I M M E L ET AL.

MW Distribution by Universal Calibration

7.00

91

DUAL CHROMATOGRAM

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

4.00

1.00

.000 15.0

25.0 RET

VOL (ml)

30.0

35.0

40.0

CONC CHROMATOGRAM !

MOLECULAR HEIGHT DISTRIBUTION

5.00

4.00

3.00

.000 2.00

Figure 3 A . Dual chromatograms showing the elution o f aspen organosolv lignin from the H P S E C - D V system. Sample loading was the same as i n Figure 2 A . Calculated molecular weights are also shown.

LIGNIN: PROPERTIES AND MATERIALS

92

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

DUAL CHROMATOGRAM

25.0

RET VOL

30.0

(ml)

35.0

40.0

CONC CHROMATOGRAM ?

MOLECULAR HEIGHT DISTRIBUTION

Figure 3 B . Dual chromatograms showing the elution of A H / N a O H lignin from the H P S E C - D V system. Sample loading was the same as i n Figure 2 A .

Figure 4 A . D u a l chromatogram showing the elution of A E S E aspen lignin from the H P S E C - D V system with an amplifier gain setting of 2 and an R I setting of l/4x. This experiment represents the minimum loading of such a sample which results i n usable signal.

RET VOL (ml)

DUAL CHROMATOGRAM

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

OS

Figure 4Β. Concentration chromatogram of three column loadings (1 mg, 0.2 mg, and 0.1 mg) of oganosolv aspen lignin on the H P S E C - D V system. R I detector setting was l x .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

ο

1 Ι

S

Β ο

so

H I M M E L ET AL.

6.

MW Distribution by Universal Calibration

95

V a l u e s for s y s t e m " p e a k p a r a m e t e r s " were f o u n d u s i n g a n a r r o w d i s ­ t r i b u t i o n p o l y s t y r e n e s t a n d a r d ( P S 6 8 K ) before c a l c u l a t i n g M W D d a t a for the l i g n i n samples f r o m u n i v e r s a l c a l i b r a t i o n . T o check software a n d i n s t r u ­ m e n t o p e r a t i o n , several n a r r o w M W D p o l y s t y r e n e a n d one b r o a d M W D p o l y m e t h y l m e t h a c r y l a t e s t a n d a r d s were t r e a t e d as u n k n o w n samples a n d s u b j e c t e d to analysis w i t h the u n i v e r s a l c a l i b r a t i o n curve assembled f r o m a l l p o l y m e r s t a n d a r d s files. It was f o u n d t h a t the M W D c o u l d be e s t i m a t e d for the " r e c a l c u l a t e d " p o l y m e r s t a n d a r d s w i t h errors between ± 5 a n d 1 0 % of the o r i g i n a l value i n d i c a t e d b y the s u p p l i e r of the s t a n d a r d (e.g., M for P S 1 1 K and M a n d M for P M M A 1 7 K - 6 ) . w

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

w

n

T a b l e I illustrates the m o l e c u l a r weight averages f o u n d f r o m u n i ­ versal c a l i b r a t i o n ( n a r r o w s t a n d a r d s ) for four aspen l i g n i n s a n d t w o q u i n o n e m e t h i d e - d e r i v e d p o l y m e r s u s i n g the U n i c a l software. T h e p o l y dispersities were the same w i t h i n the e x p e r i m e n t a l errors for a l l l i g n i n s a m ­ ples. I n c o n t r a s t , the p o l y d i s p e r s i t i e s f o u n d for the q u i n o n e m e t h i d e - d e r i v e d p o l y m e r s b y u n i v e r s a l c a l i b r a t i o n were near 1.1. T h e m o l e c u l a r weight av­ erages f o u n d for the four a c e t y l a t e d l i g n i n s s t u d i e d b y u n i v e r s a l c a l i b r a t i o n were s u b s t a n t i a l l y larger t h a n those d e t e r m i n e d f r o m p r e v i o u s work u s i n g c o n v e n t i o n a l G P C (e.g., A E S E a n d B M l i g n i n s f r o m refs. 7 a n d 12 h a d a p p r o x i m a t e l y o n e - t h i r d those values f o u n d b y H P S E C - D V i n the present study). T a b l e I. M W D of A c e t y l a t e d A s p e n L i g n i n s a n d M o d e l C o m p o u n d s f r o m Universal Calibration with Narrow Standards 1

M /M„

Samples/loading

M„

M

A E S E / 1 mg A E S E / 2 mg

1100 1900

7300 7100

34500 27000

3300

OS/1 mg OS/2 mg

1300 1000

5200 4400

16000 18000

3200

A H / N a O H / 1 mg A H / N a O H / 2 mg

2200 1300

8100 6600

38000 34000

4600

B M / 1 mg B M / 2 mg

3600 9000

17300 22000

46800 47000

11500



4.7 2.4

8700 14700

10300 16700

12400 20000

9900 16000

1.1 1.1

Q M 34/0.25 mg Q M 33/0.25 m g 1

w

M

z

M

u

— — —

w

6.7 3.7 4.0 4.4 3.7 5.0

O b t a i n e d i n T H F at 20°C w i t h R I d e t e c t i o n a n d U n i c a l 2.71 software ( V i s c o t e k , Inc.). F o r h i g h loadings the s y s t e m was set at R I = lx a n d 20 P A F S , g a i n = 2; injections (250 μΐ,) m a d e f r o m 8 m g / m L stock s o l u t i o n s . F o r l o w l o a d i n g s the detector settings were R I = l/4a? a n d 20 P A F S , g a i n = 2; injections (250 |/L) m a d e f r o m 4 m g / m L stock solutions.

T h e issue of c o l u m n l o a d i n g was further investigated b y i n j e c t i n g 200 μL samples f r o m stock organosolv l i g n i n s o l u t i o n s of 5, 1 a n d 0.5 m g / m L .

LIGNIN: PROPERTIES AND MATERIALS

96

T h e c o m p o s i t e c h r o m a t o g r a m s h o w n i n F i g u r e 4 L clearly indicates t h a t a n a p p a r e n t increase i n higher M W content occurs w h e n c o l u m n l o a d i n g s increase f r o m 0.1 m g to 0.2 m g l i g n i n . T h e 0.1 m g l o a d i n g represents the s e n s i t i v i t y l i m i t , however, of the h i g h s e n s i t i v i t y refractive i n d e x detector used i n t h i s s t u d y . H o w e v e r , the 0.2 a n d 1 m g loadings (where m o s t l i g n i n d a t a were collected i n t h i s s t u d y ) were n e a r l y i d e n t i c a l i n d i s t r i b u t i o n (see F i g u r e 4 L ) . C o m p a r i s o n of the curves i n F i g u r e 4 L w i t h closely e l u t i n g p a i r s o f s t a n d a r d p o l y m e r s i n d i c a t e d t h a t the a p p a r e n t increase i n M induced b y t h i s c o n c e n t r a t i o n effect w o u l d be < 1 0 % .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

w

Chromatographic Fractionation of Organosolv Lignin. T h e preparative μS t y r a g e l c o l u m n f r o m Y M C was l o a d e d w i t h 60 m g of organosolv l i g n i n . T h e r e s u l t i n g e l u t i o n profile is s h o w n as a n insert i n F i g u r e 5. T h i s figure shows the relative d i s t r i b u t i o n of the c h r o m a t o g r a p h i c fractions p o o l e d t o generate the five m a s t e r fractions used for f u r t h e r s t u d y . These f r a c t i o n s were chosen so t h a t the relative areas of a l l five zones were n e a r l y i d e n t i c a l . F i g u r e 5 also shows the s u p e r p o s i t i o n of the r e s u l t i n g c h r o m a t o g r a p h i c a n a l y s i s of four of these f r a c t i o n s . F r a c t i o n n u m b e r five was o m i t t e d f r o m t h i s a n a l y s i s because t h i s peak was not i n c l u d e d i n the s t a n d a r d procedure used i n e s t a b l i s h i n g baselines for the four n a t i v e l i g n i n s described earlier. T h e t o t a l weight average m o l e c u l a r weight for the entire d i s t r i b u t i o n (32) was e s t i m a t e d u s i n g the r e l a t i o n s h i p M ot W)t

= EaMi/Eci

(2)

where c is the c o n c e n t r a t i o n (here i n m i l l i g r a m s ) of each master f r a c t i o n , i , a n d M is the e s t i m a t e d M o f each master f r a c t i o n f r o m u n i v e r s a l c a l i b r a ­ t i o n . T h e value of M f o u n d u s i n g these four master fractions was 3800. W h e n c o n s i d e r i n g the M f r o m the c h r o m a t o g r a p h y of the u n f r a c t i o n a t e d organosolv l i g n i n at a 1 m g l o a d i n g was e s t i m a t e d t o be 4400, the value o b t a i n e d f r o m the organosolv fractions is i n g o o d agreement. T h i s e x p e r i m e n t was designed to e x a m i n e the possible bias the b r o a d p o l y d i s p e r s i t i e s o f the l i g n i n samples m a y have o n e s t i m a t i o n of M W D b y u n i v e r s a l c a l i b r a t i o n . T h e s e d a t a i n d i c a t e t h a t n o such c o n t r i b u t i o n exists, since the s u m m a t i o n of the i n d i v i d u a l fractions of n a r r o w ( e r ) d i s p e r s i t y l e a d t o values of M W D s i m i l a r t o those f o u n d u s i n g U n i c a l software for the unfractionated lignin sample. w

W)tot

w

Conclusions A l t h o u g h evidence exists t h a t c o n c e n t r a t i o n effects m a y be i m p o r t a n t w i t h even a c e t y l a t e d l i g n i n s i n T H F , the effect o f i n c r e a s i n g c o l u m n l o a d i n g s f r o m 1 t o 2 m g seems u n l i k e l y as the cause of the v a r i a n c e i n M W s h o w n i n T a b l e I. T h i s observation i l l u s t r a t e s the m o r e general p r o b l e m i n c u r r e n t S E C - b a s e d " a b s o l u t e " M W measurement: t h a t of a l i m i t e d c o n c e n t r a t i o n w i n d o w for a n a l y s i s . T h e l i m i t i n g value for s a m p l e c o n c e n t r a t i o n appears t o be near 1 m g per i n j e c t i o n for H P S E C - D V , w h i c h is c o m p a r a b l e t o the 0.2-1 m g per i n j e c t i o n range usable i n H P S E C - L A L L S (33). F o r studies

2.50

3.00 LOG M

3.50

4.00

W

F i g u r e 5. C o m p o s i t e M W D d i a g r a m s h o w i n g the c a l c u l a t e d d i s t r i b u t i o n s of four of the five master fractions o b t a i n e d f r o m p r e p a r a t i v e c h r o m a t o g r a p h y of organosolv aspen l i g n i n ( f r a c t i o n n u m b e r 4 to 1 f r o m left to r i g h t ) . T h e M values for the m a s t e r f r a c t i o n s f r o m left to right are 1,110, 1,310, 2,420, a n d 8,050, respectively. T h e insert shows the e l u t i o n profile of o r g a n o s o l v aspen l i g n i n f r o m the Y M C p r e p a r a t i v e μ-Styragel c o l u m n (5 x 200 c m ) . T h e 30 f r a c t i o n s collected were p o o l e d i n t o the five m a s t e r f r a c t i o n s s h o w n .

2.00

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4.50

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LIGNIN: PROPERTIES A N D MATERIALS

such as these, a n increase i n s e n s i t i v i t y o f one order o f m a g n i t u d e w o u l d be h i g h l y v a l u e d a n d s h o u l d b e considered a n area o f focus for suppliers o f S E C detection equipment. T h e d e t e r m i n a t i o n t h a t the low M W , acetylated aspen lignins e x a m ­ i n e d a c t u a l l y fit u n i v e r s a l c a l i b r a t i o n , however, must be deferred t o future studies c o m p a r i n g these d a t a t o results f r o m L A L L S a n d s e d i m e n t a t i o n e q u i l i b r i u m analysis ( i f possible). A s a result o f the dependence o f u n i v e r s a l c a l i b r a t i o n o n c o l u m n e l u ­ t i o n b e h a v i o r (i.e., anomalous behavior due t o a d s o r p t i o n o r e x c l u s i o n ) , the c o n t r i b u t i o n o f the p o l y m e r "core" a n d " s h e l l " c o m p o n e n t s ( 3 3 , 3 4 ) t o h y d r o d y n a m i c b e h a v i o r m u s t be f u l l y u n d e r s t o o d i f c o m p e t e n t a n a l y s i s o f b l o c k copolymers a n d b r a n c h e d heteropolymers is t o be m a d e . It is h o p e d t h a t w i t h the advent o f a p p r o p r i a t e M W , c o m p o s i t i o n , a n d b r a n c h e d p o l y ­ mer s t a n d a r d s , the l i m i t s o f fit o f u n i v e r s a l c a l i b r a t i o n t o b i o p o l y m e r s such as l i g n i n can b e j u d g e d . Acknowledgments W e t h a n k D r . J . A . H y a t t for the gift of s y n t h e t i c p h e n y l t e t r a m e r s a n d M a x H a n e y for h e l p f u l discussions. T h i s work was funded b y t h e B i o c h e m i c a l C o n v e r s i o n P r o g r a m at the D O E Biofuels a n d M u n i c i p a l W a s t e T e c h n o l o g y D i v i s i o n t h r o u g h F T P N o . 658. Literature Cited 1. Brauns, F . E . ; Brauns, D. A . The Chemistry of Lignin; Academic Press: New York, 1960. 2. Sarkanen, Κ. V . ; Ludwig, C . H . , Eds. Lignins: Occurrence, Formation, Structure and Reactions; Wiley-Interscience: New York, 1971. 3. Sarkanen, Κ. V . In The Chemistry of Wood; Browning, B. L . , E d . ; R. E . Krieger Publ. Co.: Huntington, 1975. 4. Marchessault, R. H . ; Coulombe, S.; Hanai, T . ; Morikawa, H . ; Robert, D. Can. J. Chem. 1982, 60, 2372. 5. Kolpak, F . J . ; Cietek, D. J . ; Fookes, W.; Call, J . J . J. Appl. Polym. Sci., Polym. Sci. Symp. 1983, 31, 491. 6. Himmel, M . E . ; Oh, Κ. K.; Sopher, D. W.; Chum, H . L . J. Chromatogr. 1983, 267, 249. 7. Faix, Ο.; Lange, W.; Beinhoff, Ο. Holzforschung 1980, 34, 174. 8. Faix, Ο.; Lange, W . ; Salud, E . C . Holzforschung 1981, 35, 3. 9. Lange, W . ; Schweers, W.; Beinhoff, O. Holzforschung 1981, 35, 119. 10. Meier, D.; Faix, O.; Lange, W . Holzforschung 1981, 35, 247. 11. Lange, W.; Faix, O.; Beinhoff, O. Holzforschung 1983, 37, 63. 12. Chum, H . L . ; Johnson, D. K.; Tucker, M . P.; Himmel, M . E . Holz­ forschung 1987, 41, 97. 13. Pellinen, J . ; Salkinoja-Salonen, M . J. Chromatogr. 1985, 328, 299. 14. Connors, W . J.; Sarkanen, S.; McCarthy, J . L . Holzforschung 1980, 34, 80. 15. Sarkanen, S.; Teller, D. C . ; Hall, J . ; McCarthy, J . L . Macromolecules 1981, 14, 426.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch006

6.

RIMMEL

ET

AL.

MW Distribution by Universal Calibration

99

16. Tirtowidjojo, S. M.S. Thesis, University of Washington, Seattle, W A , 1984, Parts 1 and 2, pp. 1-119. 17. Sarkanen, S.; Teller, D. C . ; Stevens, C . R.; McCarthy, J. L . Macromolecules 1984, 17, 2588. 18. Yau, W . W.; Kirkland, J. J.; Bly, D . D. Modern Size Exclusion Chro­ matography: Practice of Gel Permeation and Gel Filtration Chromatog­ raphy; John Wiley & Sons: New York, 1979. 19. Hyatt, J. A . Holzforschung 1987, 41, 363. 20. Chum, H . L.; Johnson, D. K.; Palasz, P. D.; Smith, C . Z.; Utley, H . P. Macromolecules 1987, 20, 2698. 21. Lundquist, K . ; Ohlsson, R.; Simonson, R. Svensk Papperstidn. 1975, 78, 390. 22. Grohmann, K . ; Torget, R.; Himmel, M . E . Biotech. Bioeng. Symp. 1986, 17, 135. 23. Chum, H . L . ; Johnson, D. K.; Ratcliff, M . ; Black, S.; Schroeder, Η. Α.; Wallace, K . In Proc. Intl. Symp. Wood and Pulp. Chem.; Can. Pulp and Paper Assoc.: Vancouver, 1985; pp. 223-227. 24. Gierer, J.; Lindeberg, O. Acta Chem. Scand. 1980, 34, 161. 25. Mark, H . Der Feste Korper; Hirzel: Leipzig, 1938; p. 103. 26. Houwink, R. J. Prakt. Chem. 1941, 157, 15. 27. Benoit, H.; Grubisic, Ζ.; Rempp, P.; Decker, D.; Zilliox, J. G . J. Chim. Phys. 1966, 63, 1507. 28. Gallot-Grubisic, Z.; Rempp, P.; Benoit, H . J. Polym. Sci. 1967, 5, 753. 29. Cassassa, E . F . Macromolecules 1976, 9, 182. 30. Frigon, R. P.; Leypoldt, J. K.; Uyeji, S.; Henderson, L . W . Anal. Chem. 1983, 55, 1349. 31. Haney, Μ. Α.; Armonas, J. E . In Proc. GPC Symp. '87; Waters Chro­ matography Corp.: Milford, M A , 1987; pp. 523-544. 32. Schachman, Η. K . Ultracentrifugation in Biochemistry; Academic Press: New York, 1959. 33. Jordan, R. C . ; Silver, S. F.; Sehon, R. D.; Rivard, R. J. ACS Symp. Ser. 1984, 245, 295. 34. Bi, L . K.; Fetters, L . J. Macromolecules 1976, 9, 732. RECEIVED February 27,1989

Chapter 7

Molecular Weight Determination of Hydroxypropylated Lignins E . J . Siochi , M . A. Haney , W. Mahn , and Thomas C. 1,2

3

3

Ward

1,2,4

Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 1

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2

The number average molecular weight of hydroxypropy­ lated lignins (HPL) was determined using gel perme­ ation chromatography with a differential viscosity de­ tector ( G P C / D V ) . Vapor phase osmometry was used to provide comparative number average molecular weight values to verify the results obtained by G P C . G P C / D V proved to be a reliable and convenient tool for the deter­ mination of absolute molecular weights of lignin deriva­ tives. The results revealed that a time dependent asso­ ciation of H P L molecules was occurring in solution. L i g n i n is a n a m o r p h o u s b i o p o l y m e r second i n n a t u r a l a b u n d a n c e o n l y t o cellulose. I t is composed o f p h e n y l p r o p a n e u n i t s l i n k e d p r i m a r i l y t h r o u g h ether bonds a n d constitutes 15-40% o f the d r y weight o f w o o d . A c o m b i n a ­ t i o n o f the a b u n d a n c e o f l i g n i n s , its v e r s a t i l i t y due t o the v a r i e t y o f sources available a n d t h e recent interest i n renewable resources have opened u p research i n t o the p o t e n t i a l a p p l i c a t i o n s o f lignins i n m a n y fields (1-5). D u e t o the inherent s t r e n g t h o f l i g n i n , i t has been favored b y researchers s t u d y ­ i n g s t r u c t u r a l m a t e r i a l s . L i g n i n s have been used as p r e p o l y m e r s for t h e m o d i f i c a t i o n o f s y n t h e t i c p o l y m e r s a n d as substitutes for various p o l y m e r i c m a t e r i a l s ( 3 , 6 - 8 ) . W h e r e the i n c o r p o r a t i o n o f lignins h a d adverse effects o n the m e c h a n i c a l properties o f the r e s u l t i n g p r o d u c t s , h y d r o x y a l k y l a t i o n o f the l i g n i n e m p l o y e d has been f o u n d t o i m p r o v e the m a t e r i a l characteristics (6)· I n a n y s t r u c t u r e / p r o p e r t y studies o n p o t e n t i a l a p p l i c a t i o n s o f l i g n i n s , a n i m p o r t a n t p a r a m e t e r is the m o l e c u l a r weight a n d m o l e c u l a r weight d i s ­ t r i b u t i o n ( M W D ) . I n r e c o g n i t i o n o f t h i s fact, a s u b s t a n t i a l n u m b e r o f papers 3 4

Current address: Viscotek Corporation, 1032 Russell Drive, Porter,TX77365 Address correspondence to this author. 0097-6156/89Λ)397-0100$06.00Λ) © 1989 American Chemical Society

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7.

SIOCHIETAL.

MW Determination of Hydroxypropylated Lignins

101

have been p u b l i s h e d w h i c h r e p o r t the use of vapor phase o s m o m e t r y ( V P O ) (8-11) a n d u l t r a c e n t r i f u g a t i o n (12-16) for t h i s p u r p o s e . M o r e recently, gel p e r m e a t i o n c h r o m a t o g r a p h y ( G P C ) has g a i n e d advocates for l i g n i n m o l e c u l a r weight d e t e r m i n a t i o n due to its ease o f use a n d the short a n a l y s i s t i m e ( 9 , 1 2 , 1 7 - 2 5 ) . A l t h o u g h G P C is h i g h l y p o p u l a r , the p u b l i s h e d d a t a t r e a t m e n t s t y p i c a l l y y i e l d o n l y relative a n d not absolute m o l e c u l a r weights. T h i s is the result o f a c a l i b r a t i o n scheme u s i n g easily accessible p o l y s t y r e n e s t a n d a r d s whose c o n f o r m a t i o n s differ f r o m l i g n i n s ( 1 4 , 2 6 , 2 7 ) . W h i l e low angle laser l i g h t s c a t t e r i n g ( L A L L S ) has been e m p l o y e d t o a v o i d c a l i b r a t i o n p r o b l e m s , other difficulties s u b s e q u e n t l y emerge. T h e s e necessitate corrections for absorbance, fluorescence a n d p o l a r i z a t i o n ( 9 , 2 8 ) . I n recent years, a n u m b e r o f v i s c o s i t y detectors have been developed for use w i t h G P C i n c o n j u n c t i o n w i t h the necessary c o n c e n t r a t i o n sensitive detectors (29-40). A l t h o u g h s u c h detectors are c o m m e r c i a l l y available ( 3 9 , 4 0 ) , t h e i r a p p l i c a t i o n to l i g n i n M W D d e t e r m i n a t i o n is r a r e . T h i s lack of usage m a y be r e l a t e d to the consensus t h a t l i g n i n s have a t h r e e - d i m e n s i o n a l n e t w o r k s t r u c t u r e w h i c h w o u l d not obey u n i v e r s a l c a l i b r a t i o n , o n w h i c h G P C / D V is based. T h e objective o f t h i s present w o r k was t o investigate the f e a s i b i l i t y o f u s i n g G P C / D V for absolute m o l e c u l a r weight d e t e r m i n a t i o n o f h y d r o x y p r o p y l a t e d l i g n i n s . I n order to verify the v a l i d i t y of the u n i v e r s a l c a l i b r a t i o n m e t h o d , v a p o r phase o s m o m e t r y ( V P O ) was used t o p r o v i d e reference n u m b e r average m o l e c u l a r weight values. C o m p a r i s o n s w i t h L A L L S results have also been m a d e a n d w i l l be r e p o r t e d i n another p u b l i c a t i o n .

Experimental Materials. H y d r o x y p r o p y l derivatives of red o a k , aspen a n d a h a r d w o o d kraft l i g n i n were s t u d i e d . T h e r e were two samples of red o a k . O n e , design a t e d as " R O : P O " , is i d e n t i c a l t o the red oak H P L , b u t was m a d e i n larger quantities to a l l o w p r e p a r a t i v e f r a c t i o n a t i o n . T h e aspen was a n o r g a n o s o l v l i g n i n o b t a i n e d f r o m B i o l o g i c a l E n e r g y C o r p o r a t i o n of V a l l e y Forge, P e n n s y l v a n i a . T h e h a r d w o o d k r a f t l i g n i n was s u p p l i e d b y W e s t v a c o , C h a r l e s t o n , S o u t h C a r o l i n a . A l l o f the above samples were d e r i v a t i z e d a c c o r d i n g to the procedure of W u a n d G l a s s e r (6). Vapor Phase Osmometry. A W e s c a n M o d e l 233 v a p o r phase o s m o m e t e r was used to o b t a i n n u m b e r average m o l e c u l a r weights. T h e l i g n i n s o l u t i o n s were m a d e u p w i t h H P L C grade t e t r a h y d r o f u r a n ( T H F ) a n d s h a k e n m a n u a l l y u n t i l the s o l u t i o n s were clear. T h e e x p e r i m e n t s were c o n d u c t e d at 30° C . N u m b e r average m o l e c u l a r weights were d e t e r m i n e d by m u l t i s t a n d a r d c a l i b r a t i o n (41), a procedure f o u n d to g r e a t l y enhance r e p r o d u c i b i l i t y a n d a c c u r a c y o f the results. E x p e r i m e n t s were c o n d u c t e d i m m e d i a t e l y after s a m p l e p r e p a r a t i o n a n d three d a y s l a t e r . Gel Permeation Chromatography. Polymer Laboratories narrow distribut i o n p o l y s t y r e n e s t a n d a r d s w i t h n o m i n a l m o l e c u l a r weights o f 1250, 2150, 3250, 5000, 9000, 34500, 68000 a n d 170000 g / m o l e were dissolved i n H P L C

102

LIGNIN: PROPERTIES AND MATERIALS

grade T H F . These s t a n d a r d s were used for the c o n s t r u c t i o n o f the u n i v e r s a l c a l i b r a t i o n curve. A p p r o x i m a t e l y 2.5 m g / m l s o l u t i o n s o f the l i g n i n s were p r e p a r e d i n H P L C grade T H F . T h e s o l u t i o n s were m a d e u p i m m e d i a t e l y before G P C was c o n d u c t e d a n d s h a k e n m a n u a l l y for a couple o f m i n u t e s u n t i l the s o l u ­ t i o n s were a clear b r o w n color. G P C a n a l y s i s was c a r r i e d o u t o n a W a t e r s 1 5 0 C A L C / G P C e q u i p p e d w i t h a n o p t i c a l deflection t y p e differential re­ f r a c t i v e i n d e x detector h a v i n g a s e n s i t i v i t y o f 1 χ 1 0 ~ ARl u n i t s a n d a V i s c o t e k M o d e l 100 differential v i s c o s i t y detector. T h e c h r o m a t o g r a p h i c c o n d i t i o n s were: flow rate 0.9 m l / m i n , i n j e c t i o n v o l u m e 200 μΐ, w i t h C o l ­ u m n R e s o l u t i o n repacked m i c r o s t y r a g e l c o l u m n s h a v i n g pore sizes o f 500 Â , 1 0 Â , 1 0 À , 1 0 Â a n d Ult r ast y r ag e l™ c o l u m n s w i t h pore d i a m e t e r s o f 100 Â a n d 1 0 Â connected i n series. T e m p e r a t u r e was set at 3 0 ° C for b o t h the G P C a n d the differential viscosity detector. E x p e r i m e n t s were c o n d u c t e d o n the first d a y a n d the t h i r d day o f s a m p l e p r e p a r a t i o n . 6

3

4

5

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6

Results and Discussion Vapor Phase Osmometry. T h e c a l i b r a t i o n c u r v e used t o d e t e r m i n e n u m ber average m o l e c u l a r weights b y V P O is s h o w n i n F i g u r e 1. T h e s t a n d a r d s used were p o l y s t y r e n e w i t h n o m i n a l m o l e c u l a r weights o f 1250, 2150 a n d 5000 g / m o l e a n d sucrose octaacetate whose m o l e c u l a r weight is 678.6 g / m o l e . T o use the c a l i b r a t i o n curve, a AV (voltage change r e l a t e d t o the l o w e r i n g o f solvent vapor pressure i n s o l u t i o n ) versus c o n c e n t r a t i o n p l o t for the H P L s a m p l e was generated. T h e slope o f s u c h a g r a p h was d e t e r m i n e d a n d used t o o b t a i n the n u m b e r average m o l e c u l a r weight b y i n t e r p o l a t i o n f r o m the c a l i b r a t i o n curve. D e t a i l s o f t h i s u n c o n v e n t i o n a l m u l t i s t a n d a r d c a l i b r a t i o n w i l l be p u b l i s h e d elsewhere (41). T h e results o f the m o l e c u l a r weight d e t e r m i n a t i o n o f the h y d r o x y p r o p y l a t e d l i g n i n s b y V P O are s h o w n i n T a b l e I. It m a y be n o t e d t h a t for a l l s a m p l e s , there was a b o u t a 2 0 % increase i n a p p a r e n t m o l e c u l a r weights between freshly p r e p a r e d s o l u t i o n s a n d those tested three d a y s l a t e r . It is p o s t u l a t e d t h a t s u c h a n increase was due t o a t i m e dependent a s s o c i a t i o n o f the h y d r o x y p r o p y l a t e d l i g n i n molecules i n s o l u t i o n . Gel Permeation Chromatography. A n e x a m p l e of a G P C / D V d u a l c h r o m a t o g r a m is s h o w n i n F i g u r e 2. T h e b o l d e r trace is the D R I s i g n a l w h i l e the finer trace is due t o the v i s c o s i t y s i g n a l . It m a y be n o t e d t h a t the v i s c o s i t y s i g n a l is s i g n i f i c a n t l y noisier t h a n the D R I trace. T h i s is a result o f the H P L s a m p l e m o l e c u l a r weight b e i n g near the lower detection l i m i t o f the differential v i s c o s i t y detector. A s u m m a r y o f the results o b t a i n e d f r o m G P C / D V o n the first d a y a n d the t h i r d day after s o l u t i o n p r e p a r a t i o n is s h o w n i n T a b l e I I . F o r R e d O a k a n d R O : P O , the n u m b e r average m o l e c u l a r weight decreased b y a p p r o x i m a t e l y 6% f r o m the first d a y t o the t h i r d day. H o w e v e r , the i n t r i n s i c viscosities increased. A c c o r d i n g to t r a d i t i o n a l p o l y m e r s o l u t i o n theory (42), the p r o d u c t o f i n t r i n s i c v i s c o s i t y a n d m o l e c u l a r weight y i e l d s the h y d r o d y n a m i c v o l u m e ; specifically, i t has been s h o w n t h a t the m o l e c u l a r weight t h a t

7.

SIOCHIETAL.

MW Determination of Hydroxypropylated Lignins

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch007

0.002 η

SLOPE ( m V L / g ) F i g u r e 1. V P O c a l i b r a t i o n curve.

103

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch007

104 LIGNIN: PROPERTIES AND MATERIALS

•a

ο

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ο

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[L,] )

c

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A c c o r d i n g l y , t h e weight-average molecular weight, M for t h e s y s t e m of i n t e r a c t i n g species at a n y t i m e d u r i n g t h e a s s o c i a t i v e / d i s s o c i a t i v e process c a n be w r i t t e n as W1



_ Z c , / ( ™ c + i [ C W i ] o + rnj[Li]

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[L,] ))

c

0

E c i K I C J + rmlL,])

where < m m / > = 5 3 / c / ( [ ^ / ] - [ ^ / ] ο ) / ( Σ / ( [ ^ ' ] [^j]o)) ~ d e r s t o o d t h a t a u n i q u e r e l a t i o n s h i p exists between c a n d /. T h e number-average ( w i t h respect t o the i n d i v i d u a l c o m p o n e n t s re­ leased) p r o d u c t o f the m o l e c u l a r weights, < m m\ > , o f i n t e r a c t i n g species, { C , L / } , w i l l r e m a i n constant i f the e v o l u t i o n w i t h t i m e o f {[L{\ — [L/]o) follows e x a c t l y t h e same k i n e t i c course for each L\. T h i s is r e m i n i s c e n t o f earlier findings t h a t t h e relative ratios o f k r a f t l i g n i n c o m p o n e n t s w i t h m o l e c u l a r weights below 3500 d o not v a r y w i t h the degree o f a s s o c i a t i o n for the s a m p l e as a whole (6). A n a p p r o p r i a t e l y p o s i t i o n e d r a t e - d e t e r m i n i n g step i n the sequence o f dissociative events w o u l d impose s u c h a r e s t r i c t i o n u p o n the s y s t e m . I f the step i n question were t o e x h i b i t first order b e h a v ­ ior, so also w o u l d the changes i n M a n d a b s o r p t i v i t y a c c o m p a n y i n g the o v e r a l l dissociative process. c

m

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Associative/Dissociative Homology among Kraft Lignin Samples T h e a s s o c i a t i v e / d i s s o c i a t i v e processes i n w h i c h k r a f t l i g n i n species p a r t i c i pate are reversible: association a n d d i s s o c i a t i o n take place respectively at h i g h a n d low k r a f t l i g n i n concentrations i n aqueous a l k a l i n e s o l u t i o n . F o r e x a m p l e , a k r a f t l i g n i n s a m p l e t h a t has been preassociated ( d u r i n g i n c u b a t i o n at 190 g L * " i n 1.0 M i o n i c s t r e n g t h aqueous 0.6 M N a O H ) s p o n taneously dissociates w h e n d i l u t e d i n aqueous 0.10 M N a O H to 0.5 g L " ( F i g u r e 6). Conversely, a k r a f t l i g n i n s a m p l e t h a t has been predissociated ( t h r o u g h i n c u b a t i o n at 0.5 g L " i n aqueous 0.10 M N a O H a n d subsequent recovery b y u l t r a f i l t r a t i o n w i t h a n o m i n a l l y 500 m o l e c u l a r weight cutoff m e m b r a n e ) associates spontaneously w h e n dissolved to a level of 160 g L " i n 1.0 M i o n i c s t r e n g t h aqueous 0.40 M N a O H ( F i g u r e 7). O n t o a l l such a s s o c i a t i v e / d i s s o c i a t i v e processes, the effects of o x i d a t i v e covalent cleavage reactions w i l l be a p p e n d e d t o v a r y i n g extents d e p e n d i n g u p o n the p r e v a i l i n g circumstances. C o n s e q u e n t l y the m o l e c u l a r weight d i s t r i b u t i o n s depicted by the c o r r e s p o n d i n g e l u t i o n profiles e x h i b i t p o i n t s of intersection t h a t m a y v a r y quite w i d e l y ( F i g u r e s 4 a n d 6). H o w e v e r , the k r a f t l i g n i n species capable of i n t e r a c t i n g w i t h one another can be r e a d i l y separated f r o m those components t h a t , o w i n g to covalent m o d i f i c a t i o n , c a n n o t . T h i s m a y be a c c o m p l i s h e d t h r o u g h the s t r a i g h t f o r w a r d e x p e d i ent o f p a r t l y r e l a x i n g the i m p e d i m e n t s to a s s o c i a t i o n i m p o s e d b y s o l u t i o n c o n d i t i o n s ; a p p r o p r i a t e l y e l a b o r a t e d c h r o m a t o g r a p h i c f r a c t i o n a t i o n of the m a c r o m o l e c u l a r complexes w i l l t h e n complete the t a s k . T o t h i s end k r a f t l i g n i n samples possessing different degrees of associat i o n i n aqueous s o d i u m h y d r o x i d e solutions c a n be secured b y a c i d i f i c a t i o n to p H 7.5 a n d freeze-drying. T h e r e u p o n d i s s o l u t i o n i n a p o r t i o n of eluent c o n t a i n i n g 0.325 M N a O H a n d subsequent f r a c t i o n a t i o n t h r o u g h S e p h a d e x L H 2 0 w i t h aqueous 3 5 % dioxane separates the s a m p l e i n t o two groups of species: a subset o f associated complexes a p p e a r i n g at the v o i d v o l u m e is segregated f r o m the r e m a i n i n g components e l u t i n g j u s t after the salt b a n d ( F i g u r e 8; cf. réf. 8). A f t e r freeze-drying, r e f r a c t i o n a t i o n o f the l e a d i n g p e a k t h r o u g h Sephadex L H 2 0 w i t h aqueous 3 5 % dioxane allows a net 606 5 % of the o r i g i n a l k r a f t l i g n i n to be recovered as a n associated salt-free specimen. T h e m o l e c u l a r weight d i s t r i b u t i o n s depicted b y the Sephadex G 1 0 0 / aqueous 0.10 M N a O H e l u t i o n profiles ( F i g u r e 9) of these recovered k r a f t l i g n i n p r e p a r a t i o n s reflect the degrees of association for the c o n s t i t u e n t subsets o f species i n the o r i g i n a l samples. T h e y e x h i b i t a c o m m o n i n t e r section p o i n t , a n d as such represent the m o l e c u l a r weight d i s t r i b u t i o n s of p r e p a r a t i o n s t h a t are homologous f r o m a n a s s o c i a t i v e / d i s s o c i a t i v e p o i n t of v i e w : the r e l a t i o n s h i p between successive members of the series is u n i f o r m l y confined to s y s t e m a t i c differences i n t h e i r degrees o f association w i t h o u t p e r t u r b a t i o n s a r i s i n g f r o m the effects of covalent cleavage reactions. T h i s h a r m o n i o u s o u t c o m e f r o m a s i m p l e procedure has f a r - r e a c h i n g i m p l i c a t i o n s . T h a t the species a p p e a r i n g at the v o i d v o l u m e i n aqueous 3 5 % dioxane f r o m Sephadex L H 2 0 are associated is r e a d i l y c o n f i r m e d b y the corr e s p o n d i n g size-exclusion c h r o m a t o g r a p h i c profiles f r o m a 1 0 À pore-size 1

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Figure 7. Association of predissociated kraft lignin sample (92% retained by nominally 500 molecular weight cutoff ultrafiltration membrane) during incubation at 160 gL" in 1.0 M ionic strength aqueous 0.40 M N a O H for ( l ) 0 h , (2) 50 h and (3) 480 h. 1

salt band

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elution volume Figure 8. Kraft lignin fractionation into two subsets of species during desalting by elution with aqueous 3 5 % dioxane through Sephadex L H 2 0 of an initially 4.5 g L ' sample solution at 2.3 M ionic strength containing 0.32 M aqueous N a O H . 1

DUTTAETAL.

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p o l y ( s t y r e n e d i v i n y l b e n z e n e ) c o l u m n . W h i l e the i n t e r m o l e c u l a r forces caus­ i n g association i n aqueous dioxane necessarily differ f r o m those i n aqueous a l k a l i n e s o l u t i o n , t h e i r respective s t o i c h i o m e t r i c selectivities towards the i n d i v i d u a l k r a f t l i g n i n components must be d i r e c t l y c o m p l e m e n t a r y . T h e r e l a t i v e l y r a p i d association f a c i l i t a t e d b y l o w e r i n g the p H is p r e s u m a b l y m e d i a t e d b y h y d r o g e n b o n d i n g (9) a n d / o r d i p o l a r i n t e r a c t i o n s ; the slower associative processes encountered i n aqueous alkaline s o l u t i o n s are p r o b a b l y caused b y n o n b o n d e d o r b i t a l i n t e r a c t i o n s , the c o n c o m i t a n t s of w h i c h c o n ­ t r i b u t e t o the long-wavelength absorbance changes i n the u l t r a v i o l e t - v i s i b l e s p e c t r u m ( F i g u r e 1).

T h e Behavior of < m m\ > during Association and Dissociation Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch012

c

It has not been possible e x p e r i m e n t a l l y t o detect s y s t e m a t i c differences i n the u l t r a c e n t r i f u g e s e d i m e n t a t i o n e q u i l i b r i u m weight-average m o l e c u l a r weight c a l i b r a t i o n curves for the Sephadex G 1 0 0 / aqueous 0.10 M N a O H e l u t i o n profiles of k r a f t l i g n i n p r e p a r a t i o n s w i t h different degrees of associa­ t i o n ( F i g u r e 10). C o n s e q u e n t l y the same r e l a t i o n s h i p has been e m p l o y e d t o c a l c u l a t e the o v e r a l l weight- a n d n u m b e r -average m o l e c u l a r weights, M a n d M , of the p r e p a r a t i o n s as associative or dissociative processes are underway. w

n

A c c o r d i n g l y , the average p r o d u c t of the m o l e c u l a r weights, < m m\ >, of i n t e r a c t i n g k r a f t l i g n i n species (vide supra: Implications at the Molecular Level) c a n be e v a l u a t e d n u m e r i c a l l y b y p l o t t i n g M versus l/M : the slope at a n y p o i n t o n the r e s u l t i n g curve is given b y —2 < m m / > (4). It is hereby evident t h a t the value, 1.03 χ 1 0 , o f < m m / > c h a r a c t e r i z i n g the r e l a t i o n s h i p between the members of the homologous series of k r a f t l i g n i n p r e p a r a t i o n s is, w i t h i n e x p e r i m e n t a l error, i d e n t i c a l i n m a g n i t u d e t o those encountered d u r i n g association of the o r i g i n a l k r a f t l i g n i n s a m p l e at 195 g L " " i n 1.0 M i o n i c s t r e n g t h aqueous 0.4 M N a O H ( F i g u r e 11), d i s s o c i a t i o n of the preassociated kraft l i g n i n p r e p a r a t i o n ( F i g u r e s 6 a n d 11), a n d association o f the predissociated k r a f t l i g n i n p r e p a r a t i o n ( F i g u r e s 7 a n d 11). c

w

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D u r i n g d i s s o c i a t i o n of the o r i g i n a l k r a f t l i g n i n s a m p l e at 0.46 g L " i n aqueous 0.10 M N a O H ( F i g u r e 4), however, the apparent value, 5.1 χ 1 0 , o f < m m\ > is considerably lower ( F i g u r e 11). Indeed the m a n n e r i n w h i c h M varies w i t h 1 / M d u r i n g the d i s s o c i a t i o n of the preassociated k r a f t l i g n i n p r e p a r a t i o n ( F i g u r e s 6 a n d 11) suggests t h a t < m m\ > s i m i l a r l y becomes s m a l l e r w h e n a c o m p a r a b l e range of degree of association has been reached. P r e s u m a b l y the m a g n i t u d e of < m m\ > under these c o n d i t i o n s is influenced b y a d d i t i o n a l c o n t r i b u t i o n s a r i s i n g f r o m covalent cleavage of i n d i v i d u a l k r a f t l i g n i n c o m p o n e n t s , the effects of w h i c h w o u l d be m o r e extensive w h e n the degree of association is s m a l l e r , the p H higher, a n d the s o l u t i o n more d i l u t e ( w h e r e u p o n the s t o i c h i o m e t r i c r a t i o of dissolved oxygen to i n d i v i d u a l k r a f t l i g n i n c o m p o n e n t s is larger). I n t h i s c o n n e c t i o n i t s h o u l d be p o i n t e d out t h a t , i n aqueous a l k a l i n e s o l u t i o n s c o n t a i n i n g the highest k r a f t l i g n i n concentrations where a s s o c i a t i o n is favored, the p H tends t o approach a value a r o u n d 11.6, j u s t above the region where the 1

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Figure 9. Apparent molecular weight distributions representing a homolo­ gous series of kraft lignin samples secured by desalting after association and dissociation in aqueous alkaline solutions for: (1) 300 h, (2) 144 h and (3) 48 h at 170 g L in 1.0 M ionic strength aqueous 0.40 M N a O H ; (4) 0 h; (5) 144 h and (6) 644 h at 0.50 g L ' in aqueous 0.10 M N a O H . (Sephadex G100/aqueous 0.10 M N a O H elution profiles monitored at 320 nm.) 1

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Figure 10. Molecular weight calibration curves for kraft lignin samples dif­ fering in degree of association eluted from Sephadex G100 with aqueous 0 . 1 0 M N a O H : « > ) associated sample after 385 h at 180 g L in 1.0 M ionic strength aqueous 0.40 M N a O H ; (O) original preparation; ( • ) dis­ sociated sample precipitated upon acidification to p H 3.0 after 2000 h at 0.50 gL" in aqueous 0.10 M N a O H . 1

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m o l e c u l a r weights of the m a c r o m o l e c u l a r complexes f a l l most r a p i d l y d u r i n g t i t r a t i o n of the component phenolic groups w i t h h y d r o x i d e (9). R e m a r k a b l y , the m a g n i t u d e of < m m / > d e l i n e a t i n g the associative or dissociative influences u p o n m o l e c u l a r weight d i s t r i b u t i o n does not appear to be affected b y the s m a l l v a r i a t i o n s i n c o m p o n e n t c o m p o s i t i o n r e s u l t i n g f r o m differences i n the p r e p a r a t i v e histories of the samples. Indeed the same constant value of < ra ra/ > prevails d u r i n g a s s o c i a t i o n a n d d i s s o c i a ­ t i o n despite m a r k e d changes i n the relative p o p u l a t i o n s of the c o n s t i t u e n t species. B o t h processes t h u s e m b o d y r e s t r i c t i o n s whereby the i n d i v i d u a l components are c a p t u r e d b y or released f r o m the m a c r o m o l e c u l a r complexes at respective rates of w h i c h the k i n e t i c forms are i n d e p e n d e n t of m o l e c u l a r weight. I n the context i m p o s e d b y the dissolved k r a f t l i g n i n p r e p a r a t i o n , therefore, the e q u i l i b r i u m constants for a l l p a i r s of i n t e r a c t i n g species are o p e r a t i o n a l l y the same as one another. c

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch012

c

C o n t r a r y t o a priori expectations (19), t h e n , the e q u i l i b r i u m constant for the association of k r a f t l i g n i n components does n o t increase w i t h the degree of p o l y m e r i z a t i o n . R a t h e r the b e h a v i o r encountered indicates t h a t the rates of association a n d dissociation are governed b y a p a r t i c u l a r rate d e t e r m i n i n g step. S u c h a r e s t r i c t i o n s t r o n g l y suggests t h a t the i n d i v i d u a l m o l e c u l a r species interact w i t h c o m p l e m e n t a r y l o c i o n the c o r r e s p o n d i n g m a c r o m o l e c u l a r complexes i n a specific order. It is difficult to conceive h o w s e l e c t i v i t y o n t h i s scale c o u l d be sustained i n a s y s t e m w i t h o u t a h i g h level of s t r u c t u r a l r e g u l a r i t y i n , a n d molecular o r g a n i z a t i o n a m o n g , the species involved.

Further Evidence for Nonrandom Interactions Lignin Species

between Kraft

T h e r e are other quite independent i n d i c a t i o n s t h a t the associative processes t a k i n g place i n l i g n i n samples are not r a n d o m . T h i s is exemplified by the c o m p o s i t i o n of a p a r t i a l l y dissociated k r a f t l i g n i n p r e p a r a t i o n secured b y p r e c i p i t a t i o n ( 5 9 % of o r i g i n a l sample) u p o n a c i d i f i c a t i o n t o p H 3.0 of a 0.50 g L s o l u t i o n i n aqueous 0.10 M N a O H t h a t h a d been i n c u b a t e d for 2000 h . P a u c i d i s p e r s e fractions selected f r o m the Sephadex G l O O / a q u e o u s 0.10 M N a O H e l u t i o n profile of the p r e p a r a t i o n can be separated i n t o t w o subsets of components Β a n d C b y e l u t i n g w i t h water t h r o u g h S e p h a d e x G 2 5 i n the presence of a h i g h ( i n i t i a l l y 2.0 M ) i o n i c s t r e n g t h salt b a n d (8). T h e components i n subsets Β a n d C respectively c o n t r i b u t e p r i m a r i l y t o the higher a n d lower m o l e c u l a r weight regions of the Sephadex G 1 0 0 / a q u e o u s 0.10 M N a O H e l u t i o n profile ( F i g u r e 12). T h e b e h a v i o r of the k r a f t l i g n i n species d u r i n g e l u t i o n t h r o u g h Sephadex G 2 5 is d e t e r m i n e d b y three coupled p h y s i c o c h e m i c a l processes, viz. a d s o r p t i o n at h i g h s o l u t i o n ionic strengths of the lower m o l e c u l a r weight components o n t o the gel, i n t e r m o l e c u l a r association, a n d diffusion of the higher m o l e c u l a r weight entities t h r o u g h the salt b a n d . T h e o v e r a l l effect facilitates more complete s e p a r a t i o n between the s m a l l e r a n d larger k r a f t l i g n i n species w h e n the differences i n t h e i r m o l e c u l a r weights are greater. T h e weight-average m o l e c u l a r weights of the c o m p o n e n t subsets - 1

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Figure 11. Relationship between M and M during associative/dissoci­ ative processes between molecular kraft lignin species in aqueous alkaline solutions: ( Q ) desalted homologous series of samples with different de­ grees of association; association of (O) preparation at 180 gL" and ( Λ ) predissociated sample at 160 g L ' , both in 1.0 Af ionic strength aqueous 0.40Af N a O H ; (O) dissociation of preassociated sample and ( φ ) dissoci­ ation and covalent cleavage of preparation, both at 0.50 g L ' in aqueous 0.10 Af N a O H . w

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Figure 12. Contributions of component subsets Β ( φ ) and C ( • ) to Sephadex G100/0.10 Af aqueous N a O H elution profile for dissociated kraft lignin sample precipitated upon acidification to p H 3.0 after 2000 h at 0.50 gL in 0.10 M aqueous N a O H . -1

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B a n d C are j u x t a p o s e d i n F i g u r e 13 to those of the p a r e n t paucidisperse fractions f r o m the p a r t i a l l y dissociated k r a f t l i g n i n p r e p a r a t i o n . T h i s c o m p a r i s o n establishes t h a t a p a r t i c u l a r subset of components c h a r a c t e r i z e d b y a weight-average m o l e c u l a r weight o f 3500 c a n be s p o n t a n e o u s l y l i b e r a t e d f r o m the entire range of k r a f t l i g n i n species w i t h m o l e c u l a r weights i n i t i a l l y f a l l i n g between 10,000 a n d 23,000. A n i m p o r t a n t p h y s i c o c h e m i c a l c o n c o m i t a n t of the a s s o c i a t i v e / d i s s o c i a tive processes i n w h i c h kraft l i g n i n components p a r t i c i p a t e can be detected i n the u l t r a v i o l e t - v i s i b l e s p e c t r a of paucidisperse fractions i n aqueous a l kaline s o l u t i o n derived f r o m k r a f t l i g n i n p r e p a r a t i o n s characterized b y different degrees o f a s s o c i a t i o n . T h e r a t i o of the a b s o r p t i v i t y at 230 n m to t h a t at 300 n m generally decreases w i t h i n c r e a s i n g frequency o f p h e n o x ide moieties a m o n g the species present (22). E x c e p t i n the very lowest reaches of the m o l e c u l a r weight range, t h i s r a t i o for those c o m p o n e n t s w i t h m o l e c u l a r weights less t h a n 3500 is independent of degree o f a s s o c i a t i o n for the entire k r a f t l i g n i n p r e p a r a t i o n ( F i g u r e 14). O n the other h a n d , the frequencies of u n p r o t o n a t e d phenoxide groups a m o n g the higher m o l e c u l a r weight species clearly increases w i t h degree of association for the s a m p l e as a w h o l e . These observations are consistent w i t h the s u p p o s i t i o n (6) t h a t the associative processes involve preferential interactions between the subset of components w i t h m o l e c u l a r weights below 3500 a n d the c o m p l e m e n t a r y higher m o l e c u l a r weight entities; a c c o m p a n y i n g p r o t o n a t i o n of the p h e n o x ide moieties, w h i c h tends to reduce the charge d e n s i t y o n the associated complexes, e v i d e n t l y need not be complete.

Association in Nonaqueous Polar Solvents W h e n the p h e n o x i d e moieties o f the k r a f t l i g n i n components p a r t i c i p a t i n g i n associated c o m p l e x f o r m a t i o n are f u l l y p r o t o n a t e d , far more extensive a s s o c i a t i o n can occur i n a c c o m m o d a t i n g solvents. S u c h a n o u t come m a y be r e a d i l y d e m o n s t r a t e d for the series of k r a f t l i g n i n p r e p a r a t i o n s differing homologously w i t h respect to their degrees of association i n aqueous 0.10 M N a O H ( F i g u r e 9). W h e n c a l i b r a t e d w i t h paucidisperse p o l y s t y r e n e s t a n d a r d s , the c o r r e s p o n d i n g e l u t i o n profiles ( F i g u r e 15) i n D M F f r o m 1 0 À pore-size p o l y ( s t y r e n e - d i v i n y l b e n z e n e ) e x h i b i t a p p a r e n t m o l e c u l a r weight d i s t r i b u t i o n s characterized b y weight-average m o l e c u l a r weights 1.5 to 1.9 χ 1 0 times greater t h a n those i n aqueous 0.10 M N a O H (Table II). 6

4

W h e n measured t h r o u g h a 26 n m b a n d w i d t h interference filter (reject­ i n g most fluorescence), R a y l e i g h scattered light intensities ( m u l t i p l i e d b y r e c i p r o c a l s o l u t i o n t r a n s m i t t a n c e to correct for absorbance) f u r n i s h weightaverage m o l e c u l a r weights for the same series of k r a f t l i g n i n p r e p a r a t i o n s i n D M F t h a t are between 190 a n d 1100 times larger t h a n those i n aqueous 0.10 M N a O H ( T a b l e I I ) . T h e trends i n , r a t h e r t h a n the absolute values of, the r e p o r t e d n u m b e r s have the greater significance. T h e forms of the respective Z i m m plots ( F i g u r e 16) are t y p i c a l of a s s o c i a t i n g m a c r o m o l e c u ­ l a r species (23): the apparent second v i r i a l coefficients, c a l c u l a t e d f r o m the

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ο

0.0

0.5

1.0 V

1.5

R

Figure 13. Comparison of weight-average molecular weights for component subsets Β (φ) and C ( • ) with those for complete paucidisperse fractions ( • ) isolated from Sephadex G100/0.10 Af aqueous N a O H elution profile of the dissociated kraft lignin sample precipitated upon acidification to pH 3.0 after 2000 h at 0.50 g L in 0.10 Af aqueous NaOH. 1

DUTTA ET AL.

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12.

k

Association Between Kraft Lignin Components

171

230

'300

5.0

10.0 Mw

x

10"

15.0

20.0

3

Figure 14. Variation with molecular weight exhibited by ratios of absorbance values at 230 and 300 nm for paucidisperse kraft lignin fractions in aqueous 0.10 Af N a O H from ( ^ ) associated sample after 385 h at 180 gL" in 1.0 M ionic strength aqueous 0.40 M N a O H ; (O) original preparation; ( • ) dissociated sample precipitated upon acidification to p H 3.0 after 2000 h at 0.50 gL* in aqueous 0.10 M N a O H . 1

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172

I

I

I

20

10

5

1

2x10

7

extrapolated molecular weight calibration from polystyrenes Figure 15. Apparent molecular weight distributions in D M F of kraft lignin samples secured by desalting after association and dissociation in aqueous alkaline solutions for: (1) 300 h and (2) 144 h at 170 g L in 1.0 A f ionic strength aqueous 0.40 A f N a O H ; (3) 0 h; (4) 144 h and (5) 644 h at 0.50 gL" in aqueous 0.10 A f N a O H . (Profiles from 10 À pore-size 20Λ» particle poly(styrene-divinylbenzene) column monitored at 320 nm.) 1

1

6

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Figure 16. Z i m m plot of 514.5 nm light-scattering data characterizing associated kraft lignin sample in D M F following desalting after incubation at 170 g L for 300 h in 1.0 M ionic strength aqueous 0.40 M N a O H . 1

LIGNIN: PROPERTIES AND MATERIALS

174 Table II. C o m p a r i s o n of Homologous A q u e o u s 0.10 M N a O H

K r a f t Lignin Samples i n D M F and

a

Parameter Mjv,NaOH

e

M DMF .DMF

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3

4.67 χ 1 0

5.89 χ 1 0

3

1.3 x 1 0

5

190

W

cm mol

Original Kraft Lignin

8.7 χ 1 0

5

W
0.35 d l / g for C , 0.38 d l / g for C a n d 0.43 d l / g for C derivatives) were synthesized f r o m 4 , 4 ' - d i h y d r o x y - 3 , 3 ' - d i m e t h o x y b e n z a l a z i n e [VIII] a n d d i c a r b o x y l i c a c i d chlorides b y c o n v e n t i o n a l low t e m p e r a t u r e s o l u t i o n p o l y c o n d e n s a t i o n , as s h o w n i n Scheme 4. T h e t h e r m a l s t a b i l i t y of the samples was s t u d i e d b y T G . A s s h o w n i n T a b l e I, the d e c o m p o s i t i o n t e m p e r a t u r e s (T

α

ε ο Β Ο

α.

& α ο

3 UH

Ο

225

LIGNIN: PROPERTIES AND MATERIALS

226

G r a p h i t e s w i t h larger surface areas or greater porosities have a dis­ t i n c t l y lower p e r c o l a t i o n t h r e s h o l d . It is assumed t h a t the c o n d u c t i v i t y of a c o m p o u n d depends u p o n the s t r u c t u r e d agglomerates being sufficiently close to each other, or i n direct contact above the p e r c o l a t i o n p o i n t , a n d o n the continuous current p a t h w a y s created thereby (14-15).

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Mechanism of Conductivity W h e n s o d i u m lignosulfonate or sulfur l i g n i n are c o m p o u n d e d , for instance, w i t h iodine or b r o m i n e , complexes supposedly f o r m (16-17). These systems are conductors w i t h m i x e d i o n i c a n d electronic n a t u r e . P r e s u m a b l y they are charge transfer complexes, since the electronic c o n d u c t i v i t y p r e d o m i n a t e s (18-19). These c o m p o u n d e d m a t e r i a l s f o r m charge transfer s t r u c t u r e s (20). W a t e r is supposed to i n t r o d u c e i o n i c c o n d u c t i v i t y to the s y s t e m . I m p u r i t i e s affect c o n d u c t i v i t y , too (21). I n any case, the m a i n m o d e l s of c o n d u c t i v i t y are p r o b a b l y based o n the band model a n d / o r the hopping model.

Lg(S/cm)

1

0

I

2

1

4

1

1

6

8



10

ι

12 Mass-?i

14

F i g u r e 4. C o m p o u n d i n g sulfur l i g n i n w i t h g r a p h i t e (a) a n d w i t h g r a p h i t e a n d b r o m i n e (b).

16.

KUUSELAETAL.

Modification to Electrically Conducting Polymers 227

Conclusions T h e r e has l o n g been a n interest i n u n d e r s t a n d i n g t h e m e c h a n i s m o f c o n ­ d u c t i v i t y . I n g r a p h i t e , t h e electrons are t h e m a i n current c a r r i e r s , b u t i n t e r c a l a t i o n w i t h b r o m i n e increases the c o n d u c t i v i t y o f t h i s c o m b i n a t i o n . M o d i f i e d l i g n i n m a t e r i a l s m a y serve as components i n ( s e m i ) c o n d u c t i n g systems. A l l heterogeneous a n d a m o r p h o u s p o l y m e r i c complexes are n o w o f interest for possible future e m p l o y m e n t i n e l e c t r i c a l l y c o n d u c t i n g m a t e r i a l s .

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Literature C i t e d 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

21.

Hrutfiord, B. F.; McCarthy, J. L . Tappi 1964, 47, 381. Rezanowich, Α.; Goring, D. A . I. J. Colloid Sci. 1960, 15, 452. Turunen, J. Ph.D. Thesis, University of Helsinki, Helsinki, 1963. Lindberg, J. J.; Turunen, J.; Hortling, B. Finnish Patent No. 50 998, 1982. Lindberg, J. J.; Turunen, J.; Hortling, B. U.S. Patent No. 410 711, 1982. Levon, K . Ph.D. Thesis, University of Tokyo and University of Helsinki, Tokyo, 1986. Hortling, B. Ph.D. Thesis, University of Helsinki, Helsinki, 1979. Laakso, J.; Hortling, B.; Levon, K.; Lindberg, J. J. Polymer Bull. 1985, 14, 138. Aldssi, M . Polym.-Plast. Technol. Eng. 1987, 26(1), 45. Kaila, E . ; Kinanen, Α.; Levon, K.; Turunen, J.; Osterholm, J.-E.; Lind­ berg, J. J. U.S. Patent No. 4 610 809, 1986. Lindberg, J. J.; Levon, K.; Kuusela, T . A . Acta Polymerica 1988, 39(1/2), 47. Levon, K.; Kinanen, Α.; Lindberg, J. J. Polym. Bull. 1986, 16, 433. Kagan, Η. B. Pure and Appl. Chem. 1976, 46, 177. Wessling, B.; Volk, H . Synthetic Metals 1986, 16, 127. Wessling, B. Macromol. Chem. 1984, 185, 1265. Neoh, K . G . ; Tan, T . C . ; Kang, Ε. T . Polymer 1988, 29, 553. Kang, E . T . ; Tan, T . C . ; Neoh, K. G . Eur. Polym. J. 1988, 24, 371. Ratner, Μ. Α.; Schriver, D. F . Chem. Rev. 1988, 88, 109. Hardy, L . C . ; Schriver, D. F . J. Am. Chem. Soc. 1985, 107, 3823. Stranks, D. R.; Heffernan, M . L . ; Lee Dow, K . C . ; McTigue, P. T . ; Withers, G . R. A . In Chemistry: A Structural View; Cambridge Uni­ versity Press, 1970; Chapter 25, p. 422. Jernigan, J. T . ; Chidsey, C . E . D.; Murray, R. W . J. Am. Chem. Soc. 1985, 107, 2824.

RECEIVED May 29,1989

Chapter 17

Production and Hydrolytic Depolymerization of Ethylene Glycol Lignin R. W. Thring , E . Chornet , R. P. Overend , and M . Heitz 1

1

1,2

1

Département de Génie Chimique, Faculté des Sciences Appliquées, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada Conseil National de Recherches du Canada, Ottawa, Ontario K1A 0R6, Canada 1

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2

A prototype solvolytic lignin has been isolated from Populus deltoides using ethylene glycol as solvent in a process development unit. The characteristics of this lignin by elemental analysis, methoxyl content, thermogravimetric analysis, gel permeation chromatography, F T I R , and C N M R , suggest that this is a native-type lignin. Depolymerization of this lignin by alkaline hydrolysis produces reasonable yields of monomeric compounds: at optimum conditions of 2% sodium hydroxide, and a treatment severity corresponding to 300°C and 1 h reaction conditions, a maximum of 11% of identifiable monomers, based on the initial lignin, are produced, of which 9% are catechol and its methyl and ethyl derivatives. 13

H y d r o l y s i s o f l i g n i n i n acidic a n d basic m e d i a has received a t t e n t i o n due t o the r a t h e r few a n d s i m p l e d e g r a d a t i o n p r o d u c t s o b t a i n e d . A c i d - c a t a l y z e d h y d r o l y s i s reactions a p p l i e d t o isolated l i g n i n have been s t u d i e d b y a n u m ber o f workers. L u n d q u i s t (1), for e x a m p l e , s u b j e c t e d B j o r k m a n l i g n i n t o acidolysis a n d o b t a i n e d significant yields o f m o n o m e r i c p r o d u c t s . A r e v i e w o f the w o r k p r i o r t o 1971 has been m a d e b y W a l l i s (2). A l k a l i n e degradations, w h i c h also involve h y d r o l y t i c reactions, c a n s p l i t the l i g n i n a n d y i e l d useful low m o l e c u l a r f r a g m e n t s . T h e O H ~ g r o u p has l o n g been k n o w n t o cleave l i g n i n b o n d s a n d is one o f the t w o p r i m a r y c a t a l y t i c agents ( S is the other) responsible for the d i s s o l u t i o n o f l i g n i n i n the k r a f t process. A l k a l i n e h y d r o l y s i s , as c o m p a r e d t o other m e t h o d s o f l i g n i n d e g r a d a t i o n , has certain advantages. T h e c a t a l y t i c reagents are i n e x p e n s i v e a n d available c o m m e r c i a l l y , a n d require no elaborate m e t h o d o f p r e p a r a t i o n . =

0097-6156/89/0397-0228$06.00/0 © 1989 American Chemical Society

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229

A l s o , the yields o f the m o n o m e r i c p r o d u c t s c a n be significant a n d the p r o d ­ uct s p e c t r u m as a whole is not extensive. It is established (3) t h a t these h y d r o x y l groups w i l l o n l y cleave c e r t a i n C - O - C b o n d s , n a m e l y the f o l l o w i n g :

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1. α-aryl ether b o n d s p r o v i d e d t h e y c o n t a i n a free p h e n o l i c O H ~ g r o u p i n the p a r a p o s i t i o n of the α-aryl ether g r o u p or a free alcoholic O H " g r o u p o n the /?-carbon a t o m . 2. / ? - a r y l ethers i f the p h e n o l i c O H ~ g r o u p i n the p a r a p o s i t i o n t o the / ? - a r y l ether side c h a i n is etherified a n d i f there is a free alcoholic O H ~ g r o u p b o u n d t o the a - a n d / o r 7~position(s) o f the p r o p a n e side c h a i n . T h e b e h a v i o r o f m i l l e d w o o d l i g n i n a n d i t s various m o d i f i c a t i o n s t o ­ w a r d s a l k a l i ( s o d i u m h y d r o x i d e ) t r e a t m e n t s agreed well w i t h the results o f m o d e l e x p e r i m e n t s (4). C l a r k a n d G r e e n (5) s t u d i e d the p r o d u c t i o n o f phenols f r o m alkaline h y d r o l y s i s o f k r a f t l i g n i n . T h e l i g n i n was cooked at 260-310°C i n s o l u t i o n s o f s o d i u m h y d r o x i d e a n d s o d i u m sulfide. P r i n c i p a l p r o d u c t s i d e n t i f i e d a n d quantified were g u a i a c o l , catechol, m e t h y l - a n d e t h y l - g u a i a c o l s , m e t h y l a n d e t h y l - catechols, a n d p h e n o l . A m a x i m u m q u a n t i t y o f these, a m o u n t ­ i n g t o 1 1 % o f the l i g n i n , o c c u r r e d w h e n the l i g n i n was cooked i n 4 % N a O H at 3 0 0 ° C for 30 m i n u t e s . C a t e c h o l was f o u n d t o be the m o s t a b u n d a n t m o n o m e r i c p r o d u c t , t h a t i s , a b o u t 5.3% o f the l i g n i n at these o p t i m u m conditions. Demethylation of guaiacyl compounds and degradation of o t h ­ ers t o o k place w h e n s o d i u m s u l p h i d e was i n c l u d e d d u r i n g c o o k i n g , w h i c h resulted i n reduced y i e l d s o f t o t a l p h e n o l i c c o m p o u n d s i d e n t i f i e d . H a g g l u n d a n d E n k v i s t (6) developed a l a b o r a t o r y scale m e t h o d for m a n u f a c t u r i n g m e t h y l sulfide f r o m k r a f t b l a c k l i q u o r b y pressure h e a t i n g after a d d i t i o n o f s o d i u m sulfide. T h i s process was l a t e r t a k e n over b y C r o w n - Z e l l e r b a c h i n the U n i t e d States a n d developed i n p i l o t p l a n t a n d f u l l scale. However, the y i e l d is o n l y about 7% o f the i n i t i a l l i g n i n u t i l i z e d i n the process. E n k v i s t a n d co-workers (7) pressure heated k r a f t b l a c k liquors w i t h a d d i t i o n s o f s m a l l a m o u n t s o f N a S a n d N a O H for 10-20 m i n u t e s at 250290°C i n b a t c h as w e l l as i n s i m p l e continuous a p p a r a t u s . T h e a d d i t i o n o f s o d i u m sulfide was f o u n d t o increase the f o r m a t i o n o f ether-soluble m a t e r i a l . T h e highest y i e l d s o f ether-soluble phenols o c c u r r e d w i t h pressure h e a t i n g at a b o u t 291°C o f spent k r a f t l i q u o r c o n t a i n i n g 20.4% o f o r g a n i c s u b s t a n c e after a d d i t i o n of 3.2% N a S a n d 1.6% N a O H . T h e m a x i m u m y i e l d o f ethersoluble m a t e r i a l was 3 3 % o f the organic substance, w i t h catechol a n d i t s nearest homologues c o m p r i s i n g 5%. A n o t h e r p r o d u c t t h a t is p r o d u c e d c o m m e r c i a l l y f r o m the alkaline h y ­ d r o l y s i s o f l i g n i n is v a n i l l i n . It was f o u n d t h a t the y i e l d c o u l d be i m p r o v e d b y the presence o f o x y g e n d u r i n g the alkaline h y d r o l y s i s r e a c t i o n . A n u m b e r o f c o m m e r c i a l ventures have been based o n t h i s procedure ( 8 , 9 ) . T h e focus o f o u r work is t o p r o d u c e a p r o t o t y p e s o l v o l y t i c l i g n i n , c h a r ­ acterize i t , a n d degrade i t t o lower m o l e c u l a r weight chemicals b y h y d r o l y s i s w i t h s o d i u m h y d r o x i d e . T h e breakage o f a r o m a t i c ether linkages has been s h o w n t o be a d o m i n a n t r e a c t i o n i n alkaline d e l i g n i f i c a t i o n processes. It is therefore o f interest t o use t h i s a p p a r e n t l y s i m p l e a n d p r o m i s i n g a p p r o a c h t o investigate the c h e m i c a l u t i l i z a t i o n o f o u r l i g n i n . 2

2

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230

T h e efficiency o f ethylene g l y c o l - w a t e r as a d e l i g n i f y i n g solvent has been d e m o n s t r a t e d b y G a s t a n d P u i s (10). R e s u l t s showed t h a t sufficiently delignified p u l p s c o u l d be o b t a i n e d . A l s o , the l i g n i n s p r o d u c e d showed p r o m i s i n g results as extenders i n phenolic resin adhesives. E t h y l e n e g l y c o l p u l p i n g has been p r e v i o u s l y s t u d i e d i n o u r l a b o r a t o r i e s ( 1 1 , 1 2 ) . W h e n a p p l i e d t o Populus deltoïdes, i t acts as a " p r o t e c t i v e " s o l vent for cellulose w h i c h is o n l y s l i g h t l y d e p o l y m e r i z e d even at t e m p e r a t u r e s as h i g h as 220-230°C. U n d e r these c o n d i t i o n s the l i g n i n c a n be scavenged f r o m the w o o d m a t r i x a n d dissolved i n the ethylene g l y c o l . A f r a c t i o n a t i o n o f the m a i n c o n s t i t u t i v e p o l y m e r s can t h u s be achieved. T h e present w o r k a i m s at u s i n g the l i g n i n f r a c t i o n as feedstock for alkaline d e p o l y m e r i z a t i o n to monomeric products. T h i s p a p e r , t h e n , describes the p r e p a r a t i o n a n d c h a r a c t e r i z a t i o n o f a solvolysis l i g n i n prepared u n d e r c o n d i t i o n s t h a t are very different t o p r e v i o u s s o l v o l y t i c l i g n i n p r e p a r a t i o n s . I n p a r t i c u l a r , n o water, a c i d or base is used i n t h i s process d u r i n g the d e l i g n i f i c a t i o n step. T h e l i g n i n is t h e n a c i d p r e c i p i t a t e d a n d h y d r o l y z e d i n d i l u t e aqueous s o l u t i o n t o p r o d u c e m o n o m e r i c s u b s t i t u t e d phenols.

Experimental Materials. A i r d r i e d w o o d (Populus deltoïdes) was g r o u n d t o pass t h r o u g h a screen o f 0.5 m m mesh size. These "fines" were used i n the subsequent s o l v o l y t i c studies. T h e chemicals used were: ethylene g l y c o l ( p r a c t i c a l grade); s o d i u m h y d r o x i d e ( p r a c t i c a l grade); e t h a n o l ( 9 5 % ) ; d i e t h y l ether. C a l i b r a t i o n - p h e n o l s were purchased f r o m A l d r i c h C h e m i c a l s L i m i t e d a n d A l f a Chemicals Limited. Set-up for Ethylene Glycol Lignin Production. A process development u n i t ( P D U ) , p r e v i o u s l y described b y C h o r n e t a n d c o w o r k e r s (11), was used for the e x p e r i m e n t s . A t y p i c a l p r e p a r a t i o n consists of i n i t i a l l y m i x i n g 1-1.2 k g o f w o o d m e a l w i t h 10 1 o f ethylene g l y c o l . T h e m i x t u r e is allowed t o s t a n d overnight for i m b i b i t i o n t o take place. T o enhance solvent t o s u b s t r a t e p e n e t r a t i o n , the s l u r r y is homogenized at 200°C i n the p r e t r e a t m e n t s e c t i o n o f the P D U . It is t h e n p u m p e d t h r o u g h the t r e a t m e n t section w h i c h consists o f a t u b u l a r reactor at 220°C. T h e p r o d u c t s l u r r y is collected i n a receiver. T h e d e t a i l e d procedure a n d choice o f c o n d i t i o n s above have been p u b l i s h e d elsewhere ( 1 1 , 1 2 ) . T h e p r o d u c t s l u r r y is s u c t i o n filtered, w h i l s t h o t , a n d the residue washed w i t h hot ethylene g l y c o l (at 100°C). T h e l i q u i d p r o d u c t a n d first w a s h i n g are c o m b i n e d a n d stored i n the refrigerator t o be used l a t e r . F o r i s o l a t i n g the l i g n i n f r o m the g l y c o l / h e m i c e l l u l o s e s o l u t i o n , i t was necessary t o use d i l u t e aqueous H C 1 as a p r e c i p i t a t i n g c a t a l y s t . T h e best c o n d i t i o n s f o u n d were for 0 . 0 5 % aqueous H C 1 ( a c i d : black l i q u o r = 3:1) at Τ = 5 0 6 0 ° C . B y t h i s procedure 7 0 - 8 0 % o f the l i g n i n f r o m the w o o d is recovered. Lignin Characterization. E l e m e n t a l a n a l y s i s , T G A , m e t h o x y l content, G P C , F T I R , and C N M R were used t o characterize o u r p r o t o t y p e solvolytic lignin. 1 3

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Typical of most isolated lignins, an elemental analysis of glycol lignin in our laboratories using a Perkin Elmer 240C instrument showed it to contain 61.85% C , 6.25% H , 0.16% N , and 33.83% Ο (by difference). Methoxyl con­ tent determinations were made according to the method initially proposed by Zeisel (13) and later modified by Haluk (14). Methoxyl and ash content were 20% and 0.11%, respectively. T h e presence of sugars was determined to be less than 1%. A comparison between the thermal degradation rate of glycol lignin and kraft Indulin A T by T G A showed that the former de­ graded at a faster rate than the latter. T h e maximum rate of weight loss was about twice that of kraft lignin and occurred at about 360° C , compared to 400°C for kraft. G P C analysis of acetylated glycol lignin was carried out on a Varian 5000 Liquid Chromatograph equipped with two P L gel columns (50Àand 500Â) connected in series. Tetrahydrofuran was used as eluent. T h e column set was calibrated with monodisperse polystyrene standards for molecular weight determination. Molecular weight averages for derivatized glycol lignin were calculated to be: M = 986 and M = 4762. n

w

The infrared spectrum of glycol lignin is shown in Figure 1. A 5 D X B Nicolet F T I R spectrometer in diffuse reflectence mode was used. T h e sample was prepared by the K B r disk method. Assignment of absorption bands is based on information from Herget (15) and Winston (16). Infrared spectra of glycol and milled wood lignin from the same wood appeared to be similar. One notable difference was the large carbonyl band at 1738 c m " due to carbohydrates present in the M W L . T h e sample of M W L used was known to contain 6-8% sugars. The C N M R spectrum (90 M H z , 8.4 T , 2 seconds delay) of glycol lignin is presented in Figure 2. DMSO-de was used as solvent. Assignment of the major signals is based on the work of Lapierre et ai (17). T h e spectrum is very similar to that of milled wood lignin except that at the low field there appear to be more pronounced aliphatic peaks. Identification of these were not undertaken because the glycol lignin was isolated from as-received hardwood which was not extractives-free. 1

1 3

Depolymerization. Subsequent depolymerization of this lignin was carried out in a 500 ml magnetically stirred autoclave. A typical procedure for the experiments was to load the autoclave with 5 g of dry lignin (dried at 6 0 ° C overnight), 100 ml solvent, and 0-6 g sodium hydroxide. T h e bomb was sealed, secured onto its support frame, then the gas inlet, outlet, and pressure gauge were connected. After purging the reactor with nitrogen to remove air, the stirrer was set at 500 rpm and switched on. T o start a run, the reactor was immersed in a preheated salt bath and the temperature and time were recorded by computer for subsequent calculation of the reaction ordinate, to be defined later. Typically, the desired reaction temperature ( ± 3 ° C experimental error) was reached within the first ten minutes of heating. After the desired treatment was attained, the reactor was quenched in a cold water bath. The stirrer and computer recording were stopped

F i g u r e 1. I n f r a r e d s p e c t r u m o f g l y c o l l i g n i n .

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—ι—

150

—ι—

160

—ι—

170

140 120

—I—

F i g u r e 2.

130

—ι—

1

3

—T— 110

100 PPM

—ι—

90

—r—

80

—r—

70

C N M R spectrum of glycol lignin.

3

G guaiacyl S « syringyl CH = c a r b o h y d r a t e

Assignments according to Laplerre et a l . (1982)

60

—r—

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50

40

D

30

Ci

i

ι

n

z Ci

S

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when the reactor temperature reached its initial value. The bomb was depressurized, if necessary, removed from its frame, opened, and drained of its contents. After reaction, the slurry product consisted of a liquid mixture together with some insoluble material. This slurry was filtered and the residue thor­ oughly washed with water. Further separation of the reaction products was carried out as shown in Figure 3. A n aliquot of the liquid was acidified, after ethanol removal (if necessary) with 10% (v/v) HC1 to a p H of 1-2, then filtered. The filtrate was extracted with diethyl ether till the aqueous layer was judged colorless by eye. After removal of the ether by rotary evaporation, the extract was analyzed by capillary gas chromatography. T h e solvolytic treatment and the recovery procedures employed yielded about 75% of the original Klason lignin present in the wood. This percent­ age could be further optimized but was not attempted in the present work. The recovered lignin was subjected to alkaline depolymerization. Yields presented throughout the paper are expressed as percentages of the recov­ ered lignin. Material balances during the depolymerization step were within 5% closure for all the experiments reported. Gas Chromatographic Analysis. Ether-soluble fractions from the hydrol­ ysis runs were analyzed by capillary G C (Hewlett-Packard Model 5890A gas chromatography D B - 5 column of 30 m length, 0.25 m m I.D.; flame ionization detector; 1.5 ml H e / m i n ; split injection 1:100; oven tempera­ ture programmed from 65° C to 220° C at 3°C/min (hold 140° C for 5 min and 220°C for 10 min). Products were acetylated by adding 1-2 ml acetic anhydride and 2 drops of pyridine to the sample and heating at 60° C for 1 h. The peaks assigned to phenol, o- and p- cresol, guaiacol, 4-methyl, 4-ethyl- , 4-propylguaiacol, catechol, 4-methyl-, 4-ethylcatechol, syringol, vanillin, acetovanillone, syringaldehyde, and acetosyringone, were identical (retention time) to those of pure compounds. Identification of peaks was further confirmed by comparing mass spectral fragmentation patterns of products in the sample to pure compounds by G C / M S . For quantitative estimation of identified monomers, response factors were calculated, using 4-ethyl-resorcinol as an internal standard. T h e rela­ tive error in the determination of all the compounds was ± 4 % .

Results and Discussion Most of the results obtained from the hydrolysis experiments were analyzed and represented as a function of R a reaction ordinate, previously defined and used (18). It is defined as C 1

(1) where

To =constant (taken to be 100°C) λ =constant (taken to be 14.75°C t =time (in min.).

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HYDROLYSIS PRODUCT MIXTURE

Filtration + Water Wash REACTOR RESIDUE

LIQUIDS1. Ethanol Removal (If necessary) 2. Acidify to pH 1-2 3. Filtration + Wash

RESIDUAL LIGNIN

LIQUID Ether Extraction

AQUEOUS ^ > LAYER

^ORGANIC LAYER

ι

Ether Removal

EXTRACT (GC Analysis) (Ether Fraction) F i g u r e 3. P r o c e d u r e for s e p a r a t i o n o f h y d r o l y s i s p r o d u c t s .

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236

T h e r e a c t i o n o r d i n a t e is u t i l i z e d here as a means o f c o m b i n i n g the effects o f t e m p e r a t u r e a n d t i m e . I n presenting a n d discussing o u r results, the d a t a is presented o n plots of the d e r i v e d d a t a versus l o g i o R C o n v e r s i o n of l i g n i n to l i q u i d a n d gaseous p r o d u c t s was d e t e r m i n e d as follows: % conversion = ( W i - (W + W )/Wi) x 100 (2) 0

x

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where

2

W{ = weight of i n i t i a l d r y l i g n i n (g) W\ = weight of reactor residue (g) W2 = weight of r e s i d u a l l i g n i n (g)

Effect of Solvent. F i g u r e 4 shows the h y d r o l y s i s of g l y c o l l i g n i n i n 3 % s o d i u m h y d r o x i d e u s i n g water o n l y a n d a n e t h a n o l / w a t e r m i x t u r e as s o l vent. A s seen, conversion c a n be a p p r o x i m a t e d b y a l i n e a r increase w i t h severity of t r e a t m e n t , for b o t h cases. A s i m i l a r result was f o u n d i n the a l kaline h y d r o l y s i s o f k r a f t l i g n i n i n 2 % s o d i u m h y d r o x i d e s o l u t i o n b y C l a r k a n d G r e e n (5). W h e n water o n l y is used, the m a x i m u m y i e l d of ether s o l uble m a t e r i a l is about 2 0 % of the o r i g i n a l l i g n i n , w i t h m o s t of the l i g n i n d e c o m p o s i n g t o v o l a t i l e p r o d u c t s at higher t r e a t m e n t severities. H o w e v e r , the q u a n t i t y of ether soluble m a t e r i a l o b t a i n e d u s i n g the s o l vent m i x t u r e was higher a n d reached a m a x i m u m of a p p r o x i m a t e l y 2 5 % of the o r i g i n a l l i g n i n . T h i s suggests t h a t the presence of e t h a n o l enhances the d e g r a d a t i o n of l i g n i n i n a l k a l i n e m e d i a . A l s o , i t appears t h a t for either solvent, there is a c r i t i c a l value o f reaction t e m p e r a t u r e a n d t i m e ( a n d o b v i o u s l y o f R ) b e y o n d w h i c h the q u a n t i t y of ether soluble m a t e r i a l r e m a i n s essentially the same. T h u s , i t can be s a i d t h a t i n u s i n g either solvent, o n l y a f r a c t i o n o f the g l y c o l l i g n i n is h y d r o l y z e d i n t o a n ether soluble m a t e r i a l containing monomeric compounds. T h e s p e c t r a of m o n o m e r i c p r o d u c t s i n the ether e x t r a c t , w h e n either solvent was used i n the r e a c t i o n , were v e r y s i m i l a r . C o m p o u n d s i d e n t i fied were: p h e n o l , o c r e s o l , p-cresol, g u a i a c o l , 4 - m e t h y l - , 4 - e t h y l - , a n d 4 - n p r o p y l - g u a i a c o l , catechol, 4 - m e t h y l - a n d 4-ethyl-catechol, v a n i l l i n , s y r i n g o l , s y r i n g a l d e h y d e , acetovanillone a n d acetosyringone. C o n f i r m a t i o n o f t h e i r i d e n t i t y was c a r r i e d out b y c o m p a r i n g r e t e n t i o n t i m e s a n d mass s p e c t r a l f r a g m e n t a t i o n p a t t e r n s w i t h those of a u t h e n t i c c o m p o u n d s . F i g u r e 5 shows p l o t s of the y i e l d s of p h e n o l , g u a i a c o l a n d s y r i n g o l versus R u s i n g water o n l y a n d a 5 0 / 5 0 ethanol-water m i x t u r e , respectively. F o r the same r e a c t i o n c o n d i t i o n s , the y i e l d s of each of the c o m p o u n d s , especially g u a i a c o l a n d s y r i n g o l , are higher w h e n water o n l y is used. It is apparent t h a t the presence of e t h a n o l i n h i b i t s the d e p o l y m e r i z a t i o n o f g l y c o l l i g n i n t o the m o n o m e r s cited above. T h e complete set of d a t a p o i n t s is s h o w n as a f u n c t i o n o f t e m p e r a t u r e i n F i g u r e 6. T h e e x p e r i m e n t s r e p o r t e d below were c a r r i e d o u t u s i n g water as the solvent. 0

0

Effect of Alkali Concentration. F i g u r e 7 A depicts t h a t the v a r i a t i o n of the conversion o f g l y c o l l i g n i n w i t h s o d i u m h y d r o x i d e c o n c e n t r a t i o n reaches a p l a t e a u at about 6 0 % . A l s o , the ether soluble m a t e r i a l r e m a i n s constant

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Water

log (fymin) 10

F i g u r e 4. Effect o f solvent o n conversion a n d ether solubles of g l y c o l l i g n i n depolymerized i n 3% N a O H .

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238

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ETHANOL/WATER

4.8

5.8

6.5

log (R /min) 10

0

Figure 5. Effect of solvent on monomeric product yields in 3% N a O H .

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240

Figure 7. Effect of alkali concentration on conversion and product yields (logxoRo = 7.7).

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at a maximum of 20% of the initial lignin with increasing concentration of sodium hydroxide. It is interesting to note that an aqueous treatment of glycol lignin without using sodium hydroxide under the same conditions reported in Figure 7A yields an ether soluble fraction of about 10%. The variation of catechol and total monomers identified with N a O H concentration is shown in Figure 7B. A maximum of approximately 11% total phenols and 6% catechol is reached at 2% N a O H with increasing alkaline concentration for the same treatment severity. It should be noted that Clark and Green (5) also obtained a maximum of 11% phenolic compounds when they cooked kraft lignin in 4% N a O H at 300°C for 30 minutes. The quantity of catechol was found to be 5.3% of the initial lignin under these conditions. Figure 7C shows that phenol reaches a minimum of 0.5% and stays constant around 1% with increasing concentration of sodium hydroxide. This indicates that the production of phenol from glycol lignin is relatively unaffected by alkaline hydrolysis. Guaiacol, on the other hand, reaches a maximum at 1% N a O H and then rapidly decreases with increasing concentration of sodium hydroxide. This increase in demethoxylation and/or demethylation of guaiacol with alkaline concentration has also been ascertained by Sarkanen and co-workers (19), who investigated the rate of hydrolysis by sodium hydroxide of methoxyl groups in lignin models and lignin. Catechol Production at Optimum Conditions. It has already been demonstrated that the production of monomeric compounds reaches a maximum when glycol lignin is cooked in 2% N a O H at a treatment severity corresponding to a reaction temperature and time of 300°C and 1 h, respectively. It was then necessary to see if higher yields could be achieved when the severity of treatment (R ) is varied. Figure 8A indicates that conversion and ether soluble material vary in the same manner as when 3% N a O H was used. However, the ether solubles only reach a maximum of 20% at higher treatment severities. The distribution of the identified total phenols and total catechols obtained with increasing reaction ordinate is shown in Figure 8B. The increasing amount of catechols in the total phenols identified implies that these are secondary lignin degradation products, probably originating from primary products such as vanillin, syringol, and syringaldehyde. These were found to occur at lower treatment severities in our experiments. As R is increased, reduction in the yields of all monomeric products occurs, demonstrating the increasing influence of pyrolytic reactions in the lignin to produce volatile liquid and gaseous products. As indicated in the separation scheme in Figure 6, a solid residue was recovered from the liquid hydrolysis products. The carbon-to-oxygen ratio of this material was found to increase rather dramatically with increasing R , as seen in Figure 8C. This ratio can either be taken as a measure of the degree of condensation, i.e., a highly condensed lignin means that it has a large number of interunit carbon-carbon bonds, or it can be interpreted as being the result of extensive demethoxylation. The differing levels of 0

0

0

LIGNIN: PROPERTIES AND MATERIALS

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242

Figure 8. Effect of treatment severity on glycol lignin depolymerization in 2% N a O H . C / O = carbon/oxygen ratio in residual lignins.

