Adhesives from Renewable Resources 9780841215627, 9780841212374, 0-8412-1562-6

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ACS SYMPOSIUM SERIES 385 Adhesives from Renewable Resources Richard W. Hemingway,

EDITOR

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.fw001

U.S. Department of Agriculture

Anthony H. Conner, E D I T O R U.S. Department of Agriculture

Susan J. Branham,

ASSOCIATE EDITOR

U.S. Department of Agriculture

Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division at the 194th Meeting of the American Chemical Society, New Orleans, Louisiana, August 30-September 4, 1987

American Chemical Society, Washington, DC 1989

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Library of Congress Cataloging-in-Publication Data

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.fw001

Adhesives from renewable resources Richard W. Hemingway, editor, Anthony H . Conner, editor, Susan J . Branham, associate editor. p. cm.—(ACS Symposium Series, 0097-6156; 385). Developed from a symposium sponsored by the Cellulose, Paper, and Textile Division at the 194th Meeting of the American Chemical Society, New Orleans, Louisiana, August 30-September 4, 1987." Bibliography, p. Includes indexes. ISBN 0-8412-1562-6 1. Adhesives—Congresses. 2. Renewable natural resources—Congresses. I. Hemingway, Richard W., 1939- . II. Conner, Anthony H . III. Branham, Susan J . IV. American Chemical Society. Cellulose, Paper, and Textile Division. V . American Chemical Society. Meeting (194th: 1987: New Orleans, La.). VI. Series. TP967.A5345 668'3—dc19

1989

88-39293 CIP

Copyright ©1989 American Chemical Society All Rights Reserved. The appearance of 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, M A 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 me mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance ot 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 oy law. PRINTED IN THE U N I T E D STATES O F A M E R I C A

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

ACS Symposium Series M. Joan Comstock, Series Editor

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.fw001

1988 ACS Books Advisory Board Paul S. Anderson Merck Sharp & Dohme Research Laboratories Harvey W. Blanch University of California—Berkeley

Vincent D. McGinniss Battelle Columbus Laboratories Daniel M . Quinn University of Iowa

Malcolm H . Chisholm Indiana University

James C. Randall Exxon Chemical Company

Alan Elzerman Clemson University

E . Reichmanis A T & T Bell Laboratories

John W. Finley Nabisco Brands, Inc. Natalie Foster Lehigh University Marye Anne Fox The University of Texas—Austin Roland F. Hirsch U.S. Department of Energy G. Wayne Ivie U S D A , Agricultural Research Service Michael R. Ladisch Purdue University

C. M . Roland U.S. Naval Research Laboratory W. D. Shults Oak Ridge National Laboratory Geoffrey K. Smith Rohm & Haas C o . Douglas B. Walters National Institute of Environmental Health Wendy A . Warr Imperial Chemical Industries

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Foreword

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.fw001

The A C S SYMPOSIUM SERIES 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 ADVANCES IN CHEMISTRY SERIES 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.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Preface

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.pr001

T H E OBJECTIVE O F THIS SYMPOSIUM was to include research on a broad

range of natural products directed to a wide variety of bonding applications. The speakers described research on adhesive polymers derived from lignins, tannins, carbohydrates, terpenes, and proteins for applications as diverse as tire-cord bonding and eye surgery. Byproducts of the forest products industry are potentially primary sources of natural resource-based adhesives. Because this industry is both a producer of huge tonnages of residues and a major consumer of adhesives, this book focuses on adhesives from renewable resources derived from trees. Composites made from wood will remain the primary materials used for the construction of homes and their furnishings for the foreseeable future. The date of the symposium on which this book is based marked the 15th anniversary of the severe petroleum shortage of 1973-1974. M u c h of the research presented in this volume was begun in the early 1970s in response to shortages of petroleum-based adhesives for the forest products industry when the nation was in the midst of a record-setting demand for housing materials. Left with this indelible memory, the forest products industry has supported the development of adhesives from renewable resources. The chapters presented i n this book show that new alternatives based on renewable resources will be available should supplies of resins derived from petrochemicals become inadequate again. Outstanding opportunities for the development of high-value specialty polymers are highlighted by work presented here on polymers derived from mollusks. This book is the product of the efforts of chemists from around the world. O u r thanks go first to the authors who so kindly contributed papers and patiently responded to our requests. We thank the American Chemical Society for providing a venue for the symposium that made this book possible. W e also thank the clerical support staff of the U . S . Department of Agriculture, Forest Service at both the Southern Forest Experiment Station and the Forest Products Laboratory, who tirelessly worked to make this a meaningful enterprise. R I C H A R D W. H E M I N G W A Y

ANTHONY H. CONNER

Southern Forest Experiment Station Forest Service U.S. Department of Agriculture Pineville, LA 71360

Forest Products Laboratory Forest Service U.S. Department of Agriculture Madison, W I 53705-2398

June 12, 1988 ix In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 1 Adhesives from Renewable Resources Historical Perspective and

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

Wood Industry Needs Alan L. Lambuth Boise Cascade Corporation 220 South T h i r d Street Boise, ID 83702

The wood products industry has a long and successful history of utilizing adhesives based on renewable resources. Their performance was adequate to see us through World War II and beyond. But the tremendous postwar expansion in the petrochemical industry provided compounds for synthetic resin adhesives so inexpensively, they steadily displaced natural adhesives. When embargo threatened key petrochemicals in 1973, their availability dropped and prices increased abruptly. Industry reacted with an immediate partial return to natural adhesives. A s oil's availability improved and prices became more competitive, synthetic resin adhesives again became the industry standard. W i t h over 70% of all wood products now bonded, industry is concerned about future sources of adhesives in the event that oil supplies are again disrupted by world events. There is strong support for research into adhesives based on renewable resources with emphasis on: 1) Phenol, methanol, urea, and resorcinol-acting compounds; 2) copolymeric adhesives involving synthetic resins and natural polymers; 3) new adhesive mechanisms and substrate treatments; 4) greater exterior durability for animal and vegetable protein adhesives. F r o m t h e days o f e a r l y E g y p t i a n a r t i s a n s u n t i l t h e r e l a t i v e l y recent p a s t , t h e w o o d w o r k i n g i n d u s t r y was entirely dependent o n n a t u r a l adhesives for a l l forms o f b o n d e d j o i n e r y . T h e s e a p p l i c a t i o n s were t h e n l a r g e l y p r e e m p t e d b y low-cost, d u r a b l e s y n t h e t i c adhesive p o l y m e r s developed f r o m p e t r o c h e m i c a l s . Since t h e v o l u m e a n d u t i l i t y o f b o n d e d w o o d p r o d u c t s have g r e a t l y e x p a n d e d a n d t h e c o n t i n u i n g a v a i l a b i l i t y o f s y n t h e t i c adhesives i s now s o m e w h a t u n c e r t a i n , m o r e 0097-6156/89/0385-0001$06.00/0 « 1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

2

ADHESIVES F R O M RENEWABLE RESOURCES

t h o r o u g h research i n t o n a t u r a l adhesive p e r f o r m a n c e a n d resources is clearly i n d i c a t e d . T h i s overview chapter a t t e m p t s t o project w o o d i n d u s t r y needs a n d suggests a p p r o p r i a t e areas for i n v e s t i g a t i o n .

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

History T h e r e is a 58-year-old reference t h a t gives a f a i r l y clear p i c t u r e of the w o o d w o r k i n g i n d u s t r y ' s adhesive choices f r o m , say, the I n d u s t r i a l R e v o l u t i o n i n the m i d - 1 7 0 0 ' s u n t i l a b o u t 1930. T h e 1929 U . S . D e p a r t m e n t of A g r i c u l t u r e B u l l e t i n by T . R . T r u a x e n t i t l e d " T h e G l u i n g of W o o d " lists the five classes of adhesives used m o s t i n w o o d w o r k i n g d u r i n g t h a t l o n g t i m e s p a n . T h e s e i n c l u d e d a n i m a l glues, l i q u i d glues, casein a n d vegetable p r o t e i n glues, s t a r c h glues, a n d b l o o d a l b u m i n glues. L i q u i d glues were described as a lower s t r e n g t h variety o f f i s h or a n i m a l glue t h a t h a d been s t a b i l i z e d w i t h a c i d for l o n g - t e r m storage i n r e a d y to-use f o r m . P a s s i n g reference was also m a d e t o a n u m b e r of other "adhesive substances" s u c h as s o d i u m s i l i c a t e , m u c i l a g e , pastes, r u b b e r cements, p h e n o l aldehyde c o m p o u n d s , a s p h a l t s , g u m s , a n d shellacs t h a t were used o c c a s i o n a l l y for w o o d b o n d i n g at the t i m e . Since there were r e a l l y n o other o p t i o n s , the c h e m i s t r y a n d a p p l i c a t i o n of these n a t u r a l l y d e r i v e d p o l y m e r s evolved t o a fine art t h a t was s u m m a r i z e d o c c a s i o n a l l y i n s u c h p u b l i c a t i o n s as the one m e n t i o n e d . F u l l y exterior d u r a b l e adhesives s i m p l y d i d not exist at t h a t t i m e . However, c e r t a i n n a t u r a l glues such as a l k a l i n e - d i s p e r s e d casein a n d b l o o d adhesives d i d develop a significant degree of water resistance. W i t h adequate surface p r o t e c t i o n , t h e y c o u l d be m a d e t o serve e x t e r i o r purposes o n a n i n t e r m i t t e n t basis. T h i s was the state of adhesive technology g o i n g i n t o W o r l d W a r I. It was at t h a t p o i n t t h a t a n urgent need arose for d u r a b l e w o o d glues t o b o n d w o o d l a m i n a t i o n s i n t o a i r c r a f t p r o p e l l e r stock a n d other w o o d e n elements i n t o the panels a n d frames of the planes themselves. I n the absence of better a l t e r n a t i v e s , b o t h b l o o d a n d casein glues were f u r t h e r i m p r o v e d i n d u r a b i l i t y b y the a l t e r a t i o n of t h e i r proteins w i t h v a r i o u s c h e m i c a l dénaturants a n d b y the a p p l i c a t i o n of heat d u r i n g cure. I n t h i s f o r m , p r o t e i n glues served the A l l i e d war effort e x t r e m e l y w e l l , w h i l e l a y i n g the g r o u n d w o r k for the advanced b l o o d a n d casein glue technology of l a t e r years. T h e Second W o r l d W a r saw the extensive use of a l k a l i n e - d i s p e r s e d s o y b e a n a n d b l o o d glues i n p l y w o o d for a l l k i n d s of c o n s t r u c t i o n , p a c k a g i n g , a n d t r a n s p o r t a t i o n uses. T h u s , b o t h vegetable a n d a n i m a l p r o t e i n glues c o n t r i b u t e d heavi l y t o w a r t i m e l o g i s t i c successes. D u r i n g t h i s c r i s i s , w i t h p e t r o l e u m i n c r i t i c a l l y short s u p p l y , a t r u l y exterior b l o o d - b a s e d adhesive was developed i n v o l v i n g the r e a c t i o n o f alkaline-dispersed soluble b l o o d w i t h cresylic acids. P l y w o o d b o n d e d w i t h t h i s adhesive was s t i l l p e r f o r m i n g w e l l i n u n p r o t e c t e d outside l o c a t i o n s a g e n e r a t i o n after i t was m a d e . F r o m a b o u t 1930 t o the present, casein glues have been used successfully for b o n d i n g h i g h - s t r e n g t h softwood l u m b e r i n t o g l u e d l a m i n a t e d beams a n d arches for i n t e r i o r or covered exterior service. E v e n earlier, u n t i l perhaps 1900, casein

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

1.

LAMBUTH

Historical Perspective

3

glues were used t o l a m i n a t e s i m p l e r s t r u c t u r a l m e m b e r s . Because of t h e i r v e r y t o l e r a n t a s s e m b l y p r o p e r t i e s a n d s t r o n g , g a p - f i l l i n g gluelines, these glues were p a r t i c u l a r l y w e l l s u i t e d t o t h i s h e a v y s t r u c t u r a l a p p l i c a t i o n a n d also t o the e n d grain joinery of m i l l work. A n i m a l a n d s t a r c h glues, e s p e c i a l l y because o f t h e i r low color a n d ease o f a p p l i c a t i o n o n c o m p l e x j o i n t surfaces, were the adhesives o f choice i n the f u r n i t u r e a n d c a b i n e t i n d u s t r i e s f r o m c o l o n i a l days u n t i l the advent o f s y n t h e t i c e m u l s i o n adhesives after W o r l d W a r I I . Service c o n d i t i o n s were l i m i t e d t o d r y i n t e r i o r a p p l i c a t i o n s , of course. L e a v i n g a c h a i r o u t i n the r a i n m e a n t d i s m a n t l i n g a n d regluing.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

T h e s e are j u s t a few o f the e x a m p l e s t h a t c a n be c i t e d w i t h respect t o the h i s t o r i c a l a n d c o m p a r a t i v e l y recent uses of n a t u r a l adhesives b y t h e w o o d w o r k i n g i n d u s t r y , hence, t h e i r f a m i l i a r i t y . A d v e n t of Synthetics A s a result of successfully m e e t i n g the challenge o f W o r l d W a r I I , large o i l r e f i n i n g a n d p e t r o c h e m i c a l i n d u s t r i e s were i n place, each w i t h s u b s t a n t i a l i d l e c a p a c i t y , j u s t after the w a r .

T h e e c o n o m i c pressure t o develop new o u t l e t s

for t h i s p r o d u c t i v e c a p a c i t y was t r e m e n d o u s . T h e s y n t h e t i c resin a n d p l a s t i c s i n d u s t r i e s as we k n o w t h e m t o d a y a p p e a r t o have been a c t u a l l y created at t h a t t i m e b y t h i s pressure.

T r u e , r e s o r c i n o l - f o r m a l d e h y d e resins for b o n d i n g

w h i t e o a k i n t o minesweeper frames a n d b i r c h veneer i n t o h e l i c o p t e r blades were developed d u r i n g the w a r to meet n a t i o n a l emergencies, b u t o n the basis t h a t cost was no o b j e c t . I t ' s also t r u e t h a t p h e n o l - f o r m a l d e h y d e resins, i n i t i a l l y as d r i e d films o n p a p e r a n d l a t e r as l i q u i d resin s y r u p s for adhesive f o r m u l a t i n g , h a d been k n o w n since the e a r l y 1930's. H o w e v e r , the cost o f the c h e m i c a l r a w m a t e r i a l s t o m a k e these s y n t h e t i c resins was sufficiently h i g h d u r i n g t h a t p e r i o d to effectively l i m i t t h e i r uses t o s p e c i a l t y or m i l i t a r y a p p l i c a t i o n s . T h i s s i t u a t i o n changed a b r u p t l y w i t h the p o s t w a r a v a i l a b i l i t y o f r e l a t i v e l y low-cost, h i g h - v o l u m e p e t r o c h e m i c a l s . It was a l r e a d y k n o w n t h a t p h e n o l i c resin adhesives set a s t a n d a r d o f p e r f o r m a n c e for e x t e r i o r d u r a b i l i t y t h a t c o u l d n o t be r e a s o n a b l y m a t c h e d w i t h n a t u r a l adhesives o f a n y e x i s t i n g t y p e . T h i s fact r e p resented a s t r o n g s t i m u l u s for c o m m e r c i a l research t o o p t i m i z e the p e r f o r m a n c e a n d e x t e n d the a p p l i c a t i o n s o f p h e n o l i c resins. It o n l y r e m a i n e d for the prices of p h e n o l , r e s o r c i n o l , a n d f o r m a l d e h y d e to b e c o m e low e n o u g h for p h e n o l i c a n d p h e n o l - r e s o r c i n o l resins t o take over large segments o f the b o n d e d w o o d m a r k e t . T h i s o c c u r r e d between 1945 a n d a b o u t 1950. T h e a c c o m p a n y i n g T a b l e I o f resin p r o d u c t i o n v o l u m e s f r o m 1942 t h r o u g h 1959, a d a p t e d f r o m the 1962 e d i t i o n of I r v i n g S k e i s t ' s " H a n d b o o k o f A d h e s i v e s , " i l l u s t r a t e s t h i s r a p i d g r o w t h clearly. B y 1978, the a n n u a l c o n s u m p t i o n o f p h e n o l i c , u r e a , a n d v i n y l adhesives for a l l purposes h a d each passed the b i l l i o n - p o u n d l e v e l . I n i t i a l l y , o n l y the e x t e r i o r - b o n d e d p r o d u c t m a r k e t s fell t o the s y n t h e t i c s . G l u e d p r o d u c t s o f i n t e r i o r or i n t e r m e d i a t e d u r a b i l i t y c o n t i n u e d t o be l a r g e l y

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

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the d o m a i n of n a t u r a l adhesives ( m a i n l y s o y b e a n , casein, a n d b l o o d ) o n the basis of t h e i r very fast hot-press t i m e s or cold-press c a p a b i l i t y u n t i l the early 1960's. A t t h a t p o i n t , the prices of c o m m o d i t y p e t r o c h e m i c a l s b e c a m e so low u n d e r w o r l d w i d e c o m p e t i t i v e pressures t h a t a c o m p e l l i n g case c o u l d be m a d e for u s i n g exterior s y n t h e t i c resin adhesives t o b o n d essentially a l l s t r u c t u r a l w o o d p r o d u c t s , b o t h exterior a n d i n t e r i o r . F o r e x a m p l e , i t b e c a m e cheaper a n d s i m pler t o purchase a d d i t i o n a l h o t presses i n order t o reach the p l y w o o d p r o d u c t i o n c a p a c i t y offered u n t i l t h e n o n l y b y the faster c u r i n g p r o t e i n glues. W i t h t h i s change, the conversion t o s y n t h e t i c resin adhesives was n e a r l y complete.

T a b l e I. P r i n c i p a l S y n t h e t i c R e s i n s P r o d u c e d for A d h e s i v e s , 1942-1959

1

( m i l l i o n s of p o u n d s )

Year 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 ( P r e l i m . )

Phenolics

Vinyls

2.6 12.7 26.3 22.0 22.3 31.9 22.3 28.6 31.5 41.9 42.4 106.6 109.6 166.7 169.1 183.4 162.0 209.6 E x c l u d e s l a m i n a t i n g . Source:

1.5 10.0 15.0 13.0 16.9 10.0 10.0 11.9 15.5 22.8 17.8 26.9 29.0 37.7 43.9 46.7 52.1 59.5 U.S.

Urea and Melamine Types

Total 4.1

27.1 30.4

22.7 68.4 65.4

37.5 45.6 50.0

76.7 87.5 82.3 40.8 81.3 85.6 132.6 143.4 78.7 79.8 140.0 63.5 197.0 86.2 224.8 106.7 311.1 115.2 328.2 107.8 337.9 113.2 327.0 134.1 403.2 Tariff C o m m i s s i o n statistics.

A s i m i l a r s t o r y of t e c h n i c a l development, raw m a t e r i a l cost r e d u c t i o n , a n d adhesive o p t i m i z a t i o n can also be t o l d for the a m i n o resins, the u r e a a n d m e l a m i n e p o l y m e r s . E s p e c i a l l y because of t h e i r versatile h o t - a n d c o l d - c u r i n g c a p a b i l i t i e s , t h i s development also led to the widespread replacement of n a t u r a l adhesives. T h e r a p i d p o s t w a r g r o w t h of a m i n o resins, a l o n g w i t h phenolics

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

1.

LAMBUTH

5

Historical Perspective

a n d v i n y l s , shows p l a i n l y i n the T a r i f f C o m m i s s i o n figures for a n n u a l r e s i n p r o duction.

Since the i n i t i a l use o f u r e a adhesives for p l y w o o d i n 1937, entire

new i n d u s t r i e s have a r i s e n . T h e c o m m o d i t y m a n u f a c t u r e o f p a r t i c l e b o a r d a n d m e d i u m density

fiberboard

is a f a m i l i a r e x a m p l e .

T h u s , the p i c t u r e emerges o f a m u l t i f a c e t e d w o o d p r o d u c t s i n d u s t r y f o u n d e d l a r g e l y o n n a t u r a l adhesives b u t successfully weaned o n t o s y n t h e t i c resins b y a c o m b i n a t i o n of low m a t e r i a l costs a n d f o r m e r l y u n a t t a i n a b l e p e r f o r m a n c e p r o p e r t i e s . A s a result of t h i s i m p r o v e d p e r f o r m a n c e , the development o f other

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useful b o n d e d w o o d p r o d u c t s was h e a v i l y s t i m u l a t e d .

Threat to Supply T h e w o o d w o r k i n g i n d u s t r y , now converted a l m o s t w h o l l y t o s y n t h e t i c s , grew a n d p r o s p e r e d for a decade between 1963 t o 1973. T h e n , the w o r l d w i d e crude o i l crisis a b r u p t l y forced p e t r o c h e m i c a l s u p p l i e r s t o place t h e i r p r o d u c t s o n a l l o c a t i o n . W h e t h e r t h e shortage was real or c o n t r i v e d , t h i s i n t e r r u p t i o n o f access t o low-cost, s e e m i n g l y endless r a w m a t e r i a l supplies for s y n t h e t i c r e s i n a d h e sives deeply shocked the w o o d w o r k i n g i n d u s t r y . T h i s was e s p e c i a l l y significant because b y 1973 a b o u t 7 0 % o f a l l w o o d p r o d u c t s r e q u i r e d g l u i n g i n one f o r m or a n o t h e r . T h u s , the t h r e a t t o e x i s t i n g m a r k e t s was v e r y r e a l a n d v e r y l a r g e . W o o d p r o d u c t m a n u f a c t u r e r s reacted t o t h i s crisis b y seeking i m m e d i a t e a l t e r n a t i v e s wherever possible. I n m a n y cases, the older n a t u r a l adhesives were s t i l l a v a i l a b l e , were s t i l l a p p r o v e d b y c e r t i f y i n g agencies, a n d were a g a i n pressed i n t o service. I n o t h e r cases, s u c h as the s t r u c t u r a l flakeboard, w a f e r b o a r d , a n d s t r a n d b o a r d i n d u s t r i e s , no w o r k a b l e p r i o r a l t e r n a t i v e s e x i s t e d . F o r t h e m , i t was p h e n o l i c , i s o c y a n a t e , or p o s s i b l y a m i n o resins, or n o t h i n g . T h e choices were to operate as efficiently as possible o n a reduced basis or s i m p l y shut d o w n , as a n u m b e r o f c o m m o d i t y w o o d w o r k i n g p l a n t s d i d at t h a t t i m e . T h e o i l crisis o f 1973 is l o n g gone, of course, b u t the m e m o r y of i t is i n d e l i b l y s t a m p e d o n the w o o d w o r k i n g i n d u s t r y . W h a t i f there were a n o t h e r o i l e m b a r g o or a s u d d e n r e g i o n a l w a r ?

( C u r r e n t events i n the M i d d l e E a s t m a k e t h i s a

d i s t i n c t p o s s i b i l i t y . ) O r s i m p l y , w h a t is g o i n g t o h a p p e n as w o r l d o i l reserves b e c o m e i n c r e a s i n g l y l i m i t e d i n the n o t - t o o - d i s t a n t f u t u r e , a n d the t r a n s p o r t a t i o n / e n e r g y i n d u s t r i e s p r e e m p t the r e m a i n i n g s u p p l y ? T h e r e are reassurances, t o be sure, s u c h as t h i s recent s t a t e m e n t f r o m t h e A p r i l 1987 issue o f B u s i n e s s Month: Forget O P E C ' s $ 1 8 - a - b a r r e l g o a l . E u r o p e a n a n a l y s t s say the price o f o i l w i l l r e m a i n far below t h a t for at least the n e x t five years because o f s l u g g i s h d e m a n d i n the i n d u s t r i a l i z e d economies a n d the discovery o f vast new reserves i n S o u t h A m e r i c a , W e s t e r n E u r o p e a n d the F a r E a s t . T m t a l k i n g a b o u t $15 o i l i n the first h a l f o f the 1 9 9 0 V says Rotterdam Analyst Walter Ten Brinck.

E c o n o m i s t s at the P a r i s -

based I n t e r n a t i o n a l E n e r g y A g e n c y agree. Says one, " I c a n ' t see o i l

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES FROM RENEWABLE RESOURCES

above $15 for a s u s t a i n e d p e r i o d unless there's a m a j o r i n t e r n a t i o n a l crisis. A n d i f t h a t h a p p e n s , w e ' l l a l l have m o r e t o w o r r y a b o u t t h a n t h e price o f o i l . " S u c h i n d i c a t i o n s of c o n t i n u i n g o i l s u p p l y a n d price a l l o w us t o believe t h a t we c a n l o o k f o r w a r d t o business as u s u a l i n the n e a r - t e r m f u t u r e .

However,

b o t h f r o m the s t a n d p o i n t o f i n t e r r u p t a b i l i t y a n d also e v e n t u a l p r i c e a n d s u p p l y , the w o o d w o r k i n g i n d u s t r y s t r o n g l y favors current research i n t o renewable r a w m a t e r i a l s a n d p r a c t i c a l adhesive systems based u p o n t h e m . T h i s c a n be seen i n t h e a n n u a l review o f t h e U S D A Forest Service's research budgets a n d

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

p r o j e c t s b y the N a t i o n a l Forest P r o d u c t s A s s o c i a t i o n ' s C o m m i t t e e o n R e s e a r c h Evaluation.

F o r the last 9 years t h i s i n d u s t r y g r o u p has s t r o n g l y a n d consis-

t e n t l y r e c o m m e n d e d research i n t o a l t e r n a t i v e w o o d - b o n d i n g systems based o n renewable resources.

L i k e w i s e , groups o f w o o d w o r k i n g c o m p a n i e s have h e l p e d

s u p p o r t a c a d e m i c research i n t o new adhesive concepts a n d renewable r a w m a t e r i a l sources.

Suggested Research T h e research e m p h a s i z e d b y i n d u s t r y f a l l s r o u g h l y i n t o f o u r categories.

First,

the recovery or p r o d u c t i o n o f t o d a y ' s s y n t h e t i c resin r a w m a t e r i a l s d i r e c t l y f r o m renewable resources or as b y p r o d u c t s i n waste s t r e a m s f r o m i n d u s t r i e s t h a t u t i l i z e r e n e w a b l e resources themselves, s u c h as p u l p a n d p a p e r . E x a m p l e s w o u l d be: 1. T h e recovery of p h e n o l , cresols, a n d g u a i a c o l b y e x t r a c t i o n f r o m k r a f t p u l p i n g process b l a c k l i q u o r . 2. T h e s t e a m p y r o l y s i s o f k r a f t black l i q u o r t o y i e l d specific p h e n o l i c c o m pounds by thermal decomposition. 3. T h e e x t r a c t i o n a n d possible c h e m i c a l m o d i f i c a t i o n o f r e s o r c i n o l - a c t i n g c o m p o u n d s f r o m a v a r i e t y of tree b a r k s , n u t shells, a n d o t h e r n a t u r a l residues w h i c h are h i g h i n a p p r o p r i a t e t a n n i n s . 4. T h e p r o d u c t i o n of m e t h a n o l v i a selective f e r m e n t a t i o n or direct h y d r o génation o f c a r b o n m o n o x i d e . 5. T h e o x i d a t i o n o f m e t h a n e f r o m a v a r i e t y of n a t u r a l sources t o f o r m a l d e h y d e . ( T h e w o r l d ' s a t m o s p h e r e is g a i n i n g i n m e t h a n e content at the rate o f 1% a year.) 6. T h e b u l k e x t r a c t i o n o f hemicelluloses a n d pentosans f r o m w o o d y b i o m a s s a n d t h e i r conversion t o f u r a n c o m p o u n d s . 7. T h e direct fixation of a t m o s p h e r i c n i t r o g e n a n d i t s conversion i n t o a m m o nia, then urea, then melamine.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

1.