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d e m e t h o x y l a t i o n are s h o w n as p a r a l l e l lines i n F i g u r e 8 C where the o r i g i n a l l i g n i n ( 2 0 % OCH3) appears as b e i n g progressively d e m e t h o x y l a t e d w i t h i n c r e a s i n g t r e a t m e n t severity. A q u a l i t a t i v e test o n the s o l u t i o n s i n d i c a t e d the presence of m e t h a n o l w h i c h provides further evidence of d e m e t h o x y l a tion.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch017

Conclusions T h i s s t u d y has a g a i n d e m o n s t r a t e d the effectiveness of a l k a l i n e h y d r o l y s i s as a p r i m e m e t h o d of l i g n i n d e g r a d a t i o n t o r e a d i l y identifiable p h e n o l i c products. If, as a c r i t e r i o n of value t o the s t u d y of l i g n i n d e p o l y m e r i z a t i o n b y a l kaline h y d r o l y s i s , the m a x i m u m y i e l d of o x y g e n - b e a r i n g , p h e n y l p r o p a n o i d derivatives is chosen, t h e n the c o n d i t i o n s of such a s t u d y have been o p t i m i z e d here at a t r e a t m e n t severity corresponding t o a r e a c t i o n t e m p e r a t u r e of 300°C for 1 h o u r . U n d e r these c o n d i t i o n s , 2 0 % of the l i g n i n is recovered as ether-solubles of w h i c h 5 5 % is identifiable as m o n o m e r i c d e r i v a t i v e s . T h e rest of t h i s m a t e r i a l p r o b a b l y consists of d i m e r i c - t y p e c o m p o u n d s not identified b y c a p i l l a r y gas c h r o m a t o g r a p h y . F r o m t h i s work i t is e v i d e n t , t h e n , t h a t the h y d r o l y s i s of g l y c o l l i g n i n w i t h s o d i u m h y d r o x i d e does y i e l d a rather significant a m o u n t of catechol a n d i t s m e t h y l a n d e t h y l derivatives. A m a x i m u m q u a n t i t y of these, w h i c h a m o u n t e d to 9 % of the o r i g i n a l l i g n i n , was o b t a i n e d at the c o n d i t i o n s c i t e d above. T h e above results appear consistent w i t h a m o d e l for l i g n i n p r o p o s e d b y P e p p e r et al (20) w h i c h consists of a core s t r u c t u r e t o w h i c h are a t t a c h e d the m o r e r e a d i l y accessible s i d e - c h a i n u n i t s . T h e s e u n i t s comprise t h a t fragment of l i g n i n w h i c h is easily degraded a n d released as low m o l e c u l a r weight identifiable p r o d u c t s b y any d e g r a d a t i o n procedure. I n v i e w of our results, a possible route for l i g n i n d e p o l y m e r i z a t i o n c o u l d consist of p r o d u c i n g a n organosolv l i g n i n b y m e t h o d s analogous t o those used i n our w o r k . T h e l i g n i n thus p r o d u c e d can be d i r e c t l y t r e a t e d u n d e r a l k a l i c o n d i t i o n s at m i l d severities (logio R — 7.7) t o recover a low m o l e c u l a r weight f r a c t i o n i n w h i c h m o n o m e r i c p r o d u c t s are p r e d o m i n a n t . A s far as the ethylene g l y c o l l i g n i n is concerned, i t has been s h o w n t o be a n a t i v e - l i k e l i g n i n w h i c h can be p r o d u c e d a n d recovered b y direct s o l v o l y t i c t r e a t m e n t of the i n i t i a l lignocellulosic s u b s t r a t e . It w o u l d also be possible to remove the hemicelluloses v i a a n a q u e o u s / s t e a m t r e a t m e n t p r i o r to s o l v o l y t i c s e p a r a t i o n of the l i g n i n a n d cellulose. S u c h a n o p t i o n w o u l d f a c i l i t a t e the recovery of the three m a i n c o n s t i t u t i v e fractions of lignocellulosics i n significant y i e l d s . W o r k i n t h i s d i r e c t i o n is n o w underway. 0

Acknowledgments T h e a u t h o r s are i n d e b t e d t o J . B u r e a u , J . P . L e m o n n i e r , J . B o u c h a r d , a n d P . V i d a l for t h e i r t e c h n i c a l s u p p o r t . F i n a n c i a l c o n t r i b u t i o n s of N S E R C , N R C C a n d F C A R are g r a t e f u l l y acknowledged.

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch017

Literature C i t e d 1. Lundquist, K . Acta Chem. Scand. 1973, 21, 2597. 2. Wallis, A . F . A . In Lignins: Occurrence, Formation, Structure and Reactions; Sarkanen, Κ. V . , Ludwig, C . F . , Eds.; Wiley-Interscience: New York, 1971; pp. 345-372. 3. Gierer, J.; Noren, I. Acta Chem. Scand. 1962, 16, 1713. 4. Gierer, J.; Lenz, B.; Noren, I.; Soderberg, S. Tappi 1964, 47(4), 233. 5. Clark. I. T . ; Green, J. Tappi 1968, 51(1), 44. 6. Hagglund, E . ; Enkvist, T . U.S. Patent 2 711 430, 1955. 7. Enkvist, T . ; Turunen, J.; Ashorn, T . Tappi 1962, 45(2), 128. 8. Tomlinson, G . H . ; Hibbert, H . Am. Chem. Soc. 1936, 58, 345. 9. Salvesen, J. R.; Brink, D. L.; Diddaus, D. G.; Owzarski, P. U.S. Patent 2 434 626, 1948. 10. Gast, D.; Puls, J. EEC Proc. 1985, p. 949. 11. Chornet, E . ; Vanasse, C . ; Overend, R. P. Entropie 1986, 130/131, 89. 12. Vanasse, C . M.Sc. Thesis, Univ. of Sherbrooke, Québec, Canada, 1986. 13. Zeisel, S. Monatsh Chem. 1985, 6, 989. 14. Haluk, J. P.; Metche, M . Cell. Chem. Technol. 1986, 20, 31. 15. Herget, H . L . In Lignins: Occurrence, Formation, Structure, and Reactions; Sarkanen, Κ. V . , Ludwig, C . H . , Eds.; Wiley-Interscience: New York, 1971; pp. 267-293. 16. Winston, M . H . Ph.D. Thesis, North Carolina State University, Raleigh, N C , 1987. 17. Lapierre, C . ; Lallemand, J. Y . ; Monties, Β. I. Holzforschung 1982, 36(6), 275. 18. Heitz, M . ; Carrasco, F.; Rubio, M . ; Brown, Α.; Chornet, E . ; Overend, R. P. Biomass 1987, 13, 255. 19. Sarkanen, Κ. V . ; Chirkin, G . ; Hrutfiord, B. F . Tappi 1963, 46(6), 375. 20. Pepper, J. M . ; Steck, W . F . ; Swoboda, R.; Karapally, J. C . Adv. Chem. Ser. 1966, 59, 238. RECEIVED May 29,1989

Chapter 18

New Trends in Modification of Lignins Henryk Struszczyk

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

Institute of Chemical Fibres, 19 C. Sklodowska Str., 90-570 Lodz, Poland

New trends in the modification of lignins related to the formation of polymeric materials with such special properties as thermal stability, fire resistance and use as carriers for controlled release, bioactive compounds are discussed. Several properties of new polymeric materials, especially their thermal behavior, were studied. The activation energy of the thermal degradation process was found to be in the range of 21-176 k J / m o l for several derivatives. Practical agricultural tests with lignin-based carriers containing chemically bound 2,4-D demonstrated that lignin is capable of providing herbicide release over prolonged time periods. T h e w o r l d w i d e increase i n t h e price o f p e t r o l e u m a n d coal has created a n interest i n a l t e r n a t i v e sources o f r a w m a t e r i a l s . B i o m a s s is a n a t t r a c t i v e renewable r a w m a t e r i a l c o m p r i s i n g a l l types o f a g r i c u l t u r a l a n d s i l v i c u l t u r a l v e g e t a t i o n . T h e s e renewable resources have recently been considered m a j o r a l t e r n a t i v e r a w m a t e r i a l s for the c h e m i c a l i n d u s t r y . L i g n i n s represent t h e second most a b u n d a n t p o l y m e r i c c o m p o n e n t o f b i o m a s s . L i g n i n s i n spent p u l p i n g l i q u o r s o f c h e m i c a l p u l p i n g processes have so far been used as a n energy source, where they d o n o t a l w a y s live up t o their f u l l economic p o t e n t i a l . L i g n i n s , o w i n g t o their reactive sites w h i c h are m a i n l y a r o m a t i c as w e l l as a l i p h a t i c h y d r o x y l groups, have been p o t e n t i a l r a w m a t e r i a l s for the m a n u f a c t u r e o f new p o l y m e r s (1-7). T h i s p a p e r presents t w o different directions o f l i g n i n m o d i f i c a t i o n r e search: • m o d i f i c a t i o n b y at least d i f u n c t i o n a l reactive modifiers t o f o r m s p e c i a l types o f p o l y m e r i c m a t e r i a l s characterized by, a m o n g others, t h e r m a l s t a b i l i t y , fire resistance, a n d c h e m i c a l resistance; a n d 0097-6156/89A)397-0245$06.00A) © 1989 American Chemical Society

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• m o d i f i c a t i o n of lignins or of l i g n i n derivatives to f o r m p o l y m e r i c carriers for c o n t r o l l e d release b i o a c t i v e substances.

Special Lignin-Based Polymeric Materials T w o m a i n l i g n i n types were used for these i n v e s t i g a t i o n s : kraft l i g n i n (Ind u l i n A T , W e s t v a c o C o . , U S A ) , a n d (a) l i g n i n sulfonates ( U l t r a B 0 0 2 , R a u m a R e p o l a O y , F i n l a n d ) w i t h a n i n t r i n s i c viscosity of 8.0 m L g , a t o t a l h y d r o x y l content of 1 4 . 5 % a n d a p h e n o l i c h y d r o x y l content of 4.7%; (b) l i g n i n sulfonates (Borresperse Ν A ) w i t h a n i n t r i n s i c v i s c o s i t y of 5.0 m L g , a t o t a l h y d r o x y l group content of 1 4 . 9 % a n d a p h e n y l i c h y d r o x y l c o n ­ tent of 3.7%; a n d (c) l i g n i n sulfonates ( U l t r a z i n e N A S ) w i t h a n i n t r i n s i c v i s c o s i t y of 12.1 m L g " , a t o t a l h y d r o x y l group content of 1 5 . 1 % , a n d a p h e n y l i c h y d r o x y l content of 4 . 2 % ( b o t h p r o d u c e d b y B o r r e g a a r d Inc., Norway). C h l o r o p h o s p h a z e n e s ( N P C I 2 ) , i n the f o r m o f h e x a c h l o r o c y c l o t r i p h o s phazene ( m . p . 112-113°C, Inabate C o . , J a p a n ) as w e l l as cyclic oligomers ( m . p . 87-91°C, P o l a n d ) a n d t e r e p h t h a l o y l chloride ( M e r c k , F R G ) , served as reactive modifiers. T h e m o d i f i c a t i o n of l i g n i n s b y at least d i f u n c t i o n a l reactive modifiers was c a r r i e d out i n three systems: i n s o l u t i o n ( A ) , i n suspension ( B ) , a n d i n s o i l d state ( C ) i n the presence of hydrogen chloride acceptors (8-10). T h e m o d i f i c a t i o n i n s o l u t i o n ( A ) was carried out b y d i s s o l v i n g l i g n i n s (1.0 g) a n d a c o r r e s p o n d i n g a m o u n t of hydrogen chloride acceptor i n a s u i t a b l e s o l ­ vent. D i f u n c t i o n a l reactive modifier (chlorophosphazenes or t e r e p h t h a l o y l chloride) dissolved i n a s u i t a b l e solvent was next a d d e d dropwise d u r i n g c o n t i n u o u s a g i t a t i o n . T h e m i x t u r e was allowed to react at the b o i l i n g p o i n t for 3 h . T h e r e a c t i o n m i x t u r e was p o u r e d i n t o ice w a t e r , a n d the s o l i d p r e c i p i t a t e was centrifuged at 66.6 rps for 15 m i n . It was washed sev­ eral t i m e s w i t h dioxane a n d water, or w i t h 5 % s o d i u m b i c a r b o n a t e s o l u t i o n a n d w a t e r , to o b t a i n a n e u t r a l reaction p r o d u c t , a n d i t was d r i e d ( 8 , 1 0 - 1 3 ) . T h e l i g n i n m o d i f i c a t i o n s i n suspension ( B ) were c a r r i e d out u s i n g lignins (1.0 g) dispersed i n a s u i t a b l e m e d i u m c o n t a i n i n g also the hydrogen chloride acceptor. D i f u n c t i o n a l reactive modifier dissolved i n a s u i t a b l e s o l ­ vent was next added dropwise d u r i n g continuous a g i t a t i o n . T h e r e a c t i o n m i x t u r e was allowed to react at the b o i l i n g p o i n t for 3 h . T h e p u r i f i c a t i o n process was c a r r i e d out as described before (8,10-12). T h e l i g n i n m o d i f i c a t i o n s i n s o l i d ( C ) were c a r r i e d out u s i n g l i g n i n s (1.0 g) m i x e d w i t h c o r r e s p o n d i n g a m o u n t s of hydrogen chloride acceptor a n d chlorophosphazenes. T h e reaction was carried out b y h e a t i n g at a t e m p e r a t u r e of 100°C, i.e., above the m e l t i n g p o i n t of chlorophosphazene. T h e r e a c t i o n m i x t u r e was p o u r e d i n t o ice water, a n d t h e n the s o l i d p r o d u c t was p u r i f i e d as described before (9). T h e properties of the derivatives o b t a i n e d were d e t e r m i n e d b y the u s u a l a n a l y t i c a l methods (8-17). D i f f e r e n t i a l t h e r m a l a n a l y s i s ( D T A ) was p e r f o r m e d i n a i r w i t h a n O D 102 D e r i v a t o g r a p h ( M O M , H u n g a r y ) u s i n g 100 m g samples at a h e a t i n g rate of 1 0 ° C / m i n . D i f f e r e n t i a l t h e r m o g r a v i m e t r y ( D T G ) a n d t h e r m o g r a v i m e t r y - 1

- 1

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1

18.

STRUSZCZYK

New Trends in Modification of Lignins

247

( T G ) were c a r r i e d o u t w i t h a D u P o n t T h e r m a l A n a l y z e r , T y p e 990, w i t h a 10 m g s a m p l e i n a i r . T h e s a m p l e weight was recorded against t e m p e r a t u r e i n a range o f 20-600°C a t a h e a t i n g rate o f 1 0 ° C / m i n . T h e h y d r o l y t i c resistance o f the p r o d u c t s w a s i n v e s t i g a t e d q u a n t i t a ­ t i v e l y i n 0.4 Ν p o t a s s i u m h y d r o x i d e a n d 0.5 Ν s u l f u r i c a c i d s o l u t i o n s b y m i x ­ i n g powdered m a t e r i a l s (40 m g ) i n a s u i t a b l e solvent (20 m L ) a t 5 0 ± 0 . 1 ° C for 24 h .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

Modification of Lignins with

Chlorophosphazenes

T h e m o d i f i c a t i o n o f lignins w i t h chlorophosphazenes allows t h e m a n u f a c ­ ture o f p r o d u c t s characterized b y flame resistance a n d t h e r m a l s t a b i l i t y . T h i s c a n be a t t r i b u t e d t o the a r o m a t i c s t r u c t u r e o f the l i g n i n - p h o s p h a z e n e p o l y m e r as well as t o the presence o f such flame i n h i b i t i n g elements as phos­ p h o r o u s , n i t r o g e n a n d s u l f u r . O t h e r useful properties m a y also result f r o m t h i s c o m b i n a t i o n . It has p r e v i o u s l y been r e p o r t e d (8-13) t h a t the m o d i f i c a ­ t i o n provides crosslinked p r o d u c t s w i t h s u i t a b l y l o w c h l o r i n e content. T h i s is a consequence o f i n c o m p l e t e s u b s t i t u t i o n o f the phosphazenes cycles. A d ­ d i t i o n a l m o d i f i c a t i o n o f the r e a c t i o n p r o d u c t s b y c h e m i c a l c o m p o u n d s w i t h reactive h y d r o x y l o r a m i n e groups reduces t h e u n r e a c t e d chlorine content a n d i m p r o v e s p r o d u c t properties (8-13). Some properties o f the derivatives o b t a i n e d are presented i n T a b l e I . A novel m o d i f i c a t i o n m e t h o d , i n s o l i d state, has recently been tested (9). S i m p l i c i t y as w e l l as effectiveness seem t o h o l d promise for t h i s t e c h ­ nique (9). Some e x p e r i m e n t a l results are s u m m a r i z e d i n T a b l e I I . A n a d d i t i o n a l m o d i f i c a t i o n o f l i g n i n s w i t h h y d r o x y l or a m i n e g r o u p c o n t a i n i n g c o m p o u n d s was f o u n d t o further i m p r o v e the p r o d u c t properties (Table III). T h e results reveal t h a t U l t r a z i n e N A S lignosulfonates have the highest r e a c t i v i t y t o w a r d chlorophosphazenes. T h i s m u s t p r o b a b l y be e x p l a i n e d w i t h t h e i r s t r u c t u r e , their higher p u r i t y , their higher m o l e c u l a r weight, a n d their higher d i s p e r s i n g a b i l i t y i n contrast t o other lignosulfonates. T h e m o d i f i c a t i o n o f lignins b y chlorophosphazenes allows the f o r m u l a ­ t i o n o f p o l y m e r i c m a t e r i a l s characterized b y : • H i g h flame resistance: T h e derivatives are d i s t i n g u i s h e d by h i g h flame resistance a n d failure t o glow completely, whereas the u n m o d i f i e d l i g n i n s i g n i t e d easily a n d sustained a flame (kraft) or glowed r a p i d l y (lignosulfonates) ; • H i g h h y d r o l y t i c resistance against aqueous a c i d a n d base: T h e m o d ­ ified l i g n i n s were f o u n d n o t t o consume m o r e a l k a l i t h a n t h e p a r e n t l i g n i n (i.e., 50-80 m g K O H / g of derivative as c o m p a r e d t o 85 m g K O H / g o f parent l i g n i n ) ; • C h e m i c a l resistance t o t h e a c t i o n o f o r g a n i c solvents; • L o w m a n u f a c t u r i n g costs i n c o m p a r i s o n t o other types o f phosphazene polymers; a n d • C o n t i n u o u s i m p r o v e m e n t s o f chlorophosphazene-modified l i g n i n s , a l ­ l o w i n g the e v a l u a t i o n o f a wide range o f a p p l i c a t i o n s .

American Chemical Society Library 1155 16th St., N.W. Washington. O.C. 20036

Ultra

Ultra

Borresperse NA

Ultrazine NAS

Ultrazine NAS

3/B

4/B

5/B

6/B

6a/B

2

trimer

olig.

olig.

trimer

olig.

olig. trimer

NPC1 2

6.085

12.160

12.160

2.146

8.584

12.208 3.052

NPC1

13.746

27.492

7.492

4.848

19.392

24.364 6.091

Pyridine

0.038

0.192

0.185

0.035

1.003

1.033 0.600

3

Y i e l d of Product (g)

3.86

8.76

5.90

1.01

2.55

6.76 1.20

Ρ

2.60

3.43

3.90

S

Cl

1.10

1.31

1.46

--

0.44

1.35 --

Chemical Content. %

1250 1200 1200

1210 1030

1260 1210 1212

1260 1210

P=N

1160 1025 1170 1045

1170

1155 1030 1165 1030

1158 1025

POC

Infrared Frequency of Units . cm"

A l l reactions were c a r r i e d out on l i g n i n s (1.0 g) at the b o i l i n g point i n dioxane as a solvent (A) or i n suspension (B).

a

Indulin Indulin

Lignin

Type of

1/A 2/A

Symbol of Sample

Reagents amount, nuno 1

Table I. Properties of the Lignin Modification Products

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

2

3 .06 4,.40 5,.61

0,.99

13 .75

6.09

3

Ρ

Ultrazine NAS

10

a

Ρ * pyridine. A l l reactions were c a r r i e d out on l i g n i n s (1.0 g) using oligomers of NPC1 .

4..90 4..10

5,.62 0..15

182,.20

12.16

3

NaOH

Borresperse ΝΑ

9

2.,19 3.,43

6.,83 0.,81

27,.49 *

12.16

6

Ρ

Borresperse ΝΑ

8

2.,64 3.,96 4.,40

0.,79

27,.49

Cl

S

Ρ

3

12.16

Acceptor

Content,

3

2

%

Ρ

NPC1

Reaction Time, h

Acceptor Type

Chemical Y i e l d of Product , g

Borresperse ΝΑ

Type of Lignin

Reagent Amount, mmol

7

Symbol of Sample

Table I I . Modification Parameters and Derivative Properties Using S o l i d State Reaction

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

1

5

12

13

Borresperse NA

Indulin AT

Indulin AT

Type of Lignin Used

diethylamine

diethylamine

n-propanol

Type of Modifying Compound

0.142

0.612

1.097

3

Y i e l d of Product , g

4.10

7.42

5.82

Ρ

4.73

S

Chemical Content. %

0.65

1.00

1.22

Cl

Reactions were c a r r i e d out using 0.145 mol of diethylamine or 0.0213 mol of n-propanol.

1

11

a

Symbol of Initial Product

Symbol of Sample

Table I I I . Properties of A d d i t i o n a l l y Modified Products

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

1240,1220

1260,1210

1255,1210

Infrared Frequency of P-N Unit, cm

-1

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New Trends in Modification of Lignins

251

T h e m o d i f i c a t i o n of l i g n i n s b y chlorophosphazenes d i s t i n c t l y increases h y d r o g e n b o n d i n g energy of the p r o d u c t s o b t a i n e d , i.e., 17-23 k J / m o l as c o m p a r e d to 14-20 k J / m o l for the parent l i g n i n . T h i s p h e n o m e n o n , w h i c h was a d d i t i o n a l l y confirmed b y X - r a y d a t a ( 1 0 , 1 2 ) , shows the a u g m e n t a t i o n of the p r o b a b l e f o r m a t i o n of regions w i t h increased degree of s u p e r m o l e c u l a r order.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

Thermal Behavior of Lignins Modified by

Chlorophosphazenes

T h e t h e r m o g r a v i m e t r i c ( T G ) as w e l l as difference t h e r m o g r a v i m e t r i c ( D T G ) analysis d a t a are s u m m a r i z e d i n T a b l e I V . T h e t h e r m o g r a m s of selected derivatives are presented i n F i g u r e 1. T h e T G as w e l l as D T G d a t a (Table I V ) show a higher t h e r m a l s t a b i l ­ i t y of lignosulfonates. T h e derivatives o b t a i n e d are d i s t i n g u i s h e d by higher t h e r m a l s t a b i l i t y i n c o m p a r i s o n w i t h the parent l i g n i n s , p a r t i c u l a r l y i n the case o f a d d i t i o n a l m o d i f i c a t i o n s b y n - p r o p o n o l or d i e t h y l a m i n e ( T a b l e I V , S a m p l e s 11 a n d 13). T h e increase i n t h e r m a l s t a b i l i t y m u s t be e x p l a i n e d w i t h the cross-linked s t r u c t u r e as w e l l as the s a t u r a t i o n w i t h such a r o m a t i c groups as p h e n y l p r o p a n e a n d phosphazene. T h e increased phosphorous content increases at the same t i m e the flame resistance. I n a l l cases, low a m o u n t s of v o l a t i l e p r o d u c t s f o r m e d i n the e x o t h e r m i c d e g r a d a t i o n process effectively stifled flame development ( T a b l e I V ) . T h e r m a l b e h a v i o r studies of the lignin-phosphazene derivatives show t h a t their d e g r a d a t i o n process results i n v o l a t i l e a n d n o n - v o l a t i l e p r o d u c t s . A s s u m i n g first-order r e a c t i o n k i n e t i c s for the t h e r m a l d e g r a d a t i o n , r e a c t i o n constant (k) a n d a c t i v a t i o n energy ( E ) c a n be c a l c u l a t e d b y d y n a m i c T G A ( 1 8 , 1 9 ) . T h e Ε-value can thus be c a l c u l a t e d f r o m the leastsquare slope of the p l o t of log k versus r e c i p r o c a l absolute t e m p e r a t u r e as s h o w n i n F i g u r e 2. T h e a c t i v a t i o n en­ ergy values for the t h e r m a l d e g r a d a t i o n of selected derivatives as w e l l as u n m o d i f i e d l i g n i n s are s u m m a r i z e d i n T a b l e V . A s c a n be seen f r o m F i g u r e 2, a d u a l segment a p p r o x i m a t i o n was nec­ essary i n the case of some l i g n i n s as well as derivatives. T h i s p h e n o m e n o n indicates t h a t p y r o l y s i s takes place b y two m e c h a n i s m s i n the t e m p e r a t u r e range s t u d i e d w h i l e the d e g r a d a t i o n of, for e x a m p l e , U l t r a z i n e N A S c o u l d be e x p l a i n e d b y a single m e c h a n i s m . T h e k r a f t l i g n i n as w e l l as U l t r a B 0 0 2 have a higher value of Ε as c o m p a r e d to other l i g n i n sulfonates. T h i s m a y result f r o m differences i n the l i g n i n s t r u c t u r e . T h e m o d i f i c a t i o n of l i g n i n s w i t h chlorophosphazenes results i n changes of Ε t h a t correspond to the degree of s u b s t i t u t i o n a n d the phosphorous content (Table V ) . L i g n i n m o d i f i c a t i o n w i t h chlorophosphazenes is a n e x a m p l e of h o w t h i s renewable resource m a y be u t i l i z e d i n s p e c i a l p o l y m e r i c m a t e r i a l s .

Lignin Modification with Terephthaloyl Chloride A n o t h e r p o t e n t i a l l i g n i n m o d i f i c a t i o n m e t h o d concerns the r e a c t i o n w i t h d i f u n c t i o n a l a c i d chlorides, especially t e r e p h t h a l o y l chloride, to f o r m crossl i n k e d p o l y m e r i c m a t e r i a l s ( 1 , 1 0 , 1 4 , 2 0 ) . Several studies have dealt w i t h

a

325 280,370

--

Borresperse NA Ultrazine NAS

300-398 250-495 472-495 250-350 240-430

250-300

250-300

280 280,289

270-310 270-330

275 300

225-300

— 235-350

— 305 250,570

— 350



4 .5 3 .5

1,.8 3 .4

4,.0

11,.0 8,.0 6,.0 12,.0

4.,2

3 .5 6,.7 5,.8 2..0

7..1 5..0

4..1 4..0

8..0

15.,0 14.,0 9.,0 20..0

5.,5

7..0 9,.3 8,.5 3..3

28,.2 12 .1

13,.0 22,.6

29,.0

25..0 20..0 10..0 27..0

16.,2

12,.5 18..0 12..8 11..8

44,.9 26 .1

76,.3 29 .8

35,.0

30,.0 45,.0 13,.0 33,.0

24.,0

22,.2 26,.1 22,.4 22..0

51 .3 31 .5

86 .1 63 .1

46,.0

41,.0 56,.0 16,.0 42,.0

32..8

30,.8 45,.2 32,.4 28,.4

Range of Percentage of Mass Loss at Temp, of Max. Different Temperatures Rate of Mass Loss, °C 100°C 200°C 300°C 400°C 500°C

492

393 292,489

5,.61

4..40 5,.02 5..90 6,.83

2..55

1,.20 6,.76 5..82 7,.42

Ρ Content, %

Temperature of Maximum Rate of Mass Loss, °C

Indulin AT U l t r a B002

Ultrazine NAS

NA NA NA NA

Modified by n-propanol. ^Modified by diethylamine.

--

10

Borresperse Borresperse Borresperse Borresperse

7 9 5 8

AT AT AT AT

U l t r a B002

b

a

Indulin Indulin Indulin Indulin

Type of l i g n i n

3

1 2 ll 13

Symbol of Sample

Table IV. TG and DTG Analysis of the Products of Modification by Chlorophosphazenes

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

45 .0

88,.1 64,.4

56,.0

48,.1 75..0 20,.0 51,.0

50.,1

43,.5 61,.3 40..7 34..1

600°C

S

S

Β

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

18.

F i g u r e 1. T h e r m o g r a m s o f u n m o d i f i e d (parent) l i g n i n s : k r a f t l i g n i n (a); U l t r a B 0 0 2 (b); Borresperse Ν A (c); a n d U l t r a z i n e N A S (d), as w e l l as t h e i r derivatives: l ( a i ) ; 2 ( a ) ; l l ( a ) ; 1 2 ( a ) ; 3 ( b i ) ; 1 3 ( c i ) ; 1 0 ( d i ) . 2

3

4

LIGNIN: PROPERTIES AND MATERIALS

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254

' 1A

1,5

16

t)

1,8

1,4

2p

1.

1 0

3

(°K'«')

F i g u r e 2. A r r h e n i u s plot for selected l i g n i n s a n d their derivatives f r o m d y ­ n a m i c T G A d a t a : kraft l i g n i n ( 1 , φ ) ; Borresperse Ν A (2, 0 ) ; U l t r a z i n e N A S (3, x ) ; Borresperse N A derivatives of s y m b o l # 7 ( 4 , d ) ; Borresperse Ν A derivatives of s y m b o l # 9 (5, Δ ) ; a n d U l t r a z i n e N A S derivatives of s y m b o l # 1 0 (6, © ) .

Table V. A c t i v a t i o n Energy of the Thermal Degradation Process.

Sample

Type of Lignins

--

Borresperse NA Ultrazine NAS U l t r a B002 Indulin AT

7 9 8

10

Borresperse NA Borresperse NA Borresperse NA Ultrazine NAS

Ρ Content, %

4.40 5.62 6.83 5.61

kJ/mol

Temperature Range, °C

46.0 33.3 162.4 176.7

250-350 250-350 250-350 350-400

70.0 44.0 34.8 41.0

250-350 250-350 250-350 250-350

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t h i s r e a c t i o n a n d r e p o r t e d o n l i m i t e d success. A recent r e i n v e s t i g a t i o n of this r e a c t i o n has p r o d u c e d m e l t a b l e a r o m a t i c ester-like p o l y m e r i c m a t e r i ­ als. T h e m o d i f i c a t i o n of l i g n i n sulfonates w i t h t e r e p h t h a l o y l chloride i n solvent or suspension (10) p e r m i t s the f o r m a t i o n of l i g n i n - b a s e d p o l y m e r s w i t h ester groups. T h e p r o d u c t s are characterized b y several advantages: m e l t i n g p o i n t is observed between 290 a n d 330° C ; h y d r o l y t i c a n d c h e m i c a l resistance is good; t h e r m a l s t a b i l i t y is increased; color is w h i t e to yellow; the p r o d u c t can be m i x e d i n the m e l t w i t h other p o l y m e r s ; the presence of such f u n c t i o n a l groups as sulfonates p e r m i t s the a p p l i c a t i o n as additives to m o d i f y other p o l y m e r properties. S o m e results of the m o d i f i c a t i o n of l i g n i n sulfonate U l t r a B 0 0 2 b y r e a c t i o n w i t h t e r e p h t h a l o y l chloride are s u m m a r i z e d i n T a b l e V I . T h e t o ­ t a l h y d r o x y l content of the lignosulfonates as well as t h e i r derivatives are presented i n T a b l e V I I . T h e h y d r o l y t i c resistance of selected p r o d u c t s is e v a l u a t e d i n T a b l e V I I I . T h e results presented i n Tables V I - V I I I stress sev­ eral advantages of the derivatives w i t h t e r e p h t h a l o y l chloride. T h e m o d i ­ fied l i g n i n sulfonates were i n s o l u b l e , or o n l y very s l i g h t l y soluble, i n o r g a n i c solvents. T h e y were, however, soluble i n d i m e t h y l sulfoxide. O r d e r e d s t r u c ­ tures were identified b y X - r a y studies ( 1 6 , 1 7 ) . T h e m o d i f i c a t i o n of lignins w i t h t e r e p h t h a l o y l chloride is of interest to the t h e r m a l properties of the derivatives (15). These are presented i n T a b l e I X . T h e results reveal t h a t a n e x o t h e r m i c t e m p e r a t u r e event is shifted to higher t e m p e r a t u r e as a consequence of m o d i f i c a t i o n . T h e e n d o t h e r m i c t e m p e r a t u r e event can be a t t r i b u t e d to the glass t r a n s i t i o n a n d the m e l t i n g process of the derivatives. T h e a c t i v a t i o n energy of the d e g r a d a t i o n process was c a l c u l a t e d for several samples based o n the results of d y n a m i c T G studies ( T a b l e X ) . A d i s t i n c t decrease i n a c t i v a t i o n energy is observed i n the case of U l t r a B 0 0 2 . A t the same t i m e , the Ε values seem t o correspond w i t h the higher t e m p e r a t u r e of the m o d i f i c a t i o n . T h e m o d i f i c a t i o n of l i g n i n sulfonates w i t h t e r e p h t h a l o y l chloride p r o ­ duces new p o l y m e r i c m a t e r i a l s c o n t a i n i n g ester groups. T h i s m o d i f i c a t i o n can be used to u t i l i z e lignins also for i m p r o v e m e n t of c h e m i c a l fiber p r o p ­ erties. T h i s is presently under i n v e s t i g a t i o n .

Modified Lignins as the Carriers for Controlled Release Prepara­ tions In the hope of finding large m a r k e t s for l i g n i n s , a review of p o t e n t i a l a g r i ­ c u l t u r a l a p p l i c a t i o n s has been c o n d u c t e d ( 1 , 6 , 1 4 ) . M o d i f i c a t i o n of l i g n i n s w i t h bioactive c o m p o u n d s c o n t a i n i n g s u i t a b l e reactive groups p e r m i t s the f o r m a t i o n o f various derivatives characterized b y a w i d e range o f release rate of active c o m p o n e n t . 2 , 4 - d i c h l o r o p h e n o x y a c e t i c a c i d ( 2 , 4 - D ) as a s t a n d a r d herbicide c o n ­ t a i n i n g reactive c a r b o x y l i c f u n c t i o n a l i t y was used i n the present s t u d y . A d ­ d i t i o n a l l y , the l i g n i n sulfonates of " K l u t a n " ( N i e d o m i c e , P o l a n d ) a n d the r e a c t i o n residues f r o m v a n i l l i n p r o d u c t i o n ( L S - W , W l o c l a w e k , P o l a n d ) were also used. T h e carriers c o n t a i n i n g c h e m i c a l b o u n d 2 , 4 - D used the f o l l o w i n g preparations:

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256

Table VI. E f f e c t of Modification with Terephthaloyl Chloride on the Properties of the U l t r a B002 Product.

Reagent Molar Ratio

Color of Product

Dioxane

1:1.10 1:1.65 1:2.20

yellow yellow yellow

Water

1:0.55 1:1.10 1:1.65 1:2.20

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Reaction Medium

It.yellow It.yellow It.yellow It.yellow

Yield of Product

Chemical Content, 3

C

H

S

M.p. °C

0.419 0.359 0.399

53..8 55..3 58..5

3.95 4.17 4.20

0.95 0.84 0.75

310-316 318-321 327-331

0.250 0.475 0.576 1.038

54..0 45..3 51..5 56..8

4.09 3.95 3.87 4.10

0.76 1.36 1.00 0.79

298-311 306-314 311-320 309-322

a

A l l reactions were c a r r i e d out on a l i g n i n (1.0 g) at 30°C f o r 15 min.

Table VII. Total Hydroxyl Content of Lignin Sulfonates and Their Derivatives with Terephthaloyl Chloride.

Symbol of Sample

Tvpe of Lignin

Total Hydroxyl Content. %

.. NA-2-20 NA-2-70

Borresperse NA Borresperse NA Borresperse NA

14.9 1.9 1.5

R-2-10 R-2-70

U l t r a B002 U l t r a B002 U l t r a B002

14.5 0.1 0.1

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L D : l i g n i n sulfonates m o d i f i e d b y 2 , 4 - D (21) L S D : l i g n i n sulfonates modified by t e r e p h t h a l o y l chloride a n d subse­ q u e n t l y b y 2 , 4 - D (22) L F : l i g n i n sulfonates m o d i f i e d b y p h e n o l a n d f o r m a l d e h y d e a n d t h e n b y 2 , 4 - D (23). Table VIII. Hydrolytic Resistance of the Lignins Modified with Terephthaloyl Chloride Average Amount of H S 0 (g) Consumed by 1 g of Product (χ 10" ) 2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch018

Type of Product

4

3

Average Amount of KOH Consumed by 1 g of Product (χ 10" ) 3

Modified Borresperse NA

50-200

10-50

Modified U l t r a B002

50-300

10-50

Borresperse NA

450

85

U l t r a B002

450

85

A p p l i c a t i o n o f several types o f l i g n i n sulfonates as carriers i n connec­ t i o n w i t h reactive herbicides (21-23) p e r m i t s t h e development o f effective c o n t r o l l e d release ( C R ) p r e p a r a t i o n s . T h e properties o f c h e m i c a l l y b o u n d l i g n i n 2 , 4 - D - b a s e d herbicides are s u m m a r i z e d i n T a b l e X I . Several p r e p a r a t i o n s were subjected t o s t a n d a r d release a n a l y s i s i n a n aqueous m e d i u m (14). T h e release d a t a are s h o w n i n F i g u r e 3. T h e s e d a t a suggest t h a t the l i g n i n sulfonate 2 , 4 - D - b a s e d p r e p a r a t i o n s have the c a p a c i t y for releasing herbicide a c t i v i t y over a prolonged t i m e p e r i o d . T h e most i m p o r t a n t v e r i f i c a t i o n o f C R p r e p a r a t i o n s is t h e i r p r a c t i c a l test u n d e r a g r i c u l t u r a l c o n d i t i o n s . S u c h a performance test was c a r r i e d out at t h e P l a n t P r o t e c t i o n I n s t i t u t e ( P o z n a n , P o l a n d ) u s i n g t w o doses of Pielik, a P o l i s h 2 , 4 - D p r e p a r a t i o n i n 8 5 % p u r i t y : " a " dose o f 1 k g o f Pielik per 1 h a , a n d " b " dose o f 2 k g o f Pielik per 1 h a . E p i p h y f i c p r e p a r a t i o n s were a p p l i e d at three stages: d i r e c t l y after g e r m i n a t i o n o f three types o f test plants (sunflower, wetch a n d w h i t e m u s t a r d ) (I); one week after g e r m i n a t i o n (II); a n d t w o weeks after g e r m i n a t i o n (III). T h e weight loss o f t h e p l a n t s was d e t e r m i n e d u n t i l 30 days following a p p l i c a t i o n . T h e test results are summarized i n Table X I I . T h e s e results reveal t h a t L S D - 6 ( W ) was the most effective p r e p a r a t i o n w h e n a p p l i e d i n the higher dose (b). T h e other p r e p a r a t i o n s were c h a r a c ­ terized b y a lower p r a c t i c a l a c t i o n w i t h i n the test p e r i o d . A t t h e same t i m e these p r e p a r a t i o n s have effectively acted for a longer p e r i o d t h a n t h a t s t u d i e d i n the test o f T a b l e X I I . It c a n be concluded t h a t l i g n i n sulfonates m o d i f i e d b y r e a c t i o n w i t h herbicide f u n c t i o n a l i t y (21-23) c a n be used as p o t e n t i a l carriers for c o n ­ t r o l l e d release herbicides. T h i s a p p l i c a t i o n o f l i g n i n sulfonates offers several advantages b o t h for a g r i c u l t u r e a n d for t h e e n v i r o n m e n t .

Borresperse NA

Borresperse NA

U l t r a B002

U l t r a B002

Na-2-70

R-2-10

R-2-70

Borresperse NA U l t r a B002

Tvpe of Lienin

NA-2-20

Symbol of Sample

355 410

348 420

355

380 435

200 185

370 450

370 450

375

405 462

322 330

400 470

400 470

400

425 470

425 450

Temperature of exothermic °C Event Start Max. End

100 250

100 250

100 250

100 250

120 342

120 330

122 340

122 358



130 355

125 345

130 350

130 367

Temperature of endothermic °C Event Start Max End

Table IX. Thermal Properties of Lignosulfonates Modified by Terephthaloyl Chloride.

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New Trends in Modification of Lignins

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Table X. A c t i v a t i o n Energy of the Degradation Process of Selected Lignin Sulfonates as well as t h e i r Derivatives with Terephthaloyl Chloride

Type of Lignins

Ε kJ/mol

Temperature Range, °C

Borresperse NA U l t r a B002

46.0 162.4

250-350 250-350

NA-2-10 NA-2-70

Borresperse NA Borresperse NA

49.0 95.0

250-350 250-350

R-2-10 R-2-70

U l t r a B002 U l t r a B002

21.4 48.1

250-350 250-350

Type of Sample

Table XI. Properties of 2,4-D Modified Lignin Sulfonates

Chemical Content. %

Symbol of Sample

Tvpe of Lignin

LD-3 LD-3(W) LD-3(K)

Borresperse NA LS-W Klutan

57..1 46..5 41,.2

LSD-6(W) LSD-6

LS-W Borresperse NA

52..3 57,.1

LF-2

Borresperse NA



a

a

C

S

Cl

2,4-D Content. %

4.38 3.43 3.28

4.14 4.52 5.35

6 .38 7 .97 7 .14

19.,2 24.,8 22.,2

4.11 3.99

2.38 1.43

0 .73 0 .74

Η

4 .53

The reaction conditions were reported previously (21-23).

2.,24 2.,31 14.,1

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RelQase substance amount, in relation to initial amount

0

10

20

30

40 Τ

[days]

Figure 3. Release curves of 2, 4-D from preparations of: L S D - 6 (a); L F - 2 (b); L D - 3 (c); and standard 2, 4-D (d).

Table XII. Test Results of the E f f e c t of 2,4-D Containing Preparations on Plant Growth.

Average Wt. Loss. % Type of Preparation

Dose

I

II

III

Average Weight Loss from 3 Stages, %

LD-3

a b

41.8 53.7

60.8 57.7

43.4 63.7

48.7 58.4

LD-3(W)

a b

36.8 70.0

50.5 51.7

35.7 61.2

41.0 60.9

LD-3(K)

a b

61.5 55.8

49.8 59.8

58.5 79.3

56.6 64.9

LSD-6(W)

a b

54.0 63.7

56.0 82.5

59.2 73.7

56.4 73.3

LSD-6

a b

55.8 59.0

63.2 60.5

49.7 65.3

56.2 61.6

a b

70.3 72.7

81.2 69.3

49.3 72.7

66.9 71.6

Standard 2,4-D (Pielik)

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L i g n i n u t i l i z a t i o n studies have been c o n d u c t e d i n several fields. H o w ­ ever, n o p r a c t i c a l , c o m m e r c i a l process has yet emerged for the m a n u f a c t u r e o f l i g n i n - b a s e d p o l y m e r i c m a t e r i a l s . T h i s is u n d o u b t e d l y related t o such factors as p r o d u c t inhomogeneity, r e a c t i v i t y differences, a n d also w i t h lack of f a m i l i a r i t y w i t h t h i s t y p e o f r a w m a t e r i a l . It s h o u l d be also stressed t h a t l i g n i n s are o n l y b y - p r o d u c t s f r o m p u l p m a n u f a c t u r e . However, t h e u t i l i z a t i o n o f l i g n i n s i n p o l y m e r i c m a t e r i a l s seems t o b e possible. Acknowledgment

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It i s a pleasure t o acknowledge the c o n t r i b u t i o n o f m y assistant, M r s . K . W r z e s n i e w s k a - T o s i k , for her continued c o o p e r a t i o n . Literature C i t e d 1. Sarkanen, Κ. V.; Ludwig, C . H., Eds. Lignins; Wiley-Interscience: New York, 1971. 2. Simonescu, C . I. Cell. Chem. Technol. 1978, 12, 577. 3. Naraian, H . Indian Chem. Manuf. 1981, 19(6), 11. 4. Lindberg, J. J.; Melartin, J. Kem. Kemi 1982, 9(11), 736. 5. Glasser, W . G . ; Hsu, Ο. H . ; Reed, D. L . ; Forte, R. C . 1979 Cana­ dian Wood Chemistry Symposium Proceedings; Harrison Hot Springs, Canada. 6. Allan, G . G . ; Balaba, W.; Dutkiewicz, J.; Struszczyk, H . Chemicals from Western Hardwoods and Agricultural Residues; Semi-Annual Re­ port, April 1979, NSE-7708979; Univ. of Washington, Seattle, U S A . 7. Chen, R.; Kokta, Β . V . ; Valade, J. L . J. Appl. Polym. Sci. 1979, 24, 1609. 8. Struszczyk, H.; Laine, J. E . Polish Patent 125877, 1981. 9. Struszczyk, H . Polish Patent Appl. P-265167, 1987. 10. Struszczyk, H.; Krajewski, K . Polish Patent 134256, 1982. 11. Struszczyk, H . ; Laine, J. E . J. Macromol. Sci.-Chem. 1982, A17(8), 1193. 12. Struszczyk, H . Fire and Materials 1982, 6(1), 7. 13. Struszczyk, H . J. Macromol Sci.-Chem. 1986, A23(8), 973. 14. Struszczyk, H . ; Wrześniewska-Tosik, K . Proc. Inter. Symp. on Fibre Sci. and Technol.; Hakone, Japan, 1985, p. 336. 15. Struszczyk, H . ; Allan, G . G . ; Balaba, W . Proc. of Euchem '80 Conf.; Helsinki, Finland, 1980. 16. Struszczyk, H . Proc. Hungarian Symp. on Thermal Analysis; Budapest, Hungary, 1981. 17. Struszczyk, H . Proc. of 31st IUPAC Conf. Macro '87; Merseburg, Ger. Dem. Rep., 1987. 18. Ramian, M . V . J. Appl. Polym. Sci. 1970, 14, 1323. 19. Tang, W . G . U.S. For. Serv. Res. Pap. FPL 71, 1967. 20. Van der Klashort, G . H.; Forbes, C . P.; Psotta, K . Holzforschung 1983, 37(6), 279. 21. Struszczyk, H.; Wrześniewska-Tosik, K . Polish Patent 141253, 1985. 22. Struszczyk, H.; Wrześniewska-Tosik, K . Polish Patent 141254, 1985. 23. Struszczyk, H.; Wrześniewska-Tosik, K . Polish Patent 141255, 1985. RECEIVED April 18,1989

Chapter 19

Application of Computational Methods to the Chemistry of Lignin Thomas Elder

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch019

School of Forestry, Auburn University, Auburn, AL 36849

Computational and theoretical techniques have been used to describe a wide range of compound classes, but have been only sparingly utilized in studies on the properties and reactions of lignin. A brief summary of the capabilities and limitations of molecular mechanics and molecular orbital calculations is presented, along with a survey of specific applications to lignin that have been reported in the literature. A n e x a m i n a t i o n of the other articles i n t h i s text serves as a n excellent i l l u s t r a t i o n of the diverse a n a l y t i c a l m e t h o d s t h a t have been successfully a p p l i e d to lignocellulosic m a t e r i a l s . T h e p r a c t i t i o n e r s of w o o d c h e m i s t r y have r a p i d l y a s s i m i l a t e d a n d a d a p t e d m o d e r n i n s t r u m e n t a l c h e m i s t r y to their specific p r o b l e m s . I n contrast, the techniques of c o m p u t a t i o n a l c h e m i s t r y have not been w i d e l y used i n such a n e n v i r o n m e n t . T h e c u r r e n t p a p e r w i l l a t t e m p t t o describe the c a p a b i l i t i e s , o p p o r t u n i t i e s , a n d l i m i t a t i o n s of s u c h a n a p p r o a c h , a n d discuss the results t h a t have been r e p o r t e d for l i g n i n related c o m p o u n d s . T h e t e r m " c o m p u t a t i o n a l c h e m i s t r y " can refer i n its broadest sense to a w i d e range of m e t h o d s t h a t have been developed t o give insight i n t o the f u n d a m e n t a l b e h a v i o r of c h e m i c a l species. S u c h m e t h o d s i n c l u d e , b u t are not necessarily l i m i t e d to, those related to q u a n t u m mechanics (1), m o l e c u l a r mechanics (or force-field c a l c u l a t i o n s ) (2), p e r t u r b a t i o n theory (3), g r a p h theory (4), or s t a t i s t i c a l t h e r m o d y n a m i c s (5). F o r the purposes of t h i s chapter, c o m m e n t s w i l l be r e s t r i c t e d to force-field a n d q u a n t u m based c a l c u l a t i o n s , since these are the techniques t h a t have been used i n w o r k o n l i g n i n . F u r t h e r m o r e , these methods have been reviewed i n a very readable b o o k b y C l a r k (6). A b r i e f p e r u s a l of the p r e v i o u s l y cited references w i l l reveal the h i g h l y i n v o l v e d n a t u r e of the m a t h e m a t i c a l f o r m a l i s m t h a t has led to these t e c h niques. T h i s p r o b l e m is offset, to some extent, b y the ready a v a i l a b i l i t y of 0097-6156/89/0397-0262$06.00/0 © 1989 American Chemical Society

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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well-developed software, a n d i m p r o v e m e n t s i n the speed, capacity, a n d costs associated w i t h c o m p u t e r h a r d w a r e . These advances enable users to c o n centrate o n the i n t e r p r e t a t i o n of results, r a t h e r t h a n the intricacies o f the m a t h e m a t i c s . A w e a l t h of p r o g r a m s are available, for e n v i r o n m e n t s r a n g i n g f r o m p e r s o n a l c o m p u t e r s to s u p e r c o m p u t e r s , at very reasonable cost f r o m the Q u a n t u m C h e m i s t r y P r o g r a m E x c h a n g e at I n d i a n a U n i v e r s i t y . I n spite of the m i n i m a l a p p l i c a t i o n s of c o m p u t a t i o n a l c h e m i s t r y to the c h e m i s t r y of w o o d , the techniques have become h i g h l y developed a n d s o p h i s t i c a t e d i n t h e i r a b i l i t y t o calculate c h e m i c a l p r o p e r t i e s for a w i d e v a r i e t y o f c o m p o u n d classes. M e t h o d s based o n q u a n t u m m e c h a n i c s , c o m m o n l y referred to as m o l e c u l a r o r b i t a l c a l c u l a t i o n s , have been the t o p i c of n u m e r o u s b o o k s , reviews, a n d research papers ( 7 , 8 , 9 , 1 0 ) . These t e c h niques are concerned w i t h the d e s c r i p t i o n of electronic m o t i o n , a n d the s o l u t i o n of the Schrodinger e q u a t i o n to determine the energy of m o l e c u l a r systems. Since the exact s o l u t i o n of the Schrodinger e q u a t i o n is o n l y p o s s i ble for t w o - p a r t i c l e systems, a p p r o x i m a t i o n s must be i n v o k e d for even the simplest organic molecules. Molecular Orbital Calculations. T h e most s o p h i s t i c a t e d a n d t h e o r e t i c a l l y rigorous of the m o l e c u l a r o r b i t a l methods are ab initio c a l c u l a t i o n s . T h e s e are p e r f o r m e d w i t h a p a r t i c u l a r m a t h e m a t i c a l f u n c t i o n d e s c r i b i n g the shape of the a t o m i c o r b i t a l s w h i c h combine to p r o d u c e m o l e c u l a r o r b i t a l s . T h e s e f u n c t i o n s , or basis sets, m a y be chosen based o n a convenient m a t h e m a t i c a l f o r m , or their a b i l i t y to reproduce c h e m i c a l properties. C o m m o n l y used b a sis sets are a c o m p r o m i s e between these two extremes, b u t s t r i c t ab initio c a l c u l a t i o n s use o n l y these m a t h e m a t i c a l functions to describe electronic m o t i o n . Representative of ab initio methods is the series of G A U S S I A N p r o g r a m s f r o m C a r n e g i e - M e l l o n U n i v e r s i t y (11). In general, these c a l c u l a t i o n s are c o m p u t a t i o n a l l y quite intensive, a n d require a large a m o u n t of c o m p u t e r t i m e even for r e l a t i v e l y s m a l l molecules. In order to p e r f o r m c a l c u l a t i o n s on larger molecules i n a reasonable a m o u n t of t i m e , a p p r o x i m a t i o n s are m a d e , w h i c h m a y i n v o l v e the neglect of c e r t a i n terms, or the i n c l u s i o n of e x p e r i m e n t a l l y d e t e r m i n e d p a r a m e ters. T h e best k n o w n a n d simplest e x a m p l e of t h i s level of a p p r o x i m a t i o n are H i i c k e l M o l e c u l a r O r b i t a l ( H M O ) c a l c u l a t i o n s , w h i c h treat o n l y p i electrons, i n conjugated h y d r o c a r b o n s , w i t h neglect of overlap (1). W h i l e o b v i o u s l y l i m i t e d i n use, H M O m e t h o d s are s t i l l used i n c e r t a i n research applications. A v a r i e t y of m o r e advanced, all-electron methods of t h i s t y p e are a v a i l able, a n d are generally referred to as s e m i - e m p i r i c a l c a l c u l a t i o n s . T h e a c r o n y m s used to n a m e the i n d i v i d u a l m e t h o d s are descriptive of the m a n ner i n w h i c h a t o m i c overlap c a l c u l a t i o n s are p e r f o r m e d . A m o n g the m o r e w i d e l y used s e m i - e m p i r i c a l m e t h o d s are those of complete neglect of differential overlap ( C N D O / 2 ) (12), modified i n t e r m e d i a t e neglect of differe n t i a l overlap ( M I N D O / 3 ) (13), a n d m o d i f i e d neglect of d i a t o m i c overlap ( M N D O ) (14). T h e r e l a t i v e m e r i t s of a n u m b e r of m o l e c u l a r o r b i t a l m e t h o d s have been discussed i n the l i t e r a t u r e ( 1 5 , 1 6 , 6 ) . T h e m e t h o d s c i t e d differ f u n d a m e n -

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t a l l y i n t h a t the C N D O / 2 m e t h o d was developed to m i m i c the results of ab initio c a l c u l a t i o n s , w h i l e the l a t t e r t w o approaches are concerned w i t h the r e p r o d u c t i o n of e x p e r i m e n t a l results. It has been s a i d t h a t the a i m of D e w a r ' s g r o u p was to develop a n " M O spectrometer" t h a t c a n p r o v i d e results w i t h e x p e r i m e n t a l accuracy i n a reasonable t i m e (6). T h e results f r o m m o l e c u l a r o r b i t a l c a l c u l a t i o n s c a n be d i v i d e d i n t o two general categories, d e a l i n g w i t h energy a n d electronic p o p u l a t i o n s . T h e w e a l t h of i n f o r m a t i o n t h a t c a n be o b t a i n e d is i l l u s t r a t e d i n F i g u r e 1 (17). S u c h d a t a are useful i n the i n t e r p r e t a t i o n of e x p e r i m e n t a l results, a n d the p r e d i c t i o n of the course of novel reactions. Molecular Mechanics Calculations. I n sharp contrast t o the m o l e c u l a r orb i t a l c a l c u l a t i o n s t h a t are related to q u a n t u m mechanics, a n d a t t e m p t to describe the m o t i o n of electrons i n a f r a m e w o r k of fixed n u c l e i , m o l e c u l a r m e c h a n i c s , or force field, c a l c u l a t i o n s c o m p l e t e l y ignore the presence of electrons. T h e s e techniques, w h i c h have been reviewed b y O s a w a a n d M u s s o (18), B u r k e r t a n d A l l i n g e r (2), a n d A l l i n g e r (19), treat m o l e c u l a r systems classically, representing the a t o m s as masses a n d the b o n d s w h i c h connect t h e m as springs. I n the simplest f o r m , springs t h a t obey H o o k e ' s L a w are used, w h i l e i n m o r e c o m p l i c a t e d systems, s u c h as those i n v o l v i n g h y d r o g e n - b o n d e d i n t e r a c t i o n s , M o r s e p o t e n t i a l s or other f u n c t i o n s m a y be used ( 1 9 , 2 ) . M o l e c u l a r mechanics c a l c u l a t i o n s represent the energy of a c o m p o u n d as the s u m of the energy of s t r e t c h i n g , b e n d i n g , v i b r a t i o n , t o r s i o n , n o n - b o n d e d i n t e r a c t i o n s , a n d terms t h a t couple these m o t i o n s . I n i t i a l l y , m o l e c u l a r mechanics m e t h o d s were developed for the i n t e r p r e t a t i o n of v i b r a t i o n a l s p e c t r a , b u t m o r e recently they have been a p p l i e d to a n u m b e r of other p h e n o m e n a a n d properties (19). A n u m b e r of force-field m e t h o d s have been described (20-24), a n d w h i l e c o n c e p t u a l l y s i m i l a r , the p o t e n t i a l f u n c t i o n s a n d p a r a m e t e r i z a t i o n s t h a t are used m a y be q u i t e different (2). M o l e c u l a r mechanics c a l c u l a t i o n s have been c a r r i e d out o n a w i d e range of c h e m i c a l c o m p o u n d s i n c l u d i n g h y d r o c a r b o n s , h e t e r o a t o m i c molecules, steroids, c a r b o h y d r a t e s a n d proteins. F u r t h e r m o r e , a v a r i e t y of i n f o r m a t i o n has been o b t a i n e d such as heats of f o r m a t i o n , r o t a t i o n a l b a r r i e r s , a n d rates of r e a c t i o n ( 1 8 , 2 , 1 9 ) . T h e m a j o r advantage of t h i s m e t h o d over other c o m p u t a t i o n a l methods is t h a t i t is reasonably fast to p e r f o r m i n c o m p a r ison to f o r m a l m o l e c u l a r o r b i t a l c a l c u l a t i o n s .

Applications of Computational Methods to Lignin W i t h t h i s i n t r o d u c t i o n to the methods of c o m p u t a t i o n a l chemistry, the a t t e n t i o n of t h i s p a p e r w i l l now t u r n t o specific a p p l i c a t i o n s related to the c h e m i s t r y of l i g n i n . A s p r o m i s e d at the b e g i n n i n g of t h i s p a p e r , the discussion w i l l address not o n l y the capabilities a n d o p p o r t u n i t i e s t h a t m a y accrue f r o m t h i s t y p e of research, b u t w i l l also consider the l i m i t a t i o n s of the techniques. O n e of the basic a s s u m p t i o n s is t h a t a l l c a l c u l a t i o n s are done o n isol a t e d gas-phase molecules. T h i s is o b v i o u s l y a large s h o r t c o m i n g for l i g n i n c h e m i s t r y for a n u m b e r of reasons. T h e reactions of i m p o r t a n c e i n l i g n i n

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Resonance energy

Energy of the molecule

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Bond order

Thermodynamic stabiity

Electric charge ι—* Transition energies

Electron spectra Ionization potential

Highest occupied MO

MO LCAO

Length and energy of the bond: force constants: vibra­ tion frequencies

Bond order Free Coefficients of AO in MO

valence Electric charges

w

Reactivity, degree of conjugation Reactivity, cfpole moments

Transition probabilities

Spectral and optical properties

Figure 1: Electronic characters obtained by the molecular orbital method their applications.

(Reprinted

with

permission

from

ref.

17. Copyright

Academic Press.)

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

and 1977

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w o r k , specifically those related to p u l p i n g a n d b l e a c h i n g , take place i n aque­ ous systems, a n d l i g n i n is a large heterogeneous p o l y m e r . T h e s o l v a t i o n questions m a y be overcome to some extent b y a d d i t i o n a l c a l c u l a t i o n s . F o r e x a m p l e , the m o l e c u l a r mechanics m e t h o d described b y W e i n e r a n d K o l l m a n (24) has the a b i l i t y to a p p l y a given dielectric constant to the molecule, a n d corrections to gas-phase c a l c u l a t i o n s have been r e p o r t e d (25,26).

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T h e i n d e t e r m i n a t e a n d p o l y m e r i c n a t u r e of l i g n i n c a n , of course, be addressed b y the u t i l i z a t i o n of j u d i c i o u s l y chosen m o d e l c o m p o u n d s . T h i s is u s u a l l y the strategy i n basic e x p e r i m e n t a l studies o n l i g n i n , a n d the same logic s h o u l d a p p l y to c o m p u t a t i o n a l methods. I n a d d i t i o n , the lack of basic t h e r m o d y n a m i c d a t a for c o m p o u n d s of interest is a l i m i t a t i o n , since i n most s i t u a t i o n s there are no e x p e r i m e n t a l values to w h i c h c o m p u t e d results m a y be c o m p a r e d . T h e v a l i d a t i o n proce­ dure t o w h i c h the m e t h o d s are subjected, however, includes a large range of c o m p o u n d s for w h i c h e x p e r i m e n t a l d a t a is d o c u m e n t e d . W h i l e t h i s is not direct evidence t h a t for specific c o m p o u n d s the results w i l l be repre­ sentative of e x p e r i m e n t a l results, i t is one of the a s s u m p t i o n s t h a t has been m a d e i n the work o n l i g n i n . T h e s e difficulties n o t w i t h s t a n d i n g , the methods of c o m p u t a t i o n a l c h e m i s t r y represent a u n i q u e a p p r o a c h to the questions of w o o d science, a n d r a t h e r t h a n a s u m m a r y d i s m i s s a l , s h o u l d be e x a m i n e d to determine their a p p l i c a b i l i t y . I n spite of such difficulties, t h e o r e t i c a l c a l c u l a t i o n s have been successfully used i n w o r k related to m a t e r i a l s science ( 2 7 , 2 8 ) , a n d i n n u m e r o u s b i o c h e m i c a l a p p l i c a t i o n s (29). T h e a p p l i c a t i o n of c o m p u t a t i o n a l methods to l i g n i n c h e m i s t r y are be­ i n g researched m a i n l y b y i n d i v i d u a l s a n d groups i n the U n i t e d States, a n d Soviet U n i o n , C z e c h o s l o v a k i a , a n d F i n l a n d . O n e of the earliest papers o n t h i s t o p i c was concerned w i t h the use of H i i c k e l M o l e c u l a r O r b i t a l m e t h o d s i n the s t u d y of l i g n i n r e a c t i v i t y (30). It was r e p o r t e d t h a t the c a l c u l a t e d l o c a l i z a t i o n energies were related to the r e a c t i o n rates of phenols, a n d t h a t c a l c u l a t i o n s o n free r a d i c a l s t r u c t u r e s c o u l d be of i m p o r t a n c e i n the e l u ­ c i d a t i o n of factors t h a t influence the p o l y m e r i z a t i o n of l i g n i n precursors. F u r t h e r m o r e , G l a s s e r a n d co-workers (31-36) have used s i m u l a t i o n t e c h ­ niques to m o d e l the p o l y m e r i z a t i o n a n d reactions of l i g n i n . In a s t u d y d i r e c t l y related to the c o u p l i n g of phenols to f o r m the l i g n i n p o l y m e r , M a r t e n s s o n a n d K a r l s s o n (37) used P a r i s e r - P a r r - P o p l e c a l c u l a ­ tions to e x a m i n e the π-electron s p i n densities of a v a r i e t y of p h e n o x y r a d ­ icals. T h e s p i n density, representative of u n p a i r e d electron character, was f o u n d to be consistently highest at the phenolic o x y g e n i n each of the r a d i c a l s t r u c t u r e s t h a t were considered. T h i s has been i n t e r p r e t e d as t h e o r e t i c a l evidence t h a t is i n accordance w i t h e x p e r i m e n t a l d a t a i n d i c a t i n g t h a t the /?-0-4 linkage is the p r e d o m i n a n t m o d e of c o m b i n a t i o n i n softwood l i g n i n . T h e a d d i t i o n of m e t h o x y , aroxy, a n d a r y l s u b s t i t u e n t s o r t h o to the p h e n o ­ l i c oxygen was f o u n d to effectively d i l u t e the s p i n densities t h r o u g h o u t the r a d i c a l s t r u c t u r e s r e p o r t e d . In p a r t i c u l a r , the s p i n density of the p o s i t i o n p a r a to the phenolic oxygen seems to be reduced at the expense of the car­ b o n to w h i c h the s u b s t i t u e n t is a t t a c h e d . T h e r e l a t i v e l y h i g h s p i n density

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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at t h i s p o s i t i o n as a result of s u b s t i t u t i o n does n o t , however, represent a site o f elevated r e a c t i v i t y , because o f steric h i n d r a n c e , or t h e r m o d y n a m i c c o n s t r a i n t s (38).

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R e l a t e d research has been r e p o r t e d b y E l d e r a n d W o r l e y (39), i n w h i c h M N D O was used t o e x a m i n e the s t r u c t u r e of c o n i f e r y l a l c o h o l , a n d i t s c o r r e s p o n d i n g phenolate a n i o n a n d free r a d i c a l . T h i s m e t h o d represents a n i m p r o v e m e n t over the P P P m e t h o d , i n t h a t M N D O is a n a l l - e l e c t r o n t e c h n i q u e , a n d performs geometry o p t i m i z a t i o n s . It was f o u n d t h a t the c a l c u l a t e d s p i n densities a n d charge values for the reactive sites d i d not correlate q u a n t i t a t i v e l y w i t h observed b o n d frequency, b u t i t was observed t h a t p o s i t i o n s w i t h p a r t i a l negative charge a n d p o s i t i v e s p i n densities are the p o s i t i o n s t h r o u g h w h i c h the p o l y m e r i z a t i o n has been f o u n d t o o c c u r . T h e most extensive a n d s y s t e m a t i c s t u d y of the c h e m i s t r y of l i g n i n w i t h t h e o r e t i c a l m e t h o d s has been p e r f o r m e d b y R e m k o a n d co-workers. T h e i r w o r k has i n v o l v e d the n a t u r e of i n t r a m o l e c u l a r (40-43) a n d i n t e r ­ m o l e c u l a r (44-48) h y d r o g e n b o n d i n g of l i g n i n m o d e l c o m p o u n d s , s p e c t r a l t r a n s i t i o n s (49-52), a n d c o n f o r m a t i o n a l a n a l y s i s (53). T h e m e t h o d s used have i n c l u d e d C N D O / 2 a n d P C I L O ( P e r t u r b a t i v e C o n f i g u r a t i o n I n t e r a c ­ t i o n u s i n g L o c a l i z e d O r b i t a l s ) (54). C o n f o r m a t i o n a l studies of d i m e r i c l i g n i n m o d e l c o m p o u n d s have been r e p o r t e d b y R e m k o a n d S e k e r k a (53), a n d G r a v i t i s a n d E r i n s (55) f r o m the Soviet U n i o n . G r a v i t i s a n d E r i n s (55) used the p a i r w i s e a t o m - a t o m p o t e n t i a l f u n c t i o n ( A A P F ) m e t h o d , a force-field t e c h n i q u e , to d e t e r m i n e the c o n f o r m a t i o n of /J-0-4 l i n k e d d i m e r s . It was f o u n d t h a t the a r o m a t i c rings, i n the most stable a r r a n g e m e n t , e x h i b i t a folded s t r u c t u r e , w i t h the rings i n p a r a l l e l planes. I n a s i m i l a r , b u t s o m e w h a t m o r e extensive s t u d y of d i m e r i c l i g n i n m o d e l c o m p o u n d s , R e m k o a n d S e k e r k a (53), u s i n g P C I L O , f o u n d t h a t the lowest energy of the /?-0-4 d i m e r corresponded to t w o c o n f o r m a t i o n s , one of w h i c h was a p l a n a r s t r u c t u r e , w h i l e the other h a d a r o t a t i o n o f 120° between the a r o m a t i c r i n g s . A c c o r d i n g t o R e m k o a n d S e k e r k a (53), t h i s d i s c r e p a n c y is due to the u t i l i z a t i o n of different c o m p u t a t i o n a l m e t h o d s . F u r t h e r m o r e , a l t h o u g h the d i m e r s i n b o t h papers were β-0-4 l i n k e d , they were not i d e n t i c a l , a n d were not s u b s t i t u t e d w i t h h y d r o x y l or m e t h o x y l groups. In c o n j u n c t i o n w i t h a s t u d y o n the r e a c t i v i t y of d i m e r i c q u i n o n e m e thides, E l d e r et a l . (56) e x a m i n e d the p h y s i c a l a n d electronic s t r u c t u r e of g u a i a c y l g l y c e r o l - / ? - c o n i f e r y l ether, w h i c h is s u b s t i t u t e d i n a m a n n e r repre­ sentative o f the l i g n i n p o l y m e r . C a l c u l a t i o n s were p e r f o r m e d u s i n g A M B E R ( A s s i s t e d M o d e l B u i l d i n g w i t h E n e r g y Refinement) (24), w h i c h is a forcefield m e t h o d , a n d the energetic m i n i m u m was d e t e r m i n e d t o be a folded s t r u c t u r e s i m i l a r to t h a t r e p o r t e d by G r a v i t i s a n d E r i n s (55). S i n c e the properties o f a n y m a t e r i a l are r e l a t e d t o i t s s t r u c t u r e , the c o n f o r m a t i o n a l aspect of these studies cannot be neglected. T h e e m p h a s i s of the l a t t e r paper (56) was, however, p r i m a r i l y concerned w i t h the elec­ t r o n i c s t r u c t u r e of the d i m e r i c m o d e l c o m p o u n d , a n d how t h i s i n f o r m a t i o n m i g h t be c o m p a r e d to e x p e r i m e n t a l facts. U p o n c o m p l e t i o n o f the c a l c u ­ l a t i o n s , i t b e g a n to appear t h a t the results were seriously flawed. It was

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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f o u n d , s u r p r i s i n g l y , t h a t the a l p h a c a r b o n of the q u i n o n e m e t h i d e has a slight negative charge. Since the p r i n c i p a l r e a c t i o n of k r a f t p u l p i n g is p r o ­ posed to involve n u c l e o p h i l i c a t t a c k of t h i s p o s i t i o n by either s u l f h y d r y l or h y d r o x i d e ions, how can these electronic d a t a be reconciled? F u r t h e r e x a m i n a t i o n of the results i n d i c a t e d t h a t b y i n v o c a t i o n of P e a r s o n ' s H a r d - S o f t A c i d - B a s e ( H S A B ) t h e o r y (57), the results are c o n ­ sistent w i t h e x p e r i m e n t a l o b s e r v a t i o n . A c c o r d i n g t o P e a r s o n ' s theory, w h i c h has been generalized t o i n c l u d e nucleophiles (bases) a n d electrophiles (acids), i n t e r a c t i o n s between h a r d reactants are p r o p o s e d t o be dependent o n c o u l o m b i c a t t r a c t i o n . T h e c o m b i n a t i o n of soft reactants, however, is t h o u g h t to be due t o overlap of the lowest u n o c c u p i e d m o l e c u l a r o r b i t a l ( L U M O ) of the electrophile a n d the highest o c c u p i e d m o l e c u l a r o r b i t a l ( H O M O ) of the nucleophile, the so-called frontier m o l e c u l a r o r b i t a l s . It was f o u n d t h a t , c o m p a r e d to a l l other positions i n the quinone m e t h i d e , the a l p h a c a r b o n h a d the greatest L U M O electron density. It appears, therefore, t h a t the frontier m o l e c u l a r o r b i t a l i n t e r a c t i o n s are o v e r r i d i n g the u n f a v o r a b l e c o u l o m b i c c o n d i t i o n s . T h i s i n t e r p r e t a t i o n also s u p p o r t s the preferential r e a c t i o n of the s u l f h y d r y l i o n over the h y d r o x i d e i o n i n k r a f t p u l p i n g . I n c o m p a r i s o n t o the h y d r o x i d e i o n , the s u l f h y d r y l is r e l a t i v e l y soft, a n d i n P e a r s o n ' s theory, soft reactants w i l l b o n d p r e f e r e n t i a l l y t o soft r e a c t a n t s , w h i l e h a r d acids w i l l favorably combine w i t h h a r d bases. Since the a l p h a p o s i t i o n is the softest i n the entire molecule, as evidenced b y the L U M O density, the softer s u l f h y d r y l i o n w o u l d be m o r e l i k e l y to a t t a c k t h i s p o s i t i o n t h a n the h y d r o x i d e . T h e influence of frontier m o l e c u l a r o r b i t a l s has also been d e m o n s t r a t e d i n work o n the c h l o r i n a t i o n of l i g n i n m o d e l c o m p o u n d s (58). I n t h i s w o r k , electronic parameters were c o m p a r e d to the difference i n energy between g r o u n d state molecules a n d c h l o r i n a t e d i n t e r m e d i a t e s . T h e results i n d i ­ cated t h a t for c o n i f e r y l a l c o h o l , the p o s i t i o n e x h i b i t i n g the greatest negative charge is the m e t h o x y l oxygen, w h i l e the p o s i t i o n w i t h the greatest electron density i n highest o c c u p i e d m o l e c u l a r o r b i t a l area is p a r a to the p h e n o l i c h y d r o x y l . T h e H O M O is the frontier m o l e c u l a r o r b i t a l of interest i n t h i s r e a c t i o n , since the c o n i f e r y l a l c o h o l is the n u c l e o p h i l e a n d the c h l o r o n i u m i o n is the e l e c t r o p h i l e . F a v o r a b l e r e a c t i o n indices n o t w i t h s t a n d i n g , these p o s i t i o n s have the two highest energy barriers to c h l o r i n a t i o n . S i m i l a r l y , the ^ - c a r b o n i n the a l i p h a t i c s i d e c h a i n has the lowest energy b a r r i e r , b u t does not have cor­ r e s p o n d i n g l y great negative charge or H O M O electron density. It c a n be seen t h a t steric considerations m a y be s t r o n g l y i n f l u e n c i n g the r e a c t i v i t y o f these sites, w i t h the c a r b o n b e i n g l a r g e l y u n h i n d e r e d , w h i l e the others w i t h greater r e a c t i o n barriers are s t r o n g l y h i n d e r e d . If these three positions are neglected, l e a v i n g a r o m a t i c p o s i t i o n s a n d the α - c a r b o n of the s i d e c h a i n , i t is f o u n d t h a t the size o f the negative charge does not reflect the order of the energy differences. I n c o n t r a s t , the H O M O electron density at the various p o s i t i o n s increases i n the same sequence as the energy b a r r i e r t o w a r d c h l o r i n a t i o n . It m a y be c o n c l u d e d , therefore, t h a t the c h l o r i n a t i o n r e a c t i o n is m o r e sensitive t o w a r d o r b i t a l c o n t r o l , a n d steric a r g u m e n t s , t h a n s i m p l e c o u l o m b i c a t t r a c t i o n .

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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T h e u t i l i z a t i o n o f Pearson's hard-soft acid-base theory t o i n t e r p r e t the reactions o f l i g n i n has also been described i n w o r k f r o m the Soviet U n i o n b y Z a r u b i n a n d K i r y s u n (59). B e y o n d t h i s specifically related paper, researchers i n the Soviet U n i o n have been quite active i n the a p p l i c a t i o n o f n u m e r i c a l m e t h o d s t o l i g n i n - r e l a t e d problems ( 6 0 , 6 1 ) . I n a n a t t e m p t t o relate c a l c u l a t e d results t o e x p e r i m e n t a l findings f o r m o n o m e r i c , l i g n i n m o d e l c o m p o u n d s , p r e l i m i n a r y w o r k has c o m p a r e d t h e ­ o r e t i c a l l y d e t e r m i n e d electron densities a n d c h e m i c a l shifts r e p o r t e d f r o m c a r b o n - 1 3 nuclear m a g n e t i c resonance spectroscopy (62). A l t h o u g h c h e m ­ i c a l shifts are a f u n c t i o n o f numerous factors, o f w h i c h electron density is o n l y one, b o t h theoretical a n d e m p i r i c a l r e l a t i o n s h i p s o f t h i s n a t u r e have been explored for a v a r i e t y o f c o m p o u n d classes, a n d are reviewed b y E b r a heem a n d W e b b (63), M a r t i n et a l . (64), N e l s o n a n d W i l l i a m s (65), a n d F a r n u m (66). Regression analyses i n d i c a t e d t h a t a m o d e l o f C - 1 3 N M R shift v s . electron density, f o r a l l c o m p o u n d s a n d carbons, resulted i n a p o o r fit o f the d a t a w i t h a significance level o f 0.0879 a n d a n R - s q u a r e d o f 0.0347. I n c l u s i o n of a factor defining the p o s i t i o n of each carbon y i e l d e d a significant r e l a t i o n s h i p , b u t s t i l l gave low correlation coefficient o f 0.2508. S o r t i n g the d a t a b y each c a r b o n indicates significant linear r e l a t i o n s h i p s for carbons 4 a n d 6 w i t h i n t h e a r o m a t i c r i n g , a n d t h e a a n d β carbons i n t h e side c h a i n . These results m a y p r o v i d e a more general p i c t u r e for the r e a c t i v i t y of l i g n i n . F r o m t h i s brief i n t r o d u c t i o n , i t is obvious t h a t the e x e c u t i o n o f the c a l ­ c u l a t i o n s a n d the i n t e r p r e t a t i o n o f the results are s t i l l i n their i n i t i a l stages. It is the contention o f the a u t h o r t h a t the insight into l i g n i n c h e m i s t r y t h a t m a y be o b t a i n e d b y these methods deserves careful c o n s i d e r a t i o n . Literature Cited 1. Lowe, John P. Quantum Chemistry; Academic Press, Inc.: New York, 1978. 2. Burkert, Ulrich; Allinger, N . L . Molecular Mechanics; A C S Monograph 177; American Chemical Society: Washington, D C , 1982. 3. Dewar, M . J. S.; Dougherty, R. C . The Theory of Organic Chemistry; Plenum Press: New York, 1975. 4. Trinajstic, N . Chemical Graph Theory; C R C Press: Boca Raton, F L , 1983. 5. McQuarrie, Donald A . Statistical Thermodynamics; Harper and Row, Inc.: New York, 1973. 6. Clark, T . A Handbook of Computational Chemistry. A Practical Guide to Chemical Structure and Energy Calculations; Wiley-Interscience: New York, 1985. 7. Dewar, M . J . S. The Molecular Orbital Theory of Organic Chemistry; McGraw-Hill: New York, 1969. 8. Flurry, Robert L . , Jr. Molecular Orbital Theories in Bonding of Or­ ganic Molecules; Marcel Dekker, Inc.: New York, 1968.

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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9. Murrell, J . N.; Harget, A . Semi-Empirical, Self-Consistent-Field Mole­ cular Orbital Theory of Molecules; Wiley-Interscience: New York, 1972. 10. Pople, J . Α.; Beveridge, D. L. 1970. Approximate Molecular Orbital Theory; McGraw-Hill: New York, 1977. 11. Binkley, J . S.; Whiteside, R. Α.; Hariharan, P. C.; Seeger, R.; DeFrees, D. J.; Schlegel, H. B.; Frisch, M. J.; Pople, J . Α.; Kahn, L. R. Gaussian 82 Release A. Carnegie-Mellon Univ., Pittsburgh, PA, 1982. 12. Pople, J. Α.; Segal, G. A . J. Chem. Phys. 1966, 4 4 , 3289. 13. Bingham, R. C.; Dewar, M. J . S.; Lo, D. H. J. Am. Chem. Soc. 1975, 9 7 , 1285. 14. Dewar, M . J . S.; Thiel, W. J. Am. Chem. Soc. 1977, 9 9 , 4899. 15. Halgren, Thomas Α.; Kleier, D. Α.; Hall, John H., Jr.; Brown, Leo D.; Lipscomb, W. N. J. Am. Chem. Soc. 1978, 1 0 0 , 6595. 16. Dewar, M . J . S.; Ford, G . P. J. Am. Chem. Soc. 1979, 1 0 1 , 5558. 17. Volkenstein, M . V . Molecular Biophysics; Academic Press: New York, 1977. 18. Osawa, Eiji; Musso, H. Angewante Chemie-International Edition in English 1983, 2 2 , 1. 19. Allinger, N. L. Adv. Phys. Org. Chem. 1976, 13, 1. 20. Lifson, S.; Warshel, A . J. Chem. Phys. 1968, 4 9 , 5116. 21. Engler, E . M.; Andose, J. M., Scheleyer, P. von R. J. Am. Chem. Soc. 1973, 9 5 , 8005. 22. Fitzwater, S.; Bartel, L. S. J. Am. Chem. Soc. 1976, 9 8 , 5107. 23. Allinger, N. L. J. Am. Chem. Soc. 1977, 9 9 , 8127. 24. Weiner, Paul K.; Kollman, Peter A . J. Comput. Chem. 1981, 2, 287. 25. Tvaroska, Igor; Kosar, Τ. Am. Chem. Soc. 1980, 1 0 2 , 6929. 26. Tvaroska, I. Biopolymers 1982, 2 1 , 1887. 27. Hayns, M . R. Int. J. Quantum Chem. 1982, 2 1 , 217. 28. Calais, Jean-Louis. Int. J. Quantum Chem. 1982, 2 1 , 231. 29. Lowdin, Per-Olov. Proceedings of the International Symposium on Quantum Biology and Quantum Pharmacology; John Wiley & Sons: New York, 1987. 30. Lindberg, J. Johann; Henriksson, A. Fin. Kemist. Medd. 1970, 7 9 , 30. 31. Glasser, Wolfgang G.; Glasser, H. Macromolecules 1974, 7, 17. 32. Glasser, Wolfgang G.; Glasser, H. Holzforschung 1974, 2 8 , 5. 33. Glasser, Wolfgang G.; Glasser, H. Cell. Chem. Tech. 1976, 1 0 , 23. 34. Glasser, Wolfgang G.; Glasser, H. Cell. Chem. Tech. 1976, 10, 39. 35. Glasser, Wolfgang G.; Glasser, H.; Nimz, H. Macromolecules 1976, 9, 866. 36. Glasser, Wolfgang G.; Glasser, H.; Morohoshi, N. Macromolecules 1981, 1 4 , 253. 37. Martensson, O.; Karlsson, G. Arkiv Kemi 1968, 3 1 , 5. 38. Glasser, Wolfgang G. In Pulp and Paper, Third Edition; Casey, James P., Ed.; John Wiley & Sons: New York, 1980. 39. Elder, T . J . ; Worley, S. D. Wood Sci. Tech. 1984, 1 8 , 307. 40. Remko, Milan; Polcin, J . Chem. Zvesti. 1976, 3 0 , 170. 41. Remko, Milan; Polcin, J. Z. Phys. Chem. (Leipzig) 1977, 2 5 8 , 219.

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

19.

42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52.

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53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66.

ELDER

Application of Computational Methods

271

Remko, Milan; Polcin, J . Z. Phys. Chem. (Neue Folge) 1980, 120, 1. Remko, Milan. Adv. Mol. Relaxation and Int. Proc. 1979, 14, 315. Remko, Milan; Polcin, J . Z. Phys. Chem.(NeueFolge) 1977, 106, 249. Remko, Milan; Polcin, J. Z. Phys. Chem. (Neue Folge) 1981, 125, 175. Remko, Milan; Polcin, J . Z. Phys. Chem. (Neue Folge) 1981, 126, 195. Remko, Milan. Adv. Mol. Relaxation and Int. Proc. 1979, 14, 37. Remko, Milan. Z. Phys. Chem. (Neue Folge) 1983, 134, 129. Remko, Milan; Polcin, J . Chem. Zvesti 1977, 31, 171. Remko, Milan; Polcin, J . Monatsh. Chem. 1977, 108, 1313. Remko, Milan; Polcin, J . Z. Naturforsch 1977, 32a, 59. Remko, Milan; Polcin, J . Collect. Czech. Chem. Commun. 1980, 45, 201. Remko, Milan; Sekerka, I. Z. Phys. Chem. (Neue Folge) 1983, 134, 135. Diner, S.; Malrieu, J. P.; Jordan, F.; Gilbert, M . Theor. Chim. Acta. 1969, 15, 100. Gravitis, J . ; Erins, P. J. Appl. Polym. Sci.: Appl. Polym. Symp. 1983, 37, 421. Elder, T . J.; McKee, M . L.; Worley, S. D. Holzforschung 1988, 42, 233. Fleming, Ian. Frontier Orbitals and Organic Chemical Reactions; John Wiley & Sons: London, 1976. Elder, T . J.; Worley, S. D. Holzforschung 1985, 39, 173. Zarubin, M . Ya.; Kirysun, M . F. Fourth International Symposium on Wood and Pulping Chemistry, 1987, p. 407. Jakobsons, J . , Gravitis, J . Khim. Drev. 1985, 1985, 110 (Chemical Abstracts 103 : 87243). Gravitis, J . ; Kokorevics, Α.; Ozols-Kalnins, V. Khim. Drev. 1986, 1986, 107 (Chemical Abstracts 104 : 131736). Kringstad, K. P.; Mörck, R. Holzforschung 1983, 37, 237. Ebraheem, Κ. A. K.; Webb, G . A. Prog. NMR Sped. 1977, 11, 149. Martin, G . J.; Martin, M . L.; Odiot, S. Org. Mag. Res. 1975, 7, 2. Nelson, G . L.; Williams, E . A. Prog. Phys. Org. Chem. 1976, 12, 229. Farnum, D. G . Adv. Phys. Org. Chem. 1975, 11, 123.

RECEIVED May 29,1989

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 20

Differential Scanning Calorimetry and N M R Studies on the Water—Sodium Lignosulfonate System Hyoe Hatakeyama , Shigeo Hirose , and Tatsuko Hatakeyama 1

1

2

Industrial Products Research Institute, 1-1-4 Higashi, Tsukuba, Ibaraki 305, Japan Research Institute for Polymers and Textiles, 1-1-4 Higashi, Tsukuba, 1

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

2

Ibaraki 305, Japan The phase transition and nuclear magnetic relaxation of the water-sodium lignosulfonate (NaLS) system with var­ ious water contents ranging from 0 to ca. 2.3 (grams of water per gram of sodium lignosulfonate) were evaluated by differential scanning calorimetry and nuclear magnetic resonance spectroscopy. It was found that at least two different kinds of water existed in the system: i.e., freez­ ing water and non-freezing bound water. The longitu­ dinal and transverse relaxation times of the water-NaLS system were measured as functions of water content and temperature. A minimum value for the H longitudi­ nal relaxation time (Τ ) was observed at a temperature around —25°C. A sudden decrease in H transverse re­ laxation time (T ) was also observed at a similar temper­ ature. The change of Τ and T of Na in the system corresponded well with the motion of H in water. 1

1

1

2

1

2

23

1

It is generally k n o w n t h a t polyelectrolytes are h i g h l y soluble i n water t h r o u g h h y d r a t i o n of ionic groups. However, a t t e n t i o n has not been p a i d to the p h y s i c o - c h e m i c a l properties of h i g h l y concentrated aqueous s o l u t i o n s of polyelectrolytes. W e have already reported that there are t w o k i n d s of w a t e r , i.e. freezing water a n d non-freezing water, a r o u n d the ionic groups i n the w a t e r - s o d i u m poly(styrenesulfonate) ( N a P S S ) , the w a t e r - s o d i u m cel­ lulose sulfate ( N a C S ) , a n d the w a t e r - c a t i o n salts of c a r b o x y m e t h y l c e l l u l o s e ( M e C M C ) systems (1-3). J u d g i n g f r o m the e x p e r i m e n t a l results o b t a i n e d b y differential s c a n n i n g c a l o r i m e t r y ( D S C ) a n d b y nuclear m a g n e t i c res­ onance ( N M R ) spectroscopy, water molecules are s t r o n g l y b o n d e d to the i o n i c groups a n d f o r m a h y d r a t i o n shell. In this study, we chose the w a t e r - s o d i u m lignosulfonate ( N a L S ) s y s t e m , w i t h various water contents r a n g i n g f r o m 0 to ca. 2.3 g r a m s of water per 0097-6156/89A)397-0274$06.00A) Ο 1989 American Chemical Society

20.