LAMBUTH

7

Historical Perspective

S o m e of these are e x i s t i n g - e v e n c l a s s i c a l - processes, b u t t h e y a l l share a basis o f renewable resource d e r i v a t i o n . T h e list c o u l d go o n .

A s a common

d e n o m i n a t o r , the o u t p u t i n t h i s research category is specific o r g a n i c c o m p o u n d s for r e a c t i o n i n t o the s y n t h e t i c adhesive p o l y m e r s we k n o w a n d use t o d a y . I t is u n d e r s t o o d t h a t the prices o f c h e m i c a l c o m p o u n d s d e r i v e d f r o m these sources w i l l be s u b s t a n t i a l l y higher i n m o s t cases. However, o r g a n i c c h e m i c a l prices i n general w i l l be e q u a l l y higher due t o g l o b a l l i m i t a t i o n s o n access or s u p p l y of crude o i l a n d n a t u r a l gas. T h e second category of i n d u s t r y - f a v o r e d adhesive research involves s y n t h e t i c

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

resins of recognizable p e r f o r m a n c e based o n p a r t i a l or t o t a l r e p l a c e m e n t

of

a c r i t i c a l p e t r o c h e m i c a l c o n s t i t u e n t s u c h as p h e n o l w i t h a f u n c t i o n a l o r g a n i c c o m p o u n d or residue d e r i v e d f r o m renewable sources. E x a m p l e s here i n c l u d e :

1. T h e i n s t i t u t i o n of f r a c t i o n a t e d or c h e m i c a l l y m o d i f i e d l i g n i n for p a r t or a l l o f the p h e n o l i n the synthesis o f p h e n o l - f o r m a l d e h y d e resins.

This

w o u l d p a r t i c u l a r l y i n c l u d e the newer f o r m s o f l i g n i n recovered w i t h m i n i m u m s t r u c t u r a l a l t e r a t i o n a n d also those r e p r e s e n t i n g v i r t u a l l y c o m p l e t e depolymerization to phenylpropane units.

2. T h e s u b s t i t u t i o n of selected a n d p o s s i b l y m o d i f i e d c a r b o h y d r a t e s for p a r t or a l l of the p h e n o l i n the synthesis of p h e n o l - f o r m a l d e h y d e resins.

3. T h e r e a c t i o n of i s o l a t e d a n d p r o b a b l y f u n c t i o n a l i z e d t a n n i n s f r o m n a t u r a l sources w i t h f o r m a l d e h y d e t o y i e l d low t e m p e r a t u r e - c u r i n g thermoset adhesives. T h e s e resins m a y be s u i t a b l e for use alone or i n c o m b i n a t i o n w i t h c o n v e n t i o n a l r e s o r c i n o l - f o r m a l d e h y d e or p h e n o l - r e s o r c i n o l - f o r m a l d e h y d e resins.

4. T h e i n c o r p o r a t i o n of a n i m a l or vegetable p r o t e i n c o n s t i t u e n t s i n t o p h e n o l i c resins t o f o r m e x t e r i o r d u r a b l e adhesives o f f a s t - c u r i n g or s p e c i a l properties.

5. T h e c r e a t i o n o f d i f u n c t i o n a l or m u l t i f u n c t i o n a l i s o c y a n a t e molecules e n t i r e l y ' b a s e d o n renewable resource c h e m i s t r y .

6. T h e development o f useful adhesive c o m p o s i t i o n s based o n the i n t e r a c t i o n of i s o c y a n a t e resins w i t h n a t u r a l p o l y m e r s s u c h as l i g n i n , p r o t e i n s , a n d carbohydrates.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

T h e t h i r d category of adhesive research t h a t is p a r t i c u l a r l y i n t e r e s t i n g t o the w o o d w o r k i n g i n d u s t r y relates t o the development o f e n t i r e l y new adhesive concepts, i n c l u d i n g p r e t r e a t m e n t s of w o o d surfaces t o enhance the b o n d i n g c a p a b i l i t i e s o f c o n v e n t i o n a l adhesives. T h i s w o u l d even i n c l u d e the u n l i k e l y b u t t e m p t i n g p o s s i b i l i t y of a u t o a d h e s i o n of w o o d t o itself. E x a m p l e s here are fewer but tantalizing:

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1. T h e adhesion or " w e l d i n g " of w o o d surfaces t o each other o n the basis of a c h e m i c a l p r e t r e a t m e n t of the surfaces a n d p r o b a b l y heat a c t i v a t i o n . 2. T h e recovery a n d r e a c t i v a t i o n of n a t u r a l adhesive or l i v i n g s t r u c t u r e p o l y mers i n t o crosslinkers for r a w or treated w o o d surfaces. E x a m p l e s of these w o u l d be: • activated lignins • c a r b o h y d r a t e s converted in situ t o crude yet f u n c t i o n a l f u r a n resins • solubilized chitin • recovered m a r i n e bioadhesives a c t i v a t e d t o b o n d w o o d • the conversion of cellulose itself or cellulose derivatives i n t o d u r a b l e adhesives for w o o d T h e f o u r t h research category m e n t i o n e d i n the N F P A review relates t o e n h a n c i n g the performance of established n a t u r a l adhesives for w o o d b o n d i n g t o p r o v i d e d u r a b i l i t y equivalent t o t h a t of the s y n t h e t i c s . T h i s is especially desirable where n a t u r a l adhesives presently offer significant p e r f o r m a n c e advantages over s y n t h e t i c s i n t e r m s of fast hot-press t i m e s , short-cycle c o l d cure, or i m p r o v e d g a p - f i l l i n g p r o p e r t i e s . Specific examples w o u l d i n c l u d e : 1. B l o o d glues w i t h p e r m a n e n t l y b o i l - p r o o f a n d m o l d - r e s i s t a n t b o n d s . ( B o t h h o t - a n d c o l d - s e t t i n g f o r m u l a t i o n s w o u l d be desirable.) 2. S o y b e a n - b a s e d , q u i c k - c l a m p i n g cold-press glues of exterior d u r a b i l i t y a n d m o l d resistance. 3. W e a t h e r p r o o f a n d p e r m a n e n t l y m o l d - r e s i s t a n t casein-based l a m i n a t i n g glues. ( T h i s w o u l d i n c l u d e b o t h l o w - s t a i n i n g f o r m u l a t i o n s for d o o r a n d m i l l work assembly a n d m o r e h i g h l y a l k a l i n e l u m b e r - l a m i n a t i n g adhesives.) 4. Q u i c k - s e t t i n g collagen-based adhesives for f u r n i t u r e a n d cabinet assembly t h a t w o u l d become p e r m a n e n t l y i n s o l u b i l i z e d against the effects o f h i g h h u m i d i t y i f not a c t u a l w e t t i n g after n o r m a l c o l d cure. 5. S p r a y a b l e exterior adhesives of c o m p e t i t i v e performance for s t r u c t u r a l panels such as flakeboards, waferboards, a n d s t r a n d b o a r d s based o n renewable resources. ( A b l o o d - l i g n i n adhesive for oriented s t r a n d b o a r d or w a f e r b o a r d w o u l d be a n example.)

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

1.

LAMBUTH

Historical Perspective

9

It s h o u l d be p o i n t e d o u t t h a t some n a t u r a l adhesives a n d c o n s t i t u e n t s r e m a i n i n general use t o d a y , m o s t l y because the properties t h e y c o n t r i b u t e are n o t yet p r o v i d e d b y s y n t h e t i c adhesives, or at as favorable a p r i c e . S u c h c u r r e n t uses include: 1. A l k a l i n e - d i s p e r s e d amylaceous m a t e r i a l s i n p h e n o l i c p l y w o o d adhesives for i m p r o v e d assembly t i m e tolerance a n d prepress t a c k . 2. P a r t i a l l y i n s o l u b i l i z e d a n i m a l b l o o d as a very efficient f o a m i n g agent i n a i r - e x t e n d e d p h e n o l i c p l y w o o d glues. T h e b l o o d solids are also considered

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

active e x t e r i o r adhesive s o l i d s . 3. C a s e i n - s o y b e a n adhesives for a s s e m b l i n g flush d o o r s i n s h o r t , r o o m - t e m p e r a t u r e - c u r i n g cycles. 4. F u l l y s o l u b l e a n i m a l b l o o d i n u r e a r e s i n glues for h a r d w o o d p l y w o o d

to

i m p r o v e water resistance. 5. S t r a i g h t casein l u m b e r l a m i n a t i n g adhesives for t h e i r s u p e r i o r o p e n a n d closed b e a m assembly t i m e tolerance a n d g a p - f i l l i n g p r o p e r t i e s .

I n v i e w of these suggestions a n d e x a m p l e s , i t is evident t h a t the w o o d p r o d ucts i n d u s t r y r e t a i n s i t s f a i t h i n n a t u r a l adhesives a n d t h e i r c a p a b i l i t i e s even i n t h i s e r a o f s y n t h e t i c s . It is l i k e l y t h a t the i n d u s t r y w i l l continue t o t u r n t o t h e m w i t h o u t r e s t r a i n t as t h e i r p r i c e or p e r f o r m a n c e d i c t a t e s . T h e desire, of course, is t o keep the v a r i o u s w o o d - b o n d i n g o p e r a t i o n s f u n c t i o n i n g as efficiently as free market conditions and competitive innovation w i l l permit.

Industry Priorities I n a r e s t r i c t i v e s i t u a t i o n where p e t r o c h e m i c a l s are n o longer freely a v a i l a b l e , essential p r i o r i t i e s emerge. T h e first p r i o r i t y , of course, is t o m a i n t a i n the p e r f o r m a n c e o f a n y g i v e n w o o d p r o d u c t as near n o r m a l as possible a n d adequate for the i n t e n d e d p u b l i c use.

O u r current l i a b i l i t y a n d i m p l i e d w a r r a n t y laws

prevent the i n d u s t r y f r o m d o i n g otherwise. A s a second p r i o r i t y , w o o d w o r k i n g c o m p a n i e s w i l l consider p a y i n g whatever a m o u n t is necessary t o o b t a i n adhesives t h a t p e r m i t the m a n u f a c t u r e of on-grade p r o d u c t s at n o r m a l p r o d u c t i o n rates a n d costs. T h e a s s u m p t i o n is t h a t the entire c o m p e t i n g i n d u s t r y w i l l have t o i n c u r t h i s same increased adhesive cost, so the p r o d u c t price s t r u c t u r e w i l l r e m a i n u n i f o r m b u t at a h i g h e r l e v e l . T h e t h i r d p r i o r i t y , t h a t o f c h a n g i n g p l a n t process or r e d u c i n g p l a n t capacity, w i l l o n l y be i m p l e m e n t e d after a l l reasonable a l t e r n a t i v e s have been e x h a u s t e d . T h e s e r e d u c t i o n s m a y take the f o r m o f longer press t i m e s , m o r e c o m p l e x

or

l i m i t e d assembly procedures, or r e s t r i c t i v e h a n d l i n g r e q u i r e m e n t s d i c t a t e d by the o p e r a t i n g characteristics o f a v a i l a b l e adhesives. L o s s o f p r o d u c t i v e c a p a c i t y

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

for a n y o f these reasons means h i g h e r u n i t costs t h a t c a n q u i c k l y reverse the modest profit m a r g i n s o n c o m m o d i t y w o o d p r o d u c t s . T h e r e m a i n i n g choice, of course, is s h u t d o w n . Since s h u t d o w n represents a clear loss b o t h t o the p r o d u c e r a n d the p u b l i c , there is a n expressed w i l l i n g n e s s w i t h i n the w o o d p r o d u c t s i n d u s t r y t o accept (even i f r e l u c t a n t l y ) considerable p r o d u c t i o n change i n the interests of c o n t i n u e d o p e r a t i o n . F r o m t h i s i n d u s t r y p o s i t i o n , the message t o adhesive scientists seems clear a n d s u p p o r t i v e a l t h o u g h p e r h a p s i n d i r e c t . N a m e l y :

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch001

1. T h e w o o d w o r k i n g i n d u s t r y sees a considerable p a r t o f i t s f u t u r e i n g l u e d products of increasing volume and sophistication. 2. E s p e c i a l l y because of i t s v u l n e r a b i l i t y t o i n t e r r u p t i o n i n p e t r o c h e m i c a l a d hesive raw m a t e r i a l supplies, the w o o d w o r k i n g i n d u s t r y s t r o n g l y endorses research i n t o p r o d u c t i o n adhesives based o n renewable resources. 3. T h e fact t h a t adhesives based o n renewable resources m a y not be f u l l y c o m p e t i t i v e i n price or performance w i t h t o d a y ' s p r o d u c t i o n adhesives s h o u l d n o t be a deterrent t o t h e i r development a n d o p t i m i z a t i o n . 4. M o r e i m p o r t a n t l y , i t s h o u l d be u n d e r s t o o d t h a t f a i l u r e b y i n d u s t r y t o i m m e d i a t e l y a d o p t a n d u t i l i z e a n adhesive based o n renewable resources is i n n o w a y a reflection o n i t s p e r f o r m a n c e or v a l u e . A s far as the w o o d w o r k i n g i n d u s t r y is concerned, i t represents v i t a l reserve technology t h a t w i l l be i m p l e m e n t e d as c i r c u m s t a n c e s r e q u i r e . 5. F i n a l l y , for those adhesive developments based o n renewable resources t h a t are i m m e d i a t e l y c o m p e t i t i v e a n d / o r u n i q u e i n p e r f o r m a n c e , the w o o d p r o d u c t s i n d u s t r y w i l l do i t s share to assist w i t h t h e i r e v a l u a t i o n a n d use. C o m m e r c i a l g u i d a n c e t o w a r d t h i s end w i l l be freely p r o v i d e d .

Conclusion T h e s e t h o u g h t s a n d suggestions are i n d u s t r i a l l y o r i e n t e d , t o be sure. T h e y arise f r o m p r a c t i c a l need a n d reflect concern for f u t u r e adhesive s u p p l y . C o l l e c t i v e l y , the v a r i o u s forms o f w o o d u t i l i z a t i o n represent a n e x t r e m e l y large a n d diverse m a r k e t for adhesives, p r o b a b l y the largest i n the w o r l d t o d a y . T h u s , i n d u s t r i a l c o m m e n t s seem a p p r o p r i a t e . A p a r t f r o m i d e n t i f i e d needs, however, the w o o d p r o d u c t s i n d u s t r y recognizes t h e value o f research i n t o t h e c h e m i c a l s t r u c t u r e a n d adhesive m e c h a n i s m s of n a t u r a l p o l y m e r s u n r e l a t e d t o c u r r e n t p r o b l e m s . T h e n e x t echelon o f t e c h n i c a l development c a n be expected t o arise f r o m t h i s research. It is also acknowledged t h a t c e r t a i n o f the adhesive p e r f o r m a n c e c h a r acteristics requested c a n n o t be a c c o m p l i s h e d w i t h the c u r r e n t level o f scientific i n f o r m a t i o n . F i n a l l y , i t is the w o o d p r o d u c t s i n d u s t r y ' s v i e w t h a t n a t u r a l a d h e sives a n d resources w i l l i n e v i t a b l y p l a y a n i m p o r t a n t p a r t i n i t s f u t u r e . T h u s , they represent a significant a n d p o t e n t i a l l y p r o d u c t i v e area for current adhesive research. R E C E I V E D May 27,1988

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 2 Lignin in Adhesives Introduction and Historical Perspective

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

Norman

G.

Lewis

and

Thomas

R.

Lantzy

W o o d Chemistry and Biochemistry Department of Forest Products V i r g i n i a Polytechnic Institute and State University Blacksburg, VA 24061

Lignins, complex organic polymers produced by all vascular terrestrial plants and second in abundance only to cellulose, are the substances holding plant fibers together. They are recovered mainly as byproducts from woodpulping operations with about 75 million tons produced annually worldwide. Over the last hundred years or so, there has been an enormous effort to develop lignin-based adhesives, but this has met with no real commercial success principally due to product variability, dark color, and lack of chemical reactivity. Lignin-based adhesives normally require excessively long curing times and high curing temperatures during composite board production. However, they can be employed as extenders in diverse wood-composite resins with no significant deterioration in the mechanical properties of the board products. This is particularly true if the lignins are activated chemically (e.g., by methylolation). Several recent reports have been directed toward improving even further the lignin chemical reactivity (e.g., in the synthesis of soda bagasse lignin-formaldehyde-resorcinol and lignin-isocyanate resins). Apparently, these developments surmount previous difficulties and allow for some cautious optimism for the future. T e r r e s t r i a l vascular p l a n t s have evolved w i t h a u n i q u e c a p a c i t y t o synthesize l i g n i n , whose m a i n p h y s i o l o g i c a l functions are t o p r o v i d e r i g i d i t y a n d s t r e n g t h to p l a n t cell w a l l s a n d t o act as a b a r r i e r t o i n f e c t i o n (1). N e x t t o cellulose, l i g n i n i s n a t u r e ' s second most a b u n d a n t o r g a n i c m a t e r i a l a n d is often described as the m a t e r i a l b i n d i n g p l a n t fibers together (#). 0097-6156/89/0385-0013$06.00/0 * 1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

14

ADHESIVES F R O M RENEWABLE RESOURCES

I n g y m n o s p e r m s , l i g n i n is f o r m e d f r o m j>-coumaryl (1) a n d c o n i f e r y l (2) a l cohols, whereas, i n angiosperme, s i n a p y l a l c o h o l (3) is also i n v o l v e d (3). L i g n i f i c a t i o n is generally viewed t o occur e x c l u s i v e l y v i a the r a n d o m , d e h y d r o g e n a t i v e p o l y m e r i z a t i o n o f m o n o l i g n o l s (1) - (3) (^), a r e a c t i o n r e q u i r i n g b o t h H2O2 a n d peroxidase (5) ( F i g u r e 1). It is also w e l l k n o w n t h a t the r a t i o of m o n o l i g n o l s (1) - (3) i n v o l v e d i n the l i g n i f i c a t i o n process is species (6), t i m e (7), l i g h t (8) a n d m o r p h o l o g i c a l o r i g i n (9,10) dependent. L i g n i f i c a t i o n c a n a p p a r e n t l y also be influenced b y g r a v i t a t i o n a l forces experienced b y p l a n t s d u r i n g g r o w t h (11-19). T h e f o l l o w i n g conclusions c a n be m a d e w i t h regard t o current knowledge of the l i g n i f i c a t i o n process: 1) s t r i c t e n z y m a t i c c o n t r o l l e a d i n g t o the f i n a l p r o d u c t a p p a r e n t l y does n o t o c c u r a n d 2) b o t h r e g u l a t o r y processes c o n t r o l l i n g i t s d e p o s i t i o n a n d s t r u c t u r e in situ are p o o r l y u n d e r s t o o d . L i g n i n f o r m a t i o n i n p l a n t s of m a n y f a m i l i e s of A n g i o s p e r m a e , p a r t i c u l a r l y those i n C o m m e l i n i d a e of C r o n q u i s t (SO) (i.e., grasses), suffers f r o m a n a d d i t i o n a l c o m p l i c a t i o n due t o the presence of c e l l - w a l l - b o u n d h y d r o x y c i n n a m i c acids, s u c h as p - c o u m a r i c (4) (21), ferulic (5) (22,23), 5 - h y d r o x y f e r u l i c (6) (24), d i f e r u l i c (7) (23,25,26), a n d 4 , 4 / - d i h y d r o x y t r u x i l l i c (8) acids (27) ( F i g u r e 2). T h e s e acids have l o n g been s p e c u l a t e d t o b e i n v o l v e d d i r e c t l y i n l i g n i f i c a t i o n , a n d t h i s is o n l y n o w b e i n g c l a r i f i e d . T h i s c l a r i f i c a t i o n was achieved b y a d m i n i s t e r i n g specifically C - l a b e l l e d forms of ferulic a c i d (5) t o wheat ( Triiicum aestivum L . ) . Subsequent a n a l y s i s of the p l a n t tissue (28) a n d i s o l a t e d l i g n i n s (29) b y s o l i d a n d s o l u t i o n state C - N M R , respectively, revealed t h a t these acids were c o v a l e n t l y b o n d e d t o l i g n i n . 1 3

1 3

Lignin and Papermaking T h e discovery of l i g n i n a n d i t s subsequent use i n adhesive f o r m u l a t i o n s are i n t e r t w i n e d w i t h t e c h n o l o g i c a l developments i n the p u l p a n d p a p e r i n d u s t r y . S u r p r i s i n g l y , i t is not generally a p p r e c i a t e d t h a t the massive w o r l d w i d e p r o d u c t i o n of p u l p a n d p a p e r , u s i n g w o o d as a resource, o n l y b e g a n a b o u t 1850 or so. T h i s is i n spite of the fact t h a t f o r m a t i o n of p a p e r f r o m w o o d (e.g., b y t r e a t m e n t o f m u l b e r r y b a r k w i t h lye) h a d been developed b y T s ' a i L u n i n 105 A . D . i n C h i n a (SO) a n d perhaps even earlier b y others (31). However, b y the t i m e t h i s t e c h n o l o g y reached the W e s t e r n H e m i s p h e r e v i a the M i d d l e E a s t , w o o d h a d l o n g been replaced b y other p l a n t m a t e r i a l s o f higher cellulosic c o n tent (e.g., c o t t o n , l i n e n , flax). W o o d r e m a i n e d forgotten as a source of p a p e r u n t i l R e n e A . F . de R e a m u r (1683-1757) n o t e d t h a t wasps p r o d u c e d a p a p e r l i k e nest f r o m w o o d (30). I n 1839, P a y e n discovered t h a t w o o d was n o t homogeneous b u t c o n t a i n e d cellulose a n d a n " i n c r u s t i n g m a t e r i a F (32-34) for w h i c h S c h u l t z e coined the t e r m l i g n i n i n 1865 (35). A s s h o w n i n T a b l e I, c h e m i c a l w o o d p u l p i n g processes were developed t o dissolve away l i g n i n , hemicelluloses, a n d extractives (30). T h e s e represent the m a j o r w o o d p u l p i n g processes i n o p e r a t i o n today.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LEWIS AND LANTZY

Lignins in Adhesives: Introduction

-Η©· OH

free-radical coupling

1, R R «H r

2

2, R «OCH ,R aH 1

3

2

3, R .R «OCH

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

t

2

Lignin

3

F i g u r e 1. L i g n i n f o r m a t i o n f r o m m o n o l i g n o l s (1) - (3).

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

16

ADHESIVES F R O M RENEWABLE RESOURCES

T a b l e I. M a j o r C h e m i c a l P u l p i n g Processes Type

Developer(s)

Soda Sulphite Kraft

T i l g h m a n (1857) D a h l (1884)

Burgess a n d W a t t (1854)

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

Sources of Lignin E s s e n t i a l l y a l l of the l i g n i n c o m m e r c i a l l y a v a i l a b l e is i s o l a t e d as b y p r o d u c t s f r o m either the s u l p h i t e or the k r a f t process. T a b l e II gives a very conservative i d e a of a n n u a l l i g n i n p r o d u c t i o n i n the U n i t e d States (2) a n d w o r l d w i d e (36). T a b l e I I . E s t i m a t e d A n n u a l P r o d u c t i o n of L i g n i n ( m i l l i o n s of tons) U n i t e d States

Worldwide

Kraft lignin

Type

20

Lignosulphonates (Sulphite pulping)

1.5

75 15

I n a d d i t i o n t o k r a f t or s u l p h i t e l i g n i n s , there are a n u m b e r of other p r o cesses w h e r e b y l i g n i n c o u l d p o t e n t i a l l y be recovered (e.g., b y a c i d o l y s i s , s t e a m e x p l o s i o n , organosolv, b i o l o g i c a l t r e a t m e n t , etc). T h e e x i s t i n g a n d p o t e n t i a l processes for l i g n i n recovery are described briefly i n the f o l l o w i n g sections. Kraft Pulping. T h i s is the m a j o r w o o d p u l p i n g process a n d p o t e n t i a l l y represents the p r i m a r y source of t e c h n i c a l l i g n i n . D u r i n g p u l p i n g , cellulosic fibers are o b t a i n e d f r o m w o o d b y t r e a t m e n t w i t h solutions of s o d i u m h y d r o x i d e a n d s u l p h i d e at elevated t e m p e r a t u r e s , pressure a n d h i g h p H . T h e hemicelluloses ( a n d some cellulose) are degraded t o give m a i n l y isosaccharinic acids, the c h e m i s t r y of w h i c h has been adequately described elsewhere (37). O n the other h a n d , the l i g n i n released f r o m the cell w a l l d u r i n g p u l p i n g increases i n m o l e c u l a r size as d e l i g n i f i c a t i o n proceeds (38) a n d is h i g h l y p o l y disperse (39). K r a f t spent p u l p i n g l i q u o r s thus consist of l i g n i n ( « 4 7 % ) , h y d r o x y acids ( « 2 8 % , e.g., i s o s a c c h a r i n i c a c i d ) , i n o r g a n i c s , a n d s m a l l q u a n t i t i e s of other organics (37). L i g n i n c a n be i s o l a t e d f r o m these spent p u l p i n g l i q u o r s as a p r e c i p i t a t e b y a c i d i f i c a t i o n . A l m o s t a l l k r a f t l i g n i n is b u r n e d for energy recovery; however, a b o u t 35,000 tons are p r o d u c e d a n n u a l l y i n the U n i t e d States for v a r i o u s c h e m i c a l b y p r o d u c t s (2). Sulphite Pulping. T h i s is a generic t e r m used t o describe various s u l p h i t e c h e m i c a l w o o d p u l p i n g processes c a r r i e d out at different pH's a n d p u l p y i e l d s (37). ( T h e t e r m y i e l d refers t o the q u a n t i t y o f fiber recovered f r o m the o r i g i n a l wood.)

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

2.