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275

g r a m o f N a L S . T h e t h e r m a l properties a n d H a n d N a nuclear m a g n e t i c r e l a x a t i o n times o f the s y s t e m were investigated. T h e phase t r a n s i t i o n t e m ­ peratures o f the w a t e r - N a L S s y s t e m were measured as a f u n c t i o n o f water content. A t the same t i m e , the b o u n d water content was d e t e r m i n e d f r o m the e n t h a l p y o f t r a n s i t i o n . F u r t h e r m o r e , a d e t a i l e d s t u d y o f the l o n g i t u d i ­ n a l a n d transverse r e l a x a t i o n times ( T i a n d T 2 ) was c a r r i e d o u t , a n d the m o l e c u l a r c o r r e l a t i o n times ( r ) a n d a c t i v a t i o n energies (E ) o f water i n the s y s t e m were e s t i m a t e d . 1

2 3

a

c

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

Experimental Sample Preparation. A s the N a L S s a m p l e , W A F E X , w h i c h was s u p p l i e d b y H o l m e n A B , Sweden, was used after p u r i f i c a t i o n a c c o r d i n g t o t h e m e t h o d r e p o r t e d by L e o p o l d (4). T h e a m o u n t o f sulfonic a c i d groups was deter­ m i n e d b y t i t r a t i n g a n aqueous s o l u t i o n o f purified lignosulfonic a c i d w i t h 1/5 Ν s o d i u m h y d r o x i d e . T h e lignosulfonic a c i d was o b t a i n e d f r o m N a L S b y passing i t t h r o u g h a n a m b e r l i t e I R - 1 2 0 B ( H ) c o l u m n . T h e sulfonate group content o f the N a L S was 1.6 m e q / g . T h e water content (W ) o f each s a m p l e was defined b y +

c

W (g/g) e

where W sample.

w

(1)

= W {g)IW,(g) w

is the weight o f added water a n d W

s

is the d r y weight o f each

Differential Scanning Calorimetry (DSC). T h e phase t r a n s i t i o n o f t h e w a t e r - p o l y e l e c t r o l y t e systems was measured u s i n g a P e r k i n - E l m e r differ­ e n t i a l s c a n n i n g calorimeter, D S C - I I , a n d a D u P o n t m o d e l 910 differential s c a n n i n g c a l o r i m e t e r . T h e s c a n n i n g rate for h e a t i n g a n d c o o l i n g e x p e r i ­ ments was 1 0 ° C / m i n . D S C curves were o b t a i n e d i n the t e m p e r a t u r e range f r o m 50 t o — 120°C. A l u m i n u m sample pans for v o l a t i l e samples were p r e treated b y h e a t i n g w i t h water t o 120°C i n a n autoclave i n order t o a v o i d any r e a c t i o n between a l u m i n u m a n d water d u r i n g h e a t i n g a n d c o o l i n g r u n s . A f t e r the D S C measurement, the s a m p l e was weighed a g a i n t o c o n f i r m t h a t no weight loss h a d t a k e n place. T h e t e m p e r a t u r e a n d e n t h a l p y o f c r y s t a l ­ l i z a t i o n o f sorbed water were c a l i b r a t e d u s i n g pure water as the s t a n d a r d . T h e b o u n d water content was c a l c u l a t e d b y the m e t h o d r e p o r t e d p r e v i o u s l y (1)· Nuclear Magnetic Resonance (NMR) Spectroscopy. Longitudinal and transverse r e l a x a t i o n times ( T i a n d T 2 ) o f H a n d N a i n t h e w a t e r polyelectrolytes systems were measured u s i n g a N i c o l e t F T - N M R , m o d e l N T - 2 0 0 W B . T 2 was measured b y the M e i b o o m - G i l l v a r i a n t o f the C a r r P u r c e l l m e t h o d (5). However, i n the case o f very r a p i d r e l a x a t i o n , t h e free i n d u c t i o n decay ( F I D ) m e t h o d w a s a p p l i e d . T h e s a m p l e t e m p e r a t u r e w a s changed f r o m 30 t o —70°C w i t h the assistance o f t h e 1180 s y s t e m . T h e accuracy o f the t e m p e r a t u r e c o n t r o l was ± 0 . 5 ° C . 1

2 3

LIGNIN: PROPERTIES AND MATERIALS

276 Results and Discussion

DSC. F i g u r e 1 shows D S C c o o l i n g curves of the w a t e r - N a L S s y s t e m h a v i n g various W 's f r o m 0.46 to 2.31 g / g . W h e n a s a m p l e w i t h water is cooled f r o m 50°C at the rate o f 1 0 ° C / m i n , a b r o a d peak ( P * ) is observed i n i t i a l l y , followed by a s h a r p peak representing c r y s t a l l i z a t i o n of water ( P j ) . H o w ever, as s h o w n i n F i g u r e 1, o n l y P * is observed i f W is lower t h a n ca. 0.5 g / g . T h e t e m p e r a t u r e for P j increases w i t h increasing W , w h i l e , o n the other h a n d , the t e m p e r a t u r e for P * decreases w i t h i n c r e a s i n g W . This feature of P * is different f r o m t h a t of the b r o a d peak representing freezi n g b o u n d w a t e r , P / / , w h i c h is observed w h e n water is b o u n d to the h y d r o x y l groups of p o l y m e r s such as l i g n i n , cellulose a n d p o l y ( h y d r o x y s t y r e n e ) derivatives h a v i n g no i o n i c groups (6-9). P / j appeared at a t e m p e r a t u r e lower t h a n t h a t of the c r y s t a l l i z a t i o n peak of water ( P / ) . O n the other h a n d , P * appears at a t e m p e r a t u r e higher t h a n t h a t o f Pj. A n e x o t h e r m i c peak s i m i l a r to P * was also observed i n the case of h i g h l y concentrated aqueous s o l u t i o n s of N a C S a n d N a P S S (1,2). T h e r e fore, i t is supposed t h a t P * is observed w h e n the molecules i n the waterp o l y e l e c t r o l y t e systems rearrange to a stable state h a v i n g lower energy t h a n the n o r m a l state of water. T h i s suggests t h a t the molecules i n the waterN a L S s y s t e m assume a loosely ordered state i n the range between the t e m peratures where P * a n d P / appear. T h e t e x t u r e of the s a m p l e was observed u s i n g a p o l a r i z e d l i g h t m i croscope e q u i p p e d w i t h a t e m p e r a t u r e controller. A l t h o u g h the W o f the s a m p l e c o u l d not be kept e n t i r e l y constant o w i n g to the s t r u c t u r e of the s a m p l e cell, a t e x t u r e s h o w i n g a n e m a t i c t y p e of m o l e c u l a r a r r a n g e m e n t was observed at a t e m p e r a t u r e c o r r e s p o n d i n g to t h a t between P * a n d P j . H o w e v e r , the t e x t u r e observed i n the w a t e r - N a L S s y s t e m was not as clear as those observed i n the w a t e r - N a P S S a n d the w a t e r - N a C S systems. T h i s unclear t e x t u r e observed i n the w a t e r - N a L S s y s t e m m a y be a t t r i b u t e d to the inhomogeneous c h e m i c a l s t r u c t u r e of N a L S . F i g u r e 2 shows the phase d i a g r a m of the w a t e r - N a L S s y s t e m . T h i s d i a g r a m was o b t a i n e d b y c o o l i n g the s y s t e m at a rate o f 1 0 ° C / m i n , i n d i c a t i n g t h a t the s y s t e m changes f r o m the i s o t r o p i c l i q u i d phase t h r o u g h the m e s o m o r p h i c phase to the c r y s t a l l i n e phase. T h e t e m p e r a t u r e o f c r y s t a l l i z a t i o n ( T ) increases w i t h increasing W a n d levels off at W ca. 1.5 g / g . T h e t e m p e r a t u r e ( T * ) c o r r e s p o n d i n g to the appearance o f P * decreases w i t h i n c r e a s i n g W a n d becomes difficult to observe i f W increases above ca. 2.3 g / g . T h e a m o u n t of freezing water i n the w a t e r - N a L S s y s t e m can be c a l c u l a t e d f r o m the enthalpy, a s s u m i n g the c r y s t a l l i z a t i o n e n t h a l p y of water to be 333 J / g (7). T h u s , c

c

c

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

c

c

c

c

c

c

c

W

f

= (AHj/myW,

where Wf is the a m o u n t of freezing water a n d AHj e n t h a l p y of the s y s t e m .

(2) is the c r y s t a l l i z a t i o n

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

20.

HATAKEYAMA ET AL.

Water-Sodium Lignosulfonate System

277

F i g u r e 1. D S C c o o l i n g curves of the w a t e r - N a L S s y s t e m w i t h v a r i o u s water contents, W (g/g). c

LIGNIN: PROPERTIES AND MATERIALS

278

However, the value of Wj is less t h a n the t o t a l a m o u n t of water i n the s y s t e m , since water w h i c h is t i g h t l y b o u n d to the h y d r o p h i l i c groups of a p o l y electrolyte cannot be frozen (1,2). T h e r e f o r e , the t o t a l a m o u n t of water i n the s y s t e m is given b y W

(3)

= Wf + W f

c

n

where Wf is the a m o u n t of freezing water a n d W f is t h a t of non-freezing water. F i g u r e 3 shows the r e l a t i o n s h i p between W Wf a n d W f. T h e value of Wf increases i n p r o p o r t i o n to W at water contents higher t h a n the specific c r i t i c a l a m o u n t w h i c h is o b t a i n e d b y the e x t r a p o l a t i o n of the l i n e a r Wf vs. W plots to the h o r i z o n t a l a x i s . T h e c r i t i c a l value o b t a i n e d is 0.56 g / g . T h i s a m o u n t corresponds to a n a m o u n t less t h a n the p o i n t at w h i c h the water i n the w a t e r - N a L S s y s t e m can no longer be c r y s t a l l i z e d . A s s h o w n i n F i g u r e 3, W f does not change a p p r e c i a b l y w i t h i n c r e a s i n g W. n

C1

n

c

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

c

n

c

H NMR. F i g u r e 4 shows the change of T i values for * H of water i n the w a t e r - N a L S s y s t e m w i t h the inverse absolute t e m p e r a t u r e ( K " * ) . T h e T i value decreases w i t h decreasing W a n d w i t h decreasing t e m p e r a t u r e i n the t e m p e r a t u r e range above — 2 5 ° C , where a m i n i m u m value for T i is o b ­ served. T h e Τχ m i n i m u m occurs at a t e m p e r a t u r e lower t h a n t h a t at w h i c h water molecules i n the s y s t e m become r i g i d . In the t e m p e r a t u r e range be­ low —25°C, a steep increase i n the T i value is observed w i t h decreasing temperature. F i g u r e 5 shows the change of T 2 values for * H of water w i t h the inverse absolute t e m p e r a t u r e . A sudden decrease i n T 2 values is seen at almost the same temperatures at w h i c h the m i n i m u m i n T i is observed. The T 2 values give a n average representation of the m o t i o n of water molecules i n the s y s t e m . Therefore, i f we consider the m o l e c u l a r m o t i o n of water i n the w a t e r - N a L S s y s t e m h a v i n g a c e r t a i n W , the T 2 values at higher t e m p e r a t u r e s are characteristic of more m o b i l e w a t e r , w h i l e the T 2 values at lower t e m p e r a t u r e s are characteristic of more r e s t r i c t e d w a t e r . It is u s u a l l y not possible to d i s t i n g u i s h various p e r t u r b e d sites i n a n N M R e x p e r i m e n t . Therefore, i t is c u s t o m a r y to l i m i t the n u m b e r o f sites to two representing the free (Pf) a n d b o u n d (Pi,) fractions w i t h Pf + Pb = 1. If we assume = 1/7*, (i = 1, 2), t h e n l

1

c

c

Ri = PfRif

(4)

+ PR h

ih

In the case of free water, the extreme n a r r o w i n g c o n d i t i o n is fulfilled a n d t h u s Rif = R f = Rf. T h u s , f r o m E q u a t i o n 4, we can w r i t e 2

(R

x

- PfRf)l(R

A c c o r d i n g to Woessner et al. water can be expressed as

2

- PfRf)

= Rn/R2b

(5)

(10,11), the r e l a x a t i o n rates of the b o u n d

20.

HATAKEYAMA ET AL.

Water-Sodium Lignosulfonate System

279

NaLS-HzO 2.0

"5 W.

/

1.0

ι y*^

0

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

C)

ι

ι

ι

1.0

w

c

2.0

/ g/g

F i g u r e 3. R e l a t i o n s h i p between water content (W ), (Wf) a n d non-freezing water content (W f). c

freezing water content

n

Figure 4. Temperature dependence of the H longitudinal relaxation time of water i n the water-NaLS system.

Figure 5. Temperature dependence of the H transverse relaxation time of water i n the water-NaLS system.

LIGNIN: PROPERTIES AND MATERIALS

280 J _

_

T

~ 2

2i

1

3r

ci

+

where Σ% = 1> d G is the i n t e r a c t i o n constant d e t e r m i n i n g the m a g ­ n i t u d e of the r e l a x a t i o n , u>o the a n g u l a r resonance frequency, a n d r - the c o r r e l a t i o n t i m e . T h e above expressions allow for m u l t i p l e c o r r e l a t i o n t i m e s i n the systems. However, i f we assume t h a t the r e l a x a t i o n of b o u n d water i n the w a t e r N a L S s y s t e m is d e t e r m i n e d b y one average c o r r e l a t i o n t i m e r , we c a n combine E q u a t i o n s 5, 6, a n d 7, to give a

n

ct

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

c

w h i c h is a f u n c t i o n o n l y of u r . It m i g h t be a n o v e r s i m p l i f i c a t i o n to o n l y consider one type of average b o u n d water. However, for p r a c t i c a l purposes, i t seems reasonable to use t h i s c a l c u l a t i o n m e t h o d as a s t a r t i n g p o i n t for the e v a l u a t i o n of b o u n d water i n the w a t e r - N a L S s y s t e m . F i g u r e 6 shows the c a l c u l a t e d r values p l o t t e d vs. inverse absolute t e m p e r a t u r e . I n the t e m p e r a t u r e range below —15°C, i t is seen t h a t the r values are not dependent o n W b u t dependent o n t e m p e r a t u r e . T h e r value increases f r o m ca. 3 x 1 0 ~ sec at — 15°C to ca. 3 x 1 0 ~ sec at - 6 0 ° C . T h i s shows t h a t the b o u n d water i n the s y s t e m is i n the state between viscous l i q u i d a n d n o n - r i g i d s o l i d i n t h i s t e m p e r a t u r e range. A s seen f r o m the figure, the l n r vs. t e m p e r a t u r e " " (K" ) plots are a p p a r e n t l y l i n e a r . T h e t e m p e r a t u r e dependence of r m a y be expressed w i t h considerable accuracy b y the A r r h e n i u s e q u a t i o n i n the f o r m (12) 0

c

c

c

c

c

8

7

1

c

1

c

r

c

= r exp

(Ea/RT)

0

(9)

where E is the a c t i v a t i o n energy for the r e l a x a t i o n process of the b o u n d w a t e r . T h e value o f E was f o u n d to be c a . 24 k J / m o l . T h i s value cor­ responds w e l l w i t h the a c t i v a t i o n energy of the b o u n d water p r e v i o u s l y r e p o r t e d (2). a

a

Na NMR. F i g u r e 7 shows the change o f T i values for N a i n the w a t e r N a L S s y s t e m w i t h the inverse absolute t e m p e r a t u r e at various W ' s . T h e I n T i plots are linear i n the t e m p e r a t u r e range where T i values c o u l d be observed i n t h i s e x p e r i m e n t . A t temperatures lower t h a n — 2 0 ° C , i t was difficult to measure the Τχ value of N a b y the 180-T-90 degree pulse m e t h o d because of the extreme b r o a d e n i n g of the l i n e w i d t h of the N M R peaks. F r o m the slopes of the r e l a x a t i o n rate ( l n T ^ " ) vs. inverse absolute t e m p e r a t u r e , the apparent a c t i v a t i o n energy (E ) of the r e l a x a t i o n process was c a l c u l a t e d . T h e value o b t a i n e d was ca. 12 k J / m o l . T h i s value corre­ sponds w e l l w i t h the a c t i v a t i o n energy for N a i n persulfonate i o n o m e r s w i t h water (13). 2 3

23

c

2 3

1

a

2 3

20.

HATAKEYAMA ET A L

Water-Sodium Lignosulfonate System

e/ c

281

e

0 ι

10"

-20 ι ι Wc 209 157 136 1· 21 1· 01 0-80 0 60

ο • _

δ Α

• • χ

u φ

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

«ίο-

I

-40 I

-60 ι

ι

ί

7

êfn

Λ/Α

* * χ'* 1 Ε£

t i l ΙΟ"

8

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1

ι

ι

ι

36

48 (1000/Τ)/Κ-'

F i g u r e β. T e m p e r a t u r e dependence of the average c o r r e l a t i o n t i m e of water i n the w a t e r - N a L S s y s t e m .

θ / °c 30

20

10

0

-10

—ι

u (Λ Ε

2

·

33

34 35

3-6 37 3·β

(1000/Ό/Κ -I

F i g u r e 7. T e m p e r a t u r e dependence of the i n the w a t e r - N a L S s y s t e m .

2 3

39

N a longitudinal relaxation time

LIGNIN: PROPERTIES AND MATERIALS

282

θ

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30 20

001

/

°C

10

0

-10

-20

3 3 3Λ 35 36 37 3-8 3 9 A O (1000/T)/K H

Wc

- O -

138

- · -

1.18

-Δ-

1.02

-*r

0.76

F i g u r e 8. T e m p e r a t u r e dependence of the i n the w a t e r - N a L S s y s t e m .

2 3

" • -

0.62

N a transverse r e l a x a t i o n t i m e

20.

HATAKEYAMA ET A L

Water-Sodium Lignosulfonate System

283

F i g u r e 8 shows the change o f T 2 values o f N a w i t h inverse absolute t e m p e r a t u r e . A s seen f r o m F i g u r e 8, t w o types o f transverse r e l a x a t i o n s are observed. O n e is "slow" a n d the other a "fast" r e l a x a t i o n . T h i s means t h a t t h e transverse r e l a x a t i o n decays i n a n o n - e x p o n e n t i a l m a n n e r . N o n e x p o n e n t i a l r e l a x a t i o n due t o q u a d r u p o l e r e l a x a t i o n was characterized b y H u b b a r d (14). A c c o r d i n g t o his c a l c u l a t i o n , the transverse r e l a x a t i o n s p r o ­ duced b y a quadrupole i n t e r a c t i o n are t h e s u m o f two o r more d e c a y i n g e x p o n e n t i a l s . A s s h o w n i n F i g u r e 8, the longer transverse r e l a x a t i o n t i m e (T25) decreases w i t h decreasing t e m p e r a t u r e , a l t h o u g h t h e shorter t r a n s ­ verse r e l a x a t i o n t i m e ( T 2 / ) does not change m u c h w i t h t e m p e r a t u r e . T h e s u d d e n decrease o f the T25 value a t a r o u n d — 15°C m a y reflect the i n f l u ­ ence o f the c r y s t a l l i z a t i o n o f water i n the w a t e r - N a L S s y s t e m . T h i s result is quite reasonably e x p l a i n e d i f we assume t h a t the s o d i u m i o n is s u r r o u n d e d b y the non-freezing water a n d t h a t this non-freezing water is s u r r o u n d e d b y the free water. Therefore, t h e m o t i o n o f the free water i n the s y s t e m i n d i r e c t l y affects t h a t o f the s o d i u m i o n .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch020

2 3

Literature Cited 1. Hatakeyama, T . ; Nakamura, K.; Yoshida, H . ; Hatakeyama, H . Thermochmica Acta 1985, 88, 223. 2. Hatakeyama, H.; Iwata, H.; Hatakeyama, T . In Wood and Cellulosics; Kennedy, J . F . , et al., Eds.; Ellis Horwood: Chichester, 1987; C h . 4. 3. Nakamura, K . ; Hatakeyama, T . ; Hatakeyama, H . In Wood and Cellulosics; Kennedy, J . F . , et al., Eds.; Ellis Horwood: Chichester, 1987; Ch. 10. 4. Leopold, B. Acta Chem. Scand. 1952, 6, 64. 5. Meiboom, S.; Gill, D. Rev. Sci. Inst. 1958, 29, 688. 6. Hatakeyama, T . ; Hirose, S.; Hatakeyama, H . Makromol. Chem. 1983, 184, 1265. 7. Nakamura, K . ; Hatakeyama, T . ; Hatakeyama, H . Textile Res. J. 1981, 51, 607. 8. Hatakeyama, T . ; Ikeda, Y . ; Hatakeyama, H . Makromol. Chem. 1987, 188, 1875. 9. Nakamura, K . ; Hatakeyama, T . ; Hatakeyama, H . Polymer 1983, 24, 871. 10. Woessner, D. E . ; Zimmerman, J. R. J. Chem. Phys. 1963, 67, 1590. 11. Woessner, D. E . ; Snowden, B. S. J. Colloid and Interface Sci. 1970, 34, 290. 12. Farrar, T . C . ; Becker, E . D. Pulse and Fourier Transform NMR; Aca­ demic: New York, 1971; p. 57. 13. Komoroski, R. A . In Ions in Polymers; Eisenberg, Α . , Ed.; American Chemical Society: Washington, D C , 1980; C h . 10. 14. Hubbard, P. S. J. Chem. Phys. 1970, 53, 985. RECEIVED March 17,1989

Chapter 21

Preparation and Testing of Cationic Flocculants from Kraft Lignin Erkki Pulkkinen, Airi Mäkelä, and Hannu Mikkonen

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch021

Department of Chemistry, University of Oulu, SF-90570 Oulu, Finland

Kraft lignin has been reacted to a quaternary ether derivative over several hours at temperatures ranging from room temperature to 65°C. Based on the nitrogen content (2.7-3.7%) of the purified product, 42-61% of the hydroxyl groups of lignin were etherified. The yield with respect to reagent was usually over 50%. In laboratory tests the lignin-based cationic ether effectively precipitated inorganic colloids from wastewaters. It is w e l l k n o w n t h a t the a c e t y l a t i o n , for e x a m p l e , of a r o m a t i c a n d a l i p h a t i c h y d r o x y l groups i n kraft l i g n i n can d r a s t i c a l l y change the s o l u b i l i t y of l i g n i n . T h e same occurs w h e n h y d r o x y l groups of kraft l i g n i n are reacted w i t h epoxy reagents h a v i n g q u a t e r n a r y a m m o n i u m groups i n the molecule.

NaOH *

iin-OH + C H o - C H C H ~

v

-

z

,



s

l

o

w

Ο

\

ν

glycidyltrimethylammonium chloride

Hgnin-OC^CHC^i^C^^CI

G

CH CHCH N®(CH3) CI + NaOH 2

CI

2

3

OH

N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride 0097-6156/89A)397--0284$06.00A) © 1989 American Chemical Society

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

0

21. P U L K K I N E N E T A L

Preparation and Testing of Cationic Flocculants

285

E v e n t h o u g h 3.0-4.4 m m o l s (from a t o t a l of 7.2 m m o l s ) of h y d r o x y l groups per g r a m of l i g n i n were c a t i o n i z e d b y these reagents, the p r o d u c t s were c o m p l e t e l y water soluble a n d effective flocculants. I n t h i s p a p e r we discuss the p r e p a r a t i o n a n d testing these c a t i o n i c l i g n i n derivatives.

Experimental Materials. C o m m e r c i a l k r a f t l i g n i n , I n d u l i n A T (Westvaco C o r p . ) , has a c o m b i n e d phenolic a n d a l i p h a t i c h y d r o x y l group content of 7.2 m m o l / g as d e t e r m i n e d b y q u a n t i t a t i v e S i N M R spectroscopy (1). T h e p i n e k r a f t l i g n i n f r o m the N u o t t a s a a r i m i l l of V e i t s i l u o t o C o r p . , F i n l a n d , has a corr e s p o n d i n g h y d r o x y l content of 7.7 m m o l / g . T h e g l y c i d y l t r i m e t h y l a m m o n i u m chloride reagent, c o n t a i n i n g 6 3 . 3 % e p o x y f u n c t i o n a l i t y , was a p r o d u c t of R a i s i o C o r p . , F i n l a n d . N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride was prepared i n the l a b o r a t o r y (2,3). P r a e s t o l 41 I K ( S t o c k hausen C o r p . ) was used as a reference c a t i o n i c flocculant.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch021

2 9

Flocculation Tests (4). A conventional j a r test procedure w i t h a s i x - p l a c e m u l t i p l e stirrer s y s t e m ( P h i p p s & B i r d , Inc.), a n d c r y s t a l l i n e s i l i c a p a r ticles ( M i n - U - S i l 5, P e n n s y l v a n i a G l a s s a n d S a n d C o r p . ) , or a l t e r n a t i v e l y m a t e r i a l dredged f r o m the b o t t o m of a waterway, were used as a c o l l o i d a l reference. A f t e r s t i r r i n g the m a i n b a t c h of the s i l i c a (600 or 1800 m g M i n U - S i l 5 i n 4000 m L of deionized water) for a n h o u r , 2 m L aqueous H C 1 was a d d e d a n d the p H adjusted w i t h s o l i d N a H C 0 3 to 4. T h e d r e d g i n g effluent (3700 m g / l i t e r , p H 5.1) was used as such as a s e t t l i n g reference. T o p e r f o r m the j a r test, 600 m L of the b a t c h d i s p e r s i o n was i n t r o d u c e d i n t o each 800 m L decanter flask a n d the dispersions were s t i r r e d at 100 r p m w h e n the flocculant dosages were a d d e d . Thereafter s t i r r i n g was c o n t i n u e d at 100 r p m for 20 m i n . , at 30 r p m for 20 m i n . , a n d t h e n allowed t o settle for 30 m i n . u n d i s t u r b e d . R e s i d u a l t u r b i d i t i e s were measured b y a H a c h t u r b i d i m e t e r o n 25 m L a l i q u o t s of the s u p e r n a t a n t l i q u i d s t a k e n 2 c m b e low the surface a n d p l o t t e d as f o r m a z i n t u r b i d i t y percent u n i t s (% F T U ) against flocculation dosage i n p p m solids. Stability of Floe. A f t e r s e t t l i n g for 30 m i n u t e s a n d m e a s u r i n g the r e s i d u a l t u r b i d i t y , a dispersion (600 m L ) was p o u r e d i n t o another flask a n d b a c k t o the o r i g i n a l flask. T h e p o u r i n g back a n d f o r t h was t h e n repeated t w i c e . A f t e r s e t t l i n g for 30 m i n . , the r e s i d u a l t u r b i d i t i e s were measured as before. Gelling of Lignin with Formaldehyde. A 5.12 g s a m p l e of a s o d i u m salt of l i g n i n ( 4 0 % nonvolatiles ( N . V . ) , 1 5 % N a O H d i g n i n ) was reacted w i t h 3 7 % C H 0 (0.71 m o l e / 1 0 0 g l i g n i n ) at 9 0 ° C i n a test tube (height 10 c m , w i d t h 2 cm) u n t i l g e l l i n g occurred after 130 m i n . T h e gel t i m e was measured w i t h a T e c a n G e l a t i o n T i m e r , G T 3 (disc 14 m m ) . 2

Reaction of Lignin and Gelled Lignin with Glycidyltrimethylammonium Chloride. G l y c i d y l t r i m e t h y l a m m o n i u m chloride was added t o a preprepared s o d i u m salt of l i g n i n (pre-stirred i n a s t e a m b a t h for 2 h) a n d the r e a c t i o n m i x t u r e was s t i r r e d at 60-70°C for 3 h ( T a b l e I). C a t i o n i z i n g the gelled l i g n i n (reacted w i t h C H 2 O for 130 m i n . ) was essentially

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LIGNIN: PROPERTIES AND MATERIALS

286

c a r r i e d out i n the same way except t h a t the solids content of the r e a c t i o n m i x t u r e was 2 9 % i n s t e a d of 4 4 % . I n the r e a c t i o n of l i g n i n w i t h N - ( 3 - c h l o r o 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride the m o l a r r a t i o s of reagent to N a O H was 1:1 a n d h y d r o x y l groups to reagent 1:1. T h e r e a c t i o n was c a r r i e d out at r o o m t e m p e r a t u r e at 5 2 % N . V . T a b l e I. R e a c t i o n of K r a f t L i g n i n w i t h G l y c i d y l t r i m e t h y l a m m o n i u m C h l o ride 0

Weight

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch021

Components Indulin A T Total O H hydroxyl carboxyl Reagent (63.2%) NaOH H 0 2

a

grams

grams

2.09

2.0

2.64 0.3 4.0

1.67 0.3

9.03

3.97

mmoles 17.2 14.4 2.8 11.0 7.5

Molar Ratio 1 1 0.76

Nonvolatiles

1 0.68

0.43

(N.V.):

44%

A f t e r r e a c t i n g at 60-70°C for 3 h , the isolated a n d d r i e d p r o d u c t weighed 4.5 g a n d , after p u r i f i c a t i o n w i t h b o t h e t h a n o l a n d u l t r a f i l t r a t i o n , p r o v i d e d 2.34 g p r o d u c t c o n t a i n i n g 2.7 a n d 2 . 9 % N , respectively. T h e l i g n i n recoveries i n p u r i f i c a t i o n were 80.3 a n d 8 2 . 8 % .

Purification of Cationized Lignin. T h e p u r i f i c a t i o n was c a r r i e d out either b y u l t r a f i l t r a t i o n of the n e u t r a l i z e d p r o d u c t m i x t u r e t h r o u g h a D i a f l o U M 2 m e m b r a n e ( A m i c o n C o r p . , exclusion l i m i t 1000 M W ) or b y s l u r r y i n g a finely g r o u n d 1 g s a m p l e of d r y crude c a t i o n i c ether at r o o m t e m p e r a t u r e i n 160 m L 9 4 % e t h a n o l . T h e filtered powder was washed w i t h 50 m L 9 4 % e t h a n o l a n d t h e n w i t h 10 m L d i e t h y l ether a n d b r o u g h t to a constant weight i n a v a c u u m desiccator. T h e u l t r a f i l t r a t i o n was preferred w h e n the n i t r o g e n content of the p u r i f i e d c a t i o n i c ether exceeded 3%. Results A s is presented i n F i g u r e 1, the flocculation test w i t h s i l i c a as a c o l l o i d a l reference can be used to o p t i m i z e the reaction t i m e . B y l e t t i n g the r e a c t i o n w i t h l i g n i n a n d N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride advance at r o o m t e m p e r a t u r e for 100 h i n s t e a d of 50 h , the dosage req u i r e m e n t of the r e a c t i o n m i x t u r e was reduced to about half. T h e r e s i d u a l t u r b i d i t y already was sufficiently reduced after r e a c t i n g for 50 h . F i g u r e 2 indicates t h a t the flocculation performance of the c a t i o n i c l i g n i n ether p u rified b y u l t r a f i l t r a t i o n ( 2 . 9 % N ) or b y w a s h i n g w i t h e t h a n o l ( 2 . 7 % N ) was equal.

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Preparation and Testing of Cationic Flocculants

287

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21. P U L K K I N E N E T A L

F i g u r e 2. Effect of p u r i f i c a t i o n o n flocculation p e r f o r m a n c e : (O) unpurified; ( φ ) purified b y leaching w i t h e t h a n o l ; ( Δ ) purified b y u l t r a f i l t r a t i o n .

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LIGNIN: PROPERTIES AND MATERIALS

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288

A s seen i n T a b l e I, there was enough e p o x y reagent to convert o n l y 7 6 % of h y d r o x y l groups to the c a t i o n i c ether. A s s u m i n g t h a t the n i t r o ­ gen content (2.9%) f o u n d i n the purified s a m p l e ( 8 0 . 2 % l i g n i n recovery) is e q u a l l y d i s t r i b u t e d t h r o u g h the whole c a t i o n i c l i g n i n , one can e s t i m a t e t h a t 4 2 % of the h y d r o x y l groups were reacted a n d 5 5 % of the reagent was c o n s u m e d i n the d e r i v a t i z a t i o n . F i g u r e s 3 a a n d 3b show t h a t the flocculation performance of the p u ­ rified c a t i o n i c l i g n i n d e r i v a t i v e , prepared under the c o n d i t i o n s described i n T a b l e I, is e q u a l to t h a t o f the c o m m e r c i a l reference ( P r a e s t o l 41 I K ) . F i g u r e s 4 a a n d 4 b , o n the other h a n d , reveal t h a t the same c a t i o n i c l i g n i n derivative behaves p o o r l y i n the s t a b i l i t y test when c o m p a r e d to the c o m ­ m e r c i a l reference. F i g u r e s 4 a a n d 4b further show t h a t b y condensing the s o d i u m salt of l i g n i n w i t h formaldehyde ( 1 5 % N a O H d i g n i n , 0.7 mole C H 2 O per 100 g l i g n i n ) at 9 0 ° C for 130 m i n . , a n d subsequently r e a c t i n g the gelled p r o d u c t w i t h g l y c i d y l t r i m e t h y l a m m o n i u m chloride, the flocculation perfor­ m a n c e i n the s t a b i l i t y tests was i m p r o v e d , b u t d i d not reach t h a t of the c o m m e r c i a l reference. It can be assumed t h a t the b r i d g i n g a b i l i t y of l i n e a r c a t i o n i c p o l y a c r y l a m i d e s contributes p o s i t i v e l y i n the s t a b i l i t y test. A n i m p r o v e m e n t i n the flocculation a b i l i t y of the p u r i f i e d c a t i o n i c l i g n i n ether due to a n increase i n the m o l e c u l a r weight is clearly seen i n F i g u r e 5. T h e same figure reveals a moderate g a i n i n the flocculation perfor­ m a n c e relative to P r a e s t o l 41 I K w h e n the c a t i o n i c l i g n i n ether h a d 3.4% Ν i n s t e a d of 2 . 9 % Ν as i n the j a r test s h o w n i n F i g u r e 3a. A series of reactions was c a r r i e d out i n order to o p t i m i z e the r e a c t i o n conditions. A s seen i n T a b l e II, at best 3.7% of n i t r o g e n was f o u n d i n the p u r i f i e d c a t i o n i c l i g n i n , w h e n the r e a c t i o n t i m e was 5 or 8 h at 5 5 ° C ( E x p e r i m e n t s 1 a n d 3). P e r h a p s the reaction t i m e a n d t e m p e r a t u r e s h o u l d be lowered f u r t h e r . A t 3.7% Ν some 6 2 % of the h y d r o x y l groups, p r e s u m a b l y i n c l u d i n g a l l p h e n o l i c O H groups, were reacted. Since the procedure i n these e x p e r i m e n t s i n c o r p o r a t e d a smaller a m o u n t of water to avoid a base-catalyzed o p e n i n g of the o x i r a n e r i n g , h i g h solids contents (52-64%) were encountered. It is a d v i s a b l e to a d d p o w d e r e d l i g n i n first to the alkaline s o l u t i o n a n d m i x i n i t i a l l y at r o o m t e m p e r a t u r e a n d t h e n at the r e a c t i o n t e m p e r a t u r e . A s a m i x i n g device we used a r o u n d b o t t o m flask a t t a c h e d to a r o t a r y evaporator at a t m o s p h e r i c pressure a i d e d w i t h m a g n e t i c s t i r r i n g i n the flask. W h e n the s o d i u m salt o f l i g n i n a p p e a r e d to be homogeneous, the c a t i o n i c reagent was i n t r o d u c e d . T h e i n c o m p l e t e recovery b y u l t r a f i l t r a t i o n (56-92%) i n the e x p e r i m e n t s s h o w n i n T a b l e II engenders a n error when the n i t r o g e n content of the retentate is projected to represent t h a t of the whole s a m p l e . A s a m a t t e r o f fact, i n E x p e r i m e n t 1 we o b t a i n e d 1 g c a t i o n i c l i g n i n h a v i n g 3.7% n i t r o g e n b y u l t r a f i l t r a t i o n whereas b y e t h a n o l w a s h i n g 0.65 g w i t h 3.2% n i t r o g e n was o b t a i n e d . P o s s i b l y the l a t t e r m a t e r i a l was of higher m o l e c u l a r weight.

Reaction Mechanism U n d e r the e x p e r i m e n t a l c o n d i t i o n s there w i l l be c o m p e t i t i o n between

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

a

Preparation and Testing of Cationic Flocculants

289

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21. P U L K K I N E N E T A L

F i g u r e 3. T e s t i n g of flocculation performance against (a) s i l i c a d i s p e r s i o n ; (b) d r e d g i n g effluent; ( Q ) c a t i o n i c l i g n i n ether; ( # ) P r a e s t o l 4 1 1 K .

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch021

290

F i g u r e 4. C o m p a r i s o n of flocculation performance i n s t a b i l i t y test (a) against s i l i c a d i s p e r s i o n ; (b) against d r e d g i n g effluent; (O) c a t i o n i c l i g n i n ether; ( Δ ) C H 0 - c o n d e n s e d c a t i o n i c l i g n i n ether; (φ) P r a e s t o l 41 I K . 2

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

21. P U L K K I N E N E T A L

Preparation and Testing of Cationic Flocculants

291

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% FTU

60 Γ

50 Γ

40 Γ

30 L

20 r*

10 h

0.02

0.04

0.06

0.08

0.1

0.12

ppm

F i g u r e 5. Effect o f m o l e c u l a r weight o n flocculation p e r f o r m a n c e o f c a t i o n i c l i g n i n d e r i v a t i v e : (Ç)) I n d u l i n A T , M 23000, N : 3.3%; ( Δ ) I n d u l i n A T , M 6300, N : 3.7%; ( * ) P r a e s t o l 41 I K , M i n - U - S i l 5 450 m g / l i t e r . w

w

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

292

LIGNIN: PROPERTIES AND MATERIALS

T a b l e II. C o n d i t i o n s for C a t i o n i z i n g L i g n i n

a

Reaction Cationic Lignin Exp. No.

Molar Ratios OH:Reagent:NaOH

Temp. °C

Time h

% Ν

% Recovery

Reagent % Yield

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch021

Reaction with Glycidyltrimethylammonium Chloride 1 2 3 4 5 6

1:0.9:0.2 1:0.9:0.2 1:0.9:0.2 1:1.0:0.2 1:1.0:0.2 1.1.0:0.2

Reaction with 7 8 9

52 52 52 65 65 65

74 65 69 51 58 42

56 65 63 68 61 92

3.7 3.6 3.7 3.3 3.4 2.7

5 8 8 5 8 20

N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride

1:0.9:0.9 1:1.0:1.0 1:0.6:0.6

r.t. 65 65

50 51 44

70 65 74

2.9 3.2 2.1

50 10 12

4

E x p e r i m e n t s 1-6 were carried out i n a 1 g s a m p l e of I n d u l i n A T at 5 6 % N . V . I n e x p e r i m e n t 7 a 2 g s a m p l e of I n d u l i n A T was reacted at 5 2 % N . V . N u o t t a s a a r i l i g n i n (2 a n d 5 g) was reacted i n e x p e r i m e n t s 8 a n d 9 at 64 a n d 5 8 % N . V . , respectively. A l l the samples were p u r i f i e d b y u l t r a f i l t r a t i o n a n d the l i g n i n % recovery was d e t e r m i n e d f r o m the % n i t r o g e n a n d the y i e l d of the retentate. Reagent y i e l d s are corrected for u l t r a f i l t r a t i o n losses. R o o m temperature.

Lignin-O® + CHg-CHCHgN^CH^CI® H 0 2

lignin-OCH CHCH N®(CH3) CP 2

2

—=->

3

lignin-OCH CHCH N«iCH3) CP 2

2

3

OH O r P + CH -CHCH N®(CH ) CP 2

2

3

3

H 0 2

CH^CHCH^CHgJgCI© • OH

O® 9

CH -CHCH N®(CH ) Cr + OH© 2

2

3

3

OH OH

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

21. P U L K K I N E N E T A L .

Preparation and Testing of Cationic Flocculants 293

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch021

n u m b e r o f nucleophiles for opening the oxirane r i n g . Since t h e m o l a r a m o u n t o f s o d i u m h y d r o x i d e , w h i c h is first i n t r o d u c e d i n t o t h e r e a c t i o n m i x t u r e , nearly reaches t h e corresponding contents o f phenolic a n d c a r b o x y lie acid groups (Table I ) , l i g n i n phenoxide a n d c a r b o x y l a t e moieties must be t h e d o m i n a n t nucleophilic species a t the b e g i n n i n g . T h e m a i n reactions can be expressed b y the following equations. W h e t h e r o r n o t the reagent w i l l react w i t h t h e secondary h y d r o x y l group generated i n each r i n g o p e n i n g is at present u n k n o w n . T h e c h l o r o h y d r i n reaction w i t h s o d i u m h y d r o x i d e is assumed t o b e a two-step process i n w h i c h a r a t e - d e t e r m i n i n g i n t r a m o l e c u l a r displacement of chloride i o n b y negatively charged oxygen follows a p r i o r e q u i l i b r i u m between the h y d r o x i d e i o n a n d the h y d r o x y l group o f the h a l o h y d r i n (5). CI

CI

CHo-CHo + O H

ι

2

2

9

^

f a S t

^ CHo-CHo

*

I

OH

O

CI I CHo-CHo

ι

slow _ — >

2

9

CHo-CH + C r

9

\

y Q Ο Indeed, we have found t h a t N - ( 3 - c h l o r o - 2 - h y d r o x y p r o p y l ) t r i m e t h y l a m m o n i u m chloride is r e a d i l y converted w i t h s o d i u m h y d r o x i d e t o g l y c i d y l t r i ­ m e t h y l a m m o n i u m chloride, w h i c h obviously further reacts a t a slower rate w i t h l i g n i n nucleophiles t o f o r m cationic l i g n i n derivatives. 2

2

0

Conclusion E v e n a p a r t i a l conversion o f t h e h y d r o x y l groups o f kraft l i g n i n i n t o a c a t i o n i c ether derivative c o n t a i n i n g quaternary a m m o n i u m groups i m p a r t s water s o l u b i l i t y t o the derivative w h i c h is a p r o m i s i n g c a n d i d a t e as a p o t e n ­ t i a l flocculant i n l i q u i d / s o l i d separations i n i n d u s t r i a l a n d m u n i c i p a l water treatment. Literature C i t e d 1. 2. 3. 4.

Nieminen, M . ; Pulkkinen, E . ; Rahkamaa, E . Holzforschung, in press. Paschall, E . F . U.S. Patent 2 876 217, 1959. Paschall, E . F.; Minkema, W . H . U.S. Patent 2 995 513, 1961. Hudson, R. E., Jr.; Wagner, E . G . J. Am. Water Works Assoc. 1981, 40, 218-23. 5. Frost, Α. Α.; Pearson, R. G . Kinetics and Mechanism; John Wiley & Sons: New York, 1962; C h . 12, p. 288.

RECEIVED March 17,1989

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 22

Synthesis and Characterization of Water-Soluble Nonionic and Anionic Lignin Graft Copolymers John J. Meister, Damodar R. Patil, Cesar Augustin, and James Z. Lai

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

Department of Chemistry, University of Detroit, Detroit, MI 48221-9987

A general method of grafting lignin has been developed which allows solvent extracted lignin, steam exploded lignin, and kraft lignin to be converted to complex polymers. The lignins grafted have been obtained from aspen, poplar, and pine. The lignins are research samples, pilot plant products and commercial products from paper production. The types of materials made to date will be illustrated with a series of polymers made as industrial process chemicals. Nonionic copolymers of virtually any composition and molecular weight can be made from lignin and 2-propenamide. A graft terpolymer of lignin has been made by free radical reaction of 2-propenamide and 2,2-dimethyl-3-amino4-oxohex-5-ene-1-sulfonic acid in the presence of kraft pine lignin. The water soluble product is a thickening agent and has limiting viscosity number in water at 30°C which increases as the fraction of sulfonated repeat units in the molecule increases. The grafting reaction is rapid and yields of 80 weight % or more can be obtained in as little as 30 minutes from reactions run in 1,4-dioxacyclohexane or dimethylsulfoxide. The reaction is initiated by a hydroperoxide, chloride ion, and lignin. Hydroxide radicals produced with iron (2+) do not appear to produce grafting. Adding 50 mole % sulfonated monomer to the reaction mixture produces graft copolymers with 12 to 24 times larger limiting viscosity numbers when compared to nonionic poly(lignin-g-1amidoethylene). Adding 20 mole % sulfonated monomer to the reaction mixture increases product limiting viscosity number by a factor of 2 to 5. 0097-6156/89A)397-0294$06.00A) © 1989 American Chemical Society

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22.

MEISTER E T AL.

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295

E v e r y year the U . S paper i n d u s t r y produces over 33 m i l l i o n m e t r i c tons of kraft l i g n i n (1). M o s t of t h i s biomass is b u r n e d as fuel b u t s m a l l a m o u n t s are used as binders, asphalt a d d i t i v e s , or cement a d d i t i v e s . L a r g e r fractions of t h i s waste w o u l d be used i n other i n d u s t r i a l or c o m m e r c i a l processes i f an e c o n o m i c a l way existed to convert l i g n i n i n t o a m a r k e t a b l e p r o d u c t w i t h sufficient profit m a r g i n to compensate for the loss o f the f u e l . A way to make such a conversion has n o w been p r o d u c e d ( 2 , 3 ) . M o r e over, we have developed a c h e m i s t r y for l i g n i n t h a t is a p p a r e n t l y general. It is general i n the lignins used i n t h a t a whole series of lignins w i t h d r a w n f r o m w o o d b y different techniques have been grafted b y t h i s m e t h o d , as s h o w n b y the d a t a of T a b l e I. Since we recognize the p o t e n t i a l for l i g n i n u t i l i z a t i o n i l l u s t r a t e d b y the b r e a d t h of the c h e m i s t r y we have developed, we have u n d e r t a k e n a b r o a d a n d detailed s t u d y of t h e r m o p l a s t i c a n d t h e r moset c o p o l y m e r s of l i g n i n . These derivatives of l i g n i n are b e i n g prepared and e x a m i n e d for their p o t e n t i a l as process chemicals or c o m m e r c i a l a n d engineering m a t e r i a l s . A l l of the samples received were used "as i s " a n d were l a b o r a t o r y , p i l o t p l a n t , or c o m m e r c i a l l y - p r o d u c e d l i g n i n s . T h e reaction converts l i g n i n to a water-soluble c o p o l y m e r or p l a s t i c b y graft p o l y m e r i z a t i o n . T h e graft copolymer is formed b y c o n d u c t i n g a free-radical p o l y m e r i z a t i o n of an a p p r o p r i a t e m o n o m e r o n a n y of the lignins described i n T a b l e I. T h i s report w i l l describe p r e p a r a t i o n a n d testing of water-soluble, graft copolymers made w i t h 2-propenamide a n d 2 , 2 dimethyl-3-amino-4-oxohex-5-ene-l-sulfonic acid i n nitrogen-saturated, organic or a q u e o u s / o r g a n i c solvent c o n t a i n i n g l i g n i n , c a l c i u m chloride, a n d a h y d r o p e r o x i d e . W h i l e the c o p o l y m e r i z a t i o n can be r u n b y a n u m b e r of c o m m o n m e t h o d s , we have used s o l u t i o n p o l y m e r i z a t i o n to prepare l a b o r a t o r y or p i l o t p l a n t scale samples of c o p o l y m e r . W e have s h o w n g r a f t i n g can be done u s i n g a n y of the l i q u i d s i n T a b l e II, w h i c h are now k n o w n to be effective i n s o l u t i o n p o l y m e r i z a t i o n of graft copolymers. T h i s p o l y m e r i z a t i o n process gives us easy heat c o n t r o l a n d r a p i d p r o d u c t i o n of p r o d u c t s for t e s t i n g . T h i s reaction produces graft copolymers t h a t possess side chains c o n t a i n i n g repeated p o l a r u n i t s or m u l t i p l e , i o n i c bonds w h i c h dissociate i n p o l a r solvents. T h e p r o d u c t can be an a n i o n i c or nonionic water-soluble c o p o l y m e r w i t h a l i m i t i n g viscosity n u m b e r i n the range of 0.2 to 11 d L / g . T h e p r o d u c t s increase the viscosity of aqueous s o l u t i o n , act as flocculati n g / d e f l o c c u l a t i n g agents, t h i n n i n g agents, dispersing agents, a n d sequester c a l c i u m ions. I n the following sections, the s y n t h e t i c procedure, p u r i f i c a t i o n procedures, c h a r a c t e r i z a t i o n results, p r o o f of g r a f t i n g , tests of the role of i r o n i n the i n i t i a t i o n of g r a f t i n g , a n d d e t e r m i n a t i o n of extent of r e a c t i o n as a f u n c t i o n of t i m e w i l l be described. Experimental Synthesis. T h e p o l y m e r i z a t i o n can be r u n i n any one of several solvents, listed i n T a b l e I I . D i m e t h y l s u l f o x i d e has been used as the solvent for a l l reactions reported here. In other solvents, the p r o d u c t often precipitates as

LIGNIN: PROPERTIES AND MATERIALS

296

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Table I.

Lignins Grafted with Hydroperoxy/chloride

Chemistry

Source Pine

a

Aspen

b

Yellow Poplar

0

Extraction Method Kraft

Solvent Extracted

Steam Exploded

a

P i n e l i g n i n s from the Westvaco Corporation of Charleston, SC. ^Aspen l i g n i n from the Solar Energy Research Institute, of Golden, CO. Yellow poplar l i g n i n s from BioRegional Energy Associates, of Floyd, VA.

c

Table I I .

Liquids Useful in Solution Polymerization of Graft Copolymers

3

Dimethyl S u l f o x i d e (DMSO) 1,4-Dioxacyclohexane Water Dimethylformamide a

a

a

Most frequently used l i q u i d s .

1-Methyl-2-pyrrolidinone Dimethylacetamide Pyridine

22.

MEISTER ET A U

Water-Soluble Lignin Graft Copolymers

297

the reaction proceeds. T h i s reaction can be successfully r u n w i t h c o n c e n t r a tions or mole ratios of the reactants i n the following ranges: (1) 25 weight % or less reactable solids content; (2) h y d r o p e r o x i d e to c a l c i u m chloride: 0.25 to 32; (3) h y d r o p e r o x i d e to l i g n i n ( M ) : 21 to 113; a n d (4) 0.01 to 0.95 weight f r a c t i o n of m o n o m e r i n reactable solids. T o a d r y E r l e n m e y e r flask of a p p r o p r i a t e size, a d d one h a l f of the r e a c t i o n solvent. A l l reactants, i n c l u d i n g the d r y mass of h y d r o p e r o x i d e , s h o u l d not constitute more t h a n 23 weight % of the r e a c t i o n m i x t u r e or an i n s o l u b l e p r o d u c t may be p r o d u c e d . A d d d r y l i g n i n a n d d r y c a l c i u m chloride to the reaction vessel a n d cap w i t h a s e p t u m or r u b b e r s t o p p e r . I n a separate vessel, dissolve 2-propenamide i n about one quarter to one h a l f of the solvent a n d , i f a p p r o p r i a t e , i n a t h i r d vessel dissolve a second m o n o m e r i n the final one quarter of the solvent. S a t u r a t e b o t h m o n o m e r s o l u t i o n s w i t h N b y b u b b l i n g w i t h the gas for 10 m i n u t e s . S a t u r a t e the l i g n i n s o l u t i o n w i t h N2 for 10 m i n u t e s . A d d the h y d r o p e r o x i d e to the m i x t u r e , b u b b l e w i t h N2 for 5 minutes, cap, a n d stir for 10 m i n u t e s . W h i l e s t i r r i n g the l i g n i n reaction s o l u t i o n , further saturate the m o n o m e r s o l u t i o n s w i t h N 2 . A d d the 2-propenamide s o l u t i o n to the l i g n i n s o l u t i o n w i t h s t i r r i n g a n d under a n N2 b l a n k e t . W a i t 1 m i n u t e . A d d the second m o n o m e r s o l u t i o n to the r e a c t i o n vessel i n the same way. S t i r a n d cap the r e a c t i o n under a n N2 b l a n k e t . P l a c e the reaction vessel i n a 3 0 ° C b a t h for 48 hours. T h e reaction is t e r m i n a t e d w i t h a s m a l l v o l u m e of aqueous, 1% h y d r o q u i n o n e s o l u t i o n a n d a v o l u m e of water equal to 1/3 of the r e a c t i o n s o l u t i o n v o l u m e is added to the p r o d u c t . T h i s s o l u t i o n is added to 10 t i m e s its v o l u m e of 2-propanone a n d the p o l y m e r is recovered by filtration. T h e solids are redissolved i n water. T o remove c a l c i u m i o n f r o m the p r o d u c t , an a m o u n t of Na2C2Û4 equal to the moles of C a C l 2 a d d e d to the r e a c t i o n is placed i n the s o l u t i o n . T h e CaC2Û4 p r e c i p i t a t e is removed b y filtration. T h e filtrate is d i a l y z e d against d i s t i l l e d water for 3 to 5 days u s i n g # 6 Spectropore d i a l y s i s t u b i n g . T h e d i l u t e aqueous s o l u t i o n is t h e n freeze d r i e d to recover the p r o d u c t .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

n

2

Assays. A n a l y t i c a l procedures for d e t e r m i n i n g o x i d i z i n g equivalents b y i o d i n e / t h i o s u l f a t e t i t r a t i o n , l i g n i n content b y U V assay, 1-amidoethylene content b y K j e l d a h l assay, l i m i t i n g viscosity n u m b e r , a n d e l e m e n t a l c o m p o s i t i o n are given i n ref. 4. T h e elemental assay for sulfur was done b y A S T M m e t h o d D 3177-82 w i t h the correction t h a t i n step 7.3, the s o l u t i o n is brought to p H ~ 3.8 w i t h 6 M H C 1 rather t h a n 2.5 M N a O H as i n c o r r e c t l y specified i n the procedure. Size exclusion c h r o m a t o g r a p h y was done w i t h a m o b i l e phase of p H = 13, 0.1 M N a C l . A l l solutions were filtered t h r o u g h an 8 μτη N u c l e o p o r e filter before use. T h e flow rate was 0.5 m L / m i n . a n d the mobile phase was not degassed. T h e injected s a m p l e size was 10 μL a n d the c o l u m n s were m a i n t a i n e d at 43°C d u r i n g a l l separations. S p e c t r a were taken f r o m 200 to 420 n m a n d absorbance at 220 n m was p l o t t e d ver­ sus t i m e for e l u t i o n profile. T o t a l p e r m e a t i o n volume of the c o l u m n s was 44 m L a n d t o t a l p e r m e a t i o n t i m e was 88 m i n . E l e m e n t a l analyses were also performed o n most samples a n d these d a t a were used to calculate the repeat u n i t content of the p r o d u c t s u s i n g

LIGNIN: PROPERTIES AND MATERIALS

298 the f o l l o w i n g r e l a t i o n s h i p s : WP

S

= 5.0745 χ Ν - 2.217 x S

WP

N

R

N

/

= 7.1499 x S

S

= (2.2889 χ Ν -

S)(S~ ) l

where S = weight percent sulfur i n s a m p l e ; Ν = weight percent n i t r o g e n i n s a m p l e ; WP = weight percent o f s a m p l e as s o d i u m l - ( 2 - m e t h y l p r o p - 2 N yl-sulfonate) a m i d o e t h y l e n e repeat u n i t s ; WPs = weight percent o f s a m p l e as 1-amidoethylene u n i t s ; a n d RNJS is the m o l a r r a t i o of a m i d e repeat u n i t s to N - s u b s t i t u t e d , sulfonate c o n t a i n i n g repeat u n i t s . Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

S

Materials. L i g n i n , w h i c h makes u p the backbone of the graft c o p o l y m e r s , is a crosslinked, o x y p h e n y l p r o p y l p o l y m e r t h a t acts as a n i n t e r c e l l u l a r glue i n w o o d y p l a n t s . M o s t l i g n i n used i n these studies is a c o m m e r c i a l p r o d ­ uct. T h e m a t e r i a l is a k r a f t pine l i g n i n prepared i n "free a c i d " f o r m w i t h a number-average m o l e c u l a r weight of 9600, a weight-average m o l e c u l a r weight o f 22,000, a n d a p o l y d i s p e r s i t y i n d e x o f 2.29. T h e ash content o f the l i g n i n is 1.0 weight percent or less. T h e m a t e r i a l was used as received. E l e m e n t a l analysis is C 61.66, Ν 0.89, Η 5.73, S 1.57, C a 0.08, a n d Fe 0.014 weight percent. O t h e r lignins used are described i n the text w i t h the results of the reaction or test. 2 - P r o p e n a m i d e ( c o m m o n n a m e a c r y l a m i d e ) used i n a l l reactions was reagent grade m o n o m e r t h a t was r e c r y s t a l l i z e d f r o m t r i c h l o r o m e t h a n e after hot filtration a n d d r i e d under v a c u u m ( P < 1.3 P a ) at r o o m t e m p e r a t u r e for 24 h . T h e a n i o n i c m o n o m e r , 2 , 2 - d i m e t h y l - 3 - i m i n o - 4 - o x o h e x - 5 - e n e - l sulfonic a c i d , was purified b y h e a t i n g a 15.2 weight percent s o l u t i o n i n m e t h a n o l to 6 5 ° C , filtering the hot s o l u t i o n , recovering the p r e c i p i t a t e d m o n o m e r f r o m the cool s o l u t i o n , a n d v a c u u m d r y i n g the s o l i d at r o o m t e m ­ perature for 24 h r . D i m e t h y l s u l f o x i d e was s t a b i l i z e d reagent grade m a t e r i a l t h a t was freshly v a c u u m d i s t i l l e d at 5 0 ° C before use. C a l c i u m chloride a n d other salts used were reagent grade m a t e r i a l s a n d were used as s u p p l i e d . Gases used i n the syntheses were s t a n d a r d c o m m e r c i a l grade c y l i n d e r gases. T h e d i a l y s i s m e m b r a n e used was S p e c t r a p o r no.6, a 1000 u p p e r molecular-weight-cutoff cellulose, 45 m m d i a m e t e r , m e m b r a n e t u b i n g m a d e b y S p e c t r u m M e d i c a l Industries, L o s Angeles, C A . Equipment. L i g n i n s p e c t r a were r u n o n a P e r k i n - E l m e r L a m b d a 3, U V v i s i b l e spectrophotometer. Freeze d r y i n g was done o n a F T S S y s t e m s M o d e l F D X - 1 - 8 4 l y o p h i l i z e r . W e i g h i n g s were done o n a M e t t l e r B 6 b a l ­ ance. T h e viscometers used i n f l u i d p r o p e r t y measurements were C a n o n Fenske c a p i l l a r y viscometers or a B r o o k f i e l d L V T cone a n d p l a t e viscometer. Size e x c l u s i o n separations were performed w i t h a V a r i a n m o d e l 5000 h i g h performance l i q u i d c h r o m a t o g r a p h e q u i p p e d w i t h a R h e o d y n e 10/zL fixedloop injector. T h e c o l u m n s used i n this work were T S K - G e l g u a r d c o l u m n ; T S K - 4 0 0 0 - p w c o l u m n ; a n d T S K - 5 0 0 0 - p w c o l u m n , p l u m b e d i n sequence. T h e detector was a H e w l e t t - P a c k a r d H P - 1 0 4 0 A h i g h speed s p e c t r o p h o t o m e t r i c detector w i t h its s u p p o r t i n g c o m p u t e r , the H P - 8 5 , c o n t a i n i n g 16k

22.

MEISTER ET AL.

Woter-Soluble Lignin Graft Copolymers

299

bytes of a d d i t i o n a l memory. T h i s detector can p e r f o r m absorbance m e a ­ surements at wavelengths f r o m 190 to 600 n m a n d can detect a n d store a n entire s p e c t r u m of the contents of the detector cell over the above wave­ l e n g t h range every second. T h i s c a p a c i t y allows s p e c t r a to be t a k e n at n u ­ merous times d u r i n g the e l u t i o n of a c h r o m a t o g r a p h i c peak a n d is c r i t i c a l to p r o v i n g the existence of graft copolymers b y m u l t i v a r i a t e curve r e s o l u t i o n (4,5).

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

Results and Discussion Ρ oly (lignin-g-(l-amidoethylene)). These nonionic molecules are s m a l l i n size, r e a d i l y adsorbed o n s i l i c a surfaces, a n d prone to c o m p l e x d i - a n d t r i valent m e t a l ions f r o m aqueous s o l u t i o n ( 2 , 3 ) . S y n t h e t i c results for several samples of p o l y ( l i g n i n - g - ( l - a m i d o e t h y l e n e ) ) are given i n T a b l e I I I . N o t e t h a t these reactions show t h a t c o p o l y m e r c a n be p r o d u c e d w i t h large weight fractions of l i g n i n i n the molecule. T h i s c h e m i s t r y can be used to place short sidechains o n l i g n i n . O t h e r l i g n i n s can be reacted w i t h t h i s chemistry. T a b l e I V shows s y n t h e t i c d a t a for the p r e p a r a t i o n of p o l y ( l i g n i n g - ( l - a m i d o e t h y l e n e ) ) f r o m several different lignins. S a m p l e 1 is a k r a f t pine l i g n i n grafted i n a reaction c o i n i t i a t e d w i t h s o d i u m c h l o r i d e . T h e l i g n i n used i n these studies is the c o m m e r c i a l p r o d u c t described under Materials. S a m p l e 2 was r u n w i t h a s t e a m - e x p l o d e d , solvent-extracted aspen l i g n i n . T h i s backbone, provide b y the S o l a r E n e r g y Research I n s t i t u t e , G o l d e n , C o l o r a d o , as D J L X 1 3 is a n I - O - T E C H process, w o o d e x t r a c t . A f ­ ter s t e a m decompression to d i s r u p t the w o o d fiber, the w o o d was e x t r a c t e d w i t h t e t r a c h l o r o m e t h a n e at a p p r o x i m a t e l y r o o m t e m p e r a t u r e a n d r e d u c e d pressure. T h e w o o d was then e x t r a c t e d w i t h m e t h a n o l at 60°C a n d reduced pressure. T h e l i g n i n sample used was recovered as the m e t h a n o l e x t r a c t . S a m p l e s 3 a n d 4 are results o n a yellow p o p l a r l i g n i n . T h e m a t e r i a l was p r o d u c e d b y B i o R e g i o n a l E n e r g y Associates of F l o y d , V i r g i n i a . It is p r o ­ duced b y s t e a m e x p l o d i n g the w o o d , w a s h i n g w i t h w a t e r , e x t r a c t i n g w i t h a l k a l i , a n d p r e c i p i t a t i n g w i t h m i n e r a l a c i d . T h e l i g n i n has a h i g h c a r b o x y l i c a c i d content a n d a h i g h level of phenolic h y d r o x y l groups. T h e m o l e c u l a r weight of the p r o d u c t was 1,000 to 1,200. S a m p l e s 5 a n d 6 are p o l y ( l i g n i n g - ( l - a m i d o e t h y l e n e ) ) copolymers made w i t h k r a f t pine l i g n i n a n d r u n as controls at the same t i m e as the reactions were r u n o n p o p l a r l i g n i n . Y i e l d a n d p r o d u c t properties are c o m p a r a b l e for samples 4, 5, a n d 6 b u t the y i e l d of s a m p l e 3 is low. T h i s low y i e l d may be due to loss o f p r o d u c t d u r i n g dialysis. D a t a for a series of graft copolymers m a d e u s i n g 2-propenamide are given i n T a b l e V for copolymers synthesized i n d i m e t h y l s u l f o x i d e . These d a t a show t h a t m a x i m u m y i e l d is o b t a i n e d w h e n the chloride i o n to l i g n i n mole r a t i o is 492. T h e reaction o n l i g n i n w i t h 2 - p r o p e n a m i d e is general i n the c o m p o s i t i o n a n d p r o d u c t properties t h a t m a y be acheived. T a b l e V shows the s p e c t r u m of l i g n i n contents, 2-propenamide contents, a n d reagent ratios t h a t can be used to produce a f u n c t i o n a l c o p o l y m e r of differing c o m ­ p o s i t i o n , s t r u c t u r e , a n d p h y s i c a l properties.

300

LIGNIN: PROPERTIES AND MATERIALS

T a b l e I I I . Y i e l d and L i m i t i n g V i s c o s i t y Number f o r Lignin-(2-propenamide) Reactions 8

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

sample no. 1 2 3°

b

c

anhyd CaCl2 in reaction m i x t u r e , wt % 4.0 2.0 2.2

1 3

limiting viscosity no., dL/g

yield g/wt$

3.36 / 90.8 3.64 / 98.4 1.5 /100.0

0.59 0.46 0.21

wt % polymerized 2-propenlignin amide 7.5 6.95 12.4

67.6 73.4 48.3

Ca after ashing 4.91 2.25 6.94

A l l r e a c t i o n m i x t u r e s c o n t a i n e d 20.0 mL o f oxygen-bubbled, i r r a d i a t e d dioxane, 0.5 g o f l i g n i n , and 0.15 mL o f e e r i e s u l f a t e solution. R e a c t i o n s r u n i n a Pyrex f l a s k and c o n t a i n e d 1,4d i o x a n e i r r a d i a t e d f o r 3 h and 0.045 mol (3.2 g) o f 2-propenamide. D e t e r m i n e d i n d i s t i l l e d water a t 30 C. R e a c t i o n run w i t h 0.014 mol (1.0 g) o f 2-propenamide.

T a b l e IV.

P o l y ( l i g n i n - g - ( 1 - a m i d o e t h y l e n e ) ) formed from L i g n i n s and C o i n i t i a t o r s

Composition o f R e a c t i o n ( g ) 2-propene C h l o r i d e HydroperSample L i g n i n amide Salt oxide Solvent 0.50 0.482 mL 21.28 0.68 3.21 0.50 3.20 0.62 0.482 mL 21.28 0.51 0.482 mL 21.30 ,62 21 0.50 20 0.482 mL 21.33 ,62 0.50 0.482 mL 21.39 ,64 3.27 0.50 0.482 mL 21.29 3.22 ,63 a

a

Various

Yield Lignin (g/wt.g) Type 3.46/93.3 Kraft 3.48/94.05 I-O-Tech 2.48/66.67 P o p l a r 3.50/86.48 P o p l a r 3.20/84.88 K r a f t 3.26/87.63 K r a f t

T h e same number o f moles o f c h l o r i d e i o n i s used i n sample 1 and samples 2 t o 4. Sample 1 r e c e i v e d sodium c h l o r i d e w h i l e samples 2 to 4 received calcium chloride.

3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20

1

0.137

4.601 7.00

76.045 66.946 65.79

15.047 13.284 13.034 12.37

0.77 0.35 0.44 0.306

70.07 89.36 90.35 88.73

3.16/2.58 4.31/3.306 4.40/3.34 4.73/3.283

0.15 0.15 0.15 0.15

0.40/.3532

0.25/.2208

0.152/.1342

0.80/.7064

0.50

0.50

0.50

0.50

0.50

0.50

g i v e n as

weight

of

crude

to

pure

the

2-hydroperoxy-

d i m e t h y l s u l f o x i d e save

1,4-dioxacyclohexane.

mL o f

ratios

run in

1,4-dioxacyclohexane.

Results

(§)

run i n 20.0

marked

reactions

for

= Some

lost

units recovery.

repeat during

i n

yield

0.2

11.41

to pure polymer.

on

recovered

pure product

0.679

0.325

15.52 5.62

1.65 0.88

5.45 14.95

0.33

6.54 12.24 13.74

1.007 0.558

8.13

based the

is

product

70.98

79.43

57.41

52.95

57.52

crude percent

of

14.062

15.802

11.516

10.63

11.515

39.53

71.43

14.162 7.950

66.43

ratios Weight

are

1-amidoethylene product

=

recovered. 1-amido

listed recovered.

yields

product

The

*

C

0.56

78.26

4.08/2.896

0.15

0.15

0.1

0.523

88.38

0.15

0.50

0.276

61.29

1.25/.919 3.27/

0.15

0.4/.3532

0.5

0.50

0.15/.1325

0.0113

0.50

3.20 3.20

1.00

0.275

57.14

1.49/.857

0.15

0.15/.1325

0.50

1.00

0.288

70.87

1.12/1.063

0.15

0.15/.1325

0.10 0.0512

0.50

0.192

73.64

0.15

1.00

0.565

57.58

1.84/1.44 2.14/1.105

0.15

0.15/.1325

0.50

1.00

0.15/.1325

0.0107 0.50

0.50

2.00

0.478

84.36

2.68/2.109

0.15

0.15/.1325

0.0516

0.50

2.00

samples

All

19 20

17 18

15 16

14

13

13.197

3.54 6.26 58.81 11.67

0.395

83.64

3.04/2.091

0.15

0.15/.1325

0.10

0.50

2.00

12

0.0949 6.88 59.12 11.74

0.372

84.77

3.10/2.119

0.15

0.15/.1325

0.50

0.50

2.00

0.395

13.734

0.801

77.38

3.46/2.863

0.15

0.15/.1325

4.16 69.42

0.010

4.94 68.89

13.641

0.50

0.757

5.48 68.41

13.55

0.15

0.15/.1325

Ο.0515

0.50

0.666

0.15

0.15/.1325

0 . Ι­

0.50

0.615

0.15

0.416

0.50

0.50 84.53

0.15

0.416

0.50

0.50

2.48

2.86

2.89

89.37

4.07/3.307 3.90/3.128

0.15

0.416

0.50

0.50

0.50

6.03 7.21

0.415

4.94

67.91

13.45

62.31

0.73

5.38

67.38

13.34

57.83

0.15

0.40/.3532

0.0503 0.0102

0.69

0.56

69.32

3.30V2.565 2.72V2.14

0.10

0.50

0.15

Ca 2.789

0.40/3532

(1)

0.50

Composition Lignin 6.50 76.73

1-amido

Product

0.15

[n]

0.40/.3532

0.50

Ν 15.21

0

(dL/g) 0.322

Yield wt* 75.68

+

Ce( 4)

Data

g 4.71/2.799

b

DMSO

(mL,.05M)

R0_H

(g) 0.50

CaCl.

3

11

9 10

8

§

ë

e

7fi

6

5

4

3

2

amide(g)

Number

Lignin

Reactants

Lignin-co-O-araidoethylene) samples.

2-propen-

V.

Sample

Table

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

302

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

T h e above d a t a , w h e n a n a l y z e d for the effects o f i n d i v i d u a l r e a c t a n t s , shows t h a t chloride i o n is a c r i t i c a l reactant i n c o n t r o l l i n g the y i e l d a n d l i m i t i n g v i s c o s i t y n u m b e r o f the p r o d u c t c o p o l y m e r . T o q u a n t i f y t h i s effect as a first step i n o p t i m i z i n g t h i s synthesis, a series o f tests were r u n i n the above solvent s y s t e m w i t h each r e a c t i o n h a v i n g a different level o f choride i o n content. T h e results o f the reactions are given i n T a b l e V I . T h e c o m ­ p o s i t i o n , r e a c t i o n c o n d i t i o n s , a n d y i e l d for these reactions are also l i s t e d i n T a b l e V I . T h e c o n c e n t r a t i o n o f l i g n i n a n d 2 - p r o p e n a m i d e were k e p t at a r o u n d 1.9 a n d 11.8 t o 1 2 . 5 % b y weight, respectively, w h i l e v a r y i n g the c a l ­ c i u m chloride content f r o m 0.97 t o 3.78 weight % , as s h o w n i n T a b l e V I I . T h i s n o n i o n i c graft c o p o l y m e r i z a t i o n produces a m a x i m u m y i e l d w h e n c o n ­ c e n t r a t i o n o f the c a l c i u m c h l o r i d e is at 2 . 4 1 % b y weight o f t o t a l r e a c t i o n mass, as s h o w n i n F i g u r e 1. Poly(lignin-g-((l-amidoethylene)-co-(sodium l'(2-methylprop-2N-yl-l-sulfonate) amidoethylene))). A s t r o n g l y a n i o n i c p o l y e l e c t r o l y t e c a n be m a d e f r o m l i g n i n b y c o n d u c t i n g a graft p o l y m e r i z a t i o n i n the presence o f 2p r o p e n a m i d e a n d 2 , 2 - d i m e t h y l - 3 - i m i n o - 4 - o x o h e x - 5 - e n e - l - s u l f o n i c a c i d or its s a l t s . D a t a f r o m 22 reactions are given i n T a b l e V I I I . T h i s c o m p o u n d w i l l be c a l l e d c o p o l y m e r 2. A l l reactions, w i t h the e x c e p t i o n o f n u m b e r 10, c o n t a i n e d 0.50 g of k r a f t pine l i g n i n . T h i s series o f reactions was r u n t o d e t e r m i n e : (1) the dependence o f y i e l d o n reactant c o n c e n t r a t i o n s ; (2) a n e s t i m a t e o f extent o f r e a c t i o n as a f u n c t i o n o f t i m e ; a n d (3) the effect o f i r o n c o n t a m i n a t i o n o n r e a c t i o n y i e l d . P r o o f o f graft c o p o l y m e r i z a t i o n m u s t be p r o v i d e d for these r e a c t i o n p r o d u c t s . A l l too frequently, m a t e r i a l s s y n ­ thesized i n the presence o f a possible b a c k b o n e are assumed t o be graft c o p o l y m e r i z e d (7). I n place o f assumed s y n t h e t i c success, we have used a p r e v i o u s l y developed size e x c l u s i o n c h r o m a t o g r a p h y m e t h o d to verify t h a t s i d e c h a i n a n d b a c k b o n e are c h e m i c a l l y b o u n d (2-5). I n t h i s t e c h n i q u e , the absorbance s p e c t r a f r o m 200 t o 6 0 0 n m o f the effluent f r o m the c h r o m a t o g ­ r a p h y c o l u m n is t a k e n i n real t i m e t h r o u g h o u t the e l u t i o n o f a p e a k . T h e s e s p e c t r a a l l o w i d e n t i f i c a t i o n o f the m a t e r i a l i n the detector cell a n d s h o w the presence o f b a c k b o n e or s i d e c h a i n at a n y p o i n t i n the e l u t i o n profile. Size e x c l u s i o n c h r o m a t o g r a m s for pure l i g n i n a n d s a m p l e 8, T a b l e V I I I , are s h o w n i n F i g u r e 2. T h e c o p o l y m e r s a m p l e produces a n absorbance peak at 34 m i n f r o m the i n j e c t i o n o f 10 uL of 1.46 g / d L s a m p l e 8 i n m o b i l e phase. T h e l i g n i n c h r o m a t o g r a m shows a n absorbance m a x i m u m at 38.5 m i n after i n j e c t i o n of 10 μΙ> o f 0.45 g / d L o f l i g n i n . E l u t i o n o f c o p o l y m e r 8 s t a r t s at 25 m i n , 7 m i n ahead o f the 32 m i n s t a r t o f e l u t i o n o f l i g n i n f r o m the c o l u m n s under i d e n t i c a l c o n d i t i o n s . Since the earlier e l u t i o n o f c o p o l y m e r 8 shows i t is a larger-molecular-size m a t e r i a l , these c h r o m a t o g r a m s p r o v i d e s t r o n g s u p p o r t for the f o r m a t i o n o f graft c o p o l y m e r . F i n a l p r o o f is p r o ­ v i d e d b y the u l t r a v i o l e t s p e c t r a o f the e l u t i n g p o l y m e r s . T w o s p e c t r a o f s a m p l e 8 effluent t a k e n at 29.29 a n d 31.96 m i n b o t h s h o w the c h a r a c t e r ­ i s t i c a b s o r p t i o n m a x i m a at 220 n m a n d shoulder at 286 n m c h a r a c t e r i s t i c o f l i g n i n . T h e 31.96 m i n s p e c t r a o f s a m p l e 8 effluent is s h o w n i n F i g u r e 3. Since r e a c t i o n p r o d u c t l i g n i n is e l u t i n g f r o m the c o l u m n before any pure l i g n i n is seen i n the detector, the reaction m u s t have enlarged the r e a c t e d

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303

T a b l e V I . S y n t h e t i c Data o f P o l y ( l i g n i n - g - 2 - p r o p e n a m i d e )

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

Reactant (weight i n grams) Sample Number Lignin 24-124-1 0.50 24-124-2 0.50 0.50 24-124-3 0.50 24-124-4 0.51 24-134-1 0.51 24-134-2 0.50 24-134-3

Ε CaCl 0.250.38 0.50 0.63 0.77 0.92 1.05

_A 3.21 3.20 3.20 3.20 3.20 3.21 3.23

DMSQ 21.29 21.21 21.27 21.28 22.03 21.35 21.53

(mL) 0.50 0.50 0.50 0.50 0.50 0.50 0.50

CI mmole 4.50 6.85 9.01 11.35 13.87 16.58 18.92

R e a c t i o n parameter Ca/g Yield C l / L Cl/H % 0.97 9.00 1.07 92.17 1.47 13.7 1.63 94.59 1.93 18.02 2.15 96.56 2.41 22.70 2.71 99.20 2.85 27.40 3.31 93.00 3.47 32.51 3.96 87.33 3.92 37.84 4.34 84.18

Note : A: 2-propenamide. E: 30 % hydrogen p e r o x i d e ( e q u i v a l e n t weight : 8.383 meq/mL). Ca/g: c a l c i u m c h l o r i d e c o n t e n t (wt $ ) . C l / L : c h l o r i d e c o n t e n t p e r u n i t weight o f l i g n i n . Cl/H : molar r a t i o o f c h l o r i d e t o hydrogen p e r o x i d e .

Table V I I .

The C o m p o s i t i o n o f R e a c t i o n M i x t u r e s Used t o Make L i g n i n G r a f t Copolymers

Sample number

Total mass

Lignin wt>

24-124-1 24-124-2 24-124-3 24-124-4 24-134-1 24-134-2 24-134-3

25.75 25.79 25.97 26.11 27.01 26.49 26.81

1.94 1.94 1.93 1.91 1.89 1.93 1.86

CaCl. wt* 2

0.97 1.47 1.93 2.41 2.85 3.47 3.92

Monomer wt*

Monomer mmole/g

Yield

12.47 12.41 12.32 12.26 11.85 12.12 12.05

1.75 1.75 1.73 1.72 1.67 1.71 1.69

92.17 94.59 96.56 99.20 93.00 87.33 84.18

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304

F i g u r e 1. Y i e l d vs. c a l c i u m chloride content per t o t a l mass i n reactions of the n o n i o n i c c o p o l y m e r .

4.66 1.87 1.86 15.99 1.86 1.86 1.87 1.87 1.76 1.86

1.86 1.87 1.86 1.87 1.87 1.86

2.57 2.56 2.56 2.56 2.56 2.57

H766

5.16 5.16

4.66 4.66 4.66

1.60 1.60 1.60 1.60 1.60 1.60 1.60 2.58 2.56 21.98 2.56 2.56 2.57 2.56 2.57 2.57

(g>

2-prop< ηΑ amide

30 20 20 20 20 20

0.14 0.15 0.15 0.15 0.15 0.26

30 30 30 30 30 219

20 20 20 20 15 20

Dimethyl sulfoxide (mL) 20 50 50 40

Ce(4+) solution (mL) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 1.28 0.15 0.15 0.15 0.15 0.20 0.15

70.28 51.63* 72.72 18.26 68.29 71.27

0.50 0.50 0.50 0.51 0.50 0.50

Reaction #10

0.34 0.335 0.338 0.34 0.34 0.34

Β Yield (fi) (wt %) 0.15 70.12 0.15 86.98 0.25 78.40 0.40 69.82 0.15 78.79 0.15 77.27 0.15 87.28 0.39 67.89 0.39 79.49 3.35 91.02 0.36 80.69 0.34 315.64 0.34 69.89 0.34 66.79 0.34 18.50 0.34 45.06

2

CaCl. (g) 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.53 4.35 0.50 0.50 0.50 0.50 0.50 0.50

= some product l o s t during p u r i f i c a t i o n . ) A l l reactions, save #10, contained 0.50 g of l i g n i n . contained 4.39 g o f l i g n i n .

17 18 19 20 21 22

9 10 11 12 13 11» 15 16

8

4 5 6 7

3

Sample Number 1 2

Table VIII. Synthesis Data and Physical C h a r a c t e r i s t i c s of Graft Terpolymer

42.55 44.36 42.26 41.77 42.84

42.47 42.25 44.38 44.73 43.88 44.90 42.80

43.31

c 35.41 36.77 36.88 37.74 39.85 38.03 36.51

6.79 7.40 6.89 6.50 6.67 6.50

10.60 11.32 9.91 9.25 10.78 10.76

3

mole s-χ g 0 0 .754 1.5x10" 9.41 1.87x10 9.26 .184 0 0 1.55x10- 3 .780

Repeat Units (wt $) 1-amidoAssays (wt. %) ethylene Η Ν S 14.1 5.94 9.78 7.03 9.54 21.51 6.17 8.39 6.20 22.79 9.19 8.49 22.60 8.47 6.39 9.23 8.61 6.79 9.39 28.63 6.40 9.95 22.33 8.73 16.56 7.74 10.29 6.33 10.92 5.65 42.89 6.65 42.1 10.76 5.66 6.29 43.78 6.21 11.34 6.49 10.84 44.39 4.79 6.83 38.40 6.46 4.70 9.62 6.58 10.82 4.32 45.33 6.82 44.05 4.69 10.73 11.41 6.74 4.75 47.37

D 62.6 61.1 58.8 59.1 55.1 63.7 65.9 40.4 36.2 44.4 34.2 33.6 30.9 33.5 34.0

A) = 2,2-dimethyl-3-imino-4-oxohex-5-ene-1-sulfonic a c i d . B) = Hydroperoxide. Samples 1 to 7: Values are weight o f 1,4-dioxa-2hydroperoxycycloexane i n g. Samples 8 to 22: Values are amount of aqueous solution of 1,2-dioxy-3,3-dimethylbutane i n mL. Equivalent/mL = 7.23x10~ . D) = N-substituted 1-amidoethylene.

[η] (dL/g) 10.52 11.40 7.40 9.30 12.59 6.81 10.46 .953 2.46 1.97

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

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LIGNIN: PROPERTIES AND MATERIALS

Figure 2. Size exclusion chromatogram of lignin and the anionic copolymer as monitored by absorbance at 220 nm.

Figure 3. A n ultraviolet absorbance spectrum of the anionic copolymer showing the characteristic absorbance pattern of lignin.