LEWIS AND LANTZY

17

Lignins in Adhesives: Introduction

I n the a c i d s u l p h i t e l o w - y i e l d p u l p i n g process, w o o d is t r e a t e d w i t h s o l u t i o n s of a m m o n i u m , s o d i u m , calcium, or magnesium s u l p h i t e / b i s u l p h i t e at low p H ( « 1-2) a n d a t elevated t e m p e r a t u r e s a n d pressures. D u r i n g t h i s t r e a t m e n t , ess e n t i a l l y a l l o f the l i g n i n s , hemicelluloses, a n d e x t r a c t i v e s are " d i s s o l v e d " away, l e a v i n g b e h i n d a fiber o f very h i g h cellulosic content. T h e hemicelluloses u n d e r g o severe h y d r o l y s i s , affording m a i n l y w a t e r - s o l u b l e monosaccharides i n t h e spent s u l p h i t e l i q u o r ( S S L ) . T h e s u l p h o n a t e d l i g n i n fragments released i n i t i a l l y d u r i n g d e l i g n i f i c a t i o n ( « 3 0 - 4 0 % l i g n i n removal) are m a i n l y m o n o m e r i c

compounds

c o n t a i n i n g either m o n o - , d i - , o r t r i - s u l p h o n i c acids (3,40). H o w e v e r , as d e l i g n i f i c a t i o n proceeds, t h e l i g n i n released f r o m t h e c e l l w a l l i s o f i n c r e a s i n g m o l e c u l a r

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

size a n d h i g h l y p o l y disperse (40). C o n s e q u e n t l y , l o w - y i e l d spent s u l p h i t e l i q u o r s ( S S L ) recovered after w o o d p u l p i n g l a r g e l y consist o f l i g n o s u l p h o n a t e s ( « 5 5 % ) , w o o d sugars ( « 2 5 - 3 0 % , e.g., glucose, m a n n o s e , etc.), i n o r g a n i c s , a n d other o r ganics i n s m a l l e r a m o u n t s (37). D e p e n d i n g u p o n the p u l p i n g process e m p l o y e d , l i g n o s u l p h o n a t e s c a n b e recovered as either a m m o n i u m , c a l c i u m , s o d i u m , o r m a g n e s i u m salts (35).

Currently, only about 2 0 % of a l l S S L materials pro-

d u c e d are used as c h e m i c a l p r o d u c t s (e.g., as i n e x p e n s i v e b i n d e r s f o r a n i m a l feed a n d d i r t r o a d s , a n d as dispersants i n o i l - w e l l d r i l l i n g a n d

cement/concrete

admixtures). Acidolysis. A c i d o l y s i s l i g n i n s are recovered f r o m processes w h e r e b y p l a n t m a t e r i a l (e.g., w o o d ) is saccharified b y t r e a t m e n t w i t h m i n e r a l acids, s u c h as s u l p h u r i c o r h y d r o c h l o r i c acids (41)· T h e l i g n i n is recovered p r i m a r i l y as a n i n s o l u b l e residue. T h i s process h a s been used i n E u r o p e i n t h e p a s t , b u t is n o t commercially important i n the Western Hemisphere. Steam Explosion. S t e a m - e x p l o s i o n l i g n i n s are o b t a i n e d f r o m w o o d (or some other p l a n t m a t e r i a l ) t h a t h a s been s u b j e c t e d briefly t o h i g h t e m p e r a t u r e s a n d pressures followed b y r a p i d decompression (42). T h i s process i s used t o a l i m i t e d extent t o d a y p a r t i c u l a r l y for t h e processing o f l o w - q u a l i t y h a r d w o o d s .

The

l i g n i n s recovered are o f r e l a t i v e l y l o w m o l e c u l a r weight ( M « 700) a n d soluble n

i n either a l k a l i o r c e r t a i n o r g a n i c solvents (42,43). Organosolv. O r g a n o s o l v l i g n i n s are o b t a i n e d as r e l a t i v e l y l o w - m o l e c u l a r - w e i g h t entities b y t r e a t m e n t o f p l a n t tissue w i t h aqueous s o l u t i o n s o f o r g a n i c solvents, n o r m a l l y c o n t a i n i n g trace a m o u n t s o f m i n e r a l acids (44)-

Solvents i n c l u d e

e t h a n o l , m e t h a n o l , b u t a n o l , acetic a c i d , e t h y l acetate, p h e n o l , e t c . T o d a t e , t h i s a p p r o a c h h a s n o t been c o m m e r c i a l i z e d d u e t o t h e q u a n t i t i e s o f o r g a n i c solvents c o n s u m e d a n d t h e l o w q u a l i t y o f the p u l p fiber o b t a i n e d . Enzymatic Liberation. T h i s is a process w h e r e b y l i g n i n - r i c h residues are o b tained b y treatment of plant material w i t h cellulases/hemicellulases/pectinases, etc.

T h e s e l i g n i n p r e p a r a t i o n s m a y m o r e closely resemble " n a t i v e " l i g n i n d u e

to t h e v e r y m i l d processing c o n d i t i o n s e m p l o y e d .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

18

ADHESIVES F R O M RENEWABLE RESOURCES

Lignin in Wood-Composite Adhesives

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

It is w o r t h w h i l e t o review the U . S . m a r k e t size for the four p r i n c i p a l resins c u r ­ r e n t l y used i n w o o d - p a n e l p r o d u c t s t o d a y (^5). T h e s e are p h e n o l - f o r m a l d e h y d e ( P F ) , urea-formaldehyde ( U F ) , melamine-formaldehyde ( M F ) , and resorcinolf o r m a l d e h y d e ( R F ) ( T a b l e I I I ) . W h e n these p r o d u c t i o n figures are c o m p a r e d t o the q u a n t i t i e s o f l i g n i n p o t e n t i a l l y a v a i l a b l e ( T a b l e I I ) , i t is i m m e d i a t e l y o b v i o u s t h a t a l l w o o d adhesives c o u l d be replaced b y o n l y a very s m a l l f r a c t i o n o f the l i g n i n p r o d u c e d a n n u a l l y d u r i n g c h e m i c a l w o o d p u l p i n g processes.

T a b l e I I I . U . S . P r o d u c t i o n of T h e r m o s e t t i n g R e s i n s (1983) i n M e t r i c T o n s (χ 1 0 ) 3

Resin

1

RF UF MF PF Totals

Total

Wood Products

15.5 586.0 90.0 660.0

1.5 440.0 5.0 297.0

1,351.5

743.5

* R F = resorcinol-formaldehyde U F = urea-formaldehyde M F = melamine-formaldehyde P F = phenol-formaldehyde

T h e r e have been m a n y a t t e m p t s t o replace these resins w i t h l i g n i n d e r i v a ­ tives for w o o d c o m p o s i t e adhesives s u i t a b l e for p l y w o o d , p a r t i c l e b o a r d a n d w a f e r b o a r d . M o s t of these studies have been e m p i r i c a l i n n a t u r e , a n d few have achieved f u r t h e r c o n s i d e r a t i o n for i n d u s t r i a l a p p l i c a t i o n . A s w o o d b i n d e r s , t e c h ­ n i c a l l i g n i n s are v a r i a b l e i n q u a l i t y a n d p o o r l y reactive i n c o m p a r i s o n t o c o n ­ v e n t i o n a l resin systems s u c h as p h e n o l - f o r m a l d e h y d e ( P F ) resins. C o n s e q u e n t l y , t h e y are n o t u t i l i z e d o n t h e i r o w n . Indeed, i f t h e y were, t h i s w o u l d adversely affect p r o d u c t i o n q u a l i t y a n d t i m e s , a n d necessitate e q u i p m e n t changes. I n the w o o d c o m p o s i t e i n d u s t r y , resins h a v i n g s u c h deleterious effects are n o t l i k e l y t o be used even if savings could be made in terms of material costs. Progress t o w a r d p r o d u c i n g i n d u s t r i a l l y acceptable l i g n i n adhesives c a n be b r o k e n d o w n i n t o t w o m a i n categories as either 1) l i g n i n - b a s e d b i n d e r s (by themselves as s u c h or i n c h e m i c a l l y m o d i f i e d f o r m ) , or 2) as c o p o l y m e r s ( w i t h other r e a c t a n t adhesives). Lignosulphonates. C r u d e S S L c a n be o b t a i n e d as a b r o w n i s h , s p r a y - d r i e d powder or as a viscous, hygroscopic, d a r k - c o l o r e d l i q u i d . S S L a n d the l i g n o ­ s u l p h o n a t e s present i n i t have been the focus o f n u m e r o u s efforts to p r o d u c e a n

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

2.

LEWIS AND LANTZY

19

Lignins in Adhesives: Introduction

i n d u s t r i a l l y useful adhesive. E s s e n t i a l l y , there are t w o m e t h o d s o f c u r i n g S S L based adhesives, n a m e l y , b y t h e r m o s e t t i n g o r b y free-radical p o l y m e r i z a t i o n .

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

W i t h respect t o t h e r m o s e t t i n g , i t h a s been w e l l d o c u m e n t e d t h a t crude C a based S S L c a n be used as a p a r t i c l e b o a r d adhesive (46)- T h i s a p p l i c a t i o n h a s been e v a l u a t e d o n a m i l l - s c a l e basis i n D e n m a r k , F i n l a n d , a n d S w i t z e r l a n d , b u t h a s n o t been a d o p t e d o n a c o m m e r c i a l scale. T h i s is because resin c u r i n g r e q u i r e d b o t h h i g h press a n d autoclave temperatures as w e l l as l o n g h e a t i n g t i m e s . W h i l e t h i s development was a " t e c h n i c a l " success, i t was - a c c o r d i n g to N i m z (36) - never c o m m e r c i a l i z e d due t o t h e frequency o f fires experienced during mill-scale trials. Subsequent a t t e m p t s t o i m p r o v e the properties (i.e., r e a c t i v i t y ) o f S S L adhesives have essentially e m p l o y e d either a c i d i f i c a t i o n o f C a - b a s e d S S L o r m e m b r a n e filtration o f the crude p u l p i n g l i q u o r s . A c i d i f i c a t i o n o f C a - S S L w i t h concentrated H2SO4 gave a n adhesive s u i t a b l e for p a r t i c l e b o a r d a p p l i c a t i o n s (47). However, processing parameters s t i l l required h i g h press t e m p e r a t u r e ( « 204 ° C ) , press t i m e s (5-7 m i n ) , a n d pressure (400 p s i ) . T h e very l o w p H ( < 1) o f t h e resin used m a y also have a l o n g t e r m corrosive effect o n n a i l s , staples, etc., a n d engender w o o d d e t e r i o r a t i o n . M e m b r a n e filtration o f S S L shows s o m e w h a t greater p r o m i s e . T h i s a p p r o a c h was first r e p o r t e d b y Forss et a l . (48,49) * t h e development o f K A R A T E X , a P F / l i g n i n adhesive b i n d e r c o n t a i n i n g either l i g n o sulphonates o r k r a f t l i g n i n s o f n o m i n a l m o l e c u l a r weight > 5000 as d e t e r m i n e d by passage t h r o u g h a m e m b r a n e . A p p l y i n g t h i s a p p r o a c h , S h e n a n d C a l v e (50) e x a m i n e d t h e w a f e r b o a r d b i n d i n g properties o f a n a m m o n i u m - b a s e d S S L t h a t h a d been subjected t o m e m b r a n e filtration. B o a r d pressing c o n d i t i o n s were s t i l l excessive (e.g., 8 m i n at 210 ° C for 1 1 - m m - t h i c k w a f e r b o a r d ) . Best b o a r d properties were o b t a i n e d w i t h t h e l o w - m o l e c u l a r weight permeate ostensibly o f < 5,000 m o l e c u l a r weight a n d c o n t a i n i n g s u l p h o n a t e d l i g n i n s a n d m o n o s a c c h a rides. O n t h e other h a n d , t h e l i g n o s u l p h o n a t e retentate ( > 5,000 m o l w t ) gave b o a r d s o f unacceptable m e c h a n i c a l properties. n

It s h o u l d be recognized at t h i s p o i n t t h a t 1) t h e l i g n o s u l p h o n a t e s ( < 5,000 m o l w t ) l a r g e l y consist o f the m o n o m e r s c o n t a i n i n g m o n o - , d i - o r t r i - s u l p h o n i c acids as p r e v i o u s l y described (3,40), a n d 2) t h e m e c h a n i c a l properties o f t h e waferboards were d e t e r m i n e d largely b y monosaccharide, r a t h e r t h a n l i g n o s u l p h o n a t e , content (51). It was subsequently proven, under c o n t r o l l e d l a b o r a t o r y c o n d i t i o n s , t h a t the rate o f t h e r m o s e t t i n g o f b o t h h i g h a n d l o w m o l e c u l a r weight l i g n o s u l p h o n a t e s can be i m p r o v e d b y increasing the m o n o s a c c h a r i d e c o n tent o f t h e adhesive (52). I n a n analogous m a n n e r , f o r m a l d e h y d e was s h o w n to b e capable o f s l i g h t l y i n c r e a s i n g t h e rate o f t h e r m o s e t t i n g , p r e s u m a b l y b y increasing the rate of crosslinking. However, w h i l e t h e use o f f r a c t i o n a t e d NH4-SSL r e m a i n s a " t e c h n i c a l success," t h e t h e r m o s e t t i n g rates are s t i l l very l o w i n c o m p a r i s o n t o P F resins. Therefore, t h e l i k e l i h o o d o f p r o d u c i n g a c o m m e r c i a l l y acceptable t h e r m o s e t t i n g l i g n o s u l p h o n a t e - b a s e d resin is s t i l l very f a r f r o m reality.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

20

ADHESIVES F R O M RENEWABLE RESOURCES

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

L i g n o s u l p h o n a t e s i n crude S S L c a n also be o x i d a t i v e l y p o l y m e r i z e d b y either c h e m i c a l (36,53) or b i o c h e m i c a l (54) means. I n the f o r m e r process, o x i d a n t s such as h y d r o g e n p e r o x i d e , c a t a l y z e d b y s u l p h u r d i o x i d e (or p o t a s s i u m f e r r i c y a n i d e ) , c a n b e used t o cure fermented C a - b a s e d S S L . T h i s was f o u n d t o be s u i t a b l e as a n adhesive for m e d i u m - d e n s i t y i n t e r i o r - g r a d e p a r t i c l e b o a r d (36,53). O p t i m u m b o n d i n g c o n d i t i o n s used 2 0 % o f a t e c h n i c a l S S L ( 5 4 % ) , 9 % o f a 3 5 % H2O2 s o l u t i o n , 4 % a m m o n i u m c h l o r i d e a n d 0.6% SO2 for b o n d i n g p a r t i c l e b o a r d at 120 ° C w i t h a press t i m e o f 5 m i n . D i f f i c u l t i e s experienced p r e v i o u s l y i n c o n t r o l l i n g the e x o t h e r m i c n a t u r e o f t h i s c u r i n g r e a c t i o n have a p p a r e n t l y been resolved. W h e t h e r t h i s development w i l l receive c o m m e r c i a l endorsement r e m a i n s t o be seen. A n o t h e r a p p r o a c h t o c u r i n g S S L b y o x i d a t i v e p o l y m e r i z a t i o n e m p l o y s the use o f e n z y m e s (54)- I n t h a t s t u d y , S S L was t r e a t e d w i t h the w h i t e - r o t fungus Fomes annosus a n d a l a c c a s e - i n d u c i n g phenoloxidase u n t i l the s o l u t i o n reached a " h o n e y l i k e " consistency. T h i s viscous l i q u i d was t h e n s u b s e q u e n t l y used t o b o n d w o o d p a r t i c l e s together at a pressure o f 0.03 k g c m " . It now needs t o be e s t a b l i s h e d w h e t h e r the m e c h a n i c a l properties o f these b o a r d s s u r v i v e accelerated a g i n g tests. T h e a p p l i c a t i o n o f l i g n o s u l p h o n a t e s as a n extender or co-reactant i n P F or U F resins has been w e l l s t u d i e d , i n d u s t r i a l l y a p p l i e d , a n d e x t e n s i v e l y d o c u m e n t e d i n a recent comprehensive review (36). Since t h a t s t u d y , waferboards have been p r o d u c e d w i t h excellent m e c h a n i c a l properties after b e i n g b o n d e d at 204 ° C , 4 t o 5 m i n , 3375 k P a w i t h a l i g n o s u l p h o n a t e - P F resin (55). T h e p h e n o l i c r e s i n was m o d i f i e d b y use o f K 3 F e ( C N ) e s t a b i l i z e d l i g n o s u l p h o n a t e s ; b o t h p h e n o l a n d the l i g n o s u l p h o n a t e s were used i n a p p r o x i m a t e l y e q u a l p r o p o r t i o n s . W i t h r e g a r d t o p o t e n t i a l l i g n i n u t i l i z a t i o n , p e r h a p s some of the best rep o r t e d results have been e n u n c i a t e d by Forss et a l . (48,49). A s described p r e v i o u s l y , spent s u l p h i t e l i q u o r ( S S L ) was s u b j e c t e d t o m e m b r a n e filtration, a n d the l i g n o s u l p h o n a t e retentate ( > 5,000 n o m i n a l m o l e c u l a r weight cutoff) was used t o replace f r o m 40 t o 7 0 % o f P F resin w i t h no significant d e t e r i o r a t i o n i n m e c h a n i c a l b o a r d p r o p e r t i e s . P a r t i c l e b o a r d , p l y w o o d , a n d fiberboard were t h e n p r o d u c e d i n F i n l a n d u s i n g resins c o n t a i n i n g h i g h m o l e c u l a r weight l i g n o s u l p h o n a t e s a n d P F i n m i l l - s c a l e t r i a l s under n o r m a l processing c o n d i t i o n s , a n d t h i s use was a p p a r e n t l y successful (48,49). A w i d e l y s t a t e d advantage o f t h i s u l t r a f i l t r a t i o n a p p r o a c h is t h a t l i g n i n derivatives can be c o m m e r c i a l l y p r o d u c e d w i t h less p r o d u c t v a r i a b i l i t y . H o w e v e r , i t does not a p p e a r t h a t t h i s m e t h o d o l o g y is c u r r e n t l y b e i n g used c o m m e r c i a l l y t o p r o d u c e l i g n i n - b a s e d adhesives. 2

T h e use o f S S L or l i g n o s u l p h o n a t e s i n other p o l y m e r i c adhesive systems has also been e x a m i n e d [e.g., w i t h p o l y a c r y l a m i d e , p r o t e i n s / a l d e h y d e s , p o l y e t h y l e n e o x i d e , p o l y e t h y l e n e i m i n e , epoxides, m e l a m i n e , styrene o x i d e , p o l y i s o c y a n a t e s (36)]. S o f a r , these procedures, for different reasons, have n o t led t o a n y m a j o r p r a c t i c a l a p p l i c a t i o n (36). It w o u l d , however, be i n t e r e s t i n g t o r e e x a m i n e some o f these processes u s i n g n o t crude spent s u l p h i t e l i q u o r s , b u t i n s t e a d those purified by membrane filtration.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

2.

LEWIS AND LANTZY

21

Lignins in Adhesives: Introduction

Kraft Lignins. K r a f t l i g n i n s are n o r m a l l y o b t a i n e d as b r o w n p o w d e r s h a v i n g very b r o a d m o l e c u l a r weight d i s t r i b u t i o n s a n d v a r i a b l e p r o p e r t i e s . B o t h color a n d p r o d u c t v a r i a b i l i t y are disadvantages t h a t do n o t l e n d themselves t o easy acceptance b y resin m a n u f a c t u r e r s . T h e y are m a i n l y u n s u i t a b l e as t h e r m o s e t ­ t i n g adhesives since press t i m e s r e q u i r e d are t o o l o n g , press t e m p e r a t u r e s t o o h i g h , a n d b o a r d / p a n e l m e c h a n i c a l properties p o o r .

T h i s p o o r resin r e a c t i v ­

i t y is r e a d i l y e x p l a i n a b l e ; the p h e n o l i c content o f k r a f t l i g n i n is l o w , there are n o r m a l l y s u b s t i t u e n t s ortho a n d para t o a n y p h e n o l i c h y d r o x y l f u n c t i o n a l i t i e s , a n d i t s m o l e c u l a r size m a y prevent efficient c r o s s l i n k i n g reactions due t o steric constraints.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

K r a f t l i g n i n s are e s s e n t i a l l y a c i d - i n s o l u b l e , b u t u p t o 3 5 % b y weight of l i g n i n i n s o l u t i o n c a n be achieved u n d e r a l k a l i n e c o n d i t i o n s . H o w e v e r , as s u c h , these so­ l u t i o n s are t o o viscous t o be of a n y p r a c t i c a l use i n l i q u i d adhesive f o r m u l a t i o n s . O n e m e a n s t o reduce v i s c o s i t y difficulties has been t o o b t a i n h i g h solids ( « 4 0 % ) , l o w - v i s c o s i t y l i g n i n s o l u t i o n s b y e m p l o y i n g p h e n o l - H 2 0 or p h e n o l : H 2 Ο : N a O H (or NH3) as solvents (56).

T h i s a p p r o a c h was used t o give a p l y w o o d adhesive

w i t h excellent b o a r d p r o p e r t i e s (57).

T h e adhesive was p r e p a r e d i n a t w o -

step process b y p a r t i a l l y c o n d e n s i n g p h e n o l a n d f o r m a l d e h y d e together u n d e r alkaline conditions.

T h e r e s u l t i n g condensate was t h e n reacted w i t h a l i g n i n

concentrate a n d f o r m a l d e h y d e i n the presence o f a l k a l i t o p r o d u c e a resin o f 3 7 . 2 % s o l i d s content, p H 11.4, a n d a v i s c o s i t y o f 460 c P . L i k e l i g n o s u l p h o n a t e s , the use o f k r a f t l i g n i n as extenders or co-react a n t s i n P F a n d U F resins has been w e l l e x p l o r e d a n d o c c a s i o n a l l y i m p l e m e n t e d (36,58-60).

R e f e r r i n g a g a i n t o the w o r k by Forss (48,49),

some o f the best

results c l a i m e d , as regards P F r e p l a c e m e n t , were o b t a i n e d u s i n g h i g h m o l e c ­ u l a r weight k r a f t l i g n i n s . Indeed, p r o p e r t i e s a p p e a r e d s u p e r i o r t o those u s i n g lignosulphonates. I n r e a l t e r m s , t h o u g h , the p r o b l e m s t h a t k r a f t ( a n d o t h e r l i g n i n s ) face are those o f p o o r r e a c t i v i t y , p r o d u c t v a r i a b i l i t y , a n d d i s c o l o r a t i o n . I n order for m o r e reactive k r a f t l i g n i n adhesives t o be m a d e , t h e y m u s t be c h e m i c a l l y m o d i f i e d i n some m a n n e r . T h i s c a n be done b y a v a r i e t y o f means (e.g., i n t r o d u c t i o n o f reactive c r o s s l i n k i n g sites o n t o the l i g n i n molecules b y means o f h y d r o x y m e t h y l a t i o n , e p o x i d a t i o n , i s o c y a n a t i o n , a n d the l i k e ) . H y d r o x y m e t h y l a t i o n ( m e t h y l o l a t i o n ) was first r e p o r t e d as a means o f a c t i ­ v a t i n g k r a f t l i g n i n s for c r o s s l i n k i n g reactions w i t h P F resins (61-63).

I n these

studies, i t was d e m o n s t r a t e d t h a t b a s e - c a t a l y z e d c o n d e n s a t i o n o f f o r m a l d e h y d e w i t h s o f t w o o d k r a f t l i g n i n i n t r o d u c e d C H O H groups m a i n l y at C - 5 of the a r o ­ 2

m a t i c r i n g a n d , t o a lesser extent at Cp ( F i g u r e 3).

These authors

(61-63)

i n d i c a t e d t h a t o f a l l the C - 5 a n d C/j p o s i t i o n s i n softwood l i g n i n , o n l y 0.33 a n d 0.03, respectively, were a v a i l a b l e for c o n d e n s a t i o n w i t h f o r m a l d e h y d e . T h e Cp p o s i t i o n s require a c t i v a t i o n for c o n d e n s a t i o n b y either a n adjacent C - c a r b o n y l a

or b y the presence o f a C , / ? - d o u b l e b o n d . T h e s e findings were u n a m b i g u o u s l y a

c o n f i r m e d i n a recent i n v e s t i g a t i o n by C h e n a n d G r a t z l (64).

H o w e v e r , even

w i t h the i n t r o d u c t i o n o f these a d d i t i o n a l c r o s s l i n k i n g sites, the r a t e o f c o n -

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

ADHESIVES F R O M RENEWABLE RESOURCES

F i g u r e 3. P r o p o s e d h y d r o x y m e t h y l a t i o n reactions of l i g n i n

(61-64)-

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

2.

Lignins in Adhesives: Introduction

LEWIS AND LANTZY

23

d e n s a t i o n o f m e t h y l o l a t e d k r a f t l i g n i n s is s t i l l far less t h a n t h a t for P F resins C o n s e q u e n t l y , t h e y are n o t used o n t h e i r o w n a n d need t o be a p p l i e d i n

(65).

c o m b i n a t i o n w i t h P F resins

(65-71).

Interestingly, s o d a bagasse l i g n i n is m u c h m o r e reactive t o w a r d f o r m a l d e h y d e t h a n other l i g n i n s , a feature a t t r i b u t a b l e t o fewer s u b s t i t u e n t s at C - 3 a n d C - 5 T h i s m a t e r i a l , after m e t h y l o l a t i o n , r e s o r c i n o l g r a f t i n g , a n d m i x i n g w i t h

(72).

p h e n o l i c r e s i n , p r o d u c e s c o l d - s e t t i n g w o o d adhesives s u i t a b l e for s t r u c t u r a l f i n gerjoints a n d g l u l a m . Epoxy Resins.

T h e use o f l i g n i n i n o r g a n i c p o l y i s o c y a n a t e - l i q u i d a r o m a t i c

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch002

e p o x i d e b i n d e r s has also been e v a l u a t e d ( 7 5 ) .

A c c o r d i n g t o t h e a u t h o r s , the

l i g n i n served o n l y as a d i l u e n t , a l t h o u g h f a i r l y h i g h levels o f s u b s t i t u t i o n ( «

35%)

b y l i g n i n were achieved. Lignin Isocyanates. I n the v e r y near f u t u r e , i s o c y a n a t e adhesives are l i k e l y t o grow i n i m p o r t a n c e i n the w o o d p a n e l i n d u s t r y . I n t h i s r e g a r d , a n u m b e r of i n v e s t i g a t i o n s have a t t e m p t e d t o i m p r o v e t h e w o o d - b o n d i n g p r o p e r t i e s of l i g n i n b y r e a c t i o n w i t h isocyanates, or b y i n c l u s i o n o f i s o c y a n a t e f u n c t i o n a l ities i n t o t h e l i g n i n p o l y m e r .

F o r e x a m p l e , G a m o (74)

was able t o prepare

a n adhesive s u i t a b l e for p r o d u c i n g 3-ply p l y w o o d w i t h acceptable cal p r o p e r t i e s .

mechani-

T h i s was achieved by r e a c t i n g 20 p a r t s o f i s o c y a n a t e s o l u t i o n

( m e t h y l e n e d i i s o c y a n a t e : t o l u e n e , 3:1) w i t h 100 p a r t s k r a f t l i g n i n - f o r m a l d e h y d e resin.