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Water-Soluble Lignin Graft Copolymers

l i g n i n molecule b y f o r m i n g a graft c o p o l y m e r . A s p e c t r u m of pure l i g n i n effluent at 36.96 m i n is also given i n F i g u r e 3. These d a t a c o n f i r m t h a t graft c o p o l y m e r has been m a d e . Mechanistic Studies. R e a c t i o n s 1 to 7 were r u n w i t h different mole r a t i o s of l i g n i n to h y d r o p e r o x i d e a n d chloride i o n to h y d r o p e r o x i d e . A m a x i m u m y i e l d of 87 w t . % of p o l y m e r i z a b l e mass i n the r e a c t i o n is o b t a i n e d w h e n the l i g n i n to hydroperoxide mole r a t i o is 4.17 x 1 0 ~ a n d the chloride i o n to h y d r o p e r o x i d e mole r a t i o is 7.21. These ratios o c c u r i n s a m p l e 2. P r e v i o u s studies (2) have s h o w n t h a t the mole r a t i o s between l i g n i n , chloride i o n , a n d h y d r o p e r o x i d e c o n t r o l y i e l d i n the graft c o p o l y m e r i z a t i o n of p o l y ( l i g n i n - g - ( l - a m i d o e t h y l e n e ) ) . These same r a t i o s c o n t r o l y i e l d i n the f o r m a t i o n of p o l y ( l i g n i n - g - ( l - ( 2 - m e t h y l p r o p - 2 N - y l ) s u l f o n i c a c i d ) a m i d o e t h y l e n e ) - c o - ( l - a m i d o e t h y l e n e ) ) ) . These results i m p l y t h a t the g r a f t i n g m e c h a n i s m involves l i g n i n , chloride i o n , a n d h y d r o p e r o x i d e . A n i n i t i a t i o n reaction w h i c h is c o m p a t i b l e w i t h a l l findings t o date is the a t tack o n l i g n i n b y a hydroperoxide-(chloride ion) c o m p l e x to create a site for free r a d i c a l p r o p a g a t i o n . S u c h complexes have been seen i n E S R studies of h y d r o p e r o x i d e s (8). Samples 8 a n d 9 of T a b l e V I I I show t h a t t h i s g r a f t i n g r e a c t i o n c a n also be r u n w i t h a n a l t e r n a t i v e h y d r o p e r o x i d e , 1 , 2 - d i o x y - 3 , 3 - d i m e t h y l b u t a n e . T h i s c o m m e r c i a l l y available h y d r o p e r o x i d e can be used i n place of 1,4dioxacyclohexane-2-hydroperoxide. S a m p l e 10 shows t h a t a m o u n t s o f c o p o l y m e r as large as 40g can be made i n single pot reactions. R e a c tions 11 to 16 of T a b l e V I I I were i d e n t i c a l c o m p o s i t i o n tests r u n for different a m o u n t s of t i m e . S a m p l e 11 was t e r m i n a t e d after 31 m i n , s a m p l e 12 after 1 h r , samples 15 a n d 16 after 3 h r , sample 14 after 24 h r , a n d s a m p l e 13 after 48 h r . These d a t a were gathered to d e t e r m i n e the m i n i m u m d u r a t i o n of the r e a c t i o n . T h e results showed t h a t h i g h yields (samples 11 a n d 16) can be o b t a i n e d i n reaction times as short as 30 m i n . S e v e r a l samples (12 a n d 15) show low yields after reaction t i m e s as l o n g as 3 h r b u t these results were o b t a i n e d f r o m a c o n t a m i n a t e d reaction or a r e a c t i o n c o n t a i n i n g less t h a n the a p p r o p r i a t e a m o u n t of solvent, respectively. P r e v i o u s reactions r u n i n 1,4-dioxacyclohexane gave h i g h yields i n short r e a c t i o n t i m e s ( 2 , 9 ) . These d a t a s u p p o r t a free r a d i c a l p o l y m e r i z a t i o n m e c h a n i s m for ethene m o n o m e r s a d d i n g to l i g n i n ( 2 , 9 ) . Free r a d i c a l reactions have rates w h i c h are insensitive t o change of solvent. S a m p l e s 17 to 22 were i d e n t i c a l , 48 h r reactions r u n w i t h different a m o u n t s o f i r o n ( 2 + ) i n the reaction m i x t u r e . S a m p l e s 17 a n d 21 c o n t a i n o n l y the i r o n added as a 104 p p m c o n t a m i n a n t of l i g n i n . T h e r e a c t i o n m i x ture, i n these cases, contains 9.28 x 1 0 ~ moles of F e . T h e m o l e r a t i o between h y d r o p e r o x i d e a n d i r o n is 1,340. Since i r o n i n n e u t r a l or a c i d i c sol u t i o n is not reduced i n the presence of h y d r o p e r o x i d e , i f the h y d r o p e r o x i d e Fe were a c t i n g as a Fen ton's i n i t i a t o r for free r a d i c a l p o l y m e r i z a t i o n , o n l y 2 % of the l i g n i n i n the reaction m i x t u r e c o u l d be grafted a n d the l i g n i n content of the reaction p r o d u c t w o u l d be 0.2 w t . % . R e a c t i o n p r o d u c t s u s u a l l y c o n t a i n e d between 6 a n d 10 w t . % l i g n i n , a l i g n i n c o n c e n t r a t i o n w h i c h c o u l d not occur unless e x t r e m e l y large a m o u n t s of c h a i n transfer

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

2

7

2 +

2 +

LIGNIN: PROPERTIES AND MATERIALS

308

took place. Since l i g n i n forms less reactive, q u i n o i d - t y p e structures w h e n p r o t o n a b s t r a c t e d , h i g h p r o p a g a t i o n rates c o u l d not be achieved b y c h a i n transfer mechanisms. T o c o n f i r m t h a t F e was not a reagent active i n the i n i t i a t i o n o f t h i s r e a c t i o n , several more reactions were r u n w i t h larger concentrations o f F e . R e a c t i o n 22 has a n R 0 2 H / F e mole r a t i o o f 160 b u t has about t h e same y i e l d as a n u n c o n t a m i n a t e d r e a c t i o n , # 1 7 a n d 2 1 . R e a c t i o n 19 has a n R 0 2 H / F e mole r a t i o o f 13.3 b u t a g a i n shows n o change i n y i e l d f r o m t h a t of a n u n c o n t a m i n a t e d r e a c t i o n . S a m p l e 20 has a 1.35 mole r a t i o o f RO2H to F e a n d shows a sharp decrease i n reaction y i e l d a n d g r a f t i n g . Here, the a p p r o x i m a t e l y 1:1 mole r a t i o o f peroxide t o i r o n s h o u l d produce a h i g h c o n c e n t r a t i o n o f h y d r o x i d e radicals a n d extensive p o l y m e r i z a t i o n i f these radicals are p a r t of the p o l y m e r i z a t i o n process. Instead o f a h i g h y i e l d , however, the reaction y i e l d was less t h a n one t h i r d o f t h a t o b t a i n e d i n the absence o f i r o n . Therefore, a F e n t o n ' s i n i t i a t i o n m e c h a n i s m for t h i s react i o n is inconsistent w i t h the d a t a a n d p r o b a b l y does not occur. E l e m e n t a l analysis d a t a of T a b l e V I I I showed t h a t p r o d u c t c o m p o s i t i o n is p r o x i m a t e to, b u t n o t equal t o , reaction m i x t u r e c o m p o s i t i o n . 2 +

2 +

2+

2+

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch022

2 +

Properties. T h e l i m i t i n g viscosity number values of these graft copolymers show t h a t the molecules are s h a r p l y expanded b y the a d d i t i o n o f a n i o n i c m o n o m e r t o t h e c h a i n . R e a c t i o n s (3) r u n w i t h the same n u m b e r o f moles of nonionic m o n o m e r (0.045) a n d p r o d u c i n g a p p r o x i m a t e l y the same y i e l d of p r o d u c t gave l i m i t i n g viscosity numbers o f 0.50 d L / g . I n reactions 1 to 7 where 50 m o l e % o f the m o n o m e r is now sulfonated, i o n i c m o n o m e r , the l i m i t i n g viscosity n u m b e r is 12 to 24 times higher. F o r p r o d u c t s 8 to 10, the reaction m i x t u r e contained 20 mole % sulfonated m o n o m e r . T h e l i m i t i n g viscosity numbers for samples 8 t o 10 are 2 t o 5 times higher t h a n those of the n o n i o n i c copolymer, p o l y ( l i g n i n - g - ( l - a m i d o e t h y l e n e ) ) (3). T h e a d d i t i o n of sulfonated repeat u n i t s makes the p o l y m e r a better t h i c k e n i n g agent a n d m a y make i t a better c o m p l e x i n g or flocculating/deflocculating agent. Conclusions A general m e t h o d of g r a f t i n g l i g n i n has been developed w h i c h allows solvent e x t r a c t e d l i g n i n , s t e a m e x p l o d e d l i g n i n , a n d kraft l i g n i n t o be converted t o c o m p l e x p o l y m e r s . T h e l i g n i n s grafted have been o b t a i n e d f r o m aspen, p o p l a r , a n d pine. T h e lignins are research samples, p i l o t p l a n t p r o d u c t s , a n d c o m m e r c i a l p r o d u c t s f r o m paper p r o d u c t i o n . T h e types of m a t e r i a l s m a d e t o date are i n d u s t r i a l process chemicals a n d are n o n i o n i c a n d a n i o n i c graft copolymers of l i g n i n . E x t e n s i v e studies o n the nonionic c o p o l y m e r , p o l y ( l i g n i n - g - ( l - a m i d o e t h y l e n e ) ) , show t h a t the m a t e r i a l c a n be m a d e w i t h a b r o a d s p e c t r u m o f l i g n i n s , t h a t p r o d u c t properties c a n be controlled b y c o n t r o l o f reaction chloride i o n content a n d m o n o m e r content, a n d t h a t v i r t u a l l y a n y l i g n i n content, molecular weight, a n d sidechain content c a n be achieved b y c o n t r o l of synthesis variables. A graft t e r p o l y m e r of l i g n i n has been m a d e by free r a d i c a l reaction o f 2-propenamide a n d 2 , 2 - d i m e t h y l - 3 - a m i n o - 4 - o x o h e x - 5 - e n e - l - s u l f o n i c a c i d i n

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the presence o f k r a f t pine l i g n i n . T h e water soluble p r o d u c t is a t h i c k e n i n g agent a n d has a l i m i t i n g viscosity n u m b e r i n water at 30°C w h i c h increases as the f r a c t i o n o f sulfonated repeat u n i t s i n the molecule increases. T h e g r a f t i n g reaction is r a p i d a n d yields o f 80 w t . % or more can be o b t a i n e d i n as l i t t l e as 30 m i n f r o m reactions r u n i n 1,4-dioxacyclohexane or d i m e t h y l sulfoxide. T h e reaction appears t o be i n i t i a t e d b y a h y d r o p e r o x i d e , chloride i o n , a n d l i g n i n t h o u g h the exact steps of the i n i t i a t i o n are not k n o w n . Since the a d d i t i o n o f F e t o the reaction reduces y i e l d at h y d r o p e r o x i d e t o F e mole ratios of about 1, h y d r o x i d e radicals p r o d u c e d w i t h F e do not appear to produce g r a f t i n g . A d d i n g 50 mole % sulfonated monomer to the r e a c t i o n m i x t u r e produces graft copolymers w i t h 12 t o 24 times larger l i m i t i n g v i s cosity numbers w h e n compared t o nonionic p o l y ( l i g n i n - g - l - a m i d o e t h y l e n e ) . A d d i n g 20 mole % sulfonated m o n o m e r t o the reaction m i x t u r e increases p r o d u c t l i m i t i n g viscosity n u m b e r b y a factor o f 2 t o 5. 2 +

2 +

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2 +

For 2-propenamide, the reaction p r o d u c e d a m a x i m u m y i e l d w h e n the c a l c i u m chloride content is at 2 . 4 1 % b y weight o f t o t a l r e a c t i o n mass. I n these nonionic copolymers, the l i m i t i n g viscosity n u m b e r is decreased w i t h an increase o f c a l c i u m chloride content. T h e e l u t i o n v o l u m e o f c o p o l y mers d u r i n g size exclusion c h r o m a t o g r a p h y i n basic aqueous mobile phase is s m a l l e r t h a n t h a t o f l i g n i n . U l t r a v i o l e t spectroscopy a n d size e x c l u sion c h r o m a t o g r a p h y verify the f o r m a t i o n o f graft c o p o l y m e r . These graft copolymers are h i g h l y water soluble, w i l l increase the v i s c o s i t y o f aqueous solutions, a n d can be used as t h i c k e n i n g agents a n d d i s p e r s i n g agents. A cknowledgment s T h i s work was p a r t i a l l y s u p p o r t e d b y the N a t i o n a l Science F o u n d a t i o n under a w a r d number C P E - 8 2 6 0 7 6 6 a n d under N a t i o n a l Science F o u n d a t i o n grant C B T - 8 4 1 7 8 7 6 . S u p p o r t of the copolymer testing p r o g r a m b y A a n d R P i p e l i n e C o m p a n y is gratefully acknowledged. K e v e n A n d e r l e , George M e r r i m a n , J a m e s Z . L a i , D a m o d a r R . P a t i l , M u L a n S h a , N a n c y C h e w , C h i n T i a L i , T h o m a s Bûchers, Cesar A u g u s t i n , H a r v e y C h a n n e l l , a n d others completed a sizable p o r t i o n o f t h i s w o r k a n d their a i d a n d effort is greatly appreciated a n d acknowledged. Literature C i t e d 1. Goheen, D. W . ; Hoyt, C . H . In Kirk-Othmer Encycl. Chem. Technol., 3rd Ed., 1981, 295. 2. Meister, J. J.; Patil, D . R.; Field, L . R.; Nicholson, J. C . J. Polym. Sci., Polym. Chem. Ed. 1984, 22, 1963-1980. 3. Meister, J. J.; Patil, D. R.; Channell, H. J. Appl. Polym. Sci. 1984, 29, 3457-3477. 4. Meister, J. J.; Patil, D. R.; Field, L. R. Macromolecules 1986, 19, 803. 5. Nicholson, J. C.; Meister, J. J.; Patil, D. R.; Field, L . R. Anal. Chem. 1984, 56, 2447-2451. 6. Meister, J. J. In Water-Soluble Polymers in Enhanced Oil Recovery; Stahl, G . Α.; Schulz, D. N . , Eds.; Plenum Publ. Co.: New York, 1988; Ch. 2.

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7. Meister, J . J. In Renewable-Resource Materials: New Polymer Sources; Carraher, C . E., Jr.; Sperling, L . H . , Eds; Plenum Press: New York, 1985; pp. 305-322. 8. Dixon, W . T . ; Norman R. O. C . J. Chem. Soc. 1963, 5, 3119-3124. 9. Meister, J . J.; Patil, D. R. Macromolecules 1985, 18, 1559-1564.

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RECEIVED May 29,1989

Chapter 23

Characteristics and Potential Applications of Lignin Produced by an Organosolv Pulping Process J . H . Lora , C. F. W u , Ε. K. Pye , and J. J. Balatinecz 1

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Repap Technologies Inc., 2650 Eisenhower Avenue, P.O. Box 766, Valley 2

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1

Forge, PA 19482 Faculty of Forestry, University of Toronto, Toronto, Ontario M5S 1A4, Canada The A L C E L L process, a proprietary organosolv pulping process, produces a novel lignin by-product. This lignin has many physical and chemical properties which distin­ guish it from lignins produced by the kraft and sulfite processes. It has a low molecular weight (M ~ 1000), is highly hydrophobic and insoluble in neutral or acidic aqueous media, but soluble in moderate to strong alka­ line solutions and certain organic solvents. It has a T in the range of 130°C. This material, soon to be produced in tonnage quantities from a commercial-scale demon­ stration plant in New Brunswick, Canada, has many po­ tential applications. It shows strong promise as a partial replacement on an equal weight basis for P F resins in waferboard, OSB and other wood composites. The re­ sults of tests of boards made from this material having different characteristics will be presented. Other appli­ cations for this novel lignin will be discussed. n

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O r g a n o s o l v p u l p i n g has been o f considerable interest as a l a b o r a t o r y process for m o s t o f this century, b u t u n t i l recently has not received serious a t t e n t i o n for development as a c o m m e r c i a l process. W i t h i n the last decade, increas­ i n g concern a b o u t t h e c a p i t a l cost a n d scale o f e c o n o m i c a l l y v i a b l e new kraft p u l p m i l l s , together w i t h the p r o b l e m s o f e n v i r o n m e n t a l i m p a c t of c o n v e n t i o n a l c h e m i c a l p u l p p r o d u c t i o n , have caused several c o m p a n i e s t o seriously consider c o m m e r c i a l development o f a l t e r n a t i v e s . A m o n g the a d ­ vantages t o organosolv p u l p i n g processes w h e n c o m p a r e d t o kraft are lower c a p i t a l costs, s m a l l e r scale for e c o n o m i c a l l y a t t r a c t i v e o p e r a t i o n ( w h i c h allows the use o f s m a l l e r w o o d resource areas), significantly lower e n v i r o n ­ m e n t a l i m p a c t , a n d the p r o d u c t i o n o f b y - p r o d u c t s of p o t e n t i a l l y significant c o m m e r c i a l interest. 0097-6156/89/0397-0312$06.00A) © 1989 American Chemical Society

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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M o n t r e a l - b a s e d R e p a p E n t e r p r i s e s C o r p o r a t i o n Inc., is e m b a r k e d o n a c o m m e r c i a l i z a t i o n p r o g r a m for a n organosol ν p u l p i n g process, k n o w n as the A L C E L L process. T h i s process, developed by R e p a p ' s s u b s i d i a r y , R e p a p Technologies Inc., of V a l l e y Forge, P e n n s y l v a n i a , f r o m earlier w o r k of C P . A s s o c i a t e s of M o n t r e a l , is a n aqueous e t h a n o l - b a s e d organosolv p r o ­ cess w h i c h , i n p i l o t p l a n t studies, has p r o d u c e d h a r d w o o d p u l p s t h a t after b l e a c h i n g have c o m p a r a b l e q u a l i t y to bleached k r a f t p u l p s . I n a d d i t i o n , it p r o d u c e s a l i g n i n b y - p r o d u c t h a v i n g i n t e r e s t i n g a n d u n i q u e p r o p e r t i e s . T h i s l i g n i n recovered f r o m p i l o t p l a n t cooks of various h a r d w o o d s has been e x a m i n e d for its c h e m i c a l a n d p h y s i c a l properties a n d has been tested i n n u ­ merous a p p l i c a t i o n s w i t h significant success a n d interest. I n e a r l y 1989 the m a t e r i a l w i l l be available i n tonnage q u a n t i t i e s as a b y p r o d u c t o f a 3 3 - t o n of p u l p / d a y c o m m e r c i a l d e m o n s t r a t i o n p l a n t . It is a n t i c i p a t e d t h a t large a m o u n t s of A L C E L L l i g n i n w i l l be available once the process is w i d e l y used i n d u s t r i a l l y . T h i s paper deals w i t h the characteristics o f A L C E L L l i g n i n as p r o d u c e d f r o m different h a r d w o o d s a n d h a r d w o o d m i x t u r e s a n d discusses p r e l i m i n a r y d a t a a n d o p p o r t u n i t i e s for c o m m e r c i a l a p p l i c a t i o n .

Production In the A L C E L L process, c o n v e n t i o n a l h a r d w o o d chips are cooked i n b a t c h e x t r a c t o r s w i t h a n aqueous e t h a n o l l i q u o r at a p p r o p r i a t e t e m p e r a t u r e s , p H , and t i m e . I n the process l i g n i n , hemicellulose a n d other various c o m p o n e n t s of w o o d are e x t r a c t e d f r o m the chips i n t o the aqueous e t h a n o l f o r m i n g a black liquor. T h i s b l a c k l i q u o r is flashed a n d t h e n the l i g n i n is recovered by a p a t e n t e d p r e c i p i t a t i o n technique followed b y s e t t l i n g , c e n t r i f u g a t i o n (or fil­ t r a t i o n ) a n d d r y i n g . T h e result is a fine, b r o w n , free-flowing powder. M o r e details o n h o w A L C E L L l i g n i n is o b t a i n e d c a n be f o u n d i n the l i t e r a t u r e (1.2).

Properties A L C E L L l i g n i n has a low m o i s t u r e content (less t h a n 2 % w a t e r ) . It has a b u l k density of 0.57 k g / L . T h e m a t e r i a l is soluble i n some o r g a n i c solvents and also i n d i l u t e aqueous a l k a l i s o l u t i o n s . It is i n s o l u b l e i n w a t e r under n e u t r a l or a c i d i c c o n d i t i o n s . A L C E L L l i g n i n s t h a t have been a n a l y z e d for m o l e c u l a r weight have a n u m b e r average m o l e c u l a r weight lower t h a n 1,000 a n d p o l y d i s p e r s i t i e s be­ tween 2.4 a n d 6.3 ( G l a s s e r , W . G . , p e r s o n a l c o m m u n i c a t i o n , 1984, V i r g i n i a Polytechnic Institute and State University, Blacksburg, V A ) . M o r e detailed studies are s t i l l r e q u i r e d to correlate e x t r a c t i o n a n d recovery c o n d i t i o n s w i t h m o l e c u l a r weight i n f o r m a t i o n . A L C E L L l i g n i n s n o r m a l l y have softening p o i n t s i n the 138-147° C range. D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y studies of a s p e n , b i r c h a n d red oak A L C E L L l i g n i n s ( M c G h i e , A . R . , p e r s o n a l c o m m u n i c a t i o n , 1984, U n i v e r s i t y of P e n n s y l v a n i a , P h i l a d e l p h i a , P A ) show a n e n d o t h e r m i c peak between 50 a n d 75° C ( F i g u r e 1). T h e r m o g r a v i m e t r i c a n a l y s i s suggests t h a t t h i s peak

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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F i g u r e 1. D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r i c analysis of A L C E L L l i g n i n s .

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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p r o b a b l y corresponds to loss of absorbed w a t e r . B e t w e e n 100 a n d 125°C a b r o a d e n d o t h e r m i c peak s t a r t s . T h i s i n d i c a t e s the onset o f c h a i n segment m o t i o n a n d corresponds t o the glass t r a n s i t i o n t e m p e r a t u r e . T h e b r o a d e n d o t h e r m i c peak has a m a x i m u m at a b o u t 2 0 0 ° C . A t t h i s t e m p e r a t u r e a n e x o t h e r m i c r e a c t i o n s t a r t s w h i c h is a c c o m p a n i e d b y increased weight loss. It m u s t be n o t e d t h a t between 100 a n d 2 0 0 ° C there are three s m a l l peaks s u p e r i m p o s e d o n the b r o a d e n d o t h e r m i c p e a k . T h e y seem to o c c u r at a b o u t the same t e m p e r a t u r e s for a l l samples a n a l y z e d . F u r t h e r w o r k is r e q u i r e d to d e t e r m i n e the significance of t h i s o b s e r v a t i o n . In spite of its low degree of p o l y m e r i z a t i o n , A L C E L L l i g n i n to some extent resembles l i g n i n i n i t s n a t i v e state. F o r i n s t a n c e , w h e n reacted w i t h p h l o r o g l u c i n o l under a c i d c o n d i t i o n s A L C E L L l i g n i n gives a p u r p l e c o l ­ o r a t i o n . T h i s suggests t h a t some of the c i n n a m a l d e h y d e e n d u n i t s c h a r a c ­ teristic o f l i g n i n i n i t s n a t i v e state are s t i l l present i n A L C E L L l i g n i n a n d / o r t h a t some have f o r m e d d u r i n g the e x t r a c t i o n process. T a b l e I shows a t y p ­ i c a l e l e m e n t a l a n a l y s i s for aspen A L C E L L l i g n i n . A s a reference aspen m i l l e d w o o d l i g n i n ( M W L ) has been i n c l u d e d . T a b l e I. E l e m e n t a l A n a l y s i s Aspen A L C E L L Lignin (%)

A s p e n M W L (3) (%) 59.96 6.19 33.85

64.04 6.20 29.65 0.11 17.09

c H 0 Ash Methoxyl

20.42

C formulae for the M W L a n d the A L C E L L l i g n i n are respectively C9Hs.74O3.02 ( O C H 3 ) 7 a n d C H . 5 0 2 . 4 5 ( O C H ) i . 4 - A s observed, the A L C E L L l i g n i n has less oxygen a n d less m e t h o x y l per C u n i t t h a n the M W L . These differences i n d i c a t e t h a t the A L C E L L l i g n i n has undergone some m o d i f i c a t i o n s w h i c h m a y i n c l u d e self-condensation, c o n d e n s a t i o n w i t h f u r f u r a l generated i n the A L C E L L process, a n d / o r i n c o r p o r a t i o n o f e t h a n o l . T h e low c a r b o h y d r a t e a n d low ash content together w i t h the h i g h c a r b o n content t r a n s l a t e i n t o a h e a t i n g value of a b o u t 26,700 J / g (11,500 B t u / l b ) . U V spectra of neutral solutions of A L C E L L lignins exhibited m a x i m u m at 205-210 n m a n d at 275-281 n m w h i c h are c h a r a c t e r i s t i c of other l i g n i n p r e p a r a t i o n s . A l k a l i - n e u t r a l difference s p e c t r a e x h i b i t e d three m a x i m a at a b o u t 252-254 n m , 296-300 a n d 363-366 n m w h i c h i n d i c a t e the presence of a r o m a t i c h y d r o x y l , o>conjugated h y d r o x y Is, a n d c o n j u g a t e d c a r b o n y l groups. T h e l a t t e r includes c a r b o n y l groups i n the α-position as w e l l as those i n c i n n a m a l d e h y d e u n i t s m e n t i o n e d above. T h e a l k a l i - n e u t r a l differ­ ence s p e c t r u m of A L C E L L l i g n i n s reduced w i t h s o d i u m b o r o h y d r i d e shows an a l m o s t complete e l i m i n a t i o n of the peak at 360-366 n m a n d a n increase 9

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i n the 296-300 n m peak, t h u s c o n f i r m i n g the presence of conjugated carb o n y l groups. T h e a l k a l i - n e u t r a l difference s p e c t r a of reduced samples also show a shoulder at about 330 n m , w h i c h indicates the presence of some α , β e t h y l e n i c groups p r o b a b l y i n the f o r m of p h e n y l c o u m a r o n e t y p e s t r u c t u r e s . P h e n y l c o u m a r o n e s t r u c t u r e s have been f o u n d a m o n g the p r o d u c t s of a c i d degradation of lignins (4,5). I n general, the I R s p e c t r a of A L C E L L l i g n i n s is v e r y s i m i l a r t o the I R s p e c t r a of m i l l e d w o o d l i g n i n s . P e r h a p s the most s t r i k i n g difference is the increase i n a b s o r p t i o n at 1700-1720 c m w h i c h is a t t r i b u t e d to the presence of ^ - u n c o n j u g a t e d ketone groups. T h i s b a n d is c o m m o n t o other l i g n i n s generated under m i l d a c i d c o n d i t i o n s , such as a u t o h y d r o l y s i s or s t e a m e x p l o s i o n l i g n i n s ( 3 , 6 , 7 ) . R e c e n t l y , F T I R has been used o n red oak A L C E L L l i g n i n s (8). B y the use of d e c o n v o l u t i o n a n d second-derivative spectroscopy, r e s o l u t i o n was enhanced d r a m a t i c a l l y , a n d very weak bands not v i s i b l e i n the o r i g i n a l s p e c t r u m became apparent ( F i g . 2). Some of the d a t a suggests the presence of v i n y l a n d t r a n s - d i s u b s t i t u t e d olefins i n the s a m p l e e x a m i n e d . T h e use o f these enhancement techniques is expected to p l a y a very i m p o r t a n t role i n future s t r u c t u r a l studies. T h e phenolic n a t u r e of the A L C E L L l i g n i n translates i n t o r e a c t i v ­ ity w i t h formaldehyde. T h u s , w h e n formaldehyde a n d A L C E L L l i g n i n (2.2 moles of f o r m a l d e h y d e / C u n i t ) are heated at 9 6 ° C a n d p H 10.8 for 75 m i n u t e s , about 1.6 moles H C H O are i n c o r p o r a t e d for each C u n i t of A L C E L L l i g n i n . T h i s figure is i n the range of figures r e p o r t e d for sulfite l i g n i n s (1.6-2.1 mole H C H O / C u n i t ) a n d is higher t h a n w h a t has been r e p o r t e d for k r a f t lignins (0.1-0.5 mole H C H O / C u n i t ) (9).

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Applications F o r m a n y years w o o d chemists have t r i e d to find a p p l i c a t i o n s for l i g n i n s other t h a n their use as fuel. T h e a m o u n t of proposed p r o d u c t s a n d a p p l i ­ cations is considerable. F o r instance, a recent l i t e r a t u r e survey o n l i g n i n u t i l i z a t i o n includes more t h a n 3700 references, m o s t l y patents (10). In spite of t h i s massive a m o u n t of work o n p r o d u c t s , processes a n d a p p l i c a ­ t i o n s , less t h a n 2 % of l i g n i n available i n spent l i q u o r s f r o m c o n v e n t i o n a l p u l p i n g processes are recovered a n d m a r k e t e d for n o n - f u e l a p p l i c a t i o n s i n the U . S . A L C E L L l i g n i n c o u l d compete i n m a n y a p p l i c a t i o n s n o w b e i n g filled b y lignosulfonates a n d k r a f t l i g n i n , b u t i t is believed t h a t u n i q u e h i g h e r value m a r k e t s can be developed. These a p p l i c a t i o n s w i l l be h e l p e d b y the low m a r g i n a l cost of p r o d u c i n g A L C E L L l i g n i n a n d w i l l take advantage of its phenolic n a t u r e a n d r e a c t i v i t y w i t h formaldehyde as w e l l as of the p r o p e r t i e s t h a t differentiate i t f r o m other l i g n i n s . T h e l a t t e r i n c l u d e h y d r o p h o b i c i t y , lack of i n o r g a n i c c o n t a m i n a n t s , low m o l e c u l a r weight, n a r r o w m o l e c u l a r weight d i s t r i b u t i o n , m e l t ability, b i o d e g r a d a b i l i t y , e n v i r o n m e n t a l a c c e p t a b i l i t y , etc. S o m e of the a p p l i c a t i o n s for A L C E L L l i g n i n t h a t have been e x p l o r e d or considered are s h o w n i n T a b l e I I . O n e a p p l i c a t i o n t h a t has been r e p o r t e d

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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RED OflK LIGNIN

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1900

1700

1500 1300 1100 WAVENUMQER (CM'*)

900

Figure 2. F U R spectra of red oak A L C E L L lignin. (Reprinted from ref. 8. Copyright 1987 American Chemical Society.)

T a b l e II. A L C E L L L i g n i n A p p l i c a t i o n s

• W o o d adhesives • MF loalmd ien gr e tcaormdpa no ut sn d s • Diesel fuel a d d i t i v e • P a p e r m a k i n g additives • Slow release of a g r i c u l t u r a l , v e t e r i n a r y • c e u t i c a l chemicals

and pharma-

• IFnrsi cutliaotni o nm amt eartiearlisa l s • Surfactants • A s p h a l t extender • • RMuebdbi cear l areinforcement ications • E n g i n e e r i npgp lplastics • Antioxidants • L i g n i n - d e r i v e d chemicals •

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LIGNIN: PROPERTIES AND MATERIALS

318

i n the l i t e r a t u r e (11) is the use of t h i s l i g n i n after h y d r o x y p r o p y l a t i o n as a c o m p o n e n t i n fire-resistant p o l y u r e t h a n e foams. Recent w o r k has concentrated o n the use of A L C E L L l i g n i n as a s u b s t i t u t e for p h e n o l - f o r m a l d e h y d e resins i n w o o d adhesives, p a r t i c u l a r l y waferb o a r d . Some of the results o b t a i n e d w h e n a P F resin (Bakélite 9111) was replaced w i t h different levels of h a r d w o o d A L C E L L l i g n i n i n w a f e r b o a r d m a n u f a c t u r e w i l l be briefly discussed below. T a b l e I I I shows the c o n d i t i o n s used for w a f e r b o a r d m a n u f a c t u r e .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch023

T a b l e I I I . C o n d i t i o n s U s e d for W a f e r b o a r d M a n u f a c t u r e A d h e s i v e weight, % o n wafers W a x emulsion (Paracol 802N) Pressure Temperature T i m e at t e m p e r a t u r e

2.6% 1.7% 3,800 K P A (550 psig) 200° C 5 min.

I n i t i a l l y three A L C E L L l i g n i n samples were e v a l u a t e d : a c i d ( p H 3.95), n e u t r a l ( p H 7.51), a n d a l k a l i n e ( p H 8.96). T h e m o i s t u r e content of l i g n i n P F b o n d e d boards ranged f r o m 4.1 to 4.8%, w h i c h is w e l l w i t h i n the 8% allowable l i m i t of c o m m e r c i a l grade w a f e r b o a r d . T h e thickness s w e l l i n g of b o a r d s b o n d e d w i t h 5 0 % or less l i g n i n ranged f r o m 14.7 to 1 7 . 1 % after 24 hours i m m e r s i o n . It c o m p a r e d w e l l w i t h the c o n t r o l a n d was s i g n i f i c a n t l y better t h a n the 2 5 % m a x i m u m allowable i n C a n a d i a n S t a n d a r d s A s s o c i a t i o n ( C S A ) S t a n d a r d s . S i m i l a r l y , water a b s o r p t i o n values were w i t h i n acceptable l i m i t s w h e n l i g n i n content was under 5 0 % . B o a r d s b o n d e d w i t h 1 0 0 % A L C E L L l i g n i n d i d not give a w a t e r p r o o f b o n d a n d d e l a m i n a t e d following 24 hours i m m e r s i o n . A s observed i n F i g u r e 3, boards b o n d e d w i t h 3 0 % a c i d , n e u t r a l , or a l k a l i n e A L C E L L l i g n i n have a l m o s t i d e n t i c a l i n t e r n a l b o n d i n g ( I B ) as the c o n t r o l . W h e n l i g n i n content increased, the I B became lower, especially for n e u t r a l A L C E L L l i g n i n . B o a r d s b o n d e d w i t h 5 0 % or less l i g n i n met the m i n i m u m C S A requirement w h i c h is 50 p s i . B o a r d s b o n d e d w i t h alkaline l i g n i n h a d the highest I B a m o n g a l l the l i g n i n - c o n t a i n i n g boards. B o a r d s b o n d e d w i t h u p t o 5 0 % A L C E L L l i g n i n h a d m o d u l u s of r u p t u r e ( M O R ) t h a t surpassed the m i n i m u m C S A requirement b y 4 0 % or m o r e . A l l of the boards c o n t a i n i n g l i g n i n h a d a lower M O R t h a n the c o n t r o l ( 1 0 0 % = P F resin). A s s h o w n i n F i g u r e 4, the replacement of P F resin b y A L C E L L l i g n i n under the c o n d i t i o n s used i n t h i s s t u d y resulted i n a decrease i n M O R . A c i d l i g n i n showed the highest M O R a m o n g l i g n i n - c o n t a i n i n g b o a r d s . A t 1 0 0 % s u b s t i t u t i o n there was no significant difference i n M O R a m o n g the l i g n i n s w i t h different p H levels. T h e M O R r e t e n t i o n , w h i c h is the r a t i o of wet M O R to d r y M O R , is s h o w n i n F i g u r e 5. A L C E L L l i g n i n tends to preserve the M O R s t r e n g t h at

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LORAETAL.

Lignin Produced by an Organosol Pulping Process

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch023

23.

319

-4-3

β β Ο

-4-3

Ο

>> -4J

.3

> PQ H-1

eô M

S3 bO

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

320

LIGNIN: PROPERTIES AND MATERIALS

6\ Ο

Ο m

c ο υ πτπτπ

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch023

Û Ζ LU Ο LU

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. Lignin

Neutral Type

Alkaline

Control

F i g u r e 5. M O R r e t e n t i o n v s . l i g n i n t y p e a n d content.

Acid

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch023

LEGEND

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989. MOR—+—Wet MOR

I

pH

I

Control Dry M O R

8

F i g u r e 6. L i g n i n p H vs. d r y a n d wet M O R .

Lignin

6

—β— Dry

4

I

2

I

0

I

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch023

I

I

12

Control Wet M O R

10

23.

LORA ET AL.

Lignin Produced by an Organosolv Pulping Process

323

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch023

least as w e l l as P F resin alone when 5 0 % or less l i g n i n was used. B o a r d s b o n d e d w i t h 3 0 % alkaline a n d n e u t r a l l i g n i n appeared t o r e t a i n over 8 0 % of t h e i r d r y M O R s t r e n g t h . T h i s indicates t h a t boards b o n d e d w i t h c e r t a i n l i g n i n - P F m i x t u r e s m a y have a better weather resistance c a p a b i l i t y t h a n the c o m m e r c i a l P F resins. S o m e o f the most recent w o r k has focused o n evaluations o f A L C E L L lignins outside t h e p H range i n i t i a l l y s h o w n i n F i g u r e 6. W h e n A L C E L L l i g n i n replaced 3 0 % o f the P F resin a n d i t s a l k a l i n i t y o r t h e a c i d i t y were increased, d r y M O R values above 9 0 % o f the M O R o f the c o n t r o l ( 1 0 0 % P F resin) were o b t a i n e d . T h i s shows the i m p o r t a n c e o f p H o n performance. F u t u r e w o r k w i l l i n c l u d e a more detailed look at f o r m u l a t i o n s , pressing c o n d i t i o n s , a n d d e r i v a t i z a t i o n as a way o f o b t a i n i n g a better adhesive. Conclusions Several a p p l i c a t i o n s have been explored w i t h significant success a n d i n t e r ­ est u s i n g organosolv l i g n i n available f r o m a p i l o t p l a n t . T h i s l i g n i n e x h i b i t s i n t e r e s t i n g p h y s i c o c h e m i c a l properties w h i c h d i s t i n g u i s h i t f r o m l i g n i n s p r e ­ v i o u s l y available o n a c o m m e r c i a l scale. L a r g e r volumes are expected t o be available b y t h e e n d o f t h e decade s t i m u l a t i n g t e c h n i c a l a n d m a r k e t developments for t h i s p r o d u c t . Literature C i t e d 1. 2. 3. 4. 5. 6. 7. 8.

9. 10. 11.

Lora, J . H . ; Aziz, S. Tappi J. 1985, 68(8), 94-97. Williamson, P. N. Pulp and Paper Canada 1987, 88(12), 47-49. Lora, J . H.; Wayman, M . Can. J. Chem. 1980, 58(7), 669-676. Adler, E . ; Lundquist, K . Acta Chem. Scand. 1963, 17, 13-26. Sarkanen, Κ. V . ; Ludwig, C . H . , Eds. Lignins; John Wiley and Sons: New York, 1971; 253. Marchessault, R. H.; Coulombe, S.; Morikawa, H . ; Robert, D. Can. J. Chem. 1982, 60(18), 2372-82. Chua, M . G . S.; Wayman, M . Can. J. Chem. 1979, 57(19), 2603-11. Byler, D. M . ; Gerasimowicz, W . V . ; Susi, H.; Cronlund, M . ; Lora, J . H. Polym. Prep. (Am. Chem. Soc., Div. Polym. Chem.) 1987, 28(2), 260-261. Gillespie, R. H . FPRS Adhesives Symp. Proc. 1985. Boye, F. Utilization of Lignins and Lignin Derivatives; Bib. Ser. No. 292; Inst. of Paper Chem., Appleton, WI. Glasser, W . G . ; Leitheiser, R. H . Polym. Bull. 1984, 12, 1-5.

RECEIVED February 27,1989

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 24

Organosolv Lignin-Modified Phenolic Resins Phillip M . Cook and Terry Sellers, Jr. 1

1

2

Eastman Kodak Company, Eastman Chemicals Division, P.O. Box 1972, Kingsport, TN 37662 Forest Products Utilization Laboratory, P.O. Drawer FΡ, Mississippi State, MS 39762

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

2

An adhesive system for structural wood panels is demon­ strated in which at least 35% of the resin solids of a phenol-formaldehyde resin are successfully replaced with organosolv hardwood lignin. The bulk properties of the lignin were characterized before and after its purifica­ tion with aqueous sodium bicarbonate solution. Phenolic resins are described that have been prepared from both purified and non-purified (crude) lignin. The nature of residues removed from the lignin during purification and their effects on resin adhesive properties are also briefly described. Evaluations of the lignin-modified phenolic resins were carried out on a small scale by measuring the lap-shear strength of parallel laminated maple blocks, and on a large scale by performing strength and dimen­ sional tests on southern pine flake boards (waferboard or strandboard types). Flake board tests included internal bond, static bending (modulus of rupture, M O R ) , water absorption, and thickness swelling. The M O R was mea­ sured on both dry specimens and specimens subjected to accelerated aging wet-dry cycles. Both maple block and flakeboard evaluations included available commer­ cial phenolic resins as controls. L i g n i n makes u p a b o u t one-quarter o f the weight o f d r y w o o d a n d is sec­ o n d o n l y t o cellulose as t h e most a b u n d a n t n a t u r a l l y o c c u r r i n g p o l y m e r . P u l p i n g m e t h o d s w h i c h use o r g a n i c solvents are p a r t i c u l a r l y well-suited t o solubilize the lignins for l i g n i n isolation a n d are r e a d i l y c o u p l e d w i t h solvent recovery (1). D e s p i t e these facts, there are n o large v o l u m e o r g a n o s o l v p u l p ­ i n g processes or c o m m e r c i a l p r o d u c t s based u p o n organosolv l i g n i n ( O S L ) i n the U n i t e d States. 0097-6156/89/0397-0324$06.00/0 © 1989 American Chemical Society

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

24.

COOK & SELLERS

Organosolv Lignin-Modified Phenolic Resins

325

L i g n i n s are p h e n o l i c - l i k e p o l y m e r s t h a t f r o m t i m e t o t i m e have been considered for use as a p h e n o l replacement i n p h e n o l - f o r m a l d e h y d e ( P F ) resins. T o d a y , however, very l i t t l e l i g n i n is used i n p h e n o l i c resins. P u r i f i e d k r a f t l i g n i n s have been suggested as a p h e n o l s u b s t i t u t e , b u t the price o f such l i g n i n s has been s t r u c t u r e d to be e q u a l to t h a t of p h e n o l , a n d resin adhesive suppliers have resisted i t s use. V e r y l i t t l e has been p u b l i s h e d o n the use of O S L i n phenolic adhesives despite the fact t h a t these l i g n i n s are generally f o u n d to have a higher p u r i t y a n d r e a c t i v i t y t h a n l i g n i n s f r o m conventional p u l p i n g methods. T h e most p r o m i n e n t w o o d adhesives used over the last q u a r t e r of a c e n t u r y have been a m i n o p l a s t a n d p o l y p h e n o l i c types (2). I n the U n i t e d States, p o l y p h e n o l i c adhesives continue t o be p r e d o m i n a n t l y used for p r o d u c t i o n of weather-resistant w o o d p r o d u c t s , such as s t r u c t u r a l p l y w o o d s and flake boards (3). P h e n o l i c r e s i n prices have increased over the past decade, generally p a r a l l e l i n g p h e n o l prices. T h i s increase has o c c u r r e d i n p a r t due to a c o n t i n u i n g erosion of U n i t e d States p h e n o l m a n u f a c t u r i n g c a p a c i t y a n d the c o r r e s p o n d i n g increase i n a v a i l a b i l i t y o f p h e n o l f r o m other countries. A n y significant increase i n the price of o i l (the source of phenol) itself or i n t e r r u p t i o n i n s u p p l y w i l l o n l y c o m p o u n d the p r o b l e m a n d raise p h e n o l prices even higher. T h e o b j e c t i v e o f t h i s w o r k was to d e m o n s t r a t e the u t i l i t y o f organosolv red oak l i g n i n (a projected cheaper p o l y p h e n o l t h a n phenol) i n p h e n o l i c adhesives for w o o d composites. T h i s w o r k i n v o l v e d three stages: 1. A n a l y t i c a l c h a r a c t e r i z a t i o n of red oak O S L . 2. R e s i n synthesis of O S L - m o d i f i e d p h e n o l - f o r m a l d e h y d e resins. 3. E v a l u a t i o n of l i g n i n - m o d i f i e d resins used to b o n d m a p l e blocks a n d s o u t h e r n p i n e flake boards. Results and Discussion Analytical Characterization. A s expected, red oak O S L c o n t a i n s m u c h less sulfur a n d ash b u t more c a r b o h y d r a t e s t h a n k r a f t l i g n i n ( T a b l e I) (kraft l i g n i n i n c l u d e d for c o m p a r i s o n ) . T h e m o l e c u l a r weight a n d p o l y d i s p e r s i t y ( T a b l e II) are less for red oak O S L t h a n for k r a f t l i g n i n ( I n d u l i n A T , W e s t vaco, C h a r l e s t o n , S C ) , a n d O S L has g o o d s o l u b i l i t y i n o r g a n i c solvents ( T a b l e I). S o l u b i l i t y i n r e f l u x i n g methylene chloride was s u r p r i s i n g l y h i g h . P u r i f i c a t i o n of the O S L b y aqueous r e s l u r r y i n 1 0 % s o d i u m b i c a r b o n a t e s o l u t i o n increases the softening t e m p e r a t u r e ( T a b l e II). T h e r m o g r a v i m e t r i c weight loss for the O S L is s i m i l a r to t h a t of k r a f t l i g n i n . E x c e p t for a s l i g h t l y elevated m e t h o x y l content, the N M R a n d d e g r a d a t i o n results i n T a b l e II are w i t h i n the expected range for a h a r d w o o d lignin. OSL Impurities. It was also of interest to d e t e r m i n e the i m p u r i t i e s removed f r o m crude O S L b y r e s l u r r y i n aqueous s o d i u m b i c a r b o n a t e , w h i c h was done to i m p r o v e its usefulness i n p h e n o l i c resins ( C o o k , P . M . , E a s t m a n K o d a k at K i n g s p o r t , T N , p e r s o n a l c o m m u n i c a t i o n s , 1987). E x t r a c t i o n a n d acetyl a t i o n procedures, i n v o l v i n g methylene c h l o r i d e , acetic a n h y d r i d e p y r i d i n e

LIGNIN: PROPERTIES AND MATERIALS

326

T a b l e I. L i g n i n c h a r a c t e r i z a t i o n ( b u l k a n d soi l u b i l i t y properties) Amount Kraft Lignin

Crude OSL

% %

97

97

97

A s h , 775°C

1.94

1.13

3.48

Carbohydrates: (Extraction-HPLC)

%

3.0

1.1

0.7

Combustion: C H Ν S

% % % %

59.85 5.87 0.27 0.24

60.94 5.63 Trace 0.04

61.99 5.65 0.52 1.68

E x t r a c t i o n (weight loss): E t h e r , reflux H e p t a n e , reflux M e t h y l e n e chloride, reflux Water, 25°C Water, 60°C W a t e r , 100°C

% % % % % %

6 < 1 50 5 12 5*

Non-volatiles

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

Purified OSL

Basis

A n a l y t i c a l Text

* S a m p l e agglomerates S o l u b i l i t y (25° C ) : Methanol Ethanol n-Propanol 2-Propanol Acetic A c i d Acetone 2-Butanone Acetonitrile E t h y l Acetate

1

3 < 1 11 2 6 3*

severely. g/L g/L g/L g/L g/L g/L g/L g/L g/L

-

105 53 35 15 108 104 96 86 59

-

-

-

-

I n d u l i n A T b y Westvaco, C h a r l e s t o n , S C ; a purified pine l i g n i n . a n d water, were followed w h i c h p r o d u c e d three residues f r o m the i m p u r i ­ ties a n d each was s u b m i t t e d for G C / M S a n d H N M R analyses. R e s i d u e 1 proved to be nearly a l l l i g n i n - r e l a t e d p r o d u c t s . Residues 2 a n d 3 were f o u n d p r i n c i p a l l y to c o n t a i n f u l l y acetylated m o n o m e r i c C5 a n d Ce sugars w h i c h were also C i alcoholic glycosides. R e s u l t s of G C / M S investigations of the residues i n d i c a t e d t h a t the l o w - m o l e c u l a r - w e i g h t i m p u r i t i e s (e.g., m o n o - f u n c t i o n a l l i g n i n - r e l a t e d species, waxes, a n d c a r b o h y d r a t e s ) s h o u l d be removed to i m p r o v e the O S L r e a c t i v i t y . T h e extent of i m p u r i t y r e m o v a l can be a p p r o x i m a t e d by m e a s u r i n g gelation t i m e (i.e., the higher the i m p u ­ r i t y content, the longer the gel t i m e ) . F o r e x a m p l e , the g e l a t i o n t i m e (using 1

24.

COOK & SELLERS

327

Organosolv Lignin-Modified Phenolic Resins

T a b l e II. P h y s i c a l a n d c h e m i c a l c h a r a c t e r i z a t i o n of l i g n i n Amount

Basis

Crude OSL

Purified OSL

Kraft Lignin

softening-initial: (TMA)

°C

89

124

124

softening-final : (TMA)

°C

111

138

169

% % % % % %

1 3 5 18 44 55

0 1 2 10 38 49

1 3 6 12 26 51

2227 906 2.46

2030 925 2.19

2479 523 4.32

22.04 (1.55) 1.33

-

13.70 (0.81) < 1

0.60-0.65 0.55-0.60 1.90-1.95 3.60-3.70 1.15-1.25

-

0.57-0.62 0.70-0.72 2.50-2.55 4.25-4.30 1.35-1.40

A n a l y t i c a l Test T

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

T

T G A (weight loss): 50°C 100°C 200°C 300°C 400°C 500°C

G P C m o l e c u l a r properties: (CH C1 /HFIP, Styragel Col.) M 2

1

2

W

M

N

M /M W

N M R analysis: OCH

%

3

Syringyl/guaiacyl Bonds: OH (Phenolic) O H (Aliphatic) H (Aromatic) H (Aliphatic) H (Hydroxyl)

N

(bonds/Cg unit) ratio per per per per per

C9 C9 C9 C9 C9

unit unit unit unit unit

Source: G l a s s e r , W . G . R e p o r t to P . M . C o o k . L o c a t e d at E a s t m a n C h e m i c a l D i v i s i o n , Research L a b o r a t o r y , P . O . B o x 1972, K i n g s p o r t , T N 27662 (1984). 1

I n d u l i n A T b y Westvaco, C h a r l e s t o n , S C ; a purified pine l i g n i n .

a S u n s h i n e G e l Tester) at 100°C (212°F) was 21 minutes for a P F resin sol u t i o n , 26 minutes for a purified O S L / P F resin b l e n d , a n d 53 m i n u t e s for an u n p u r i f i e d O S L / P F resin b l e n d . T h e procedure involves b l e n d i n g d r y l i g n i n solids w i t h a P F resin s o l u t i o n to a 2 3 % l i g n i n c o n c e n t r a t i o n a n d a d j u s t i n g w i t h water a n d 5 0 % s o d i u m h y d r o x i d e to the p H (e.g., 1 1 . 1 ± ) a n d viscosity (e.g., 500 ± 50 c P ) of the P F resin. Block Lap-Shear Results. F o r l a m i n a t e d m a p l e w o o d , this w o r k i n d i c a t e d a m a x i m u m of 4 0 % of the P F resin solids can be replaced w i t h O S L w i t h o u t

LIGNIN: PROPERTIES AND MATERIALS

328

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d e t r i m e n t a l l y affecting adhesive properties ( T a b l e III) ( C o o k , P . M . , E a s t m a n K o d a k at K i n g s p o r t , T N , p e r s o n a l c o m m u n i c a t i o n s , 1987). O r g a n o solv l i g n i n - P F resins were at least equivalent t o the c o m m e r c i a l (control) resin a n d o u t - p e r f o r m e d k r a f t l i g n i n - b a s e d P F resins at the 3 5 % a n d 4 0 % solids replacement levels ( T a b l e I I I ) . P u r i f i e d O S L generally y i e l d e d better results t h a n u n p u r i f i e d . A d i s t r a c t i n g q u a l i t y of k r a f t l i g n i n resins is the s u l f u r - l i k e odor p r o d u c e d d u r i n g resin p r e p a r a t i o n a n d p a n e l hot pressing. Use o f O S L alleviates t h i s p r o b l e m . T h e reasons w h y O S L o u t - p e r f o r m e d k r a f t l i g n i n i n t h i s w o r k are not clear, b u t are likely r e l a t e d to the m o l e c u l a r weight characteristics of the O S L a n d its ease of s o l u b i l i z a t i o n . B a s e d u p o n the p r o p o s e d s t r u c t u r e s of h a r d w o o d a n d softwood l i g n i n s , the c o n t r a r y w o u l d have been p r e d i c t e d (i.e., the higher s y r i n g y l / g u a i a c y l r a t i o s of h a r d w o o d w o u l d be expected to be more d e t r i m e n t a l to b o n d i n g ) . T a b l e I I I . Selected m a p l e b l o c k test results Dry Bond

4-Hour Boil

Strength Lignin Shear Wood Shear Wood Retention Replacement Strength Failure Strength Failure ( D r y / W e t ) (%) (MPa) (%) (MPa) (%) (%)

Resin T y p e

1

Control P F OSL-PF (crude l i g n i n )

0

5.18

80

3.08

0

60

24

4.99

100

2.54

30

51

OSL-PF (CH C1 extracted)

34

5.35

100

3.02

40

57

Kraft L - P F (Indulin A T )

35

4.25

90

1.83

0

43

OSL-PF (NaHC0 washed)

40

5.60

60

3.37

30

60

40

4.14

40

1.90

10

46

45

2.68

20

1.00

0

37

2

2

2

3

Kraft L - P F (Indulin A T ) OSL-PF (crude l i g n i n ) 1

2

2

M u l t i p l y M P a b y a factor of 145 to convert to p s i . T h i s resin also contained 1% m e l a m i n e .

Flake Board Test Results. R e s u l t s f r o m i n i t i a l screening tests l o o k e d p r o m i s i n g for the use of k r a f t pine l i g n i n a n d organosolv h a r d w o o d l i g n i n at 2 5 % s u b s t i t u t i o n for p h e n o l i n P F resins used to b o n d flake boards. Therefore, t h i s s t u d y was designed to concentrate o n i m p r o v i n g the O S L - P F cook p r o cedure, increase the p h e n o l s u b s t i t u t i o n to 3 5 % , a n d measure these effects b y e x p a n d i n g the b o a r d test c r i t e r i a (4). I n general, the p u r i f i e d O S L - P F

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329

resins as well as the u n p u r i f i e d O S L - P F resins p e r f o r m e d e q u a l t o , or b e t ­ ter t h a n , the c o n t r o l c o m m e r c i a l resins a n d the c o n t r o l resins c o n t a i n i n g c o m p a r a b l e s u b s t i t u t i o n a m o u n t s of p e c a n shell flour (vs. O S L ) i n a l l test p a n e l properties e x a m i n e d (Table I V ) . T a b l e I V . Selected test results of flake boards

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

Physical Property Density

L a b o r a t o r y Test R e s u l t s Sampling of F o u r Control Resin Β 35% O S L USA Mills 100% P F 3 5 % P S Purified Crude (1986)

Units avg.

kg/m

1

3

650-700

(average o f boards was 753)

Internal bond M o d u l u s of rupture

avg.

kPa

340-460

510

386

717

538

avg.

MPa

22-38

33

33

34

34

Accelerated aging

%of dry M O R

50-70

76

75

77

70

Water absorption

%

25-34

33

35

25

19

Thickness swell

%

12-15

16

25

15

11

R e s i n solids applied

%

3-5

5

3.25

5

5

These panels were b o n d e d w i t h a r e s i n s o l u t i o n c o n t a i n i n g 6 5 % P F and 3 5 % p e c a n shell ( P S ) flour, d e l i v e r i n g 3.25% resin solids to the furnish. N o t e : T o convert m e t r i c to E n g l i s h u n i t s — k g / m to l b / f t , m u l t i p l y b y a factor of 0.0624; k P a to p s i , m u l t i p l y b y a factor of 0.145; M P a to p s i , m u l t i p l y b y a factor of 145.

1

3

3

Use of p o w d e r e d l i g n i n s as a n extender at 2 5 % to 3 5 % replacement of P F solids i n l i q u i d c o m m e r c i a l resins is i m p r a c t i c a l because of p r o b l e m s of d i s p e r s i o n , viscosity, a n d s t a b i l i t y w h i c h h i n d e r subsequent u n i f o r m resin s p r a y a p p l i c a t i o n . However, s u b s t i t u t i o n of l i g n i n for p h e n o l at levels of 35 weight percent, or higher, i n cooked l i g n i n - p h e n o l - f o r m a l d e h y d e c o p o l y m e r s is p r a c t i c a l . W h i l e i m p u r e (crude) O S L cooked into a P F resin a n d used to b o n d flake boards y i e l d e d s i m i l a r b o a r d properties to cooked p u r i f i e d O S L i n P F resins, the i m p u r e l i g n i n was troublesome d u r i n g the cook procedures, f o r m i n g gels u p o n l o n g m e t h y l o l - l i g n i n c o n d e n s a t i o n . I m p u r e l i g n i n was m o r e g r i t t y t h a n purified l i g n i n a n d some extraneous m a t e r i a l m a y have settled r a t h e r t h a n dissolve or suspend i n the cooked resins. I m p u r e l i g n i n required a n a d j u s t m e n t i n the water i n b o t h steps of the cook t o y i e l d a satisfactory n o n - v o l a t i l e solids content. If a n y coarse l i g n i n settled i n the cooked resin, t h i s m a y p a r t i a l l y e x p l a i n the lower percent n o n - v o l a t i l e solids p h e n o m e n o n w i t h resins i n c o r p o r a t i n g i m p u r e l i g n i n .

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330

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

Conclusions It has been d e m o n s t r a t e d t h a t red oak O S L c o u l d be used t o replace 3 5 % to 4 0 % o f the p h e n o l (or phenolic resin solids) i n p h e n o l - f o r m a l d e h y d e resins used t o l a m i n a t e m a p l e w o o d a n d t o b o n d s o u t h e r n p i n e flake b o a r d s (waferb o a r d a n d / o r s t r a n d b o a r d ) w i t h o u t adversely affecting the p h y s i c a l b o n d p r o p e r t i e s . W h i l e t h i s p u l p i n g process a n d b y - p r o d u c t l i g n i n do not c o m m e r c i a l l y exist at t h i s t i m e i n the U n i t e d States, lignins f r o m such processes are projected to cost 4 0 % to 5 0 % less t h a n p h e n o l as a p o l y m e r r a w m a t e rial. It is r e c o m m e n d e d t h a t a r e s l u r r y of crude O S L i n a n organic s o l vent or 1 0 % aqueous salt (e.g., N a H C O a ) s o l u t i o n be p e r f o r m e d to remove l o w - m o l e c u l a r - w e i g h t (mono-functional) species, waxes, a n d c a r b o h y d r a t e s . T h i s p u r i f i c a t i o n leads to a n i m p r o v e m e n t i n O S L r e a c t i v i t y a n d c o n t r i b u t e s to the usefulness of O S L as a P F resin extender or P F c o p o l y m e r r a w m a t e r i a l . It is presumed t h a t extraneous removed m a t e r i a l s i n the crude l i g n i n react w i t h f o r m a l d e h y d e b u t do not lead to p r o d u c t i v e c r o s s - l i n k i n g p o l y mer f o r m a t i o n . T h e success o b t a i n e d i n t h i s s t u d y o n b o n d i n g flake b o a r d a n d m a p l e blocks s u p p o r t s the p o s s i b i l i t y of u s i n g O S L i n resins for b o n d i n g crosswise l a m i n a t e s (i.e., p l y w o o d ) . Subsequent research conducted at the M i s s i s s i p p i Forest P r o d u c t s U t i l i z a t i o n L a b o r a t o r y o n O S L - P F resins for b o n d i n g p l y w o o d has been e q u a l l y successful.

Experimental Wood Pulping and Lignin Purification. T h e w o o d p u l p i n g i n v o l v e d red oak w o o d c h i p s , aqueous organic solvent, a n d a n a c i d c a t a l y s t , w h i c h were p r o cessed at 120 to 140°C. T h e r e s u l t a n t p u l p was washed w i t h more aqueous solvent, w a t e r - s l u r r i e d a n d cooled. T h e l i g n i n was i s o l a t e d by r e m o v i n g the solvent under v a c u u m , replacement of solvent w i t h water, l i g n i n prec i p i t a t i o n , filter cake water w a s h i n g , a n d d r y i n g . T h e l i g n i n was p u r i f i e d b y s l u r r i n g one p a r t of d r y O S L i n five p a r t s of a 1 0 % aqueous s o d i u m b i c a r b o n a t e s o l u t i o n at 6 0 ° C for one h o u r . T h e s l u r r y was cooled to r o o m t e m p e r a t u r e a n d filtered. T h e filter cake was washed w i t h water u n t i l the filtrate was less t h a n 7.5 p H . T h e filter cake was then d r i e d i n a forced-air oven at 50 to 5 5 ° C , w i t h a weight y i e l d of 9 0 % to 9 5 % . T h e r e s u l t a n t d r y and loose l i g n i n was used w i t h o u t further processing such as g r i n d i n g . Analytical Characterization. T h e l i g n i n s were characterized a n a l y t i c a l l y by the f o l l o w i n g m e t h o d s : H N M R s p e c t r a , gel p e r m e a t i o n c h r o m a t o g r a p h y (5), gas c h r o m a t o g r a p h y (6), t h e r m a l measurements, e l e m e n t a l a n a l y s i s , sugar content, e x t r a c t i o n s , s o l u b i l i t y , a n d c o m b u s t i o n properties. 1

Resin Preparation. T w o approaches to resin p r e p a r a t i o n were used w i t h regard t o the i n i t i a l stages of condensation, d e p e n d i n g o n w h e t h e r the resin was i n t e n d e d for l a m i n a t i n g m a p l e blocks or for b o n d i n g s o u t h e r n pine flake boards. F o r m a p l e block resins, the steps i n v o l v e d were as follows: a d d i t i o n of water, s o d i u m h y d r o x i d e ( o p t i o n a l ) a n d l i g n i n , w h i c h were heated a n d

COOK & SELLERS

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24.

Organosolv Lignin-Modified Phenolic Resins

331

h e l d u n t i l a homogeneous m i x t u r e was o b t a i n e d ; a d d i t i o n of either 1 0 0 % of the p h e n o l or 1 0 % to 2 0 % of the formaldehyde r e q u i r e d i n the cook a n d heated t o 75 t o 9 0 ° C for 30 to 90 m i n u t e s ; a d d i t i o n of the r e m a i n d e r of the p h e n o l (unless a l l was a d d e d i n i t i a l l y ) , a n d f o r m a l d e h y d e , h o l d i n g at 60 to 7 5 ° C for 30 t o 90 m i n u t e s . F o r m a p l e block b o n d i n g , a series o f cooks were m a d e i n w h i c h 2 4 % to 4 5 % of the resin solids were replaced w i t h O S L or k r a f t l i g n i n . F o r flake b o a r d resins the steps i n c l u d e d the f o l l o w i n g : a p r e p o l y m e r synthesis of m e t h y l o l - l i g n i n condensation for 30 to 90 m i n u t e s , t h e n a sequential m e t h y l o l - l i g n i n , p h e n o l - f o r m a l d e h y d e c o n d e n s a t i o n (resin synthesis) step, w h i c h varied f r o m 3 to 5 hours cook t i m e (4). F o r flake b o a r d resins, cooks were m a d e w i t h 2 5 % a n d 3 5 % of the p h e n o l replaced w i t h p u r i f i e d a n d u n p u r i f i e d O S L . V a r i o u s properties of the resins were d e t e r m i n e d b y s t a n d a r d m e t h o d s , i n c l u d i n g n o n - v o l a t i l e solids, viscosity, p H , free f o r m a l d e h y d e , free p h e n o l , alkalinity, a n d gel t i m e . I n b o t h studies, c o m m e r c i a l resins were o b t a i n e d a n d used as controls. T a b l e V provides t y p i c a l s t o i c h i o m e t r i c d a t a of resin reactants i n v e s t i g a t e d for b o t h resin types. T a b l e V . T y p i c a l s t o i c h i o m e t r i c properties of resin reactants A m o u n t by Resin T y p e Reactant

Blocks (mol)

Flake Board (mol)

W a t e r (sufficient for desired n o n - v o l a t i l e solids) Phenol Formaldehyde Organosolv l i g n i n Sodium hydroxide Urea

1.00 1.8-3.0 0.25-0.80 0.40-0.65 -

1

1

1.00 2.98 0.25 0.64 0.09

A s s u m e a m o l e equivalent u n i t of 200 for organosolv l i g n i n , based o n a t y p i c a l a n a l y z e d C9 l i g n i n u n i t .

Maple Block Screening Method. A series of e x p e r i m e n t a l procedures were p e r f o r m e d o n b o n d i n g m a p l e block w o o d ( C o o k , P . M . , E a s t m a n K o d a k at K i n g s p o r t , T N , p e r s o n a l c o m m u n i c a t i o n s , 1987). T h e procedure a d o p t e d was the A S T M D 905 s t a n d a r d , m o d i f i e d as follows: S u g a r m a p l e (Acer saccharum) w o o d , 76 b y 25 b y 5.7 m m i n size (3 inches l o n g , 1 i n c h w i d e , and 0.25 i n c h t h i c k ) , w i t h 6% m o i s t u r e content was p l a n e d to o b t a i n fresh surfaces for b o n d i n g . T h e desired a m o u n t of resin ( w i t h no m i x additives) was weighed (58.6 g / m , 12 l b / 1 0 0 0 f t , resin solids basis) a n d a p p l i e d t o one block surface a n d t h e n a second clean block was o v e r l a p p e d so t h a t 25 square m m (1 square inch) surface area c o m m o n to each block was coated. T h e resin coated blocks were placed d i r e c t l y i n the hot press (no c l a m p t i m e ) . T h e blocks were hot pressed at 177°C (350°F) for 4 to 6 m i n u t e s at 3.44 M P a (500 p s i ) . A l l b o n d e d blocks were allowed to 2

2

332

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

s t a n d (post cure) at a m b i e n t temperatures for 24 hours p r i o r to t e s t i n g . T e n b o n d e d b l o c k s were tested d r y a n d ten were tested after a n acceler­ ated a g i n g regimen (4 h b o i l i n water, cool, a n d test wet) for each r e s i n . T h e lap-tension-shear s t r e n g t h of the test specimens was measured u s i n g a n I n s t r o n m a c h i n e , a n d s u b j e c t i v e estimates of the percent w o o d failure (or b o n d failure) were observed a n d recorded. T h e d a t a were subjected to s t a t i s t i c a l analysis. Flake Board Screening Method. T h i s phase of the s t u d y has been p r e v i ­ o u s l y r e p o r t e d i n more d e t a i l b y Sellers et al. (4) b u t c a n be s u m m a r i z e d as follows. D i s c - c u t s o u t h e r n pine flakes (wafers a n d / o r strands) were o b ­ t a i n e d f r o m c o m m e r c i a l flake b o a r d plants i n the S o u t h e r n U n i t e d States. T h e flakes were a p p r o x i m a t e l y 76 m m (3 i n . ) l o n g , 19 to 38 m m (0.75 to 1.5 i n . ) w i d e , a n d 0.5 to 0.8 m m (0.020 to 0.030 i n . ) t h i c k a n d adjusted to 2 . 5 % m o i s t u r e content at the t i m e of use. E a c h resin t y p e was a p p l i e d at 5 % a n d 7% resin solids rates. T h e m a t c o n f i g u r a t i o n was homogeneous a n d h a n d felted i n sufficient size to o b t a i n a t r i m m e d p a n e l m e a s u r i n g 560 b y 610 b y 12.5 m m (22 b y 24 by 0.5 i n . ) . T h e m a t s were hot pressed at 205°C ( 4 0 0 ° F ) for 6 minutes w i t h a dual-pressure regimen ( 5 . 5 1 / 2 . 7 5 M P a , 8 0 0 / 4 0 0 p s i ) . T h e i n i t i a l h i g h pressure was d r o p p e d after one m i n u t e i n t o the cycle a n d the panels were pressed to 1 2 . 7 - m m (0.5-in.) m e t a l stops i n the hot press. T h e target density was 745 k g / m (46 l b / f t ) . T h r e e panels per resin t y p e a n d a p p l i c a t i o n rate were m a d e . R e s i n types i n c l u d e d the c o n t r o l c o m m e r c i a l resins (no l i g n i n content), l i g n i n - m o d i f i e d P F resins, a n d c o n t r o l P F resins c o n t a i n i n g a n inert filler (pecan shell flour) at the same loads as the l i g n i n s u b s t i t u t e d resins. Screening tests for p a n e l perfor­ m a n c e i n c l u d e d i n t e r n a l b o n d ( I B ) , d r y s t a t i c b e n d i n g ( m o d u l u s of r u p t u r e , M O R ) , accelerated a g i n g M O R (strength r e t e n t i o n after a n A m e r i c a n P l y ­ w o o d A s s o c i a t i o n performance 6-cycle test), a n d d i m e n s i o n a l tests [water a b s o r p t i o n ( W A ) a n d thickness swell ( T S ) ] . T h e s t a t i s t i c a l a n a l y s i s was a two-factor e x p e r i m e n t (resin type-resin a p p l i c a t i o n level), u s i n g a n a n a l ­ ysis of variance a n d Τ tests ( L S D ) for g r o u p i n g for the various p h y s i c a l properties tested. 3

3

Product Disclaimer T h e use of t r a d e , firm, or c o r p o r a t i o n names i n this p u b l i c a t i o n is for the i n f o r m a t i o n a n d convenience of the reader. S u c h use does not c o n s t i t u t e an official endorsement or a p p r o v a l b y the M i s s i s s i p p i Forest P r o d u c t s U t i l i z a ­ t i o n L a b o r a t o r y ( M F P U L ) , M i s s i s s i p p i S t a t e U n i v e r s i t y , or the E a s t m a n K o d a k C o m p a n y of any p r o d u c t or service to the e x c l u s i o n of others w h i c h m a y be s u i t a b l e . A cknowledgment s A p p r e c i a t i o n is expressed to the following M F P U L employees: D r . A . L . W o o t e n (retired) for resin synthesis; G a r y S t o v a l l a n d George M i l l e r for resin a n d flake b o a r d s a m p l e p r e p a r a t i o n a n d t e s t i n g ; a n d L y n n P r e w i t t for G F C work. M a t e r i a l s were d o n a t e d i n s u p p o r t of t h i s project b y B o r d e n

24.

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Incorporated, Chembond Corporation, E a s t m a n K o d a k Company, Georgia P a c i f i c C o r p o r a t i o n , L o u i s i a n a Pacific C o r p o r a t i o n , a n d S o u t h e a s t e r n R e ­ d u c t i o n C o m p a n y . T h i s w o r k was s u p p o r t e d by t w o research grants f r o m Eastman Kodak Company.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch024

Literature

Cited

1. Chemical Week 1984, 134(1), 26, 28. 2. Conner, A . H.; Lorenz, L . F . J. Wood Chem. Technol. 1986, 6(4), 591613. 3. Sellers, T . , Jr. Plywood and Adhesive Technology, Marcel Dekker: New York, 1985; pp. 349-373. 4. Sellers, T . , Jr.; Wooten, A . L . ; Cook, P. M . Proc. Structural Wood Composites: New Technologies for Expanding Markets; Forest Products Research Society, Madison, WI, 1988, Proc. No. 47359, 43-50. 5. Glasser, W . G . ; Glasser, H . R.; Morohoshi, N. Macromol. 1981, 14(2), 252-262. 6. Glasser, W . G . ; Barnett, C . Α.; Sano, Y . J. Appl. Polym. Sci., Appl. Polym. Symp. 1983, 37, 441-460. RECEIVED February 27,1989

Chapter 25

Wood Adhesives from Phenolysis Lignin A Way To Use Lignin from Steam-Explosion Process Hiro-Kuni Ono and Kenichi Sudo

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch025

Forestry and Forest Products Research Institute, Ministry of Agriculture, Forestry, and Fisheries, P.O. Box 16, Tsukuba Norin, Ibaraki 305, Japan

The lignin extracted from steam exploded pulp was phenolated in the presence of sulfuric acid. The degree of phenolation was calculated to be in excess of one mole/lignin (C ) unit on the basis of C N M R measurements. The phenolated lignin was methylolated in order to prepare adhesive resins. The cure behavior of the adhesive resins was examined by Torsional Braid Analysis (TBA). Results revealed that the phenolated steam explosion lignin-based resins had intrinsic retardation in cure as compared to a commercial phenolic resin. This defect, however, was partly overcome by increasing their pH values. The adhesives from these resins generally provide excellent bond strength comparable to phenolic resin. 9

13

The steam explosion process is a recent development in wood processing ( 1 , 2 ) . Much attention has been paid to this process from the viewpoint of total wood utilization. Cellulose and hemicellulose from this process can be converted into sugars of commercial value by enzymatic methods (3). However, the conversion of lignin from this process (steam explosion lignin) into useful materials continues to present difficulties. Preparation of adhesives from it is considered to be a feasible way to solve this problem. Steam explosion lignin is reported to have more reactive functional groups (4), and to contain no sulfur, as compared to kraft (thio) lignin and lignin sulfonates. The absence of blocked reactive functional groups in the lignin must be an advantage to various chemical modifications by which the lignin would be utilized as an adhesive of commercial use. The addition of phenol-formaldehyde precondensate to lignin or methylolated lignin has been known as a way to introduce phenolic reactivity into lignin, and this is usually applied to the preparation of lignin-based 0097-6156/89A)397-0334$06.00A) © 1989 American Chemical Society

In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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adhesives (5-10). In this case, all the lignin does not combine with the precondensate. Some part of it is considered to function as filler. T h e amount of lignin added is usually limited by some strength requirement. In order to make lignin molecules contribute to bond strength, lignin should be incorporated into the phenolic main chain structure by a phenolysis reaction, for instance. There have been two kinds of lignin phenolysis reactions reported. Muller and Glasser have prepared phenolated lignins by a two-step reaction (11). Kraft, acid hydrolysis, and steam explosion lignins were allowed to react with formaldehyde before the methylolated lignins were combined with phenol. The adhesion quality of the pheno­ lated lignin/phenol-formaldehyde resins was investigated, and the pheno­ lated steam explosion lignin/phenol-formaldehyde resin was found to have slightly lower bond strength than the kraft lignin/phenol-formaldehyde and a neat phenolic resin. It was suggested that a considerable amount of syringyl propane units in the steam explosion aspen lignin was partly respon­ sible for the lower bond strength as compared to the neat phenolic resin (12). The other phenolysis reaction is the direct reaction of phenol with the substituted propyl side chain of lignin. Wacek et al. elucidated the chem­ istry of this reaction by oxidation (13). They concluded that condensation occurred between the o- or p-position of phenol and lignin's α-position sub­ stituted by O H , O - R i , = 0 or = C - R 2 ( R i and R 2 : lignin residue). This mechanism has been confirmed by Kratzl et al. by using radioactive C labeled lignin (14). Kobayashi et al. have prepared phenolated lignin by applying this phenolysis method in order to obtain thiolignin-based mold­ ing compounds (15). This method is suitable for hardwood lignins so far as they have sufficient functional groups at their α-positions of the propyl side chain. Since the steam explosion process has usually been applied to hardwoods, the latter phenolysis method is of interest from the viewpoint of adhesive preparation as compared to the former phenolysis. 1 4

Experimental Materials. Lignin (SEL) was extracted with dilute alkali from steam ex­ ploded white birch (Betula plaiyphylla) pulp. T h e pulp was prepared at 200°C for 10 minutes. The C N M R measurement of its acetylated prod­ uct provided a methoxy:aryl ratio of 1.48, and this is in good agreement with Obst and Landucci's value of 1.44 (16). The molecular weight of C6-C3 units of S E L was calculated to be about 180. Chemical reagents were the first grade in the Japanese industrial standard. They were used as received. A commercial phenolic resin (D-17 of Ohshika Co.) was used in order to compare with bond strength of lignin-based adhesives. A commercial ad­ ditive (Hot Ρ of Ohshika Co.) and an extender (wheat flour: Akahana of Nisshin Co.) were used for the adhesive formulation. 1 3

Phenolysis of SEL. Phenol (120 g) was charged into a 300 ml round bot­ tom flask equipped with thermometer, stirrer and cooler. S E L (60 g) was added slowly so that it could dissolve thoroughly. Sulfuric acid (0.5 ml) was then added as a catalyst. T h e typical sulfuric acid:SEL charge ratio

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was 1.5 m M o l e / g . T h e r e a c t i o n schedule consisted of 1 h r of w a r m - u p p e ­ r i o d a n d 3 hrs of phenolysis at 170° C , followed b y r e m o v a l of u n r e a c t e d p h e n o l under reduced pressure. T h e p h e n o l a t e d S E L was a b l a c k substance w h i c h dissolved more easily i n organic solvents, especially i n alcohols, t h a n d i d S E L . T h e softening p o i n t of the p h e n o l a t e d S E L was a b o u t 140°C. O t h e r phenolysis l i g n i n s , w i t h different charge ratios of s u l f u r i c a c i d , were p r e p a r e d to c o m p a r e w i t h the a m o u n t of b o u n d p h e n o l . Preparation of Phenolated SEL-Formaldehyde Resins. Phenolated S E L f o r m a l d e h y d e resins ( L P ' s ) were prepared i n a m a n n e r s i m i l a r t o resolet y p e p h e n o l - f o r m a l d e h y d e resin b y u s i n g a n alkaline c a t a l y s t . I n a 100 m l flask e q u i p p e d w i t h t h e r m o m e t e r , stirrer a n d cooler, a n a p p r o p r i a t e a m o u n t of f o r m a l i n was c o m b i n e d w i t h the equivalent a m o u n t of m e t h a n o l as a d i s s o l v i n g a i d , a n d 5 0 % aqueous N a O H s o l u t i o n (3.2 g). T h e p o w d e r o f the p h e n o l a t e d S E L (20 g) was t h e n s l o w l y added to the m i x t u r e , a n d it was forced to dissolve t h o r o u g h l y b y a g i t a t i o n . T h e r e a c t i o n schedule consisted of 15 m i n u t e s of w a r m - u p p e r i o d , 60 minutes of m e t h y l o l a t i o n at 6 0 ° C a n d 10 m i n u t e s of w a r m - u p p e r i o d to 8 0 ° C , followed b y c o n d e n s a t i o n at 8 0 ° C . A f t e r the reaction was complete, m e t h a n o l a n d some water were removed under reduced pressure, r e s u l t i n g i n a black viscous resin. T h r e e f o r m a l d e h y d e charge levels of 1.5, 3 a n d 5 moles were e m p l o y e d based o n f u n c t i o n a l i t y of the p h e n o l a t e d S E L for the resin p r e p a r a t i o n . S o l i d content of the three resins was adjusted w i t h water to a r o u n d 4 6 % . P r e p a r a t i o n of the three resins was carefully c o n t r o l l e d i n order to adjust t h e i r viscosities to a r o u n d 0.3 P a s , w h i c h is supposed to be i n a desirable range for adhesive a p p l i c a t i o n . L P ' s f r o m formaldehyde charge ratios of 1.5, 3 a n d 5 were n a m e d as L P - Α , L P - B , a n d L P - C , respectively. M e t h y l o l a t i o n of S E L i t s e l f was also carried out i n the same m a n n e r as L P p r e p a r a t i o n i n order to c o m p a r e their b o n d s t r e n g t h w i t h those of L P ' s . Adhesive Formulation. A d h e s i v e s for t e s t i n g consisted of 100 parts resin, 10 p a r t s wheat flour as extender, 4 parts c o m m e r c i a l a d d i t i v e , a n d 2 p a r t s w a t e r . T h i s f o r m u l a t i o n is r e c o m m e n d e d b y Japanese b o a r d m a n u f a c t u r e r s . A d h e s i v e s w i t h o u t wheat flour were also f o r m u l a t e d to e x a m i n e the b o n d s t r e n g t h of the neat l i g n i n based resins. Specimen for Tensile Shear Adhesion Test. S i n g l e l a p specimens for shear s t r e n g t h tests were m a d e f r o m b i r c h test panels ( l e n g t h : 80 m m , w i d t h : 25 m m , d e p t h : 3 m m ) . T w o of the panels were g l u e d w i t h the adhesives i n a s p r e a d i n g rate of 1.5 g / 1 0 0 c m for single glue l i n e . B o n d i n g area of the specimens was 25 x 13 m m . T h e specimens were first pressed i n a n a m b i e n t t e m p e r a t u r e for a n h o u r under a pressure o f 0.78 M P a a n d t h e n hot-pressed at 140°C under a pressure of 0.98 M P a for 6 m i n u t e s . 2

C NMR Spectroscopy. C N M R measurements were c a r r i e d out u s i n g a J E O L J M N - G S X 400 spectrometer for q u a n t i t a t i v e a n a l y s i s i n order to e x a m i n e the a m o u n t of b o u n d p h e n o l i n the p h e n o l a t e d S E L ' s . T h e a n a l y s i s was c o n d u c t e d i n D M S O - d b y u s i n g gated d e c o u p l i n g technique. 1 3

13

6

Gel Permeation

Chromatography

(GPC).

M o l e c u l a r weight d i s t r i b u t i o n s of

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p h e n o l y s i s l i g n i s d u r i n g the phenolysis were e x a m i n e d at 60° C i n T H F as m o b i l e phase b y u s i n g a T o y o S o d a H P L C - 8 0 2 U R gel p e r m e a t i o n c h r o m a t o g r a p h e q u i p p e d w i t h t w o 60 c m p o l y s t y r e n e gel c o l u m n s i n series ( T S K - G E L H G 2 5 0 0 a n d G 1 0 0 0 ) . T h e c h r o m a t o g r a m s were m o n i t o r e d b y refractometer.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch025

Torsional Braid Analysis. L P - Α , L P - B , a n d L P - C were coated o n glass b r a i d s a n d t h e i r cure b e h a v i o r s were e x a m i n e d b y u s i n g a R H E S C A R D 1 1 0 0 A t o r s i o n a l b r a i d a n a l y z e r . T h e i r r e l a t i v e r i g i d i t y changes a l o n g w i t h cure t e m p e r a t u r e ( h e a t i n g rate was l ° C / m i n ) were m o n i t o r e d i n order to e x a m i n e the cure speed of the L P resins. T h e r e l a t i v e r i g i d i t y changes d u r ­ i n g cure at 140°C were also m e a s u r e d to e x a m i n e the cure speed dependence o n resin p H . Tensile Shear Strength Measurement. T h e tensile shear b o n d s t r e n g t h was d e t e r m i n e d i n accordance w i t h Japanese s t a n d a r d J I S Κ 6851 ( n o r m a l a n d repeated b o i l i n g test) b y u s i n g a T o y o S e i k i S t r o g r a p h W tensile tester. I n the n o r m a l test, the test specimens were c o n d i t i o n e d for at least 48 hrs at 2 0 ± 5 ° C under a relative h u m i d i t y of 65 ± 2 0 % before tensile shear s t r e n g t h was m e a s u r e d . I n the repeated b o i l i n g test, the specimens were i m m e r s e d i n b o i l i n g water for 4 hrs, d r i e d at 6 0 ± 3 ° C for 20 hrs a n d i m m e r s e d a g a i n i n b o i l i n g water for 4 h r s , followed b y i m m e r s i o n i n water at r o o m t e m p e r a t u r e u n t i l cooled. T h e specimens were tested i n wet state. S i x specimens were tested for each resin. Results and Discussion Optimum Reaction Period between Phenol and Lignin. T h e e n d p o i n t of the p h e n o l y s i s r e a c t i o n c a n be e s t i m a t e d b y the p e r i o d w h e n the c o n s u m p t i o n of p h e n o l reaches e q u i l i b r i u m . P h e n o l y s i s p r o d u c t s were m o n i t o r e d b y G P C d u r i n g the r e a c t i o n . T h e change i n m o l e c u l a r weight d i s t r i b u t i o n d u r i n g the p h e n o l y s i s is s h o w n i n F i g u r e 1. T h e increase o f the peak at 19 m i n clearly demonstrates t h a t p o l y m e r i z a t i o n of S E L occurs as the r e a c t i o n proceeds. T h e r a t i o of peak area of p h e n o l a t e d l i g n i n (16 to 28.7 m i n i n e l u t i o n t i m e ) to t h a t of u n r e a c t e d p h e n o l (27.9 m i n ) vs. r e a c t i o n t i m e is s h o w n i n F i g u r e 2. U n r e a c t e d p h e n o l d i m i n i s h e s r a p i d l y at the e a r l y stage of the r e a c t i o n before r e a c h i n g e q u i l i b r i u m w i t h i n 3 h r s . T h i s was defined as o p t i m u m p h e n o l y s i s r e a c t i o n p e r i o d . Functionality Measurement of Phenolated Lignin. It is i m p o r t a n t to have knowledge of the f u n c t i o n a l i t y of the p h e n o l a t e d l i g n i n f r o m the p o i n t of v i e w of f u r t h e r c h e m i c a l m o d i f i c a t i o n . T h e a m o u n t of b o u n d p h e n o l i n the p h e n o l y s i s r e a c t i o n has been measured b y t i t r a t i n g the p h e n o l e x t r a c t e d f r o m the r e a c t i o n m i x t u r e (15). T h i s i n d i r e c t m e t h o d measures the u n r e ­ acted p h e n o l a n d determines b o u n d p h e n o l as the difference between the i n i ­ t i a l charge a n d the t i t r a t e d p h e n o l . T h i s is sometimes m i s l e a d i n g . * H N M R spectroscopy is another c a n d i d a t e for the d e t e r m i n a t i o n of the a m o u n t of b o u n d p h e n o l . H o w e v e r , t h i s c a l c u l a t i o n is difficult since the n u m b e r of p r o t o n s before a n d after the phenolysis r e a c t i o n is u n k n o w n .

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400

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343

Wood Adhesives from Phenolysis Lignin

ι

/

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20 40 60 80 100 CURING PERIOD (min)

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F i g u r e 5. C u r e rate dependence o n p H for the p h e n o l a t e d s t e a m e x p l o s i o n l i g n i n - b a s e d resin L P - B .

T h i s m i g h t be e x p l a i n e d w i t h f a i l u r e t o crosslink sufficiently. S a n o et a l . have also r e p o r t e d t h a t phenolysis of h a r d w o o d l i g n i n sulfonates enhances adhesion properties (22). It is t h u s clearly d e m o n s t r a t e d t h a t the i n t r o d u c ­ t i o n o f p h e n o l i n t o l i g n i n improves adhesion properties.