O t h e r approaches involve r e a c t i o n o f k r a f t l i g n i n w i t h p r o p y l e n e

oxide

t o afford h y d r o x y p r o p y l l i g n i n s t h a t c a n t h e n be reacted w i t h p o l y m e t h y l e n e p o l y p h e n y l e n e i s o c y a n a t e or h e x a m e t h y l e n e d i i s o c y a n a t e ( 7 5 ) .

In a somewhat

s i m i l a r m a n n e r , l i g n i n - m o d i f i e d p o l y u r e t h a n e adhesives have been p r e p a r e d from 4,4/-diphenylmethane-diisocyante-lignin-maleic anhydride-propylene oxide c o p o l y m e r s ( 76,77). T h e use o f l i g n i n , essentially as a d i l u e n t (extender), t i g a t e d (78).

has also been inves-

I n t h i s case, d i - or p o l y i s o c y a n a t e s were reacted w i t h ethylene

or p r o p y l e n e carbonates i n a s o l u t i o n c o n t a i n i n g l i g n i n . T h e s e m i x e d ethylene and

p r o p y l e n e c a r b o n a t e - c o n t a i n i n g o r g a n i c p o l y i s o c y a n a t e s were s u i t a b l e as

p a r t i c l e b o a r d adhesives.

S team-Explosion,

Acidolysis, Organosolv,

and Cellulase Lignins.

S t e a m - e x p l o s i o n l i g n i n s have received some a t t e n t i o n as adhesives m a i n l y because t h i s process offers some p o t e n t i a l for u t i l i z i n g l o w - q u a l i t y h a r d w o o d s .

Like

k r a f t l i g n i n , these p r e p a r a t i o n s also require a c t i v a t i o n [e.g., b y h y d r o x y m e t h y l a t i o n (79),

i s o c y a n a t i o n (75,80)]

to achieve any t y p e o f acceptable w o o d c o m -

p o s i t e adhesive p r o p e r t i e s . A c i d o l y s i s l i g n i n s , o r g a n o s o l v , a n d cellulase l i g n i n s are p r e s e n t l y l a b o r a t o r y curiosities due t o a lack of c o m m e r c i a l i z a t i o n . W h e t h e r these l i g n i n s w i l l offer any advantages at a l l w i t h respect t o resin adhesives c u r r e n t l y used r e m a i n s t o be e s t a b l i s h e d . P r e l i m i n a r y e x p e r i m e n t s [e.g., w i t h a c i d o l y s i s l i g n i n s (81)] not d e m o n s t r a t e d a n y s u p e r i o r q u a l i t i e s t o date.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

have

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ADHESIVES F R O M RENEWABLE RESOURCES

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Conclusions C o n s i d e r a b l e research a c t i v i t y has been directed t o w a r d p r o d u c i n g w o o d c o m ­ posite adhesives f r o m l i g n i n , a n d t h i s has been a c c o m p a n i e d b y very l i t t l e p r a c ­ t i c a l success i n t e r m s o f c o m m e r c i a l i m p l e m e n t a t i o n . B y themselves, a n d r e ­ gardless o f source, l i g n i n s offer n o advantages i n t e r m s o f c h e m i c a l r e a c t i v i t y , p r o d u c t q u a l i t y , o r color w h e n c o m p a r e d t o c o n v e n t i o n a l w o o d c o m p o s i t e adhe­ sives. A t l o w replacement levels (10 t o 3 0 % ) , l i g n i n s c a n a n d w i l l continue t o be e m p l o y e d as extenders for U F a n d P F resins. W h e n t h e y are used as extenders, best results are o b t a i n e d w h e n c h e m i c a l l y a c t i v a t e d (e.g., b y m e t h y l o l a t i o n ) . H o w e v e r , l i g n i n m a y f i n d a p p l i c a t i o n as a s u i t a b l e w o o d - c o m p o s i t e adhesive i n adhesive f o r m u l a t i o n s i f c h e m i c a l l y m o d i f i e d i n some m a n n e r . I n t h i s respect, the recent developments w i t h s o d a bagasse l i g n i n - r e s o r c i n o l - f o r m a l d e h y d e a n d l i g n i n - i s o c y a n a t e adhesives a l l o w for some c a u t i o u s o p t i m i s m for the f u t u r e .

Literature Cited 1. Higuchi, T. "Biosynthesis of Lignin" In Biosynthesis and Biodegradation of Wood Com­ ponents; Higuchi, T. Ed., Academic Press, Inc.: Orlando, 1985; Chapter 7, p. 141. 2. Lin, S. Y. "Lignin Utilization: Potential and Challenge" In Progress in Biomass Con­ version, Academic Press, Inc.: Orlando, 1983; Vol. 4, 31-78. 3. Luthe, C. E.; Lewis, N. G. Holzforschung 1986, 4 0 (Suppl.), 153-157. 4. Freudenberg, K.; Neish, A. C. In Constitution and Biosynthesis of Lignin; SpringerVerlag: Berlin, 1968. 5. Harkin, J. M.; Obst, J. R. Science 1973, 1 8 0 , 296-298. 6. Gross, G. G. "Recent Advances in the Chemistry and Biochemistry of Lignins," Recent Adv. Phytochem. 1979, 12, 177-220 (Plenum Press). 7. Nakamuri, Y.; Fushiki, H.; Higuchi, Τ. Ρhytοchemistry 1974, 1 3 , 1777-84. 8. Tomimura, T.; Sasoa, Y.; Yokoi, T.; Tereshima, N. Mokuzai Gakkaishi 1980, 2 6 , 55863.

9. Musha, Y.; Goring, D.A.I. J. Wood Sci. Technol. 1979,9, 45-48. 10. Whiting, P.; Goring, D.A.I. J. Wood Sci. Technol. 1983, 16, 261-267. 11. Siegel, S. M.; Siegel, Β. Z.; Chen, J. "Gravity, Lignification and Plant Evolution" In. Life in the Universe Billingham, J. Ed., M I T Press: Cambridge, MA, 1981; pp. 307-316.

12. Chen, N.; Siegel, S. M.; Siegel, Β. Z. Life Sciences and Space Research 1980, 18, 193-98. 13. Siegel, S. M. Life Sciences and Space Research; Holmquist, R., Ed., 1979, 17, 147-160. 14. Siegel, S. M.; Carrol, P.; Umeno, I.; Corn, C. Recent Advances in Ρhytοchemistry 1972, 4, 223-238.

15. a.Cowles, J.; Jahns, G.; LeMay, R.; Omran, R. Plant Physiol. 1986, 8 0 (Suppl. 4): 9 (Abstract). b. Cowles, J.; LeMay, R.; Omran, R.; Jahns, G. Plant Physiol. 1986, 8 0 (Suppl. 4): 9 (Abstract). 16. Cowles, J. R.; Scheld, H.; LeMay, R.; Peterson, C. Ann.

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18. Siegel, S.; Speitel, T.; Shiraki, D.; Fukumoto, J. In COSPAR,Life Sciences and Space Research; Holmquist, R., Ed.; Pergamon Press; 1977, XVI, 105-109. 19. Waber, J.; Williams, B. J.; Dubin, J.; Siegel, S. M. Physiol Planta. 1975, 34, 18-21. 20. Cronquist, A. In The Evolution and Classification of Flowering Plants, London: Nelson 1968.

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29. Eberhardt, T. L. M.S. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, VA, 1988. 30. Hunter, D. Papermaking. The History and Technique of an Ancient Craft. Dover Publications Inc.: New York, 1978. 31. McGovern, J. Tappi 1982, 6 5 , 12, 57-58. 32. Payen, A. Compt. rend. 1838, 7, 1052. 33. Payen, A. Compt. rend. 1839, 8, 51, 169. 34. Payen, A. Compt. rend. 1940, 10, 941. 35. Sjostrom, E. Wood Chemistry: Fundamentals and Applications, Academic Press: New York, 1981; Chapter 4, 68. 36. Nimz, H. "Lignin-Based Wood Adhesives" In Wood Adhes. Chem. Technol., Pizzi, Α., Ed.; Dekker, New York, 1983; Chapter 5, 247-88. 37. Sjostrom, E. Wood Chemistry: Fundamentals and Applications, Academic Press: New York, 1981; Chapter 7, 104-44. 38. Procter, A. R., Yean, W. Q.; Goring, D.A.I. Pulp. Pap. Mag. Canada 1967, T 4 4 5 - 5 3 . 39. Sarkanen, S.; Teller, D.C.;Abramowski, E.; McCarthy, J. L. Macromolecules 1982, 15,

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40. Bialski, A. M.; Luthe, C. E.; Fong, J. L.; Lewis, N. G. Can. J. Chem. 1986, 64, 7, 1336-44.

41. Fengel, D.; Wegener, G. In Wood: Chemistry, Ultrastructure, Reactions, W. de Gruyter, Berlin, 1984. 42. Lora, J. H.; Wayman, M. Tappi 1978, 6 1 , 6, 47-50. 43. Marchessault, R. H.; St. Pierre, J. In Future Sources of Organic Raw MaterialsCHEMRAWN; St. Pierre, L. E.; Brown, G. R., Eds.; Pergamon Press, 1978, 613. 44. Glasser, W. G. "Lignin" In Encyclopedia of Polymer Science and Engineering, John Wiley and Sons, Inc., 1987, 8, 795-851.

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45. Adhesives for the Composite Wood Panel Industry (Final Report January 13, 1986). Office of Scientific and Technical Information, U.S. Dep. of Energy DOC/CE/40646-T5 ( D E 86010847), 140 pp. 46. Pedersen, A.H.F.; Rasmussen, J. (Danske Splaanplade Ko) D A S 1 303 355, 1963. 47. Shen, K. C. "Binding Lignocellulosic Materials," U.S. Patent 4 193 814, 1980. 48. Forss, K.; Fuhrmann, A. Papper och Tra 1976, No. 11, 817-824. 49. Forss, K. G.; Fuhrmann, A. For. Prod. J. 1979, 2 9 , 7, 39-43. 50. Shen, K.C.;Calve, L. Adhes. Age 1980, 25-29 (August). 51. Calve, L.; Frechet, J. M. J. Appl. Polym. Sci. 1983, 2 8 , 1969-80.

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52. Bialski, A. M.; Bradford, H.; Lewis, N. G.; Luthe, C. E. J. Appl. Polym Sci. 1986, 3 1 , 1363-72. 53. Nimz, H. H.; Hitze, G. Cell. Chem. Tech. 1980, 14, 371-82. 54. Haars, Α.; Huttermann, A. U.S. Patent 4 532 921, 1984. 55. Kambanis, S. M.; Berchem, Α.; Gregoire, D.; Rybricky, J. U.S. Patent 4 537 941, 1985. 56. Adams, J. W.; Schoenherr, M. W. U.S. Patent 4 303 562, 1981. 57. Hollis, J. W., Jr.; Schoenherr, M. W. U.S. Patent 4 306 999, 1981. 58. Sehgal, V. K.; Gupta, R.C.;Madan, R. N. Ind. J. For. 1978, 1, 4, 299-301. 59. Campbell, A. G.; Walsh, A. R. J. Adhes. 1985, 18, 4, 301-14. 60. Muller, P.C.;Kelley, S. S.; Glasser, W. G. J. Adhes. 1984, 17, 3, 185-206. 61. Ball, F. J. "Chemistry of Lignin and Its Applications," paper presented at TAPPI Res. Conf., October, Tarrytown, New York, 1965. 62. Falkehag, S. I.; Marton, J.; Adler, E. Adv. Chem. Ser. 1966, 5 9 , 75-88. 63. Marton, J.; Marton, T.; Falkehag, S. I.; Adler, E. Adv. Chem. Ser. 1966, 5 9 , 125-144. 64. Chen, C. L.; Gratzl, J. S. "Utilization of Kraft Lignin as Adhesive for the Manufacture of Reconstituted Wood," U.S. Forest Service, So. For. Exp. Sta., Final Report 19 83 084, 1985. 65. Dolenko, A. J.; Clarke, M. R. For. Prod. J. 1978, 2 8 , 8, 41-6. 66. Clarke, M. R.; Dolenko, A. J. U.S. Patent 4 113 675, 1978. 67. Enkvist, T.E.E. U.S. Patent 3 864 291, 1975. 68. Sudan, Κ . K.; Berchen, A. U.S. Patent 4 324 747, 1982. 69. Rosenberg, G. N. Canadian Patent 1 136 693, 1982. 70. Kryzsik, Α.; Young, R. A. For. Prod. J. 1986, 3 6 , 11-12, 39-44. 71. Chow, S. J. Wood Sci. Technol. 1983, 1 7 , 1-11. 72. V a n der Klashorst, G. H.; Cameron, F. Α.; Pizzi, A. Holz Roh-Werkst. 1985, 4 3 , 11, 477-81. 73. Gaul, J. M.; Nguyen T. U.S. Patent 4 486 557, 1984. 74. Gamo, M. J. Appl. Polym. Sci.: Appl. Polym. Symp. 1984, 40 (Wood Adhesives), 101-26. 75. Glasser, W. G.; Saraf, V. P.; Newman, W. H. J. Adhes. 1982, 14, 3-4, 233-55. 76. Hsu, O.H.H.; Glasser, W. G. Wood Sci. 1976, 9, 2, 97-103. 77. Glasser, W. G.; Hsu, Ο. H.-H. U.S. Patent 4 017 474, 1977. 78. Gaul, J. M.; Nguyen, T. U.S. Patent 4 359 507, 1982. 79. Gardner, D. J.; Sellers, T. J. For. Prod. J. 1986, 3 6 , 5, 61-7. 80. Newman, W. H.; Glasser, W. G. Holzforschung 1985, 3 9 , 6, 345-53. 81. Santana, M.A.E.; Winston, M. H.; Kelley, M. W.; Goldstein, I. S. International Sym­ posium on Wood and Pulping Chemistry, April 27-30, 1987, Paris, France, pp. 49-54. R E C E I V E D May 27, 1988

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch003

Chapter 3 Search for Lignin Condensation Reactions with Modern N M R Techniques Lawrence L. L a n d u c c i Forest Products Laboratory Forest Service U . S . Department of Agriculture One Gifford Pinchot Drive Madison, W I 53705

A common feature of lignin condensation reactions and phenol/resorcinol formaldehyde curing reactions is the formation of methylene bridges between aryl units. Although this reaction is necessary for resin curing, it may be a detriment to efficient delignification in pulping systems. This condensation reaction of lignin was investigated by treatment of loblolly pine milled-wood lignin with alkali in the presence of formaldehyde or lignin model compounds. B y the use of a C-label, it was established that formaldehyde liberated from a lignin model ultimately resulted in methylene bridges between lignin aryl units. Formaldehyde liberation from lignin and model compounds, by reverse-aldol reaction, also resulted in the formation of vinyl ether structures. W i t h modern N M R techniques, it was demonstrated that alkaline treatment of milled-wood lignin at 140 ° C resulted in the formation of vinyl ether structures, whereas, after 50 ° C treatments, no vinyl ether was detected. 13

L i g n i n c o n d e n s a t i o n reactions have been s t u d i e d for m a n y years, m a i n l y because t h e y p o s s i b l y interfere w i t h efficient d e l i g n i f i c a t i o n o f w o o d . N u m e r o u s m o d e l c o m p o u n d studies established t h e various types o f c o n d e n s a t i o n reactions t h a t m a y o c c u r between l i g n i n fragments (1-5) o r between l i g n i n a n d c a r b o h y d r a t e s (1,2,6,7) d u r i n g a l k a l i n e p u l p i n g . A n i m p o r t a n t class o f c o n d e n s a t i o n reactions involves f o r m a l d e h y d e . F o r t y years a g o , i t was discovered t h a t f o r m a l d e h y d e is released f r o m isol a t e d l i g n i n s b y either a c i d o r alkaline t r e a t m e n t . I t w a s c o n c l u d e d t h a t t h e This chapter not subject to U.S. copyright Published 1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

f o r m a l d e h y d e c a m e f r o m the p r i m a r y a l c o h o l groups ( γ - h y d r o x y m e t h y l ) o f the p r o p y l side c h a i n (8). A b o u t 20 years l a t e r , i t was recognized t h a t t h e f o r m a l d e ­ hyde t h a t is c o n t i n u o u s l y released d u r i n g p u l p i n g m a y react w i t h l i g n i n i n accordance w i t h t h e w e l l - k n o w n reactions between p h e n o l a n d f o r m a l d e h y d e (9). Since t h e n , m a n y investigators have p u b l i s h e d results o f studies o n m o d e l c o m p o u n d s , w h i c h are consistent w i t h t h e e l i m i n a t i o n o f f o r m a l d e h y d e f r o m a q u i n o n e m e t h i d e (II; F i g u r e 1), generated f r o m a p h e n y l p r o p a n e u n i t w i t h a free C - 4 p h e n o l i c g r o u p (I) b y a reverse a l d o l r e a c t i o n a n d f o r m a t i o n o f a v i n y l ether (III) (10). Subsequent a d d i t i o n o f f o r m a l d e h y d e t o free p h e n o l i c u n i t s ( u s u a l l y at t h e 5-position) m a y t h e n occur t o give s t r u c t u r e V ( F i g u r e 2). U l t i m a t e l y , t h e new h y d r o x y m e t h y l groups condense w i t h e l i m i n a t i o n o f water a n d f o r m a l d e h y d e o r condense at a free C - 5 p o s i t i o n w i t h e l i m i n a t i o n o f w a t e r , r e s u l t i n g i n f o r m a t i o n o f a m e t h y l e n e b r i d g e s t r u c t u r e (VI) (10,11). O n e o f the m o s t n o t e w o r t h y studies u t i l i z e d V I I as a m o d e l c o m p o u n d ( F i g u r e 3) w i t h a C - l a b e l i n the 7 - h y d r o x y m e t h y l g r o u p . A l k a l i n e t r e a t m e n t o f t h i s m o d e l c o m ­ p o u n d resulted i n a c o m p l e x m i x t u r e . C - N M R spectroscopy o f t h e m i x t u r e showed t h a t m u c h o f the l a b e l ended u p i n m e t h y l e n e bridges between a r y l u n i t s (12). C l e a r l y , p h e n o l - f o r m a l d e h y d e t y p e reactions f o r m a c o m m o n b o n d between p u l p i n g c h e m i s t r y a n d adhesives c h e m i s t r y . I n fact, t h e reactions o f a d d e d f o r m a l d e h y d e t o l i g n i n s a n d t h e u t i l i z a t i o n o f the p h e n o l i c n a t u r e o f l i g n i n t o p r o d u c e P F resins have been s t u d i e d extensively (13-15). A l t h o u g h for a d ­ hesives P F - c o n d e n s a t i o n reactions are i m p o r t a n t , they are a nuisance d u r i n g p u l p i n g . T h e i m p e t u s for a m o r e complete u n d e r s t a n d i n g o f l i g n i n c o n d e n s a t i o n reactions is t h e h o p e o f i n c r e a s i n g t h e efficiency o f d e l i g n i f i c a t i o n b y p r e v e n t i n g or m i n i m i z i n g c o n d e n s a t i o n reactions d u r i n g p u l p i n g as w e l l as c o n t r o l l i n g a n d m a n i p u l a t i n g t h e m for p r a c t i c a l a n d u n i f o r m adhesives. Because o f t h e c o m ­ p l e x i t y o f l i g n i n , t h e t y p e a n d extent o f c o n d e n s a t i o n reactions t h a t o c c u r d u r i n g a l k a l i n e p u l p i n g are s t i l l n o t w e l l u n d e r s t o o d . M o s t o f the i n f o r m a t i o n r e g a r d i n g these reactions is s p e c u l a t i o n based o n studies w i t h m o d e l c o m p o u n d s . 1 3

1 3

T h i s s t u d y was a p r e l i m i n a r y effort t o detect a n d characterize s t r u c t u r e s i n t h e l i g n i n p o l y m e r t h a t result f r o m c o n d e n s a t i o n reactions d u r i n g a l k a l i n e t r e a t m e n t . T h e o n l y m e t h o d capable o f o b s e r v i n g t h i s c o m p l e x p o l y m e r w i t h the necessary d e t a i l o n a n a t o m i c scale is C - N M R spectroscopy. E n o r m o u s progress has been m a d e i n t h e c a p a b i l i t i e s o f N M R e s p e c i a l l y i n t h e last few years, a n d very few o f the m o d e r n techniques have yet been a p p l i e d t o l i g n i n . I n order t o f a c i l i t a t e the detection o f c o n d e n s a t i o n s t r u c t u r e s , l i g n i n was t r e a t e d w i t h a l k a l i i n the presence o f C - l a b e l e d f o r m a l d e h y d e or m o d e l c o m ­ p o u n d s ( F i g u r e 3) e n r i c h e d w i t h C at the 7-position o n the side c h a i n . I n t h i s m a n n e r , t h e d e t e c t i o n o f cross condensations between the m o d e l a n d t h e l i g n i n was f a c i l i t a t e d . C o n v e n t i o n a l a n d m o d e r n N M R e x p e r i m e n t s were t h e n u t i l i z e d t o e x a m i n e the t r e a t e d l i g n i n s . 1 3

1 3

1

3

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

3.

LANDUCCI

29

Lignin Condensation Reactions

y CH 0H

H C=0 2

CH|^-H

2

β CHOLïgnin

JjHOLignin

rCHOLignin

CH

I

temperature, c e

F i g u r e 8. D S C t h e r m o g r a m s of l i g n i n h y d r o x y m e t h y l a t e d under different s o d i u m t o l i g n i n r a t i o s : a) 1.0, b ) 0.75, c) 0.5, a n d d) 0.25.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

9.

GILLESPIE

123

Wood Adhesives from Kraft Lignin

emphasize t h a t extended press t i m e s are r e q u i r e d t o cure the l i g n i n adhesives c o m p a r e d t o P F adhesives.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch009

R e d u c t i o n i n E n e r g y D e m a n d for C u r i n g H y d r o x y m e t h y l a t e d L i g n i n . O n e m e t h o d of r e d u c i n g the energy requirements for c r o s s l i n k i n g of m e t h y l o l a t e d l i g n i n s w o u l d be t o i n c o r p o r a t e a d i f u n c t i o n a l m a t e r i a l h a v i n g m u c h greater react i v i t y w i t h m e t h y l o l groups t h a n they have for themselves a n d w o u l d , therefore, f u n c t i o n as a c r o s s l i n k i n g agent. D i i s o c y a n a t e s are such m a t e r i a l s a n d t h e y are available w i t h b l o c k i n g groups t h a t allow t h e i r use i n water systems w i t h o u t p r e m a t u r e r e a c t i o n w i t h w a t e r , alcohols, acids, or other reactive m a t e r i a l s . A n e x a m p l e is Isoset C X - 1 1 . T h i s was a d d e d at different stages i n f o r m u l a t i n g the l i g n i n adhesive at either 10 or 2 0 % o f the t o t a l m i x t u r e weight, a n d t w o - p l y b i r c h panels were b o n d e d for shear s t r e n g t h tests. T h e H M L was p r e p a r e d w i t h the f o l l o w i n g m o l e r a t i o s : I n d u l i n A T 1.0, f o r m a l i n 1.0, s o d i u m h y d r o x i d e 0.5, t r i e t h y l e n e g l y c o l ( T E G ) 0.5, water 20.0, a n d acetic a c i d 0.5. T h e shear s t r e n g t h results are s h o w n i n T a b l e I I I . T a b l e I I I . Shear S t r e n g t h of D i i s o c y a n a t e - M o d i f i e d L i g n i n A d h e s i v e

Formulation

Storage Storage Time Time Press Prior to After T i m e at CX-11 CX-11 150 ° C Addition Addition (min)

HML + oxalic + 1 0 % C X - 1 1 25 days

Shear S t r e n g t h Vaccum Pressure 4 - H o u r Dry Soak Boil (psi) (psi) (psi)

18 h r

5 10

880 1,020

620 930

755 760

1 hr

5 10

1,325 1,710

965 1,155

900 1,135

+ 10% C X - 1 1 3 hr

20 h r

5

1,065

545

665

HML -1- 2 0 % C X - 1 1 3 h r

1 hr

5 10

1,325 1,655

880 1,140

815 1,090

20 h r

5

965

360

410

HML + 10% C X - 1 1 3 hr

HML

HML + 20% C X - 1 1 3 hr

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch009

A n e x p l o r a t o r y e x p e r i m e n t t o determine c o m p a t i b i l i t y a n d w o r k i n g p r o p e r ties consisted of a d d i n g the c r o s s l i n k i n g agent t o a f o r m u l a t e d adhesive t h a t h a d been stored at r o o m t e m p e r a t u r e after its use t o o b t a i n the d a t a s h o w n i n F i g ure 3. T h e l i q u i d c r o s s l i n k i n g agent was easily i n c o r p o r a t e d b y slow a d d i t i o n t o the adhesive w i t h s t i r r i n g a n d w i t h o u t any noticeable e x o t h e r m . A f t e r s t a n d i n g overnight, the m i x t u r e appeared foamy, i n d i c a t i n g some r e a c t i o n between the d i i s o c y a n a t e a n d o x a l i c a c i d or water generating c a r b o n d i o x i d e . T h e wet shear s t r e n g t h o b t a i n e d w i t h t h i s f o r m u l a t i o n was e n c o u r a g i n g even w h e n pressing for o n l y 5 m i n u t e s at 150 ° C a n d 150 p s i , as c o m p a r e d w i t h results w i t h o u t diisocyanate addition. Since the d i i s o c y a n a t e a d d i t i o n t o H M L w o u l d not require o x a l i c a c i d (its presence m i g h t even be d e t r i m e n t a l to the desired r e a c t i o n ) , a d d i t i o n a l f o r m u l a t i o n s were prepared f r o m H M L after p r e c i p i t a t i o n b y acetic a c i d t o a p H of a p p r o x i m a t e l y 5.5. T h e c r o s s l i n k i n g agent was added at 1 0 % t o the m i x t u r e weight i n one case a n d at 2 0 % i n another. B i r c h panels were b o n d e d w i t h each f o r m u l a t i o n a p p r o x i m a t e l y 1 h o u r after the a d d i t i o n of the c r o s s l i n k i n g agent at 5- a n d 10-minute press t i m e s . T h e f o r m u l a t i o n s were stored at r o o m t e m p e r a t u r e o v e r n i g h t , a n d panels were t h e n b o n d e d w i t h 5-minute press t i m e s . T h e d a t a i n T a b l e III show t h a t at 1 0 % a d d i t i o n of c r o s s l i n k i n g agent, h i g h wet shear s t r e n g t h developed even at a press t i m e of 5 m i n u t e s . T h e 2 0 % a d d i t i o n d i d n o t p r o d u c e as h i g h wet shear s t r e n g t h as was developed b y the 1 0 % a d d i t i o n . T h e highest shear s t r e n g t h was o b t a i n e d s o o n after m i x i n g the c r o s s l i n k i n g agent i n t o the m i x t u r e , a n d overnight storage at r o o m t e m p e r a t u r e was d e c i d e d l y d e t r i m e n t a l . W h i l e the o p t i m u m c o n c e n t r a t i o n s a n d w o r k i n g properties of t h i s s y s t e m r e m a i n t o be defined, the results o b t a i n e d t o date i n d i c a t e t h a t b l o c k e d diisocyanates c a n p r o v i d e increased r e a c t i v i t y for c u r i n g H M L . H i g h wet s t r e n g t h b o n d s c a n be o b t a i n e d under c o n d i t i o n s t h a t appear t o a p p r o x i m a t e those c u r r e n t l y used i n c o m m e r c i a l p r a c t i c e w i t h p h e n o l i c adhesives, b u t a d d i t i o n a l research w i l l be r e q u i r e d t o s u b s t a n t i a t e t h i s e x p e c t a t i o n . S u m m a r y and Conclusions A w o o d adhesive p r o d u c i n g h i g h shear s t r e n g t h a n d water resistance was prep a r e d f r o m a p u r i f i e d k r a f t l i g n i n m a t e r i a l w i t h o u t the need for c o p o l y m e r i z a t i o n w i t h p h e n o l . T h e l i g n i n was h y d r o x y m e t h y l a t e d b y r e a c t i o n w i t h f o r m a l d e h y d e i n a l k a l i n e m e d i u m , p r e c i p i t a t e d b y a c i d i f i c a t i o n t o a p H o f a p p r o x i m a t e l y 5.5, c a t a l y z e d w i t h o x a l i c a c i d , a n d h o m o g e n i z e d t o a s m o o t h b r u s h a b l e consistency. A satisfactory f o r m u l a t i o n consisted of the f o l l o w i n g m o l a r q u a n t i t i e s , w i t h l i g n i n assigned a m o l e c u l a r weight of 180: l i g n i n 1.0, s o d i u m h y d r o x i d e 0.5, f o r m a l d e h y d e 1.0, t r i e t h y l e n e g l y c o l 0.5, water 20.0, acetic a c i d 0.5, a n d o x a l i c a c i d 0.4. H i g h - q u a l i t y b o n d s w i t h h i g h wet s t r e n g t h were developed w h e n h y d r o x y m e t h y l a t i o n was c a r r i e d out for at least 2 days at r o o m t e m p e r a t u r e , or 5 hours at 50 ° C , or 1 h o u r at 80 ° C . U n d e r the best c o m p o n e n t concentrations a n d r e a c t i o n c o n d i t i o n s e v a l u a t e d , h i g h wet s t r e n g t h b o n d s r e q u i r e d 10- to 15-

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

9.

GILLESPIE

Wood Adhesives from Kraft Lignin

US

m i n u t e press t i m e s at 150 ° C a n d 150 p s i , w h i c h is l o n g e r t h a n n o r m a l l y r e q u i r e d for a p h e n o l i c a d h e s i v e . W i t h t h e a d d i t i o n o f a b l o c k e d d i i s o c y a n a t e t o t h e H M L , h i g h wet s t r e n g t h b o n d s were o b t a i n e d at s h o r t e r press t i m e s , i n d i c a t i n g t h a t t h e s l u g g i s h r e a c t i v i t y o f H M L i n c o n d e n s a t i o n r e a c t i o n s m a y be o v e r c o m e

by

s u c h c r o s s l i n k i n g agents.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch009

Literature

Cited

1. Gillespie, R. H . Proc. Symposium-Wood Adhesives in 1985: Status and Needs, 1985 May 14-16, Madison, WI, sponsored by the U.S. Forest Products Laboratory in cooperation with the Forest Products Research Society and the University of Wisconsin, 1987. 2. Dolenko, A . J.; Clarke, M. R. Forest Prod. J. 1978, 28(8), 41-6. 3. Merewether, J . W . T . Tappi 1962, 45(2), 159-63. 4. Whalen, D . M. Tappi 1975, 58(5), 110-12. 5. Clarke, M. R.; Dolenko, A . J. U.S. Patent 4 113 675, 1978, 6. Calve, L.; Shields, J. 1982. Development of Lignin Adhesives, E N F O R Project C-209, F O R I N T E K Canada Corporation, Eastern Laboratory, 800 Montreal Road, Ottawa, Ontario K1G 3Z5. 7. Enkvist, T.U.E. U.S. Patent 3 864 291, 1975. 8. Gamo, M. J. Appl. Polym. Sci. 1984, 40, 101-26. 9. Marton, J.; Marton, T . ; Falkehag, S. I. In Lignin Structure and Reactions, A C S Symposium Series No. 59; American Chemical Society: Washington, DC, 1966; pp. 126-27. 10. Christiansen, A . W . ; Gollob, L. J. Appl. Polym. Sci. 1987, 30, 2279-89. R E C E I V E D November 11, 1988

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 10 Room-Temperature Curing Adhesives Based on Lignin and Phenoloxidases Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch010

Annegret Haars, Alireza Kharazipour, H e l m u t Z a n k e r , and A l o y s H u t t e r m a n n 1

Institute of Forest Botany University of Gottingen Busgenweg 2, D-3400 Gottingen Federal Republic of Germany

A n effective adhesive for wood materials, e.g. particleboards, con­ sists of spray-dried lignin, particularly lignosulfonate, and a phe­ noloxidase containing culture fluid of filamentous fungi grown on dilute lignin solutions in the presence of cheap C and Ν sources in a fermenter. Wood laminates bonded with this two-component room­ -temperature curing adhesive had tensile strengths above 2.0 M P a . The underlying reaction mechanism is the crosslinking of lignin via oxidative polymerization catalyzed by the phenoloxidase. The pro­ duction of this adhesive includes the total utilization of waste lignins a) directly as one component of the binding system and b) indirectly as nutrient source of the phenoloxidase-producing fungi. T h e p u l p i n g i n d u s t r y releases a b o u t 40 m i l l i o n tons o f l i g n i n a n n u a l l y , w h i c h are s t i l l far f r o m b e i n g u t i l i z e d effectively. Indeed, o n l y 2 0 % o f t h i s vast p o t e n t i a l is used f o r v a r i o u s i n d u s t r i a l purposes, t h e rest b e i n g b u r n t . Irrespective o f SO2 e m i s s i o n d u r i n g the b u r n i n g o f waste p u l p i n g effluents, the process represents a n enormous d i s s i p a t i o n o f a renewable raw m a t e r i a l t h a t c o u l d b e better u t i l i z e d . A m o n g t h e m a n y considerations r e g a r d i n g l i g n i n u t i l i z a t i o n , t w o seem t o be very i m p o r t a n t t o any increase i n l i g n i n ' s m a r k e t value: 1. A p p l i c a t i o n s s h o u l d m a k e use o f the p o l y m e r i c s t r u c t u r e o f l i g n i n . 2. T h e m a r k e t has t o be large enough t o absorb e n o r m o u s q u a n t i t i e s of lignin. C u r r e n t address: G . A . Pfleiderer, Postfach 14 80, D-8430 Neumarkt/Opf. 0097-6156/89/0385-0126$06.00/0 ·

1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

10.

HAARS E T AL.

Room-Temperature Curing Adhesives

127

T h e a l r e a d y large tonnage of l i g n i n s p r o d u c e d i n p u l p i n g w o o d w i l l f u r t h e r increase because of the i n c r e a s i n g need for h i g h - v a l u e c h e m i c a l p u l p a n d because the m a i n use t o d a y - t h e f o o d i n d u s t r y - w i l l need m u c h less l o w - v a l u e l i g n i n as a p e l l e t i z i n g agent.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch010

I n t h i s respect, the m o s t i m p o r t a n t f u t u r e a p p l i c a t i o n o f l i g n i n w i l l be as a n a t u r a l p l a s t i c i n the field of general p o l y m e r a p p l i c a t i o n s , especially as adhe­ sives for w o o d composites. T h e adhesive properties o f l i g n i n , its r e a c t i v i t y w i t h f o r m a l d e h y d e , a n d i t s s t r u c t u r a l s i m i l a r i t y w i t h p h e n o l i c adhesives i n v i t e d i n v e s t i g a t i o n of the a p p l i ­ c a b i l i t y o f l i g n i n i n adhesive resin systems. Therefore, d u r i n g the past several years, n u m e r o u s a t t e m p t s have been m a d e to replace the expensive p e t r o c h e m ­ i c a l resins t o t a l l y or p a r t i a l l y w i t h the renewable r a w m a t e r i a l l i g n i n (1). H o w e v e r , the polydisperse character a n d the a c c o m p a n y i n g i m p u r i t i e s cre­ a t e d significant p r o b l e m s for the u t i l i z a t i o n o f t e c h n i c a l b y p r o d u c t l i g n i n s ( f r o m spent sulfite l i q u o r a n d k r a f t b l a c k l i q u o r ) as extenders for p e t r o c h e m i c a l resins. P h e n o l i c resins, for e x a m p l e , react p r i m a r i l y w i t h the low m o l e c u l a r weight l i g nosulfonates so t h a t the percentage o f phenolics t h a t c o u l d be replaced r e m a i n e d r a t h e r l o w . T h i s disadvantage was c i r c u m v e n t e d b y the " K a r a t e x " adhesive de­ veloped b y Forss a n d coworkers (2). E v e n i n t h i s a d v a n c e d process ( w h i c h produces a n n u a l l y n e a r l y 4,000 tons of adhesive), the h i g h m o l e c u l a r weight l i g n i n f r a c t i o n , o b t a i n e d b y u l t r a f i l t r a t i o n , c a n replace o n l y « 4 0 % o f p h e n o l i c resins. A n o t h e r p r o b l e m for the u t i l i z a t i o n o f l i g n o s u l f o n a t e as a n adhesive is the h i g h content o f sulfonate groups, w h i c h causes a hygroscopic character a n d t h u s prevents t h e i r conversion t o a water-resistant p o l y m e r . K r a f t l i g n i n seems t o be b e t t e r s u i t e d because o f i t s water i n s o l u b i l i t y . However, f r o m the esti­ m a t e d a n n u a l p r o d u c t i o n o f 2 χ 1 0 tons, o n l y 0 . 1 % is i s o l a t e d a n d m a r k e t e d (3). M a n y of the m i l l s b u r n i n g black l i q u o r for recovery o f the chemicals are a l r e a d y o p e r a t i n g above recovery furnace capacity, so a use for t h i s l i g n i n w o u l d help t o u n b u r d e n t h e i r o p e r a t i o n s . 7

F i n a l l y , i t s h o u l d be s t a t e d t h a t the processes t h a t use l i g n i n alone as t h e r m o s e t t i n g resin i n p a r t i c l e b o a r d s (4-6) d i d not find i n d u s t r i a l a p p l i c a t i o n , whereas, the processes u s i n g l i g n i n i n c o m b i n a t i o n w i t h s y n t h e t i c resins (2,7) are e c o n o m i c a l l y feasible t h o u g h the r e m a i n i n g p r o p o r t i o n o f s y n t h e t i c resin is still relatively high (60%). O n e reason for the l i m i t e d o p p o r t u n i t i e s for r e p l a c i n g p h e n o l i c resins w i t h l i g n i n is the r a t h e r low content of p h e n o l i c groups (0.6 a n d 0.3 p h e n o l i c O H groups p e r m o n o m e r i n K r a f t a n d sulfite l i g n i n , respectively (8)). Therefore, new developments focus o n the " a c t i v a t i o n " o f the l i g n i n m o l e c u l e , for e x a m ­ ple, b y the synthesis o f h y d r o x y a l k y 1 derivatives for use i n c o m b i n a t i o n w i t h m e l a m i n e or isocyanate (9). O t h e r new a n d i n t e r e s t i n g i n v e s t i g a t i o n s i n t o the use o f m o r e " a c t i v e " l i g n i n i n c o m b i n a t i o n w i t h s y n t h e t i c resins, i n a d d i t i o n t o o u r c h a p t e r , are r e p o r t e d elsewhere i n t h i s b o o k .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

128

ADHESIVES F R O M RENEWABLE RESOURCES

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch010

Experimental

Methodology

T h e a p p r o a c h we used t o m a k e l i g n i n a s u i t a b l e " p a r t n e r " i n a n adhesive f o r m u ­ l a t i o n is based o n the f o l l o w i n g considerations. O u r i d e a was t o use the l i g n i n not m e r e l y as f i l l i n g m a t e r i a l , where i t is o b v i o u s l y inferior t o the m o r e active p h e n o l i c resins because o f the few p h e n o l i c groups a n d condensed s t r u c t u r e of l i g n i n . R a t h e r , we t h o u g h t t h a t lignosulfonate itself c o u l d be a g o o d b i n d i n g agent even w i t h o u t a d d i t i o n of s y n t h e t i c resins, i f new a c t i v e sites were i n t r o ­ d u c e d . " A c t i v e sites" means, for e x a m p l e , the d i s i n t e g r a t i o n of the condensed s t r u c t u r e , the a d d i t i o n o f p h e n o l i c h y d r o x y l s , the s p l i t t i n g o f m e t h y l ethers so t h a t new p h e n o l i c groups are f o r m e d , the i n t r o d u c t i o n o f new f u n c t i o n a l groups (for e x a m p l e , c a r b o x y l groups), a n d last b u t not least, the f o r m a t i o n o f r a d i c a l s t h a t t h e n c o u l d react t o f o r m a n o x i d a t i v e p o l y m e r i z a t e . B o t h the a c t i v a t i o n o f l i g n i n a n d i t s c r o s s l i n k i n g to f o r m a b i n d e r for w o o d m a t e r i a l c o u l d be p e r f o r m e d b y a single b i o t e c h n o l o g i c a l process based o n the o b s e r v a t i o n t h a t enzymes are often m u c h m o r e powerful c a t a l y s t s i n the c o n ­ version o f 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 molecules t h a n m a n m a d e chemicals can ever be. T h e b i n d i n g c a p a c i t y o f the l i g n i n - b a s e d e n z y m a t i c adhesive is based o n the f o l l o w i n g reactions (10-12). T h e e n z y m e used is a p h e n o l o x i d a s e , also c a l l e d " l a c c a s e " , classified b y I U P A C as m o n o p h e n o l , d i h y d r o x y - L - p h e n y l a l a n i n e : o x y ­ gen oxido-reductase ( E . C . 1.14.18.1). T h i s r e l a t i v e l y unspecific c o p p e r - c o n ­ t a i n i n g e n z y m e catalyzes the one-electron o x i d a t i o n of a r o m a t i c substrates (e.g., phenols) b y c o u p l i n g t o the four-electron r e d u c t i o n o f m o l e c u l a r o x y g e n t o w a ­ ter. I n o u r case, the p h e n o l i c substrate is l i g n i n . T h e i n i t i a l one-electron o x i d a ­ t i o n o f l i g n i n b y phenoloxidase, peroxidase a n d oxygenase y i e l d s r a d i c a l c a t i o n i n t e r m e d i a t e s t h a t c a n react i n t w o ways: 1. T h e y react w i t h water t o f o r m new p h e n o l i c groups (e.g.), v i a d e m e t h y l a t i o n . T h i s r e a c t i o n represents the " a c t i v a t i o n " o f the l i g n i n m o l e c u l e because new active p h e n o l i c groups, w h i c h c a n be f u r t h e r o x i d i z e d , are f o r m e d (13). 2. T h e y react w i t h each other t o f o r m a n o x i d a t i v e p o l y m e r i z a t e . T h i s r e a c t i o n represents t h e c r o s s l i n k i n g , a n d t h u s t h e a c t u a l g l u i n g process. T h u s , the a c t i v a t i o n a n d c r o s s l i n k i n g of the l i g n i n are p e r f o r m e d i n one step. I n t h i s way, the a p p a r e n t average m o l e c u l a r weight of l i g n o s u l f o n a t e is increased u p t o 1 χ 1 0 D a l t o n s ( F i g u r e 1). W e measured t h i s by Sepharose G P C a n d c a l i ­ b r a t e d the c o l u m n b y m o l e c u l a r weight d e t e r m i n a t i o n s o f several f r a c t i o n s i n a n a n a l y t i c a l u l t r a c e n t r i f u g e (14). T h e curve w i t h the b r o a d d i s t r i b u t i o n i n F i g u r e 1 shows n a t i v e l i g n o s u l f o n a t e ; the s h a r p peak is the same l i g n o s u l f o n a t e after e n z y m a t i c p o l y m e r i z a t i o n . T h i s p o l y m e r i z a t e was s t i l l water-soluble because 6

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

F i g u r e 1. M o l e c u l a r weight d i s t r i b u t i o n ( d e t e r m i n e d b y Sepharose C L 6 B G P C ) o f l i g n o s u l f o n a t e before (filled circles) a n d after (open circles) i n c u b a t i o n w i t h phenoloxidase.

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of the sulfonate groups. However, water-soluble organosol ν l i g n i n f r a c t i o n s be­ came w a t e r - i n s o l u b l e after e n z y m a t i c p o l y m e r i z a t i o n , a n d t h i s is i m p o r t a n t for a w a t e r - r e s i s t a n t adhesive (11). O f course, a n e n z y m e a p p l i e d t o a t e c h n i c a l process i n such a d i m e n s i o n as adhesives for w o o d m a t e r i a l s has t o have c e r t a i n p r o p e r t i e s . It m u s t be:

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1. P r o d u c i b l e i n large q u a n t i t i e s o n cheap n u t r i e n t s . 2. 3. 4. 5.

H i g h l y reactive w i t h t e c h n i c a l l i g n i n s . S t a b l e at r o o m t e m p e r a t u r e . M o r e t h e r m o t o l e r a n t t h a n enzymes u s u a l l y are. A p p l i c a b l e as a crude p r e p a r a t i o n 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 .

W e f o u n d t h a t a l l these c o n d i t i o n s were fulfilled b y e x t r a c e l l u l a r p h e n o l o x i dases p r o d u c e d b y a g r o u p of filamentous f u n g i called w h i t e - r o t basidiomycetes (15). A m o n g the m a n y species a n d s t r a i n s tested, the fungus Trametes versi­ color, a frequent i n h a b i t a n t of the woods of the N o r t h e r n H e m i s p h e r e , showed the m o s t active e n z y m e p r o d u c t i o n . It was a n especially g o o d c a n d i d a t e for our purposes because i t c o u l d be a d a p t e d to very cheap n u t r i e n t sources. T h e s u l ­ fite l i q u o r itself, c o n s i s t i n g m a i n l y of lignosulfonate a n d sugars, was s u i t a b l e i n d i l u t e f o r m for g r o w t h of the fungus a n d for i n d u c i n g phenoloxidase p r o d u c t i o n . T h e e n z y m e a c t i v i t y was d e t e r m i n e d u s i n g 2 , 6 - d i m e t h o x y p h e n o l as the s u b ­ strate (16). T h e phenoloxidase a c t i v i t y o b t a i n e d w h e n t h i s fungus was g r o w n o n d i l u t e sulfite l i q u o r was 12 t o 15 U / m L , w h i c h was a m u l t i p l e of the p r o ­ d u c t i o n o n sole c a r b o h y d r a t e w i t h o u t l i g n i n (11 17). F o r use as a n adhesive c o m p o n e n t , t h i s e n z y m e s o l u t i o n has to be f u r t h e r c o n c e n t r a t e d , b y u l t r a f i l t r a ­ t i o n or e v a p o r a t i o n . T o save energy, i t was desirable t o increase the e n z y m e p r o d u c t i o n of the fungus. W e tested m a n y phenols a n d l i g n i n s a n d f o u n d t h a t l i g n i n s o b t a i n e d b y a n organosol ν p u l p i n g process h a d a n e a r l y t e n f o l d c a p a c i t y for e n z y m e i n d u c t i o n (12). T h e s e results were o b t a i n e d i n 5 0 0 - m L s h a k i n g c u l ­ tures. T h e next step was t o transfer the e n z y m e p r o d u c t i o n t o a larger scale. W e were able t o grow the fungus Trametes versicolor i n a 3 0 - L fermenter scale o n 0 . 1 % organosol ν l i g n i n i n the presence of a cheap a d d i t i o n a l C-source p r o ­ d u c i n g 70 U / m L of e x t r a c e l l u l a r phenoloxidase. A f t e r r e m o v a l of the m y c e l i u m by filtration a n d subsequent sterile filtration of the e n z y m e - c o n t a i n i n g n u t r i e n t b r o t h , t h i s p r e p a r a t i o n was stable at r o o m t e m p e r a t u r e for at least a m o n t h a n d c o u l d be 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 as a c o m p o n e n t i n the l i g n i n - b a s e d adhesive. T h e t h e r m o s t a b i l i t y of the phenoloxidase was u n u s u a l l y h i g h c o m ­ p a r e d t o m o s t enzymes; even h e a t i n g u p t o 65 ° C d i d not destroy the a c t i v i t y . C o n s i d e r i n g t h a t lignosulfonate contains 0.3 p h e n o l i c O H - g r o u p s per m o n o m e r a n d t h a t the K value of phenoloxidase t o w a r d phenols lies between 1 0 " a n d 1 0 " M , a n e n z y m e c o n c e n t r a t i o n of 400 U / m L i n the aqueous s o l u t i o n of 45 t o 5 0 % l i g n i n s h o u l d be sufficient t o cause the a c t i v a t i o n a n d c r o s s l i n k i n g w i t h i n a reasonable t i m e , so t h a t a sufficient b i n d i n g c a p a c i t y is o b t a i n e d ( T a b l e I). }

m

4

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

2

10.

HAARS E T A L

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Room- Temperature Curing Adhesives

T h e e n z y m e s o l u t i o n represents one c o m p o n e n t o f the t w o - c o m p o n e n t w o o d adhesive s y s t e m . T h e second c o m p o n e n t is m e r e l y s p r a y - d r i e d sulfite l i q u o r . T h e adhesive p r e p a r a t i o n was as follows. T h e b i o c o m p o n e n t is m i x e d w i t h t h e s p r a y - d r i e d sulfite l i q u o r at a r a t i o o f a p p r o x i m a t e l y 2 p a r t s o f sulfite l i q u o r a n d a p p r o x i m a t e l y 1 p a r t o f aqueous e n z y m e s o l u t i o n , so t h a t t h e d r y m a t t e r content o f the adhesive is between 50 a n d 6 0 % . T h i s m i x t u r e is h o m o g e n i z e d a n d heated u p t o 50 ° C t o reduce i t s viscosity. T h e test b o a r d s were p r o d u c e d b y m i x i n g 150 g o f adhesive w i t h 1 k g o f w o o d chips a n d pressing t h e m a t a t a t e m p e r a t u r e of 190 ° C for 5 m i n u t e s at 30 k g / c m . It has t o be kept i n m i n d t h a t t h e h e a t i n g process is not necessary for g l u i n g w i t h t h i s p h e n o l o x i d a s e - l i g n i n adhesive. O f course, t h e p o l y m e r i z a t i o n is c a r r i e d o u t at r o o m t e m p e r a t u r e . T h e h e a t i n g serves o n l y t o remove t h e water w i t h i n a short t i m e . W e b o n d e d b o a r d s at 24 ° C , a n d t h e y h a d t h e same tensile s t r e n g t h as u r e a - f o r m a l d e h y d e a n d p h e n o l f o r m a l d e h y d e b o n d e d b o a r d s t h a t m u s t be pressed at a b o u t 200 ° C t o o b t a i n polymerization (Table I).

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2

Table I. Tensile Strengths of Lignin-Based Two-Component Wood Bonding Systems Compared to Synthetic Resins Versai Tensile Strength Type of Resin a. Synthetic resins: Urea-formaldehyde Phenol-formaldehyde

c. Lignin-phenoloxidase resins: S A i + 320 U / m L (CA++) S A + 320 U / m L (CA++/Mg++) S A + 320 U / m L (Mg++) S A i -f organosol ν lignin + 320 U / m L

£C£

0.52 0.62

190 190

0.25 0 0.25

24 24 24

0.64

24 24 24 24

2

3

3

Temperature

(MPa)

b. Controls (only one component): Spray-dried sulfite liquor S A i Lyophilized enzyme (320 U / m L ) Spray-dried S A i - f denaturated enzyme

2

1

0.51 0.60 0.05

^ h e minimum standard requirement for 19-mm V20 particleboards is 0.35 M P a . M e a n values of 10 replicates tested by DIN 52365. S A = sulfite liquor.

2

3

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

Results a n d Discussion

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I n a l l cases, the m i n i m u m G e r m a n s t a n d a r d requirement of 0.35 M P a is exceeded by l i g n i n - p h e n o l o x i d a s e resins ( T a b l e I). I n m o s t cases, the break o c c u r r e d i n the w o o d a n d n o t i n the g l u e l i n e . A s c a n be seen i n S e c t i o n Β of the t a b l e , no c o m p o n e n t alone, w h e t h e r the e n z y m e or the sulfite l i q u o r , is capable of m e e t i n g s t a n d a r d r e q u i r e m e n t s . A synergistic effect is o b t a i n e d i f the c o m p o n e n t s are m i x e d . T h e c a t i o n of the sulfite l i q u o r has n o significant effect o n the tensile s t r e n g t h ; c o m p a r a b l e results were o b t a i n e d b o t h w i t h m a g n e s i u m a n d c a l c i u m sulfite l i q u o r s . T h o u g h the contact area between adhesive a n d w o o d is m u c h larger i n p a r t i cleboards t h a n i n w o o d l a m i n a t e s , o n l y 7 5 % of the tensile s t r e n g t h was o b t a i n e d w h e n the l i g n i n - b a s e d adhesive was a p p l i e d as t h e r m o s e t t i n g s y s t e m i n p a r t i cleboards ( T a b l e I I ) . T h e f o l l o w i n g reasons m a y be a p p l i c a b l e : 1. T h e c u r i n g t i m e at r o o m t e m p e r a t u r e under pressure was m u c h longer (8 h) i n the c o l d - s e t t i n g s y s t e m t h a n i n the p a r t i c l e b o a r d p r o ­ d u c t i o n ( T a b l e I I ) . Indeed, the tensile s t r e n g t h c o u l d be increased w h e n the p a r t i c l e b o a r d was pressed at r o o m t e m p e r a t u r e for some h o u r s . H o w e v e r , t h i s procedure is of course not a p p l i c a b l e i n a t e c h ­ n i c a l process. 2. Besides the shorter c u r i n g t i m e , the s p r a y i n g procedure also p l a y s a role i n d e t e r m i n i n g tensile s t r e n g t h . T h e r e l a t i v e l y h i g h v i s c o s i t y of the adhesive caused some p r o b l e m s t h a t c a n , however, easily be overcome i n a t e c h n i c a l process.

T a b l e I I . V e r s a i Tensile S t r e n g t h of L i g n i n - B a s e d A d h e s i v e U s e d t o B o n d P a i r s of W o o d Laminates and W o o d Chips (Particleboard) 1

Procedure and Properties 1) M i x i n g procedure of the adhesive: time and temperature

Wood Laminates

Wood Chips

10 m i n - 2 2 ° C

30 m i n - 2 2 ° C

8 h-22°C

5 mi n - 1 9 0 ° C

0.55 M P a

0.22 M P a

2) P r e s s i n g procedure: time and temperature 3) Tensile s t r e n g t h

C o m p o s i t i o n of the adhesive: O n e p a r t s p r a y - d r i e d , m i l l e d sulfite l i q u o r c o n ­ t a i n i n g c a . 2 0 % sugar a n d 1.5 p a r t s concentrated c u l t u r e filtrate of Trametes versicolor (grown o n 0 . 1 % organosolv l i g n i n i n a 25 L fermenter), c o n t a i n i n g 420 U / m L phenoloxidase a c t i v i t y .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

10.