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T a b l e I I . Tensile Shear B o n d S t r e n g t h of A d h e s i v e s f r o m P h e n o l y s i s L i g n i n i n N o r m a l Test a n d after R e p e a t e d B o i l T r e a t m e n t B o n d Strength (10 Pa) (Standard Deviation) 5

Normal

Repeated B o i l

Adhesives from L P - B w i t h extender w i t h o u t extender

47.2 (8.8) 65.3 (9.6)

52.9 (6.1) 43.5 (3.3)

Adhesives from L P - C w i t h extender w i t h o u t extender

41.5 (9.6) 68.4 (7.8)

55.6 (7.9) 51.4 (6.7

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Adhesives

Adhesives from methylolated S E L w i t h extender 45.9 (9.2) w i t h o u t extender 32.0 (10.1)

0 0

A d h e s i v e f r o m c o m m e r c i a l phenolic resin w i t h extender 62.6 (6.6)

47.3 (11.5)

T h e two p h e n o l a t e d S E L adhesives w i t h wheat flour do not p r o v i d e g o o d b o n d s t r e n g t h i n the n o r m a l test, b u t p r o v i d e excellent s t r e n g t h after repeated b o i l . T h e b o n d s t r e n g t h increment after repeated b o i l i n d i c a t e s the occurrence of post-cure i n the p h e n o l a t e d S E L adhesives. T h e a c i d i t y of the wheat flour m i g h t r e t a r d resin cure b y r e d u c i n g the p H of the adhesives (23). L P - C p r o v i d e d better b o n d q u a l i t y as c o m p a r e d to L P - B . Since the difference between L P - B a n d L P - C lies i n the f o r m a l d e h y d e r a t i o c h a r g e d , t h i s f i n d i n g suggests t h a t a s t o i c h i o m e t r i c charge m i g h t not be adequate for the f o r m a t i o n o f m e t h y l o l groups i n L P ' s . T h e r e m i g h t be a p r o b l e m w i t h the r e a c t i o n of f o r m a l d e h y d e w i t h the p h e n o l a t e d S E L as c o m p a r e d to p h e n o l . G e n e r a l l y s p e a k i n g , the p h e n o l a t e d S E L adhesives w i t h o u t wheat flour p r o v i d e b o n d strengths c o m p a r a b l e t o the p h e n o l i c resin i n n o r m a l a n d r e p e a t e d - b o i l tests. It has been r e p o r t e d t h a t the resin f r o m the r e a c t i o n of f o r m a l d e h y d e w i t h the m i x t u r e of the two-step p h e n o l a t e d s t e a m e x p l o s i o n l i g n i n a n d p h e n o l has also p r o v i d e d c o m p a r a b l e b o n d s t r e n g t h (12). It is n o t e w o r t h y t h a t the p h e n o l a t e d S E L l i g n i n was d i r e c t l y m e t h y l o l a t e d w i t h o u t any a d d i t i o n of p h e n o l . A l t h o u g h there are s t i l l some p r o b l e m s , such as the ineffective m e t h y l o l a t i o n o f the p h e n o l a t e d S E L a n d the selection o f a s u i t a b l e extender, i t c a n generally be concluded t h a t phenolysis is a p r o m i s i n g m e t h o d to develop s t e a m e x p l o s i o n l i g n i n i n t o a t t r a c t i v e adhesives c o m p a r a b l e t o c o m m e r c i a l p h e n o l i c resin. Conclusions Q u a n t i t a t i v e a n a l y s i s o f phenolysis l i g n i n b y C N M R has i n d i c a t e d t h a t the a m o u n t o f p h e n o l b o u n d to the s t e a m e x p l o d e d l i g n i n is u n e x p e c t e d l y 1 3

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large as c o m p a r e d t o t h i o l i g n i n . T h e s t e a m explosion l i g n i n itself c o u l d re­ act w i t h f o r m a l d e h y d e , r e s u l t i n g i n t h e r m o s e t t i n g resins. T h i s r e s i n , h o w ­ ever, d i s p l a y e d p o o r adhesion properties, especially i n t h e repeated b o i l test. T h e p h e n o l a t e d l i g n i n - f o r m a l d e h y d e resins p r o v i d e d excellent adhe­ sives c o m p a r a b l e t o a c o m m e r c i a l phenolic resin. P h e n o l y s i s appears t o b e a p r o m i s i n g m e t h o d t o u t i l i z e s t e a m e x p l o s i o n l i g n i n s as adhesives.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch025

Acknowledgments T h i s research was funded b y the B i o m a s s Transfer P r o g r a m o f the Japanese M i n i s t r y o f A g r i c u l t u r e , F o r e s t r y a n d Fisheries. T h e a u t h o r s w o u l d like t o express their t h a n k s t o M r . H . O h a r a for e x t r a c t i n g l i g n i n a n d t o M s . Y a o X i n o f the Forest P r o d u c t s Research I n s t i t u t e o f H e i l o n g i a n g P r o v i n c e i n C h i n a for p r e p a r i n g the p h e n o l a t e d l i g n i n d u r i n g her ten m o n t h s leave a t their I n s t i t u t e . Literature C i t e d 1. Dietrichs, Η. H.; Sinner, M . ; Puls, J . Holzforschung 1978, 32, 193. 2. Marchessault, R. H . ; St.-Pierre, J . In Future Sources of Organic Raw Materials-CHEMRAWN I; St.-Pierre, L . E.; Brown, G . R., Eds.; Pergamon: New York, 1980; p. 613. 3. Shimizu, K . ; Sudo, K . ; Nagasawa, S.; Ishihara, M . Mokuzai Gakkaishi 1983, 29, 428. 4. Sudo, K . ; Shimizu, K . ; Sakurai, K. Holzforschung 1985, 39, 281. 5. Johansson, I. J . Ger. Offen. 2 624 673, 1976. 6. Forss, K . J.; Fuhrmann, A . G . M . Ger. Offen. 2 601 600, 1976. 7. Adams, J . W.; Schoenherr, M . W . U.S. Pat. 4 306 999, 1981. 8. Enkvist, T . U . E . U.S. Pat. 3 864 291, 1975. 9. Sakakibara, A . Japanese Pat. 51-22497, 1976. 10. Clarke, M . R.; Dolenko, A . J. U.S. Pat. 4 113 675, 1978. 11. Muller, P. C . ; Glasser, W . G . J. Adhesion 1984, 17, 159. 12. Muller, P. C . ; Kelley, S. S.; Glasser, W . G . J. Adhesion 1984, 17, 185206. 13. von Wacek, Α.; Daubner-Rettenbacher, H . Monatsch. Chem. 1950, 81, 266. 14. Kratzl, K . ; Buchtela, K.; Gratzl, J . ; Zauner, J . ; Ettingshausen, O. Tappi 1962, 45, 113. 15. Kobayashi, Α.; Haga, T . ; Sato, K. Mokuzai Gakkaishi 1966, 12, 305. 16. Obst, J . R.; Landucci, L . L . Holzforschung 1986, 40, 87. 17. Robert, D. R.; Bardet, M . ; Gagnaire, D. Proc. Inter. Symp. Wood and Pulping Chem., Tsukuba Science City, Japan, 1983, Supp. Vol., p. 1. 18. Landucci, L . L . Holzforschung 1985, 39, 355. 19. Lapierre, C . ; Monties, B. Holzforschung 1984, 38, 333. 20. Fujita, N.; Ogasawara, K . Netsukoukasei Jyushi 1982, 3, 31. 21. Steiner, P. R.; Warren, S. R. Holzforschung 1981, 35, 273. 22. Sano, Y . ; Ichikawa, A . Mokuzai Gakkaishi 1987, 33, 47. 23. Sellers, T . , Jr. Plywood and Adhesive Technology; Marcell Dekker: New York, 1985; C h . 19. RECEIVED February 27,1989 In Lignin; Glasser, W., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 26

Modification of Lignin at the 2- and 6-Positions of the Phenylpropanoid Nuclei Gerrit H . van der Klashorst

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch026

Renewable Resources Chemicals Programme, Division of Processing and Chemical Manufacturing Technology, CSIR, P.O. Box 395, Pretoria, South Africa

Lignin model compounds were reacted with formaldehyde in acid medium at positions meta to the aromatic hydroxy groups. Both phenolic and etherified phenolic lignin model compounds were shown to give fast polymerization or hydroxymethylation of the meta positions depending on the conditions used. This reaction differs from the reaction of formaldehyde with phenolic lignin model compounds under alkaline conditions, where the reaction with formaldehyde always occurs at positions ortho/para to the aromatic hydroxy group. The conditions developed for the polymerization and hydroxymethylation were also evaluated on industrial lignin. The reaction of formaldehyde with the meta positions of lignin clearly have considerable potential for the use of lignin, particularly heavily condensed alkali lignin, in polymeric applications. L i g n i n , present as a waste m a t e r i a l i n the spent liquors o f the p u l p i n g i n d u s t r y , constitutes a p o t e n t i a l l y useful raw m a t e r i a l for the p r o d u c t i o n o f various p o l y m e r i c p r o d u c t s . T h i s has repeatedly been d e m o n s t r a t e d i n the past b y i t s a p p l i c a t i o n i n p r o d u c t s r a n g i n g f r o m w o o d adhesives t o plastics (1). I n these applications the l i g n i n is crosslinked t o increase i t s molecular mass or to f o r m a r i g i d three-dimension ally crosslinked s t r u c t u r e . T h e features o n l i g n i n t h a t were u t i l i z e d for these p o l y m e r i z a t i o n or m o d i f i c a t i o n reactions are as follows (compare F i g . 1): 1. 2. 3. 4.

phenolic hydroxy group; aliphatic hydroxy group; u n s u b s t i t u t e d 3- or 5-positions o n C9 u n i t s ; a n d structures t h a t c a n f o r m q u i n o n e m e t h i d e intermediates. 0097-6156/89/0397-0346$06.00/0 © 1989 American Chemical Society

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch026

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E x a m p l e s where the phenolic h y d r o x y groups were u t i l i z e d i n c l u d e the p r e p a r a t i o n of l i g n i n epoxies b y reaction w i t h e p i c h l o r o h y d r i n (2), ester ifications w i t h b i s - a c i d chlorides (3) a n d c y a n u r i c chloride (4), a n d p o l y m e r i z a t i o n w i t h a z i r i d i n e s (5). T h e a l i p h a t i c h y d r o x y groups have been used as the p o l y o l c o m p o n e n t of urethane resins (6). In m a n y of these a p p l i c a t i o n s p h e n o l i c h y d r o x y groups have been a l k o x y l a t e d to afford more a l i p h a t i c alcohols. T h e u n s u b s t i t u t e d 3- a n d 5-positions o n the C9 u n i t s of a l k a l i l i g n i n have been used i n two types of p o l y m e r i z a t i o n r e a c t i o n s — e l e c t r o p h i l i c d i s placement reactions a n d free r a d i c a l o x i d a t i v e c o u p l i n g reactions. The e l e c t r o p h i l i c displacement reaction approaches i n c l u d e d the use of l i g n i n in p h e n o l formaldehyde resins (7), urea formaldehyde resins (8), a n d the c r o s s l i n k i n g of l i g n i n w i t h d i a z o n i u m salts (9). O x i d a t i v e c o u p l i n g reactions v i a free r a d i c a l m e c h a n i s m s y i e l d e d l i g n i n based adhesives o f h i g h s t r e n g t h In t h i s paper a n a d d i t i o n a l a p p r o a c h t h a t can be used for the m o d i f i c a t i o n or p o l y m e r i z a t i o n of especially a l k a l i l i g n i n is discussed. T h a t is: T h e Modification of Lignin Phenylpropane Units

at

the

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6-Positions

of

the

It was s h o w n b y S a r k a n e n et al. t h a t h a r d a n d softwood m o d e l c o m p o u n d s undergo p r o t o d e d e u t e r a t i o n i n acidic m e d i u m preferably o n positions 2 a n d 6 (9). T h e y suggested t h a t the observed 2, 6 - p r o t o d e d e u t e r a t i o n reactions s h o u l d also h o l d for other reagent species. E l e c t r o p h i l e s other t h a n protons were indeed s h o w n to react w i t h l i g n i n m o d e l c o m p o u n d s at the 2- a n d 6-positions i n acidic m e d i a : K r a t z l a n d W a g n e r investigated the reaction of p a r a p h e n o l i c b e n z y l alcohols i n a l k a line a n d acidic solutions (10). W h e n 4 - h y d r o x y - 3 - m e t h o x y b e n z y l a l c o h o l 4 was reacted w i t h the 4 - a l k y l s u b s t i t u t e d p h e n o l 5 under alkaline c o n d i tions, the expected ortho l i n k e d p r o d u c t (6) was isolated. However, under acidic c o n d i t i o n s the methylene linkage formed meta to the phenolic h y d r o x y group ( F i g . 2). Y a s u d a a n d T e r a s h i m a (11) recently showed t h a t l i g n i n under K l a s o n l i g n i n d e t e r m i n a t i o n c o n d i t i o n s afforded m e / a - l i n k e d p r o d u c t s . V a n i l l y l a l c o h o l (4) y i e l d e d after reflux i n 5 % sulfuric a c i d , m d a - l i n k e d p r o d u c t (8) ( F i g . 3). These examples thus clearly show 4 - h y d r o x y - 3 - m e t h o x y p h e n y l a n d 4h y d i O x y - 3 , 5 - d i m e t h o x y p h e n y l a l k a n e s ( t y p i c a l of the l i g n i n s t r u c t u r e ) to be reactive at positions 2 a n d 6 towards e l e c t r o p h i l i c s u b s t i t u t i o n reactions under acidic c o n d i t i o n s . T h e subject m a t t e r of t h i s paper deals w i t h the development of procedures whereby the 2- a n d 6- (i.e., meta) positions are u t i l i z e d for the p o l y m e r i z a t i o n a n d m o d i f i c a t i o n of l i g n i n . Polymerization of Lignin Model Compounds. T h e controlled polymerizat i o n of several l i g n i n m o d e l c o m p o u n d s at the "meta" positions was subseq u e n t l y a t t e m p t e d (13): T h e h a r d w o o d l i g n i n m o d e l 13 was reacted i n acidic aqueous dioxane to afford d i m e r s , t r i m e r s , tetramers or higher oligomers ( F i g . 4 A ) .

American Chemical Society library 1155 16th St., HM» Washington, DC. 20036

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F i g u r e 2. T h e r e a c t i o n of v a n i l l y l alcohol (4) w i t h a reactive p h e n o l ( £ ) .

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch026

26.

Figure 3. Self-condensation of vanillyl alcohol ( 4 ) and 3,4-dimethoxybenzyl alcohol ( 8 ) in acid (11).

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch026

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VAN DER KLASHORST

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T h e etherified h a r d w o o d l i g n i n m o d e l H reacted at a s i m i l a r rate as the phenolic m o d e l i n d i c a t i n g the etherification of the phenolic g r o u p has a s m a l l effect o n the reaction rate. W h e n t h i s reaction was repeated at 5 5 ° C w i t h a n excess f o r m a l d e h y d e , some m et α-hydroxy m e t h y l a t e d p r o d u c t s were obtained (Fig. 4 B ) . P h e n o l i c a n d etherified softwood l i g n i n m o d e l c o m p o u n d s were also successfully crosslinked at the meta positions. S p e c i a l care was t a k e n t o assign the s t r u c t u r e o f the d i m e r (22) ( F i g . 4 C ) . W i t h N M R - S P I (selec­ tive p o p u l a t i o n inversion) techniques it was u n e v o c a b l y proved t h a t the m e t h y l e n e linkage was s i t u a t e d at the 6-positions (13).

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch026

Mechanism T h e m e c h a n i s m for the reactions o n the 2- a n d 6-positions is based o n t w o factors ( F i g . 5): i n d u c t i o n b y the a l k y l g r o u p ; a n d resonance effects o f the methoxy group. A l k y l groups w i t h o u t a n y o x y - f u n c t i o n o n the α - c a r b o n are electron d o n a t i n g by i n d u c t i o n a n d w i l l enhance the electron density o n the 2-, 4-, a n d 6-positions o f the l i g n i n a l k y l r i n g s . D u r i n g alkaline p u l p i n g a m a j o r p o r t i o n of α-oxy-functions are lost due to condensation reactions, i.e., m e t h y l e n e linkage f o r m a t i o n w i t h the α-carbon as b r i d g e . A l k a l i l i g n i n , a n d especially h i g h l y condensed a l k a l i l i g n i n , can therefore be expected to have a h i g h n u m b e r of ηοη-α-oxy-substituted side chains. A l k a l i l i g n i n c a n therefore be expected to have a h i g h r e a c t i v i t y towards m o d i f i c a t i o n at positions 2 a n d 6. D u r i n g the i n v e s t i g a t i o n o n h a r d - a n d softwood m o d e l c o m p o u n d s i t was observed t h a t the d i m e t h o x y m o d e l c o m p o u n d s ( h a r d w o o d ) were a b o u t five times more reactive t h a n the m o n o m e t h o x y m o d e l c o m p o u n d s . T h i s illustrates the beneficial effect of the presence of the second m e t h o x y g r o u p (by resonance effects). F r o m the results o n the m o d e l c o m p o u n d s i t was clear t h a t : • 1 - a l k y l s u b s t i t u t e d s y r i n g y l a n d g u a i a c y l m o d e l c o m p o u n d s react w i t h f o r m a l d e h y d e i n acidic m e d i u m at positions 2 a n d 6. • T h e formed b e n z y l i c alcohols were u n s t a b l e i n a c i d a n d reacted fast w i t h a second m o d e l c o m p o u n d to f o r m m e t h y l e n e l i n k e d p o l y m e r s . • E t h e r i f i e d phenolic models reacted at the same p o s i t i o n s a n d s i m i l a r rates as d i d the phenolic models. • T h e d i m e t h o x y , i.e., h a r d w o o d , m o d e l c o m p o u n d s reacted faster t h a n d i d the m o n o m e t h o x y m o d e l c o m p o u n d s . Meta

Hydroxymethylation

In the above p a r a g r a p h i t was s h o w n t h a t the l i g n i n C9 u n i t s can be p o l y ­ m e r i z e d at the 2- a n d 6-positions w i t h formaldehyde i n a c i d i c aqueous dioxane. T h e p o l y m e r i z a t i o n reaction proceeds p r e s u m a b l y v i a a h y d r o x y m e t h y l a t e d i n t e r m e d i a t e w h i c h was isolated i n low y i e l d s o n l y w h e n large excesses of formaldehyde were e m p l o y e d . If the h y d r o x y m e t h y l a t i o n o f the meta p o s i t i o n can be achieved i n h i g h y i e l d it w o u l d clearly afford a very

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reactive i n t e r m e d i a t e . T h e h y d r o x y m e t h y l a t i o n of the meta p o s i t i o n was subsequently a t t e m p t e d o n m o d e l c o m p o u n d s (14). T h e h y d r o x y m e t h y l a t i o n of the h a r d w o o d m o d e l (13) was first a t t e m p t e d b y u s i n g a 20 m o l a r excess formaldehyde i n 1 , 1 N H C 1 i n 5 0 % aqueous dioxane (14). Since I S has two reactive sites (2 a n d 6), t h i s means a ten-fold excess of formaldehyde per reactive site. T h e r a t i o of h y d r o x y m e t h y l a t i o n to m e t h y l e n e linkage f o r m a t i o n was d e t e r m i n e d b y H - N M R analysis. 1

Samples were t a k e n at different intervals, n e u t r a l i z e d , e x t r a c t e d a n d a c e t y l a t e d for H N M R analyses. T h e coefficients of the integrals of the a l i p h a t i c (62.0-2.2) a n d the a r o m a t i c (62.3-2.5) acetoxy groups of the p r o t o n N M R s p e c t r a , were t a k e n as the yields of h y d r o x y m e t h y l a t i o n . T h e degree of d i m e r f o r m a t i o n v i a a m e t h y l e n e linkage (crosslinking) was e s t i m a t e d b y the coefficient of the integrals of the p r o t o n N M R s p e c t r a of m e t h o x y groups s i t u a t e d adjacent to the n e w l y f o r m e d b o n d — o f w h i c h the resonances are shifted upfield (63.4-3.7)—and t h a t of the t o t a l m e t h o x y resonances (63.4-4.0). T h e large excess of formaldehyde resulted i n the h y d r o x y m e t h y l a t i o n of 13 i n yields of about 5 0 % h y d r o x y m e t h y l a t i o n . T h i s y i e l d was o b t a i n e d w i t h i n 15 minutes a n d r e m a i n e d constant for over 6 hours. T h e n u m b e r of u n s u b s t i t u t e d a r o m a t i c positions decreased f r o m 0 . 6 / m o d e l c o m p o u n d after 15 minutes to 0.2 after 1 hour reaction t i m e . However, after o n l y 15 minutes about one methylene linkage per m o d e l c o m p o u n d o c c u r r e d , i n d i c a t i n g s u b s t a n t i a l methylene linkage f o r m a t i o n . The rae^a-hydroxymethylation y i e l d was very dependent o n large excess formaldehyde used a n d insensitive to a c i d c o n c e n t r a t i o n a n d t e m p e r a ture. A f t e r extensive e x p l o r a t i o n of the reaction c o n d i t i o n variables i t was discovered t h a t a decrease i n water content of the solvent results i n the increase of h y d r o x y m e t h y l a t i o n yields. E v e n t u a l l y c o n d i t i o n s were devised to achieve close to 1 0 0 % m e i a - h y d r o x y m e t h y l a t i o n w i t h no m e t h y l e n e l i n k age f o r m a t i o n . B o t h softwood a n d h a r d w o o d m o d e l c o m p o u n d s gave o n l y m o n o - m e / a - h y d r o x y m e t h y l a t i o n ( F i g . 6). T h i s is p r o b a b l y due t o the dea c t i v a t i o n b y the electron p u l l i n g effect of the i n t r o d u c e d h y d r o x y m e t h y l group.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch026

1

T h e reactions o n the m o d e l are s u m m a r i z e d i n T a b l e I. T h e s u i t a b i l i t y of the different conditions f o u n d for the me 1.0. Recovered i n 4 5 % y i e l d of parent k r a f t l i g n i n . O n l y the values for P E G 400 a n d 4,000 are i n c l u d e d . V a l u e s for N C O / O H r a t i o of 1.5 a n d 2.1 were averaged t o give a single point.

are i n c l u d e d i n t h i s discussion. It s h o u l d be n o t e d t h a t t h i s N C O / O H is q u i t e h i g h , t h o u g h several studies have s h o w n t h a t t h i s is r e q u i r e d for l i g n i n based p o l y u r e t h a n e s . E v e n w i t h these l i m i t s , the N C O / O H r a t i o influences the observed glass t r a n s i t i o n t e m p e r a t u r e (T^) a n d u l t i m a t e s t r a i n of some of the networks (15). However, generally t h i s influence is r e l a t i v e l y s m a l l c o m p a r e d t o the other differences w h i c h are discussed. T h e effect o f the N C O / O H r a t i o is n o t e d where i t is considered i m p o r t a n t . Glass Transition Temperature. T h e effect of l i g n i n content o n the T ^ of f i l m s crosslinked w i t h H D I a n d a r o m a t i c isocyanates is s h o w n i n F i g u r e s 1 a n d 2, respectively. T h e r e is a p o s i t i v e r e l a t i o n s h i p between l i g n i n content a n d T ^ . T h e T ^ of the P E G - e x t e n d e d H D I p o l y u r e t h a n e s is c o n s i s t e n t l y above t h a t of the networks c o n t a i n i n g c h a i n - e x t e n d e d h y d r o x y p r o p y l l i g n i n ( C E H P L ) . T h e T o f the networks w h i c h are based solely o n h y d r o x y p r o p y l l i g n i n ( H P L ) are higher t h a n a n y of the soft s e g m e n t - c o n t a i n i n g m a t e r i a l s . T h e T ^ o f p o l y u r e t h a n e s crosslinked w i t h a r o m a t i c isocyanates shows n o difference between the P E G - e x t e n d e d a n d the C E H P L n e t w o r k s . T h e Τ values for b o t h types o f networks follow the same r e l a t i o n s h i p . N e t w o r k s w i t h o u t soft segment content generally have a higher T ^ t h a n those w i t h 9

g

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406

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.

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F i g u r e 1. Effect of l i g n i n content o n the glass t r a n s i t i o n t e m p e r a t u r e (T^) o f n e t w o r k s c r o s s l i n k e d w i t h H D L F o r m u l a t i o n t y p e A (*); t y p e Β ( • ); and type C (φ).

10 Lignin

20 Content

30 (wt.

40 %)

F i g u r e 2. Effect o f l i g n i n content o n the glass t r a n s i t i o n t e m p e r a t u r e (T^) o f n e t w o r k s c r o s s l i n k e d w i t h a r o m a t i c i s o c y a n a t e . F o r m u l a t i o n t y p e A (*); t y p e Β (• ); a n d t y p e C ( # ) .

31. K E L L E Y E T A L .

Soft-Segment Content of Lignin-Based Polyurethanes 407

a d d e d soft segment. T h e T ^ values of non-extended networks are essentially i n s e n s i t i v e t o l i g n i n content. In most cases the T ^ values are related d i r e c t l y t o the l i g n i n content of the n e t w o r k . Soft segment-free networks s h o w m o r e scatter t h a n those c o n t a i n i n g a l k y l e t h e r components, a n d t h i s m a y be a t t r i b u t e d t o the crosslink d e n s i t y of the m a t e r i a l s . T h e m e t h o d of soft segment i n c o r p o r a t i o n , s i m p l e a d d i t i o n or covalently b o n d e d , has a m i n i m a l i m p a c t o n T A comparison of the H D I a n d a r o m a t i c i s o c y a n a t e - c r o s s l i n k e d n e t w o r k s , at a given l i g n i n c o n t e n t , shows t h a t the H D I - c r o s s l i n k e d p o l y u r e t h a n e s generally have a lower T ^ t h a n the a r o m a t i c isocyanate-crosslinked n e t w o r k s .

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r

Modulus of Elasticity. T h e effect of l i g n i n content o n m o d u l u s o f e l a s t i c i t y ( M O E ) depends o n the m e t h o d used t o a d d the soft segment ( F i g u r e s 3 a n d 4 ) . T h e m o d u l i o f networks w i t h o u t soft segment, or networks where the soft segment ( P E G ) has s i m p l y been a d d e d t o the m i x t u r e , are r e l a t i v e l y i n s e n s i t i v e t o l i g n i n content. A t h i g h l i g n i n contents, above 30 w t . % , the M O E is s i m i l a r for a l l networks. T h e m o d u l i of the a r o m a t i c i s o c y a n a t e crosslinked networks were generally higher t h a n those c r o s s l i n k e d w i t h H D I for the H P L - P E G networks ( F i g . 4). O n l y i n the case of C E H P L c a n the M O E of the n e t w o r k s be s u b s t a n t i a l l y m o d i f i e d b y r a i s i n g the soft segment content. A s the l i g n i n content is reduced f r o m 30 t o about 20 weight percent, the M O E declines b y m o r e t h a n t w o orders of m a g n i t u d e . It is i n t e r e s t i n g to note the differences b e tween the networks prepared w i t h the f r a c t i o n a t e d l i g n i n a n d a d d e d P E G (i.e., f o r m u l a t i o n t y p e C , T a b l e I), a n d the C E H P L p o l y o l (i.e., f o r m u l a t i o n t y p e A , T a b l e I). T h e f r a c t i o n a t e d l i g n i n p r o d u c e d networks t h a t were r e l a t i v e l y insensitive t o l i g n i n content. T h e m o d u l i of these networks were s l i g h t l y below those p r o d u c e d f r o m the H P L w i t h a d d e d P E G . I n c o n t r a s t , the C E H P L - b a s e d networks showed a p r e d i c t a b l e decrease i n m o d u l u s w i t h d e c l i n i n g l i g n i n content. I n a fashion s i m i l a r to T ^ , the M O E values for the C E H P L - b a s e d networks are generally lower at a given l i g n i n content w h e n crosslinked w i t h H D I c o m p a r e d to those networks crosslinked w i t h a r o m a t i c isocyanates. Ultimate Strength. I n contrast t o T ^ a n d M O E , the u l t i m a t e (tensile) s t r e n g t h of l i g n i n - b a s e d p o l y u r e t h a n e s is very sensitive t o the m e t h o d of p r e p a r a t i o n ( F i g u r e s 5 a n d 6). A t a given l i g n i n content, the networks crosslinked w i t h a r o m a t i c isocyanates are consistently stronger t h a n those e m p l o y i n g H D I . W i t h i n a n isocyanate t y p e , a n d at a constant l i g n i n c o n t e n t , network s t r e n g t h was f o u n d t o progressively decrease f r o m n e t w o r k s w i t h o u t soft segment to networks w i t h a d d e d P E G t o C E H P L - b a s e d n e t w o r k s . W i t h i n a given set of n e t w o r k s , there does a p p e a r t o be a p o s i t i v e r e l a t i o n s h i p between l i g n i n content a n d u l t i m a t e s t r e n g t h , except for soft segment-free n e t w o r k s (i.e., t y p e D ) . F o r the p o l y u r e t h a n e s crosslinked w i t h H D I ( F i g u r e 5), networks w i t h a d d e d P E G a n d C E H P L - b a s e d networks followed s i m i l a r trends. T h e netw o r k s w i t h a d d e d P E G show s l i g h t l y higher s t r e n g t h values at a given l i g n i n content. I n c o n t r a s t , the s t r e n g t h values of n e t w o r k s w i t h o u t soft segment

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408

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20 Content

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40 %)

F i g u r e 3. Effect of l i g n i n content o n the m o d u l u s o f networks c r o s s l i n k e d w i t h H D I . F o r m u l a t i o n t y p e A (*); t y p e Β (• ); a n d t y p e C ( φ ) .

log

MOE (MPa) 4

10 Lignin

20 Content

30 (wt.

40 %)

F i g u r e 4. Effect o f l i g n i n content o n the m o d u l u s o f n e t w o r k s c r o s s l i n k e d w i t h a r o m a t i c isocyanates. F o r m u l a t i o n t y p e A (*); t y p e Β (• ); t y p e C ( · ) ; and type D ( Δ ) .

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10 Lignin

20 Content

30 (wt.

40 %)

F i g u r e 5. Effect o f l i g n i n content o n the u l t i m a t e s t r e n g t h o f n e t w o r k s crosslinked w i t h H D I . F o r m u l a t i o n t y p e A (*); t y p e Β (• ); a n d t y p e C

(·)·

10 Lignin

20 Content

30 (wt.

40 %)

F i g u r e 6. Effect o f l i g n i n content o n the u l t i m a t e s t r e n g t h o f n e t w o r k s crosslinked w i t h a r o m a t i c isocyanates. F o r m u l a t i o n t y p e A (*); t y p e Β (• ); type C ( φ ) ; and type D ( Δ ) .

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content a c t u a l l y increase w i t h decreasing l i g n i n content. T h i s a n o m a l o u s t r e n d is due t o a n increase i n the crosslink density w i t h decreasing l i g n i n content (25). I n the case of p o l y u r e t h a n e s crosslinked w i t h a r o m a t i c isocyanates, the trends are less clear t h a n for the H D I - b a s e d m a t e r i a l s . T h e C E H P L based networks do show a p r e d i c t a b l e , m o n o t o n i e decrease i n s t r e n g t h as the l i g n i n content declines ( F i g . 6). F o r networks w i t h a d d e d P E G , there is considerable scatter i n the s t r e n g t h values. T h e d a t a o f K r i n g s t a d et al. (20), w h i c h covers a w i d e range of l i g n i n contents, shows a slight decline i n s t r e n g t h as the l i g n i n content decreases. T h e s t r e n g t h values o f S a r a f et ai ( 1 5 , 1 6 ) , t h a t are based o n H P L a n d t h a t cover a l i m i t e d range of l i g n i n contents, show n o consistent r e l a t i o n s h i p between l i g n i n content a n d s t r e n g t h . A g a i n , networks prepared w i t h o u t a n y a d d e d soft segment show a n increase i n s t r e n g t h w i t h decreasing l i g n i n content. A s w i t h the H D I crosslinked networks, t h i s is due to a n increase i n the crosslink density w i t h decreasing l i g n i n content. Ultimate Elongation. T h e u l t i m a t e elongations of p o l y u r e t h a n e s crosslinked w i t h H D I a n d a r o m a t i c isocyanates are s h o w n i n F i g u r e s 7 a n d 8, respectively. G e n e r a l l y , the u l t i m a t e e l o n g a t i o n of the a r o m a t i c i s o c y a n a t e crosslinked networks is below t h a t of the H D I - c r o s s l i n k e d m a t e r i a l s . W i t h two exceptions, the u l t i m a t e elongations of a l l networks are l o w . T h i s is consistent w i t h the r e l a t i v e l y h i g h M O E a n d s t r e n g t h values for the H P 1 P E G and H P L - b a s e d materials. T h e exceptions to the generally low e l o n g a t i o n values are for networks p r e p a r e d f r o m f r a c t i o n a t e d l i g n i n w i t h a d d e d P E G , a n d for C E H P L - b a s e d n e t w o r k s . T h e p o l y u r e t h a n e s prepared f r o m f r a c t i o n a t e d l i g n i n w i t h a d d e d P E G show m o d e r a t e u l t i m a t e elongations of 2 0 - 2 5 % . T h e e l o n g a t i o n p r o p erties of the C E H P L networks are even larger; u l t i m a t e elongations of greater t h a n 5 0 % are observed for b o t h H D I a n d T D I - c r o s s l i n k e d m a t e rials. Discussion C o n s i d e r i n g t h i s group of studies, the most effective a p p r o a c h t o i n c o r p o r a t i n g large weight fractions of l i g n i n i n t o a p o l y u r e t h a n e network depends o n the properties w h i c h are desired of the final p r o d u c t . A t a given l i g n i n content, the highest m o d u l i are consistently p r o v i d e d b y a r o m a t i c i s o c y a n a t e - c r o s s l i n k e d p o l y u r e t h a n e s . T h e T ^ of these m a t e r i a l s is consist e n t l y higher t h a n t h a t achieved w i t h H D I . T h i s h i g h T ^ s h o u l d t r a n s l a t e i n t o a h i g h heat deflection or use t e m p e r a t u r e . T h e l i m i t a t i o n of the a r o m a t i c isocyanate m a t e r i a l s is t h e i r b r i t t l e n a t u r e , w h i c h is reflected i n low elongations at break. If toughness is not the l i m i t i n g c o n s i d e r a t i o n , t h e n the s i m p l e a d d i t i o n of P E G soft segment appears t o offer a n a t t r a c t i v e route t o the p r o d u c t i o n of p o l y u r e t h a n e s w i t h 25 t o 30 w t . % l i g n i n . It is i m p o r t a n t t o note t h a t b o t h of the studies considered here have e m p l o y e d m o d i f i e d l i g n i n s . T h e relative advantage of h y d r o x y p r o p y l a t i o n (16) over f r a c t i o n a t i o n (19) w o u l d d e p e n d o n the r e l a t i v e cost o f either procedure.

31. K E L L E Y E T A L

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Elongation

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100 h

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F i g u r e 7. Effect of l i g n i n content o n the u l t i m a t e e l o n g a t i o n of n e t w o r k s crosslinked w i t h H D I . F o r m u l a t i o n t y p e A (*); t y p e Β (• ); a n d t y p e C

(·)· Elongation

(%)

100

10 Lignin

20 Content

30 (wt.

40 %)

F i g u r e 8. Effect o f l i g n i n content o n the u l t i m a t e e l o n g a t i o n of n e t w o r k s crosslinked w i t h a r o m a t i c isocyanates. F o r m u l a t i o n t y p e A (*); t y p e Β (• ); type C ( # ) ; and type D ( Δ ) .

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Only one of the approaches considered here, chain-extension with propylene oxide of hydroxypropyl lignins, allowed for the preparation of net­ works with substantial elongation at break. Typical of most polyurethanes, an increase in the elongation at break resulted in a corresponding decrease in modulus and strength. This represents the most complex modification procedure of those discussed, although process development could probably simplify this modification for adoption on industrial scale. It is worth noting that a recent study has shown that it is possible to prepare polyurethane networks with high ultimate strains from fraction­ ated kraft lignin, P E G and toluene diisocyanate (27). T h e lignin content of these films ranged from 10 to 40 percent. The ultimate strength and mod­ ulus values were generally below those of the H P L - P E G networks. Phase separation was noted for some of the films, which could account for the large ultimate strains. Conclusions Several alternative schemes for the preparation of polyurethane networks with lignin have been discussed. For the studies reviewed, properties gener­ ally varied directly with lignin content. In general, T ^ , M O E , and ultimate strength all increased as the lignin content of the networks increased. U l ­ timate strain decreased with increasing lignin content. Hexamethylene di­ isocyanate generally produced networks with inferior mechanical properties when compared to aromatic diisocyanates. If a particular end use application does not require a high degree of toughness, then there exist two approaches for the preparation of high strength networks. Fractionation of unmodified lignin or modification of the whole lignin, through hydroxypropylation, both provide polyols for networks with high strength and modulus. Which of these approaches is most practical would depend on the relative cost of the fractionation or hydroxypropylation procedure. If a high ultimate strain is required for the network, then the preparation of chain-extended hydroxypropyl lignin becomes necessary. Literature C i t e d 1. Lin, S. Y . In Progress in Biomass Conversion; Tilman, D. Α.; Jahn, E . C . , Eds.; Academic Press: New York, 1983; Vol. 4. 2. Glasser, W . G . ; Kelley, S. S. In Encyclopedia of Polymer Science and Engineering; Mark, H . F . ; Bikales, N . M . ; Ovenberger, C . G . ; Menges, G . , Eds.; John Wiley: New York, 1987; Vol. 8, 2nd E d . , pp. 795-852. 3. Nichols, R. F . U.S. Patent 2 854 422, 1958. 4. Kratzl, K.; Buchtela, K.; Gratzl, J . ; Zauner, J.; Ettinghausen, O. Tappi 1962, 45, 113. 5. Glasser, W . G . ; Hsu, Ο. H.-H. U.S. Patent 4 017 474, 1977. 6. Lambuth, A . L . U.S. Patent 4 279 788, 1981. 7. Falkehag, S. I. Appl. Polym. Symp. 1975, 28, 247. 8. Glasser, W . G . ; Barnett, C . Α.; Rials, T . G . ; Saraf, V . P. J. Appl. Polym. Sci. 1984, 29, 1815.

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31.

KELLEY

ET

AL.

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9. Glasser, W . G . ; Wu, C . - F . ; Selin, J.-F. In Wood and Agricultural Residues—Research, on Use for Fuels and Chemicals; Soltes, E . J., Ed.; Academic Press: New York, 1983; pp. 149-166. 10. Forss, K . ; Fuhrmann, A . Paperi ja Puu 1976, 11, 817. 11. Ball, F . J.; Dougherty, W . K.; Moore, H . H . Can. Patent 654 728, 1962. 12. Hsu, Ο. H.-H.; Glasser, W . G . Wood Sci. 1976, 9, 97. 13. Lange, W . ; Faix, O.; Beinhoff, O. Holzforschung 1983, 37, 63. 14. Rials, T . G . ; Glasser, W . G . J. Wood Chem. Tech. 1984, 4, 331. 15. Saraf, V . P.; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29, 1831. 16. Saraf, V . P.; Glasser, W . G . ; Wilkes, G . L . ; McGrath, J. E . J. Appl. Polym. Sci. 1985, 30, 2207. 17. Saraf, V . P.; Glasser, W . G . ; Wilkes, G . L . J. Appl. Polym. Sci. 1985, 30, 3809. 18. Rials, T . G . ; Glasser, W . G . Holzforschung 1984, 38, 191. 19. Yoshida, H . ; Mörck, R.; Kringstad, K . P.; Hatakeyama, H . J. J. Appl. Polym. Sci. 1987, 34, 1187. 20. Kringstad, K . P.; Mörck, R.; Reimann, Α.; Yoshida, H . Proc. 4th Inter. Symp. Wood and Pulping Chem.; Paris, 1987; Vol. 1, 67-69. 21. Mörck, R.; Yoshida, H . ; Kringstad, K . P.; Hatakeyama, H . J. Holzforschung 1986, 40 (Suppl.), 51. 22. Kelley, S. S.; Ward, T . C.; Rials, T . G . ; Glasser, W . G . J. Appl. Polym. Sci., in press. 23. Pigoff, K . A . In Encyclopedia of Polymer Science and Engineering; Mark, H . F . ; Gaylord, N . G . ; Bikales, N . M . , Eds.; John Wiley: New York, 1981; Vol. 11, pp. 507-561. 24. Kelley, S. S.; Glasser, W . G . ; Ward, T . C . J. Wood Chem. Tech. 25. Kelley, S. S.; Glasser, W . G . ; Ward, T . C . J. Appl. Polym. Sci. 1988, 36, 759. 26. de Oliveira, W . ; Glasser, W . G . J. Appl. Polym. Sci., in press. 27. Reimann, Α.; Mörck, R.; Kringstad, K . P. In Lignin: Structure and Materials; Glasser, W . G . ; Sarkanen, S., Eds.; A C S Symp. Ser., in press. RECEIVED February 27,1989

Chapter 32

Starlike Macromers from Lignin Willer de Oliveira

1,2

and Wolfgang G. Glasser

1,2

Department of Wood Science and Forest Products, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

1

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2

Multifunctional polymeric segments with controlled chemical and molecular characteristics (i.e., macromers) can be prepared from hydroxypropyl lignin (HPL) by either partial capping of O H groups followed by alkyl ether chain extension; or by grafting with mono functional linear chain segments. Star-like macromers may either serve as segmental components in block copolymers, or as thermoplastic elastomers with distinct crystallinity of one phase. Examples given include partially ethylated H P L which was chain-extended with propylene oxide; and star-block polymers of H P L with monofunctional cellulose tri-acetate of D P 12. Analytical results correspond to structural characteristics. T h e E n c y c l o p e d i a o f P o l y m e r Science a n d E n g i n e e r i n g defines m a c r o m e r s as " p o l y m e r s o f m o l e c u l a r weight r a n g i n g f r o m several h u n d r e d t o tens of t h o u s a n d s , w i t h a f u n c t i o n a l g r o u p at t h e c h a i n e n d t h a t c a n f u r t h e r p o l y m e r i z e " (1). B r a n c h e d or s p h e r i c a l molecules m a y p r o d u c e m a c r o m e r s w i t h m o r e t h a n t w o t e r m i n a l reactive f u n c t i o n a l groups, a n d these resemble star-like a r c h i t e c t u r e . M a c r o m e r s have g a i n e d usefulness i n the synthesis o f graft, b l o c k , a n d segmented p o l y m e r s , often w i t h m u l t i p h a s e m o r p h o l o g y . T h e m a c r o m e r must have a well-defined m o l e c u l a r weight a n d m o l e c u l a r weight d i s t r i b u t i o n (1). L i g n i n s i s o l a t e d f r o m organosolv p u l p i n g a n d s t e a m e x p l o s i o n have been s h o w n t o be o f low m o l e c u l a r weight, i n t h e range of_1000 o r below ( M ) , a n d o f n a r r o w m o l e c u l a r weight d i s t r i b u t i o n (M /M c a . 3) (2-5). T h i s reflects p e n t a m e r i c c o m p o s i t i o n o n the average, a n d t h i s is w i t h i n the m o l e c u l a r weight range t h a t is t y p i c a l for m a c r o m e r s . R e c e n t advances i n the a r t o f f r a c t i o n a t i n g l i g n i n s a n d l i g n i n derivatives w i t h r e g a r d t o m o l e c u l a r weights (6-8) create t h e p r o m i s e o f i s o l a t i n g m a c r o m e r i c l i g n i n fractions o f n a r r o w m o l e c u l a r weight d i s t r i b u t i o n ; a n d advances i n the field o f w

n

0097-6156/89/0397-0414$06.00/0 © 1989 American Chemical Society

n

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Starlike Macromers from Lignin

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c h e m i c a l m o d i f i c a t i o n of l i g n i n , w h i c h have p r o d u c e d l i g n i n s w i t h u n i f o r m t e r m i n a l f u n c t i o n a l i t y a n d g o o d s o l u b i l i t y (9-11), help meet the r e q u i r e m e n t for c o n t r o l l e d r e a c t i v i t y . H y d r o x y p r o p y l l i g n i n w i t h extended p r o p y l ether chains have recently been r e p o r t e d (12) t h a t are viscous l i q u i d s w i t h u n i f o r m t e r m i n a l h y d r o x y l f u n c t i o n a l i t y o n a l k y l ether c h a i n s t h a t r a d i a t e f r o m a c e n t r a l l i g n i n core. W i t h a n average h y d r o x y l f u n c t i o n a l i t y of a b o u t 1.2 per p h e n y l propane (Cg) repeat u n i t , a l i g n i n m a c r o m e r w o u l d possess a f u n c t i o n a l i t y of about 6 (13). S t a r - l i k e m a c r o m e r s result f r o m a p a r t i a l r e d u c t i o n of f u n c t i o n a l i t y , s u c h as b y c a p p i n g w i t h a m o n o f u n c t i o n a l ether or c a r b a m a t e s u b s t i t u e n t , followed b y c h a i n e x t e n s i o n w i t h a n a l k y l e n e oxide (13); or by the a d d i t i o n of p r e f o r m e d , m o n o f u n c t i o n a l c h a i n segments (14). W h e r e a s degree of c a p p i n g controls the n u m b e r of a r m s per s t a r i n the former case, s t o i c h i o m e t r y determines i t i n the l a t t e r . T h i s paper examines two types of h y d r o x y p r o p y l l i g n i n based m a c r o mers, a n d these are i l l u s t r a t e d s c h e m a t i c a l l y i n F i g u r e 1. M a c r o m e r s w i t h propylene oxide ( P O ) are f o r m e d b y r e d u c i n g the n u m b e r of available h y d r o x y l groups o n H P L followed b y c h a i n e x t e n s i o n w i t h P O ; a n d m a c r o m e r s w i t h cellulose triacetate ( C T A ) are synthesized b y a t t a c h i n g a m o n o f u n c t i o n a l C T A c h a i n to a l i m i t e d n u m b e r of t e r m i n a l O H groups o n H P L v i a a suitable grafting reaction. Experimental Materials. Hydroxypropyl lignin (HPL): O r g a n o s o l v (aqueous e t h a n o l ) l i g n i n f r o m aspen, s u p p l i e d b y R e p a p Technologies Inc. ( f o r m e r l y the B i o l o g i c a l E n e r g y C o r p o r a t i o n ) of V a l l e y Forge, P A , was h y d r o x y p r o p y l a t e d b y r e a c t i o n w i t h propylene oxide i n the u s u a l m a n n e r (9). T h i s d e r i v a t i v e was i s o l a t e d a n d purified as described p r e v i o u s l y (9). Cellulose triacetate segments: C e l l u l o s e t r i a c e t a t e , s u p p l i e d b y E a s t m a n K o d a k C o m p a n y of K i n g s p o r t , T N , was d e p o l y m e r i z e d i n accordance w i t h a m e t h o d b y S t e i n m a n n (15), a n d t h i s was N C O c a p p e d b y r e a c t i o n w i t h toluene d i i s o c y a n a t e as r e p o r t e d p r e v i o u s l y (14). A C T A segment w i t h a n average degree of p o l y m e r i z a t i o n of 12 ( c o r r e s p o n d i n g t o a n M of n

3600 gM (14).

) a n d a n average of 0.9 equivalents of N C O / m o l e , was i s o l a t e d

Methods. Reaction with DESO4: T h e h y d r o x y l f u n c t i o n a l i t y of H P L was reduced by r e a c t i o n w i t h d i e t h y l s u l p h a t e i n accordance w i t h earlier w o r k (13). T h e r e a c t i o n p r o d u c t was i s o l a t e d b y l i q u i d - l i q u i d e x t r a c t i o n a n d dialysis. Chain extension with PO: P a r t i a l l y b l o c k e d h y d r o x y p r o p y l l i g n i n derivatives were reacted w i t h propylene oxide i n toluene, u s i n g K O H as c a t a l y s t , for the purpose of c r e a t i n g extended p r o p y l ether chains. T h i s has been r e p o r t e d elsewhere (13). Grafting of CTA segments: M o n o f u n c t i o n a l C T A segments were a t t a c h e d t o H P L b y d i s s o l v i n g b o t h components i n ethylene chloride (ca. 2 0 % c o n c e n t r a t i o n ) a n d h e a t i n g the m i x t u r e for 1 h o u r i n the presence of T 9 c a t a l y s t s ( U n i o n C a r b i d e ) . T h e r e a c t i o n p r o d u c t was p o u r e d onto a

Figure 1. Schematic representation of two types of hydroxypropyl ligninbased macromers.

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1 1

S

32.

D E OLIVEIRA & GLASSER

Starlike Macromersfrom Lignin

T E F L O N m o l d ; the solvent was allowed t o evaporate; a n d the r e s u l t i n g film was k e p t i n a desiccator for 1 week before f u r t h e r t e s t i n g . Analytical Methods: U V spectroscopy was p e r f o r m e d o n a V a r i a n / C a r y 219 S p e c t r o m e t e r . H I h y d r o l y s i s followed the m e t h o d o f Hodges, et a l . (16) i n c o n j u n c t i o n w i t h the s e p a r a t i o n o f a l k y l iodides b y gas c h r o m a t o g r a p h y . T o t a l h y d r o x y l content was d e t e r m i n e d as u s u a l (17). G l a s s t r a n s i t i o n t e m p e r a t u r e s (T^) were d e t e r m i n e d b y p r e p a r i n g p o l y m e r i c blends o f l i g n i n derivatives w i t h c o m m e r c i a l t h e r m o p l a s t i c s h a v i n g T^ values at least 20° different f r o m those o f the derivatives. T h e s e blends were m i x e d i n the m e l t followed b y i n j e c t i o n m o l d i n g i n t o a d o g bone s h a p e d m o l d . T h e s e m o l d s were tested b y d y n a m i c m e c h a n i c a l t h e r m a l a n a l y s i s and t a n d e l t a peak t e m p e r a t u r e s were t a k e n as T (18). S w e l l i n g studies were p e r f o r m e d i n d i m e t h y l f o r m a m i d e ( D M F ) . X - r a y s c a t t e r i n g ( W A X S ) was performed o n a P h i l i p s Defractometer u s i n g a C u K a source i n the usual manner.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch032

9

Results and Discussion Macromers with propylene oxide. H y d r o x y p r o p y l (organosolv) l i g n i n ( H P L ) is a low m o l e c u l a r weight ( p r e ) p o l y m e r w i t h a n u m b e r average m o l e c u l a r weight o f ca^_ 1200 gM~ a n d a p p r o x i m a t e l y 6 equivalents o f h y d r o x y l groups per M (13). S t a r - l i k e m a c r o m e r c o n f i g u r a t i o n w i t h propylene oxide is d e t e r m i n e d b y b o t h degree o f c a p p i n g o f h y d r o x y l g r o u p s a n d degree o f c h a i n e x t e n s i o n . A l t h o u g h n u m e r o u s alternatives exist r e g a r d i n g c a p p i n g chemistry, convenience dictates the use o f d i e t h y l sulfate for O H r e d u c t i o n (13). A p a r t i a l l y e t h y l ether c a p p e d h y d r o x y p r o p y l l i g n i n d e r i v a t i v e y i e l d s a m i x t u r e of m e t h y l , ethyl, and isopropyl iodide when treated w i t h H I . T h e i r q u a n t i t a t i v e s e p a r a t i o n b y gas c h r o m a t o g r a p h y ( F i g . 2) y i e l d s i n f o r m a t i o n o n l i g n i n a n d p r o p y l ether content, a n d o n degree o f c a p p i n g (13). T h e degree o f c h a i n extension w i t h propylene oxide c a n also be a n a l y z e d b y H - N M R spectroscopy o f a c e t y l a t e d derivatives ( F i g . 3), a n d b y U V spectroscopy ( F i g . 4). W h e r e H - N M R spectroscopy is c o m p l i c a t e d b y the presence o f o v e r l a p p i n g e t h o x y a n d p r o p o x y signals, U V spectroscopy is l i m i t e d t o the d e t e r m i n a t i o n of n o n - U V a b s o r b i n g mass (i.e., e t h o x y p l u s propoxy groups). T h e r e l a t i o n s h i p between target m a c r o m e r f u n c t i o n a l i t y , degree o f c a p p i n g , a n d average m a c r o m e r m o l e c u l a r weight is i l l u s t r a t e d i n F i g . 5. T h i s r e l a t i o n s h i p reveals t h a t , for a target t r i f u n c t i o n a l s t a r - l i k e m a c r o m e r o f M 1500, a p p r o x i m a t e l y 6 0 % o f O H groups i n the p a r e n t H P L need t o b e b l o c k e d . T h e degree o f c h a i n e x t e n s i o n o n the r e m a i n i n g h y d r o x y groups determines the p o l y e t h e r n a t u r e o f the m a c r o m e r . E a r l i e r work o n c h a i n extended H P L s has s h o w n t h a t these d e r i v a tives p r o d u c e u n i f o r m (i.e., single phase) p o l y m e r s w i t h T ^ v a r y i n g i n accordance w i t h the G o r d o n - T a y l o r r e l a t i o n s h i p (12). P o l y u r e t h a n e s f r o m c h a i n - e x t e n d e d H P L s were f o u n d t o be r u b b e r - l i k e at r o o m t e m p e r a t u r e w i t h m o d u l u s d e c l i n i n g as l i g n i n content is reduced (8). S t a r - l i k e s t r u c t u r e determines f u n c t i o n a l i t y , T ^ , viscosity, a n d several other p r o p e r t i e s t h a t influence u t i l i t y as p o l y m e r segment. X

n

n

LIGNIN: PROPERTIES AND MATERIALS

418

Mel

n-Prl Etl

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Iso-Prl

Ar

0

3

6

9

Retention Time in Minutes F i g u r e 2. G a s c h r o m a t o g r a m o f a m i x t u r e o f a l k y l i o d i d e

12

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32. D E OLIVEIRA & GLASSER Starlike Macromersfrom Lignin 419

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420 LIGNIN: PROPERTIES AND MATERIALS

32.

D E OLIVEIRA & GLASSER

Starlike Macromers from Lignin

421

T h e engineering of l i g n i n - b a s e d macromers w i t h propylene oxide t o t a r get specifications appears as a useful technique for f o r m u l a t i n g c o m p o n e n t s for b l o c k copolymers a n d segmented thermosets. Macromers with cellulose triacetate. A n a l t e r n a t i v e m a c r o m e r synthesis route involves the g r a f t i n g of m o n o f u n c t i o n a l , preformed (linear) p o l y m e r chains o n t o a l i g n i n p r e p o l y m e r . W h e r e a d i f u n c t i o n a l c h a i n segment serves as c r o s s l i n k i n g agent, m o n o f u n c t i o n a l segments result i n s t a r - l i k e s t r u c tures. T h e r m o p l a s t i c elastomers are p r o d u c e d i f the m o n o f u n c t i o n a l , l i n e a r segment is glassy or c r y s t a l l i z a b l e (19). T h e schematic i l l u s t r a t i o n of F i g . 1 reveals t h a t s t o i c h i o m e t r y dictates the average n u m b e r of r a d i a t i n g a r m s , and t h u s f u n c t i o n a l i t y per M . D e p e n d i n g o n the c h e m i c a l a n d m o l e c u l a r characteristics of the a r m s b e i n g a t t a c h e d , two phase m o r p h o l o g y results f r o m phase d e m i x i n g . T h i s m a y be revealed a n a l y t i c a l l y b y differential s c a n n i n g c a l o r i m e t r y ( D S C ) , a m o n g other m e t h o d s .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch032

n

C e l l u l o s e triacetate ( C T A ) w i t h m o n o f u n c t i o n a l i t y ( t e r m i n a l N C O groups) was prepared a n d reacted w i t h H P L b y solvent c a s t i n g (14). S o m e e x p e r i m e n t a l results are s u m m a r i z e d i n T a b l e I. Between 1 a n d 12 C T A segm e n t s per H P L m a c r o m e r p r o d u c e copolymers w i t h between 60 a n d 9 5 % C T A content. D S C reveals single glass t r a n s i t i o n t e m p e r a t u r e s w h i c h v a r y w i t h c o m p o s i t i o n , a n d m e l t i n g p o i n t s ( T ) . T h e results suggest t h a t T ^ varies i n accordance w i t h the F o x r e l a t i o n s h i p i n d i c a t i n g a m i s c i b l e a m o r p h o u s phase. T h e m e l t i n g p o i n t ( T ) also varies s l i g h t l y i n r e l a t i o n t o c o m p o s i t i o n , a n d i t is f o u n d t o be highest w i t h the highest H P L content. H e a t of fusion ( H ) declines f r o m 1 to 0.5 c a l g " w h e n C T A content declines f r o m 95 t o 6 0 % . S o l f r a c t i o n is u s u a l l y above 9 0 % , unless C T A content increases t o 9 0 % or above. T h i s suggests t h a t the C T A c o m p o n e n t c o n t a i n e d a s m a l l a m o u n t o f d e r i v a t i v e w i t h higher f u n c t i o n a l i t y . m

m

1

m

T a b l e I. P r o p e r t i e s of M a c r o m e r s w i t h C T A T (°C) g

C T A arms CTA per M Content (wt.%) n

1 2.5 6 12

60 80 90 95

Experimt.

Theory

T (°C)

113 123 125 126

112 124 130 133

252 250 239 246

Sol H ( c a l g - *) F r a c t i o n (%) (%)

m

m

0.5 0.5 0.8 1.0

93 93 89 82

T h e r e s u l t i n g s t a r - l i k e m a c r o m e r s w i t h C T A were s o l i d m a t e r i a l s w i t h d i s t i n c t c r y s t a l l i n i t y , even at 20 a n d 4 0 % H P L ( F i g . 6). T h i s suggests t h a t even short C T A chains (i.e., D P 12) have the a b i l i t y t o organize i n t o a c r y s t a l l i n e l a t t i c e , thereby s e r v i n g as pseudo-crosslinks. D e p e n d i n g o n the c h e m i c a l n a t u r e , a n d the m o l e c u l a r weight, m u l t i p h a s e m a t e r i a l s result w i t h v a r i a b l e m e c h a n i c a l properties. A b o v e T of the c h a i n segment, m

LIGNIN: PROPERTIES AND MATERIALS

422

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100

r

Figure 5. Theoretical relationship between required degree of capping and M for star-like macromers having (A) 3, (B) 4, and (C) 5 functional groups. (Note: For H P L having 1.3 O H groups C9 on the average, and a molar substitution of 1.0.) n

Figure 6. Wide angle X-ray scattering (WAXS) results of C T A - H P L copolymers. (A) C T A (control); (B) copolymer with 80% C T A content; and (C) copolymer with 60% C T A content.

32.

D E OLIVEIRA & GLASSER

Starlike Macromersfrom Lignin

423

these materials are fluids that may be processed with typical thermoplastic process technology; and below T they are tough structural materials. m

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch032

Conclusions The low molecular weight character of lignin and lignin derivatives (es­ pecially those derived from organosolv pulping and steam explosion), the superior solubility character of lignin derivatives, and the availability of molecular fractionation know-how, all invite the synthesis of macromers with controlled properties from lignin for use in graft, block, and segmented copolymers. This may be achieved by either capping hydroxyl functionality followed by chain extension with alkylene oxides; or by attaching preformed monofunctional chain segments. Both method of synthesis and chemistry of linear chain segment, determine processability and material properties. Acknowledgment Financial support for this study was provided, in part, by the government of Brazil, and by an industry-university cooperative with the Center for Innovative Technology of Virginia. Thanks also go to Mrs. Barnett for experimental assistance with several instrumental analyses. Literature C i t e d 1. Kawakami, Y. In Ency. Polym. Sci. Eng.; Kroschwitz, J. I., Ed.; John Wiley & Sons: New York, 1987, Vol. 9, pp. 195-204. 2. Glasser, W . G . ; Barnett, C . Α.; Rials, T . G . ; Saraf, V . P. J. Appl. Polym. Sci. 29(5), 1815-30 (1984). 3. Glasser, W . G . ; Barnett, C . Α . ; Muller, P. C . ; Sarkanen, Κ. V . J. Agric. Food Chem. 1983, 31(5), 921-930. 4. Lora, J. H.; Aziz, S. Tappi J. 1985, 68(8), 94-97. 5. Marchessault, R. H.; Coulombe, S.; Morikawa, H.; Robert, D . Can. J. Chem. 1982, 60(18), 2372-2382. 6. Faix, O.; Lange, W . ; Beinhoff, O. Holzforschung 1980 34, 174-6. 7. Morck, R.; Yoshida, H . ; Kringstad, K . P. Holzforschung 1986 40 (Suppl.), 51-60. 8. Kelley, S. S.; Glasser, W . G . ; Ward, T . C . J. Appl. Polym. Sci., in press. 9. Wu, L . C . - F . ; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29, 1111-23. 10. Christian, D . T . ; Look, M . ; Nobell, A ; Armstrong, T. S. U.S. Patent 3,546,199, 1970. 11. Mozheiko, L . N.; Gromova, M . F . ; Bakalo, L . Α . ; Sergeyeva, V . N . Polym. Sci. USSR 1981, 23(1), 126-132. 12. Kelley, S. S.; Glasser, W . G . ; Ward, T . C . J. Wood Chem. Technol. 1988, 8(3), 341-359. 13. de Oliveira, W . ; Glasser, W . G . J. Appl. Polym. Sci., in press. 14. Demaret, V . ; Glasser, W . G . J. Appl. Polym. Sci., in press. 15. Steinmann, H . W . Polym. Prep. 1970, 11(1), 285.

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LIGNIN: PROPERTIES AND MATERIALS

16. Hodges, K . L.; Rester, W . E . ; Wiederrick, D . L.; Grover, T . A . Anal. Chem. 1979, 51(13), 2172. 17. Siggia, S.; Hanna, J. G . Quantitative Organic Analysis via Functional Groups; J. Wiley & Sons, 1978, pp. 12-14. 18. Glasser, W . G.; Knudsen, J. S.; Chang, C.-S. J. Wood Chem. Technol. 1988, 8(2), 221-234. 19. Legge, N . R.; Holden, G.; Schroeder, H . E . , Eds. Thermoplastic Elastomers; Hauser Publishers, 1987; 575 pp.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch032

RECEIVED May 29,1989

Chapter 33

Hydroxypropyl Lignins and Model Compounds Synthesis and Characterization by Electron-Impact Mass Spectrometry John A . Hyatt

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

Research Laboratories, Eastman Chemicals Division, Eastman Kodak Company, Kingsport, TN 37662

A n iterative method for the controlled rational syn­ thesis of chain-extended hydroxypropyl derivatives of both aliphatic and aromatic hydroxyl compounds, based on oxymercuration of allyl ethers, is described. It is shown that the degree of chain extension in such com­ pounds can be determined by electron impact mass spectrometry. Degradation of hydroxypropylated lignins by catalytic hydrogenolysis followed by capillary gas chromatography-mass spectrometry is demonstrated to be a method for establishing the presence and degree of chain extension in the hydroxypropyl lignin polymers. O n e a t t r a c t i v e a p p r o a c h , pioneered b y G l a s s e r a n d co-workers (1), t o t h e conversion o f l i g n i n i n t o a higher-value m a t e r i a l comprises r e a c t i o n o f l i g n i n w i t h propylene oxide or ethylene oxide t o produce a n a l i p h a t i c p o l y o l s u i t ­ able for use i n p r e p a r i n g network p o l y m e r s such as p o l y u r e t h a n e foams a n d plastics. L i g n i n s are c o m p l e x m i x t u r e s o f m o d e r a t e - t o - h i g h m o l e c u l a r weight p h e n y l p r o p a n o i d p o l y m e r s w h i c h bear phenolic a n d p r i m a r y a n d secondary a l i p h a t i c h y d r o x y l groups (2), a n d conversion o f t h i s m a t e r i a l f r o m , i n effect, a m i x t u r e o f different types o f alcohols t o a substance h o ­ mogeneous i n terms o f h y d r o x y l type a n d r e a c t i v i t y g r e a t l y improves i t s u t i l i t y as a p o l y o l . Hydroxypropylation of lignins can be carried out under a variety of c o n d i t i o n s , b u t the most successful approach has i n v o l v e d r e a c t i o n o f l i g n i n w i t h propylene oxide i n t h e presence o f basic c a t a l y s t s ; t h e l i g n i n is sus­ p e n d e d i n toluene or dissolved i n aqueous base ( 3 , 4 ) . T h e v a r i a t i o n o f p o l y o l properties w i t h p r e p a r a t i v e m e t h o d (4) brings u p a f u n d a m e n t a l question o f h y d r o x y p r o p y l l i g n i n s t r u c t u r e : I n t h e r e a c t i o n o f l i g n i n s w i t h propylene oxide ( F i g . 1), w h a t is the p r o d u c t d i s t r i b u t i o n a n d degree o f c h a i n extension o f a l k o x y p r o p y l groups? A r e there a significant n u m b e r o f 0097-6156/89/0397-0425$06.00/ϋ © 1989 American Chemical Society

426

LIGNIN: PROPERTIES AND MATERIALS

hydroxypropylated aliphatic hydroxy Is in the product, or does most of the propylene oxide reside on the phenolic hydroxyls of the lignin nucleus? Although techniques such as N M R spectroscopy can provide valuable information about the structure of hydroxypropyl lignins (4), we perceive a need for the development of synthetic methodology for model compounds which incorporate the structural features thought to be present in hydrox­ ypropyl lignins. Such compounds can be used for studies of reaction kinetics as well as for confirming spectral assignments.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

Synthesis and Mass Spectroscopy of M o d e l Compounds Although it is a simple matter to attach a single hydroxypropyl residue to a phenolic hydroxyl, the controlled synthesis of chain-extended hydrox­ ypropyl ethers is much more difficult (Fig. 2) (5). T h e difficulty is that of selectively alkylating an aliphatic hydroxyl on the substrate in the pres­ ence of aliphatic hydroxyls on hydroxypropyl groups. Thus we required a method for the preparation of compounds of the type shown in Figure 2 where η is precisely known and controlled (rather than being a statistical range of values). Our solution to this synthetic problem was the development of an iterative technique for preparing hydroxypropyl ethers from allyl ethers via oxymercuration-reduction. Figure 3 illustrates the process for the preparation of a series of three chain-extended hydroxypropyl derivatives of 2,6-dimethoxyphenol. Conversion of phenol 1 to the allyl ether 2 under phase-transfer conditions (6) was followed by oxy mer cur at ion (7) to give the intermediate organomercurial 3, which was reduced without isolation to give hydroxypropyl ether 4 in 64% overall yield. Ether 4. was then allylated to provide 5, which upon oxymercuration-reduction af­ forded hydroxypropyl derivative 6. One further iteration of the allylationoxymercuration-reduction sequence yielded the hydroxypropyl compound 7. We have found that this sequence can be generally applied to the syn­ thesis of hydroxypropyl derivatives of alcohols and phenols; yields are uni­ formly acceptable and products of the desired degree of chain extension can be prepared completely free of lower and higher oligomers. The compounds shown in Table I were prepared using this chemistry. In the course of characterizing the hydroxypropyl ethers prepared in this study, we noticed an intriguing pattern in the mass spectral fragmenta­ tion of these compounds. As shown in Table I, the degree of chain extension is reflected in the fragmentation pattern: Alcohols modified by a single hy­ droxypropyl ether unit have a strong M-58 peak, ethers of chain extension degree of 2 show a loss of m/e 116 and 58, and tripropylene glycol deriva­ tives (degree of chain extension = 3) lose m / e 174, 116, and 58. Figure 4 shows the mass spectrum of compound 6. The loss of m / e 116 for this dipropylene glycol ether leads to the base peak at m / e 168, and the loss of m / e 58 to m / e 226 is the second most important fragmentation. In the case of all of the compounds in Table I, loss of the entire propylene glycol ether side chain provided either the base peak of the mass spectrum or the second strongest peak present. It is clear from this data that the length

33.

HYATT

427

Hydroxypropyl Lignins and Model Compounds

CHJJOH

CH-O-Aryl-

j-O-CH

CH-O-ArylCH3CH—»CH

-O-CH 2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

Various Conditions

F i g u r e 1. H y d r o x y p r o p y l a t i o n o f l i g n i n .

Ο

/\

CH OH 2

CH3-CH—CH

OCH3

CH OH 2

2

CH3O

OCH3

OH

Ο

/\ CH3-CH—CH

2

(Value of η is not controllable) F i g u r e 2. H y d r o x y p r o p y l a t i o n o f phenols a n d alcohols.

Γ

M

3

N

OH

/-CH O

o

>

'-\

CH -/

C H

Ν

C H

O

*

/-CH HO

3-\

\ 3

CHaO^^^OCHa

Γ

3

2

2

2

3

' 51%

NaBH4

C

H

3

N

° CH -(

3

M

4

Oh

O ^ Y ^

Γ

4

2

CH HgOAc

NaBH -OH 76%

O

Ο ^ Ο ^ ^ Ν ^ ^ OCH3

1. CH = CH-CH Br 2. Hg(OAc)

2

XX

F i g u r e 3. I t e r a t i v e synthesis o f h y d r o x y p r o p y l ethers.

3

50%

4

3. NaBH

2

OCH

OCH CH = CH

CHaO'Ç^ 2

84%

OH

3

1

^OCH

CH3O^ ^ y ^ O C H a

3

CH 0^

2

H 0, THF

2

PTC

2

Hg(OAc)

2

CH = CH-CH Br

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

3

H

s

2 3

ο

00

6

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

33.

HYATT

Hydroxypropyl Lignins and Model Compounds

Table I.

154

8

Electron Impact Mass Spectral Fragmentation of Hydroxypropyl Lignin Model Compounds 212

429

Figure 4. Mass spectrum of Compound 6.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

ο

1

S

33.

HYATT

Hydroxypropyl Lignins and Model Compounds

431

o f a n oligo(propylene glycol) c h a i n a t t a c h e d t o a n o r g a n i c a l c o h o l c a n be d e t e r m i n e d b y e x a m i n a t i o n of i t s mass s p e c t r u m .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

Degradation and Analysis of H y d r o x y p r o p y l Lignin T h e results described above i n d i c a t e d t h a t , i f a w a y c o u l d be f o u n d t o degrade a h y d r o x y p r o p y l l i g n i n t o v o l a t i l e fragments s u i t a b l e for a n a l y s i s b y c a p i l l a r y gas c h r o m a t o g r a p h y / m a s s s p e c t r o m e t r y , m u c h c o u l d be l e a r n e d a b o u t the d i s t r i b u t i o n a n d l e n g t h of h y d r o x y p r o p y l residues present o n the l i g n i n . T h e k n o w n a b i l i t y t o degrade l i g n i n s b y hydrogenolysis (8), c o u p l e d w i t h the r e d u c t i v e s t a b i l i t y o f s i m p l e a l k y l a n d a r o m a t i c ethers, p r o m p t e d us t o e x a m i n e the scheme s h o w n i n F i g u r e 5. T w o c o n t r o l e x p e r i m e n t s were first c o n d u c t e d . I n the first, m o d e l c o m p o u n d 7 was subjected to the hydrogenolysis c o n d i t i o n s a n d t h e n a n a l y z e d b y V P C / M S . D e s p i t e hydrogenolysis at 285°C over 5 % P d / C c a t a l y s t u n der 5000 p s i H 2 , the m o d e l c o m p o u n d was recovered i n t a c t ; n o evidence of r i n g r e d u c t i o n or h y d r o x y p r o p y l c h a i n cleavage was seen i n the mass spect r u m . I n the second c o n t r o l e x p e r i m e n t , a s a m p l e of m e t h a n o l organosolv l i g n i n ( h a r d w o o d ) was h y d r o g e n a t e d under the same c o n d i t i o n s a n d the v o l a t i l e fractions recovered b y h i g h v a c u u m d i s t i l l a t i o n . V P C / M S a n a l y s i s o f the v o l a t i l e fractions ( w h i c h a m o u n t e d t o 2 8 - 3 8 % o f the l i g n i n charged) l e d t o i d e n t i f i c a t i o n o f the c o m p o u n d s l i s t e d i n T a b l e I I . It is c r u c i a l t o note t h a t none o f the c o m p o u n d s p r o d u c e d b y hydrogenolysis o f u n m o d i fied l i g n i n d i s p l a y e d a mass s p e c t r a l f r a g m e n t a t i o n of m / e 58 or a m u l t i p l e thereof. T h u s we have established t h a t h y d r o x y p r o p y l a t e d l i g n i n moieties s u r v i v e the hydrogenolysis c o n d i t i o n s , a n d t h a t the hydrogenolysis p r o d ucts of u n m o d i f i e d l i g n i n are free of s t r u c t u r e s w h i c h w o u l d interfere w i t h mass s p e c t r a l i d e n t i f i c a t i o n of h y d r o x y p r o p y l a t e d c o m p o n e n t s . W h e n the h y d r o g e n o l y s i s / d i s t i l l a t i o n / V P C / M S sequence was c a r r i e d o u t o n a s a m p l e of l i g n i n w h i c h h a d been m o d i f i e d b y r e a c t i o n w i t h p r o p y lene oxide i n toluene i n the presence of K O H / 1 8 - c r o w n - 6 c a t a l y s t , inspect i o n o f the r e s u l t i n g mass s p e c t r a for c o m p o u n d s h a v i n g m / e 58 f r a g m e n t a t i o n s ( a n d m u l t i p l e s thereof) led to i d e n t i f i c a t i o n of the m a t e r i a l s l i s t e d i n T a b l e I I I . It w i l l be seen t h a t several m o n o - h y d r o x y p r o p y l a t e d m a t e r i a l s a n d three d i - h y d r o x y p r o p y l ( c h a i n extension degree = 2) c o m p o u n d s were f o u n d . N o p r o d u c t s h a v i n g h y d r o x y p r o p y l chains longer t h a n degree 2 were f o u n d ; t h u s i t appears t h a t t h i s p a r t i c u l a r m o d i f i e d l i g n i n contains m a n y short h y d r o x y p r o p y l chains, r a t h e r t h a n a few chains o f greater degree of extension. S i m i l a r a n a l y s i s of a l i g n i n m o d i f i e d b y h y d r o x y p r o p y l a t i o n i n aqueous base y i e l d e d o n l y p r o d u c t s b e a r i n g single h y d r o x y p r o p y l residues. T h i s a p p a r e n t lack of c h a i n extension is of course consistent w i t h the fact t h a t the h y d r o x y p r o p y l a t i o n was c a r r i e d out under c o n d i t i o n s f a v o r i n g r e a c t i o n o n l y o n phenolic h y d r o x y l groups. A r e a s of u n c e r t a i n t y i n t h i s m e t h o d o f a n a l y z i n g m o d i f i e d l i g n i n s i n clude the p r o b l e m t h a t l i t t l e m o r e t h a n o n e - t h i r d of the l i g n i n is converted t o v o l a t i l e p r o d u c t s by the hydrogenolysis r e a c t i o n ; the n o n - v o l a t i l e f r a c t i o n cannot be a n a l y z e d b y V P C / M S . T h i s w i l l c o n s t i t u t e a difficulty o n l y i f the

432

LIGNIN: PROPERTIES AND MATERIALS Hydroxypropyl Lignin

1

H Pd/c, >250 ,>3000 PSI H, lf

Hydrogenated Hydroxypropyl Lignin

I

High Vacuum Distillation

Volatile Fractions Capillary VPC Mass Spectral Analysis

M-58, M-116, M-174,...etc

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

F i g u r e 5. H y d r o x y p r o p y l l i g n i n d e g r a d a t i o n a n d a n a l y s i s scheme.

Table II. Products identified in the VPC/MS Analysis of the Volatile Fraction from Unmodified Lignin

Note: None of these compounds showed m/e M-58, or multiples thereof.

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433

Table III. Compounds Identified in the VPC/MS Analysis of a Hydrogenated Hydroxypropyl Lignin Peak No.

m/e

Fragmentation

Structure CH

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786

226

3

M-15, -58

C2H5

CH

2

818

854

873

168

M-15, -58

???

Continued on next page

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434 LIGNIN: PROPERTIES AND MATERIALS

Table III. Continued

33.

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Hydroxypropyl Lignins and Model Compounds

435

d i s t r i b u t i o n a n d degree of c h a i n extension o n the p a r t of the l i g n i n molecules w h i c h r e m a i n n o n - v o l a t i l e differ f r o m t h a t o n t h e p a r t o f the molecules w h i c h are converted t o v o l a t i l e fragments. W h i l e t h i s seems a n u n l i k e l y scen a r i o , i t i s a t present i m p o s s i b l e t o establish the p o i n t w i t h a n y certainty. A second area o f u n c e r t a i n t y arises f r o m the fact t h a t the m e t h o d has been tested o n l y w i t h m o d e l c o m p o u n d s u p t o degree of c h a i n e x t e n s i o n = 3 (i.e., c o m p o u n d 7). W e d o not yet k n o w whether longer h y d r o x y p r o p y l residues w o u l d b e degraded b y these procedures; t h i s p o i n t w i l l be established i n t i m e b y the synthesis o f a d d i t i o n a l m o d e l c o m p o u n d s .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch033

Summary W e have developed a s i m p l e , i t e r a t i v e s y n t h e t i c m e t h o d for the p r e p a r a t i o n of h y d r o x y p r o p y l derivatives of phenolic a n d a l i p h a t i c alcohols w h i c h allows complete d e f i n i t i o n a n d c o n t r o l o f the degree o f c h a i n extension i n t h e p r o d ucts. T h i s m e t h o d o l o g y has been a p p l i e d t o the p r e p a r a t i o n o f a series o f l i g n i n m o d e l c o m p o u n d s h a v i n g h y d r o x y p r o p y l c h a i n e x t e n s i o n degrees o f 13. W e have s h o w n t h a t the degree of chain extension i n such c o m p o u n d s c a n be u n a m b i g u o u s l y defined b y analysis o f t h e i r electron i m p a c t mass spect r a . I t has furthermore been d e m o n s t r a t e d t h a t such c o m p o u n d s are stable to a h y d r o g e n o l y s i s / d i s t i l l a t i o n / V P C / M S sequence w h i c h , w h e n a p p l i e d t o h y d r o x y p r o p y l l i g n i n s , defines the site a n d degree o f h y d r o x y p r o p y l a t i o n o n the v o l a t i l e f r a c t i o n o f the l i g n i n residues. T o p i c s for f u r t h e r i n v e s t i g a t i o n i n c l u d e d e t e r m i n a t i o n of the degree o f c h a i n e x t e n s i o n at w h i c h the m e t h o d breaks d o w n , a n d the n a t u r e o f the l i g n i n segments w h i c h are not rendered v o l a t i l e b y hydrogenolysis. Acknowledgment W e t h a n k P r o f . W . Glasser for p r o v i d i n g several h y d r o x y p r o p y l a t e d phenols a n d l i g n i n samples used i n t h i s study. Literature C i t e d 1. Rials, T.; Glasser, W . Holzforschung 1986, 40, 353, and references cited therein. 2. Sarkanen, K . ; Ludwig, C . Lignins. Occurrence, Structure, and Reactions; Wiley-Interscience: New York, 1971. 3. Wu, L.; Glasser, W . J. Appl. Polym. Sci. 1984, 29, 1111. 4. Glasser, W.; Barnett, C.; Rials, T.; Saraf, V . J. Appl. Polym. Sci. 1984, 29, 1815. 5. Gee, G . ; Higginson, W . ; Levesley, P.; Taylor, K . J. Chem. Soc. 1959, 1338. 6. Starks, C.; Liotta, D . Phase Transfer Catalysis; Academic Press: New York, 1978. 7. House, H . Modern Synthetic Reactions; 2nd ed.; W . A . Benjamin: New York, 1972; pp. 387-396. 8. Hoffmann, P.; Schweers, W . Holzforschung 1975, 29, 74. RECEIVED March 17,1989

Chapter 34

Bleaching of Hydroxypropyl Lignin with Hydrogen Peroxide Charlotte A. Barnett

1,2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

1

and Wolfgang G . Glasser

1,2

Department of Wood Science and Forest Products, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 2

The bleaching of non-phenolic hydroxypropyl lignin (HPL) with hydrogen peroxide in homogeneous phase results in 50-90% loss of color depending on the definition of color. This is more realistically represented by a weighted absorptivity average in the visible range of the spectrum rather than by a fixed wavelength. The bleaching effect varies with the amount of hydrogen peroxide charged; with reaction time; with p H ; and with other parameters. The oxidation reaction is best carried out in aqueous alcohol, at either pH 2 or above 12-13; and with 25-50% hydrogen peroxide on lignin derivative. At 80°C, the reaction is 90% complete after 1-2 hours with hardwood organosolv lignin, but it takes longer with other lignin types. Treatment with H O introduces carboxylic acid functionality. 2

2

T h e t y p i c a l l y d a r k b r o w n color o f isolated l i g n i n p r o d u c t s a n d t h e i r d e r i v a tives constitutes a severe d r a w b a c k t o their u t i l i z a t i o n i n such s t r u c t u r a l m a t e r i a l s as engineering plastic (1). A l t h o u g h n o t o f significant d e t r i m e n t to the p h y s i c a l a n d m e c h a n i c a l properties o f l i g n i n - d e r i v e d m a t e r i a l s , color is perceived as a significant h a n d i c a p t o m a r k e t i n g i n c o m m e r c i a l p o l y m e r markets (1). T h e light a b s o r b i n g characteristics o f isolated lignins exceed those o f l i g n i n i n i t s native state (i.e., w o o d a n d other b i o m a t e r i a l s ) , a n d this has been a t t r i b u t e d t o t h e f o r m a t i o n o f various c h r o m o p h o r i c f u n c t i o n a l groups d u r i n g i s o l a t i o n (2). M o s t p r o m i n e n t l y a m o n g t h e m are c o n j u g a t e d q u i n o n o i d structures w h i c h are c o m m o n l y removed f r o m the l i g n i n 1

0097-6156/89/0397-0436$06.00/0 © 1989 American Chemical Society

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

34.

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437

of h i g h y i e l d p u l p s b y the use of h y d r o g e n peroxide (3). A vast l i t e r a ­ ture is available o n t h i s type of " l i g n i n - r e t a i n i n g " b l e a c h i n g of p u l p s , w h i c h is contrasted by the " l i g n i n - r e m o v i n g " b l e a c h i n g technology n o r m a l l y i n ­ v o l v i n g chlorine a n d / o r chlorine dioxide (4). L i g n i n - r e t a i n i n g b l e a c h i n g is k n o w n to be t r a n s i e n t since l i g h t a b s o r b i n g s t r u c t u r a l features reappear u p o n exposure to the elements, especially oxygen a n d U V - r a y s . T h i s has been a t t r i b u t e d t o the ease of quinone regeneration by p h e n o l i c f u n c t i o n a l groups (5). A more p e r m a n e n t r e m o v a l of color has been described b y L i n (6), and b y D i l l i n g a n d Sarjeant (7), for l i g n i n derivatives i n w h i c h the phe­ n o l i c f u n c t i o n a l i t y has been p a r t i a l l y b l o c k e d . These largely n o n - p h e n o l i c ( a n d s u l p h o n a t e d ) l i g n i n derivatives were bleached i n homogeneous aque­ ous phase w i t h h y d r o g e n peroxide a n d chlorine dioxide. R e d u c t i o n s i n color of 8 0 - 9 3 % were r e p o r t e d for these water soluble derivatives ( 6 , 7 ) . It was the intent of the present i n v e s t i g a t i o n t o e x a m i n e the one step b l e a c h a b i l i t y of n o n - p h e n o l i c , w a t e r - i n s o l u b l e h y d r o x y p r o p y l l i g n i n ( H P L ) derivatives w i t h h y d r o g e n peroxide i n homogeneous phase (i.e., aqueous ethanol). Experimental Materials. H y d r o x y p r o p y l l i g n i n ( H P L ) derivatives were available f r o m the f o l l o w i n g l i g n i n sources: organosolv (methanol) l i g n i n f r o m spruce, s u p p l i e d b y O r g a n o c e l l , M u n i c h , F R G e r m a n y ; organosolv ( m e t h a n o l ) l i g n i n f r o m red oak, s u p p l i e d b y a n undisclosed i n d u s t r i a l source; organosolv (ethanol) l i g n i n f r o m aspen, s u p p l i e d by R e p a p Technologies, Inc. (formerly the B i o l o g i c a l E n e r g y C o r p . ) , V a l l e y Forge, P A ; kraft l i g n i n f r o m pine ( I n ­ d u l i n A T ) , supplied by Westvaco C o r p . , N . Charleston, S C ; and kraft lignin from hardwood, supplied by Westvaco C o r p . , N . Charleston, S C . A l l lignins were d e r i v a t i z e d w i t h propylene oxide b y b a t c h reaction as r e p o r t e d p r e v i ­ ously ( 8 , 9 ) , a n d the products were separated f r o m h o m o p o l y m e r f r a c t i o n s of propylene oxide b y l i q u i d - l i q u i d e x t r a c t i o n . Methods. A t y p i c a l hydrogen peroxide b l e a c h i n g o p e r a t i o n consists of t r e a t ­ m e n t of a 2 0 % H P L s o l u t i o n i n 6 0 - 7 5 % aqueous e t h a n o l w i t h 2 5 - 5 0 % h y d r o ­ gen peroxide (by weight) o n l i g n i n derivative at 80°C. T h e r e a c t i o n m e d i u m is adjusted to p H 2 b y the a d d i t i o n of H C 1 , or to p H >12-13 b y N a O H . C o l o r loss is d e t e r m i n e d b y U V / V I S absorbance measurements o n s u i t a b l y d i l u t e d samples. A b s o r b a n c e was measured at 25 n m intervals f r o m 325 n m to 500 n m . These values were converted to a b s o r p t i v i t y ( L g"" c m " ) a n d the area under the curve was integrated f r o m 350 n m to 500 n m u s i n g software b y P o l y M a t h C o n t r o l D a t a ( © 1 9 8 4 ) . T h i s value was c o m p a r e d to c o r r e s p o n d ­ ing values o b t a i n e d w i t h the s t a r t i n g m a t e r i a l ( l i g n i n or H P L ) , a n d the color loss was c a l c u l a t e d f r o m 1

Color Loss(%) =

1-

A r e a of bleached s a m p l e A r e a of s t a r t i n g m a t e r i a l

1

χ 100

LIGNIN: PROPERTIES AND MATERIALS

438

S i m i l a r c a l c u l a t i o n s were done u s i n g seven i n d i v i d u a l wavelengths between 350 a n d 500 n m (i.e., at 25 n m intervals) a n d , u s i n g the s u m o f the a b s o r p t i v i t i e s at the 7 wavelengths, color loss was c o m p u t e d f r o m Color Loss(%) = f 1 L

«' + * ' "' "( P ) 1 αχ + 2 a + 2 a . . . + a ( s t a r t i n g m a t e r i a l ) J 2
5 0 % per h a l f - h o u r i n i t i a l l y to between 0.5 a n d 2 % after 8 hours. Significant differences are detected for response rate t o b l e a c h i n g w i t h H 2 O 2 for l i g n i n s f r o m different sources ( F i g . 4). T h i s m a y be a t t r i b u t e d to differences i n c h e m i c a l f u n c t i o n a l i t y a n d other factors. pH. L i g n i n - r e t a i n i n g b l e a c h i n g i n the p u l p a n d paper i n d u s t r y c o m m o n l y employs H 2 O 2 at alkaline p H levels ( 3 , 4 , 1 2 ) . T h i s preference m u s t be a t t r i b u t e d to the s u s p e c t i b i l i t y of the phenoxide anions t o H 2 O 2 . T h e s e ions are absent i n H P L due to the non-phenolic character of t h i s derivative t y p e . T h u s a l l p H levels have been explored i n the c u r r e n t s t u d y . T h e results i n d i c a t e t h a t effective color loss is achieved at b o t h extremes of the p H scale, at p H 2, a n d >12-13 ( F i g . 5). U n d e r alkaline c o n d i t i o n s , the i n i t i a l p H must exceed t h a t of the p K of H 2 O 2 (i.e., 11.6). It is, however, recognized t h a t the p H drops r a p i d l y i n the course of the reaction due a p p a r e n t l y t o the f o r m a t i o n of acidic f u n c t i o n a l i t y w h i c h neutralizes the a l k a l i . O n the a c i d side, effective use of H 2 O 2 requires s t r o n g l y acidic c o n d i t i o n s ( p H 2). A p H o f 1, however, was f o u n d t o result i n less t h a n o p t i m a l b l e a c h i n g , p r o b a b l y because of c h r o m o p h o r e - c r e a t i n g side-reactions. T h e c h e m i s t r y of H 2 O 2 involves the f o r m a t i o n of active reaction species f r o m h y d r o g e n peroxide under the extreme p H c o n d i t i o n s : a

H 0 + [HOf ^ 2

[H OOH]« â 2

A

d

H 0 3

2

B

~

[Η0 ] 2

θ

W h e r e a s the reactive species under acidic c o n d i t i o n s are the [ Η 2 θ Ο Η ] a n d [ Η Ο ] cations, the reactive species under a l k a l i n e c o n d i t i o n s is the [ Η θ 2 ] a n i o n . W h e r e a s the c a t i o n i c o x i d a t i o n species are stronger o x i ­ d a n t s , w i t h o x i d a t i o n p o t e n t i a l r i s i n g w i t h increasing a c i d i t y favoring a r o ­ m a t i c r i n g h y d r o x y l a t i o n b y electrophilic s u b s t i t u t i o n (3,13), the a n i o n i c species m e d i a t e a n u c l e o p h i l i c a t t a c k o n quinones a c c o r d i n g t o the scheme i l l u s t r a t e d i n F i g . 6 ( 3 , 1 0 , 1 1 ) . T h e f o r m a t i o n of new a c i d i c f u n c t i o n a l i t y results i n a r a p i d decline i n p H . T h e effect of H 2 O 2 o n H P L c h e m i s t r y a n d f u n c t i o n a l i t y can be assessed conveniently b y F T I R spectroscopy. It has recently been d e m o n s t r a t e d t h a t q u a n t i t a t i v e s t r u c t u r a l differences between lignins c a n be revealed b y φ

φ

θ

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

34.

HARNETT & GLASSER

Bleaching of Hydroxypropyl Lignin

TIME

443

(HR)

F i g u r e 4. R a t e of color loss for H P L derivatives f r o m red oak o r g a n o solv l i g n i n ( A ) , aspen organosolv l i g n i n ( B ) , pine kraft l i g n i n ( C ) , h a r d w o o d kraft l i g n i n ( D ) , a n d spruce organosolv l i g n i n ( E ) . ( O N stands for overnight.)

LIGNIN: PROPERTIES AND MATERIALS

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444

F i g u r e 6. Suggested m e c h a n i s m for the reaction of o r t h o - q u i n o n o i d s t r u c tures i n l i g n i n derivatives w i t h hydrogen peroxide under alkaline c o n d i t i o n s (according to G i e r e r , ref. 3).

34.

BARNETT& GLASSER

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t h i s m e t h o d ( 1 4 , 1 5 ) . Differences between bleached a n d unbleached h y ­ d r o x y p r o p y l lignins are i l l u s t r a t e d i n F i g u r e s 7 a n d 8. U s i n g a baselinecorrected a b s o r p t i v i t y s p e c t r u m w h i c h was autoscaled so t h a t the ether peak at 1125 c m was adjusted to 100% a b s o r p t i o n , s p e c t r a l differences between the bleached ( p H 2) a n d the unbleached l i g n i n d e r i v a t i v e are re­ vealed b y the shaded areas of F i g u r e 7. T h e most a p p a r e n t differences are i n the regions between 1600 a n d 1800 c m " , a n d between 3000 a n d 3600 c m " . M i n o r differences also appear between 1200 a n d 1300 c m " . S u b t r a c t i o n s p e c t r a for a c i d a n d alkaline-bleached l i g n i n derivatives are s h o w n i n F i g ­ ures 8 A a n d 8 B , respectively. T h e a r o m a t i c peak at 1505 c m " was t a k e n as the a b s o r p t i o n s t a n d a r d i n b o t h samples. T h i s enhances s p e c t r a l differences a n d emphasizes s t r u c t u r a l characteristics w h i c h differ i n b o t h samples. T h e p r e p a r a t i o n w h i c h was bleached w i t h H 2 O 2 under a c i d i c c o n d i t i o n s e x h i b i t s a b r o a d peak centered at 1725 c m " , a n d t h i s s t r o n g l y suggests c a r b o n y l a n d c a r b o x y l group f o r m a t i o n ( F i g u r e 8 A ) . T h e s a m p l e treated w i t h [ Η θ 2 ] ions, b y contrast, raises a s t r o n g s i g n a l at 1625 c m " , a n d t h i s reflects changes i n a r o m a t i c i t y . B o t h difference s p e c t r a also d i s p l a y weaker s i g ­ nals at lower wavenumbers, b u t they are less p r o n o u n c e d . T h e y generally s u p p o r t , however, the numerous side reactions w h i c h have been a t t r i b u t e d to h y d r o g e n peroxide a n d i t s d e g r a d a t i o n p r o d u c t s (3). P r o m i n e n t a m o n g t h e m are reactions caused by oxygen a n i o n r a d i c a l a n d h y d r o x y r a d i c a l (3). These results i n d i c a t e t h a t differences exist between the H 2 O 2 b l e a c h i n g c h e m i s t r y d e p e n d i n g o n p H ; a n d t h a t d i f f e r e n c e - F T I R spec­ troscopy is a useful m e t h o d for revealing the effect o f c h e m i c a l m o d i f i c a t i o n on chemical structure. T h u s , b l e a c h i n g of non-phenolic l i g n i n derivatives is possible at b o t h p H extremes, a n d c o n d i t i o n s m a y be chosen a c c o r d i n g to process conve­ nience. T h e f o r m a t i o n of new f u n c t i o n a l i t y d u r i n g color r e m o v a l is i n ­ e v i t a b l e , a n d t h i s can be assessed b y F T I R spectroscopy. A c i d i c c o n d i t i o n s appear to result i n the f o r m a t i o n of c a r b o n y l a n d c a r b o x y l groups, a n d alkaline H 2 O 2 is suggested to alter a r o m a t i c character. H y d r o x y l a t i o n a n d h y d r o l y s i s are encountered also. - 1

1

1

1

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

1

1

θ

1

Various Parameters. O t h e r factors affecting b l e a c h i n g were e x p l o r e d briefly, and p r a g m a t i c decisions were m a d e to determine s t a n d a r d r e a c t i o n c o n d i ­ t i o n s . T h e effect of t e m p e r a t u r e was explored over the range of 20 t o 80°C, a n d results favored elevated t e m p e r a t u r e for s t a n d a r d c o n d i t i o n s . U s i n g a 2 0 % charge of H 2 O 2 at p H 2 for 30 m i n u t e s , color loss increased f r o m 3.5% at 4 0 ° C to 2 9 . 6 % at 8 0 ° C . E t h a n o l was chosen as the solvent for reasons r e l a t i n g to other process factors (i.e., i s o l a t i o n ) . ( C h o i c e of solvent must not ignore possible reaction w i t h H 2 O 2 ) T h e selection of a 2 0 % c o n c e n t r a ­ t i o n level reflects a n effort to produce as concentrated solutions as possible a n d s t i l l p e r m i t homogeneous phase reactions at a l l p H levels. Yield. T h e g r a v i m e t r i c d e t e r m i n a t i o n of l i g n i n y i e l d f o l l o w i n g b l e a c h i n g w i t h h y d r o g e n peroxide poses difficulties t h r o u g h the need to remove i n ­ o r g a n i c reagents. A n a l t e r n a t i v e assay of l i g n i n involves d e t e r m i n a t i o n of U V absorbance at 280 n m . T h i s m e t h o d , however, does not produce i n f o r -

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

446

LIGNIN: PROPERTIES AND MATERIALS

WRVENUMBER

F i g u r e 7. F T I R s p e c t r a of unbleached H P L a n d of H P L bleached w i t h H 2 O 2 under acidic c o n d i t i o n s ; o v e r l a i d a n d scaled so t h a t the 1125 c m " " peak reflects 1 0 0 % a b s o r p t i o n . S h a d e d areas represent q u a n t i t a t i v e s t r u c t u r a l differences. 1

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Bleaching of Hydroxypropyl Lignin

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

34.