HAARS ET AL.

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Room-Temperature Curing Adhesives

A p r o b l e m t h a t s t i l l has t o be solved is the deficiency o f w a t e r resistance. T h e sulfonate groups are so p o l a r t h a t the p o l y m e r i z a t e is s t i l l w a t e r - s o l u b l e . A s was m e n t i o n e d before, w a t e r - s o l u b l e f r a c t i o n s o f o r g a n o s o l v l i g n i n s b e c a m e i n s o l u b l e i n water after e n z y m i c p o l y m e r i z a t i o n (11).

T h e r e f o r e , we h o p e d t h a t

a n a d d i t i o n o f p h e n o l - r i c h organosolv l i g n i n w o u l d i m p r o v e t h e w a t e r resistance However, as c a n be seen i n the last l i n e of T a b l e I, t h i s is n o t the case. T h e e n z y m e c o n c e n t r a t i o n was not the r a t e - l i m i t i n g f a c t o r i n the s y s t e m , because a n increase o f a c t i v i t y u p to 1,000 U / m L d i d n o t l e a d t o a higher tensile s t r e n g t h or a b e t t e r w a t e r resistance.

C u r r e n t l y , we are i n v e s t i g a t i n g

several m i x t u r e s o f less p o l a r lignosulfonates a n d k r a f t l i g n i n s . Because these

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studies are b e i n g c o n d u c t e d c o o p e r a t i v e l y w i t h a n i n d u s t r i a l p a r t n e r , t h e results m u s t b e considered c o n f i d e n t i a l at t h i s t i m e . Conclusions F u n g a l p h e n o l o x i d a s e enzymes p r o d u c e d o n waste l i g n i n c o n t a i n i n g effluents were s u i t a b l e b i o c o m p o n e n t s i n c o l d - s e t t i n g a n d t h e r m o s e t t i n g l i g n i n - b a s e d a d hesives. T h e p h e n o l o x i d a s e - l i g n i n bio-adhesive w i l l be s u i t a b l e as t h e r m o s e t t i n g glue i n p a r t i c l e b o a r d p r o d u c t i o n i f the w a t e r resistance o f the b o a r d s c a n be increased.

R e s u l t s i n t h i s area have a l r e a d y been o b t a i n e d .

T h e properties

of l i g n i n - p h e n o l o x i d a s e - b o n d e d p a r t i c l e b o a r d s revealed several advantages c o m p a r e d t o s y n t h e t i c resins:

1. T h e l i g n i n p h e n o l o x i d a s e adhesive i m p l i e s the t o t a l u t i l i z a t i o n o f waste l i g n i n , d i r e c t l y as one c o m p o n e n t o f the adhesive a n d i n d i r e c t l y as n u t r i e n t o f the p h e n o l o x i d a s e - p r o d u c i n g fungus. 2. T h e p r o d u c t i o n of e n z y m e - l i g n i n - b o n d e d p a r t i c l e b o a r d is m u c h less h a z a r d o u s t h a n the p r o d u c t i o n o f i s o c y a n a t e - b o n d e d

particle-

b o a r d , for e x a m p l e . 3. T h e bio-adhesive consists o f renewable r a w m a t e r i a l , so the p r o d u c t i o n does n o t d e p e n d o n the o i l m a r k e t . 4. T h e p h e n o l o x i d a s e - l i g n i n - b o n d e d p a r t i c l e b o a r d s are free o f a n y emission. 5. T h e p h e n o l o x i d a s e - l i g n i n adhesive is n o t o n l y a p p l i c a b l e as t h e r m o s e t t i n g adhesive b u t also as a c o l d - c u r i n g s y s t e m . A ckno wledgment s

P a r t o f t h i s w o r k was p e r f o r m e d as a n R & D p r o j e c t i n c o o p e r a t i o n w i t h the G . A . Pfleiderer C o m p a n y , N e u m a r k t , w i t h s u p p o r t o f the G e r m a n M i n i s t r y of R e s e a r c h a n d T e c h n o l o g y a n d the C o m m i s s i o n o f the E u r o p e a n C o m m u n i t y .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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O r g a n o s o l v l i g n i n was k i n d l y s u p p l i e d b y t h e O r g a n o c e l l C o m p a n y , M u n i c h , F.R.G. Literature Cited 1. Nimz, H . H. Lignin-based wood adhesives. In Wood Adhesives, Chem. and Technol. Pizzi, Α . , E d . ; Marcel Dekker Inc., N Y , 1983.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch010

2. Forss, K . ; Fuhrmann, A. Karatex-the lignin-based adhesive for plywood, particleboard and fiberboard. Paperi ja Puu. 1976, 11, 817-824. 3. Kirkman, A . G.; Gratzl, J. S.; Edwards, L. L. Kraft lignin recovery by ultrafiltration: economic feasibility and impact on the kraft recovery system. Tappi J. 1986, 69(5), 110-114. 4. Pedersen, A . H . F . ; Rasmussen, J . J. Manufacture of chipboard and the like. C a n . Pat. 743 861, 1986. 5. Nimz, H . H . ; Hitze, G . The application of spent sulfite liquors as an adhesive for particleboards. Cell Chem. Technol 1980, 14, 371-38. 6. Shen, K . C.; Calve, L. Ammonium-Based Spent Sulfite Liquor for Waferboard Binder. Reprinted: Adhesive Age, August 1980. 7. Roffael, E. Fortschritte in der Verwendung der Sulfit-ablauge als Bindemittel und Ansatzmittel bei der Herstellung von Holzspanplatten. Adhasion 1979, 23, 368-370. 8. Fengel, D . ; Wegener, G. Wood-Chemistry, Ultrastructure, Reactions, Walter de Gruyter, New York, 1984. 9. Newman, W . H . ; Glasser, W . G . Engineering plastics from lignin. 12 Synthesis and performance of lignin adhesives with Isoxyanate and Melamine. Holzforschung 1985, 39,(6) 345. 10. Haars, Α.; Huttermann, A . Process for producing a binder for wood materials. U.S. Patent 4 432 921, 1984. 11. Haars, Α.; Tautz, D . ; Huttermann, A . Bioconversion of organosoluble lignins by differ­ ent types of fungi. Resources and Conservation, 1986, 13, 37-51. 12. Haars, Α . ; Kharazipour, Α . ; Huttermann, A. Two-component wood adhesives based on lignin and phenoloxidases. Abstr., 3rd Intl. Conf. Biotechnol. Pulp Paper Industry, Stockholm, 1986. 13. Schoemaker, Η. E.; Harvey, P. J.; Bowen, R. M.; Palmer, J. M. O n the mechanism of enzymatic lignin breakdown. FEBS Letters 1985, 183, 7-12. 14. Huttermann, A . Gelchromatographie von Na-Ligninsulfonaten an Sepharose CL 6B. Holzforschung, 1977, 31(2), 45-50. 15. Kharazipour, A. Optimierung eines Verfahrens zur Herstellung von Bindemitteln fur Holzwerkstoffe auf der Basis von Ligninsulfonat und Laccase. Dissertation, Gottingen, December 1983. 16. Haars, Α . ; Huttermann, A . Function of laccase in the white-rot fungus Fomes annosus. Arch. Microbiol. 1980, 125, 233-237. 17. Huttermann, Α . ; Gebauer, M.; Volger, C.; Rosger, C . Polymerisation und Abbau von Natrium-Ligninsulfonat. Holzforschung, 1977, 31(3), 83-89. R E C E I V E D November 11, 1988

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Chapter 11 Biomass Pyrolysis Oil Feedstocks for Phenolic Adhesives H e l e n a C h u m , James D i e b o l d , J o h n Scahill, D a v i d Johnson, and Stuart Black Solar Energy Research Institute Golden, CO 80401

H e r b e r t Schroeder

R o l a n d E. K r e i b i c h

Colorado State University

4201 South 344th Street

Fort Collins, CO 80523

A u b u r n , W A 98001

Fast p y r o l y s i s o f pine sawdust i n a s m a l l v o r t e x reactor o p e r a t i n g at 10 to 20 kg/h a n d 480 t o 520 ° C produces h i g h y i e l d s o f pri­ mary p y r o l y s i s oils (over 5 5 % b y weight o n a d r y basis). T h e v o r t e x reactor t r a n s m i t s very h i g h heat fluxes t o the s a w d u s t , c a u s i n g pri­ marily d e p o l y m e r i z a t i o n o f the constituent p o l y m e r s i n t o m o n o m e r s a n d oligomers. A p r e l i m i n a r y scheme separates t h e r a w oils i n t o a c a r b o h y d r a t e - d e r i v e d aqueous f r a c t i o n a n d a p h e n o l i c - r i c h e t h y l a c ­ etate (EA) soluble f r a c t i o n . T h e EA f r a c t i o n is washed w i t h water a n d w i t h aqueous s o d i u m b i c a r b o n a t e t o remove acids y i e l d i n g 2 0 % t o 2 5 % o f the feed as phenols a n d neutrals (P/N) in t h e EA s o l u t i o n . A f t e r ΕA e v a p o r a t i o n , a novolak f o r m u l a t i o n with 5 0 % p h e n o l a n d 5 0 % o f the P/N f r a c t i o n was successfully p r e p a r e d . G e l times for t h e P/N fractions s u i t a b l y prepared are i n t e r m e d i a t e between resorcinol a n d t r a d i t i o n a l phenol-formaldehyde resins. P r e l i m i n a r y p r o j e c t e d a m o r t i z e d p r o d u c t i o n costs for the P/N f r a c t i o n are 10(16) cents per p o u n d for a 1,000(250) tons per d a y p l a n t ( $ 1 0 / d r y t o n feedstock, 1 5 % interest w i t h 20-year a m o r t i z a t i o n ) . P y r o l y s i s o f biomass is k n o w n t o produce a c o m p l e x m i x t u r e o f p h e n o l i c c o m ­ p o u n d s , w h i c h are derived p r i m a r i l y f r o m the l i g n i n f r a c t i o n o f t h e biomass (1-4)- E l d e r a n d Soltes (5, 6) have investigated a p h e n o l i c f r a c t i o n o b t a i n e d f r o m p y r o l y s i s oils m a d e i n a n u p draft gasifier b y T E C H A I R as a source o f p h e n o l i c adhesives; a phenolics f r a c t i o n was separated b y s o l u b i l i t y differences o f o i l fractions based o n s o l u b i l i t y o f acids i n aqueous b i c a r b o n a t e s o l u t i o n s a n d 0097-6156/89/0385-0135$06.00A)

c

1989 American Chemical Society

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s o l u b i l i t y o f the phenolics f r a c t i o n i n aqueous a l k a l i s o l u t i o n . A d h e s i v e f o r m u l a t i o n s were p r e l i m i n a r i l y tested, a n d the effect o f a few m e t a l ions (such as b a r i u m ) o n the gel t i m e s of adhesives was m e a s u r e d . T h e f o r m u l a t i o n s tested m e t w i t h l i m i t e d success. These results suggested t h a t these oils w o u l d have to be c h e m i c a l l y m o d i f i e d t o be a f u l l replacement for p h e n o l or c o u l d be c o n s i d ered as s i m p l e extenders for p e t r o l e u m - d e r i v e d p h e n o l . R u s s e l l a n d R e i n m a t h ( 7 ) have e m p l o y e d a s i m i l a r f r a c t i o n a t i o n m e t h o d o n oils f r o m high-pressure b i o m a s s l i q u e f a c t i o n (8). A l i m i t e d a m o u n t o f adhesive t e s t i n g was c a r r i e d o u t , a n d a few b o n d e d w o o d specimens were s h o w n t o have tensile strengths s u p e r i o r t o the adhesive b o n d o f a c o m m e r c i a l b i r c h veneer (9). T h i s chapter describes the i n i t i a l results of c o n v e r t i n g waste sawdust i n t o phenolics t h r o u g h fast p y r o l y s i s e m p l o y i n g a v o r t e x reactor a n d a very fast heat transfer t o d e p o l y m e r i z e b i o m a s s i n t o m o n o m e r i c a n d o l i g o m e r i c c o m p o n e n t s . T h e p y r o l y s i s m e t h o d a n d the c h e m i c a l f r a c t i o n a t i o n e m p l o y e d t o isolate the p h e n o l i c - r i c h f r a c t i o n used i n the subsequent adhesive gel t e s t i n g are d e s c r i b e d . R e s u l t s o f a n e c o n o m i c e v a l u a t i o n o f the process are presented as w e l l as the c h a r a c t e r i z a t i o n o f the p h e n o l i c - r i c h m a t e r i a l . A n o v o l a k a n d a resol were successfully p r e p a r e d w i t h these c o m p o u n d s . Experimental

Methodology

P r i m a r y P y r o l y s i s V a p o r G e n e r a t i o n i n t h e V o r t e x R e a c t o r (10). T h e p y r o l y s i s reactor used t o generate the p y r o l y s i s oils is s h o w n s c h e m a t i c a l l y i n F i g u r e 1. C o a r s e softwood sawdust ( < 5 m m ) was metered by a screw feeder i n t o the e n t r a i n e d s o l i d s / g a s flow f r o m the e x i t o f the recycle l o o p . T h e I D o f the 300 series stainless steel recycle l o o p was 11 m m . N i t r o g e n was used as the carrier gas r a t h e r t h a n s t e a m . T h e e n t r a i n e d particles flowed t o the n i t r o g e n ejector where t h e y were accelerated b y the supersonic j e t t o velocities over 100 m / s . T h e fastm o v i n g e n t r a i n e d solids flow t h e n entered t a n g e n t i a l l y i n t o the v o r t e x reactor. Inside the v o r t e x reactor, the b i o m a s s particles were centrifuged to the w a l l a n d were forced i n t o a n a b n o r m a l l y t i g h t h e l i c a l p a t h t h r o u g h the reactor. A s the p a r t i c l e s s l i d a n d b o u n c e d o n the w a l l , they were i n excellent t h e r m a l contact w i t h the e x t e r n a l l y heated w a l l m a i n t a i n e d at 625 ° C . U n d e r these c o n d i t i o n s , the p a r t i c l e surface is very r a p i d l y heated t o a b o u t 450 ° C , where p y r o l y s i s to oils is f a v o r e d . T h e d i a m e t e r o f the v o r t e x t u b e reactor was 13 c m , a n d i t s l e n g t h was 70 c m . A 5 - c m - d i a m e t e r , a x i a l e x i t t u b e p r o t r u d e d i n t o t h e aft e n d of the v o r t e x reactor, w h i c h served t o encourage p a r t i a l l y p y r o l y z e d feedstock a n d large char p a r t i c l e s t o enter the recycle l o o p . T h e feedstock was recycled u n t i l i t was f u l l y p y r o l y z e d , w h i c h allowed a d e c o u p l i n g o f the t i m e r e q u i r e d t o p y r o l y z e the feedstock p a r t i c l e s a n d the gaseous residence t i m e . T h e a b i l i t y of the carrier gas ejector t o create a pressure differential across the recycle l o o p d e t e r m i n e d the rate o f gas flow i n the recycle l o o p . T h e pressure o f the s y s t e m was a d j u s t e d t o m a i n t a i n the feed hopper at a b o u t 250 P a above a t m o s p h e r i c pressure ( 2 . 5 - c m water c o l u m n ) b y r e s t r i c t i n g the flow o u t o f the s y s t e m . T h e

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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char was r e m o v e d i n a hot cyclone. T y p i c a l t h r o u g h p u t for t h i s reactor is 10 t o 20 k g o f sawdust per h o u r w i t h 1- t o 2 - k g carrier gas per k i l o g r a m o f s a w d u s t . O i l C o l l e c t i o n . T h e p y r o l y s i s oils were collected i n a series o f condensers followed b y a coalescing filter t o remove r e s i d u a l aerosols, as s h o w n i n F i g u r e 2. T h e first condenser was a c y c l o n i c condenser 37 c m i n d i a m e t e r w i t h a 4 5 - c m - h i g h c y l i n d r i c a l section. T h e t a n g e n t i a l e n t r y was a r o u n d 5-cm t u b e . T h i s cyclone was w r a p p e d w i t h copper t u b i n g , t h r o u g h w h i c h c h i l l e d water c i r c u l a t e d at a b o u t 20 ° C . T h e c o o l i n g coils were e x t e r n a l l y i r r i g a t e d w i t h water t o transfer the heat f r o m the cyclone w a l l t o the c o o l i n g w a t e r . Inside a n d o u t s i d e the a x i a l o u t l e t o f the cyclone condenser were a d d i t i o n a l c o o l i n g coils. T h e p i p e c o n n e c t i n g the first a n d second condenser was also w r a p p e d w i t h a c h i l l e d water c o o l i n g c o i l a n d a d r a i n was p r o v i d e d for condensate. T h e second condenser consisted of a v e r t i c a l v o r t e x t u b e h a v i n g a 7.5-cm d i a m e t e r w i t h a r e c t a n g u l a r entrance m a d e f r o m a 1.7-cm I D t u b e a n d w i t h the a x i a l o u t l e t near the t a n g e n t i a l entrance. T h e v o r t e x t u b e condenser was cooled b y refrigerated g l y c o l at 2 ° C , w h i c h was c i r c u l a t e d t h r o u g h a copper t u b e w r a p p e d a r o u n d the O D . T h e t h i r d condenser was a 2 0 - L glass c a r b o y i m m e r s e d i n a d r y ice a n d p r o p a n o l b a t h . T h e e n t e r i n g gases were t a n g e n t i a l l y directed o n t o the I D of the carboy. T h e gas a n d aerosol s t r e a m t h e n passed t o the coalescing filter to remove the aerosols. E x c e p t for the glass carboy, the o i l c o l l e c t i o n s y s t e m was stainless steel, since the oils have been s h o w n t o be corrosive t o i r o n a n d z i n c (galvanized i r o n ) . F r a c t i o n a t i o n o f P y r o l y s i s O i l s . P y r o l y s i s o i l o b t a i n e d f r o m the v o r t e x re­ actor was f r a c t i o n a t e d a c c o r d i n g to the scheme s h o w n i n F i g u r e 3. W h o l e o i l (1 kg) was dissolved i n e t h y l acetate ( E A ) o n a 1:1 ( w / w ) basis. T h e o i l was t h e n v a c u u m filtered t h r o u g h filter paper t o remove fine c h a r . U p o n s t a n d ­ i n g , the E A / p y r o l y s i s o i l separated i n t o t w o p h a s e s - a n o r g a n i c r i c h , E A - s o l u b l e phase a n d a n E A - i n s o l u b l e phase. M o s t of the water f o r m e d d u r i n g p y r o l y s i s is c o n t a i n e d i n the E A - i n s o l u b l e phase. T h e E A - s o l u b l e p o r t i o n o f the o i l was washed w i t h water (2 χ 75 m L ) t o remove the r e m a i n i n g w a t e r - s o l u b l e derived products. T h e E A - s o l u b l e phase was t h e n e x t r a c t e d w i t h N a H C 0 ( 5 % w / w , 10 χ 200 m L ) a n d the aqueous layer saved for i s o l a t i o n of the o r g a n i c acids f r a c t i o n . T h e solvent was r e m o v e d f r o m the r e m a i n i n g E A - s o l u b l e f r a c t i o n , w h i c h c o n t a i n e d the p h e n o l i c a n d n e u t r a l s ( P / N ) f r a c t i o n s , o n a r o t o e v a p o r a t o r u n t i l n o Ε A d i s t i l l e d over. T h e Ε A was not d r i e d p r i o r t o e v a p o r a t i o n , b u t r a t h e r , water was azeotroped d u r i n g the d i s t i l l a t i o n . F i n a l water contents of each f r a c t i o n were 0.5 t o 1.0% b y weight. 3

T h e o r g a n i c acids f r a c t i o n was i s o l a t e d b y a c i d i f y i n g the aqueous layer ( p H 2) w i t h 5 0 % H3PO4, s a t u r a t i n g the s o l u t i o n w i t h N a C l , a n d e x t r a c t i n g the o r g a n i c layer w i t h fresh E A . Solvent was removed b y r o t o e v a p o r a t i o n . T h e water-soluble a n d E A - i n s o l u b l e fractions were also i s o l a t e d b y r o t o e v a p o r a t i o n .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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F i g u r e 1. S c h e m a t i c o f v o r t e x reactor for fast p y r o l y s i s .

Pyrolysis Gases Coalescing Filter

Pyrolysis Vapors 400 C

Cyclone Condenser

Dry Ice/ Propanol Vortex Condenser

F i g u r e 2. S c h e m a t i c o f p y r o l y s i s o i l c o n d e n s a t i o n t r a i n .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

11.

C H U M ET AL.

Methods

of

139

Biomass Pyrolysis Oil Feedstocks

Analysis.

Water

Content

of Fractions.

A

chromatographic

m e t h o d was e m p l o y e d u s i n g a glass c o l u m n (6 ft χ 0.2 m m I D ) p a c k e d w i t h P o r a p a k Q S . T h e c h r o m a t o g r a p h s used were a V a r i a n 3700 or a H e w l e t t P a c k a r d 5880. W a t e r contents were also d e t e r m i n e d b y the K a r l F i s h e r m e t h o d b y H u f f ­ m a n Laboratories, Golden, Colorado. Total Carboxyl employed

and Phenolic

Hydroxyl

Content.

were m o d i f i c a t i o n s o f the procedure

S c h u e r c h (11)

for l i g n i n t o t a l p h e n o l i c content.

Conductimetric titrations

described by

Sarkanen and

Spectroscopic determinations

o n t h e p h e n o l i c s a n d n e u t r a l s f r a c t i o n s were c a r r i e d o u t u s i n g the J E O L F X - 9 0 0 F o u r i e r T r a n s f o r m N M R s p e c t r o m e t e r a n d the N i c o l e t 5 S X C F o u r i e r T r a n s f o r m

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I n f r a r e d S p e c t r o m e t e r . I n a d d i t i o n , the s o l i d state C P / M A S

1 3

C - N M R spectra

were o b t a i n e d b y the R e g i o n a l N M R C e n t e r at C o l o r a d o S t a t e U n i v e r s i t y u s i n g c o n d i t i o n s d e s c r i b e d i n B r y s o n et a l . High

Performance

Size

Exclusion

(12). Chromatography.

The Hewlett-Packard

1090 l i q u i d c h r o m a t o g r a p h was used w i t h the H P 1040 d i o d e a r r a y or H P 1 0 3 7 A refractive i n d e x ( a n d H P 3392 i n t e g r a t o r ) detectors.

A fifty  (5 m m , 300

χ 7 m m ) P o l y m e r L a b o r a t o r i e s P L gel ( 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 p o l y m e r gel) c o l u m n was used a n d s t a n d a r d s were as d e s c r i b e d i n C h u m et a l .

(13).

T e t r a h y d r o f u r a n s o l u t i o n s o f o i l a n d o i l f r a c t i o n s were a n a l y z e d . Molecular-Β

earn M ass-Spectrometry.

T h i s p r o c e d u r e was c a r r i e d o u t

e q u i p m e n t d e s c r i b e d by E v a n s a n d M i l n e (14)·

on

P y r o l y s i s o f the o i l s (or frac­

t i o n s ) was p e r f o r m e d u n d e r c o n t r o l l e d c o n d i t i o n s a n d followed i n r e a l t i m e b y a free-jet, m o l e c u l a r b e a m M S . P y r o l y s i s p r o d u c t s a n d f r a g m e n t a t i o n ions were detected. A d h e s i v e T e s t i n g . A l l gel t i m e s o f the adhesive resins were d e t e r m i n e d u s i n g a s t i r r i n g a p p a r a t u s , w h i c h consisted of a 1 5 0 - m m l o n g , 2 5 - m m O D d i s p o s a b l e b o r o s i l i c a t e test t u b e t o w h i c h a t o t a l o f 5.0-g of resin p l u s a n y a d d i t i o n a l c o m p o n e n t was a d d e d . T h e v o l u m e i n the test t u b e was s u c h t h a t a p p r o x i m a t e l y 15 m m above the o u t s i d e b o t t o m e n d was filled w i t h m a t e r i a l . A 6 - m m glass r o d w i t h a f i r e - p o l i s h e d , c i r c u l a r t i p was fastened t o be p a r a l l e l t o a second 6 - m m glass r o d u s i n g two m i n i a t u r e ( 8 - m m w i d e ) w o r m - d r i v e hose c l a m p s . T h e second glass r o d was i n s e r t e d i n t o the chuck o f a low t o r q u e s t i r r i n g m o t o r . W i t h t h i s a r r a n g e m e n t , a t h i c k c y l i n d r i c a l p a t h was s t i r r e d t h a t averaged o n l y 2.5 m m f r o m the test t u b e w a l l , w i t h the result t h a t the s t i r r i n g r o d d i d not f o r m a hole i n the g e l l i n g r e s i n .

O n c e the s t i r r i n g was b e g u n , a p r e h e a t e d ,

m a g n e t i c a l l y s t i r r e d m o l t e n w a x b a t h was r a i s e d r a p i d l y s u c h t h a t t h e lower 40 m m o f the test t u b e was s u b m e r g e d . G e l t i m e s were f r o m i n i t i a l submergence of the test t u b e i n t o the w a x b a t h u n t i l the s t i r r i n g was s t o p p e d b y the g e l l i n g r e s i n . T h e s t i r r e r power s e t t i n g was kept c o n s t a n t , a n d a l l resin gel t i m e s were c o m p a r e d w i t h t h a t for fresh C a s c o p h e n 313 ( B o r d e n C h e m i c a l s l i q u i d p h e n o l f o r m a l d e h y d e resol w i t h 4 0 % s o l i d fillers used w i t h 2 . 5 % N a O H t o have a p H o f 11) d e t e r m i n e d at the same b a t h t e m p e r a t u r e . G e l t i m e s at the same b a t h t e m p e r a t u r e were r e p r o d u c i b l e w i t h i n 1 0 % o f each o t h e r a n d were often m u c h closer together. W h e n the gel t i m e was less t h a n 6 m i n u t e s , i t was r e d e t e r m i n e d

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

at a lower t e m p e r a t u r e because there were i n d i c a t i o n s t h a t , at v e r y s h o r t gel t i m e s , the rate o f heat transfer became the d e t e r m i n i n g f a c t o r . N o v o l a k s were p r e p a r e d u s i n g a p h e n o l - t o - f o r m a l d e h y d e m o l a r r a t i o o f 4:1 w i t h 5 m o l e percent o f H S 0 a d d e d as a c a t a l y s t . T y p i c a l l y , 47 g l i q u i d p h e n o l ( 9 1 . 7 % assay), 3 g p a r a f o r m a l d e h y d e , a n d 30 m L water p l u s the r e q u i r e d a c i d c a t a l y s t were a d d e d t o a three-neck, 2 5 0 - m L r o u n d b o t t o m flask. T h e flask was f i t t e d w i t h a reflux condenser a n d s t i r r e r . T h e m i x t u r e was refluxed for 2 t o 4 h o u r s w i t h the o i l b a t h at 115 ° C ; t h e n , the m i x t u r e was n e u t r a l i z e d w i t h 5 0 % ( w / w ) N a O H a n d the excess p h e n o l removed b y s t e a m d i s t i l l a t i o n for 5 t o 6 h o u r s . T h e r e m a i n i n g viscous o i l y residue was washed r e p e a t e d l y w i t h b o i l i n g water. A n o v o l a k w i t h the P / N f r a c t i o n was p r e p a r e d as described above w i t h 1:1 b y v o l u m e p h e n o l a n d P / N f r a c t i o n a n d h a l f o f the a m o u n t of f o r m a l d e h y d e . Initial wood-gluing testing w i t h this novolak indicates wood failure rather t h a n glueline f a i l u r e .

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

2

4

T o prepare m a t e r i a l for gel t e s t i n g , 2 moles o f p a r a f o r m a l d e h y d e were a d d e d per m o l e o f p h e n o l i c h y d r o x y l . T h e p H was v a r i e d b y a d d i n g aqueous 5 0 % ( w / w ) N a O H dropwise w i t h r a p i d s t i r r i n g . A l l o f t h i s was done i n the disposable b o r o s i l i c a t e test t u b e . T o t a l a m o u n t o f a l l r e s i n f o r m u l a t i o n i n the test t u b e was always a d j u s t e d t o 5.0 g. T h e p y r o l y s i s oils were u s u a l l y s o l u b i l i z e d first b y a d d i n g sufficient N a O H . Results and Discussion F a s t P y r o l y s i s G l o b a l R e a c t i o n s . T h e p y r o l y s i s o f b i o m a s s occurs t h r o u g h a large n u m b e r o f reactions t h a t c a n be g r o u p e d i n t o : 1) d e h y d r a t i o n reactions t h a t f o r m c h a r , w a t e r , a n d a s m a l l a m o u n t o f c a r b o n oxides; a n d 2) d e p o l y m e r i z a t i o n reactions t h a t f o r m m o n o m e r fragments, m o n o m e r s , a n d o l i g o m e r s , w h i c h are o f interest for p h e n o l i c adhesive p r o d u c t i o n . H o w e v e r , as s h o w n i n F i g u r e 4, the p o l y m e r fragments are very reactive, a n d they q u i t e r e a d i l y u n dergo secondary reactions t o f o r m gases a n d m o r e stable o r g a n i c c o m p o u n d s (e.g., p o l y c y c l i c a r o m a t i c t a r s ) . A t low t e m p e r a t u r e s , the d e h y d r a t i o n reactions t h a t favor char f o r m a t i o n are faster t h a n t h e d e p o l y m e r i z a t i o n reactions t h a t f o r m p r i m a r y p y r o l y s i s o i l v a p o r s . However, the d e p o l y m e r i z a t i o n reactions are s t r o n g l y favored at elevated t e m p e r a t u r e s . C o n s e q u e n t l y , i t is necessary t o q u i c k l y heat the b i o m a s s p a r t i c l e s to elevated t e m p e r a t u r e s ( > 4 0 0 ° C ) to m a x i m i z e the p y r o l y s i s o i l y i e l d s a n d t h e n t o r a p i d l y c o o l the p r o d u c t v a p o r s . T h i s r a p i d h e a t i n g requires a large heat flux be p r o v i d e d t o the b i o m a s s s u r face, w h i c h c o n v e n t i o n a l l y w o u l d be achieved by u s i n g very h i g h t e m p e r a t u r e s . However, t h e presence o f the h i g h t e m p e r a t u r e s has the u n d e s i r a b l e effect of excessively h e a t i n g the o i l vapors t o cause some o f t h e m t o decompose t o gases (15). A n a l t e r n a t e m e t h o d o f s u p p l y i n g the large heat fluxes is to use a heat transfer m e c h a n i s m t h a t has a r e l a t i v e l y large heat transfer coefficient. F o r a c h i e v i n g these heat transfer p h e n o m e n a i n a c h e m i c a l reactor, a n e x t e r n a l l y heated v o r t e x t u b e was selected (16). T h e advantage o f t h i s reactor s y s t e m

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

11.

C H U M E T AL.

141

Biomass Pyrolysis Oil Feedstock

#79, 15% water, pH 2.8 Whole Oil I DiMotw In EtOAc/FIIter

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

—•Char: 3%

ι

EtOAc Insol: 29%

I

EtOAc Sol: 71% —Water -NaHC0

WS: 37% A: 7%

3

— Evaporate

P/N: 26%

Figure 3. Pine sawdust pyrolysis o i l fractionation scheme. Yields are on a dry basis.

Secondary Tare

Macropolymerlc Blomaee Solids

Monomerlc Primary Vapors

Ollgomerlc Liquids Macropolymer Char Solids • H 0• C0 2

X

Secondary Gaeee

F i g u r e 4. B i o m a s s p y r o l y s i s g l o b a l m e c h a n i s m .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

is the h i g h y i e l d s of p y r o l y s i s oils a n d the h i g h heat transfer possible f r o m the w a l l t o the b i o m a s s , w h i c h translates t o a r e l a t i v e l y s m a l l reactor w i t h a h i g h throughput

(10).

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

O i l C o l l e c t i o n . T a b l e I shows the t e m p e r a t u r e of the process s t r e a m as i t passed t h r o u g h the heat exchangers, as w e l l as the a m o u n t a n d m o i s t u r e content of condensate collected at each l o c a t i o n . F o r R u n 83, t h i s o i l c o l l e c t i o n t r a i n d e m o n s t r a t e d a wet o i l recovery of 6 7 % of the d r y feedstock for a mass closure of 9 4 % . T h e wet o i l c o n t a i n e d a n average of 1 8 % water of p y r o l y s i s for a recovered y i e l d of 5 5 % d r y p y r o l y s i s o i l .

T a b l e I. P r i m a r y O i l C o l l e c t i o n T r a i n ( R u n 83)

Exit Temperature °C 15-Inch-diameter c y c l o n i c condenser 1-Inch-diameter transfer l i n e H X R 3-Inch-diameter v o r t e x condenser Dry-ice trap C o a l e s c i n g filter Total

50 40 30 -17 -17

Weight Percent of Dry Oil

H 0 Weight Percent in Wet Oil

50 21

20 10 8 30 31 18

23 11 5 100

2

T h e c o l l e c t i o n of the p y r o l y s i s oils is difficult due t o t h e i r tendency t o f o r m aerosols a n d also due t o the v o l a t i l e n a t u r e of m a n y of the o i l c o n s t i t u e n t s . A s the aerosols agglomerate i n t o larger droplets, they c a n be removed b y c y c l o n i c separators. However, the s u b m i c r o n aerosols cannot be efficiently collected b y c y c l o n i c or i n e r t i a l techniques, a n d c o l l e c t i o n b y i m p a c t of the aerosols due to t h e i r B r o w n i a n or r a n d o m m o t i o n m u s t be u t i l i z e d . A coalescing filter is r e l a t i v e l y p o r o u s , b u t i t contains a large surface area for the aerosol p a r t i c l e s to i m p a c t b y B r o w n i a n m o t i o n as t h e y are swept t h r o u g h b y the p y r o l y s i s gases. O n c e the aerosol droplets i m p a c t the filter fibers, t h e y are c a p t u r e d a n d coalesce i n t o large drops t h a t c a n flow d o w n the fibers a n d be collected. P y r o l y s i s Y i e l d s . Before the present c o l l e c t i o n s y s t e m h a d been developed, mass a n d e l e m e n t a l balances showed t h a t the y i e l d s of o x y g e n a t e d p y r o l y s i s oils generated i n the v o r t e x reactor m u s t be very h i g h a n d t h a t the observed large lack of mass balance closure c o u l d not be due t o large water y i e l d s . B a s e d o n e l e m e n t a l a n a l y s i s of the char, o i l , a n d gases, a char y i e l d of 1 2 . 7 % corresponds to c a l c u l a t e d y i e l d s of 6 9 % o i l v a p o r s , 1 4 % water, a n d 4 . 3 % gases. W i t h o u t the recycle l o o p , gas y i e l d s have been observed to be i n the 3 t o 4 % range of the p y r o l y z e d feedstock. However, w i t h the recycle l o o p i n s t a l l e d , the gas y i e l d s

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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C H U M ET AL.

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Biomass Pyrolysis Oil Feedstock

were seen t o increase t o a b o u t 1 4 % due t o a n increase i n the c r a c k i n g of the o i l v a p o r s t o a c h a r a c t e r i s t i c a l l y different slate of p e r m a n e n t gases (15).

Minor

changes i n the o p e r a t i o n of t h e v o r t e x reactor are e x p e c t e d t o reduce the gas y i e l d s i n the f u t u r e a n d t o result i n e n h a n c e d p y r o l y s i s o i l y i e l d s . P h e n o l i c s / N e u t r a l s f o r A d h e s i v e s . T h e f r a c t i o n a t i o n scheme d e s c r i b e d i n F i g u r e 3 allowed the i s o l a t i o n o f 2 1 % t o 3 1 % of the s t a r t i n g o i l as a P / N f r a c t i o n , as s h o w n i n T a b l e I I . T h i s f r a c t i o n consists o f 7 3 % p h e n o l i c s , e x t r a c t able b y aqueous s o d i u m h y d r o x i d e s o l u t i o n f r o m a n e t h y l acetate s o l u t i o n , a n d 2 7 % neutrals.

T h e t o t a l y i e l d of the P / N f r a c t i o n was r e p r o d u c i b l e (cf.

r u n s 79

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

a n d 83 i n T a b l e I I ) . I s o l a t i o n of the P / N f r a c t i o n f r o m o i l s condensed f r o m the c y c l o n e a n d t r a n s f e r - l i n e heat exchanger i n d i c a t e s t h a t the P / N f r a c t i o n p r e d o m i n a t e s i n the t r a n s f e r - l i n e heat exchanger condensate.

E x p e r i m e n t 78

was collected f r o m the c y c l o n i c condenser, a n d t h u s , the results c o m p a r e w e l l w i t h those f r o m e x p e r i m e n t 81 A .

T a b l e I I . F r a c t i o n a t i o n of S a w d u s t P y r o l y s i s O i l s Y i e l d s (% o n d r y o i l basis) Ethyl Acids

Phenols/

Experiment

Acetate

Water

No.

Insoluble

Soluble

78

43

25

6

21

79

29

37

7

26

81

23

39

7

31

8 1 A - cyclone

45

26

5

23

8 1 B - heat exchanger

20

28

9

47

Neutrals

T h e typical whole o i l contained about 6.2% and 0.4% phenolic hydroxy and c a r b o x y l i c a c i d contents, respectively. T h e P / N f r a c t i o n c o n t a i n e d 6 . 6 % p h e n o l i c h y d r o x y a n d n o c a r b o x y l i c a c i d content, whereas, the acids f r a c t i o n c o n t a i n e d 9 . 2 % a n d 0 . 9 % o f p h e n o l i c h y d r o x y a n d c a r b o x y l i c a c i d contents, respectively. T h e 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 of selected f r a c t i o n s of i s o l a t e d o i l c o m p o n e n t s are s h o w n i n F i g u r e 5.

T h e phenols f r a c t i o n c o n t a i n e d the

highest a p p a r e n t m o l e c u l a r weight c o m p o n e n t s , a n d t h e i r a b s o r p t i o n s p e c t r a i n the U V region resembled t h a t of l o w - m o l e c u l a r - w e i g h t l i g n i n s . F r o m the m o l e c u l a r b e a m M S o f the p y r o l y s i s p r o d u c t s o f the P / N f r a c t i o n s , a n u m b e r of p h e n o l i c c o m p o u n d s were detected:

guaiacol

(2-methoxyphenol)

( m / z 124), catechols ( m / z 110), isomers o f s u b s t i t u t e d 2 - m e t h o x y p h e n o l s a l k y l groups such as m e t h y l ( m / z 138), v i n y l ( m / z 150),

with

3-hydroxy-propen(l)-

y l ( m / z 180), a l l y l ( m / z 164), h y d r o x y e t h y l ( m / z 168), a n d e t h y l (152), m o s t l i k e l y i n the para p o s i t i o n .

I n a d d i t i o n , a few c a r b o h y d r a t e - d e r i v e d

compo-

nents are also present i n t h i s f r a c t i o n such as f u r f u r y l a l c o h o l a n d o t h e r f u r f u r a l derivatives.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

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ADHESIVES F R O M RENEWABLE RESOURCES

W h o l e Oil

Acids

F i g u r e 5. H i g h - p e r f o r m a n c e size e x c l u s i o n c h r o m a t o g r a m s o f pine sawdust p y r o l y s i s oils a n d fractions o f acids, phenols, a n d n e u t r a l s c o n t a i n e d i n the e t h y l acetate soluble o i l .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

11.

C H U M ET AL.

145

Biomass Pyrolysis Oil Feedstocks

F r o m the p r o t o n N M R o f the P / N f r a c t i o n , of the t o t a l p r o t o n i n t e n s i t y , the a r o m a t i c p r o t o n s (6.5 t o 10 p p m ) c o n s t i t u t e 5 2 % , the a l i p h a t i c (1.5 t o 3.5 p p m ) a b o u t 2 0 % , a n d the m e t h o x y region (3.0 t o 4.2 p p m ) 3 0 % , w h i c h is i n agreement w i t h the p r o p o s e d c o m p o u n d s o b t a i n e d f r o m the m o l e c u l a r b e a m M S pyrolysis experiment. T h e

1 3

C - N M R s p e c t r a o f the P / N f r a c t i o n also i n d i c a t e d

m i x t u r e s o f c o m p o u n d s w i t h a r o m a t i c c a r b o n s i n the 110 t o 148 p p m r e g i o n , a very p r o n o u n c e d m e t h o x y peak at 55.6 p p m , a n d a l i p h a t i c c a r b o n s . P r e l i m i n a r y A d h e s i v e T e s t i n g R e s u l t s . P h e n o l at a p H o f 11 w i t h t w i c e the m o l a r a m o u n t o f f o r m a l d e h y d e was c o m p a r e d w i t h C a s c o p h e n 313 ( c o m m e r c i a l

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

s o f t w o o d p l y w o o d r e s i n b y B o r d e n C h e m i c a l s ) . A t 124 ° C , C a s c o p h e n 313 t o o k 12.2 m i n u t e s t o g e l , whereas, the p h e n o l w i t h a d d e d p a r a f o r m a l d e h y d e d i d not gel even after 30 m i n u t e s . T a b l e I I I .

T a b l e I I I . G e l T i m e s for C a s c o p h e n a n d P h e n o l i c s / N e u t r a l s from Pyrolysis Oils

pH

Temperature

Gel Time,

Equivalent

Percent

^C

Minutes

Cascophen T i m e

Equivalent T i m e

118

15.3

125

12.2

130

9.7

Cascophen

1

Phenols/Neutrals

2

9.0

3

127

12.0

11.1

9.5

4

127

5.2

11.1

9.5

124

3.7

12.6

9.5

112

6.2

18.2

29 34

9.5

101

10.8

23.4

46

9.5

89

24J)

29J)

-

h g C a s c o p h e n + 0.2 m L o f 5 0 % N a O H , p H 11.5.

x

2

4g

Phenol/neutrals from

sawdust

p y r o l y s i s oils reacted

with

1

g

p a r a f o r m a l d e h y d e a n d 0.5 m L of 5 0 % N a O H . 3

0 . 2 m L of 5 0 % N a O H .

4

0 . 4 m L of 5 0 % N a O H .

O f the v a r i o u s f r a c t i o n s of p y r o l y s i s o i l , o n l y the P / N f r a c t i o n gave a p o s i t i v e gel test u n d e r these c o n d i t i o n s . I n p r e l i m i n a r y gel t e s t i n g o f the P / N e x t r a c t , a r b i t r a r i l y 1 g o f p a r a f o r m a l d e h y d e was a d d e d to 4 g o f the e x t r a c t . T h e p H of

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

the e x t r a c t was a d j u s t e d b y a d d i n g 0.2 t o 0.8 m L of 5 0 % ( w / w ) N a O H . T h e r e a p p e a r e d t o be a s t r o n g buffering o f the p H b y the e x t r a c t at a p H o f 9.5. C a s c o p h e n 313 was used for c o m p a r i s o n . T h e i n f o r m a t i o n o b t a i n e d is presented i n T a b l e I I I . A t 0.5 m L of a d d e d N a O H , the gel t i m e of the P / N f r a c t i o n was m u c h shorter t h a n t h a t of the C a s c o p h e n , w i t h a gel t i m e of o n l y 2 9 % t h a t o f C a s c o p h e n at 124 ° C , at 112 ° C , i t was 3 4 % ; a n d at 101 ° C i t was 4 6 % t h a t o f C a s c o p h e n . A t the o r i g i n a l p H of 3 o f the P / N f r a c t i o n , there was no g e l l i n g o f the m i x t u r e even at 132 ° C w i t h the same a m o u n t o f a d d e d p a r a f o r m a l d e h y d e . T h e n o v o l a k s p r e p a r e d were characterized b y s o l i d - s t a t e C - N M R spec­ t r a . T h e peaks i n the C - N M R s p e c t r a o b t a i n e d i n t h i s s t u d y were assigned o n the basis of c o m p a r i s o n s w i t h s o l u t i o n - a n d s o l i d - s t a t e C - N M R of n o ­ v o l a k s (12) a n d s o l u t i o n - s t a t e l i g n i n N M R s p e c t r a (17, 18). T h e s p e c t r a o f a p h e n o l - f o r m a l d e h y d e n o v o l a k a n d s i m i l a r n o v o l a k i n w h i c h 5 0 % b y v o l u m e of the p h e n o l was replaced b y the P / N f r a c t i o n f r o m the fast p y r o l y s i s o f p i n e sawdust are c o m p a r e d i n F i g u r e 6. T h e a u t h e n t i c n o v o l a k ( F i g u r e 6a) p r o d u c e d m a i n peaks ( f r o m d e c o n v o l u t i o n ) at 150, 130, a n d 120 p p m c o r r e s p o n d i n g t o hydroxy-substituted aromatic carbons, unsubstituted meia-aromatic carbons, a n d u n s u b s t i t u t e d p a r a - a r o m a t i c carbons, respectively; a n d i n the a l i p h a t i c re­ g i o n , the m a i n peaks are at 35 a n d 40 p p m , assigned t o ortho-para m e t h y l e n e bridges a n d para-para m e t h y l e n e bridges, respectively. T h e presence a n d i n t e n ­ sity o f s u c h peaks c o r r e s p o n d t o the f o r m a t i o n o f r a n d o m n o v o l a k s as discussed by B r y s o n et a l . (12). O n s u b s t i t u t i o n o f p h e n o l w i t h the P / N f r a c t i o n ( F i g ­ ure 6 b ) , the key peaks o f the r a n d o m n o v o l a k r e m a i n , b u t peaks c h a r a c t e r i s t i c of the types o f p h e n o l i c c o m p o u n d s present also appear such as at 155 p p m (metaa r o m a t i c carbons a t t a c h e d t o m e t h o x y g r o u p s ) , 55 p p m ( m e t h o x y g r o u p s ) , a n d 20 p p m ( a l i p h a t i c groups). K e y differences between the a u t h e n t i c n o v o l a k a n d the P / N - s u b s t i t u t e d n o v o l a k are i n r e l a t i v e p e a k intensities. W h i l e the r a t i o of u n s u b s t i t u t e d m et a- a r o m a t i c carbons t o ortho-para m e t h y l e n e bridges (130 t o 35 p p m ) i n the a u t h e n t i c s a m p l e is r o u g h l y 7:1, the r a t i o i n the P / N n o v o l a k is a p ­ p r o x i m a t e l y 4:1 ( 6 0 % o f the o r i g i n a l value). S u c h a difference is e x p e c t e d , since the P / N n o v o l a k contains a n u m b e r of met α-substituted m e t h o x y c o m p o u n d s . T h e p h e n o l - f o r m a l d e h y d e novolak has a higher r a t i o o f h y d r o x y - s u b s t i t u t e d a r o ­ m a t i c c a r b o n s (150 p p m ) to u n s u b s t i t u t e d m e t a - a r o m a t i c carbons (130 p p m ) t h a n the P / N n o v o l a k ( 4 0 % versus 3 0 % ) . 1 3

1 3

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1 3

A few p r e l i m i n a r y resols have also been m a d e w i t h a 5 0 % replacement of p h e n o l b y the P / N f r a c t i o n o f the w o o d o i l . Tests have s h o w n these adhesives t o have shear strengths a n d w o o d f a i l u r e c o m p a r a b l e t o t h a t o b t a i n e d w i t h B o r d e n ' s C a s c o p h e n 313. T h i s work is i n progress. T e c h n o e c o n o m i c A s s e s s m e n t . A l t h o u g h the use of f r a c t i o n a t e d p y r o l y s i s oils as adhesives is s t i l l i n the e a r l y phases of development, a t e c h n o l o g i c a l as­ sessment o f the process was m a d e u s i n g the best p r o j e c t i o n s a v a i l a b l e for the y i e l d s a n d o p e r a t i n g c o n d i t i o n s . A d e t a i l e d process flowsheet was m a d e w i t h mass a n d energy balances a r o u n d each m a j o r piece o f e q u i p m e n t . T h e e q u i p ­ ment was sized a n d t h e n v a l u a t e d u s i n g d a t a f r o m the l i t e r a t u r e . T h e costs

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

C H U M ET AL.

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11.

F i g u r e 6. C P / M A S

1 3

C - N M R of novolaks:

a) p h e n o l - f o r m a l d e h y d e ;

b) phe-

n o l : p h e n o l s / n e u t r a l s (1:1) p i n e sawdust p y r o l y s i s o i l f r a c t i o n a n d f o r m a l d e h y d e .

American Chemical Society Library 1155 16th St. N.W. Washington. U.C. 20036 In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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for i n s t a l l e d e q u i p m e n t were c a l c u l a t e d u s i n g s t a n d a r d cost factors (19). All costs were u p d a t e d t o f o u r t h q u a r t e r 1986 d o l l a r s u s i n g the C E cost i n d e x . T h e process flowsheet i n c l u d e d a feedstock d r y i n g step u s i n g waste process heat. T h e d r y i n g step has a significant cost, b u t any m o i s t u r e i n the feedstock w o u l d be e v a p o r a t e d first i n the p y r o l y s i s step a n d t h e n a c c u m u l a t e d i n the process where i t w o u l d have t o be e v a p o r a t e d a g a i n w i t h p r e m i u m heat i n the i n c i n ­ e r a t i o n section o f the furnace. S t e a m was used as the carrier gas at a weight r a t i o o f 1.33 t i m e s t h a t o f the feedstock. T h e energy for the d r y i n g step w o u l d be o b t a i n e d f r o m the c o o l i n g a n d c o n d e n s a t i o n o f the p y r o l y s i s process s t r e a m . T h e e x t r a c t i o n of the P / N f r a c t i o n was assumed to be b y the use o f Ε A as the solvent. T h e E A soluble acids were removed by a n aqueous s o d i u m c a r b o n a t e w a s h . T h e aqueous phase was first heated t o b o i l off the E A , w h i c h has a s i g ­ nificant s o l u b i l i t y i n w a t e r . T h e water-soluble organics were t h e n c o n c e n t r a t e d i n triple-effect evaporators p r i o r t o t h e i r i n c i n e r a t i o n i n the convection section of the p y r o l y s i s furnace. T h e economics o f the p r o d u c t i o n of the P / N f r a c t i o n were e v a l u a t e d for a 1 5 % interest rate over a 20-year a m o r t i z a t i o n p e r i o d . T h e p r o d u c t i o n costs were s h o w n t o be a s t r o n g f u n c t i o n o f p l a n t size a n d feedstock costs as s h o w n i n F i g u r e 7. T h e cost t o p r o d u c e the P / N f r a c t i o n was p r o j e c t e d t o be a b o u t $0.10 per p o u n d i n a p l a n t c o n s u m i n g 1,000 T P D feedstock cost­ i n g $10 per d r y t o n . P r o d u c t i o n i n a s m a l l 250 T P D p l a n t w o u l d a d d a b o u t $0.06 per p o u n d . Increasing the feedstock cost t o $40 per d r y t o n w o u l d a d d $0.07 per p o u n d o f P / N . I f the p l a n t were t o be i n t e g r a t e d w i t h a n e x i s t i n g forest p r o d u c t s m i l l , some o f the costs r e l a t e d t o feedstock p r e p a r a t i o n w o u l d be c o n s i d e r a b l y reduced. It was c o n c l u d e d t h a t t h i s process has considerable economic p o t e n t i a l i f i t is developed p r o p e r l y a n d the a s s u m p t i o n s m a d e are verified t h r o u g h a d d i t i o n a l research a n d development. Conclusions Fast p y r o l y s i s o f b i o m a s s provides a m e t h o d for the p r o d u c t i o n of phenolics t h a t has the p o t e n t i a l t o replace at least 5 0 % or m o r e o f the p h e n o l i n p h e n o l f o r m a l d e h y d e t h e r m o s e t t i n g resins. T h e gel tests i n d i c a t e t h a t the P / N f r a c t i o n s f r o m p i n e sawdust p y r o l y s i s w i t h p a r a f o r m a l d e h y d e have shorter gel t i m e s t h a n c o m m e r c i a l p l y w o o d resins s u c h as C a s c o p h e n 313, even w i t h o u t p r e p o l y m e r f o r m a t i o n . A n o v o l a k f o r m u l a t i o n has been p r e p a r e d u s i n g 1:1 b y v o l u m e of p h e n o l a n d P / N f r a c t i o n a n d a b o u t h a l f o f the a m o u n t o f f o r m a l d e h y d e t h a t w o u l d be used t h a n i f p h e n o l alone were e m p l o y e d . V e r y p r o m i s i n g resols have also been m a d e w i t h a s i m i l a r s u b s t i t u t i o n o f the P / N f r a c t i o n for p h e n o l . W o o d t e s t i n g a n d resin f o r m u l a t i o n development are o n g o i n g a c t i v i t i e s . T h e p r o j e c t e d economics suggest t h a t a d d i t i o n a l research a n d development o f t h i s process are fully warranted.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

11.

C H U M ET AL.

149

Biomass Pyrolysis Oil Feedstock

••Feed HDD Extn

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$/lb of Phenols and Neutrals F i g u r e 7. A m o r t i z e d costs o f phenolics a n d n e u t r a l s f r a c t i o n f r o m p i n e sawdust p y r o l y s i s c a l c u l a t e d as a f u n c t i o n o f feedstock cost a n d p l a n t size.

Note that

the c a l c u l a t i o n s i n c l u d e costs associated w i t h a l l feedstock p r e p a r a t i o n as i f t h i s were a n i n d e p e n d e n t p l a n t .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

A cknowledgment s T h i s w o r k was s u p p o r t e d b y the Office of I n d u s t r i a l P r o g r a m s of the U . S . p a r t m e n t of E n e r g y , W a s t e P r o d u c t s U t i l i z a t i o n B r a n c h , F T P 587.