Figure 8. acidic (A) spectrum) 1505 c m "

-1

Subtraction spectra of samples bleached with H2O2 under and alkaline (B) conditions. Unbleached H P L control (normal is shown in (C). (Subtraction spectra were scaled using the peak as unity.)

LIGNIN: PROPERTIES AND MATERIALS

448

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m a t i o n o n gravimetric y i e l d b u t rather o n the y i e l d of aromatic (i.e., U V absorbing) c o m p o n e n t . T h i s ignores the expected conversion of a r o m a t i c features i n t o a l i p h a t i c structures t h a t escape detection by U V spectroscopy (at 280 n m ) . Nevertheless, the c o m m o n U V spectroscopic assay produces m e a n i n g f u l results o n the y i e l d of a r o m a t i c components. T h e d a t a of F i g . 9 reveal a loss of a r o m a t i c f u n c t i o n a l i t y i n r e l a t i o n to t i m e ( F i g . 9 A ) a n d H 2 O 2 charge ( F i g . 9 B ) for a n organosolv a n d a k r a f t l i g n i n based H P L at constant p H (2), t i m e (4 hours), a n d t e m p e r a t u r e ( 8 0 ° C ) . A consistent a n d expected loss w i t h t i m e a n d H 2 O 2 charge is revealed. J u d g e d b y U V a b s o r p t i v i t y , 15-20% of the s a m p l e s ' a r o m a t i c character is lost under bleaching c o n d i ­ tions. It is d o u b t f u l t h a t t h i s i m p l i e s t h a t one of five a r o m a t i c s t r u c t u r e s i n l i g n i n has q u i n o n o i d n a t u r e , a n d t h i s m a y more reasonably be e x p l a i n e d w i t h the r e m o v a l of several types of U V a b s o r b i n g constituents. 30 r

A

20

10 Ο­ Χ

ζ ο

ο

3

2I

4

5

6

7

θ

REACTION T I M E (HR) CO CO

Ο 30 r

Β

Ο ω CM

σ

20

10

0

150 Η 0 2

CHARGE

2

(%

W/W

HPL)

F i g u r e 9. R e l a t i o n s h i p between loss of U V a b s o r p t i v i t y at 280 n m a n d ( A ) r e a c t i o n t i m e a n d ( B ) H 0 charge. P i n e kraft H P L (O) a n d aspen organosolv H P L ( • ). 2

2

34.

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

Other Blocking Agents. A l t h o u g h propylene oxide is a convenient a n d ef­ fective b l o c k i n g agent for l i g n i n , other alternatives are available. A m o n g t h e m , most n o t a b l y , is a c e t y l a t i o n . A c o m p a r i s o n o f t w o organosolv l i g n i n derivatives, f r o m aspen a n d f r o m red o a k , is given i n F i g . 10. T h e d a t a reveal t h a t b o t h c h e m i c a l m o d i f i c a t i o n reactions result i n derivatives w i t h reduced light a b s o r p t i o n characteristics, even w i t h o u t o x i d a t i v e post t r e a t ­ m e n t . P r o p y l e n e oxide a n d acetic a n h y d r i d e produce about i d e n t i c a l color loss values. B l e a c h i n g o f the acetylated r e d o a k s a m p l e resulted i n supe­ rior values as c o m p a r e d t o the c o r r e s p o n d i n g p r o p o x y l a t e d d e r i v a t i v e s . It appears t h a t b l e a c h i n g w i t h h y d r o g e n peroxide c a n be achieved w i t h n o n phenolic l i g n i n derivatives regardless o f the n a t u r e o f the b l o c k i n g g r o u p . Conclusions 1. A n a m o u n t o f 25-50% h y d r o g e n peroxide per l i g n i n d e r i v a t i v e c o n s t i ­ tutes a reasonable compromise between m a x i m u m color loss a n d effi­ cient peroxide use. T h i s achieves a color loss o f about 6 0 % o n l i g n i n , if color is defined as the Weighted a b s o r p t i v i t y average i n the range o f 350-500 n m .

6.0

^

ω

h

LIGNIN

5.0

t ζ

3 >

rr

-OAc

4.0 HPL

< or

g < rr ο ο ο

LIGNIN

3.0 BI. HPL BlrOAc

2.0 HPL

-OAc

BI. HPL

1.0 BI.-OAc

ASPEN

RED OAK

F i g u r e 10. C o l o r loss o f l i g n i n derivatives i n r e l a t i o n t o m e t h o d o f m o d i f i ­ c a t i o n a n d b l o c k i n g o f phenolic O H groups.

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LIGNIN: PROPERTIES AND MATERIALS

2. W h i l e m o r e t h a n 9 0 % o f color loss is achieved after 30 m i n . i n homogeneous phase a t 80°C w i t h some l i g n i n preparations, others, especially softwood l i g n i n s , take longer. 3. B o t h low ( p H 2) a n d h i g h ( p H 12-13) p H levels are suitable for b l e a c h i n g . F T I R spectroscopy indicates, however, t h a t the two different cond i t i o n s p r o d u c e differences i n the chemistry o f the bleached derivatives. 4. A l t h o u g h g r a v i m e t r i c y i e l d may n o t b e significantly affected b y t h e b l e a c h i n g t r e a t m e n t , a r o m a t i c i t y as i n d i c a t e d b y U V a b s o r p t i o n a t 280 n m declines b y as m u c h as 2 0 % .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

Acknowledgment T h i s s t u d y was f i n a n c i a l l y s u p p o r t e d b y a grant f r o m a n i n d u s t r y cooperative i n w h i c h the following companies were i n v o l v e d : A R C O C h e m i c a l C o r p o r a t i o n , B i o - R e g i o n a l E n e r g y Associates, A l b e r t a Forest Service, a n d B o r r e g a a r d Industries; a n d the C e n t e r o f Innovative T e c h n o l o g y o f V i r g i n i a . T h i s s u p p o r t is gratefully acknowledged. T h i s is p a r t 18 o f a p u b l i c a t i o n series dealing w i t h engineering plastics f r o m l i g n i n . E a r l i e r parts have been p u b l i s h e d i n J. Appl. Polym. Set., J. Wood Chem. TechnoL, a n d Holzforschung.

Literature C i t e d 1. Niederdellmann, G . , Gewinnung von Lignin aus Holzabfallen und Verweriung fur Hersiellung von Polyurethanhartschaumen, Forschungsbericht 03 V M 619-C 077 (Bayer A G , Leverkusen) an das Bundesministerium fur Forschung und Technologie, 1981, 48 pg. 2. Hon, D. N.-S.; Glasser, W . G . Polym.-Plast. Technol. Eng. 1979, 12(2), 159-179. 3. Gierer, J. Holzforschung 1982, 36(2), 55-64. 4. Loras, V . Chapter 5 in Pulp and Paper Chemistry and Chemical Technology;J.P. Casey, Ed.; J. Wiley & Sons: New York, 1980; Vol. 1, pp. 633-764. 5. Gellerstedt, G . ; Petterson, E . - L . Svensk Papperstidn. 1977, 80(1), 15. 6. Lin, S. Y . U.S. Patent #4,184,845, 1980. 7. Dilling, P.; Sarjeant, P. T. U.S. Patent #4,454,066, 1984. 8. Wu, L . C . - F . ; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29(4), 1111-23. 9. Glasser, W . G . ; Wu, L . C . - F . ; Selin, J.-F. Chapter in Wood and Agricultural Residues: Research on Use for Feed, Fuels, and Chemicals; Soltes, Ed J., Ed.; Academic Press, 1983, pp. 149-166. 10. Spittler, T . D.; Dence, C . W . Svensk Papperstidn. 1977, 80(9), 275-284. 11. Bailey, C . W.; Dence, C . W . Tappi 1969, 52(3), 491-500. 12. Dence, C . W . In Reactions of Hydrogen Peroxide with Lignin: Current Status in Chemistry of Delignification with Oxygen, Ozone and Perox-

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ides; Gratzl, J . S.; Nakano, J . ; Singh, R. P., Eds.; Uni: Tokyo, 1980; pp. 199-205. 13. Levitt, L . S. J. Org. Chem. 1955, 20, 1297-1310. 14. Schultz, T . P.; Nichols, D. D. International Analyst 1987, 1(9), 35-39. 15. Schultz, T . P.; Glasser, W . G . Holzforschung 1986, 40, 37-44.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch034

RECEIVED March 17,1989

Chapter 35

Polymer Blends with Hydroxypropyl Lignin Scott L . Ciemniecki

1-3

1

and Wolfgang G.

Glasser

1,2

Department of Wood Science and Forest Products, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch035

2

Polymer blends of hydroxypropyl lignin (HPL) with polyethylene (PE), with ethylene vinyl acetate copolymer (EVA), with poly(methyl methacrylate) ( P M M A ) , and with poly(vinyl alcohol) (PVA) have been examined in relation to morphological, thermal, and mechanical characteristics. The results suggest that lignin gains the ability to contribute to the properties of thermoplasts, especially modulus and occasionally strength, when the co-component to lignin contains some type of polar functionality. Whereas polyethylene shows no signs of interaction with H P L , rising vinyl acetate content produces blends with superior strength properties. Similar observations are made with P M M A ; and P V A fails to display any sign of phase separation. The greater than expected compatibility with thermoplasts containing polar functionality produces blends which are either plasticized (especially by low molecular weight lignin fractions) or antiplasticized. Interest i n p o l y m e r blends has been r i s i n g d u r i n g the past decades because b l e n d i n g is seen as a n inexpensive m e t h o d for the m o d i f i c a t i o n o f p o l y m e r p r o p e r t i e s . B l e n d i n g is t h e cheaper alternative t o t h e engineering o f plastics f r o m a m u l t i t u d e o f c o m p o n e n t s , i n order t o achieve target specifications. G i v e n the i d e a l c o m b i n a t i o n o f p o l y m e r - p o l y m e r i n t e r a c t i v e forces, a p o l y m e r b l e n d m a y be as useful as a b l o c k c o p o l y m e r w i t h m i c r o p h a s e s e p a r a t i o n p r o d u c i n g s t r e n g t h , toughness, a n d d u r a b i l i t y . A b l e n d ' s p r o p e r t i e s are largely d e t e r m i n e d b y the c o m p a t i b i l i t y o f the c o m p o n e n t p o l y m e r s since this influences m o r p h o l o g y . W h e n two p o l y m e r s are b l e n d e d p o l y m e r - p o l y m e r interactions w i l l be e x h i b i t e d i f the t h e r m o d y n a m i c e q u i l i b r i u m state p e r m i t s . T h e basic t h e r m o d y n a m i c e q u a t i o n 3

Current address: Union Camp, P.O. Box 570, Savannah, G A 31402 0097-6156/89/0397-0452$06.00A) © 1989 American Chemical Society

35. C I E M N I E C K I & G L A S S E R

Polymer Blends with Hydroxypropyl Lignin

453

w h i c h describes t h i s state is the G i b b s free-energy e q u a t i o n : AG

= AH

mix

mix

(1)

- TAS

mix

where AG i is the G i b b s free energy o f m i x i n g , AH { is the e n t h a l p y o f m i x i n g , AS i is the e n t r o p y o f m i x i n g , a n d Τ is the absolute t e m ­ p e r a t u r e . I n order for a p o l y m e r m i x t u r e t o achieve i n t i m a t e m i x i n g or "miscibility," A G must be negative. T h u s , the m i s c i b i l i t y o f a t w o c o m p o n e n t m i x t u r e depends o n the s i g n a n d m a g n i t u d e o f AH i and, t o a lesser e x t e n t , o n AS i . W h e n d e a l i n g w i t h p o l y m e r blends, three i m p o r t a n t parameters affect the m a g n i t u d e a n d sign o f AH i a n d AS ix> (1) s o l u b i l i t y p a r a m e t e r ; (2) specific i n t e r a c t i o n s ; a n d (3) m o l e c u l a r weight. T h e s o l u b i l i t y p a r a m e t e r δ is a measure o f the cohesion o f a m a t e r i a l , or o f the s t r e n g t h o f m o l e c u l a r a t t r a c t i v e forces between like molecules. T h e r e l a t i o n s h i p between the s o l u b i l i t y p a r a m e t e r a n d e n t h a l p y o f m i x i n g is given b y the H i l d e b r a n d e q u a t i o n (1): m

X

m

m

X

X

m

t

r

m

m

m

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch035

X

x

= (6

Hmix/V

X

- δ)φφ 2

2

λ

x

m

(2)

2

where V is the m o l a r v o l u m e o f the m i x t u r e , δχ^ are the s o l u b i l i t y p a r a m e ­ ters o f components 1 a n d 2, a n d are the v o l u m e fractions o f c o m p o n e n t s 1 a n d 2. T h i s e q u a t i o n expresses the concept t h a t t w o p o l y m e r s are m i s c i ­ ble w h e n t h e i r s o l u b i l i t y parameters become perfectly m a t c h e d . E q u a t i o n (2) indicates t h a t the p r e d i c t e d AH i is always p o s i t i v e or at best zero (in the absence o f other a t t r a c t i v e forces). T h u s , the H i l d e b r a n d e q u a ­ t i o n suggests t h a t phase s e p a r a t i o n r a t h e r t h a n m i s c i b i l i t y is favored w h e n AS is s m a l l . H o w e v e r , m a n y p o l y m e r s have been r e p o r t e d to be m i s c i ­ ble ( 2 , 5 ) . T h e m e c h a n i s m s responsible for p o l y m e r - p o l y m e r m i s c i b i l i t y are a t t r i b u t e d t o s u c h specific interactions between two m a c r o m o l e c u l e s as h y ­ drogen b o n d i n g , π-π c o m p l e x f o r m a t i o n , charge transfer a n d i o n i c i n t e r a c ­ t i o n s . T h e y have a l l been f o u n d to be responsible for m i s c i b i l i t y i n p o l y m e r blends (6). C o n s i d e r i n g t h a t AH i values are the net result o f b r e a k i n g solvent-solvent (1-1) a n d p o l y m e r - p o l y m e r (2-2 a n d 3-3) secondary b o n d s and c r e a t i n g new p o l y m e r - p o l y m e r (2-3) i n t e r a c t i o n s , the i m p o r t a n c e of the s o l u b i l i t y p a r a m e t e r a n d specific i n t e r a c t i o n s between two p o l y m e r s is clearly u n d e r s t o o d ( 7 , 8 ) . m

m

x

X

T h e role t h a t m o l e c u l a r weight plays i n d e t e r m i n i n g the m i s c i b i l i t y of t w o p o l y m e r s is m o s t easily described b y the AS i t e r m i n the G i b b s free energy e q u a t i o n . W h e n m i x i n g s m a l l molecules, the increase i n r a n d o m n e s s , and t h u s i n entropy, is h i g h a n d p o s i t i v e . T h i s allows the TAS p r o d u c t to o u t w e i g h the e n d o t h e r m i c heat o f m i x i n g , AH i . A negative free energy t e r m , AG, is therefore favored, a n d m i s c i b i l i t y is possible. H o w e v e r , w h e n large p o l y m e r molecules are m i x e d , the t h o u s a n d s of a t o m s i n each m o l e c u l e m u s t r e m a i n together, a n d m i x i n g cannot be n e a r l y as r a n d o m . T h u s , i t is r a r e l y possible for the TAS i t e r m t o exceed the e n d o t h e r m i c heat o f m i x i n g , AH i . I n fact, i n those rare cases i n w h i c h p o l y m e r blends e x h i b i t complete m i s c i b i l t y a n d homogeneity, i t is u s u a l l y due t o specific i n t e r a c t i o n s between the t w o p o l y m e r s . m

m

m

m

x

x

x

x

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454

It w a s t h e objective o f t h i s w o r k t o e x a m i n e the c o n t r i b u t i o n h y d r o x ­ y p r o p y l l i g n i n c a n m a k e t o t h e properties o f p o l y m e r blends w i t h several c o m m e r c i a l t h e r m o p l a s t i c s . T h i s has been t h e t o p i c o f three earlier p u b l i ­ cations (9-11).

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch035

Experimental Materials. Polyethylene (PE): L o w density polyethylene ( P E ) a n d e t h y l e n e v i n y l acetate ( E V A ) copolymers w i t h v i n y l acetate ( V A ) contents o f 9, 18, 25, 2 8 , 3 3 , a n d 4 0 % were o b t a i n e d f r o m Scientific P o l y m e r P r o d u c t s , I n c . Polymethyl methacrylate (PMMA): A n atactic P M M A w i t h a T ^ of H O C a n d a n i n t r i n s i c v i s c o s i t y o f 1.4 was o b t a i n e d f r o m Scientific P o l y m e r Products, Inc. Polyvinyl alcohol (PVA): F o u r c o m m e r c i a l l y available (Scientific P o l y ­ mer P r o d u c t s , Inc.) P V A ' s were used i n t h i s s t u d y . I m p o r t a n t p a r a m e t e r s for each were as s h o w n i n T a b l e I : T a b l e I . P o l y ( v i n y l alcohol) C h a r a c t e r i s t i c s

P V A Type 96% 88% 75% 0%

hydrolyzed hydrolyzed hydrolyzed hydrolyzed

T,(C) 77 70 60 32

δ (cal^cm / ) 3

12.6 11.8 10.6 9.6

2

M (g m o l ) w

1

96,000 96,000 3,500 unknown

Hydroxypropyl lignin (HPL): T w o different H P L p r e p a r a t i o n s were used i n t h i s s t u d y (12). B l e n d s c o n t a i n i n g P E a n d E V A u t i l i z e d a n H P L f r o m organosolv ( m e t h a n o l ) l i g n i n f r o m red oak; a n d blends c o n t a i n i n g P V A and P M M A utilized an H P L from kraft lignin ( I n d u l i n - A T from Westvaco Corporation, Charleston, S C ) . Methods. P o l y b l e n d samples were prepared b y s o l u t i o n c a s t i n g f r o m t e t r a h y d r o f u r a n ( T H F ) , o r c h l o r o f o r m ; or b y i n j e c t i o n m o l d i n g u s i n g a " M i n i - M a x M o l d e r " b y C u s t o m Scientific I n s t r u m e n t s . Specific e x p e r i m e n ­ t a l details are given elsewhere ( 9 , 1 0 , 1 1 ) . P h y s i c a l properties were d e t e r m i n e d b y differential scanning calorime­ try (dsc) w i t h a P e r k i n - E l m e r D S C - 4 i n s t r u m e n t ; a n d b y dynamic mechani­ cal thermal analysis (dmta) u s i n g a P o l y m e r L a b o r a t o r i e s d m t a i n s t r u m e n t . Stress-strain tests were p e r f o r m e d o n a n I n s t r o n T a b l e M o d e l T M - M at a cross-head speed o f 1 m m m i n . T h e Y o u n g ' s m o d u l u s w a s o b t a i n e d f r o m the tangent o f t h e i n i t i a l slope o f the force v s . elongation curve. Scanning electron microscopy (s.e.m.) employed a n A M R 900 i n s t r u m e n t . Specific e x p e r i m e n t a l details are given elsewhere ( 9 , 1 0 , 1 1 ) . 1

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Results and Discussion HPL/PE and EVA Blends. P o l y e t h y l e n e ( P E ) is b y far the m o s t i m p o r t a n t i n d u s t r i a l p o l y m e r today. Its a v a i l a b i l i t y , i t s w i d e l y u n d e r s t o o d processa b i l i t y , a n d i t s low cost a l l c o n t r i b u t e t o the interest i n m i x i n g i n the m e l t p o l y e t h y l e n e w i t h other p o l y m e r i c components. I n j e c t i o n m o l d e d blends o f H P L a n d P E (11) were f o u n d t o be i n c o m p a t i b l e over the entire b l e n d range, b y S E M , D M T A , a n d o p t i c a l i n s p e c t i o n . T h e results o f F i g u r e 1 i l ­ l u s t r a t e t h a t blends o f H P L w i t h P E (coded as E V A ( 0 ) ) r e s u l t i n a r a p i d loss o f tensile s t r e n g t h w h i c h far exceeds the rule o f m i x i n g (11). If, however, r i s i n g a m o u n t s o f v i n y l acetate are i n c o r p o r a t e d i n t o the b a c k b o n e of P E , t h u s p r o d u c i n g e t h y l e n e - c o - v i n y l acetate p o l y m e r w i t h v i n y l acetate c o n ­ tents r i s i n g f r o m 9 t o 4 0 % , a g r a d u a l increase i n i n t e r a c t i o n is i n d i c a t e d b y a rise i n tensile s t r e n g t h o f the p o l y b l e n d . T h e d a t a o f F i g u r e 1 reveal t h a t E V A w i t h 18-40% v i n y l acetate content produces p o s i t i v e d e v i a t i o n f r o m the rule o f m i x i n g i f h y d r o x y p r o p y l l i g n i n content is h i g h (i.e., between 20 and 30%) i n the case of low v i n y l acetate contents, a n d low (i.e., i n the range o f 10-20%) i f v i n y l acetate content is h i g h . T h e s e results (11) i l l u s ­ t r a t e t h a t , a l t h o u g h the l i g n i n derivative produces i m m i s c i b l e p o l y blends w i t h polyethylene a n d its c o p o l y m e r w i t h v i n y l acetate, phase c o m p a t i b i l i t y , and t h u s s t r e n g t h , increases w i t h v i n y l acetate content r i s i n g . T h e presence o f p o l a r c a r b o n y l groups is suspected t o be responsible for e n h a n c i n g t h i s observed p o l y m e r - p o l y m e r i n t e r a c t i o n . HPL/PMMA Blends. Blend Structure. A l l blends o f H P L a n d P M M A revealed a two-phase ( i m m i s c i b l e ) m o r p h o l o g y regardless of solvent, weight f r a c t i o n , m o l e c u l a r weight (of P M M A ) , or m e t h o d o f p r e p a r a t i o n (9). E x ­ t r u d e d H P L / P M M A blends e x h i b i t e d a less obvious two-phase m o r p h o l o g y (9), a n d t h i s was a t t r i b u t e d t o differences i n the rate of v i t r i f i c a t i o n (9). Thermal Characteristics. T y p i c a l dsc t h e r m o g r a m s for s o l u t i o n - c a s t and i n j e c t i o n - m o l d e d H P L / P M M A blends ( F i g . 2) reveal a n i n i t i a l scan ( F i g . 2, scan A ) w i t h two e n d o t h e r m s , at 63 a n d at 1 0 4 C , c o r r e s p o n d i n g to H P L a n d P M M A , respectively. A second scan ( F i g . 2, scan B ) i n d i c a t e s o n l y a single t r a n s i t i o n at 1 0 4 C . T h e e n d o t h e r m at 6 3 C seen i n scan A has p r e v i o u s l y been a t t r i b u t e d to e n t h a l p y r e l a x a t i o n ( 1 3 , 1 4 ) . T h i s occurs w h e n a p o l y m e r is cooled f r o m the m e l t , a n d w h e n the r a p i d rise i n v i s c o s i t y as the p o l y m e r approaches T ^ causes the p o l y m e r chains to freeze i n t o n o n e q u i l i b r i u m c o n f o r m a t i o n s . B y a n n e a l i n g at t e m p e r a t u r e s above the t w o T^ values, the respective e n d o t h e r m s are replaced w i t h a single b r o a d T ^ . C o n s i d e r i n g the S E M results, w h i c h i n d i c a t e d i m m i s c i b i l i t y a n d showed n o signs of i n t e r a c t i o n between the t w o phases, the presence o f a single T^ cannot be t a k e n as a n i n d i c a t i o n o f phase u n i f o r m i t y (15). R a t h e r , t h i s b r o a d T ^ , w h i c h i n the case of low m o l e c u l a r weight H P L spans a range of 9 0 C , is believed t o be the result of " t r a n s i t i o n a l s m e a r i n g . " T h i s p h e n o m e n o n has p r e v i o u s l y been observed w i t h b l e n d c o m p o n e n t s t h a t have T ^ values w i t h i n 2 0 C o f each other, a n d i t s i m p l y represents the o v e r l a p p i n g o f t w o T / s t o p r o d u c e a single b r o a d T ^ . T h e t a n δ peak of a d m t a t h e r m o g r a m provides a second measure of

LIGNIN: PROPERTIES AND MATERIALS

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456

0

10

20

30

HPL C O N T E N T

40 (%)

Figure 1. Relationship between (normalized) tensile strength and H P L content of injection molded blends with ethylene vinyl acetate copolymer. (Vinyl acetate content of the thermoplastic copolymer is given in parentheses.) (Strength values expressed in percent of unblended copolymer.) (From Ref. 11, with permission by Marcel Dekker, Inc.)

F i g u r e 2. D . s . c . t h e r m o g r a m s o f T H F s o l u t i o n - c a s t 4 0 % m e d i u m - M W H P L / P M M A b l e n d ; A , i n i t i a l s c a n ; Β, second s c a n . ( F r o m Réf. 9, w i t h permission by Butterworth & Co., L t d . )

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^1

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blend a n d m o r p h o l o g y . F o r P M M A , the a or glass t r a n s i t i o n appears at 1 1 2 C for m o l d e d samples, a n d at 108 a n d 1 0 4 C for s o l u t i o n cast ( T H F a n d c h l o r o f o r m , respectively) samples. A ^ - t r a n s i t i o n w h i c h is centered a r o u n d 2 0 - 5 0 C is generally a t t r i b u t e d t o r o t a t i o n o f the m e t h y l ester side g r o u p . T h e effects o f increased H P L content, a n d o f i n c r e a s i n g m o l e c u l a r w e i g h t , o n the shape o f the t a n δ curves is s h o w n i n F i g u r e 3. B l e n d t r a n s i t i o n s are seen t o increase i n w i d t h w i t h i n c r e a s i n g H P L f r a c t i o n , a n d t h i s o b s e r v a t i o n is i n d e p e n d e n t o f H P L m o l e c u l a r weight. W h e r e low m o l e c u l a r weight H P L f r a c t i o n s lower the c o m m o n T o f the b l e n d , i.e., p l a s t i c i z e the m a t e r i a l , h i g h m o l e c u l a r weight fractions have the o p p o s i t e effect, i.e., a n t i - p l a s t i c i z e the m o l e c u l a r composite s t r u c t u r e (9).

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g

HPL/PVA Blends. Blend Structure. A l l blends o f H P L w i t h a l l three ( h y d r o l y z e d ) P V A ' s h a d a c h a r a c t e r i s t i c a l l y b r o w n color. T h e y were f u l l y t r a n s p a r e n t a n d clear. T h i s is s y m p t o m a t i c o f c o m p a t i b i l i t y . S E M m i c r o ­ g r a p h s revealed d i s t i n c t phase s e p a r a t i o n w i t h P V A ( O ) blends, b u t t h e y d i s p l a y e d s m o o t h fracture surfaces w i t h 2 5 % H P L / P V A ( 9 6 ) , P V A ( 8 8 ) a n d P V A ( 7 5 ) blends (10). T h i s is c h a r a c t e r i s t i c o f homogeneous m a t e r i a l s . S E M results t h u s suggest t h a t p a r t i a l l y h y d r o l y z e d P V A blends w i t h H P L p r o d u c e at least p a r t i a l l y m i s c i b l e systems. T h i s can be e x p l a i n e d w i t h sec­ o n d a r y associations between the h y d r o x y groups of H P L a n d P V A ( > 0). ( T h e n u m b e r preceding the d e s i g n a t i o n of b l e n d c o m p o n e n t s represents the weight f r a c t i o n o f the f i r s t - m e n t i o n e d c o m p o n e n t a n d the figure i n p a r e n ­ theses f o l l o w i n g " P V A " designates the extent o f h y d r o l y s i s . ) Thermal Properties. A t y p i c a l dsc t h e r m o g r a m o f a n H P L / P V A b l e n d ( F i g . 4) shows a single T ^ a n d T (10). Differences i n the shape o f the m e l t i n g e n d o t h e r m s o f P V A ( 9 6 ) , (88), a n d (75) can be a t t r i b u t e d t o d i f ­ ferent degrees of c r y s t a l l i n i t y i n the three p o l y m e r s . C h a n g e s i n c r y s t a l l i n e s t r u c t u r e of p o l y m e r blends u s u a l l y result f r o m p o l y m e r - p o l y m e r i n t e r a c ­ t i o n s i n the a m o r p h o u s phase. S u c h i n t e r a c t i o n s result i n a r e d u c t i o n of c r y s t a l l i n i t y , thereby r e d u c i n g the e n t h a l p h y o f the phase change ( 1 6 , 1 7 ) . T h e observed reductions i n m e l t e n d o t h e r m area of H P L blends w i t h P V A ( > 0) m a y therefore i n d i c a t e the existence o f p o l y m e r - p o l y m e r i n t e r a c t i o n s between the t w o types o f m a c r o m o l e c u l e s . T ^ - a n a l y s i s o f the blends was h a m p e r e d b y the fact t h a t H P L h a d a T ^ o f 6 3 C , a n d P V A ( 9 6 ) , P V A ( 8 8 ) a n d P V A ( 7 5 ) h a d T values o f 77, 70, a n d 6 0 C , respectively. T h i s is too close for the r e s o l u t i o n o f two separate t r a n s i t i o n s . B u t a n a l y s i s o f the a c t u a l t r a n s i t i o n t e m p e r a t u r e s , r a t h e r t h a n the shape of the t r a n s i t i o n s , c a n s t i l l p r o v i d e i n f o r m a t i o n a b o u t the state of the H P L / P V A blends. m

g

T h e o r e t i c a l l y m i s c i b l e p o l y m e r blends w i l l show T ^ values t h a t are i n ­ t e r m e d i a t e between those of the parent p o l y m e r s . T h e y follow such models as the F o x or G o r d o n - T a y l o r r e l a t i o n s h i p s ( 1 8 , 1 9 ) . H o w e v e r , i n the case o f H P L / P V A blends, the T ^ d a t a d i d not follow any o f these w e l l k n o w n m o d e l s , a n d T ^ values above those of the p a r e n t p o l y m e r s were observed (10). T h e q u o t i e n t o f the e x p e r i m e n t a l b l e n d - T ^ d i v i d e d b y the p r e d i c t e d (Fox) T ^ consistently rose above 1.00 for blends exceeding 5 % H P L content (10). T h i s i n d i c a t e s m o l e c u l a r interactions between H P L a n d P V A . A n

35. C I E M N I E C K I & G L A S S E R

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150

TEMPERATURE ( C ) Figure 3. D.m.t.a. thermograms of H P L / P M M A blends; ( A ) l o w - M W H P L ; (B) m e d i u m - M W H P L ; and (C) h i g h - M W H P L . Individual curves are for: a, P M M A (control); b, 5% H P L / P M M A blend; c, 2 5 % H P L / P M M A blend; and d, 4 0 % H P L / P M M A blend. (Reprinted with permission from ref. 9. Copyright 1988 Butterworth & Co.)

F i g u r e 4. D . s . c . t h e r m o g r a m s o f 2 5 % H P L / P V A ( 7 5 ) ( A ) , P V A ( 8 8 ) ( B ) , a n d P V A ( 9 6 ) ( C ) . ( F r o m Ref. 9, w i t h p e r m i s s i o n b y B u t t e r w o r t h & C o . , L t d . )

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4t

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α

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2

c

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3 5 . CIEMNIECKI & GLASSER

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461

a m o r p h o u s c o m p o n e n t seems t o be created i n w h i c h t h e p o l y m e r s coexist i n a closely associated s t a t e , t h e r e b y r e d u c i n g free v o l u m e a n d r a i s i n g T ^ . A n o t h e r possible e x p l a n a t i o n for the observed increase i n is t h a t t h e secondary b o n d s act as q u a s i - c r o s s l i n k s w h i c h r e s t r i c t B r o w n i a n m o t i o n of t h e l o n g c h a i n molecules, t h e r e b y r a i s i n g T ^ . T a n δ curves f r o m d m t a t h e r m o g r a m s o f blends based o n c o m b i n a t i o n s o f H P L / P V A ( > 0) are s h o w n i n F i g u r e 5 (10). T h e t a n δ t r a n s i t i o n , w h i c h is a n o t h e r measure o f T , is b r o a d e n e d b y t h e presence o f H P L c o m p o n e n t , a n d i t increases above t h a t o f t h e p a r e n t p o l y m e r s consistent w i t h dsc d a t a . T h i s c a n a g a i n be e x p l a i n e d w i t h the presence o f s t r o n g i n t e r a c t i o n s between the a m o r p h o u s c o m p o n e n t s w h i c h coexist i n a closely a s s o c i a t e d state.

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y

Conclusions 1. B l e n d s o f P E , o f P M M A , a n d o f P V A ( O ) w i t h H P L o f v a r y i n g m o l e c u l a r weight p r o d u c e two-phase m a t e r i a l s . B l e n d s o f H P L w i t h P V A ( > 0) e x h i b i t at least p a r t i a l m i s c i b i l i t y .

TEMPERATURE (C) F i g u r e 5. R e l a t i o n s h i p between t a n δ o f the H P L / P V A ( 9 6 ) b l e n d s a n d H P L content; A , 0% H P L ; B , 5% H P L ; C , 2 5 % H P L ; and D , 4 0 % H P L . ( F r o m R e f . 9, w i t h p e r m i s s i o n b y B u t t e r w o r t h & C o . , L t d . )

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2. E n t h a l p y r e l a x a t i o n is often responsible for t w o e n d o t h e r m i c t r a n s i t i o n s i n the i n i t i a l dsc t h e r m o g r a m s , a n d a single, b r o a d t r a n s i t i o n i s observed i n most second scans a n d i n d m t a t h e r m o g r a m s . 3. T h e interphase between the continuous a n d the discontinuous p o l y m e r phases differs w i t h respect t o b l e n d p r e p a r a t i o n s . S o l u t i o n - c a s t blends p r o d u c e i n c l u s i o n s t h a t are p u l l e d away f r o m t h e m a t r i x , whereas i n j e c t i o n - m o l d e d blends show H P L s t r i a t i o n s t h a t are closely associated w i t h the m a t r i x . 4. U l t i m a t e properties, tensile s t r e n g t h , a n d u l t i m a t e s t r a i n t y p i c a l l y decrease w i t h t h e a d d i t i o n o f H P L ; however, c o m b i n a t i o n s o f molecules w i t h s t r o n g i n t e r a c t i o n between a m o r p h o u s c o m p o n e n t s m a y also e x h i b i t enhanced u l t i m a t e properties. Injection m o l d i n g produces s u p e r i o r m a t e r i a l properties. 5. V a r i a t i o n s i n the m o l e c u l a r weight o f H P L have n o significant effect o n the m a t e r i a l properties o f H P L / P M M A blends. 6. S o m e c o m m e r c i a l , linear ( t h e r m o p l a s t i c ) p o l y m e r s p r o d u c e blends w i t h l i g n i n a n d l i g n i n derivatives t h a t f a i l t o result i n phase s e p a r a t i o n o n macroscopic scale. P o l y b l e n d s w i t h l i g n i n derivatives sometimes r e s e m ble p l a s t i c i z e d o r a n t i - p l a s t i c i z e d m a t e r i a l s . T h e greatest c o n t r i b u t i o n l i g n i n can m a k e t o t h e r m o p l a s t i c systems is t h a t o f m o d u l u s ; a n d t h i s is t h e same as t h a t w h i c h l i g n i n makes t o t h e a m o r p h o u s c o m p o n e n t of w o o d . Acknowledgment V a l u a b l e assistance was p r o v i d e d b y D r . S. S . K e l l e y a n d D r . T . G . R i a l s , a n d t h i s is acknowledged w i t h g r a t i t u d e . F i n a n c i a l s u p p o r t was p r o v i d e d b y the N a t i o n a l Science F o u n d a t i o n under g r a n t n u m b e r C B T - 8 5 1 2 6 3 6 .

Literature Cited 1. Hildebrand, J . H . ; Scott, R. L . The Solubility of Non-Electrolytes; Dover: New York, 1964. 2. Olabisi, O.; Robeson, L . M . ; Shaw, M . T . Polymer-Polymer Miscibility; Academic Press: New York, 1979. 3. Klempner, D.; Frisch, K . C . (Eds.). Polymer Alloys; Plenum Press: New York, 1980. 4. Cooper, S. L.; Estes, G . M . (Eds.). Multiphase Polymers; Adv. Chem. Ser. 176, American Chemical Society: Washington, D C , 1979. 5. Paul, D. R.; Newman, S. (Eds.). Polymer Blends; Vols. 1 and 2; Academic Press: New York, 1978. 6. Barlow, J . W . ; Paul, D. R. Polym. Eng. Sci. 1981,21(15), 985. 7. Scatchard, G . Chem. Rev. 1931, 8, 321. 8. Hildebrand, J . H . ; Pravsnitz, J . M . ; Scott, R. L . Regular and Related Solutions; Van Nostrand Reinhold: New York, 1970. 9. Ciemniecki, S. L.; Glasser, W . G . Polymer 1988, 29, 1021. 10. Ciemniecki, S. L.; Glasser, W . G . Polymer 1988, 29, 1030.

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CIEMNIECKI&

GLASSER

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11. Glasser, W . G . ; Knudsen, J. S.; Chang, C.-S. J. Wood Chem. Tech. 1988, 8(2), 221. 12. Wu, L . C . - F . ; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29, 1111. 13. Hatakeyama, T . ; Nakamura, K . ; Hatakeyama, H . Polymer 1982, 23, 1801. 14. Rials, T . G . ; Glasser, W . G . J. Wood Chem. Technol. 1984, 4(3), 331. 15. Walsh, D. J.; Higgins, J. S.; Maconnachie, A . (Eds.). Polymer Blends and Mixtures; N A T O ASI Series E , Appl. Sci. No. 89, Nijhoff: The Hague, 1985. 16. Wenig, W . ; Karasz, F . E . ; MacKnight, W . J. J. Appl. Phys. 1975, 46, 4166. 17. Hammel, R.; MacKnight, W . J.; Karasz, F . E. J. Appl. Phys. 1975, 46, 4199. 18. Fox, T. G . Bull. Am. Phys. Soc. 1956, 1, 123. 19. Gordon, M . ; Taylor, J. S. J. Appl. Chem. 1952, 2, 493. RECEIVED May 29,1989

Chapter 36

Phase Morphology of Hydroxypropylcellulose Blends with Lignin Timothy G. Rials

1-3

1

and Wolfgang G.

Glasser

1,2

Department of Wood Science and Forest Products, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

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2

The incremental elimination of hydroxy functionality in an organosolv lignin by ethylation and acetylation dramatically influenced the state of miscibility of blends prepared with hydroxypropyl cellulose (HPC). The various blends were characterized by three distinct morphologies. At the lowest levels of component compatibility, the morphology resulted from classical phase separation of the lignin component and H P C liquid crystal (LC) mesophase formation. A miscible, amorphous blend resulted when the polymer-polymer interaction was maximized. At intermediate levels, however, the blend morphology was dominated by entropic effects leading to the development of L C superstructure dispersed in a lignin-reinforced H P C matrix. This latter case demonstrates the potential for developing high-strength cellulosic composites. In recent years, some o f the m o r e significant developments i n m a t e r i a l s t e c h nology have come i n the area o f m u l t i - c o m p o n e n t p o l y m e r systems. O n e o f the most e x c i t i n g topics is t h a t o f r i g i d - r o d composites w h i c h addresses the replacement o f the macroscopic reinforcing fiber o f conventional composites w i t h a single p o l y m e r chain (1). T h i s a c c o m p l i s h m e n t w o u l d r e t a i n the h i g h strength o f the c o m p o s i t e , w h i l e e l i m i n a t i n g such d e t r i m e n t a l aspects as p r o p e r t y anisotropy a n d interfacial defects. Significant advances t o this end have been m a d e using p r i m a r i l y l i q u i d c r y s t a l copolyesters as the r i g i d - r o d c h a i n i n various m a t r i x p o l y m e r s (2,3). S u r p r i s i n g l y , w h i l e cellulose a n d i t s derivatives also e x h i b i t L C p h e n o m e n a 3

Current address: U.S. Department of Agriculture Forest Service, Southern Forest Experiment Station, 2500 Shreveport Highway, Pineville,LA71360 0097-6156/89/0397-0464$06.00/0 © 1989 American Chemical Society

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch036

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(4), their u t i l i t y i n t h i s novel m a t e r i a l s y s t e m has received r e l a t i v e l y l i t t l e a t t e n t i o n . Recent reports have addressed t h i s interest b y p o l y m e r i z i n g a n a c r y l i c m o n o m e r i n w h i c h t h e cellulosic component is dissolved (5), a n d have p r o v i d e d some encouraging results. A more convenient a p p r o a c h i n ­ volves b l e n d i n g the cellulosic component w i t h a flexible c o i l p o l y m e r s e r v i n g as t h e m a t r i x . A l t h o u g h t h e phase behavior o f b i n a r y cellulosic systems have been extensively s t u d i e d (6-8), the r e l a t i o n s h i p s i n t e r n a r y systems r e m a i n largely unanswered, p a r t i c u l a r l y as they extend t o t h e b u l k m o r ­ phology. Recent studies i n this l a b o r a t o r y o n h y d r o x y p r o p y l cellulose ( H P C ) blends w i t h l i g n i n (9,10) have i n d i c a t e d t h a t the composite m o r p h o l o g y a n d properties are extremely sensitive t o the degree o f m i s c i b i l i t y between t h e two components. T h i s paper s u m m a r i z e s t h e observations t h a t have been m a d e w i t h p a r t i c u l a r regard t o the development o f h i g h - s t r e n g t h c o m p o s ­ ites. F o r e x p e r i m e n t a l d e t a i l s , the reader is referred t o the a b o v e referenced publications. Experimental Materials. T h e h y d r o x y p r o p y l cellulose ( K l u c e l ' L ' ) used i n t h i s s t u d y w a s s u p p l i e d b y Hercules, Inc. T h e m a n u f a c t u r e r reported a m o l a r s u b s t i t u t i o n of 4 propylene oxide u n i t s / a n h y d r o g l u c o s e u n i t , a n d a n o m i n a l m o l e c u l a r weight o f 1 0 g- m o l " . T h e l i g n i n component was a n organosolv l i g n i n ( O S L ) ( s c h e m a t i c a l l y represented i n F i g u r e 1) s u p p l i e d b y R e p a p Technologies o f V a l l e y Forge, P A , w h i c h h a d been isolated f r o m aspen w o o d . N e i t h e r r e a c t i o n c o n d i t i o n s nor y i e l d were m a d e available. T h e polystyrene equivalent n u m b e r ( < M > ) and weight [ ( < Μ > ) ] average m o l e c u l a r weight were d e t e r m i n e d b y gel p e r m e a t i o n c h r o m a t o g r a p h y as 900 a n d 3,000 g- m o l " " , respectively. T h e h y d r o x y l content o f t h e l i g n i n was i n c r e m e n t a l l y e l i m i n a t e d b y a c e t y l a t i o n a n d e t h y l a t i o n a c c o r d i n g t o p r e v i o u s l y described procedures (11). I n a d d i t i o n , m o d i f i c a t i o n w i t h propylene oxide was also used t o alter the o r i g i n a l l i g n i n s t r u c t u r e (12). T a b l e I presents a s u m m a r y o f the h y ­ d r o x y content, a n d p e r t i n e n t p h y s i c a l properties, o f the d e r i v a t i z e d l i g n i n s . 5

1

n

ω

1

Methods. I n d i v i d u a l solutions o f the b l e n d c o m p o n e n t s i n dioxane (or t e t r a h y d r o f u r a n ) were m i x e d , a n d stirred for about 12 hours before c a s t i n g into a Teflon m o l d . Solvent e v a p o r a t i o n proceeded under a m b i e n t c o n d i ­ tions for 24 hours followed b y transferral t o a v a c u u m oven at 6 0 ° C for further r e m o v a l o f solvent. T h e d r i e d blends were t h e n stored i n a v a c u u m

desiccator over P2O5. T h e glass t r a n s i t i o n ( T ^ ) a n d m e l t i n g ( T ) t e m p e r a t u r e o f the pure component p o l y m e r s a n d their blends were d e t e r m i n e d o n a P e r k i n - E l m e r ( D S C - 4 ) differential s c a n n i n g calorimeter a n d T h e r m a l A n a l y s i s D a t a S t a ­ t i o n ( T A D S ) . A l l m a t e r i a l s were a n a l y z e d a t a h e a t i n g a n d c o o l i n g rate o f 2 0 ° C · m i n " under a purge o f d r y n i t r o g e n . D y n a m i c m e c h a n i c a l p r o p e r ­ ties were d e t e r m i n e d w i t h a P o l y m e r L a b o r a t o r i e s , Inc. d y n a m i c m e c h a n i ­ cal t h e r m a l analyzer interfaced t o a H e w l e t t - P a c k a r d m i c r o c o m p u t e r . T h e m

1

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466

T a b l e I. H y d r o x y l content a n d glass t r a n s i t i o n t e m p e r a t u r e of l i g n i n s derivatized w i t h acetic a n h y d r i d e ( A c ) , d i e t h y l sulfate ( E t ) , a n d propylene oxide ( P r ) OH-Groups/C9 Molar Ratio (Reagent/OH)

Total O H

Phenolic O H

T (°C)

OSL



1.47

0.59

115

Ac-1 Ac-2 Ac-3 Ac-4 Ac-5

29 61 80 100 192

1.14 0.52 0.35 0.19 0.0

0.41 0.26 0.21 0.14 0.03

110 106 103 101 96

Et-1 Et-2 Et-3 Et-4

23 50 67 172

1.22 1.08 0.96 0.88

0.34 0.20 0.08 0.00

109 96 75 57

Pr-1



1.47

0.00

69

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Sample I D

s p e c t r a were collected at a h e a t i n g rate of 4 ° C · m i n 150°C u t i l i z i n g a single cantilever b e a m geometry.

1

f f

f r o m — 5 0 ° C to

Results and Discussion Blend Properties. O f the m o d i f i c a t i o n reactions u t i l i z e d i n the study, acetyl a t i o n y i e l d e d the widest range of s u b s t i t u t e d lignins ( T a b l e I) a n d resulted i n the greatest variety of b l e n d morphologies. A series of t h e r m o g r a m s for 20 w t . % blends prepared f r o m t h i s f a m i l y of l i g n i n s is presented i n F i g u r e 2. A l t h o u g h d a t a for the pure H P C are not s h o w n i n the figure, the T ^ was f o u n d at about 25 ° C a n d T at 212 ° C ( X = 1 6 % ) . A n a d d i t i o n a l secondorder t r a n s i t i o n for t h i s m a t e r i a l is located at about 90 ° C w h i c h has been described (13,14) as o r i g i n a t i n g f r o m a l i q u i d c r y s t a l ( L C ) mesophase. T h e u n m o d i f i e d l i g n i n b l e n d has a b r o a d glass t r a n s i t i o n centered at 4 2 ° C , res u l t i n g f r o m the c o n v o l u t i n g effects of these two t r a n s i t i o n as revealed b y d y n a m i c m e c h a n i c a l a n a l y s i s . A l s o , relative t o the pure H P C c o m p o n e n t , a depression i n the m e l t i n g t e m p e r a t u r e ( T ) of about 20° results a l o n g w i t h a r e d u c t i o n i n the degree of c r y s t a l l i n i t y . Interestingly, the b l e n d prepared f r o m the lowest D S l i g n i n e x h i b i t s a m u c h more intense T ^ w i t h a n associated loss of c r y s t a l l i n e a n d L C s u p e r s t r u c t u r e . A s the l i g n i n h y d r o x y content is further reduced, D S C analysis of the 20 w t . % b l e n d a g a i n r e s e m bles t h a t of the H P C / O S L s y s t e m i n t h a t a c r y s t a l l i n e m e l t is observed at about 190 ° C , a n d a second-order t r a n s i t i o n occurs at 4 0 ° C . U p o n complete a c e t y l a t i o n of l i g n i n a n a d d i t i o n a l feature can be identified i n the t h e r m o g r a m . W h i l e the d e v i a t i o n at 9 0 ° C ( c o m m o n to the H P C ) is s t i l l e v i d e n t , an a d d i t i o n a l t r a n s i t i o n can be f o u n d at 115°C o r i g i n a t i n g f r o m f r o m a pure l i g n i n phase. F u r t h e r evidence of the l i m i t e d c o m p a t i b i l i t y between these m

m

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F i g u r e 1. S c h e m a t i c representation of organosolv l i g n i n .

TEMPERATURE

CO

F i g u r e 2. D S C t h e r m o g r a m s of H P C blends c o n t a i n i n g 20 w t . % of acetyl a t e d l i g n i n s w i t h a degree of s u b s t i t u t i o n of: A ) 0 % , B ) 2 3 % , C ) 7 6 % , D ) 100

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468

two p o l y m e r s can be cited by the s i m i l a r i t y i n b o t h i n t e n s i t y a n d l o c a t i o n of the m e l t i n g peak. T h e above observations i n d i c a t e t h a t as the degree of s u b s t i t u t i o n of l i g n i n h y d r o x y f u n c t i o n a l i t y increases, there is a n i n i t i a l c o m p a t i b i l i t y i n ­ crease w i t h H P C followed b y a r a p i d decrease u n t i l complete i n c o m p a t i b i l i t y results after complete a c e t y l a t i o n . T h i s is further i l l u s t r a t e d b y m o n i t o r i n g the degree of c r y s t a l l i n i t y of the blends as s h o w n i n F i g u r e 3 . R e l a t i v e to the u n m o d i f i e d l i g n i n b l e n d , there occurs a m u c h more r a p i d d i s r u p t i o n of c r y s t a l l i n i t y i n the m a t e r i a l s prepared f r o m l o w D S l i g n i n s . A s the level of s u b s t i t u t i o n increases, however, the level of c r y s t a l l i n i t y retained i n the b l e n d increases u n t i l at D S = 8 7 % it remains above t h a t of the u n m o d ­ ified l i g n i n s y s t e m . R e c o g n i z i n g t h a t the decrease i n c r y s t a l l i n i t y of the b l e n d is a t t r i b u t a b l e to the i n t e r a c t i o n between the i n d i v i d u a l c o m p o n e n t s , this a p p r o a c h is consistent w i t h the above scenario of a n i n i t i a l increase i n c o m p a t i b i l i t y followed by a r a p i d decrease i n p o l y m e r - p o l y m e r m i s c i b i l i t y * . Melting Point Depression. A more q u a n t i t a t i v e e v a l u a t i o n of the r e l a t i o n ­ ships e x i s t i n g between l i g n i n s t r u c t u r e a n d b l e n d m i s c i b i l i t y is possible t h r o u g h the T depression observed i n these m a t e r i a l s . F o r s e m i - c r y s t a l l i n e b l e n d systems, such as these, the p o l y m e r - p o l y m e r i n t e r a c t i o n p a r a m e t e r , ' Β ' , can be d e t e r m i n e d t h r o u g h the following s i m p l i f i e d expression ( 1 5 ) : m

where Ύ° is the e q u i l i b r i u m m e l t i n g p o i n t of H P C ( = 2 1 3 . 1 ° C , f r o m ref. 1 6 ) ) T 2 is the m e l t i n g point of the b l e n d , AE u/^2u is the heat of m e l t i n g per u n i t v o l u m e of 1 0 0 % c r y s t a l l i n e m a t e r i a l ( = 7 . 5 2 c a l · c m , f r o m ref. 1 6 ) , a n d φι is the volume f r a c t i o n of the l i g n i n c o m p o n e n t . A plot of Δ Τ Λ / 2 vs. φ\ s h o u l d then y i e l d a straight line w i t h a slope p r o p o r t i o n a l to ' Β ' . T h e results of this treatment for the blends are presented i n T a b l e II b e l o w . A l t h o u g h a l l of the b l e n d systems are adequately m o d e l e d t h r o u g h t h i s linear a s s u m p t i o n ( R = 0 . 9 1 - 0 . 9 9 ) , it is of interest t h a t the intercept fails to pass t h r o u g h the o r i g i n , as expected. G e n e r a l l y , this behavior has been a t t r i b u t e d to a T depression r e s u l t i n g f r o m extraneous concerns such as r e d u c t i o n i n l a m e l l a r thickness of the crystallites ( 1 5 ) . Since no a t t e m p t was m a d e here to o b t a i n e q u i l i b r i u m m e l t i n g p o i n t s , t h i s is not out of the question. U n f o r t u n a t e l y , this effect eliminates the p u r e l y q u a n t i t a t i v e aspect of this analysis, b u t the figures r e m a i n v a l i d for direct c o m p a r i s o n of these blends. Μ2

2

M

- 3

2

m

Discussion. T h e overall effect of l i g n i n h y d r o x y content o n the i n t e r a c t i o n w i t h H P C is i l l u s t r a t e d i n F i g u r e 4. A s the h y d r o x y content is reduced, the i n t e r a c t i o n energy increases u n t i l a m a x i m u m is reached at a D S of ca. * I t s h o u l d be noted t h a t results o n blends p r e p a r e d w i t h the e t h y l a t e d lignins are consistent w i t h this v i e w , as w i l l become evident i n later discussion.

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18 Γ

LIGNIN

CONTENT

(Wt.%)

F i g u r e 3. R e l a t i o n s h i p between % o f c r y s t a l l i n i t y a n d l i g n i n content for blends prepared w i t h the acetylated l i g n i n series. T h e degree o f s u b s t i t u t i o n of h y d r o x y f u n c t i o n a l i t y is given w i t h each curve.

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LIGNIN: PROPERTIES AND MATERIALS

PHASE

MORPHOLOGY

REGION I Isotropic (Lignin) & Anisotropic Domains

REGION II Anisotropic Domains

REGION III M i s c i b l e , Isotropic

1

-84 0

0. 4

TOTAL

1 0.8

OH

1 1.2

1 1.6

(/C9)

F i g u r e 4. V a r i a t i o n i n the p o l y m e r - p o l y m e r i n t e r a c t i o n p a r a m e t e r , Έ ' w i t h h y d r o x y content of e t h y l l i g n i n ( X ) , l i g n i n acetate ( O ) , u n m o d i f i e d l i g n i n (*), a n d h y d r o x y p r o p y l l i g n i n (—).

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T a b l e II. S u m m a r y of m e l t i n g p o i n t depression analysis for blends of H P C and l i g n i n m o d i f i e d b y a c e t y l a t i o n ( A c ) , e t h y l a t i o n ( E t ) a n d p r o p o x y l a t i o n (Pr) Sample I D

Intercept

Slope

R

2

-'Β' (cal/cm )

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch036

3

196.8

0.98

3.00

6.820

137.6

0.95

2.13

2.322 3.187 5.337 6.104

415.6 285.5 102.4 97.8

0.95 0.98 0.91 0.94

6.45 4.43 1.59 1.52

5.281 5.514 5.212

351.9 165.6 420.7

0.99 0.97 0.98

5.46 2.56 6.52

HPC/OSL

9.675

HPC/Pr HPC/Ac-2 HPC/Ac-3 HPC/Ac-4 HPC/Ac-5 HPC/Et-1 HPC/Et-2 HPC/Et-3

4 0 % . ( T h i s region is represented b y the H P C / A c - 1 a n d H P C / E t - 4 blends w h i c h were largely a m o r p h o u s , m a k i n g it impossible to d e t e r m i n e the T depression). T h e extent of i n t e r a c t i o n then r a p i d l y d i m i n i s h e s as h y d r o x y groups are further e l i m i n a t e d u n t i l a value of —1.5 is reached u p o n c o m ­ plete s u b s t i t u t i o n . It is w o r t h e m p h a s i z i n g t h a t this curve is generated f r o m d a t a o b t a i n e d o n b o t h the e t h y l a t e d a n d acetylated l i g n i n blends; conse­ quently, the overlap t h a t is encountered i n t h i s analysis suggests t h a t the t y p e of m o d i f i c a t i o n a p p l i e d does not a p p r e c i a b l y influence the b e h a v i o r . F u r t h e r m o r e , the p a r a b o l i c shape of the curve indicates t h a t the h y d r o x y f u n c t i o n a l i t y of l i g n i n does not favorably i m p a c t c o m p o n e n t i n t e r a c t i o n t h r o u g h the establishment of i n t e r m o l e c u l a r hydrogen bonds. R a t h e r , the observed m a x i m u m occurs at a degree of s u b s t i t u t i o n w h i c h provides a very close m a t c h i n the s o l u b i l i t y parameter δ of the two p o l y m e r s [for the l i g n i n derivatives, 10.0-10.5; H P C = 10.1 (17)]. T h e r e does exist a n i n t e r ­ esting e x c e p t i o n . T h e p r o p o x y l a t e d l i g n i n derivative b l e n d a c t u a l l y reveals a slight decrease i n i n t e r a c t i o n , relative to the parent l i g n i n s y s t e m , even t h o u g h its s o l u b i l i t y parameter (δ = 9.7) ( T a b l e I) w o u l d suggest a m u c h higher level of c o m p a t i b i l i t y . T h e i m p l i c a t i o n s of t h i s observation are not yet clear, u n f o r t u n a t e l y , a n d w i l l not be e x p a n d e d o n at t h i s t i m e . m

F u r t h e r consideration of these m a t e r i a l s as a whole provides i n f o r m a ­ t i o n o n those factors c o n t r i b u t i n g to the b l e n d m o r p h o l o g y a n d , subse­ quently, i m p a c t i n g the development of h i g h - s t r e n g t h composites. W i t h i n the i n t e r a c t i o n d i a g r a m of F i g u r e 4, three d i s t i n c t regions of m o r p h o l o g i c a l b e h a v i o r can be identified. A t low levels of i n t e r a c t i o n between the l i g n i n c o m p o n e n t a n d H P C ( R e g i o n I), phase s e p a r a t i o n occurs due to the u n ­ favorable energy considerations as well as L C mesophase f o r m a t i o n . T h e heterogeneity i n t r o d u c e d b y the l i g n i n d o m a i n s has a c a t a s t r o p h i c effect o n m a t e r i a l properties. A t the other extreme ( R e g i o n III), a m i s c i b l e b l e n d is o b t a i n e d p r e s u m a b l y representing the i d e a l s i t u a t i o n ; however, i t appears

1

10

-J

5

1

1

I

25

I

30

ι

5

LIGNIN

I ι

10

ι

ι

ι

25

CONTENT

15 2 0

ι

(wt.%)

30

F i g u r e 5. Effect of l i g n i n content o n m e c h a n i c a l properties of H P C / O S L blends p r e p a r e d b y i n j e c t i o n m o l d i n g (—), dioxane c a s t i n g ( — ) , a n d p y r i ­ dine c a s t i n g (— · —).

15 2 0

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36.

F i g u r e 6. S c a n n i n g electron m i c r o g r a p h s o f freeze-fracture surfaces for i n j e c t i o n m o l d e d ( A ) , dioxane cast ( B ) , a n d p y r i d i n e cast ( C ) blends at a c o m p o s i t i o n o f 1 5 % l i g n i n . ( 2 0 0 0 X ) ( F r o m ref. 10, w i t h p e r m i s s i o n o f B u t terworth & C o . , Ltd.)

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as t h o u g h the r i g i d i t y o f the cellulosic c h a i n is largely derived f r o m interm o l e c u l a r interactions. T h e d i s r u p t i o n o f these c h a i n interactions yields a m u c h more flexible c h a i n , negating the advantages afforded b y the r i g i d - r o d . M o r p h o l o g y development i n the region o f intermediate i n t e r a c t i o n ( R e g i o n II) originates p r i m a r i l y f r o m L C mesophase f o r m a t i o n i n a m i s c i b l e phase of H P C a n d l i g n i n , a n d presents the most favorable conditions for enhanced properties. F i g u r e 5 presents the results o f tensile tests for the H P C / O S L blends prepared b y solvent-casting a n d e x t r u s i o n . A l l o f the f a b r i c a t i o n m e t h o d s result i n a tremendous increase i n m o d u l u s u p t o a l i g n i n content o f c a . 15 w t . % . T h i s c a n be a t t r i b u t e d t o the T ^ elevation o f the a m o r p h o u s H P C / O S L phase l e a d i n g t o increasingly glassy response. O f particular interest is the tensile strength o f these m a t e r i a l s . A s is s h o w n , there is es­ sentially n o i m p r o v e m e n t i n t h i s parameter for the solvent cast blends, b u t a tremendous increase is observed for the i n j e c t i o n m o l d e d b l e n d . Q u a l i t a ­ tively, this behavior is best modeled b y the presence o f oriented chains, o r mesophase s u p e r s t r u c t u r e , dispersed i n a n a m o r p h o u s m a t r i x comprised o f the compatible H P C / O S L c o m p o n e n t . T h e presence o f t h i s fibrous s t r u c ­ ture i n the injection m o l d e d samples is confirmed b y S E M analysis o f the freeze-fracture surface ( F i g u r e 6). T h i s structure is n o t present i n the s o l ­ vent cast blends, a l t h o u g h evidence o f globular domains r e m a i n i n b o t h of these blends appearing somewhat more coalesced i n t h e p y r i d i n e cast material. Conclusions A l t h o u g h specific intermolecular interactions do not appear t o c o n t r i b u t e i n this p o l y m e r blend s y s t e m , the e l i m i n a t i o n o f l i g n i n ' s h y d r o x y f u n c t i o n a l i t y does d r a m a t i c a l l y influence the level o f i n t e r a c t i o n between these p o l y m e r s . Consequently, i t is possible t o define three m o r p h o l o g i c a l regions for these m a t e r i a l s w h i c h d i r e c t l y i m p a c t the p o t e n t i a l development o f h i g h - s t r e n g t h composite m a t e r i a l s . A t i n t e r m e d i a t e levels o f i n t e r a c t i o n , t h e b l e n d m o r ­ phology is characterized b y a dispersion o f l i q u i d c r y s t a l s u p e r s t r u c t u r e i n an a m o r p h o u s H P C / O S L m a t r i x . U p o n o r i e n t a t i o n o f t h i s s u p e r m o l e c u l a r s t r u c t u r e , a d r a m a t i c enhancement o f b o t h m o d u l u s a n d tensile s t r e n g t h is observed i n d i c a t i n g the v a l i d i t y o f this a p p r o a c h for the development o f h i g h performance composites based o n cellulosics. Acknowledgments T h e authors w o u l d like t o acknowledge the assistance o f D r . S. S. K e l l e y (Tennessee-Eastman C o . ) , D r . T . C . W a r d , a n d D r . G . L . W i l k e s ( P M I L , V i r g i n i a Tech), a n d M r . C . P r i c e ( D e p t . o f Forest P r o d u c t s , V i r g i n i a T e c h ) . Literature C i t e d 1. Hwang, W . F.; Wiff, D. R.; Verschoore, C . ; Price, G . E . ; Helminiak, T . E . ; Adams, W . W . Polym. Eng. Sci. 1983, 23, 784. 2. Siegman, Α.; Dagan, Α.; Kenig, S. Polymer 1985, 26, 1326.

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RIALS

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GLASSER

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3. Paci, M . ; Barone, C.; Magagnini, P. J. Polym. Sci.-Polym. 1987, B25, 1559. 4. Gray, D. G . In Polymeric Liquid Crystals; Blumstein, Α . , Ed.; Plenum: New York, 1985; p 369. 5. Nishio, Y . ; Susuki, S.; Takahashi, T . Polymer J. 1985, 17, 753. 6. Navard, P.; Hardin, J . - M . In Polymeric Liquid Crystals; Blumstein, Α., Ed.; Plenum: New York, 1985; p 389. 7. Tseng, S.-L.; Valente, Α.; Gray, D. G . Macromolecules 1981, 14, 715. 8. Werbowyj, R. S.; Gray, D. G . Mol. Cryst. Lig. Cryst 1976, 34, 97. 9. Rials, T . G . ; Glasser, W . G . J. Appl. Polym. Sci., in press. 10. Rials, T . G . ; Glasser, W . G . Polymer, in press. 11. Rials, T . G . Ph.D. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, V A , 1986. 12. Wu, L . C . - F . ; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29, 1111. 13. Kyu, T . ; Mukheija, P.; Park, H.-S. Macromolecules 1985, 18, 2331. 14. Rials, T . G . ; Glasser, W . G . J. Appl. Polym. Sci. 1988, 36, 749. 15. Harris, J. E . ; Paul, D. R.; Barlow, J . W . In Polymer Blends and Com­ posites in Multiphase Systems; Han, C . D . , Ed.; American Chemical Society: Washington, D C , 1984; p 17. 16. Samuels, R. J. J. Polym. Sci.: A2 1969, 7, 1197. 17. Aspler, J . S.; Gray, D. G . Polymer 1982, 23, 43. RECEIVED March 17,1989

Chapter 37

Engineering Lignopolystyrene Materials of Controlled Structures Ramani Narayan , Nathan Stacy , Matt Ratcliff , and Helena L i Chum 1

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Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, IN 47907 Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401

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Well characterized, low molecular weight lignins of narrow polydispersity were reacted with a predefined molecular weight polystyryl carbanion, which was prepared by anionic polymerization. The carbanion was shown to displace mesylate groups on the lignin macromolecule forming ligno-polystyrene graft copolymers of controlled structures. The toluene extract of the reaction mixture contained largely unreacted polystyrene and about 5% of lignin-g-PS. The residue (toluene insoluble) also contained lignin-polystyrene graft copolymer. T h e g r a f t i n g o f s y n t h e t i c p o l y m e r s t o l i g n i n a n d other n a t u r a l p o l y m e r s offers t h e p o t e n t i a l o f p r e p a r i n g new class o f engineering plastics because g r a f t i n g frequently results i n t h e s u p e r p o s i t i o n o f properties r e l a t i n g t o b a c k b o n e a n d side c h a i n ( 1 , 2 ) . A n e x a m p l e is the g r a f t i n g o f 8-10% p o l y a c r y l i c a c i d o n t o h i g h density polyethylene, w h i c h gave t h e c o p o l y m e r i n creased m o d u l u s a n d softening p o i n t w h i l e l e a v i n g t h e m e l t i n g p o i n t a n d c r y s t a l l i n i t y o f the polyethylene u n c h a n g e d . T h e properties o f the graft c o p o l y m e r s w i l l , p r i m a r i l y , b e dependent o n t h e m o l e c u l a r weight o f t h e side c h a i n graft a n d t h a t o f the l i g n i n . It w i l l also d e p e n d o n t h e n a t u r e a n d n u m b e r o f side c h a i n grafts a n d t h e t y p e o f backbone-graft linkage. These t a i l o r - m a d e l i g n i n - s y n t h e t i c p o l y m e r graft c o p o l y m e r s o f c o n t r o l l e d s t r u c t u r e s c a n f u n c t i o n as c o m p a t i b i l i z e r s / i n t e r f a c i a l agents f o r b l e n d i n g l i g n i n w i t h s y n t h e t i c t h e r m o p l a s t i c s . P o l y m e r blends have been successfully used i n a n i n c r e a s i n g n u m b e r o f a p p l i c a t i o n s i n recent years as a means o f c o m b i n i n g the useful properties o f different m a t e r i a l s t o meet new m a r k e t a p p l i c a t i o n s w i t h m i n i m u m development cost (3). C u r r e n t approaches t o g r a f t i n g s y n t h e t i c p o l y m e r s o n t o l i g n i n (4-6) a n d o t h e r n a t u r a l p o l y m e r s like cellulose (7-11) i n v o l v e r a d i c a l p o l y m e r i z a t i o n m e t h o d s ( c h e m i c a l o r r a d i a t i o n ) . U s i n g r a d i c a l approaches, i t is 0097-6156/89/0397-0476$06.00/0 © 1989 American Chemical Society

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u s u a l l y more difficult to c o n t r o l or change the m o l e c u l a r weight o f the grafts, the m o l e c u l a r weights are v e r y h i g h a n d different types o f b a c k b o n e graft linkage e x i s t . F u r t h e r m o r e , the graft c o n t a i n s considerable a m o u n t s of h o m o p o l y m e r s . It is more difficult t o reproduce the graft y i e l d s , p r o p erties, a n d other features o f the graft c o p o l y m e r (12). B e c a u s e o f these p r o b l e m s , such graft c o p o l y m e r s cannot f u n c t i o n effectively as c o m p a t i b i l i z e r s / i n t e r f a c i a l agents. G l a s s e r a n d co-workers (see p u b l i c a t i o n s i n these P r o c e e d i n g s for references) have been u s i n g approaches w i t h g o o d s t r u c t u r a l c o n t r o l t h r o u g h the p r o d u c t i o n o f c h a i n - e x t e n d e d h y d r o x y p r o p y l a t e d l i g n i n s reacted w i t h other p o l y m e r i c s y s t e m s . W e are d e v e l o p i n g new s y n t h e t i c approaches t h a t allow us t o prepare renewable p o l y m e r - s y n t h e t i c p o l y m e r graft c o p o l y m e r s o f c o n t r o l l e d s t r u c t u r e s w i t h precise c o n t r o l over m o l e c u l a r weights o f the grafts a n d b a c k b o n e p o l y m e r , degree o f graft s u b s t i t u t i o n , a n d b a c k b o n e graft linkage (13-18). I n t h i s p a p e r we r e p o r t o n the p r e l i m i n a r y synthesis a n d c h a r a c t e r i z a t i o n o f l i g n i n - p o l y s t y r e n e graft c o p o l y m e r s o f c o n t r o l l e d structures. Experimental Materials. S t y r e n e ( A l d r i c h ) was p u r i f i e d b y d i s t i l l a t i o n f r o m C a U 2 before use. n - B u t y l l i t h i u m ( A l d r i c h ) was used w i t h o u t f u r t h e r p u r i f i c a t i o n . T e t r a h y d r o f u r a n ( F i s h e r Scientific) was p u r i f i e d i n a solvent s t i l l b y d i s t i l l a t i o n f r o m a s o d i u m / b e n z o p h e n o n e m i x t u r e . T o l u e n e ( F i s h e r Scientific) was used w i t h o u t f u r t h e r p u r i f i c a t i o n . Reagent grade m e t h y l e n e c h l o r i d e ( B a k e r C h e m i c a l C o . ) was d r i e d o n 5 A ° m o l e c u l a r sieves. R e a g e n t grade t r i e t h y l a m i n e ( B a k e r ) was d r i e d over K O H . M e t h a n e s u l f o n y l chloride ( A l d r i c h , 98%) was used w i t h o u t f u r t h e r p u r i f i c a t i o n . Instrumentation. U V / V i s i b l e s p e c t r a were collected o n a P e r k i n - E l m e r L a m b d a 4 s p e c t r o p h o t o m e t e r . I R s p e c t r a were collected o n a P e r k i n - E l m e r 1640 s p e c t r o p h o t o m e t e r . N M R s p e c t r a were t a k e n o n a N i c o l e t N T - 2 0 0 s p e c t r o m e t e r . D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y was r u n o n a P e r k i n - E l m e r D S C - 4 u n i t , e q u i p p e d w i t h a s y s t e m 4 microprocessor controller a n d a 3600 d a t a s t a t i o n . E l e m e n t a l analyses were r u n b y the P u r d u e m i c r o a n a l y s i s l a b o r a t o r y i n the D e p a r t m e n t o f C h e m i s t r y at P u r d u e U n i v e r s i t y a n d b y H u f f m a n L a b s ( G o l d e n , C O ) . L i g n i n g r o u p a n a l y s i s techniques are described i n references 19-21. Preparation of Mesylated Lignin. I n a 500 m l flask, 3.0 g o f the o r g a n o s o l v l i g n i n (elemental: C , 6 4 . 5 % ; H , 6 . 3 % ; O , 29.2%) was d i s s o l v e d i n a s o l u t i o n o f 60 m l C H C 1 c o n t a i n i n g 21.8 m m o l e ( ~ 3 m l ) d r y t r i e t h y l a m i n e . T h e flask was sealed a n d p u r g e d w i t h n i t r o g e n , w h i l e c o o l i n g t o 0 ° C . 17.4 m m o l e (1.3 m l ) of m e t h a n e s u l f o n y l c h l o r i d e ( M S C 1 ) was a d d e d dropwise over a 20 m i n p e r i o d w h i l e s t i r r i n g . T h e r e a c t i o n m i x t u r e was t h e n allowed t o s t i r for a n a d d i t i o n a l 60 m i n . T h e m e s y l a t e d l i g n i n was p u r i f i e d b y successive e x t r a c t i o n s at r o o m t e m p e r a t u r e i n a s e p a r a t o r y f u n n e l , u s i n g one 30 m l H 0 wash followed b y t w o washes w i t h d i l u t e (10%) H C 1 . T h e aqueous fractions were c o m b i n e d a n d back e x t r a c t e d w i t h C H 2 C I 2 . T h e c o m b i n e d 2

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C H 2 C I 2 phase was t h e n washed w i t h s a t u r a t e d NaHCC>3. B a c k e x t r a c t i o n of the c o m b i n e d NaHCC>3 washes recovered some of the emulsified p r o d ­ ucts i n C H 2 C I 2 . T h e c o m b i n e d o r g a n i c phase was t h e n washed w i t h N a C l , a n d the m e s y l a t e d l i g n i n was recovered f r o m the C H 2 C I 2 b y freeze d r y i n g w i t h N2 i n 6 7 % y i e l d . T h e m e s y l a t e d l i g n i n h a d a n a p p r o x i m a t e e l e m e n ­ t a l a n a l y s i s of C : 5 5 . 3 % , H : 5 . 6 % , 0 : 2 9 . 8 % , S : 9 . 5 % (after d i s c o u n t i n g for the presence of salt i m p u r i t i e s ) . G r o u p a n a l y s i s for the l i g n i n before m e s y l a t i o n gave 6 . 3 % p h e n o l i c O H a n d 13.6% m e t h o x y l groups, w h i l e after m e s y l a t i o n the results were 1 4 . 2 % m e t h o x y l a n d 2 3 . 5 % S O 2 C H 3 g r o u p s , respectively. * H N M R y i e l d e d peaks at 1.27 p p m ( b r o a d m , side c h a i n m e t h y l s ) , 2.98 p p m ( b r o a d m , side chains), 3.12 p p m (s, C - O 3 S C H 3 ) , 3.28 ( b r o a d m , side c h a i n ) , 3.88 ( b r o a d m , O C H 3 ) , a n d 6.4-7.5 p p m ( a r o m a t ics). I n C N M R , m a i n peaks are seen i n the range o f 153.2-104.5 p p m ( a r o m a t i c c a r b o n s ) , 56.3 p p m ( m e t h o x y l ) , 39.8 p p m ( O 3 S C H 3 i n s y r i n g y l u n i t s ) , 38.2 p p m ( O 3 S C H 3 i n g u a i a c y l u n i t s ) a n d 37.3 p p m ( O 3 S C H 3 i n side c h a i n ) . T h e N M R assignments were confirmed t h r o u g h the s y n t h e ­ sis of 2 - m e t h o x y p h e n o l a n d 2 . 6 - d i m e t h o x y p h e n o l , - ( 3 - m e t h o x y , 4-methane s u l f o n a t e p h e n y l ) ethylene glycol-methanesulfonate-/?-guaiacyl ether a n d a (3-methoxy, 4-methanesulfonate p h e n y l ) g l y c e r o l bis methanesulfonate-/?g u a i a c y l ether. N M R a n a l y s i s i n d i c a t e d t h a t the m e s y l a t e d l i g n i n is l a r g e l y free of m e t h a n e s u l f o n y l chloride a n d methanesulfonic a c i d .

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Preparation of the "Living" Polystyrene. 18 g of the " l i v i n g " p o l y m e r was p r e p a r e d b y s t a n d a r d a n i o n i c p o l y m e r i z a t i o n u s i n g η-butyl l i t h i u m . T h e r e a c t i o n was c a r r i e d o u t b y the d r o p wise a d d i t i o n of 20 m l of styrene t o 5 m l of the i n i t i a t o r s o l u t i o n i n 150 m l of neat T H F at - 7 8 ° C . T h e styrene d r i p was a d j u s t e d t o t a k e a p p r o x i m a t e l y 30 m i n for c o m p l e t i o n a n d t h e n the r e a c t i o n was allowed t o s t i r for t w o hours before the g r a f t i n g r e a c t i o n w i t h m e s y l a t e d l i g n i n was c a r r i e d o u t . T h e n u m b e r average m o l e c u l a r weight of the p o l y s t y r e n e , as d e t e r m i n e d b y H P S E C , was 9500 w i t h p o l y d i s p e r s i t y of 1.2. Preparation of the Lignin-Polystyrene Graft Copolymer. 75 m g of the m e ­ s y l a t e d l i g n i n was weighed a n d p l a c e d i n a 50 m l r o u n d b o t t o m flask. T h i s flask was t h e n p u r g e d b y repeated v a c u u m / n i t r o g e n cycles a n d left u n ­ der a p o s i t i v e pressure of n i t r o g e n . A p p r o x i m a t e l y 50 m l of the " l i v i n g " p o l y s t y r e n e s o l u t i o n , c o n t a i n i n g a p p r o x i m a t e l y 6 g of the p o l y m e r , was t h e n transferred i n t o the flask b y a double-ended needle. T h e r e s u l t i n g s o l u t i o n t u r n e d d a r k b r o w n i n a r o u n d 5-10 m i n a n d was allowed t o w a r m t o r o o m t e m p e r a t u r e . A f t e r s t i r r i n g for several h o u r s , the solvent was e v a p o r a t e d b y h e a t i n g under a n i t r o g e n flow. A f t e r a w a t e r / m e t h a n o l w a s h t o remove i o n i c residue, the s o l i d residue was placed i n soxhlet e x t r a c t i o n a p p a r a t u s a n d e x t r a c t e d w i t h toluene for 48 hrs t o remove excess p o l y s t y r e n e f r o m the r e a c t i o n m i x t u r e . A f t e r e x t r a c t i o n , the toluene was r e m o v e d b y n i t r o g e n flow a n d b o t h the toluene soluble e x t r a c t a n d the i n s o l u b l e residue were d r i e d i n a v a c u u m oven for 3-4 hrs at 55° C .

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Results and Discussion

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch037

T h e new s y n t h e t i c a p p r o a c h b e i n g a d o p t e d for the p r e p a r a t i o n o f the l i g n i n p o l y s t y r e n e graft c o p o l y m e r i n v o l v e d three steps. 1. I n t r o d u c t i o n of reactive mesylate groups o n t o the l i g n i n m a c r o m o l e c u l e b y m e s y l a t i o n o f the free - O H groups o n the l i g n i n ( F i g . 1). T h e m e s y l a t e groups are g o o d l e a v i n g groups i n n u c l e o p h i l i c d i s p l a c e m e n t reactions. 2. P r e p a r a t i o n o f desired m o l e c u l a r weight p o l y s t y r y l c a r b a n i o n ( " L i v i n g P o l y s t y r e n e " ) by a n i o n i c p o l y m e r i z a t i o n ( F i g . 2). A n i o n i c p o l y m e r i z a ­ t i o n has been used extensively t o p r o v i d e c o n t r o l over m o l e c u l a r weight w i t h n a r r o w m o l e c u l a r weight d i s t r i b u t i o n . 3. R e a c t i o n of the m e s y l a t e d l i g n i n prepared i n step 1 ( F i g . 1) w i t h the p o l y s t y r y l c a r b a n i o n ( l i v i n g polystyrene) f r o m step 2 ( F i g . 2). T h e car­ b a n i o n displaces the mesylate groups o n the l i g n i n i n a n u c l e o p h i l i c d i s ­ placement r e a c t i o n w i t h the f o r m a t i o n of the p o l y s t y r e n e - l i g n i n graft c o p o l y m e r ( F i g . 3). T h e l i g n i n selected for s t u d y was prepared b y p u l p i n g aspen w i t h m e t h a n o l / w a t e r ( 7 0 % m e t h a n o l ) w i t h a l i q u o r p H of 2.4 a n d i s o l a t e d as described earlier (19-21). T h e acetone soluble f r a c t i o n h a d a n a r r o w p o l y d i s p e r s i t y i n d e x (apparent M = 864, a p p a r e n t M = 1690) a n d c o n t a i n e d h i g h a l i p h a t i c h y d r o x y l a n d free phenolic content. B a s e d o n d e t a i l e d c h e m i ­ c a l a n d spectroscopic a n a l y s i s , three types of s t r u c t u r a l u n i t s were identified as c o m p r i s i n g the l i g n i n m a c r o m o l e c u l e a n d are s h o w n i n F i g . 1 ( 2 2 , 2 3 ) . T h e l i g n i n was m e s y l a t e d w i t h m e t h a n e s u l f o n y l c h l o r i d e f o l l o w i n g the p r o ­ cedure of C r o s s l a n d a n d Servis (24) w i t h a m o d i f i e d w o r k - u p procedure, as described i n the E x p e r i m e n t a l section. T h e l i g n i n m e s y l a t e was c h a r ­ acterized b y e l e m e n t a l a n a l y s i s , p r o t o n a n d c a r b o n N M R . B a s e d o n N M R a n a l y s i s , the l i g n i n was 8 5 % m e s y l a t e d . T h e n a r r o w d i s p e r s i t y p o l y s t y r y l c a r b a n i o n of desired m o l e c u l a r weight was prepared b y a n i o n i c p o l y m e r i z a t i o n u s i n g η-butyl l i t h i u m as the i n i ­ t i a t o r a n d was reacted w i t h the m e s y l a t e d l i g n i n as described i n the E x ­ p e r i m e n t a l section. T h e r e a c t i o n p r o d u c t was e x t r a c t e d w i t h toluene t o re­ m o v e u n r e a c t e d p o l y s t y r e n e . A n a l y s i s o f the e x t r a c t showed s m a l l a m o u n t s of l i g n i n present a l o n g w i t h the p o l y s t y r e n e . Since l i g n i n is i n s o l u b l e i n toluene, the presence of l i g n i n i n the toluene e x t r a c t m u s t be due t o the f o r m a t i o n o f a toluene-soluble l i g n i n - p o l y s t y r e n e graft c o p o l y m e r f r a c ­ t i o n . A n a l y s i s of the residue f r o m the toluene e x t r a c t i o n revealed the pres­ ence of p o l y s t y r e n e . Since p o l y s t y r e n e is r e a d i l y soluble i n toluene, the residue m u s t c o n t a i n l i g n i n - p o l y s t y r e n e graft c o p o l y m e r . L i g n i n is a c o m ­ p l e x i r r e g u l a r m a c r o m o l e c u l e c o m p o s e d of different types of s t r u c t u r a l u n i t s w i t h v a r y i n g r e a c t i v i t i e s a n d m o l e c u l a r weights. T h i s c a n easily affect the a m o u n t o f p o l y s t y r e n e grafted o n t o the different s t r u c t u r a l u n i t s l e a d i n g t o a toluene-soluble a n d a toluene-insoluble graft c o p o l y m e r p r o d u c t . n

w

Proof of Grafting. T h e presence of the l i g n i n - P S graft c o p o l y m e r i n the e x t r a c t was s h o w n b y absorbance spectroscopy, as s h o w n i n F i g u r e 4. I n F i g u r e 4(a) a d i l u t e s o l u t i o n of the e x t r a c t i n toluene shows a n absorbance

480

LIGNIN: PROPERTIES AND MATERIALS

Lignin

OH

» C

H

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( 2 5)3

Lignin

O.S0 CH 2

3

N

X = H, C H O K CHsOSOaCHa 2

Y = OH, O S 0 C H 2

Z = H, O S 0 C H 2

3f

3

Ar

F i g u r e 1. F u n c t i o n a l i z a t i o n of the l i g n i n m a c r o m o l e c u l e . ( A ) M e s y l a t i o n of - O H g r o u p s . ( B ) S t r u c t u r a l u n i t s c o m p r i s i n g the l i g n i n m a c r o m o l e c u l e .

D.J

nCH=CH

4

j

Bu-|-CH -ÇH

9

I R

2

F i g u r e 2. P r e p a r a t i o n of the monodisperse p o l y s t y r y l c a r b a n i o n o f desired m o l e c u l a r weight.

c

, "

+

Lignin

O.S0 CH 2

3



Lignin - g - PS

F i g u r e 3. C o u p l i n g of the p o l y s t y r y l c a r b a n i o n w i t h the m e s y l a t e d l i g n i n .

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37.

300

400

500

WAVELENGTH

600

(nm)

F i g u r e 4. U V / V i s i b l e absorbance s p e c t r a of (a) a d i l u t e s o l u t i o n of l i g n i n / p o l y s t y r e n e extract i n toluene a n d (b) a s a t u r a t e d s o l u t i o n of m e s y l a t e d l i g n i n i n toluene.

482

LIGNIN: PROPERTIES AND MATERIALS

o f a p p r o x i m a t e l y 1.6. I n c o m p a r i s o n , F i g u r e 4(b) shows a s a t u r a t e d s o l u t i o n o f the m e s y l a t e d l i g n i n used i n the g r a f t i n g r e a c t i o n . T h e absorbance o f t h i s s o l u t i o n is less t h a n 0.6, i n d i c a t i n g t h a t the l i g n i n is o n l y s l i g h t l y soluble i n toluene. T h e observed higher absorbance for the e x t r a c t demonstrates t h a t the l i g n i n has been s o l u b i l i z e d b y the g r a f t i n g r e a c t i o n , m o s t l i k e l y due t o f o r m a t i o n o f a graft p r o d u c t . E l e m e n t a l a n a l y s i s o f the e x t r a c t gave 9 0 . 2 8 % C , 7.94% H , a n d 1.70% O . T h e definitive presence o f o x y g e n c o n f i r m e d l i g n i n i n the e x t r a c t , since p o l y s t y r e n e has n o o x y g e n . T h e presence o f a graft p r o d u c t i n the residue was d e m o n s t r a t e d b y differential s c a n n i n g c a l o r i m e t r y ( D S C ) , as s h o w n i n F i g u r e 5. F i g u r e 5(a) shows the D S C r u n for the residue after toluene e x t r a c t i o n h a d r e m o v e d excess p o l y s t y r e n e . T h e large p e a k at a p p r o x i m a t e l y 105° C c a n be c o m p a r e d t o the reference s p e c t r u m o f p o l y s t y r e n e ( M = 4000) s h o w n i n F i g u r e 5(b). T h i s shows the presence o f a large a m o u n t o f p o l y s t y r e n e t h a t c a n n o t b e r e m o v e d b y toluene, i n d i c a t i n g t h a t i t is grafted o n t o the l i g n i n . T h e increase i n c a r b o n a n d h y d r o g e n content o f the residue ( 7 6 . 5 % C , 6.75% H , 1 6 . 7 8 % O + S ) over t h a t o f the s t a r t i n g m e s y l a t e d l i g n i n , c o n f i r m e d the presence of a g r a f t i n g p r o d u c t . F u r t h e r c o n f i r m a t i o n o f g r a f t i n g was given b y I R a n d N M R , b o t h of w h i c h showed peaks c h a r a c t e r i s t i c o f b o t h types o f p o l y m e r i n the e x t r a c t a n d the residue. N M R o f the residue showed s h a r p p e a k s at 41 p p m , 45 p p m , 126 p p m , 129 p p m a n d 147 p p m , c h a r a c t e r i s t i c of polystyrene i n addition to characteristic broad lignin peaks.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch037

n

Quantitation of Graft Copolymer. T h e a p p r o x i m a t e a m o u n t s o f p o l y s t y r e n e a n d l i g n i n i n the residue a n d e x t r a c t were d e t e r m i n e d by the d e c o n v o l u t i o n o f the absorbance d a t a at 270 n m a n d 300 n m . T h i s y i e l d e d the r a t i o s of 2 6 % p o l y s t y r e n e t o 7 4 % l i g n i n for the residue a n d 9 6 % p o l y s t y r e n e t o 4 % l i g n i n for the e x t r a c t . T h e toluene e x t r a c t is a m i x t u r e o f l a r g e l y u n r e a c t e d p o l y s t y r e n e a n d l i g n i n - g - P S . T h i s is i n reasonable agreement w i t h the e l e m e n t a l a n a l y s i s of the e x t r a c t w h i c h showed a n oxygen content o f 1.7%. T h i s corresponds to 5.8% l i g n i n content i n the e x t r a c t , based o n a 2 9 . 2 % o x y g e n content o f the s t a r t i n g l i g n i n . Conclusions M o n o d i s p e r s e p o l y s t y r e n e o f defined m o l e c u l a r weight has been grafted o n t o a w e l l c h a r a c t e r i z e d m e s y l a t e d l i g n i n o f k n o w n m o l e c u l a r weight a n d r e l a t i v e l y n a r r o w p o l y d i s p e r s i t y . T h e c h e m i s t r y i n v o l v e d the n u c l e o p h i l i c d i s p l a c e m e n t o f m e s y l a t e groups o n l i g n i n b y the p o l y s t y r y l c a r b o n i o n . P r e p a r a t i o n o f p o l y s t y r y l c a r b a n i o n b y a n i o n i c p o l y m e r i z a t i o n allows m o n o d i s perse p o l y s t y r e n e of any desired m o l e c u l a r weight t o be grafted o n t o the l i g n i n i n a r e p r o d u c i b l e a n d consistent m a n n e r . B y u s i n g w e l l c h a r a c t e r i z e d , low m o l e c u l a r weight l i g n i n s of n a r r o w p o l y d i s p e r s i t y , t a i l o r - m a d e l i g n i n - p o l y s t y r e n e graft c o p o l y m e r s c a n n o w be p r e p a r e d . T h e s e engineered l i g n i n graft c o p o l y m e r s of c o n t r o l l e d s t r u c t u r e s can f u n c t i o n as c o m p a t i b i l i z e r s / i n t e r f a c i a l agents i n p r e p a r i n g blends o f k r a f t l i g n i n s ( $ 0 . 1 0 - 0 . 3 0 / l b . ) w i t h p o l y s t y r e n e ($0.55-0.74/lb.) l e a d i n g t o new m a t e r i a l s . F u t u r e w o r k a d dresses synthesis o f l i g n i n s w i t h lower degrees o f m e s y l a t i o n a n d other g o o d

NARAYANETAL.

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37.

F i g u r e 5. D i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y of (a) l i g n i n / p o l y s t y r e n e residue and (b) the polystyrene 4000 reference.

484

LIGNIN: PROPERTIES AND MATERIALS

l e a v i n g groups, a n d the g r a f t i n g o f different m o l e c u l a r weight p o l y s t y r e n e chains. I n a d d i t i o n t o t h i s , detailed c h a r a c t e r i z a t i o n o f the graft c o p o l y m e r w i l l be c a r r i e d out a n d s t r u c t u r e - p r o p e r t y r e l a t i o n s h i p s w i l l be established. Acknowledgment T h e work was funded b y the B i o b a s e d M a t e r i a l s P r o j e c t o f the D e p a r t ­ m e n t o f E n e r g y ' s ( D O E ) E n e r g y C o n v e r s i o n a n d U t i l i z a t i o n Technologies t h r o u g h S o l a r E n e r g y Research I n s t i t u t e ( F W P D 0 7 1 ) , M r . S t a n W o l f , D O E M a n a g e r , a n d T. K o l l i e , O R N L M a n a g e r .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch037

Literature Cited 1. Hopfenberg, H . P.; Stannett, V.; Kumura-Yeh, F.; Rigney, P. T. Appl. Polym. Symp. 1970, 13, 139. 2. Stannett, V . In Block and Graft Copolymers, Burke, J. J., and Weist, V . , Eds.; Syracuse University Press: Syracuse, 1973, p. 281. 3. Paul, D . R.; Newman, S., Eds. Polymer Blends, Vol. 182; Academic Press: New York. 4. Simlonescu, Cr.; Cernatescu-Asandel, Α . ; Stoleru. Cell. Chem. Technol. 1975, 9(4), 363-380. 5. Koshijima, T.; Muraki, E. Zairyo 1976, 16(169), 834-838. 6. Meister, J. J.; Patil, D . R. Ind. Eng. Chem. Prod. Res. Ser. 1985, 24(2), 313. 7. Arthur, J. C., Jr. Appl. Polym. Symp. 1981, 36, 201. 8. Mansour, Ο. Y . ; Nagaty, A . Prog. Polym. Sci. 1985, 11, 91. 9. Bhattcharyya, S. N.; Maldas, D . Prog. Polym. Sci. 1984, 10, 171. 10. Morin, B. R.; Breusova, I. P.; Rogovin, Z. A . Adv. Polym. Sci. 1982, 42, 139. 11. Hebish, Α.; Guthrie, J. T. The Chemistry and Technology of Cellulosic Copolymers; Springer-Verlag: New York, 1981. 12. Stannett, V . ACS Symp. Ser. 1982, 187, 1. 13. Narayan, R.; Tsao, G . T. In Advances in Polymer Synthesis, Culbertson, Β . M . , and McGrath, J. E., Eds.; Plenum Press: New York, 1985; Polym. Sci. Tech. 1985, 31, 405. 14. Narayan, R.; Tsao, G . T. In Cellulose: Structure, Modification, and Hydrolysis, Young, R. Α . , and Rowell, R. M . , Eds.; Wiley: New York, 1986, pp. 117-185. 15. Narayan, R.; Shay, M . In Renewable Resource Materials, New Polymer Sources, Carraher, C . E., Jr., and Sperling, L. H., Eds.; Plenum Press: New York, 1986; Polym. Sci. Tech. 1986, 33, 137. 16. Narayan, R.; Shay, M . In Recent Advances in Anionic Polymeriza­ tion, Hogen-Esch, T. E., and Smid, J., Eds.; Elsevier: New York, 1987, pp. 441-450. 17. Biermann, C . J.; Chung, J. B.; Narayan, R. Macromolecules 1987, 20, 954. 18. Biermann, C . J.; Narayan, R. Polymer 1987, 28, 2176.

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37.

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ET

AJL

Engineering Lignopofystyrene Materials

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19. Chum, H . L . ; Johnson, D. K.; Ratcliff, M . ; Black, S.; Schroeder, Η. Α.; Wallace, K . International Symposium on Wood and Pulping Chem­ istry, Vancouver, August 26-30, 1985, pp. 223-225. Chum, H . L . ; Ratcliff, M . ; Schroeder, Η. Α.; Sopher, D. W . J. Wood Chem. Tech. 1984, 4, 505. 20. Hawkes, G . E.; Smith, C . Z.; Utley, J. H . P.; Chum, H . L . Holzforschung 1986, 40, 115-123. 21. Chum, H . L . ; Johnson, D. K . , Tucker, M . P.; Himmel, M . E. Holz­ forschung 1987, 41, 97-107. 22. Chum, H . L . ; Johnson, D . K . ; Black, S.; Baker, J.; Sarkanen, Κ. V . ; Schroeder, H . A . Proc. Inter. Symp. Wood and Pulping Chem. Paris, 1987, Vol. 1, 91-93. 23. Chum, H . L . ; Black, S.; Johnson, D. K . ; Sarkanen, Κ. V . ; Robert, D. Organosolv Pretreatment for the Enzymatic Hydrolysis of Poplars. II. Isolation and Quantitative Structural Studies of Lignins. Submitted. 24. Crossland, R. K . ; Servis, Κ. L . J. Org. Chem. 1970, 35, 3195-3196. RECEIVED February 27,1989

Chapter 38

Recent Progress in Wood Dissolution and Adhesives from Kraft Lignin Nabuo Shiraishi

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch038

Department of Wood Science and Technology, Kyoto University, Sakyo-ku, Kyoto 606, Japan

It is becoming apparent that wood components, especially lignin, are chemically modified by solvents during wood dissolution, and that the resulting wood tars or pastes become highly reactive. Attempts have therefore been made to prepare effective adhesives, moldable resins and other products from wood after dissolution in phenols or polyhydric alcohols. This review presents recent progress on wood dissolution, and on the preparation of epoxy and phenol resin adhesives from kraft lignin. V a r i o u s a t t e m p t s have been m a d e to prepare adhesives f r o m l i g n i n . T h e p r e p a r a t i o n of resol resin adhesives has been s t u d i e d especially extensively. T h e i n t r o d u c t i o n o f phenols i n t o the a or /^-position o f the s i d e c h a i n o f the p h e n y l p r o p a n e u n i t (phenolation of l i g n i n ) has been considered a key r e a c t i o n for the f o r m u l a t i o n of these types of adhesives w i t h adequate g l u ability. It is k n o w n t h a t the p h e n o l a t i o n of l i g n i n takes place under a c i d i c c o n d i t i o n s at elevated temperatures. F o r e x a m p l e , about 0.36 moles o f p h e n o l were f o u n d to be c o m b i n e d w i t h each p h e n y l p r o p a n e u n i t of a k r a f t l i g n i n w h e n t h i s was heated i n a glass a m p u l e c o n t a i n i n g 5 g o f l i g n i n , 5 g o f p h e n o l a n d 6 m m o l h y d r o c h l o r i c a c i d at 130°C for 6 h (1). A n o t h e r e x p e r i m e n t (2) i n d i c a t e d t h a t more t h a n 0.43 moles of p h e n o l were i n t r o d u c e d i n t o l i g n i n b y r e a c t i o n w i t h b o r o n trifloride ( B F ) at 6 0 ° C for 4 h . A slight m o d i f i c a t i o n of t h i s reaction (80°C for 3 h) was f o u n d to raise the i n c o r p o r a t i o n of p h e n o l i n t o l i g n i n to 0.62 moles (3). O n the other h a n d , i t has recently been d e m o n s t r a t e d t h a t u n t r e a t e d w o o d a n d / o r w o o d modified by, for e x a m p l e , esterification or e t h e r i f i c a t i o n c a n be dissolved i n several organic solvents i n c l u d i n g phenols (3-10). C h a r a c t e r i z a t i o n of the r e s u l t i n g w o o d tars has revealed a h i g h r e a c t i v i t y a n d the p r o d u c t s c a n be converted r e a d i l y i n t o adhesives, m o l d a b l e resins, etc. 3

0097-6156/89A)397-0488$06.00/0 © 1989 American Chemical Society

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489

(5-7, 9-11). It is therefore v e r y l i k e l y t h a t the l i g n i n i t s e l f is h i g h l y m o d i f i e d b y solvents, especially b y phenols. I n consequence, effective m o d i f i c a t i o n of l i g n i n can be considered t o enhance i t s r e a c t i v i t y . I n t h i s s t u d y , k r a f t l i g n i n was c h e m i c a l l y m o d i f i e d w i t h p h e n o l a n d w i t h b i s p h e n o l - A i n order t o enhance i t s p o t e n t i a l as adhesive.

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Dissolution of

Wood

T h e d i s s o l u t i o n of c h e m i c a l l y m o d i f i e d w o o d has been developed recently (3-7). T h e s o l u b i l i z a t i o n of u n t r e a t e d w o o d was f o u n d t o be possible as w e l l (7-10). A t least three m e t h o d s have been f o u n d t o be a p p l i c a b l e t o the s o l u b i l i z a t i o n of c h e m i c a l l y m o d i f i e d w o o d . T h e first e x p e r i m e n t (4) ( D i rect m e t h o d ) e m p l o y e d severe d i s s o l u t i o n c o n d i t i o n s . F o r e x a m p l e , i n 20150 m i n a t 200-250°C, w o o d samples esterified by a series o f a l i p h a t i c acids c o u l d be dissolved i n b e n z y l ether, styrene oxide, p h e n o l , r e s o r c i n o l , b e n z a l d e h y d e , aqueous p h e n o l s o l u t i o n s , etc. F o r c a r b o x y m e t h y l a t e d , a l l y l a t e d a n d h y d r o x y e t h y l a t e d w o o d s , the c o n d i t i o n s p r o v i d e d for d i s s o l u t i o n i n p h e n o l , r e s o r c i n o l or their aqueous s o l u t i o n s , f o r m a l i n , etc., b y s t a n d i n g or s t i r r i n g at 170°C for 30 t o 60 m i n (5). T h e second m e t h o d of d i s s o l u t i o n is based o n solvolysis ( S o l v o l y s i s m e t h o d ) ( 6 , 7 , 1 1 , 1 2 ) . U n d e r m i l d e r c o n d i t i o n s ( 8 0 ° C for 30 t o 150 m i n ) p h e n o l a t i o n was a c c o m p l i s h e d w i t h a n a p p r o p r i a t e c a t a l y s t , a n d the c h e m i c a l l y m o d i f i e d w o o d was dissolved i n p h e n o l (11). U n d e r s i m i l a r c o n d i t i o n s , woods d e r i v a t i z e d b y a l l y l a t i o n , m e t h y l a t i o n , e t h y l a t i o n , h y d r o x y l a t i o n a n d a c e t y l a t i o n have also been f o u n d t o dissolve i n p o l y h y d r i c alcohols, s u c h as 1 , 6 - h e x a n e d i o l , 1 , 4 - b u t a n e d i o l , 1,2-ethanediol, 1 , 2 , 3 - p r o p a n e t r i o l (glycerol), a n d b i s p h e n o l - A (6). T h e t h i r d m e t h o d of d i s s o l u t i o n is based o n the m i l d c h l o r i n a t i o n of c h e m i c a l l y m o d i f i e d w o o d a c c o r d i n g to S a k a t a a n d M o r i t a (13) ( P o s t c h l o r i n a t i o n m e t h o d ) . C h l o r i n a t i o n , i n fact, resulted i n e n h a n c e d s o l u b i l i t y of c h e m i c a l l y m o d i f i e d w o o d i n solvents, i n c l u d i n g p h e n o l . F o r e x a m p l e , c h l o r i n a t e d c y a n o e t h y l a t e d w o o d does not o n l y dissolve i n cresol even at r o o m t e m p e r a t u r e , b u t i t also dissolves (under heating) i n r e s o r c i n o l , p h e n o l and a LiCl-dimethylacetamide solution. U n m o d i f i e d w o o d has been dissolved i n various n e u t r a l o r g a n i c solvents or solvent m i x t u r e s b y a d o p t i n g the " D i r e c t m e t h o d " described above. T h i s o b s e r v a t i o n was m a d e d u r i n g a n i n v e s t i g a t i o n i n t o the r e l a t i o n s h i p between the degree of c h e m i c a l m o d i f i c a t i o n of w o o d a n d i t s s o l u b i l i t y i n o r g a n i c c h e m i c a l s . So f a r , we have f o u n d t h a t under the c o n d i t i o n s of 200-250° C for 30-150 m i n , b o t h u n t r e a t e d w o o d chips a n d g r o u n d w o o d c a n be dissolved i n the f o l l o w i n g solvents: phenols, bisphenols, p o l y h y d r i c alcohols s u c h as 1,6-hexanediols, 1 , 4 - b u t a n e d i o l , oxyethers such as m e t h y l cellosolve, e t h y l cellosolve, diethylene g l y c o l , t r i e t h y l e n e g l y c o l , p o l y e t h y l e n e g l y c o l , a n d others. T h e d i s s o l u t i o n of m o d i f i e d or u n m o d i f i e d w o o d gives rise t o t a r or paste-like solutions w i t h a h i g h w o o d c o n c e n t r a t i o n ( 7 0 % , for e x a m p l e ) . T h e dissolved w o o d components were f o u n d t o be degraded t o a c e r t a i n

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490

e x t e n t , a n d t h i s resulted i n m i x t u r e s h a v i n g h i g h r e a c t i v i t y , w i t h the ex­ c e p t i o n o f those o b t a i n e d b y the " P o s t - c h l o r i n a t i o n m e t h o d . " T h e s o l u t i o n s w i t h h i g h w o o d c o n c e n t r a t i o n c a n be used for the p r e p a r a t i o n of adhesives a n d m o l d i n g s . T h i s has opened a new field for the u t i l i z a t i o n o f w o o d materials. A t t e m p t s ( 6 , 1 1 , 1 2 , 1 4 - 1 7 ) have concentrated o n the p r e p a r a t i o n o f w o o d - b a s e d adhesives b y c u r i n g degraded or c h e m i c a l l y m o d i f i e d w o o d components w i t h reactive solvents. P h e n o l s , bisphenols a n d p o l y h y d r i c alcohols have a l l been s h o w n t o be effective reactive solvents. W i t h these s o l u t i o n s (tars or pastes), p h e n o l - f o r m a l d e h y d e resins (such as resol resins), p o l y u r e t h a n e resins, e p o x y resins, etc., have successfully been p r e p a r e d w i t h h i g h contents o f c h e m i c a l l y m o d i f i e d or u n m o d i f i e d w o o d . C u r e reac­ t i o n s t a k e place w i t h ease. G l u a b i l i t y studies have d e m o n s t r a t e d excellent performance as w o o d - b a s e d adhesives. A d h e s i v e s were f o u n d t o p e r f o r m s a t i s f a c t o r i l y even i n exterior-grade a p p l i c a t i o n s . A resol-type w o o d - b a s e d adhesive has recently satisfied the requirements o f the Japanese A g r i c u l ­ t u r a l S t a n d a r d for w a t e r p r o o f binders (22). S o l u b i l i z a t i o n c o n d i t i o n s for its p r e p a r a t i o n were 120 m i n at 250° C w i t h e q u a l a m o u n t s o f p h e n o l a n d u n t r e a t e d M a k a m b a (birch) w o o d chips. B y a d d i n g s m a l l a m o u n t s (1.64 p a r t s per 100 p a r t s o f wood-based adhesive) o f a l k y l r e s o r c i n o l as h a r d e n e r , the same adhesive was f o u n d t o b i n d p l y w o o d s even at 120°C. T h i s is a l ­ m o s t 20° C below the t e m p e r a t u r e used for c o m m e r c i a l resol-type adhesives. T h e adhesive satisfied exterior-grade s t a n d a r d s . T h i s means t h a t the r e s o l t y p e w o o d - b a s e d adhesive is s i m i l a r i n i t s r e a c t i v i t y t o u r e a - f o r m a l d e h y d e adhesives, a n d higher t h a n c o m m e r c i a l resol resin adhesives. W o o d s o l u b i l i z a t i o n has a l r e a d y been discussed i n a recent review (18) w i t h s p e c i a l e m p h a s i s o n r e a c t i v i t y . T h e l i g n i n c o m p o n e n t o f w o o d gains r e a c t i v i t y b y m o d i f i c a t i o n w i t h solvent d u r i n g s o l u b i l i z a t i o n . N u c l e o p h i l i c s u b s t i t u t i o n w i t h p h e n o l takes place at the α-position o f l i g n i n sidechains. T h i s d e r i v a t i z a t i o n o f l i g n i n is associated w i t h d e g r a d a t i o n t h a t p l a y s a n i m p o r t a n t role i n m a k i n g the w o o d - p h e n o l s o l u t i o n reactive. T h i s p o i n t was s t u d i e d i n d e t a i l b y r e a c t i n g p h e n o l w i t h isolated l i g n i n , a n d c o n v e r t i n g i t i n t o a n adhesive. T h e f o l l o w i n g s u m m a r i z e s t h i s s t u d y . Epoxy Resin Adhesives from Kraft

Lignin

E p o x y resin adhesives f r o m l i g n i n were r e p o r t e d b y T a i et ai (19,20) i n 1967. S a t i s f a c t o r y g l u a b i l i t y was f o u n d . T h e s o l u b i l i t y i n o r g a n i c solvents, however, was f o u n d t o be p o o r . I n essence, the p h e n o l i c h y d r o x y l groups o f k r a f t l i g n i n were g l y c i d y l a t e d d i r e c t l y . W e have also m a d e a n a t t e m p t to prepare l i g n i n - e p o x y resin adhesives (21). However, i n order t o i m p r o v e i t s r e a c t i v i t y , k r a f t l i g n i n was first p h e n o l a t e d w i t h b i s p h e n o l - A . F o r p h e n o l a t i o n , a s m a l l a m o u n t o f aqueous h y d r o c h l o r i c a c i d or B F - e t h y l etherate was used as c a t a l y s t , a n d t h u s t w o k i n d s o f g l y c i d y l a t i o n m e t h o d s were a d o p t e d (21). T h e p h e n o l a t i o n w i t h b i s p h e n o l - A was f o u n d to enhance the s o l u b i l i t y of the l i g n i n d e r i v a t i v e . I n fact, the l i g n i n - e p o x y resins o b t a i n e d were f o u n d to be c o m p l e t e l y soluble i n c e r t a i n o r g a n i c solvents, i n c l u d i n g acetone. 3

38.

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T h e g l u a b i l i t y of the l i g n i n - e p o x y resin was also f o u n d t o be i m p r o v e d b y p h e n o l a t i o n , a n d w a t e r p r o o f adhesives resulted (21). T h e t e m p e r a ­ t u r e dependence o f the d y n a m i c viscoelastic response was s t u d i e d o n cured l i g n i n - e p o x i d e films prepared w i t h v a r y i n g degrees o f p h e n o l a t i o n (21). T h e results revealed t h a t well-defined differences were f o u n d i n the glass t r a n ­ s i t i o n t e m p e r a t u r e ( T ^ ) , the storage m o d u l u s ( G ' ) i n the r u b b e r y p l a t e a u r e g i o n , a n d the peak height o f the l o g a r i t h m i c decrement (αχ) curve o f the cured films. T ^ a n d G i n the r u b b e r y p l a t e a u region were f o u n d t o increase w i t h a n increase i n degree of p h e n o l a t i o n . F u r t h e r m o r e , the peak height o f the αχ curve was f o u n d t o be higher for samples f r o m less p h e ­ n o l a t e d l i g n i n - e p o x i d e f i l m s . T h i s suggests t h a t the m o r e b i s p h e n o l a t e d l i g n i n forms, the m o r e crosslinks d u r i n g cure, thereby p r o d u c i n g a b e t t e r developed t h r e e - d i m e n s i o n a l network s t r u c t u r e (21). Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch038

;

T h e g l u a b i l i t y of two types of epoxy-resins, prepared f r o m l i g n i n s w i t h different degrees o f p u r i t y , was e x a m i n e d . T o k a i P u l p k r a f t l i g n i n F ( < 4 . 5 % sugars) a n d O j i k r a f t l i g n i n ( 1 1 . 7 % sugars) were used. T h e difference i n l i g n i n p u r i t y d i d n o t reveal a n y i n f e r i o r i t y i n either d r y or wet b o n d s t r e n g t h s , b u t enhanced g l u a b i l i t y was n o t e d for the less p u r i ­ fied l i g n i n , suggesting active p a r t i c i p a t i o n o f the sugar c o m p o n e n t s . B o t h e p o x y resins gave satisfactory d r y - a n d w e t - b o n d strengths after 5 m i n of hot-pressing at 140°C. A l l requirements for " F i r s t - C l a s s P l y w o o d " a c c o r d ­ i n g t o the Japanese A g r i c u l t u r e S t a n d a r d ( J A S ) were satisfied. T h e g l u a b i l i t y o f the l i g n i n - e p o x y resin adhesives was f o u n d t o be i m ­ p r o v e d by the a d d i t i o n of c a l c i u m c a r b o n a t e ( 5 0 % b y weight) t o the l i q u i d resin. T h i s m u s t be a t t r i b u t e d t o the n a t u r e o f the weak a l k a l i i n c a l c i u m c a r b o n a t e as a cure accelerator, a n d t o the reinforcement effect o f fillers. Since w o o d surfaces are a c i d i c , the a d d i t i o n o f alkaline fillers effectively alters the p H o f the glue l i n e . T h e s e results were o b t a i n e d by u s i n g h y d r o c h l o r i c a c i d as the c a t a l y s t for the p h e n o l a t i o n r e a c t i o n w i t h l i g n i n . Besides h y d r o c h l o r i c a c i d , BF3 is k n o w n t o be a n effective c a t a l y s t for the i n t r o d u c t i o n of p h e n o l groups i n t o l i g n i n . BF3 is also k n o w n as a c a t a l y s t w h i c h c a n p r o m o t e g l y c i d y l a t i o n not o n l y of phenolic b u t also of alcoholic h y d r o x y l groups. T h u s , the p r e p a ­ r a t i o n of l i g n i n e p o x y resins w i t h B F as c a t a l y s t was s t u d i e d also. T h e e p o x y value f o u n d for the s t a n d a r d l i g n i n - e p o x i d e prepared i n the presence of BF3 was 0.48, whereas t h a t of the epoxide prepared w i t h H C 1 as c a t a l y s t was 0.38. 3

T h e l i g n i n - e p o x i d e resins f r o m the r e a c t i o n w i t h BF3 were also tested as adhesives for p l y w o o d , u s i n g t r i e t h y l e n e t e t r a m i n e as c u r i n g agent w i t h hot-pressing at 140°C. T h e results of adhesion tests showed t h a t the w a t e r ­ p r o o f adhesive strengths were i m p r o v e d b y use o f BF3 as c a t a l y s t . T h e use of B F as c a t a l y s t p e r m i t t e d the a d o p t i o n of hot-pressing t i m e s as short as 3 m i n for p r e p a r i n g t h r e e - p l y p l y w o o d panels w i t h 6 m m thickness. T h i s resulted i n satisfactory w a t e r p r o o f adhesive performance. T h e a d d i t i o n o f c a l c i u m carbonate ( 5 0 % b y weight) t o the l i q u i d adhesive was a g a i n f o u n d t o enhance the w a t e r p r o o f g l u a b i l i t y . 3

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch038

Resol-Type Phenol Resin Adhesives from Kraft

Lignin

T h e r e have been m a n y a t t e m p t s t o prepare resol resin adhesives f r o m k r a f t l i g n i n (23). P h e n o l a t i o n o f l i g n i n c a n , i n these cases, also b e considered a k e y r e a c t i o n . T h a t i s , effective m o d i f i c a t i o n of l i g n i n w i t h p h e n o l c a n enhance i t s r e a c t i v i t y , r e s u l t i n g i n g o o d g l u a b i l i t y . L i g n i n was c h e m i c a l l y m o d i f i e d p r i o r t o r e s i n i f i c a t i o n , a n d the effect o f p h e n o l a t i o n was e x a m i n e d o n the g l u a b i l i t y of the resol r e s i n adhesives (23). T h e p h e n o l a t i o n was p e r f o r m e d either w i t h H C 1 ( 8 0 ° C , 60 m i n ) or w i t h o u t c a t a l y s t ( 2 0 0 ° C , 60 m i n ) . P r i o r t o adhesive t e s t i n g w i t h t h r e e - p l y p l y w o o d , 5 p a r t s of coconut husk powder were m i x e d w i t h 100 p a r t s of the resin. R e s u l t s are s h o w n i n F i g u r e 1. W e t - b o n d tensile-shear adhesion strengths are c o m p a r e d for two k i n d s of adhesives prepared u s i n g different p h e n o l a t i o n c o n d i t i o n s . T h e l i g n i n - r e s o l resin adhesive prepared w i t h o u t c a t a l y s t revealed sufficient w a t e r p r o o f adhesion s t r e n g t h t o meet or exceed the Japanese I n d u s t r i a l S t a n d a r d ( J I S ) requirement (0.98 M P a ) w i t h o n l y 6 m i n h o t - p r e s s i n g at 120°C. B y c o n t r a s t , the adhesive p r e p a r e d w i t h H C 1 as c a t a l y s t required 9 m i n of hot-pressing at the same t e m p e r a t u r e before i t reached the same level of s t r e n g t h . T h i s result emphasizes t h a t the p h e n o l a t i o n w i t h o u t c a t a l y s t results i n better m o d i f i c a t i o n of l i g n i n c o m p a r e d t o t h a t w i t h h y d r o c h l o r i c a c i d as c a t a l y s t . F u r t h e r m o r e , the l i g n i n - r e s o l resin adhesives prepared w i t h o u t c a t a l y s t c a n be c u r e d under c o n d i t i o n s u n d e r w h i c h a m i n o resin adhesives are generally used (i.e., 120°C w i t h a h o t - p r e s s i n g rate o f 1 m i n per 1 m m p l y w o o d t h i c k n e s s ) . I n order t o prepare better adhesives, the effect of p h e n o l a t i o n t i m e , p h e n o l a t i o n t e m p e r a t u r e , r e a c t i o n t i m e for resol r e s i n i f i c a t i o n , a n d degree o f l i g n i n p u r i t y were e x a m i n e d o n the adhesive p r o p e r t i e s . T h e results i n d i c a t e d t h a t o p t i m u m c o n d i t i o n s for p h e n o l a t i o n involve 2 0 0 ° C for 60 m i n a n d 60 m i n resol resinification at 9 0 ° C a n d at p H 9. T h e c o n d i t i o n s for resol resinification correspond w e l l t o those o f the c o n v e n t i o n a l m a n u f a c t u r i n g m e t h o d (24). Tests for the effect of l i g n i n p u r i t y o n the g l u a b i l i t y i n v o l v e d two k i n d s of resol resin adhesives p r e p a r e d f r o m O j i k r a f t l i g n i n ( 8 7 . 8 % p u r i t y ) a n d Tokai P u l p kraft lignin F (> 9 5 % purity). B o t h lignins produced satisf a c t o r y w e t - b o n d adhesion s t r e n g t h t h a t met J I S requirements b y a h o t pressing rate of 1 m i n per 1 m m p l y w o o d thickness. T h e difference i n l i g n i n p u r i t y h a d no effect o n g l u a b i l i t y . T h e same conclusions were d r a w n for e p o x y resin adhesives f r o m k r a f t l i g n i n . T h i s suggests t h a t p o l y s a c charide c o m p o n e n t s m a y be converted i n t o reactive m a t e r i a l s , such as 5h y d r o x y m e t h y l - 2 - f u r f u r a l , f u r f u r a l , etc., t h r o u g h h y d r o l y s i s a n d d e h y d r a t i o n d u r i n g p h e n o l a t i o n (18). F o r c o m p a r i s o n , a c o n v e n t i o n a l resol resin adhesive w i t h o u t l i g n i n was p r e p a r e d (24), a n d i t s g l u a b i l i t y was e x a m i n e d . T h i s resin was f o u n d t o require a hot-pressing rate of at least 1.5 m i n per 1 m m p l y w o o d thickness before a satisfactory w e t - b o n d adhesion s t r e n g t h was achieved at the low h o t - p r e s s i n g t e m p e r a t u r e of 120°C. T h i s indicates t h a t r e p l a c i n g a p a r t of the p h e n o l w i t h l i g n i n does not i m p l y a mere extender a d d i t i o n , b u t t h a t a p o s i t i v e role is achieved w h i c h enhances the r e a c t i v i t y of the adhesive.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch038

38.

SHiRAiSffl

Wood Dissolution and Adhesivesfrom Kraft Lignin

493

F i g u r e 1. C o m p a r i s o n of w e t - b o n d adhesion strengths o f l i g n i n - r e s o l resin adhesives p h e n o l a t e d w i t h a n d w i t h o u t a c i d c a t a l y s t . L e g e n d : φ : p h e n o l a ­ t i o n w i t h a c i d c a t a l y s t at 80°C for 60 m i n ; Ο p h e n o l a t i o n w i t h o u t c a t a l y s t at 2 0 0 ° C for 60 m i n . Note: N u m e r i c a l values i n parentheses are percentages of w o o d failure; hot-press t e m p e r a t u r e : 120°C. :

F o r the purpose of further e n h a n c i n g the r e a c t i v i t y a n d g l u a b i l i t y of kraft l i g n i n - r e s o l resin adhesives, the a d d i t i o n o f a l k y l r e s o r c i n o l was ex­ a m i n e d . T h e results of a d d i n g 2-10 p a r t s of a l k y l r e s o r c i n o l t o 100 p a r t s o f l i g n i n - r e s o l resin adhesive p r i o r to a p p l i c a t i o n i n d i c a t e a significant i m ­ p r o v e m e n t i n g l u a b i l i t y , especially i n w a t e r p r o o f g l u a b i l i t y . T h e w a t e r p r o o f g l u a b i l i t y as described b y w e t - b o n d adhesion s t r e n g t h tesing of two types of adhesives prepared w i t h a n d w i t h o u t a l k y l r e s o r c i n o l (10 parts) are c o m ­ p a r e d i n F i g u r e 2. T h e a d d i t i o n of a l k y l r e s o r c i n o l resulted i n a n i m p r o v e ­ m e n t o f w e t - b o n d adhesion s t r e n g t h . T h e adhesive met the requirements for " F i r s t - C l a s s P l y w o o d " a c c o r d i n g to J A S even after o n l y 3 m i n of h o t pressing (a h o t - p r e s s i n g rate of 0.5 m i n per 1 m m p l y w o o d thickness) at 120°C. It was also f o u n d t h a t the l i g n i n - r e s o l resin adhesives satisfied the J I S requirements for n o n - v o l a t i l e content, p H v a l u e , viscosity, gel t i m e , a n d d r y a n d wet adhesion s t r e n g t h . F u r t h e r m o r e , the low t e m p e r a t u r e c u r a b i l i t y t y p i c a l l y f o u n d i n a m i n o resin adhesives c o u l d also be achieved. T h u s , i t c a n be concluded t h a t a n effective u t i l i z a t i o n of l i g n i n is possible w i t h s i m u l t a n e o u s i m p r o v e m e n t of the properties o f resol resin adhesives.

LIGNIN: PROPERTIES AND MATERIALS

494

2.5 Ï2.0 X Ι­ Ο tr htn ο 1.0 ζ ο

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CD

έθ.5

0 0

3

6

9

12

HOT-PRESS TIME (min.) F i g u r e 2. R e l a t i o n s h i p between hot-press t i m e a n d w e t - b o n d adhesion s t r e n g t h for lignin-resol resin adhesives w i t h a n d w i t h o u t a l k y l r e s o r c i n o l . L e g e n d : Ο w i t h o u t a l k y l r e s o r c i n o l ; φ : w i t h 10 parts a l k y l r e s o r c i n o l . Note: N u m e r i c a l values i n parentheses are percentages o f w o o d failure; p h e n o l a ­ t i o n : 2 0 0 ° C , 60 m i n , w i t h o u t c a t a l y s t ; hot-press: 120°C, 6 m i n . :

Literature C i t e d 1. Kobayashi, Α . ; Haga, T . ; Sato, K . Mokuzai Gakkaishi 1966, 12, 305; Ibid. 1967, 13, 60. 2. Abe, I. Bull. Hokkaido For. Prod. Res. Inst 1970, 55, 1. 3. Shiraishi, N . Kobunshi Kako 1982, 31(11), 500. 4. Shiraishi, N . Japan Patent 1988-1992 (Appl. June 6, 1980). 5. Shiraishi, N . ; Goda, Κ. Mokuzai Kogyo 1984, 39(7), 329. 6. Shiraishi, N.; Onodera, S.; Ohtani, M . ; Masumoto, T . Mokuzai Gak­ kaishi 1985, 31(5), 418. 7. Shiraishi, N . Tappi Proc. 1987 Inter. Dissolving Pulps Conf., 95-102. 8. Shiraishi, N . ; Tsujimoto, N.; Pu, S. Japan Patent (Open) 1986-261358 (Appl. May 14, 1985). 9. Pu, S.; Shiraishi, Ν . ; Yokota, T . Abst. Papers Presented at 36th Natl. Mtg., Japan Wood Res. Soc. 1986, 179-180. 10. Shiraishi, N . Mokuzai Kogyo 1987, 42(1), 42. 11. Shiraishi, N . ; Kishi, H . J. Appl. Polym. Sci. 1986, 32, 3189. 12. Shiraishi, N.; Ito, H . ; Lonikar, S. V . ; Tsujimoto, N . J. Wood Chem. Technol. 1987, 7(3), 405. 13. Morita, M . ; Shigematsu, K.; Sakata, I. Abst. Papers Presented at 35th Natl. Mtg., Japan Wood Res. Soc. 1985, 215-216. 14. Kishi, H . ; Shiraishi, N . Mokuzai Gakkaishi 1986, 32(7), 520.

38.

SfflRAiSffl

Wood Dissolution and Adhesivesfrom Kraft Lignin

495

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15. Shiraishi, N . Mokuzai Gakkaishi 1986, 32(10), 755. 16. Ono, H.; Sudo, K.; Karasawa, J . Proc. 31st Lignin Forum 1986, 133. 17. Ono, H.; Sudo, K.; Karasawa, J. Abst. Papers Presented at 37th Natl. Mtg., Japan Wood Res. Soc. 1987, 288. 18. Shiraishi, N.; Tamura, Y . ; Tsujimoto, N . Mokuzai Kogyo 1987, 42(11), 492. 19. Tai, S.; Nagata, M . ; Nakano, J . ; Migita, N . Mokuzai Gakkaishi 1967, 13(3), 102. 20. Tai, S.; Nakano, J . ; Migita, N . Mokuzai Gakkaishi 1967, 13(6), 257. 21. Ito, H.; Shiraishi, N . Mokuzai Gakkaishi 1987, 33(5), 393. 22. Pu, S.; Shiraishi, Ν . Abst. Papers Presented at 37th Natl. Mtg., Japan Wood Res. Soc. 1987, 239. 23. Kato, K.; Shiraishi, N . Holzforschung, submitted. 24. Nakarai, Y . ; Watanabe, T. Mokuzai Gakkaishi 1965, 11, 137. RECEIVED February 27,1989

Chapter 39

Ozonized Lignin—Epoxy Resins Synthesis and Use B. Tomita , K. Kurozumi , A. Takemura , and S. Hosoya 1

1

1

2

Department of Forest Products, Faculty of Agriculture, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ko, Tokyo 113, Japan Forestry and Forest Products Research Institute, Inashiki-gun, Ibaraki-ken 305, Japan

1

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

2

Ozonization of lignin forms derivatives of muconic acid that have the unique chemical structure of conjugated double bonds with two carboxyl groups. These derivatives have great potential for chemical modification. The ozonized lignin of white birch was soluble in epoxy resin at 120°C, and the free carboxyl groups were found to react with epoxide. This paper discusses developmental work on the preparation of pre-reacted ozonized lignin/epoxy resins; the dynamic mechanical properties of cured resins; and preliminary results of the application of these resins as wood adhesives. Ozone has recently become industrially available at low cost. From the point of view of the development of complete wood utilization, the pretreatment of wood with ozone enhances the yield of glucose by enzymatic saccharification. Ozonized lignin is thereby obtained as a by-product. The ozonization of lignin produces derivatives of muconic acid that have two conjugated double bonds terminated by two carboxyl groups. It has been shown that the cleavage of aromatic nuclei of phenylpropane units in lignin occurs between C-3 and C-4 as shown in Figure 1 (1,2). When the substituents at C-3 and C-4 are hydroxy groups, free carboxyl groups are obtained after ozonization. On the other hand, the methyl ester results when these substituents are methoxy groups. Since many chemical modifications can be considered on these structures, new utilization developments are expected. The lignin isolated from white birch after steaming was ozonized. The ozonized lignin was soluble in epoxy resins at 120°C. It was also found that free carboxyl groups (introduced by ozonization) react with epoxide only by heating. Previous developmental work on the blending of lignin with epoxy resin has been reported by Ball and his co-workers (3). They synthesized 0097-6156/89/0397-0496$06.00/0 © 1989 American Chemical Society

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Resins

497

k r a f t l i g n i n / e p o x y resin blends i n m e l t state at 190°C a n d cured t h e m w i t h p h t h a l i c a n h y d r i d e at 160°C. Here the p r e p a r a t i o n o f pre-reacted, o z o n i z e d l i g n i n / e p o x y resins; the d y n a m i c m e c h a n i c a l properties of the p o l y a m i n e cured networks; a n d some a p p l i c a t i o n s of these resins as w o o d adhesives are discussed.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

Experimental Isolation and Ozonization of Lignin. T h e w o o d m e a l of w h i t e b i r c h (Betula papyrifera M a r s h . ) was steamed for 15 m i n at 180°C, a n d e x t r a c t e d w i t h water at 6 0 ° C , followed b y e x t r a c t i o n w i t h m e t h a n o l as s h o w n i n F i g ­ ure 2. T h e m e t h a n o l - s o l u b l e p a r t was d r i e d u n d e r v a c u u m after r e m o v a l of m e t h a n o l . T h e y i e l d of m e t h a n o l extract was 7 5 % based o n the a m o u n t of l i g n i n present i n the o r i g i n a l w o o d . T h e l i g n i n (50 g) was dissolved i n a m i x t u r e of dioxane (500 m l ) a n d m e t h a n o l (1,000 m l ) , a n d ozonized at 0 ° C w i t h a n oxygen flow rate of 0.5 m l / m i n a n d ozone c o n c e n t r a t i o n o f 3 % as s h o w n i n F i g u r e 3. A f t e r t r e a t m e n t w i t h ozone, the s o l u t i o n was treated w i t h a n excess a m o u n t of ether, a n d the i n s o l u b l e f r a c t i o n was filtered off, followed b y d r y i n g u n d e r v a c u u m . T h r e e samples ( N o . 1, N o . 2, a n d N o . 3) differed i n the extent of ozone t r e a t m e n t as s h o w n i n T a b l e I. T h e m o l a r equivalents were based o n the r a t i o of ozone t o each p h e n y l p r o p a n e (C9) u n i t . T h e y i e l d of each s a m p l e is also s h o w n i n T a b l e I. T a b l e I. O z o n i z a t i o n C o n d i t i o n a n d Y i e l d

Sample No. No. 1 No. 2 No. 3

M o l a r Equivalent (0 /C -unit)

Yield (%)

0.3 0.6 1.0

108.2 84.8 77.0

3

9

Gel Permeation Chromatography. E a c h ozonized l i g n i n was a n a l y z e d b y l i q u i d c h r o m a t o g r a p h ( A L C / G P C 201 w i t h R - 4 0 1 D i f f e r e n t i a l R e f r a c t o m e ter W a t e r - A s s o c i a t e s ) . C o l u m n s a n d solvent c o n d i t i o n s were as follows: μS t y r a g e l 1,000, 500, 5 0 0 , 1 0 0 Â i n series; a n d t e t r a h y d r o f u r a n at 2.0 m l / m i n . M o l e c u l a r weight was e s t i m a t e d b y use of polystyrene s t a n d a r d s . Measurement of Gel Time of Ozonized Lignin and Epoxy Resin Mixture. T h e e p o x y resin used was E p i k o t e 828 ( S h e l l C h e m i c a l C o . ) , d i g l y c i d y l ether of b i s p h e n o l - A ( D G E B A ) . O z o n i z e d l i g n i n s N o . 1 a n d N o . 3 were m i x e d w i t h D G E B A at three levels of 20, 40 a n d 80 P H R (parts per h u n d r e d p a r t s of resin), respectively, a n d m a i n t a i n e d at 120°C w i t h s t i r r i n g . T h e o z o n i z e d l i g n i n dissolved i n t o D G E B A b y h e a t i n g at 120°C for several m i n u t e s . T h e gel t i m e was d e t e r m i n e d as the t i m e w h e n the m i x t u r e solidified at 120°C. E v e r y solidified s a m p l e was completely i n s o l u b l e i n acetone.

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

498

F i g u r e 1. R e a c t i o n o f l i g n i n w i t h ozone.

WOOD 1) s t e a m i n g ( 1 8 0 ° C , 1 5 m i n ) 2) extract by water Insol.

Sol.

1) extract by M e O H Insol.

Sol. (lignin)

F i g u r e 2. L i g n i n i s o l a t i o n scheme.

39.

TOMITA ET AL,

Ozonized Ligpin-Epoxy Resins

499

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

Preparation of Ozonized Lignin/Epoxy Resins. E a c h o z o n i z e d l i g n i n (1.0 g) was m i x e d w i t h D G E B A a n d heated at 120°C w i t h s t i r r i n g as described i n the previous s e c t i o n . A f t e r h e a t i n g for 30 m i n , the m i x t u r e was cooled t o r o o m t e m p e r a t u r e . T h e solidified reactants were dissolved i n acetone (2 m l ) a n d the c u r i n g reagents, d i e t h y l e n e t r i a m i n e ( D E T A ) or h e x a m e t h y l e n e d i a m i n e ( H M D A ) , were added at 9 0 % of the s t o i c h i o m e t r i c a m o u n t t o e p o x y equivalent. C u r i n g was generally done b y h e a t i n g at 130° C for 2 hours a n d a l l o w i n g the p r o d u c t t o s t a n d at r o o m t e m p e r a t u r e for one day. A l l cured resins h a d no s o l u b i l i t y i n acetone after e x t r a c t i o n for one week. Dynamic Mechanical Measurements. F i l m s were p r e p a r e d b y c a s t i n g the acetone s o l u t i o n o f s a m p l e N o . 2 onto a Teflon sheet after a d d i n g c u r i n g agents. T h e s a m p l e was allowed to s t a n d at r o o m t e m p e r a t u r e for one day, a n d t h e n cured at 130°C for 2 h o u r s . T h e d y n a m i c m e c h a n i c a l spectroscopic d a t a were measured i n tension w i t h a R h e o v i b r o n D D V - I I ( T o y o B a l d w i n C o . L t d . ) at a frequency o f 110 H z w i t h a h e a t i n g rate o f a b o u t l ° C / m i n . Adhesive Strength Tests. T h e adherends were b i r c h (Betula maximowicziana R e g e l ) . T h e sizes o f tensile shear specimens a n d b o n d i n g areas were as follows: 2 5 m m ( w i d t h ) χ 6 5 m m (length) χ 5 m m (thickness) ana* 3.75 c m . A c e t o n e s o l u t i o n s o f the pre-reacted o z o n i z e d l i g n i n / e p o x y resins were spread j u s t after a d d i n g c u r i n g agents. T h e hot press c o n d i t i o n s were as follows: b o n d i n g pressure, 0.96 N / m m ; press t i m e , 1 h o u r ; t e m p e r a t u r e 130°C. T h e specimens were c o n d i t i o n e d at 2 0 ° C a n d 65 R H for one week before b e i n g tested. T w o types o f tests were a p p l i e d . O n e is a n o r m a l test a n d the other a c y c l i c b o i l test (soaking i n b o i l i n g w a t e r for 4 h o u r s ; d r y i n g at 60° C for 20 h r s ; s o a k i n g i n b o i l i n g w a t e r for 4 h r s ; c o o l i n g a n d t e s t i n g i n the wet state). T h e tensile shear adhesive strengths were measured w i t h a T e n s i l o n t e s t i n g m a c h i n e ( T o y o B a l d w i n C o . L t d . ) u n d e r a crosshead speed o f 10 m m / m i n . 2

2

Results and Discussion Isolation and Ozonization of Lignin. T h e yield of lignin obtained w i t h s t e a m i n g a n d successive water a n d m e t h a n o l e x t r a c t i o n was a b o u t 7 5 % o f the a m o u n t o f l i g n i n present i n w o o d . T h e lower m o l e c u l a r - w e i g h t l i g n i n p r o d u c e d by s t e a m i n g c a n be removed b y w a t e r e x t r a c t i o n . T h e i s o l a t e d l i g n i n c o n t a i n e d a s m a l l a m o u n t o f low m o l e c u l a r - w e i g h t hemicellulose a n d polysaccharides, t h o u g h i t was treated w i t h w a t e r . H o w e v e r , i t was used w i t h o u t further p u r i f i c a t i o n i n these e x p e r i m e n t s . T h e gel p e r m e a t i o n c h r o m a t o g r a m of the l i g n i n is s h o w n i n F i g u r e 4, a n d the n u m b e r average m o l e c ­ u l a r weight was e s t i m a t e d t o be about 2,000 u s i n g p o l y s t y r e n e s t a n d a r d calibration. T h e o z o n i z a t i o n was p e r f o r m e d at the three levels o f m o l a r equivalents t o p h e n y l p r o p a n e u n i t s h o w n i n T a b l e I. T h e highest y i e l d of over 1 0 0 % i n s a m p l e N o . 1 was caused b y the a d d i t i o n o f ozone t o l i g n i n . O n the other h a n d , the y i e l d decrease i n samples N o . 2 a n d N o . 3 was considered t o be the result o f r e m o v a l o f a considerable a m o u n t o f o z o n i z e d l i g n i n b y

LIGNIN: PROPERTIES AND MATERIALS

500

Lignin

(50g)

1)

dioxane(0.5L)-MeOH(lL)

2)

ozonization(0°C, flow 0.5 m L / m i n , O 3 concentration

3%)

3) dry 4) dissolve in dioxane

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

5) precipitate by ether Sol.

Insol. (Ozonized Lignin)

F i g u r e 3. Process scheme for the p r e p a r a t i o n o f o z o n i z e d l i g n i n .

F i g u r e 4. G e l p e r m e a t i o n c h r o m a t o g r a m s o f l i g n i n i s o l a t e d f r o m b i r c h a n d its o z o n i z e d l i g n i n s . S a m p l e 0: u n t r e a t e d l i g n i n ; 1: ozonized l i g n i n N o . 1; 2: o z o n i z e d l i g n i n N o . 2; 3: ozonized l i g n i n N o . 3.

39.

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501

Ozonized Lignin—Epoxy Resins

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ether e x t r a c t i o n . T h e m o l e c u l a r weight d i s t r i b u t i o n s o f o z o n i z e d l i g n i n are also c o m p a r e d w i t h the o r i g i n a l l i g n i n i n F i g u r e 4. N o o b v i o u s difference c o u l d be observed between o z o n i z e d l i g n i n s a n d u n t r e a t e d l i g n i n , p a r t l y because the lower m o l e c u l a r weight p o r t i o n o f o z o n i z e d l i g n i n was removed b y ether e x t r a c t i o n . T h e s t r u c t u r a l characteristics o f o z o n i z e d l i g n i n s , s u c h as d i s t r i b u t i o n o f f u n c t i o n a l groups, have not been d e t e r m i n e d o n these samples, b u t results w i t h s i m i l a r samples have been given p r e v i o u s l y ( 1 , 2 ) . Reaction of Ozonized Lignin and Epoxy Resin. T h e ozonized lignin dissolved i n D G E B A w i t h h e a t i n g . It began t o dissolve at a b o u t 100°C, a n d g e l a t i o n took place at 170°C. G e l a t i o n was also observed at 120°C u n d e r longer r e a c t i o n t i m e s . A f t e r g e l a t i o n , the reactants were c o m p l e t e l y i n s o l u b l e i n acetone a n d other solvents. T a b l e II shows the r e l a t i o n between gel t i m e a n d the a m o u n t of ozonized l i g n i n a d d e d t o D G E B A at 1 2 0 ° C . A s s h o w n i n T a b l e I I , either m i x i n g of h i g h l y o z o n i z e d l i g n i n ( N o . 3) or increasi n g the a m o u n t o f o z o n i z e d l i g n i n resulted i n a decrease i n gel t i m e . O n the other h a n d , i n the case o f the u n t r e a t e d l i g n i n , g e l a t i o n d i d not o c c u r even at 200°C u n d e r the same c o n d i t i o n s . T h e s e results suggest t h a t c a r b o x y l groups i n t r o d u c e d i n t o l i g n i n b y o z o n i z a t i o n react w i t h the epoxide t o f o r m t h r e e - d i m e n s i o n a l l y crosslinked n e t w o r k s . It has been r e p o r t e d b y B a l l a n d his co-workers t h a t k r a f t l i g n i n is soluble i n D G E B A at 190°C (3). H o w e v e r , no reference was m a d e to the occurrence o f g e l a t i o n . T h i s fact also s u p p o r t s the c o n c l u s i o n t h a t the g e l a t i o n takes place b y the r e a c t i o n o f c a r b o x y l groups t h a t have been i n t r o d u c e d i n t o l i g n i n b y o z o n o l y s i s . T a b l e I I . G e l T i m e o f O z o n i z e d L i g n i n a n d D G E B A at 120°C Gel time L i g n i n content ( P H R ) Ozonized lignin

20

40

60

80

No. 1 No. 3

> 300 m i n > 300 m i n

290 m i n 120 m i n

140 m i n 60 m i n

65 m i n 15 m i n

T h e l i m i t o f the a m o u n t o f ozonized l i g n i n t h a t c a n be a d d e d t o D G E B A was a b o u t 100 P H R i n s a m p l e N o . 1, a n d 80 P H R i n N o . 2 a n d N o . 3. F u r t h e r a d d i t i o n o f o z o n i z e d l i g n i n caused i n c o m p a t i b i l i t y between the t w o p o l y m e r s . A f t e r p r e - r e a c t i n g at 120°C for 30 m i n , the p r o d u c t s sol i d i f i e d b y c o o l i n g t o r o o m t e m p e r a t u r e , b u t t h e y dissolved i n acetone. T h e pre-reactant was c u r e d at r o o m t e m p e r a t u r e w i t h c o m m o n c u r i n g agents, s u c h as D E T A ( d i e t h y l e n e t r i a m i n e ) a n d H M D A ( h e x a m e t h y l e n e d i a m i n e ) . T h e a m o u n t o f c u r i n g agent was set t o 9 0 % o f the s t o i c h i o m e t r i c a m o u n t o f e p o x y equivalent, because the free c a r b o x y l groups o f the o z o n i z e d l i g n i n were considered t o consume at most 1 0 % epoxide o f D G E B A . N o acetone soluble e x t r a c t i v e s were detected i n c o m p l e t e l y c u r e d resins. T h e films c u r e d at 130°C for 1 h o u r h a d good r i g i d i t i e s a n d t o u g h ness as well as h i g h transparencies. O n the other h a n d , the resins o b t a i n e d

502

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Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

f r o m the o r i g i n a l l i g n i n a n d D G E B A under s i m i l a r c u r i n g c o n d i t i o n s were not t r a n s p a r e n t , a n d they were too b r i t t l e for film p r e p a r a t i o n . T h i s s u g gests t h a t the c r o s s l i n k i n g r e a c t i o n is o n l y between D G E B A a n d the a m i n e used as c r o s s l i n k i n g agent. T h e s e results also suggest t h a t the u n m o d i f i e d l i g n i n was o n l y m e c h a n i c a l l y blended w i t h the e p o x y n e t w o r k s , w i t h o u t c h e m i c a l b o n d i n g at the m o l e c u l a r l e v e l . Therefore, i t was c o n c l u d e d t h a t the c a r b o x y l groups i n t r o d u c e d b y o z o n i z a t i o n react c h e m i c a l l y w i t h e p o x ide r e s u l t i n g i n single phase network m a t e r i a l s . Dynamic Mechanical Properties of Ozonized Lignin/Epoxy Resins. The t e m p e r a t u r e dependence of the viscoeleastic properties are s h o w n i n F i g ures 5 a n d 6 at v a r i o u s a m o u n t s o f ozonized l i g n i n ( N o . 2) content for H M D A a n d D E T A c u r i n g reagents, respectively. T h e d i s p e r s i o n a b s o r p t i o n peaks observed at 120°C i n H M D A a n d at 150°C i n D E T A were a t t r i b u t e d t o the glass t r a n s i t i o n . R u b b e r y plateaus were recognized i n the higher t e m p e r a t u r e r e g i o n . G e n e r a l l y the a b s o r p t i o n peak due t o the glass t r a n s i t i o n shifted t o a higher t e m p e r a t u r e a n d broadened as the content o f o z o n i z e d l i g n i n increased. O n l y one dispersion peak is observed i n every s a m p l e , i n d i c a t i n g t h a t the ozonized l i g n i n / e p o x y resin s y s t e m has complete c o m p a t i b i l i t y after c u r i n g w i t h amines. However, glass t r a n s i t i o n p e a k s t e n d t o s p r e a d b r o a d l y as the ozonized l i g n i n content increases ( F i g s . 5 a n d 6). T h e s e results c o u l d be due t o a b r o a d d i s t r i b u t i o n o f c r o s s l i n k i n g d e n s i t y d e r i v e d f r o m the a d d i t i o n of ozonized l i g n i n . A s p r e a d i n g of peaks t o a lower t e m p e r a t u r e region is t h o u g h t t o be caused b y the steric h i n d r a n c e of l i g n i n . T h e m a i n c h a i n of the e p o x y resin adjacent t o the epoxide l i n k e d t o a n ozonized l i g n i n fragment m a y become h a r d t o move. T h e r e f o r e , a c o n s i d erable a m o u n t of epoxide r e m a i n e d unreacted r e s u l t i n g i n lower c r o s s l i n k i n g density. O n the other h a n d , the ozonized l i g n i n behaves as a m o r e h i g h l y crosslinked m a t e r i a l , a n d t h i s causes the a b s o r p t i o n peak t o s p r e a d t o a higher t e m p e r a t u r e . T h e s e observations suggest t h a t the new resin t e r p e n e t r a t i n g p o l y m e r n e t w o r k ; a n A B crosslinked t o the d e f i n i t i o n o f S p e r l i n g (4). It s h o u l d also be t r a n s i t i o n t e m p e r a t u r e can be m o d i f i e d at a n y levels c h a n g i n g c r o s s l i n k i n g agent as s h o w n i n F i g u r e 7.

s y s t e m forms a n i n copolymer according n o t e d t h a t the glass of lignin addition by

Bonding Tests. T h e results of w o o d b o n d i n g tests are s h o w n i n T a b l e s III a n d I V . T h e b o n d s t r e n g t h r e m a i n e d a l m o s t at the same level as o b t a i n e d w i t h e p o x y resin w i t h l i g n i n a d d i t i o n s u p t o 40 of P H R , t h o u g h i t decreased g r a d u a l l y w i t h i n c r e a s i n g b l e n d i n g r a t i o s of ozonized l i g n i n . T h e c o m p a r a t i v e l y low values s h o w n i n the n o r m a l test o f s a m p l e N o . 3 were not considered significant because the cyclic b o i l test showed the same s t r e n g t h level as s a m p l e N o . 2. T h e difference i n the degree o f o z o n i z a t i o n was n o t f o u n d t o affect the b o n d s t r e n g t h d r a m a t i c a l l y . F u r t h e r w o r k , s u c h as i n vestigations o n b o n d i n g c o n d i t i o n s , w i l l be necessary i n order t o develop p r a c t i c a l uses for t h i s adhesive s y s t e m .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

39.

TOMITAETAL.

503

Ozonized Lignin-Epoxy Resins

TEMPERATURE

I 'C )

Figure 5. Temperature dependence of viscoelastic property of ozonized lignin/epoxy resins cured with hexamethylenediamine. Ozonized lignin con­ tent in D G E B A : (1) 0 P H R ; (2) 20 P H R ; (3) 40 P H R ; (4) 80 P H R .

'

0

ι

40

80

120

160

TEMPERATURE

200

***T

240

( *C )

Figure 6. Temperature dependence of viscoelastic property of ozonized lignin/epoxy resins cured with diethylenetriamine. Ozonized lignin content in D G E B A : (1) 0 P H R ; (2) 20 ( P H R ) ; (3) 40 P H R ; (4) 80 P H R .

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

504

e

TEMPERATURE ( C ) F i g u r e 7. T e m p e r a t u r e dependence of viscoelastic p r o p e r t y o f o z o n i z e d l i g n i n / e p o x y resins cured w i t h h e x a m e t h y l e n e d i a m i n e (1) a n d d i e t h y l e n e t r i a m i n e (2) at ozonized l i g n i n content o f 80 P H R . T a b l e I I I . Tensile Shear A d h e s i v e S t r e n g t h of O z o n i z e d L i g n i n / E p o x y R e s i n s . ( N o r m a l Test) Shear S t r e n g t h ( w o o d failure) (N/mm ) 2

Sample E p i k o t e 828 No. 1 No. 2 No. 3

0 PHR 7.79

20 P H R

80 P H R

40 P H R

(65%) 8.32 (93%) 8.25 (100%) 6.66 (68%)

7.63 7.73 6.49

(45%) (63%) (33%)

5.62 6.05 5.89

(8%) (56%) (22%)

T a b l e I V . T e n s i l e Shear A d h e s i v e S t r e n g t h of O z o n i z e d L i g n i n / E p o x y R e s i n s . ( C y c l i c B o i l Test) Shear S t r e n g t h ( w o o d failure) (N/mm ) 2

Sample E p i k o t e 828 No. 1 No. 2 No. 3

0 PHR 5.72

20 P H R

40 P H R

80 P H R

(3%) 5.11 4.39 5.08

(22%) (12%) (28%)

3.89 3.91 4.51

(8%) (19%) (8%)

3.06 3.65 3.56

(4%) (2%) (2%)

39.

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505

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch039

Conclusions Ozonized lignins are soluble in epoxy resins when heated at 120°C, where the carboxyl groups react with epoxide. Therefore, pre-reacted ozonized lignin/epoxy resins were developed. The dynamic mechanical measurements showed complete compatibility between ozonized lignin and epoxy resins after curing with amines with the formation of interpenetrating polymer networks (IPN's). It was also found that the glass transition temperatures of cured resins could be modified over wide ranges by selecting different curing agents. Preliminary wood bonding tests on this new adhesive system indicate good potential. Further investigations on bonding conditions to enhance adhesion of wood are warranted. Acknowledgments This work was performed under the special research plan on "Development of Effective Utilization on Biomass Resources," 1986, by Ministry of Agriculture, Japan. Literature Cited 1. Kaneko, H.; Hosoya, S.; Nakano, J . Mokuzai Gakkaishi 1980, 26, 752. 2. Kaneko, H.; Hosoya, S.; Nakano, J . Mokuzai Gakkaishi 1981, 27, 678. 3. Ball, F. T.; Doughty, W. K.; Moorer, H. H. Canadian Patent 654 728, 1962. 4. Sperling, L. H. J. Polym. Sci., Macromol. Rev. 1977, 12, 141. RECEIVED February 27, 1989

Chapter 40

Lignin Epoxide Synthesis and Characterization World L i - S h i h Nieh

1-3

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch040

1

and Wolfgang G .

Glasser

1,2

Department of Wood Science and Forest Products, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, V A 24061 2

An epoxide resin was synthesized on the basis of lignin by reaction of epichlorohydrin (ECH) with hydroxypropyl lignin. A mixture of a quarternary ammonium salt (QAS) and potassium hydroxide (KOH) was used as catalyst. Additional KOH was added stepwise at a rate which compensated for KOH consumption during dechlorohydrogenation. The epoxidation reaction was first studied using hydroxypropyl guaiacol (HPG) as a lignin-like model compound. At room temperature, and when ECH was in excess, the reaction was completed in five days. The reaction was found to be highly dependent on the stepwise addition of KOH, and it was independent of ECH concentration. The maximum conversion of hydroxy to epoxy functionality was found to be 100 and 50% for model compound and lignin derivative, respectively. The lignin epoxide resin was crosslinked with diethylenetriamine (DETA), amine terminated poly (butadiene-co-arylonitrile) (ATBN) and phthalic anhydride (PA). Sol fraction and swelling behavior, and dynamic mechanical characteristics of the cured lignin epoxides were studied in relation to cure conditions. The major functional groups in lignin are methoxy, phenolic hydroxy, aliphatic hydroxy, and carboxy groups. During reaction with alkylene oxide, most of the functional groups of lignin, besides methoxy groups, become Current address: Mississippi State Forest Products Utilization Laboratory, Mississippi State University, Mississippi State, MS 39762

3

0097-6156/89A)397-0506$06.00/0 © 1989 American Chemical Society

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507

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch040

s u b s t i t u t e d b y h y d r o x y a l k y l groups (1). R e a c t i o n s o f a l i p h a t i c h y d r o x y groups w i t h c o m p o u n d s h a v i n g α - e p o x y g r o u p s , s u c h as e p i c h l o r o h y d r i n ( E C H ) , have been i n v e s t i g a t e d . W i t h acids as c a t a l y s t , the r e a c t i o n p r o d ­ uct consists o f a m i x t u r e of the 1,2- a n d the 1 , 3 - c h l o r o h y d r i n d e r i v a t i v e o f the parent c o m p o u n d . W h e n base is used as c a t a l y s t , the 1 , 2 - c h l o r o h y d r i n is the o n l y p r o d u c t a n d u p o n d e c h l o r o h y d r o g e n a t i o n , the α - e p o x y d e r i v a ­ tive o f the parent c o m p o u n d is f o r m e d . Bases s u c h as l i t h i u m h y d r o x i d e , s o d i u m h y d r o x i d e , s o d i u m a l k o x i d e , a n d L e w i s bases such as t r i b u t y l a m i n e a n d t r i i s o p r o p y l o l a m i n e have a l l been used i n t h i s r e a c t i o n . T h i s s y n t h e t i c route t o e p o x y - f u n c t i o n a l i z e d derivatives o f O H - f u n c t i o n a l p o l y m e r s has been successfully a p p l i e d t o cellulose, a m o n g others ( 2 , 3 ) . E p o x y resins f r o m l i g n i n a n d l i g n i n derivatives have been e x p l o r e d as well (4-10). I n some cases, k r a f t l i g n i n e p o x i d i z e d w i t h E C H i n the presence o f s o d i u m h y d r o x i d e as c a t a l y s t u n d e r w e n t irreversible h a r d e n i n g (4,5) at 100°C since epoxides are capable o f u n d e r g o i n g h o m o p o l y m e r i z a tion. Alternatively, phenolated kraft lignin, mixtures of phenol w i t h kraft l i g n i n , a n d m i x t u r e s o f p h e n o l w i t h p h e n o l a t e d k r a f t l i g n i n were a l l e p o x ­ idized w i t h E C H i n 25-40% N a O H which formed a solid epoxy polymer t h a t softened at 72-95°C (4-7). B o t h the degree o f e p o x i d a t i o n a n d the extent o f side reactions increased w i t h i n c r e a s i n g a m o u n t o f N a O H . W h e n tested as adhesive, the l i g n i n / p h e n o l - b a s e d e p o x y resin gave " g o o d " a d h e ­ s i o n t o w o o d . H o w e v e r , w h e n tested as c o a t i n g m a t e r i a l t o steel, the best results came f r o m l i g n i n / p h e n o l - b a s e d e p o x y resins m o d i f i e d w i t h u r e a f o r m a l d e h y d e a n d m e l a m i n e - f o r m a l d e h y d e varnishes. I n a s t u d y b y T a i et al. ( 8 , 9 ) , l i g n i n - b a s e d epoxy resins were synthesized f r o m k r a f t l i g n i n , b i s g u a i a c y l a t e d k r a f t l i g n i n a n d p h e n o l a t e d k r a f t l i g n i n . T h e e p o x i d a t i o n was c o n d u c t e d at 97 t o 117°C w i t h the a d d i t i o n o f 7-20 moles o f E C H p e r m o l e o f l i g n i n repeat u n i t (i.e., C 9 - u n i t ) u s i n g N a O H as c a t a l y s t . T h e e p o x y content o f the r e s u l t i n g l i g n i n derivatives was f o u n d t o be insensitive t o E C H c o n c e n t r a t i o n , b u t dependent o n the a m o u n t o f N a O H a d d e d . T h e e p o x y content was f o u n d t o increase to 0.16 e q / 1 0 0 g w i t h N a O H content i n c r e a s i n g t o 4 0 % . A t higher N a O H contents, the e p o x y content declined due to h o m o p o l y m e r i z a t i o n . M a x i m u m degree o f f u n c t i o n a l i z a t i o n w i t h epoxide groups was never achieved. T h e s o l u b i l i t y o f the l i g n i n epoxides i n o r g a n i c solvents was r e p o r t e d t o be i n the order o f p h e n o l a t e d l i g n i n e p o x ­ ide > l i g n i n epoxide > b i s g u a i a c y l a t e d l i g n i n epoxide. T h e l i g n i n epoxides were tested as adhesives o n a l u m i n u m a n d beech w o o d u s i n g a n h y d r i d e a n d d i a m i n e as c u r i n g agents. T h e l i g n i n - b a s e d e p o x y resins showed a n adhe­ sive s t r e n g t h equivalent t o resol resin w h e n w o o d was used as the adherent. D ' A l e l i o synthesized a series o f l i g n i n epoxides f r o m l i g n i n s t h a t h a d t h e i r f u n c t i o n a l groups p a r t i a l l y b l o c k e d b y esterification w i t h c a r b o x y l i c acids (10). T h e e p o x i d i z i n g agent was E C H u s i n g N a O H as c a t a l y s t a n d d i m e t h y l sulfoxide ( D M S O ) as solvent at 90-100°C for 14-24 h o u r s . T h e degree o f e p o x i d a t i o n was c o n t r o l l e d b y the a m o u n t o f N a O H a d d e d . It is obvious t h a t several o p t i o n s exist for the synthesis o f l i g n i n - b a s e d epoxide resins. T h e use o f E C H under a l k a l i n e c o n d i t i o n s seems t o b e favored. T h e degree o f e p o x i d a t i o n is c o n t r o l l e d b y the a m o u n t o f c a t a l y s t

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508

a d d e d since t h e d e c h l o r o h y d r o g e n a t i o n step consumes t h e c a t a l y s t . T h e degree o f e p o x i d a t i o n is independent o f t h e a m o u n t o f E C H as l o n g as t h i s is present i n excess. C r o s s l i n k i n g t h r o u g h h o m o p o l y m e r i z a t i o n is a p o t e n t i a l p r o b l e m w h i c h l i m i t s t h e degree o f e p o x i d a t i o n achievable.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch040

Experimental Synthesis and Characterization of Lignin-like Model Epoxide. A series o f e p o x i d a t i o n reactions were p e r f o r m e d w i t h h y d r o x y p r o p y l g u a i a c o l ( H P G ) as m o d e l c o m p o u n d a n d E C H . M o l a r r a t i o s o f E C H r H P G v a r i e d f r o m 1 t o 10. P e l l e t i z e d K O H a n d a q u a r t e r n a r y a m m o n i u m salt ( Q A S ) served as c a t a l y s t a n d reagent. T o l u e n e w a s the solvent. C a t a l y s t c o n c e n t r a t i o n a n d m e t h o d o f a d d i t i o n were v a r i e d . E x p e r i m e n t a l details are given elsewhere (11). T h e epoxidation reaction was monitored b y high performance liquid c h r o m a t o g r a p h ( H P C L ) o n a reverse phase c o l u m n . T h e r e a c t i o n p r o d u c t was i d e n t i f i e d b y I R , p r o t o n N M R a n d carbon-13 N M R spectroscopy. I n the I R s p e c t r u m , a b s o r p t i o n b a n d s at 904 c m " a n d 842 c m " were a t t r i b u t e d t o t h e e p o x y groups (12); peaks at 2.60, 2.78, a n d 3.15 p p m o n the H - N M R s p e c t r u m were assigned t o t h e three protons o f the epoxide g r o u p (13); a n d i n t h e C - N M R s p e c t r u m , t h e three g l y c i d y l c a r b o n s were identified at 4 4 . 5 , 50.6, a n d 70.6 p p m (14). 1

1

X

1 3

Synthesis and Characterization of Lignin-Based Epoxide. Lignin-based epoxides were prepared b y r e a c t i n g H P L f r o m a m i x e d h a r d w o o d o r g a n o solv l i g n i n w i t h E C H f o l l o w i n g t h e procedure developed w i t h t h e m o d e l c o m p o u n d . D e t a i l s o f the r e a c t i o n have been disclosed elsewhere (15). T h e r e a c t i o n was m o n i t o r e d b y t i t r a t i n g the epoxide groups w i t h H B r a c c o r d i n g t o D u r b e t a k i (16). S a m p l e s were t a k e n f r o m t h e r e a c t i o n m i x t u r e at threed a y i n t e r v a l s , a n d they were t i t r a t e d for t h e i r e p o x y content. T h e f r a c t i o n o f t h e t o t a l h y d r o x y groups t h a t were converted t o epoxide groups w a s defined as degree of conversion. P r o t o n s o n t h e epoxy r i n g were i d e n t i f i e d b y H - N M R , a n d g l y c i d y l carbons were detected b y C - N M R spectroscopy. 1

1 3

Epoxy Resin Characterization. E p o x y films were p r e p a r e d b y c r o s s l i n k i n g 2 g o f l i g n i n - b a s e d epoxide h a v i n g a n epoxy content o f 0.11 e q / 1 0 0 g w i t h stoichiometric amounts of diethylenetriamine ( D E T A ) a n d aminet e r m i n a t e d p o l y ( b u t a d i e n e - c o - a c r y l o n i t r i l e ) ( A T B N ) as c r o s s l i n k i n g agents. T h e films were solvent cast (methylene chloride) a n d cured at 105°C for 24 hours f o l l o w i n g solvent e v a p o r a t i o n . T o determine sol f r a c t i o n a n d degree o f s w e l l i n g , films were oven d r i e d a n d swollen t o e q u i l i b r i u m i n d i m e t h y l f o r m a m i d e ( D M F ) . W e i g h t loss w a s t a k e n as sol fraction, a n d weight increase (due t o swelling) d e t e r m i n e d t h e degree of swelling. Dynamic mechanical a n a l y s i s was p e r f o r m e d o n a P o l y m e r L a b o r a t o r i e s D y n a m i c M e c h a n i c a l T h e r m a l A n a l y z e r ( D M T A ) . Solvent-cast l i g n i n epoxide films were scanned at a h e a t i n g rate o f 4 ° C m i n " . T h e frequency w a s 1 H z a n d t h e s t r a i n level was 4 % . U n i a x i a l s t r e s s - s t r a i n t e s t i n g w a s p e r f o r m e d o n a s t a n d a r d I n s t r o n t e s t i n g m a c h i n e e m p l o y i n g a cross-head speed o f 1 m m m i n " . S a m 1

1

40.

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Lignin Epoxide

509

pies were cut w i t h a die i n a dog bone shape, f r o m solvent cast film. T e n s i l e characteristics were c a l c u l a t e d o n the basis o f i n i t i a l d i m e n s i o n s .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch040

Results and Discussion Epoxidation of HPG. T h e r e a c t i o n scheme for the e p o x i d a t i o n o f H P G is s h o w n i n F i g u r e 1. T h e generation of o x y a n i o n I I i n toluene is assisted b y (solid) K O H a n d Q A S . II reacts r a p i d l y w i t h E C H t o p r o d u c e the 1,2c h l o r o h y d r i n o f H P G , I I I . D e c h l o r o h y d r o g e n a t i o n o f I I I proceeds i m m e d i a t e l y under the p r e v a i l i n g r e a c t i o n c o n d i t i o n s w i t h f o r m a t i o n o f epoxide I V a n d K C 1 . T h e process c a n conveniently be m o n i t o r e d b y H P L C . C o m p l e t i o n is i n d i c a t e d w h e n I is depleted. T h e degree o f conversion o f I t o I V was followed i n r e l a t i o n t o t i m e a n d c a t a l y s t a d d i t i o n i n a series o f e x p e r i m e n t s w h i c h e m p l o y e d toluene as solvent at r o o m t e m p e r a t u r e . T h e results are s u m m a r i z e d i n F i g u r e 2. T h e r e a c t i o n o f I w i t h excess E C H i n the presence o f K O H (1 eq m o l o f I) a n d a n equivalent a m o u n t (by weight) o f Q A S p r o d u c e d I V i n 6 5 % y i e l d i n about 5 days ( e x p e r i m e n t A ) . F a i l u r e t o a d d a d d i t i o n a l K O H is o b v i o u s l y responsible for the low degree o f conversion. B y r a i s i n g the K O H content t o 1.25 eq m o l " o f I a n d i n c l u d i n g Q A S i n a n a m o u n t equivalent ( b y weight) t o the ( i n i t i a l ) K O H content, the r e a c t i o n becomes 7 5 % c o m plete i n a b o u t 24 hours ( e x p e r i m e n t C ) . Subsequent a n d repeated a d d i t i o n s o f K O H (1.25 eq m o l of I, each) help the degree o f conversion t o reach 1 0 0 % i n another two d a y s . Presence o f Q A S i n the secondary K O H charges w a s f o u n d t o be unnecessary. H o w e v e r , t o t a l absence o f Q A S f r o m the r e a c t i o n m e d i u m ( e x p e r i m e n t B ) prevented the r e a c t i o n f r o m ever r e a c h i n g c o m p l e t i o n b y r e d u c i n g the degree o f conversion at each step. S i n g l e a d d i t i o n s o f large excesses o f K O H t o the reagent m i x t u r e ( e x p e r i m e n t B ) f a i l e d likewise t o produce h i g h degrees o f conversion. Stepwise a d d i t i o n o f K O H ( w i t h or w i t h o u t Q A S ) is clearly seen as necessary for c o m p e n s a t i n g for K O H c o n s u m p t i o n d u r i n g d e c h l o r o h y d r o g e n a t i o n . T h e K O H / Q A S m i x t u r e was f o u n d to be m o r e efficient t h a n K O H w i t h o u t Q A S i n genera t i n g the n u c l e o p h i l i c h y d r o x y a n i o n o f H P G . Q A S d i d not interfere w i t h the d e c h l o r o h y d r o g e n a t i o n step as l o n g as K O H was c o m p e n s a t e d for. I n e x p e r i m e n t C ( F i g . 2), the e p o x i d a t i o n r e a c t i o n reached 1 0 0 % conversion o n the fifth day, t w o days after the a d d i t i o n o f the first a d d i t i o n a l a m o u n t o f K O H . A l l r o o m t e m p e r a t u r e reactions h a d higher degrees o f conversion as c o m p a r e d t o the elevated t e m p e r a t u r e e p o x i d a t i o n reactions o f H P G . T h e d e c h l o r o h y d r o g e n a t i o n step (i.e., I l l t o I V i n F i g u r e 1) was s t i l l f o u n d t o be r a p i d , even at the m i l d e r r e a c t i o n t e m p e r a t u r e . - 1

1

- 1

Epoxidation of HPL. R e s u l t s f r o m the e p o x i d a t i o n o f H P L w i t h E C H i n the presence o f K O H a n d Q A S u s i n g m e t h y l e n e chloride (at r o o m t e m p e r a t u r e ) as solvent are s h o w n i n F i g u r e 3. T h e degree o f conversion of ( a l i p h a t i c ) h y d r o x y groups of H P L to epoxide f u n c t i o n a l i t y was m o n i t o r e d b y t i t r a t i o n . P a r a m e t e r s i m p o r t a n t to the success o f t h i s r e a c t i o n i n c l u d e d (a) stepwise a d d i t i o n o f K O H , a p p r o x i m a t e l y p a r a l l e l i n g the f o r m a t i o n of K C 1 b y d e c h l o r o h y d r o g e n a t i o n ; (b) presence o f Q A S i n the r e a c t i o n m i x t u r e ; (c) a n at least five-fold s t o i c h i o m e t r i c excess o f E C H over a v a i l a b l e

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Ο

H,C0'

Ο

KOH/QAS

A

CH -CHCH CI 2

OCH I HC-O' I CH 3

0CH - toluene 2

HC-OH I CH 3

2

toluene

2

OCH

HC0CH CHCH | 2

CH

J

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+KOH OCH I „

2

3

2

OH CI.

-KCI

2

HCOCH CH-CH 2

C H ,

2

0

F i g u r e 1. R e a c t i o n scheme of the e p o x i d a t i o n o f H P G .

F i g u r e 2. Degree o f conversion o f I t o I V i n r e l a t i o n t o t i m e a n d K O H a d d i t i o n . E x p e r i m e n t Β e m p l o y e d K O H alone; a n d e x p e r i m e n t s A a n d C employed K O H and Q A S .

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o x y a n i o n f u n c t i o n a l groups; (d) m i l d r e a c t i o n t e m p e r a t u r e ; a n d (e) absence o f m o i s t u r e f r o m the r e a c t i o n m i x t u r e . F i g u r e 3 i n d i c a t e s t h a t e p o x i d a t i o n of H P L m a y reach a degree of conversion of c a . 5 0 % after 12 d a y s . A s s u m ­ i n g t h a t H P L has a h y d r o x y content of a b o u t 6-8% a n d a n u m b e r average m o l e c u l a r weight of 1500 g m o l " * , a 5 0 % conversion o f h y d r o x y groups t o epoxide f u n c t i o n a l i t y c a n be expected t o p r o d u c e a l i g n i n - b a s e d e p o x y resin w i t h a n epoxide f u n c t i o n a l i t y of about 0.2 e q / 1 0 0 g ; w i t h a n e p o x y e q u i v a ­ lent weight of 400 t o 600 g; a n d w i t h a n average o f three f u n c t i o n a l groups per ( n u m b e r average) m o l e c u l a r fragment. H i g h h y d r o x y f u n c t i o n a l i t y a n d degree o f conversion, a n d absence of low m o l e c u l a r weight c o m p o n e n t s (be­ low t r i - or t e t r a m e r i c l i g n i n structures) are c r i t i c a l p a r a m e t e r s for l i g n i n selection for successful e p o x i d a t i o n . Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch040

1

Network Characterization of Lignin-Based Epoxides. T h e formation of a p o l y m e r network requires t h a t m u l t i f u n c t i o n a l l i g n i n epoxide molecules are reacted w i t h d i - or m u l t i f u n c t i o n a l c r o s s l i n k i n g agents, such as a m i n e s or a n h y d r i d e s . M o n o f u n c t i o n a l components become c h a i n ends t h a t c o n ­ t r i b u t e t o brittleness a n d reduce s t r e n g t h ; a n d fragments w i t h o u t a n y reac­ tive f u n c t i o n a l site become fillers, plasticizers or a n t i - p l a s t i c i z e r s . W h e n a h y d r o x y b u t y l l i g n i n ( H B L ) - b a s e d epoxide w i t h a n e p o x y content of 0.11 e q / 1 0 0 g was crosslinked w i t h (a) a m i n e t e r m i n a t e d p o l y ( b u t a d i e n e c o - a c r y l o n i t r i l e ) ( A T B N ) a n d (b) p h t h a l i c a n h y d r i d e ( P A ) , insoluble m a ­ terials were f o r m e d w h i c h h a d average sol fractions ( i n D M F ) o f 10 a n d 1 4 % , respectively. T h i s indicates t h a t c r o s s l i n k i n g was q u i t e complete, a n d that little lignin remained unincorporated. Weight gained by swelling i n ­ creased l i n e a r l y w i t h A T B N content, a n d t h i s was not s u r p r i s i n g since the A T B N used was of r e l a t i v e l y h i g h m o l e c u l a r weight (6400 g m o l " " ) w h i c h i n t r o d u c e d larger free spaces i n t o the film. 1

P r e l i m i n a r y results w i t h e p o x y networks cured w i t h c o m b i n a t i o n s o f D E T A a n d A T B N are g i v e n i n T a b l e I a n d F i g u r e 4. T a b l e I. C o m p o s i t i o n of L i g n i n E p o x i d e s Composition of Crosslinking Agent by Functionality

Sample No. A Β C D Ε

1

by Weight

ATBN (%)

DETA (%)

ATBN (%)

DETA (%)

0 10 25 50 100

100 90 75 50 0

0.00 14.3 38.3 46.1 67.9

5.4 4.2 3.7 1.5 0.0

Lignin-Epoxide Content ( w t . %) 94.6 81.5 58.0 52.4 32.1

D i s t r i b u t i o n of a m i n e f u n c t i o n a l groups equivalent t o epoxide f u n c t i o n ­ ality. U s i n g a low m o l e c u l a r weight c r o s s l i n k i n g agent s u c h as D E T A , a m a -

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TIME (days) F i g u r e 3. Degree o f conversion o f h y d r o x y groups o f H P L t o epoxide f u n c tionality i n relation to reaction time a n d K O H addition.

TEMPERATURE (°C) F i g u r e 4. D M T A curves o f l i g n i n epoxides cured w i t h c o m b i n a t i o n s o f D E T A a n d A T B N . (Samples identified i n T a b l e I.)

40. NIEH & GLASSER

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terial with nearly 95% lignin derivative content is produced. Crosslinking epoxide functionality with amine-terminated rubber segments (i.e., ATBN) reduces the lignin derivative content to about 30% (Table I). Whereas the ATBN-free cured epoxy network forms a glassy, high-modulus material at room temperature (Fig. 4), rising rubber component introduces a secondary thermal transition at about —45°C which serves to reduce the glassy modulus at ambient temperatures. This amounts to a rubber-toughening effect with two-phase morphology. Whether a third transition at around 0°C, between the rubber transition at —45°C and that signifying lignin at 90°C, can be attributed to a mixed interphase between lignin and A T B N remains the subject of future studies. The mechanical properties of the cured lignin epoxides will be discussed elsewhere. Conclusions A lignin epoxide resin was synthesized from hydroxyalkyl lignin and E C H using K O H and a QAS mixture as catalyst at room temperature. Since rapid dechlorohydrogenation under reaction conditions consumes K O H , stepwise addition of K O H during epoxidation is necessary. A five-fold excess of ECH over stoichiometric requirements was required in order to prevent intramolecular crosslinking of multifunctional hydroxyalkyl lignin. The degree of conversion of hydroxy to epoxide groups was controlled by the stepwise addition of KOH rather than by E C H concentration. Swelling experiments showed that a lignin epoxide resin of 0.11 epoxy equivalents per 100g formed a network polymer when cured with DETA, PA, or A T B N . Phase separation was observed in the rubber-toughened lignin epoxide network. Cured epoxides had lignin derivative contents of up to 95%. This is part 19 of a publication series dealing with engineering plastics from lignin. Earlier parts have been published in J. Appl Polym. Sci.,J. Wood Chem. Technol., and Holzforschung.

Literature C i t e d 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Wu, L . C.-F.; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29, 1111. Wing, R. E.; Doane, W . M.; Rist, C. E. Carbohyd. Res. 1970, 12, 347. Lee, D.-S.; Perlin, A . S. Carbohyd. Res. 1982, 106, 1. Mihailo, M.; Budevska, Ch. Compt. Rend. Bulgare Sci. 1962, 15, 155; through Chem. Abstr. 1963, 58, 4452d. Mikhailov, M . ; Budevska, Khr. Izv. Inst. po Obshcha Neorg. Khim., Org. Khim. Bulgar. Akad. Nauk. 1962, 9, 187; through Chem. Abstr. 1963, 59, 4159f. Mikhailov, M.; Gerdzhikova, S. Compt. Rand. Acad. Bulgare Sci. 1965, 18, 829; through Chem. Abstr. 1966, 64, 14416h. Mikhailov, M.; Gerdzhikova, S. Compt. Rand. Acad. Bulgare Sci. 1965, 18, 43; through Chem. Abstr. 1965, 63, 794c. Tai, S.; Nagata, M.; Nakano, J.; Migita, N . J. Jap. Wood Res. Soc. 1967, 13, 102. Tai, S.; Nakano, J.; Migita, N . J. Jap. Wood Res. Soc. 1967, 13, 257. D'Alelio, G . F. U.S. Patent 3,984,353, Oct, 5, 1976.

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11. Nieh, W. L.-S. M.S. Thesis, Virginia Tech, 1986. 12. Dobinson, B.; Hofmann, W.; Stark, B. P. The Determination of Epoxide Groups; Pergamon: New York, 1969. 13. Anteunis, M . ; Borremans, F.; Van Den Bossche, R.; Verhegge, G. Org. Magn. Resonance 1972, 4, 481. 14. Everatt, B.; Haines, A . H.; Stark, B. P. Org. Mang. Resonance 1976, 8, 275. 15. Glasser, W. G.; Nieh, W. L.-S.; Kelley, S. S.; de Oliveira, W. U.S. Patent Appl.: Ser. No. 183,213 (April 19, 1988). 16. Durbetaki, A . J. Anal. Chem. 1956, 28, 2000.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch040

RECEIVED March 17, 1989

Chapter 41

Derivatives of Lignin and Ligninlike Models with Acrylate Functionality Wolfgang G . Glasser and Hong-Xue Wang

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

Department of Wood Science and Forest Products and Polymeric Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, V A 24061

Hydroxybutyl lignin, as well as lignin and lignin derivative-like model compounds, were chemically modified by reaction with isocyanatoethyl methacrylate (IEM). The acrylated derivatives were studied with regard to copolymerization characteristics with styrene (S) and methyl methacrylate (MMA). The reactivity ratios obtained suggest that lignin (model compound) acrylates form preferentially alternating copolymers with MMA and S, and that the degree of deviation from azeotropic composition varies with chemistry. Azeotropic points were between 17 and 30 mole % lignin (model compound) acrylate. Reaction of acrylated lignin derivatives with vinyl monomers produces network polymers with gel structure that shows the expected rise in sol fraction as vinyl equivalent weight increases. Lignin, especially that derived from organosolv pulping and steam explosion, is beginning to prove itself as a useful polymeric component of structural materials (1-3). Its usefulness increases dramatically following chemical modification by reaction with propylene or other alkylene oxides, since this treatment enhances lignin's solubility in organic solvents and, at the same time, reduces its glass transition temperature (4). Lignin's molecular weight characteristics and functionality features have been the basis for viewing it as a "macromeric" segment for block copolymers and segmented thermosets (5-7). Although most previous research on the use of lignin in structural polymers has dealt with its contribution to polyphenolics and polyurethanes (8), alternatives for crosslinking it with other polymer systems exist as well. These have been summarized recently (9). Among these alternatives are lignin derivatives with acrylate functionality. Acrylation of lignin has been reported by Naveau (10), who employed 0097-6156/89/0397-0515$06.00/0 © 1989 American Chemical Society

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516

b o t h m e t h a c r y l i c a n h y d r i d e a n d m e t h a c r y l y l chloride w i t h " k r a f t " l i g n i n to achieve s u b s t i t u t i o n levels of between 17 a n d 7 2 % of the m o n o m e r i c u n i t s i n l i g n i n . A n o t h e r avenue to a e r y l a t i o n presents itself t h r o u g h the a v a i l a b i l i t y of d i f u n c t i o n a l monomers h a v i n g b o t h a c r y l a t e (or v i n y l ) a n d isocyanate f u n c t i o n a l i t y . I s o c y a n a t o e t h y l m e t h a c r y l a t e ( I E M ) is one s u c h m o n o m e r t h a t m a y be used for converting t e r m i n a l h y d r o x y l f u n c t i o n a l i t y into acrylate f u n c t i o n a l i t y ( 1 1 , 1 2 ) . T h i s s t u d y examines the synthesis of a c r y l a t e d l i g n i n derivatives u s i n g I E M , a n d the c o p o l y m e r i z a t i o n characteristics of these derivatives w i t h m e t h y l m e t h a c r y l a t e ( M M A ) a n d styrene (S).

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

Experimental Materials. Difunctional Reagents: Isocyanatoethyl methacrylate ( I E M ) was s u p p l i e d b y D o w C h e m i c a l C o . as a n e x p e r i m e n t a l reagent. M e t a T M I is available f r o m C y a n a m i d , Inc. Model compounds: G u a i a c o l , M M A , a n d styrene were o b t a i n e d f r o m c o m m e r c i a l sources. H y d r o x y p r o p y l guaiacol was p r e p a r e d a c c o r d i n g to earlier studies (13). Hydroxybutyl (organosolv) lignin (HBL): T h e organosolv l i g n i n d e r i v a tive w i t h butylène oxide was prepared i n accordance w i t h earlier w o r k (14). T h e derivative h a d a h y d r o x y l content of 6.0% a n d a n u m b e r average m o l e c u l a r weight (M ) of 1500 g m o l " . n

1

Methods. Reaction with IEM: R e a c t i o n s w i t h I E M were p e r f o r m e d i n methylene chloride u s i n g d i b u t y l t i n d i l a u r a t e (ca. 1 w t . % ) as c a t a l y s t . T h e reaction m i x t u r e w i t h m o d e l c o m p o u n d or H B L was reacted at 4 0 ° C u n der d r y n i t r o g e n . T h e reaction p r o d u c t was o b t a i n e d b y p r e c i p i t a t i o n w i t h n-hexane. D e t a i l e d e x p e r i m e n t a l a n d a n a l y t i c a l results are given elsewhere Copolymerization reactions: C o p o l y m e r i z a t i o n e x p e r i m e n t s w i t h s t y rene a n d M M A employed m o l a r fractions of 20, 40, 60, a n d 8 0 % c o m o n o mers, w h i c h were reacted i n e t h a n o l : 1,2-dichlorethane 6 0 : 4 0 (by volume) m i x t u r e s a n d b e n z o y l peroxide as c a t a l y s t . P o l y m e r i z a t i o n s were c a r r i e d out at 7 0 ° C . T h e reactions were quenched b y the a d d i t i o n of m e t h a n o l as non-solvent, a n d the copolymer was isolated b y c e n t r i f u g a t i o n . C o p o l y mer analysis e m p l o y e d U V spectroscopy for copolymers w i t h M M A , a n d m e t h o x y l content d e t e r m i n a t i o n according to a procedure b y Hodges et ai (16) i n the case of styrene copolymers. R e a c t i v i t y ratios were determ i n e d i n accordance w i t h the m e t h o d b y K e l e n - T i i d o s (17) a n d t h a t b y Y e z r i e l e v - B r o k h i n a - R o s k i n ( Y B R ) (18). E x p e r i m e n t a l details a n d results are presented elsewhere (15). A c r y l a t e d l i g n i n derivatives were c o p o l y m e r i z e d w i t h M M A a n d S i n d r y methylene chloride w i t h b e n z o y l peroxide a n d Ν,Ν-dimethyl a n y l i n e as c a t a l y s t . R e a c t i o n m i x t u r e s were p o u r e d o n t o Teflon m o l d s , the solvent was evaporated at r o o m t e m p e r a t u r e i n the fume h o o d , a n d films were cured i n a n oven at 105°C for 6 hrs. E x p e r i m e n t a l details a n d results are given elsewhere (15).

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517

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

Results and Discussion T h e synthesis of a c r y l a t e d l i g n i n derivatives has been achieved earlier u s i n g a c r y l i c a c i d derivatives (10). A more convenient m e t h o d for the synthesis of o r g a n i c solvent soluble, powderous or t a r r y (i.e., after c h a i n e x t e n s i o n w i t h propylene oxide) (19) a c r y l a t e d l i g n i n derivatives employs the react i o n of h y d r o x y a l k y l l i g n i n derivatives w i t h i s o c y a n a t o e t h y l m e t h a c r y l a t e ( I E M ) . I E M represents one a m o n g several c o m m e r c i a l l y available d i f u n c t i o n a l m o n o m e r s c o m b i n i n g isocyanate a n d a c r y l a t e (or v i n y l ) f u n c t i o n a l i t y ( F i g . 1). T h e r e a c t i o n of the isocyanate g r o u p of the a c r y l a t i n g agent w i t h the O H groups of the l i g n i n derivative can be c o m p l e t e d under m i l d rea c t i o n c o n d i t i o n s c a t a l y t i c a l l y . T h e use of h y d r o x y a l k y l l i g n i n as l i g n i n c o m p o n e n t , a n d a n i s o c y a n a t e - f u n c t i o n a l a c r y l a t i n g agent, b o t h c o n t r i b u t e to s u p e r i o r s o l u b i l i t y ( i n organic solvents) a n d p r e p o l y m e r characteristics of the m o d i f i e d l i g n i n derivative. F o r the purpose of d e t e r m i n i n g (a) r e a c t i o n c o n d i t i o n s ; (b) a n a l y t i c a l m e t h o d o l o g y ; a n d (c) r e a c t i v i t y r a t i o s w i t h c o m m o n comonomer species, m o d e l c o m p o u n d studies were performed u s i n g a c r y l a t e d g u a i a c o l a n d h y d r o x y p r o p y l g u a i a c o l as f u n c t i o n a l i z e d d e r i v a tives representative of a c r y l a t e d l i g n i n ( F i g u r e 2). R e a c t i o n p r o d u c t s of the m o d e l c o m p o u n d s were isolated i n c r y s t a l l i n e f o r m , a n d t h e i r F T I R , H - N M R , a n d C N M R s p e c t r a revealed t h a t the expected m o d e l a c r y l a t e had been f o r m e d (15). T h e usefulness of a n a c r y l a t e d l i g n i n derivative as s t r u c t u r a l segment in p o l y a c r y l i c networks depends to a large extent o n its c o p o l y m e r i z a t i o n characteristics. These are conveniently defined i n terms of reactivity ratios v i s - a - v i s c o m m o n v i n y l i c comonomers ( 2 0 , 2 1 ) . R e a c t i v i t y r a t i o s are defined i n F i g u r e 3. These r a t i o s , w h i c h are available i n the l i t e r a t u r e for a wide range of m o n o m e r species ( 2 0 , 2 1 ) , are i m p o r t a n t for p r e d i c t i n g the dependence of copolymer c o m p o s i t i o n o n m o n o m e r feed c o m p o s i t i o n . W a l l (22,23) has pioneered t h i s r e l a t i o n s h i p , a n d his suggested g r a p h i c a l presentation is a d o p t e d i n F i g u r e s 4 a n d 5. Several b o u n d a r y c o m b i n a t i o n s of r e a c t i v i t y ratios are i l l u s t r a t e d i n F i g u r e 4. F o r the case i n w h i c h neither active center shows a n y preference for any m o n o m e r species, i.e., r\ = r = 1, c o p o l y m e r c o m p o s i t i o n is determ i n e d at a l l times solely by the c o n c e n t r a t i o n of the respective m o n o m e r species i n the feed c o m p o s i t i o n . T h i s defines a n azeotropic composition over the entire range of m o n o m e r feed compositions. F o r the other extreme case, the one i n w h i c h each active center adds e x c l u s i v e l y the m o n o m e r other t h a n t h a t w h i c h represents the t e r m i n u s o n the active c h a i n , i.e., r = r = 0, a n a l t e r n a t i n g c o p o l y m e r is f o r m e d i n w h i c h h a l f of the p o l y m e r c h a i n consists of h o m o p o l y m e r of M i a n d the second h a l f of h o m o p o l y m e r of M . I n the case i n w h i c h either active center shows preference for one, the more reactive, m o n o m e r , i.e., r\ > 1 a n d r < 1, the c o p o l y m e r is always richer i n t h a t m o n o m e r a n d the feed c o m p o s i t i o n is conversely richer i n the less reactive m o n o m e r . I n the final case ( F i g . 4), i n w h i c h each active center prefers cross-propagation to h o m o - p r o p a g a t i o n , i.e., r\ < 1 a n d r < 1, a t e n d e n c y exists t o w a r d a l t e r n a t i o n . C o p o l y m e r i z a t i o n s w i t h preferred a l t e r n a t i o n 1 3

2

x

2

2

2

2

518

LIGNIN: PROPERTIES AND MATERIALS

H C 3

X

C = CH

N - Ç - l ^ J 0CN-C-4^^C=CH

2

H C

OCN-CH.-CH^OOc' ISOCYANATO-ETHYL

METHACRYLATE (IEM)

3

meta - T M I

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

F i g u r e 1. T w o c o m m e r c i a l l y available d i f u n c t i o n a l c o m p o u n d s i s o c y a n a t e a n d acrylate ( v i n y l ) f u n c t i o n a l i t y .

CH (T 3

>r

cH o3

OCNHCH CH OOCC=CH 2

2

CH

0

χ

featuring

8

OCry;HOCNHCH CH OOCÇ=CH

2

2

CH

3

GA

2

CH

3

HPGA

F i g u r e 2. A c r y l a t e d l i g n i n - l i k e m o d e l c o m p o u n d s , G A a n d H P G A .

*

M,* + M,

~v-M,—Μ|

Β

k

,2

'n~M|* + M

2

k

M

2

+ M,

2, -

k M

2

+

M

*

M,

— M2

*

M

—M,*

2

2 2

2

12

where M,

GA or HPGA

M

MMA or STYRENE

2

2

HC

3

F i g u r e 3. D e f i n i t i o n o f r e a c t i v i t y r a t i o .

3

2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

41.

GLASSER &WANG

Derivatives ofLignin and Ligninlike Models

0

0.5

519

1.0

MONOMER FEED COMP. ( M, ) F i g u r e 4. R e l a t i o n s h i p between c o p o l y m e r c o m p o s i t i o n (mole f r a c t i o n M i i n c o p o l y m e r ) a n d m o n o m e r feed c o m p o s i t i o n (mole f r a c t i o n M i i n feed) for v a r i o u s r e a c t i v i t y r a t i o c o m b i n a t i o n s . A , r\ = r = 1; B , r\ > 1, r < 1; ο , Γ ι ~ r ~ 0; D , r i < 1, r < 1. ( A d o p t e d f r o m ref. 21.) 2

2

2

2

MONOMER FEED COMPOSITION (M, ) F i g u r e 5. R e l a t i o n s h i p between c o p o l y m e r c o m p o s i t i o n a n d m o n o m e r feed c o m p o s i t i o n ( m o l a r f r a c t i o n o f M i i n b o t h ) for the c o m b i n a t i o n s H P G A - c o M M A (— • — ) ; G A - c o - M M A (—A—); G A - c o - S ( — # — ) ; a n d H P G A co-S

( - 0 - ) ·

520

LIGNIN: PROPERTIES AND MATERIALS

have a n azeotropic c o m p o s i t i o n p o i n t at w h i c h c o p o l y m e r c o m p o s i t i o n corresponds to feed c o m p o s i t i o n ; a n d below a n d above w h i c h the c o p o l y m e r is richer a n d poorer, respectively, i n the m o n o m e r w h i c h is present i n the lower (molar) c o n c e n t r a t i o n . R e a c t i v i t y ratios between a c r y l a t e d l i g n i n m o d e l c o m p o u n d ( F i g . 2), defined as M i , w i t h either M M A or S, defined as M , were d e t e r m i n e d exp e r i m e n t a l l y i n accordance w i t h s t a n d a r d procedures (15). These i n v o l v e m i x i n g two different v i n y l monomers i n various m o l a r r a t i o s w i t h c a t a l y s t (i.e., b e n z o y l peroxide) a n d solvent, h e a t i n g the m i x t u r e to achieve p o l y m e r i z a t i o n , a n d recovering the p o l y m e r by the a d d i t i o n of non-solvent, a n d c e n t r i f u g a t i o n . T h e respective m o l a r m o n o m e r fractions of the c o p o l y m e r were d e t e r m i n e d b y U V - s p e c t r o s c o p y i n the cases where M M A served as M 2 , a n d b y m e t h o x y l content analysis i n those cases i n w h i c h S was the M species. T h e results were subjected to n u m e r i c a l t r e a t m e n t s a c c o r d i n g to the established r e l a t i o n s h i p s of K e l e n - T i i d o s (17) a n d Y e z r i e l e v - B r o k h i n a R o s k i n ( Y B R ) (18), a n d t h i s is described elsewhere (15). T h e r e a c t i v i t y ratios l i s t e d i n T a b l e I i n d i c a t e t h a t b o t h r\ a n d r are consistently < 1.0, a n d t h a t the p r o d u c t s of r a n d r are also a l w a y s < 1.0. T h i s suggests (20,21) t h a t preference is given to the f o r m a t i o n of a l t e r n a t i n g copolymers, a n d t h a t azeotropic p o i n t s exist at w h i c h c o p o l y m e r c o m p o s i t i o n equals monomer feed c o m p o s i t i o n . T h e r e l a t i o n s h i p between c o p o l y m e r c o m p o s i t i o n a n d m o n o m e r feed c o m p o s i t i o n is i l l u s t r a t e d i n F i g ure 5 for the various c o m b i n a t i o n s of M i a n d M . A l l c o m b i n a t i o n s reveal a d e v i a t i o n f r o m the azeotropic c o m p o s i t i o n at higher (i.e., > 40%) contents of l i g n i n - l i k e a c r y l a t e ( M i ) i n m o n o m e r feed, thereby i n d i c a t i n g preference for the f o r m a t i o n o f a l t e r n a t i n g copolymers. T h i s d e v i a t i o n is greatest for the c o m b i n a t i o n H P G A - c o - S , a n d i t is least for H P G A - c o - M M A . A z e o t r o p i c p o i n t s lie between 17 a n d 30 mole % of l i g n i n - l i k e m o d e l a c r y l a t e i n the m o n o m e r feed w i t h the balance representing either M M A or S. I m p o r t a n t s t r u c t u r a l parameters t h a t influence m a t e r i a l properties of p o l y a c r y l i c s based o n l i g n i n derivative segments w i t h t e r m i n a l a c r y l a t e f u n c t i o n a l i t y are d e t e r m i n e d b y degree of a c r y l a t i o n , a n d t h u s v i n y l e q u i v alent weight, a n d m o n o m e r r a t i o i n the c o p o l y m e r . F i g u r e 6 i l l u s t r a t e s the r e l a t i o n s h i p between m a x i m u m gel f r a c t i o n a n d v i n y l equivalent weight of a c r y l a t e d l i g n i n d e r i v a t i v e . T h i s r e l a t i o n s h i p reveals the expected increase i n sol f r a c t i o n as degree of s u b s t i t u t i o n w i t h a c r y l a t e groups o n l i g n i n declines (i.e., v i n y l equivalent weight increases). 2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

2

2

x

2

2

Conclusions Solvent soluble a n d l i q u i d (i.e., tars w i t h T ^ below a m b i e n t ) a c r y l a t e d l i g n i n derivatives have been f o r m u l a t e d b y reaction of h y d r o x y a l k y l l i g n i n d e r i v a tives w i t h i s o c y a n o t o e t h y l m e t h a c r y l a t e ( I E M ) . C o p o l y m e r i z a t i o n b e h a v i o r of a c r y l a t e d l i g n i n - l i k e m o d e l c o m p o u n d s w i t h M M A a n d styrene i n d i c a t e d a preference for the f o r m a t i o n o f a l t e r n a t i n g copolymers. D e p e n d i n g o n m o n o m e r c o m b i n a t i o n , azeotropic p o i n t s were f o u n d

GLASSER & WANG

41.

Derivatives of Lignin and Ligninlike Models

521

T a b l e I. E x p e r i m e n t a l R e a c t i v i t y R a t i o s between A c r y l a t e d L i g n i n M o d e l Compounds and M M A and S Copolymer

1

G A ( l ) - c o - M M A (2) GA(l)-co-S(2) HPGA(l)-co-MMA(2) HPGA(l)-co-S(2) 2

1

2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

3

**1

r

0.17 0.07 0.38 0.01

0.68 0.79 0.67 0.73

2

3

ΓχΓ2

0.12 0.06 0.25 0.01

A c r y l a t e d guaiacol ( G A ) and acrylated hydroxypropyl guaiacol (HPGA). W i d e error m a r g i n . D e t e r m i n e d a c c o r d i n g t o the K e l e n - T i i d o s (17) a n d the Y B R (18) re­ lationships. I00r

0

500

1000

1500

2000

VINYL EQUIVALENT WEIGHT (g/mole vinyl) F i g u r e 6. R e l a t i o n s h i p between gel f r a c t i o n a n d v i n y l equivalent weight o f several a c r y l a t e d l i g n i n derivatives. (40 w t . % l i g n i n a c r y l a t e a n d 60 w t . % MMA). between 17 a n d 30 mole % a c r y l a t e d l i g n i n m o d e l c o m p o u n d ; o n l y m o d e s t differences were noted r e g a r d i n g d e v i a t i o n s f r o m azeotropic c o m p o s i t i o n s . A c r y l a t e d l i g n i n derivatives were c o p o l y m e r i z e d w i t h v i n y l m o n o m e r s to y i e l d network m a t e r i a l s (gels) w i t h gel f r a c t i o n d e c l i n i n g as v i n y l e q u i v ­ alent weight increased. A c r y l a t e d l i g n i n derivatives are viewed as a new a n d p r o m i s i n g class of f u n c t i o n a l m a c r o m e r s f r o m l i g n i n useful for the f o r m u l a t i o n of block a n d segmented copolymers. Acknowledgment T h i s s t u d y was financially s u p p o r t e d b y a g r a n t f r o m t h e N a t i o n a l Science Foundation.

522

LIGNIN: PROPERTIES AND MATERIALS

This is part 20 of a publication series dealing with engineering plastics from lignin. Earlier parts have been published in J. Appl. Polym. Sci., J. Wood Chem. Technol, and Holzforschung, among others.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch041

Literature C i t e d 1. Glasser, W . G.; Barnett, C . Α.; Muller, P. C.; Sarkanen, Κ. V . J. Agric. Food Chem. 1983 31(5), 921-30. 2. Glasser, W . G . ; Barnett, C . Α.; Sano, Y . Appl. Polym. Symp. 1983, 37, 441-60. 3. Rials, T . G . ; Glasser, W . G . Holzforschung 1986, 40, 353-60. 4. Wu, L . C . - F . ; Glasser, W . G . J. Appl. Polym. Sci. 1984, 29(4), 1111-23. 5. Saraf, V . P.; Glasser, W . G . ; Wilkes, G . L . ; McGrath, J . E . J. Appl. Polym. Sci. 1985, 30, 2207-24. 6. Saraf, V . P.; Glasser, W . G . ; Wilkes, G . L . J. Appl. Polym. Sci. 1985, 30, 3809-23. 7. Oliveira, W . de; Glasser, W . G . J. Appl. Polym. Sci., in press. 8. Glasser, W . G . ; Sarkanen, S., Eds. Lignin: Properties and Materials; A C S Symp. Ser., in press. 9. Glasser, W . G . In Adhesives from Renewable Resources; Hemingway, R. Α.; Conner, A . H . , Eds.; A C S Symp. Ser. No. 385, 1989, C h . 4, p. 43. 10. Naveau, H . P. Cell. Chem. Technol. 1975, 9, 71. 11. Hoffman, D. K . U.S. Patent 4 320 221, 1982. 12. Frisch, K . C . U.S. Patent 4 374 969, 1983. 13. Glasser, W . G . ; Robert, D.; Hyatt, J. A . Unpublished manuscript. 14. Glasser, W . G . ; Wu, L . C.-F.; Selin, J . - F . In Wood and Agricultural Residues: Research on Use for Feed, Fuels, and Chemicals; Soltes, J., Ed.; Academic Press: New York, 1983; p. 149. 15. Wang, H . X . M.S. Thesis, Virginia Tech, Blacksburg, V A , 1987. 16. Hodges, K . L . ; Rester, W . E . ; Wiederrich, D. L.; Grover, T . A . Anal. Chem. 1979, 51, 2179. 17. Kelen, T . ; Tüdos, F. J. Macromol. Chem. 1975, A 9 , 1. 18. Yezrielev, A . I.; Brokhina, E . L . ; Roskin, Ye. S. Polymer Sci. USSR 1969, 11, 1894. 19. Kelley, S. S.; Glasser, W . G . ; Ward, T . C . J. Wood Chem. Technol. 1988, 8(3), 341. 20. Doak, K. W . "Ethylene Polymers," in Encyclopedia of Polymer Science and Engineering; Kroschwitz, J . I., Ed.; John Wiley & Sons: New York, 1986; Vol. 6, p. 383. 21. Tirrell, D. A . "Copolymerization," in Encyclopedia of Polymer Science and Engineering; Kroschwitz, J . I., Ed.; John Wiley & Sons: New York, 1986; Vol. 4, p. 192. 22. Wall, F. T . J. Am. Chem. Soc. 1941, 63, 1862. 23. Marvel, C . S.; Schertz, G . L. J. Am. Chem. Soc. 1943, 65, 2054. RECEIVED March 17, 1989

Appendix

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch042

Industrial lignin and lignin derivative products are made by these corporations.

E M P R E S A N A C I O N A L D E C E L U L O S A S SA (ENCE) E m p r e s a N a c i o n a l de Celulosas S A is the largest producer of p u l p i n the E u r o p e a n E c o n o m i c C o m m u n i t y . J o i n t l y w i t h L i t c h e m L i m i t e d , i t produces Eucalin Lignin, derived f r o m the p r o d u c t i o n of kraft p u l p f r o m E u c a l y p t u s trees. T h i s is a unique p r o d u c t w h i c h is c u r r e n t l y not available f r o m a n y other source. E a r l y research a n d development w o r k has i n d i c a t e d t h a t the s t r u c t u r e of Eucalin Lignin s h o u l d make i t i d e a l l y suited for use as a chemical i n t e r m e d i a t e . Research i n S o u t h A f r i c a has i n d i c a t e d t h a t Eucalin Lignin r a n k s between softwood a n d bagasse l i g n i n i n terms of the n u m b e r of reactive sites w i t h formaldehyde (under acidic c o n d i t i o n s ) , a n d t h a t i t allows a h i g h percentage of s u b s t i t u t i o n of phenol i n phenol-formaldehyde resins. Eucalin Lignin has the same repeating u n i t structure of a r y l propane as is t y p i c a l of other l i g n i n s . However, the r a t i o of g u a i a c y l to s y r i n g y l groups is close to one w h i c h gives, o n o x i d a t i o n , a h i g h percentage of syringaldehyde i n a d d i t i o n to v a n i l l i n . F o r further i n f o r m a t i o n contact E m p r e s a N a c i o n a l de C e l u l o s a s S A , J u a n B r a v o , 4 9 - D p d o , M a d r i d 6, S p a i n ; or L i t c h e m L i m i t e d , L a m b e r h e a d I n d u s t r i a l E s t a t e , W i g a n , Lanes W N 5 8 E G , G r e a t B r i t a i n .

0097-6156/89/0397-0524$06.00/0 © 1989 American Chemical Society

APPENDIX

525 GEORGIA-PACIFIC

Lignosite Lignosulfonate p r o d u c t s are derived f r o m t h e l i g n i n i n softw o o d trees b y the c a l c i u m bisulfite p u l p i n g process at G e o r g i a - P a c i f i c ' s m i l l in Bellingham, Washington.

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch042

G e o r g i a - P a c i f i c ' s l i g n i n sulfonate p r o d u c t s are k n o w n u n d e r the t r a d e n a m e Lignosite. D u r i n g the p r o d u c t i o n o f most Lignosite p r o d u c t s , t h e hexose sugars (glucose, mannose a n d galactose) are converted t o e t h a n o l b y continuous f e r m e n t a t i o n . D i s t i l l a t i o n o f t h e e t h a n o l increases t h e c a l c i u m l i g n i n sulfonate content t o a p p r o x i m a t e l y 8 0 % o f the l i q u o r solids. Lignosite Calcium Lignosulfonate is a n excellent s t a r t i n g m a t e r i a l for m a n y m o d i f i e d p r o d u c t s because of its h i g h p u r i t y a n d because c a l c i u m m a y easily be replaced b y a n y n u m b e r of other cations u s i n g t h e a p p r o p r i a t e soluble sulfate salts. G e o r g i a - P a c i f i c produces s o d i u m , a m m o n i u m , a n d p o t a s s i u m lignosulfonates. P r o d u c t s w i t h higher levels o f p u r i t y c a n b e p r o v i d e d b y c h e m i c a l m o d i f i c a t i o n s or b y u l t r a f i l t r a t i o n . T h e m o l e c u l a r weight, sugar content a n d ionic charge c a n a l l be adjusted t o meet specific needs. F o r further i n f o r m a t i o n contact T e c h n i c a l C e n t e r , 1754 T h o r n e R o a d , T a c o m a , W a s h i n g t o n 98421.

526

LIGNIN: PROPERTIES AND MATERIALS ITT RAYONIER C H E M I C A L PRODUCTS

R A Y L I G , R A Y M I X , R A Y K R O M E , O R Z A N , U L T R A M I X , and V A N I L L I N represent the f a m i l y of p r o d u c t s derived f r o m l i g n i n p r o d u c e d at I T T R a y o n i e r ' s softwood sulfite p u l p i n g o p e r a t i o n i n H o q u i a m , W a s h i n g t o n . A n n u a l l y more t h a n 100,000 m e t r i c tons of these p r o d u c t s are p r o duced for a v a r i e t y of i n d u s t r i a l end uses, i n c l u d i n g b i n d e r s , d i s p e r s a n t s , s u r f a c t a n t s , d r i l l i n g fluid a d d i t i v e s , concrete a d m i x t u r e s , dye d i l u e n t s a n d dispersants, feed additives, flavoring, fragrances, a n d p h a r m a c e u t i c a l s .

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch042

E n d use a p p l i c a t i o n s a n d p r o d u c t specifications are designed b y spec i a l l y a p p l y i n g c h e m i c a l m o d i f i c a t i o n s a n d p u r i f i c a t i o n procedures. T h e R A Y L I G p r o d u c t s are u n m o d i f i e d s o d i u m lignosulfonates. R A Y M I X a n d U L T R A M I X are c h e m i c a l l y desugared a n d m o d i f i e d s o d i u m lignosulfonates used i n r e t a r d i n g a n d n o n - r e t a r d i n g concrete a d mixtures. R A Y K R O M E chemicals are modified a n d m e t a l c o m p l e x e d for use p r i m a r i l y i n drilling operations. T h e O R Z A N p r o d u c t line includes s o d i u m a n d a m m o n i a l i g n i n c h e m icals s p e c i a l l y designed for a w i d e variety of i n d u s t r i a l a p p l i c a t i o n s . V A N I L L I N is w i d e l y used as a n ingredient i n food flavors, as a p h a r m a c e u t i c a l i n t e r m e d i a t e , a n d as a fragrance i n perfumes a n d other o d o r masking products. F o r further i n f o r m a t i o n , contact C h e m i c a l P r o d u c t s D e p a r t m e n t , 18000 Pacific H i g h w a y S o u t h , S u i t e 900, Seattle, W A 98188.

APPENDIX

527 REED LIGNIN/DAISHOWA

CHEMICALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch042

R e e d L i g n i n was formed i n 1982 when R e e d , Inc., a c q u i r e d the L i g n i n C h e m i c a l s D i v i s i o n of A m e r i c a n C a n a n d merged i t w i t h t h e i r L i g n o s o l C h e m i c a l s o p e r a t i o n . E a r l i e r t h i s year R e e d became p a r t of D a i s h o w a . D a i s h o w a is the largest, most diversified producer of l i g n i n p r o d u c t s i n the w o r l d , w i t h two p l a n t s l o c a t e d i n W i s c o n s i n a n d a t h i r d located i n Q u e bec. Research a n d Development effort is c a r r i e d out i n m a j o r laboratories located i n R o t h s c h i l d , W i s c o n s i n , a n d Q u e b e c C i t y , Q u e b e c . D a i s h o w a has developed more t h a n 50 d i s t i n c t l y different l i g n i n sulphonates u s i n g a b r o a d range of u n i t o p e r a t i o n s . A m o n g the processing techniques are: • • • • • • •

base exchange ozonation polymerization fractionation d e p o l y m e r i z a t i o n b y alkaline h y d r o l y s i s or h i g h pressure t r e a t m e n t s reduction, and other chemical t r e a t m e n t s .

T h e p r o d u c t s are used i n numerous i n d u s t r i a l a p p l i c a t i o n s b u t c a n generally be classified as either: • dispersants • c o m p l e x i n g agents • p r o t e i n reactives

• binders, a n d • copolymers, or • e x t r u s i o n aids.

D a i s h o w a ' s p r o d u c t s are grouped under the f o l l o w i n g trade names: • • • • • • •

Lignosol Marasperse Norlig Maracarb Peltex Ameribond Marabond

• • • • • •

Additive-A Kelig Goulac Glutrin Maracell Petrolig.

F o r further i n f o r m a t i o n contact D a i s h o w a C h e m i c a l s , P . O . B o x 2025, Q u e b e c , P . Q . G 1 K 7 N 1 , C a n a d a , or D a i s h o w a C h e m i c a l s , Inc., H i g h w a y 51, R o t h s c h i l d , W I 54474.

528

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ch042

WESTVACO POLYCHEMICALS T h e Westvaco P o l y c h e m i c a l s G r o u p produces a n d m a r k e t s a w i d e v a r i e t y of l i g n o c h e m i c a l s derived f r o m a sugar-free kraft l i g n i n source. B o t h n o n - s u l f o n a t e d a n d sulfonated derivatives are m a n u f a c t u r e d i n C h a r l e s t o n , South Carolina, U S A . Non-sulfonated lignins find u t i l i t y as emulsifiers a n d s t a b i l i z e r s i n water-based a s p h a l t emulsions, as coreactants i n phenolic b i n d e r a p p l i c a t i o n s , as negative p l a t e expanders i n lead a c i d storage batteries, as p r o t e i n coagulants i n fat r e n d e r i n g , a n d as flocculants i n waste water systems. • Emulsifiers a n d Stabilizers: B o t h anionic ( I N D U L I N C ) and c a t i o n i c ( I N D U L I N W - l ) derivatives of non-sulfonated k r a f t l i g n i n are c o m m o n l y used as stabilizers for m a k i n g a s p h a l t , w a x , or o i l - i n - w a t e r emulsions. • R e s i n C o r e a c t a n t s : F u n c t i o n a l groups i n p r o d u c t s such as R E A X 27 or R E A X 38 have led to t h e i r use as extenders for a n d coreactants w i t h phenolic resins. C o m m o n end uses include binders for t h e r m a l i n s u l a t i o n , c e i l i n g t i l e , h a r d b o a r d , a n d other thermal-pressure phenolic a p p l i c a t i o n s . T h e sulfonated lignin p r o d u c t s f u n c t i o n p r i m a r i l y as dispersants i n aqueous systems a n d help to f o r m stable dispersions of a n u m b e r of i n soluble m a t e r i a l s . F o r e x a m p l e , l i g n i n dispersants find use i n p i g m e n t s , c a r b o n b l a c k , g y p s u m , ceramics, coal s l u r r y a n d water t r e a t m e n t systems to m e n t i o n some of the more p r o m i n e n t a p p l i c a t i o n s . • D y e a n d P i g m e n t D i s p e r s a n t s : T h e R E A X sulfonated l i g n i n derivatives offer a w i d e range i n degree of s u l f o n a t i o n a n d molecular weight. These a t t r i b u t e s i m p a r t dispersion s t a b i l i t y at h i g h t e m p e r a t u r e s , i m p r o v e g r i n d i n g efficiency, a n d reduce s t a i n i n g i n b o t h l i q u i d dispersed a n d vat dye systems. • Agrichemical Dispersants: C h e m i c a l c r o s s l i n k i n g to increase m o l e c u l a r weight a n d a h i g h degree of s u l f o n a t i o n give P O L Y F O N H , O , T , a n d F the surface active properties necessary to disperse specific p e s t i cides. T h e R E A X Series of p r o d u c t s also finds a p p l i c a t i o n i n flowable a n d water dispersible granule f o r m u l a t i o n s where h i g h active ingredient levels are sought. In a d d i t i o n to these defined functions, l i g n i n p r o d u c t s are also k n o w n for their a b i l i t y to reduce the size of p a r t i c l e s , reduce s l u r r y viscosities, i n h i b i t c r y s t a l g r o w t h , sequester a n d c o m p l e x m e t a l s , a n d f u n c t i o n as i n teractive carriers. • Séquestrants: S p e c i a l l y modified sulfonated l i g n i n s can sequester alkaline e a r t h a n d heavy m e t a l s a n d s t i l l r e m a i n soluble, w h i l e w i t h n o n sulfonated l i g n i n s , the complexes become insoluble a n d can be r e m o v e d . T h e m e t a l sequestering properties of R E A X a n d P O L Y F O N p r o d u c t s find a p p l i c a t i o n i n d i s p e r s i n g i r o n i n c o o l i n g w a t e r , p r e v e n t i o n of scale deposits f r o m h a r d water i n boilers, a n d i n f o r m i n g m e t a l complexes for a g r i c u l t u r a l micronutrients. F o r further i n f o r m a t i o n contact Westvaco C o r p o r a t i o n , P o l y c h e m i c a l s D e p a r t m e n t , P . O . B o x 70848, C h a r l e s t o n H e i g h t s , S o u t h C a r o l i n a 294150848. R E C E I V E D May

29,

1989

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix001

Author Index Mahn, W., 100 Meister, John J., 58,294 Mikkonen, Hannu, 284 Milstein, O., 361 Môrck, Roland, 390 Narayan, Ramani, 476 Nicklas, B., 361 Nieh, World Li-Shih, 506 Osterholm, J. E., 219 Oh, Κ. K., 82 Ono, Hiro-Kuni, 334 Overend, R. P., 228 Patil, Damodar R., 294 Pla, F., 134 Pulkkinen, Erkki, 284 Pye, Ε. K., 312 Ratcliff, Matt, 476 Reimann, Anders, 390 Rials, Timothy G., 464 Richards, E. Glen, 58 Ritchie, R. George S., 372 Rudatin, Sri, 144 Sâgfors, Pehr-Erik, 29,124,177 Sarkanen, Simo, 155 Sellers, Terry, Jr., 324 Sen, Yasar L., 144 Shiraishi, Nabuo, 488 Siochi, E. J., 100 Stacy, Nathan, 476 Struszczyk, Henryk, 245 Sudo, Kenichi, 334 Takemura, A , 496 Tatsumoto, K., 82 Thring, R. W., 228 Tomita, B., 496 Trojanowski, J., 361 van der Klashorst, Gerrit H., 346 Wang, Hong-Xue, 515 Ward, Thomas C , 100,402 Watanabe, T., 11 Woerner, Douglas L., 144 Wu, C F., 312 Yaku, F., 11 Yano, Shoichiro, 382

Augustin, Cesar, 294 Balatinecz, J. J., 312 Barnett, Charlotte A , 436 Chornet, E., 228 Chum, Helena L i , 82,109,476 Ciemniecki, Scott L,, 452 Cook, Phillip M., 324 Cyr, Natsuko, 372 de Oliveira, Wilier, 414 Dutta, Sunil, 155 Elder, Thomas, 262 Forss, Kaj, 29,124,177 Froment, P., 134 Garver, Theodore M . , Jr., 155 Glasser, Wolfgang G., 402,414,436,452, 464,506,515 Goring, D. A . I., 2 Grohmann, K., 82 Haars, Α., 361 Haney, Μ. Α., 100 Hatakeyama, Hyoe, 205,274,382 Hatakeyama, Tatsuko, 205,274,382 Heitz, M . , 228 Himmel, M . E., 82 Hirose, Shigeo, 205,274,382 Hosoya, S., 496 Huttermann, A , 361 Hyatt, John A , 109,425 Johnson, D. K., 82,109 Kelley, Stephen S., 402 Kharazipour, A , 361 Kiran, Erdogan, 42 Kokkonen, Raimo, 29,124,177 Koshijima, T., 11 Kringstad, Knut P., 390 Kurozumi, K., 4% Kuusela, T\iula A , 190,219 Lai, James Z., 294 Levon, Kalle, 190 Levon, Kiran, 219 Li, Lixiong, 42 Lindberg, J . Johan, 190,219 Lora, J . H., 312 Mâkelâ, Airi, 284

529

LIGNIN: PROPERTIES AND MATERIALS

530

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix001

Affiliation Index

Alberta Research Council, 372 Auburn University, 262 Conseil National de Recherches du Canada, 228 Department of Chemical Engineering, 42 Division of Processing and Chemical Manufacturing Technology, CSIR, 346 Eastman Kodak Company, 33,109,324 Ecole Française de Papeterie, 134 Forest Products Utilization Laboratory, 324 Forestry and Forest Products Research Institute, 496 Government Industrial Research Institute, 11 Industrial Products Research Institute, 205,274,382 Institute of Chemical Fibres, 245 Kyoto University, 11,488 Ministry of Agriculture, Forestry, and Fisheries, 334 Neste Oy Research Centre, 219 Polymeric Materials and Interfaces Laboratory, 402,414,436,452,464,506,515

Purdue University, 476 Repap Technologies Inc., 312 Research Institute for Polymers and Textiles, 205,274,382 STFI, 390 Solar Energy Research Institute, 82,109,476 The Finnish Pulp and Paper Research Institute, 29,124,177 Universitât Gôttingen, 361 Université de Sherbrooke, 228 University of Detroit, 58,294 University of Helsinki, 190,219 University of Maine, 144 University of Minnesota, 155 University of Oulu, 284 University of Tokyo, 496 University of Toronto, 2,312 Veterans Administration Hospital, 58 Virginia Polytechnic Institute and State University, 100,402,414,436,452,464,506

Subject Index

Acetylated lignins, molecular weight distribution, 87,89-94/,95*,96 Acetylation, effect on lignin solubility, 284 Acrylation of lignin, methods, 516 Activation energies for thermal degradation, heat-resistant polyurethanes from solvolysis lignin, 385,387* Additives, effect on kraft lignin association, 152*,153 Adhesive quality of lignins board testing results, 379*,380 C N M R spectra, 375,376/ 1 3

Adhesive quality of lignins—Continued experimental procedures, 373 GPC, 375,378/ interactive sites, 373 lignin parameters for assessing quality, 375,379* lignin parameters obtained from C N M R and GPC, 375* number of methylolation sites, 373-375 parameters, 373-375 partial C - N M R spectra, 375,377/ predictions of internal bond quality, 373,395* Adhesives preparation from lignin, 488 wood-based, preparation, 490 1 3

13

LIGNIN: PROPERTIES AND MATERIALS

530

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

Affiliation Index

Alberta Research Council, 372 Auburn University, 262 Conseil National de Recherches du Canada, 228 Department of Chemical Engineering, 42 Division of Processing and Chemical Manufacturing Technology, CSIR, 346 Eastman Kodak Company, 33,109,324 Ecole Française de Papeterie, 134 Forest Products Utilization Laboratory, 324 Forestry and Forest Products Research Institute, 496 Government Industrial Research Institute, 11 Industrial Products Research Institute, 205,274,382 Institute of Chemical Fibres, 245 Kyoto University, 11,488 Ministry of Agriculture, Forestry, and Fisheries, 334 Neste Oy Research Centre, 219 Polymeric Materials and Interfaces Laboratory, 402,414,436,452,464,506,515

Purdue University, 476 Repap Technologies Inc., 312 Research Institute for Polymers and Textiles, 205,274,382 STFI, 390 Solar Energy Research Institute, 82,109,476 The Finnish Pulp and Paper Research Institute, 29,124,177 Universitât Gôttingen, 361 Université de Sherbrooke, 228 University of Detroit, 58,294 University of Helsinki, 190,219 University of Maine, 144 University of Minnesota, 155 University of Oulu, 284 University of Tokyo, 496 University of Toronto, 2,312 Veterans Administration Hospital, 58 Virginia Polytechnic Institute and State University, 100,402,414,436,452,464,506

Subject Index

Acetylated lignins, molecular weight distribution, 87,89-94/,95*,96 Acetylation, effect on lignin solubility, 284 Acrylation of lignin, methods, 516 Activation energies for thermal degradation, heat-resistant polyurethanes from solvolysis lignin, 385,387* Additives, effect on kraft lignin association, 152*,153 Adhesive quality of lignins board testing results, 379*,380 C N M R spectra, 375,376/ 1 3

Adhesive quality of lignins—Continued experimental procedures, 373 GPC, 375,378/ interactive sites, 373 lignin parameters for assessing quality, 375,379* lignin parameters obtained from C N M R and GPC, 375* number of methylolation sites, 373-375 parameters, 373-375 partial C - N M R spectra, 375,377/ predictions of internal bond quality, 373,395* Adhesives preparation from lignin, 488 wood-based, preparation, 490 1 3

13

531

INDEX A L C E L L lignins applications, 316,317*,318 C formulas, 315 dry modulus of rupture vs. lignin type and content, 318,320/ DSC analysis, 313,314/,315 elemental analysis, 315* internal bonding vs. lignin type and content, 318,319/ IR spectra, 316,317/ lignin p H vs. dry and wet modulus of rupture, 322^,323 modulus of rupture retention vs. lignin type and content, 318,321/323 molecular weight, 313 reactivity with formaldehyde, 316 softening points, 313,314/315 solubility, 313 use in waferboard manufacture, 318-323 U V spectra, 315-316 A L C E L L process description, 313 production procedure, 313 properties of lignin, 313-317 Alkali lignin, preparation, 141 Alkaline hydrolysis advantages, 228-229 phenol production, 229 vanillin production, 228 Alkalinity, effect on kraft lignin association, 147,148/149* Analytical ultracentrifugation average limiting viscosity number, 72,78* calculations, 68,70 concentration vs. sedimentation coefficient, 70,71/ determination of limiting sedimentation coefficient, 72,73/ differential molecular weight distribution, 72,77/ differential sedimentation distribution pattern, 72,75/ errors, 79-80 experimental limiting viscosity number, 78,79* integral distribution patterns, 70 integral molecular weight distribution, 72,76/ integral sedimentation distribution pattern, 72,74/ materials and solution preparation, 66-67 procedure, 70 reading of Rayleigh fringe patterns, 67-68,69/

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

9

Analytical ultracentrifugation—Continued sedimentation velocity experiments, 67 viscometry, 66 weight-average molecular weight, 72,78* Antioxidant effect, polymers formed from lignins, 198 Aromatic polyethers having phosphine oxide groups chemical structures, 217/ decomposition temperatures, 215* dissociation energies, 217/ synthesis, 215-216 T , 215*,217 Association calculation of degree, 146 kraft lignin in aqueous solution, 144-153 analytical techniques, 146 correction for concentration polarization effects, 150,151/ degree of association, 146 effect of additives, 152*,153 effect of alkalinity, 147,148/149* effect of ionic strength, 153 effect of lignin concentration, 150*,151/,152 effect of molecular weight, 147,148/149,151/ experimental materials, 146 history, 145 influencing factors, 144-145,147-153 mechanisms, 145 membrane sampling technique, 146-147 molecular weight distributions of permeates, 147-149,151/ permeate concentrations and rejection coefficients, 147,149* rejection coefficient distributions, 147,148/149 kraft lignins in nonaqueous polar solvents effect of solution on molecular weight, 169,174* intermolecular forces, 174 molecular weight distributions after desalting, 169,172/* Zimm plot, 169,173 modes, between kraft lignin components, 156-174 molecules, lignin in wood, 5-6 See also Intermolecular association, Molecular association, Self-association Associative-dissociative homology among kraft lignin samples association of predissociated sample, 163,164/ g

LIGNIN: PROPERTIES AND MATERIALS

532

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

Associative-dissociative homology among kraft lignin samples—Continued fractionation of lignin, 163,164/ molecular weight distribution, 163 Associative interactions between kraft lignin species, 157,158/159/ Average product of molecular weights, kraft lignin species influencing factors, 167 molecular weight calibration curves, 165,166/ relationship during associationdissociation, 165,167,168/ Azeotropic composition, definition, 517

Binder, features, 373 Biobonded particle boards production, 368 technological and mechanical properties, 368*,369 Biomass, renewable raw material, 245 Bleaching of hydroxypropyllignin with hydrogen peroxide advantages, 436 color loss, 437-438 color loss values, 438,440/ definition of color, 438,439-440/ effect of blocking agents, 448,450/ experimental materials and procedures, 437-438 FTIR spectra, 442,445,446-447/ hydrogen peroxide charge, 438,441/442 influencing factors, 445 mechanism of quinonoid reaction with H 0 , 442,444/ pH, 442,444/ reaction time, 442,443/ yield determination, 445,448,449/ Blending, advantages, 452 Block lap-shear test, organosolv lignin, 327,328* Bromine, compounding of sulfur lignin, 224,226/ Buffer, effect on delign ificat ion of spruce wood meal, 32,35/36,37/ 2

2

C Cationic flocculants from kraft lignin comparison of flocculation performance in stability tests, 288,290/

Cationic flocculants from kraft lignin— Continued conditions for cat ionization, 288,292* effect of molecular weight on flocculation performance, 288,291/ effect of purification on flocculation performance, 286,287/288 effect of reaction time on flocculation performance, 286,287/ flocculation tests, 285 gelling of lignin with formaldehyde, 285 preparation, 286 reaction mechanism, 288,292-293 reaction of lignin and gelled lignin with glycidyltrimethylammonium chloride, 285,286* stability of floe, 285 testing of flocculation performance, 288,289f Cellulose triacetate segments, preparation, 415 Chlorophosphazenes, modification of lignins, 247 Color definition, 438,439-440/ in pulp, role of hemilignins and glycolignin, 29 Color loss calculation, 437-438 effect of pH, 442,444/ Commercially available lignins, properties, 362 Computational chemistry advantages and disadvantages, 262-263 applications, 263 conformational studies of dimeric model compound, 267-268 coupling of phenols to form lignin polymer, 266-267 description, 262 examination of coniferyl alcohol structure, 267 history of research, 266 limitations, 264,266 methods, 262 molecular mechanics calculations, 264 molecular orbital calculations, 263-264,265/ problems with interpretation of results, 268-269 study of lignin chemistry, 267 utilization of Pearson's hard-soft acid-base theory, 268-269 Conducting polymers, applications, 221

533

INDEX Conductivity, mechanism for sulfur lignin, 223 Conformation, importance in size-exclusion chromatography, 4 Coniferyl alcohol, enzymatic dehydrogenation, 11-12 Controlled-release preparations, modified lignins as carriers, 255,257-261 Cross-linking, lignins, 200

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

D Degradation lignin role of laccase, 363-365 to form specialty polymers, 193-194,195* thermal, heat-resistant polyurethanes from solvolysis lignin, 383,384/,385 Degree of association, calculation, 146 Degree of conversion, definition, 508 Degree of swelling, definition, 508 Delignification spruce wood meal on heating with neutral phosphate buffer, 32-41 spruce wood meal on heating with water, 30-33 Delignifying solvent, ethylene glycolwater, 230 Demethylation, lignin, by laccase, ligninase, and poly-blue oxidase, Depolymerization of ethylene glycol lignin, procedure, 231,234,235/ Differential molecular weight distribution, determination, 66 Differential scanning calorimetry (DSC) elastomeric polyurethanes, 393-398 polyesters having syringyl-type biphenyl units, 213,215 polyethers and polyesters having methoxybenzalazine units, 208,210-212/· water-sodium lignosulfonate system, 275-283 Dimethylformamide, solvent for lignins, 43 Dioxane lignin, preparation, 141 Dissolution of wood applications of products, 489-490 in organic solvents, 489 methods, 489 preparation of wood-based adhesives, 480 solubilization vs. reactivity, 490

Dissolved lignin derivatives, separation, 177-178 Distributed properties, definition, 58 Distribution, description, 59 Distribution patterns, converted from sedimentation patterns, 64-66

Ε Elastomeric polyurethanes from kraft lignin-por/ethylene glycol-toluene diisocyanate system cross-link density vs. kraft lignin content, 392,395/ DSC analysis, 393-398 DSC procedure, 391 IR spectroscopy, 391 starting materials, 392,393* strain vs. polyethylene glycol content, 400/ stress and strain vs. kraft lignin content, 398,399/ swelling behavior, 392 swelling tests, 391 tensile properties, 392,398,399-400/ Τ vs. polyethylene glycol content, 394,3%/ Electrically conducting polymers formation from lignin, 198-199 formed by modification of lignin, 219-226 Elemental composition lignins, 194* water-insoluble lignin, 36* Elution lignin sulfonates with electrolyte solution, 127-130 nonsulfonated lignins with NaOH, 130 Engineering plastics, formation from lignin, 199-200 Enzyme-catalyzed adhesive system, preparation, 367 Epoxidation of hydroxypropylguaiacol degree of conversion, 509,510/ reaction scheme, 509,51Qf Epoxidation of hydroxypropyllignin, degree of conversion, 509,511,512/" Epoxy resin characterization, 508 gel time, 501* reaction with ozonized lignin, 501*,502 Epoxy resin adhesives from kraft lignin adhesion and gluability, 491 preparation, 490

534 Ethylene glycol lignin C N M R spectrum, 213,233/ catechol production at optimum conditions, 241,242/243 characterization, 230-233 depolymerization, 231,234,235/ determination of conversion to liquid and gaseous products, 236 effect of alkali concentration on product yields, 236,240/241 effect of solvent on conversion and ether solubles, 236,237/ effect of solvent on hydrolysis, 236,238-239/ effect of solvent on monomeric product yields, 236,238/ effect of temperature on product yields, 236,239/ effect of treatment severity on depolymerization, 241,242^,243 experimental materials, 230 G C analysis, 234 IR spectrum, 231,232/ set-up for production, 230 Ethylene grycol-water, efficiency as delignirying solvent, 230 Extracellular enzymes of lignin-transforming fungi laccase, 362 ligninase, 362 peroxidase and oxidase production,

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

1 3

pory-blue-oxidase, 362 reactions catalyzed, 362-363 Extraction, supercritical fluids, lignin, 42-56

Flake-board screening methods, description, 332 Flake-board test results, organosolv lignin, 328,329* Flocculants, cationic, See Cationic flocculants from kraft lignin Fractionation kraft lignin influence of functional groups on retention time, 183,186/ molar mass distribution, 183,185/ preparative RPC, 183,184/ spruce spent sulfite liquor and pine kraft black liquor, 183,185/

LIGNIN: PROPERTIES AND MATERIALS Fractionation—Continued lignin sulfonates on elution, 124-127 lignins, to improve properties, 403 lignosulfonates carbohydrate and lignosulfonate contents of hydrolyzed fractions, 178,180* molar mass distribution of high molar mass birch lignosulfonates, 180,181/ preparative G P C of birch lignosulfonates, 178,179/ preparative R P C of high molar mass lignosulfonates, 178,179f preparative R P C of low molar mass lignosulfonates, 180,181-182/184/ nonsulfonated lignins on elution, 130,131/132/ Freezing water around ionic groups, 274

Gas chromatography, ethylene glycol lignin analysis, 234 Gel permeation chromatography (GPC) analysis of lignin extracted from wood, 45-46 birch lignosulfonates, 178,179f calibration of columns, 127,128-131/ disadvantage of salt solution eluent, 127 lignin molecular weight distribution, 83 lignin sulfonates with electrolyte solution, 127,128-129/130 lignin sulfonates with water, 124,125-126/127 nonsulfonated lignins with NaOH, 130,131/132^ system and conditions, 188 use in molecular weight determination, 101 with differential viscosity detector (GPC-DV) chromatogram of red oak, 102,104/ comparison to V P O , 105,106* molecular weight distribution, 101-102,105* Gelation, lignins, 200 Glass transition temperature, lignin-based polyurethanes, 405,406/407 Glycolignin dissolution, 29-30 role in color of pulp, 29 sulfonation, 29-30 Glycolignins, description, 177 Grafting lignins, 200 synthetic polymers to lignin, 476-477

INDEX Graphite, compounding of sulfur lignin, 224,226/

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

H Heat-resistant polyurethanes from solvolysis lignin calculated activation energies for thermal degradation, 385,387* effect of lignin incorporation on retardation of thermal degradation, 383,384/ logarithmic heating rate vs. reciprocal absolute temperature, 385,386 mechanism of thermal degradation in air and nitrogen, 383,384/385 oxygen index for polyurethanes containing phosphorus, 387* preparation of materials, 383 T G A curves, 383,384/385 T G A curves for polyurethanes containing phosphorus, 387,388/ T G A measurements, 383,385,386/ thermal stability, 383-386 Hemilignins description, 177 dissolution, 29-30 role in color of pulp, 29 sulfonation, 29-30 Heterogeneity of lignin, dissolution and properties of low molar mass components, 29-41 High-performance polymers from lignin degradation products aromatic polyethers, 215*,216,217/ polyacylhydrazones, 211,213*,214,216/ polyesters having spirodioxane rings, 206-208 polyesters having syringyl-type biphenyl units, 213-214,215* polyethers and polyesters, 208-212 polyhydroxystyrene derivatives, 206-207,209/ High-performance size-exclusion chromatography (HPSEC) acetylated organosolv lignin in different eluants, 118-119,121/ a^-bis(0-4-aryl) ether bonded model polymer in different eluants, 120,121/122 calibration of column set, 112,114/ determination of molecular weight distribution, 110-122 effect of eluant on volume, 115*,116

535 High-performance size-exclusion chromatography (HPSEQ—Continued effect of lignin derivatization elution, 112,115 effect of solvent on elution, 116-120 elution of lignin model compounds, 112,114/ elution of polystyrene standards with different eluants, 116,117/ experimental procedure, 111-112,142 High-performance size-exclusion chromatography-differential viscometry (HPSEC-DV) calculation of intrinsic viscosity, 85 calibration curves, 86-87 chemicals, 83 fractionation of organosolv lignin, 96-97/ lignin samples, 84 molecular weight distribution of acetylated lignin, 87,89-94/ sources of error, 85-86 standards, 83-84 system, 84-85 Hildebrand equation, polymer blends, 453 Hydrogen bonding in molecular association, description, 145 Hydrogen peroxide, bleaching of hydroxypropyllignin, 436—450 Hydroxybutyllignin, preparation, 516 meta-Hydroxymethylation of lignin degree of dimer formation via methylene linkage, 353 experimental procedure, 353 factors influencing yield, 353 generalized reaction with formaldehyde, 357,358/ model compounds, 353,354/ rate of formaldehyde consumption, 357 reaction conditions, 353,355* utilization for production of cole-set wood adhesives, 357,359/ yields, 353 Hydroxypropylation of lignins, structure, 425-426,427/ Hydroxypropylation of phenols and alcohols iterative technique, 426,428/ pathway, 426,427/ Hydroxypropylcellulose, preparation, 465 Hydroxypropylcellulose blends with lignins analytical methods, 465-466 Wend properties, 466,467/468,469/ DSC thermograms, 466,467/ effect of lignin content on mechanical properties, 472f,474

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

536 Hydroxypropylcellulose blends with lignins— Continued effect of lignin hydroxy content on interaction with hydroxypropyl­ cellulose, 468,470/,471 factors influencing blend morphology, 471,474 hydroxyl content, 465,466* material preparation, 465 melting point depression, 468,471* percent of crystallinity vs. lignin content, 466,467/ polymer-polymer interaction parameter vs. lignin hydroxy content, 468,470/ S E M of freeze-fracture surfaces, 473/474 Τ 465,466* Hydroxypropylguaiacol, epoxidation, 509,510/ Hydroxypropyllignin(s) analysis, 431,432f,435 bleaching with hydrogen peroxide, 436-450 chain extension with propylene oxide, 415 degradation, 431,432/" electron-impact mass spectral fragmentation, 426,429* epoxidation, 509,511,512/ grafting of cellulose triacetate, 415,417 mass spectrum, 426,430/431 preparation, 415,454 products from degradation, 431,432* products from hydrogenorysis, 431,433-434* reaction with diethyl sulfate, 415 synthesis, 426,427-428/ Hydroxypropyllignin-based macromers analytical methods, 417 experimental materials, 415 experimental methods, 415,417 schematic representation, 415,416/ with cellulose triacetate,421*,422/423 with propylene oxide, 417-422 Hydroxypropyllignin-poryethylene copolymer blends, tensile strength vs. hydroxypropyllignin content, 455,456/ Hydroxypropyllignin-pory(methyl methacrylate) blends DSC thermograms, 455,457/ D M A thermograms, 455,458,459/ structure, 455 thermal characteristics, 455,457/458,459/ Hydroxypropyllignin-poly(vinyl alcohol) bien DSC thermograms, 458,460/ solubility parameter vs. hydroxypropyllignin content, 462

LIGNIN: PROPERTIES AND MATERIALS Hydroxypropyllignin-poly(vinyl alcohol) blends—Continued structure, 458 thermal properties, 458,460/461,462/*

Industrial lignins, properties, 353,355* Insolubility, lignin in wood, 3 Intermolecular association lignins, 200-201 See also Association Intermolecular interactions of lignin derivatives, types, 155-156 Internal bond quality, predictions, 375,379* Intrinsic viscosity calculation, 85 calibration for molecular weight, 4 Ionic strength, effect on kraft lignin association, 153 IR spectra, water-insoluble lignin, 36,39/ Isocyanatoethyl methacrylate, synthesis of acrylated lignin derivatives, 517,518/

J Johnston-Ogston effect, description, 63

Κ Kinetic changes, weight-average molecular weight of kraft lignin, 157-161 Kraft lignin(s) analytical RPC, 187 association, 144-153 association in nonaqueous polar solvents, 169-174 associative-dissociative homology, 163-166 average product of molecular weights during association and dissociation, 165-168 dissolution of wood, 489-490 epoxy resin adhesives, 490-491 evidence for nonrandom interactions, 167-171 fractionation, 180,183,184-186/ G P C system and conditions, 188 grafting with hydroperoxy chloride chemistry, 295,296*

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

INDEX Kraft lignin(s)—Continued molecular weight distributions, 156 preparation, 285,391 properties, 353,355* resol-type phenol resin adhesives, 492,493/494 self-association in aqueous solution, 144-153 utilization problems, 144 waste from paper industry, 295 Kraft lignin components, modes of association, 146-174 Kraft lignin-polyethylene grycol-toluene diisocyanate system, elastomeric polyurethanes, 391-400 Kraft lignin-poryether triol-diphenylmethane diisocyanate system, preparation of polyurethanes, 390

Laccase activity in organic solvents, 365-367 advantages as enzymatic binder, 367-368 application as radical donor in adhesives for particle boards, 366-367,368/,369 capacity to demethylate and solubilize lignin, 363,364/ conditions for use as biological catalyst, 366-367 function, 363,364/ kinetic parameters of oxidation, 365,366/ oxidation rates in organic solvents, 365-366,367/ properties in organic solvents, 365-367 role in lignin degradation, 363—365 Light-scattering photometry determination of Rayleigh ratio, 137 determination of weight-average molecular weights, 135 light-scattering constant, 137 values for acidic lignin fractions, 138/ values for alkali lignin fractions, 138/ weight-average molecular weight determination, 137 Lignin(s) absorption characteristics in visible region, 438,439/ acid condensation reaction of aromatic and phenolic units, 196-197 acrylation, 516-521 addition of polyethylene glycols to improve toughness and strain

537 Lignin(s)—Continued advantages for use in resins as extenders, 37 advantages in chemical utilization, 191 alkaline degradations, 228 application of computational methods to chemistry, 262-269 applications, 100 assessment of suitability as binder, 372-380 C - C and ether bonds, 191 characteristics, 403-404 conversion to polyol, 425 cross-linking, 200 deposition on cotton wool during kraft cooking, 30,31/ description, 100,177 disadvantages in chemical utilization, 190-191 dissolved during delignification of spruce wood meal, 32,35-41 effect on thermal stability and antioxidant effect of polymers, 198 enzymatic modification for technical use, 362-369 factors affecting chemical structure, 372 features used for polymerizations, 346-347 formation of electrically conducting polymers, 198-199 formation of engineering plastics, 199-200 formation of specialty polymers via degradation, 193-194,195/ fractionation to improve properties, 403 future materials, 201 gelation, 200 GPC, 499,500/ grafting, 200,476-484 high-performance polymers from degradation products, 205-217 hydrolysis in acidic and basic media, 228 improvements in strain properties, 403-404 incorporation into polyurethanes, 403 incorporation into solid materials, 402 intermolecular association, 200-201 isolation, 324,497,498/ macromolecular properties, 414-415 major functional groups, 506 mechanism for reactions on 2- and 6-positions, 352,354/ meta-hydroxymethylation, 352-359 methods for molecular weight determination, 100-101 modification at 2- and 6-positions of phenylpropane units, 347-352

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

538

LIGNIN: PROPERTIES AND MATERIALS

Lignin(s)—Continued modification to electrically conducting polymers, 219-226 modifications to improve properties, 403 organosolv, as raw material for polymers, 195 ozonization, 496-497,498/ phenolation, 488 phenolysis reactions, 335 phenylpropane building units, 346,348/ polymeric content of hardwood tree stems, 82 polymerization of lignin model compounds, 347,350-351/352 preparation of adhesives, 488 process scheme for preparation of ozonized lignin, 497,500/ production quantities, 402 properties, elemental composition, and isolation methods, 191,193,194* properties limiting commercial incorporation, 402 quantitative acetylation, 142 raw materials for polymers via degradation, 193-194,195/ reaction of vanillyl alcohol with reactive phenol, 347,348/ reaction with ethylene or propylene oxide, 403 self-condensation of vanillyl and 3,4-dimethoxylbenzyl alcohols, 347,349/ solubility, 43 structure, 191,192f sulfur, See Sulfur lignin supercritical fluid extraction from wood, 42-55 synthesis of polymers via degradation products and fragments, 196,197/ synthetic route to epoxy-functionalized derivatives of OH-functional polymers, 506 technical applications, 191,193* trends in modification, 245-260 use as phenol replacement in phenol-formaldehyde, 324 use as polymeric component of structural materials, 515-516 use as polymers, 361-362 use in industrial materials, 205 use in production of polymer products, 346 yield during isolation, 499 yield during ozonization, 499,501 water-insoluble, elemental composition, 36* See also Kraft lignin(s), Lignin in wood

Lignin concentration, effect on kraft lignin association, 150r,151/,152 Lignin degradation, role of laccase, 363-365 Lignin derivatives with acrylate functionality copolymer composition vs. monomer feed composition, 517,519f,520 copolymerization characteristics, 517 copolymerization reactions, 516-517 experimental materials, 516 gel fraction vs. vinyl equivalent weight, 520,521/ model compounds, 517,518/* reaction with isocyanatoethyl methacrylate, 516 reactivity ratios, 517,520,521* Lignin epoxide, synthesis and characterization, 506-513 Lignin in wood association of molecules, 5 behavior compatible with random network polymer, 2-4 behavior incompatible with random network polymer, 4-7 condensation reactions, 5 conformation of macromolecule, 3—4 insolubility, 3 lignin-carbohydrate bonds, 6 modified paradigm, 7 molecular weight, 3 molecular weight distribution, 4-5 noncrystallinity, 2-3 original paradigm, 2 patterns of microfibrils, 6 spherical conformation of lamellar fragments, 6 structure, 2 topochemistry, 5-6 ultrastructure, 6-7 Lignin(s) modified by chlorophosphazenes activation energy of thermal degradation process, 251,254* Arrhenius plot, 251,254/ thermal behavior, 251-256 thermograms, 251,253/ Lignin products, color problem, 436 Lignin sulfonates elution with electrolyte solution, 127,128-129f,130 elution with water, 124,125-126/127 See also Sulfonated lignins Lignin-based epoxides characterization, 508 composition, 511*

539

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

INDEX Lignin-based epoxides—Continued dynamic mechanical thermal analysis, 511 network characterization, 511/,512/,513 synthesis, 508 Lignin-based epoxy resins synthetic approaches, 507 use of epichlorohydrin in synthesis, 507-508 Lignin-based polymeric materials, preparation, 246-247 Lignin-based polyurethanes description of experimental materials, 404,405/ effect of N C O - O H ratio on properties, 404-405 experimental methods, 404 modulus of elasticity vs. lignin content, 407,408/ preparation method vs. desired properties, 410,412 source class, 404 Τ vs. lignin content, 405,406/407 ultimate elongation vs. lignin content, 410,411/ ultimate strength vs. lignin content, 407,409/410 Lignin—carbohydrate complexes aggregate formation, 18,21-22/23 chemical composition and properties, 12,13/,23,25/ conductivity vs. concentration, 18,21/ degradation pattern by carbohydrolases, 18,20/ electron microscopic observations, 12 estimation of lignin-sugar linkages, 17 extraction methods, 12 fractionation, 17 gel filtration patterns, 18,19f gel filtration with detergent addition, 18,22/ hydrophobic interactions in aqueous solution, 23,27 isolation in wood, 11 methyl ethers of monosaccharides from oligomer hydrolyzate, 15,17/ molar extinction coefficient vs. concentration, 18,21/ molecular shape, 17-18,19-20/ neutral sugar composition of subfractions, 13,15/ preparation of oligomers, 12—13 structural determinants, 23,24/ structural features, 26/27 synthesized model compounds, 13,14/15

Lignin-carbohydrate compounds, polarity, 177 Lignin-derived polyurethanes, problems with cross-linking, 390 Lignin-polystyrene graft copolymers of controlled structures DSC for presence of graft product, 482,483/ funationalization of lignin macromolecule, 479,480/ future research, 482,484 instrumentation, 477 materials, 477 preparation, 478 preparation of "living" polystyrene, 478 preparation of mesylated lignin, 477-478 preparation of monodisperse polystyrylcarbanion, 479,480/ proof of grafting, 479,481/482,483/ quantitation of graft copolymer, 482 synthesis steps, 479,480f Lignin-transforming fungi, peroxidase and oxidase production, 363,364/ Ligninase capacity to demethylate and solubilize lignin, 363,364/ function, 362 Ligninlike model epoxide, synthesis and characterization, 508 Lignosulfonate(s) composition, 219-220 isolation, 219 schematic representation of macromolecule, 220,222f fractionation, 178-184 preparation, 183,187 Living polystyrene, preparation, 478 Low-angle laser light-scattering photometry, procedure, 142 use in M W distribution, 101

M Macromers applications, 414 definition, 414 Macromers with cellulose triacetate properties, 421/ schematic representation, 416/421 wide-angle X-ray scattering, 421,422f,423 Macromers with propylene oxide H N M R spectrum of acetylated hydroxypropyllignin, 417,41S(f 1

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

540 Macromers with propylene oxide—Continued G C of alkyl iodide mixture, 417,418/ relationship among target macromer functionality, degree of caping, and average macromer molecular weight, 417,421,422/* schematic representation, 416/417 UV-absorptivity coefficient vs. non-UV-absorbing mass, 417,420/ Macromolecular conformation, lignin in wood, 3-4 Macromolecules, molecular weight distribution, 59 Maple block screening method, description, 331-332 Melting point depression, hydroxypropylcellulose blends with lignin, 468,471/ Membrane sampling technique, description, 146-147 Mesylated lignin, preparation, 477-478 Miscibility, role of molecular weight for polymers, 453 Modes of association, kraft lignin components, 156-174 Modification of lignins determination of properties of derivatives, 246-247 procedure, 246 to improve properties, 403 with chlorophosphazenes characteristics of polymers formed, 247,251 difference T G A of products, 251,252/* modification parameters and derivative properties, 247,249* properties of additionally modified products, 247,250* properties of products, 247,248* T G A of products, 251,252* with terephthaloyl chloride activation energy of degradation process, 255,259* description, 251,255 effect on properties of product, 255,256* hydrolytic resistance of modified lignins, 255,257* thermal properties of lignosulfonates, 255,258* total hydroxyl content of lignin sulfonates, 255,256* Modified lignin materials, future prospects, 221,222

LIGNIN: PROPERTIES AND MATERIALS Modified lignins as carriers for controlled-release preparations 2,4-D-modified lignin sulfonates, 257,259* agricultural applications, 255,257 effect of 2,4-D-containing preparations on plant growth, 257,260* Modulus of elasticity, lignin-based polyurethanes, 407,408/ Molar mass, lignins, 194* Molar mass distribution of lignins, determination by GPC, 124-132 Molecular association, modes, between kraft lignin components, 156-174 Molecular association of kraft lignin in aqueous solution, 144-153 Molecular mechanics calculations, 264 Molecular orbital calculations ab initio calculations, 263 advantages, 263-264 Hiickel molecular orbital calculations, 263 information obtained, 264,265/ semi-empirical calculations, 263 Molecular weight effect on kraft lignin association, 147,148/149,151/ kraft lignin species, 165-168 lignin in wood, 3 macromolecules, calculation from sedimentation coefficient, 63 See also Number-average molecular weight, Weight-average molecular weight, Zeta-average molecular weight Molecular weight distribution hydroxypropylated lignins, 100-106 apparent molecular weights, 102,103/105* experimental procedures, 101-102 G P C with differential viscosity detector, 101-106 kraft lignins, 156 lignins calibration standards, 111 determination by HPSEC, 110-122 determination by HPSEC-DV, 83-98 effect of eluant on HPSEC parameters, 115-122 effect of solvent, 110 experimental procedure, 111-112 HPSEC elution of model compounds, 112,114/ in wood, 4-5 problems with conventional methodology, 83 problems with estimation, 109,110

541

INDEX Molecular weight distribution—Continued lignins—Continued structures of model compounds, 112,113/ suitable solvents, 83 polymers determination by analytical ultracentrifugation, 61-80 measurements, 59

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

Ν

Noncrystalline, lignin in wood, 2—3 Nonfreezing water, around ionic groups, 274 Nonrandom interactions between kraft lignin species absorbancy vs. degree of association, 169,171/ contributions of component subsets, 167,168/ M comparison for component subsets, 167,169,170/ Nonsulfonated lignins, fractionation on elution with NaOH solution, 130,131/,132f Nuclear magnetic resonance (NMR) spectroscopy, water-sodium lignosulfonate system, 275-283 Number-average molecular weight determination, 134-135 effect of acetylation, 136/ effect of temperature, 135,136/ formula, 59-60 influence of molecular weight of calibrating compound, 135/,136 influence of solvent, 135,136/ V P O , 135-136/ w

Organosolv \ignin(s)—Continued preparation, 141 raw materials for polymers, 195 resin preparation, 330,331/ schematic representation, 465,467/ Organosolv-lignin-modified phenolic resins, preparation, 330,331/ Organosolv pulping advantages, 312 A L C E L L process, 313-323 development as commercial process, 312 Oxygen index definition, 387 polyurethanes containing phosphorus, 385,387/ Ozone, application, 496 Ozonization of lignin condition and yield, 497/ reaction, 496-497,498f,50Qf yield, 499,501 Ozonized lignin gel time, 501/ gel time of epoxy resin mixture, 497 GPC, 499,500/ ozonization condition and yield, 497/ process scheme, 497,500/ reaction with epoxy resin, 501/,502 Ozonized lignin-epoxy resins adhesive strength tests, 499 bonding tests, 502,504/ dynamic mechanical measurements, 499 dynamic mechanical properties, 502 preparation, 499 temperature dependence of viscoelastic property, 502,503-504/

Ρ Pearson's hard-soft acid-base theory, description, 268 On-line size-exclusion chromatography-LALLS Phenolated steam explosion ligninrecorder traces, 139,140/ formaldehyde resins, preparation, 336 weight-average molecular weight Phenolation of lignin, conditions, 488 determination, 139,141 Phenolysis lignin adhesive formulation, 336 Organosolv lignin(s) C N M R spectroscopy, 336,339,340/ analytical characterization, 326-327/,330 cure behavior, 341,342/ block lap-shear test results, 327,328/ cure rate dependence on pH, 341,343/ bulk and solubility properties, 325,326/ evaluation of adhesive bond strength, chromatographic fractionation, 96,97/ flake-board test results, 328,329/ 341,343,344/ impurities, 325-327 functionality measurement, physical and chemical characterization, 337,339,340/341 325,327/ GPC, 336-337,338 Ο

1 3

LIGNIN: PROPERTIES AND MATERIALS

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

542

Phenolysis lignin—Continued molar ratio of bound phenol to lignin unit, 339,341* optimum reaction period between phenol and lignin, 337,338/,340/ phenol consumption during phenolysis, 337,340/ preparation, 334—335 tensile shear adhesion test, 336 tensile shear strength measurement, 337 torsional braid analysis, 337 Phenolysis lignin resins cure rate, 339,341,342/ cure rate dependence on p H , 341,343/ Poly-Hue oxidase capacity to demethylate and solubilize lignin, 363,364* function, 362 Poly(l -amidoethylene) average limiting viscosity number, 72,78* concentration vs. sedimentation coefficient, 70,71/ determination of limiting sedimentation coefficient, 72,73/ differential molecular weight distribution, 72,77/ experimental limited viscosity number, 78,79* integral molecular weight distribution, 72,76/ weight-average molecular weight, 72,78* Polyacylhydrazones having guaiacyl units with alkylene groups heat capacities, 213,216/ inherent viscosities, 211,213* starting temperatures of decomposition, 211,213* synthesis, 211,214 Τ' 211,213* Porydispersity, lignins, 194* Polyelectrolytes, properties, 274 Polyesters having methoxybenzalazine units DSC, 211,212f starting temperatures of decomposition, 208* synthesis, 208,211 Polyesters having spirodioxane rings rigidity vs. 7*, 208 synthesis, 206-207 Polyesters having syringyl-type biphenyl units decomposition temperature, 213,215* DSC, 213,215 synthesis, 213-214 g

Polyethers having methoxybenzalazine units decomposition temperatures, 208* DSC, 208,210-212f synthesis, 208-209 Polyethylene, 454-455 Polyethylene glycols, addition to lignins to improve toughness and strain characteristics, 403—404 Polyhydroxystyrene derivatives effects of molecular weight on glass transition temperature, 206,209/ synthesis, 206-207 Poly[lignin-g-(l -amidoethylene)] composition of reaction mixtures, 302,303* effect of chloride ion on yield of product, 299 preparation from different lignins, 299,300* synthesis of copolymers in (CH ) SO,299,301* synthetic reaction parameters, 302,303* yield and limiting viscosity number for synthesis reactions, 299,300* yield vs. CaCl content for reactions, 302,304/ Poly{lignin-g-{ (1 -amidoethylene) copolymer SEC, 302,306/ synthetic data and physical characteristics, 302,305* U V absorbance, 302,306/307 Polymer-polymer miscibility, role of molecular weight, mechanisms, 453 Polymer blends advantages, 452 factors influencing properties, 452-453 hydroxypropyllignin experimental methods, 454 hydroxypropyl-poly(vinyl alcohol) blends, 458,460/461,462/· preparation of experimental materials, 454* hydroxypropyllign in-polyethylene copolymer blends, 455,456/ hydroxypropyllign in-pory(methyl methacrylate) blends, 455,457/458,459/ Polymerization of lignin model compounds, reaction of model compound with excess formaldehyde, 347,350-351/352 Polymers, specialty, formed upon degradation of lignins, 193-194,195* Polymethyl methacrylate, preparation, 454 Polyphenols adhesives, use and cost, 325 3

2

2

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

INDEX Polyurethanes containing phosphorus oxygen index, 385,387/ thermogravimetric curves, 387,388/ incorporation of lignins, 403 preparation, 382,383 synthesis, 391 thermal stability, 382-388 See also Lignin-derived polyurethanes Polyvinyl alcohol characteristics, 454/ preparation, 454 Preparation of sulfur lignin analysis of structure, 220,221/ methods, 220 reaction and possible structures, 221,222f Properties, hydroxypropylcellulose blends with lignin, 466—469 Pulp color, role of hemilignins and glycolignin, 29 Pyrolysis of hardwood, products, 195

Quantitative acetylation, lignins, procedure, 142

Rayleigh fringe patterns, reading, 67-68,69f Rayleigh ratio, light-scattering photometric determination, 137 Reaction ordinate, definition, 234,236 Reactivity ratios acrylated lignin derivatives, 520,521/ definition, 517,518/ determination, 520 Red oak wood chips lignin purification, 330 wood pulping, 330 Rejection coefficient, definition, 147 Resol resin adhesives, preparation, 488 Resol-type phenol resin adhesives from kraft lignin effect of acid catalyst on wet-bond adhesion strengths, 492,493/ effect of lignin purity on gluability, 492 factors influencing adhesion, 492 hot-press time vs. wet-bond adhesion strength, 493/494

543 Resol-type phenol resin adhesives from kraft lignin—Continued preparation, 492 properties, 494 Reversed-phase chromatography (RPC) of lignin derivatives advantage, 178 contents of hydrolyzed fractions, 178,180/ elution process, 178 high molar mass birch lignosulfonates, 178,179/· hydrophobic stationary phase, 178 low molar mass birch lignosulfonates, 180,181-182/",184/ pine kraft lignin, 183,184/ system and conditions, 187 Rigid-rod composites advantages, 464 synthesis approaches, 464-465

Sedimentation coefficient, definition, 61 Sedimentation equilibrium, determination of weight-average molecular weights, 135 Sedimentation patterns, conversion to distribution patterns, 64-66 Self-association kraft lignin in aqueous solution, 144-153 modes, between kraft lignin components, 156-174 See also Association Size-exclusion chromatography (SECT) calibration curves, 138-139,140/* levels of interpretation, 138 lignin molecular weight distribution, 83 Soda-AQ hardwood lignin, properties, 355 Soda bagasse lignin properties, 355 reaction with formaldehyde, 355,356/ Sodium hydroxide, effect on fractionation of nonsulfonated lignins, 130,131/132/' Sodium lignosulfonate, conductivities, 221,223/ Soft segment content, effect on properties of lignin-based polyurethanes, 403-412 Sol fraction, definition, 508 Solubility, lignin in wood, 2-3,43 Solubility parameter definition, 453 relationship with enthalpy of mixing, 453

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

544 Solubilization lignin, by laccase, ligninase, and poly-blue oxidase, 363,364* wood, effect on reactivity, 490 Solvents delignirying, ethylene glycol-water, 230 effect on HPSEC, elution of lignin model compounds, 116—120 for determination of lignin molecular weight distribution, 82-83 Solvolysis lignin, preparation, 383 Specialty polymers from lignin chemical modification, 195-196 electrically conducting polymers, 198-199 engineering plastics, 199-200 formation via degradation, 193-194,195* organosolv lignins as raw materials, 195 synthesis via degradation products and lignin fragments, 196,197/ thermal stability, 198 Spruce wood lignin, description, 29 Spruce wood meal heating with neutral phosphate buffer, 32-34 heating with phosphate buffer and dioxane, 32,34-41 heating with water, 30-33 Stability, thermal, heat-resistant polyurethanes from solvolysis lignin, 382-388 Starlike macromers from lignin, See Hydroxypropyllignin-based macromers Steam-explosion lignin phenolysis, 335-336 preparation, 335 structure, 334 Steam-explosion process, utilization, 334 Sulfonated lignins elution with electrolyte solution, 127-130 elution with water, 124-127 Sulfur lignin A - B ratios of lignin doped with bromine, 224* compounding with bromine, 224,226/ compounding with graphite, 224,226/ conductivities, 221,223* effect of doping on ESR spectra, 224,225/ effect of doping on IR spectra, 224,225/ mechanism of conductivity, 226 preparation, 220-221*,222f properties, 221 Supercritical fluid extraction applications, 42

LIGNIN: PROPERTIES AND MATERIALS Supercritical fluid extraction—Continued lignin from wood chemical and spectroscopic analyses, 45 critical properties, 45 dissolution of red spruce, 46,47/ effect of extraction fluid composition, 54,55/ effect of extraction pressure, 50,52f effect of extraction process, 50,54/ effect of solvent, 50,53/ effect of temperature, 50,51/ effect of time, 50,51/ extraction system, 43,44/45 G P C analysis, 45-46,50,51-53f influencing factors, 43 IR spectra of kraft lignin, 46,49f,50 IR spectra of red spruce residues, 46,48/ lignin content in red spruce residue, 46,47/ materials, 45

Τ

Tensile properties, elastomeric polyurethanes, 398,399-400/ Tensile shear bond strength of adhesives, phenolysis lignin, 341,343,344* Terephthaloyl chloride, modification of lignins, 255-259 Thermal behavior, lignins modified by chlorophosphazenes, 251-256 Thermal degradation, heat-resistant polyurethanes from solvolysis lignin, 383,384/385 Thermal stability heat-resistant polyurethanes from solvolysis lignin, 382-388 polymers formed from lignins, 198 Thermogravimetric analysis, heat-resistant polyurethanes, 383,385-388/ Topochemistry, lignin in wood, 5-6

U Ultimate elongation, lignin-based polyurethanes, 410,411/ Ultimate strength, lignin-based polyurethanes, 407,409/410

Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0397.ix002

INDEX Ultracentrifugal sedimentation calculation of number of fringes, 64-65 conversion of sedimentation patterns to distribution patterns, 64-66 diagram of Rayleigh fringes, 61,62/ experimental procedure, 61 Johnston-Ogston effect, 63-64 limiting sedimentation coefficient, 63 sedimentation coefficient, 61 Ultrastructure, lignin in wood, 6-7 Universal calibration application to unknown polymers, 86 chromatographic fractionation of organosolv lignin, 96,97/ development of calibration curves, 86-87 master plot, 87,88/ molecular weight distribution of acetylated lignins, 87,89-% sources of error, 85-86 via HPSEC-DV, 83-98 V Vanillin, production from lignin hydrolysis, 229 Vapor phase osmometry (VPO) calibration curve, 102,103/ comparison to G P C - D C , 105,106/ description, 101 to determine number-average molecular weight, 102,105/ Vapor pressure osmometry determination of number-average molecular weights, 134,135-136/ procedure, 142 Viscosity average molecular weight, formula, 60 W Waferboard manufacture, conditions, 318/ Water-insoluble lignin, elemental composition, 36/ Water-sodium lignosulfonate system amount of freezing water, 276,278 calculation of water content, 278 DSC cooling curves of systems with various water contents, 276,277/ U H M R spectroscopy, 278-281 ^ N a N M R spectroscopy, 280-283 phase diagram, 270,277/ procedure for DSC, 275 procedure for N M R spectroscopy, 275 l

545 Water-sodium lignosulfonate system—Continued relationship between water content, freezing water content, and nonfreezing water content, 287,279/ relaxation rates of bound water, 278,280 sample preparation, 276 temperature dependence of *H longitudinal relaxation time of water, 278,279/ temperature dependence of *H transverse relaxation time of water, 278,279/ temperature dependence of ^ N a longitudinal relaxation time, 280,281/ temperature dependence of ^ N a transverse relaxation time, 282/",283 temperature dependence of average correlation time of water, 280,281/ texture, 276 Water-soluble lignin graft copolymers assays, 297-298 experimental equipment, 298-299 experimental materials, 298 lignins grafted, 295,296/ mechanistic studies, 307-308 poly[lignin-g-(l -amidoethylene)] copolymer, 302,305/,306/307 properties, 308 synthesis, 295,297 synthesis of poly [lign in -g-(l -amidoethylene)], 299-303 Water, types around ionic groups, 274 Weight-average molecular weight calculation, 162 function, 60 Weight-average molecular weight determination light-scattering photometry, 137,138/ on-line S E C - L A L L S , 139,140/141 SEC, 138-130,140/ values for acidic lignin fractions, 138/ values for alkali lignin fractions, 138/ Wood, dissolution in organic solvents, 488-490 Wood adhesives, types, 325 Wood solubilization, effect on reactivity, 490 Wood-based adhesives, preparation, 490 World forests lignin formation, 190 yearly growth, 190

Ζ Zeta-average molecular weight, formula, 60