The

De­

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agement o f the D O E p r o g r a m m a n a g e r s , M r . A . S c h r o e d e r a n d D r . J . C o l l i n s , is g r a t e f u l l y a c k n o w l e d g e d . T h e C o l o r a d o S t a t e U n i v e r s i t y R e g i o n a l N M R ter, f u n 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 G r a n t N o .

g r a t e f u l l y a c k n o w l e d g e d for the C P / M A S

N M R spectra.

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Dr.

R. Evans kindly

p r o v i d e d the m o l e c u l a r - b e a m m a s s - s p e c t r o m e t r i c d a t a . H i s h e l p a n d t h a t of D r . T . M i l n e are g r a t e f u l l y a c k n o w l e d g e d . W e

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch011

determinations and M r .

also t h a n k M s .

F . P o s e y for

M . R a t c l i f f for the s o l u t i o n - s t a t e N M R d a t a .

water

Mr.

A.

P o w e r ( A . J . P o w e r a n d A s s o c i a t e s , B o u l d e r , C o l o r a d o ) p e r f o r m e d the e c o n o m i c assessment, w h i c h w i l l be p u b l i s h e d i n d e t a i l elsewhere. Literature Cited

1. Soltes, E. J.; Elder, T . J . In Organic Chemicals from Biomass, Goldstein, I. S., E d . ; C R C : Boca Raton, FL, 1981, p. 63. 2. Overend, R. P.; Milne, T . Α.; Mudge, L . K . , Eds.; Fundamentals Biomass Conversion, Elsevier: London, 1985.

of Thermοchemical

3. Soltes, E. J.; L i n , S . - C . In Progress Biomass Conversion; Tillman, D . Α.; John, E. C., Eds.; Academic Press: New York, Vol. 4, 1983, p. 79, and references therein. 4. Preprints of papers presented at the Denver American Chemical Society Meeting, Production, Analysis and Upgrading Oils from Biomass, Division of Fuel Chemistry Preprints, A C S : Washington, D C , Vol. 32, No. 2, 1987. 5. Elder, T . J . ; Soltes, E. J . Wood and Fiber, 1979, 12,

217.

6. Elder, T . J . The Characterization and Potential Utilization of Phenolic Compounds Found in Pyrolysis Oil. P h . D . Dissertation, Texas A & M University, 1979. 7. Russel, J . ; Reinmath, W . F . ; "Method for Making Adhesives from Biomass," Patent 4 508 886, 1985.

U.S.

8. Davis, H. G.; Eames, Μ. Α.; Figueroa, C.; Gansby, R. R.; Schlaeger, L. L.; Watt, D . W . In Fundamentals of Thermochemical Conversion of Biomass; Overend, R. P.; Milne, Τ. Α.; Mudge, L . K., Eds.; Elsevier: London, 1027, 1985. 9. Nelson, D . Α.; Molten, P. M . ; Russell, J . Α.; Hallen, R. T . Ind. Res. Dev., 23. 471-475, 1984.

Eng.

Chem. Prod.

10. Diebold, J . P.; Scahill, J . W . Division Fuel Chemistry preprints, A C S : Washington, D C ; Vol. 32, No. 2, p. 21, 1987. 11. Sarkanen, Κ. V . ; Schuerch, C. Anal. Chem., 1955, 27,

1245.

12. Bryson, R. L . ; Hatfield, G . R.; Early, Τ. Α.; Palmer, A . R.; Maciel, G . E. Macro­ molecules, 1983, 16, 1669. 13. Chum, H . L.; Johnson, D . K.; Tucker, M . P.; Himmel, M . E. Holzforschung, 1987, 97. 14. Evans, R. J . ; Milne, T . A . Energy and Fuels, 1987, 1 (2),

41,

123.

15. Diebold, J . P., The Cracking Kinetics of Depolymerized Biomass Vapors in a Contin­ uous, Tubular Reactor, Thesis T-3007, Colorado School of Mines, Golden, C O , 1985.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

11.

C H U M E T AL.

Biomass Pyrolysis OU Feedstocks

151

16. Diebold, J . P. In Proceedings of Specialist's Workshop on Fast Pyrolysis of Biomass, Copper Mountain, C O , October 19-22,1987. Solar Energy Research Institute, Golden, C O , SERI/CP-622-1096 (NTIS). 17. Nimz, H. H.; Tschirner, U.; Stahle, M.; Lehmann, R.; Schlosser, M. J. Wood Chem. Technol., 1984, 4 , 265. 18. Kringstadt, K . P.; Morck, R. Holzforschung, 1983, 37, 237. 19. Guthrie, Κ. M. Process Plant Estimating, Co. of America, C A , 1974.

Evaluation and Control, Craftsman Book

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R E C E I V E D September 6, 1988

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 12 Condensed Tannins in Adhesives Introduction and Historical Perspectives

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch012

Herbert L . Hergert Repap Technologies Inc. P . O . Box 766 2650 Eisenhower Avenue Valley Forge, P A 19482

Sequential extraction of the bark of most species of conifers and deciduous trees, using water or polar organic solvents followed by aqueous alkali, yields two fractions of polymeric polyphenols, respectively referred to as condensed tannins and phenolic acids. These materials react with formaldehyde or phenol-formaldehyde prepolymers to make suitable resins for cold-setting waterproof adhesives for wood lamination or thermosets for exterior-grade plywood. Commercial production of bark extracts from western hemlock, Douglas-fir, and redwood in North America found limited application for adhesives during the period 1955-1975. Wattle (Acacia mearnsii) bark tannins, produced in South Africa, are currently used in adhesive formulations. The availability of large quantities of pine bark residues from pulping operations in the Americas, Australia, and New Zealand located near waferboard, plywood, and wood-laminating producers who consume substantial amounts of phenolic adhesives suggests that the time is ripe for production of bark-based adhesives. Lower cost, higher yield isolation techniques, in particular, may still be needed for this objective to become a commercial reality. T h e conversion o f a n i m a l hides i n t o leather b y t r e a t m e n t w i t h water-soluble p l a n t e x t r a c t i v e s has been p r a c t i c e d since a n t i q u i t y . T h i s process became k n o w n as t a n n i n g a n d o b v i o u s l y i n v o l v e d t h e r e a c t i o n o f a n a t u r a l l y o c c u r r i n g e x t r a c tive, t a n n i n , w i t h t h e p r o t e i n i n t h e h i d e . W e n o w k n o w , o f course, t h a t t a n n i n s comprise a whole s p e c t r u m o f c h e m i c a l c o m p o u n d s , b u t generally t h e y are p o l y p h e n o l i c a n d p o l y m e r i c . T a n n i n s have been isolated f r o m a w i d e v a r i e t y of r a w m a t e r i a l s , i n c l u d i n g insect galls, f r u i t s k i n s , seed h u l l s , leaves, b a r k , a n d h e a r t w o o d . Indeed, t a n n i n s are o f nearly u b i q u i t o u s occurrence i n higher orders 0097-6156/89/0385-0155$06.00/0 « 1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch012

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of the p l a n t k i n g d o m . Since t h e y occur i n highest concentrations i n those tissues of a p l a n t exposed t o a i r , i t is generally agreed t h a t t h e i r f u n c t i o n i n a p l a n t is t o h e l p i t resist t h e i n v a s i o n o f pathogens. D u r i n g t h e e a r l y a n d m i d d l e stages o f t h e i n d u s t r i a l r e v o l u t i o n , r a p i d l y i n creasing q u a n t i t i e s o f leather were r e q u i r e d for factories a n d t r a n s p o r t a t i o n as w e l l as for f o o d p r o d u c t i o n t o s u p p l y t h e e x p l o d i n g p o p u l a t i o n s s p a w n e d b y t h i s u p h e a v a l . B y t h e b e g i n n i n g o f t h e t w e n t i e t h century, leather t a n n i n g was one o f t h e m a j o r i n d u s t r i e s i n N o r t h A m e r i c a . Since t h e i n d u s t r y r e q u i r e d r e l a t i v e l y c o n c e n t r a t e d sources o f t a n n i n s , m u c h t e c h n i c a l a t t e n t i o n w a s devoted t o analyses o f p l a n t m a t e r i a l s for t a n n i n content. O n l y t h e b a r k a n d heart w o o d of a l i m i t e d n u m b e r o f w o o d species were f o u n d t o c o n t a i n sufficient q u a n t i t i e s of w a t e r - s o l u b l e t a n n i n s t o m a k e t h e m a t t r a c t i v e for c o m m e r c i a l e x t r a c t i o n . I n the U n i t e d S t a t e s , t h e b a r k o f eastern h e m l o c k a n d some o a k species w a s t h e m a i n source o f t a n n i n s a t t h e t u r n o f t h e c e n t u r y (1). Subsequently, chestnut w o o d b e c a m e t h e m a i n source o f t a n n i n u n t i l i t l a r g e l y d i s a p p e a r e d because o f chestnut b l i g h t . I m p o r t e d e x t r a c t s f r o m quebracho a n d , t o a lesser extent f r o m m i m o s a (Acacia Sp.), g r a d u a l l y d i s p l a c e d domestic t a n n i n p r o d u c t i o n . T h e r a p i d g r o w t h o f the p u l p a n d p a p e r i n d u s t r y f o l l o w i n g W o r l d W a r I I c o u p l e d w i t h a renewed scientific interest i n u t i l i z a t i o n o f b a r k a n d w o o d residues l e d t o investigative p r o g r a m s o n b a r k a n d w o o d t a n n i n s . T h e leather i n d u s t r y was c o n t i n u i n g t o decline i n i m p o r t a n c e , so other a l t e r n a t i v e s were needed. O n e of these w a s replacement o f p h e n o l i n whole or i n p a r t i n p h e n o l - f o r m a l d e h y d e adhesive f o r m u l a t i o n s . T h i s w o r k progressed t o t h e p o i n t where c o m m e r c i a l q u a n t i t i e s o f p o l y p h e n o l i c e x t r a c t i v e s were m a d e a n d s o l d for adhesive a p p l i c a t i o n . E x c e s s i v e c a p a c i t y a n d l o w p e t r o c h e m i c a l l y derived p h e n o l prices i n t h e 1960's l e d t o t h e demise o f t h i s effort i n t h e U n i t e d States (2,3). M o r e recently, there has been a renewed r e c o g n i t i o n o f the p o t e n t i a l o f b a r k d e r i v e d p o l y p h e n o l s for adhesives as a result o f i m p r o v e d u n d e r s t a n d i n g o f t h e c h e m i c a l s t r u c t u r e o f these m a t e r i a l s (4,5), n e w types o f f o r m u l a t i o n s (6), a n d the fact t h a t t a n n i n s are b e i n g c o m m e r c i a l l y used i n adhesives i n S o u t h A f r i c a ( 7 ) , t h u s s e r v i n g as a p r o t o t y p e for u t i l i z a t i o n i n other p a r t s o f t h e w o r l d . I n order t o p r o p e r l y assess t h e current developments i n t h i s field, t h i s overview w i l l p r o v i d e a h i s t o r i c a l perspective o n adhesives based o n t a n n i n s as w e l l as a s u m m a r y o f t h e e x t r a c t i o n techniques a n d c h e m i c a l s t r u c t u r e s . F i n a l l y , areas where a d d i t i o n a l w o r k c o u l d be f r u i t f u l w i l l be suggested. Raw

Materials

T a n n i n s generally c a n be classified i n t o t w o b r o a d categories: h y d r o l y z a b l e a n d condensed. T h e h y d r o l y z a b l e t a n n i n s consist o f m a n y i n d i v i d u a l c o m p o u n d s a n d oligomers,' b u t a l l are based o n c o m b i n a t i o n s o f g a l l i c a c i d or i t s derivatives a n d s i m p l e sugars such as glucose o r r h a m n o s e . H y d r o l y s i s w i t h d i l u t e m i n e r a l a c i d or enzymes results i n d e g r a d a t i o n t o g a l l i c o r ellagic a c i d ( a d i m e r f o r m e d f r o m g a l l i c acid) a n d t h e sugar c o m p o n e n t , hence t h e n a m e , h y d r o l y z a b l e t a n n i n s .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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157

For e x a m p l e , c o r a l a g i n (1), a c o m p o n e n t of e u c a l y p t u s t a n n i n s , y i e l d s g a l l i c a c i d ( 2 ) , ellagic a c i d (3) a n d glucose w h e n h y d r o l y z e d i n d i l u t e s u l f u r i c a c i d ( F i g u r e 1). M o s t of the c h a r a c t e r i z a t i o n studies have been done o n those t a n n i n s i s o l a t e d f r o m f r u i t s , leaves, or g a l l s . V e r y l i t t l e is k n o w n a b o u t the h y d r o l y z a b l e t a n n i n s f r o m the w o o d a n d b a r k of h a r d w o o d s except for e u c a l y p t u s , o a k , a n d m a p l e (4 S). A l t h o u g h the studies have not been extensive, i t seems q u i t e l i k e l y t h a t h y d r o l y z a b l e t a n n i n s do not occur i n conifers, b u t t h e y often co-occur w i t h condensed t a n n i n s i n h a r d w o o d s . T h e r e are n o l i t e r a t u r e references t h a t suggest u t i l i t y for h y d r o l y z a b l e t a n n i n s i n adhesive f o r m u l a t i o n s , so n o f u r t h e r m e n t i o n w i l l be m a d e of t h e m i n t h i s overview. Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch012

f

C o n d e n s e d t a n n i n s , o n the other h a n d , occur i n the b a r k of a l l conifers a n d h a r d w o o d s e x a m i n e d t o date, a n d they are frequently present i n the w o o d . T h e y are p r i m a r i l y responsible for the t a n t o b r o w n color of w o o d after i t is exposed t o a i r . I n t h e i r purest f o r m , condensed t a n n i n s are colorless, b u t they become colored very r e a d i l y once i s o l a t e d because of t h e i r p r o p e n s i t y t o o x i d i z e to quinones. T h e p r i m a r y characteristic of the water-soluble condensed t a n n i n s (4) is d e h y d r a t i o n / o x i d a t i o n t o intensely colored a n t h o c y a n i d i n p i g m e n t s (5) w h e n refluxed i n b u t a n o l a n d h y d r o c h l o r i c a c i d ( F i g u r e 2). F o r t h i s reason, there has been a tendency t o refer t o these c o m p o u n d s as " p r o a n t h o c y a n i d i n s " i n the last few years. P r i o r t o t h a t , t h e y were referred t o as " l e u c o a n t h o c y a n i d i n s " (i.e., the colorless c h e m i c a l f o r m of a n t h o c y a n i d i n s ) . A l l references earlier t h a n the l a t e 1950's, w h e n the s t r u c t u r e of these substances was j u s t b e g i n n i n g t o be u n d e r s t o o d , used the t e r m "condensed" t a n n i n . A n o t h e r characteristic of the condensed t a n n i n s was u s u a l l y observed d u r i n g leather tannage w i t h these m a t e r i a l s . A q u e o u s suspensions of t a n n i n t h a t were a c i d i c f r o m the t a n n i n g process g r a d u a l l y p r e c i p i t a t e d i n s o l u b l e m a t e r i a l s k n o w n as " t a n n e r ' s r e d s " o r phlobaphenes. These substances, d e r i v e d f r o m the t a n n i n , were n o longer soluble i n w a t e r , b u t they c o u l d be dissolved i n p o l a r solvents such as e t h a n o l or acetone or i n aqueous base. Since most species of b a r k c o n t a i n a n e x t r a c t i v e f r a c t i o n t h a t p h y s i c a l l y resembles the t a n n e r ' s reds, t h e y are referred t o as phlobaphenes i n the l i t e r a t u r e . V e r y l i t t l e c h a r a c t e r i z a t i o n w o r k has been done o n t h i s f r a c t i o n , a n d there is s u b s t a n t i a l reason t o believe t h a t the b a r k p h l o b a p h e n e f r a c t i o n contains a variety of w a t e r - i n s o l u b l e p o l y m e r s , some of t h e m t o t a l l y u n r e l a t e d to the condensed t a n n i n f a m i l y . I n a d d i t i o n t o the water-soluble a n d i n s o l u b l e members of the condensed t a n n i n f a m i l y , b o t h o f w h i c h are soluble i n p o l a r o r g a n i c solvents, there is a t h i r d related fraction, usually called a "phenolic acid." T h i s material can only be i s o l a t e d b y e x t r a c t i o n w i t h aqueous a l k a l i n e s o l u t i o n s or w i t h s o d i u m sulfite or bisulfite s o l u t i o n at elevated t e m p e r a t u r e s a n d pressures. Since the t a n n i n s a n d phlobaphenes are also soluble i n aqueous base, t h e y w i l l b e c o e x t r a c t e d f r o m b a r k a l o n g w i t h the p h e n o l i c acids w h e n b a r k is e x t r a c t e d w i t h base. T h i s is i m p o r t a n t t o r e m e m b e r i n the subsequent discussion o n b a r k - b a s e d adhesives.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

ADHESIVES F R O M RENEWABLE RESOURCES

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158

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HERGERT

Tannins in Adhesives: Introduction

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch012

12.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

159

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ADHESIVES F R O M RENEWABLE RESOURCES

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Isolation of C o n d e n s e d

Tannins

B a r k or h e a r t w o o d , the p r i m a r y r a w m a t e r i a l s for t a n n i n p r o d u c t i o n , c o n t a i n m a n y extraneous substances. T h e b r o a d categories of c o m p o u n d s are l i s t e d i n T a b l e I, a n d , as c a n be seen, n o single category is i s o l a t a b l e b y s i m p l e solvent e x t r a c t i o n . M o s t w o r k o n the use of t a n n i n s for adhesives has i n v o l v e d a hot water or m i l d a l k a l i n e e x t r a c t . T h e reason for t h i s is q u i t e s i m p l e : the value of the p r o d u c t for the i n t e n d e d e n d use c o u l d not s u p p o r t the cost of subsequent r e f r a c t i o n a t i o n or p u r i f i c a t i o n . C a r b o h y d r a t e i m p u r i t i e s are p a r t i c u l a r l y u n d e s i r a b l e , so investigators over the years have u s u a l l y e x p e n d e d m u c h effort i n t r y i n g t o find a p a r t i c u l a r p l a n t species t h a t w o u l d y i e l d a n e x t r a c t h i g h i n t a n n i n content a n d low i n the offending c a r b o h y d r a t e " c o n t a m i n a n t s . " Insofar as c h e m i c a l s t r u c t u r e studies are concerned, progress was slow u n t i l c h r o m a t o g r a p h i c techniques were devised i n the last decade (9-11) for s e p a r a t i o n of the d i m e r i c a n d t r i m e r i c p r o a n t h o c y a n i d i n s f r o m the higher p o l y m e r s , sugars, etc., present i n a n e x t r a c t . T h i s p e r m i t t e d i n d i r e c t d e d u c t i o n of the s t r u c t u r e of the higher p o l y m e r i c fractions (e.g., the true t a n n i n s ) .

T a b l e I. M a t e r i a l s E x t r a c t a b l e f r o m B a r k or H e a r t w o o d w i t h V a r i o u s T y p e s of Solvents Solvent T y p e of E x t r a c t i v e W a x , f a t s , terpenes Flavones Flavanols Stilbenes Proanthocyanidins Solvent-soluble lignin S i m p l e sugars Pectins Arabinogalactans Xylans A s h (oxalates, etc.) "Polyphenolic acids" "Lignin"

Petroleum Ether

Ethyl Ether

Ethanol

X

X X X X

X X X X X X X

Hot Water

X X X X X X X

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Aqueous Alkali X X X X X X X X X X X X X

12.

HERGERT

161

Tannins in Adhesives: Introduction

C h e m i c a l Structure of Condensed

Tannins

T h r o u g h a n i m p r e s s i v e a r r a y o f e x p e r i m e n t s c o n d u c t e d over the last 15 years, i t has been s h o w n t h a t the aqueous e x t r a c t s c o n t a i n a series o f c o m p o u n d s based o n a s u b s t i t u t e d flavonoid s t r u c t u r e . F o r purposes o f t h i s o v e r v i e w , i t does not a p p e a r t o b e a p p r o p r i a t e t o go i n t o a l o t of d e t a i l . M a i n l y , i t is i m p o r t a n t t o keep i n m i n d t h a t : 1) the

flavonoid

s u b s t i t u t i o n p a t t e r n seems t o be c h a r a c t e r i s t i c

for a g i v e n species; 2) s t e r e o c h e m i s t r y c a n v a r y at the 2, 3, a n d 4 p o s i t i o n s i n the C - r i n g ( F i g u r e 3); 3) the B - r i n g can have a v a r i a b l e p a t t e r n o f one, two or

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch012

three h y d r o x y l g r o u p s ; 4) the b o n d j o i n i n g the m o n o m e r i c u n i t s extends

from

the 4 p o s i t i o n i n the C - r i n g t o the 6 or 8 p o s i t i o n of the Α-ring; a n d 5) the t e r m i n a t i n g u n i t m a y differ i n s u b s t i t u t i o n p a t t e r n o r s t e r e o c h e m i s t r y f r o m a l l the o t h e r u n i t s i n t h e c h a i n . W a t e r s o l u b i l i t y seems t o be p r i m a r i l y a f u n c t i o n of c h a i n l e n g t h .

I n the

p r o c y a n i d i n p o l y m e r s ( F i g u r e 3, 6 ) , chains w i t h a D P greater t h a n a b o u t 8 are not s o l u b l e i n w a t e r . T h i s suggests t h a t the " p h l o b a p h e n e " f r a c t i o n m a y s i m p l y be a h i g h e r m o l e c u l a r weight v e r s i o n of the w a t e r - s o l u b l e t a n n i n s , w h i l e t h e soc a l l e d p h e n o l i c acids are of even h i g h e r m o l e c u l a r weight, c r o s s l i n k e d , or t i g h t l y complexed to cell w a l l carbohydrates through an alkali-labile linkage. M i m o s a ( F i g u r e 3, 7) a n d quebracho t a n n i n s ( F i g u r e 3, 8) differ f r o m the conifer b a r k t a n n i n s i n t h a t t h e Α-ring is based o n r e s o r c i n o l r a t h e r t h a n p h l o r o g l u c i n o l . T h e s e t a n n i n s also t e n d to have a higher degree o f water s o l u b i l i t y a n d less l i k e l i h o o d o f r e a r r a n g i n g t o h i g h l y colored b y p r o d u c t s , t h u s m a k i n g t h e m m o r e a t t r a c t i v e for leather t a n n i n g . G e n e r a l l y , the h o t - w a t e r e x t r a c t of a b a r k or h e a r t w o o d source o f t a n n i n w i l l c o m p r i s e a b o u t 60 t o 6 5 % t a n n i n p o l y m e r s as m e a s u r e d b y a s t a n d a r d h i d e powder

a b s o r p t i o n test.

T h e r e m a i n d e r w i l l be a m i x t u r e o f sugars, p e c t i n ,

h e m i c e l l u l o s e , a n d lower m o l e c u l a r weight ( < 3 0 0 ) p o l y p h e n o l s . C o l d - w a t e r ex­ traction w i l l y i e l d a somewhat higher p u r i t y t a n n i n extract, but overall yields based o n the weight o f s t a r t i n g m a t e r i a l w i l l be lower.

Quebracho wood and

m i m o s a b a r k are u n u s u a l i n t h a t t h e i r w a t e r e x t r a c t has a m e a s u r e d " p u r i t y " u p t o 75 t o 8 0 % .

T h e " t a n n i n s " i n each case consist o f a series o f

oligomers

w i t h a D P o f 2 t o a b o u t 7 t o 9, d e p e n d i n g u p o n e x t r a c t i o n c o n d i t i o n s . Cleavage Reactions a n d

Rearrangement

T o b e t t e r u n d e r s t a n d the r e a c t i v i t y o f the condensed t a n n i n s i n adhesive f o r m u ­ l a t i o n s , i t is i m p o r t a n t t o recognize m o l e c u l a r changes a c c o m p a n y i n g e x t r a c t i o n o f the t a n n i n s w h e n sulfites or a l k a l i are used t o enhance y i e l d . A m o d e l p o u n d s t u d y o n c a t e c h i n ( F i g u r e 4,11)

com­

(27) showed t h a t t r e a t m e n t w i t h s o d i u m

b i s u l f i t e s o l u t i o n at 170 ° C for 30 m i n o p e n e d the flavan r i n g w i t h f o r m a t i o n of a sulfonate g r o u p o n the 2 p o s i t i o n (12).

T h i s was b e l i e v e d t o e x p l a i n the

f o r m a t i o n o f t a n n i n sulfonates d u r i n g a c o m m e r c i a l process i n v o l v i n g bisulfite e x t r a c t i o n o f western h e m l o c k b a r k (3,13). M o r e recently, i t has been f o u n d

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

162

ADHESIVES F R O M RENEWABLE RESOURCES

oh oh

mimosa

bark

( 2 0 - 23)

6 w e s t e r n h e m l o c k (3.12-14) r|«oh; r , r 3 « h r2«0h; r|,r3«h

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2

pine bark (j5-.i9) r,«oh; r ,r3«h r , , r 3 «0h, r «h 2

quebracho

wood

(24-26)

2

F i g u r e 3. P r o a n t h o c y a n i d i n s e x t r a c t a b l e f r o m b a r k or h e a r t w o o d w i t h v a r i o u s types o f solvents.

F i g u r e 4. S u l f o n a t i o n reactions o f condensed t a n n i n s .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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(28) t h a t the i n t e r f l a v o n o i d b o n d is m u c h m o r e l i k e l y t o be cleaved t h a n the p y r a n r i n g . T h e 4 —• 6 or 4 —• 8 b o n d s are b r o k e n w i t h c o n c o m i t a n t s u l f o n a t i o n at the 4 p o s i t i o n ( 1 0 ) . W h e n the t a n n i n does not have a h y d r o x y l g r o u p i n the 5 - p o s i t i o n , as is the case w i t h m i m o s a a n d quebracho t a n n i n s , the i n t e r f l a v o n o i d b o n d is m u c h m o r e stable. I n t h i s instance, s u l f o n a t i o n p r i m a r i l y leads t o the f o r m a t i o n of s u b s t i t u t i o n at the C - 2 a t o m (29). E v e n t h o u g h the precise de­ t a i l s of these s u l f o n a t i o n reactions need further c l a r i f i c a t i o n , i t seems reasonable t o conclude t h a t w a t e r - i n s o l u b l e t a n n i n s c a n be converted t o lower m o l e c u l a r weight fractions w i t h s o l u b i l i z i n g sulfonate groups i n the 2 a n d / o r 4 p o s i t i o n s by t r e a t m e n t w i t h s o d i u m sulfite or bisulfite at elevated t e m p e r a t u r e s . T h i s re­ a c t i o n is s u i t a b l e , therefore, for e x t r a c t i o n of phlobaphenes a n d " p h e n o l i c a c i d s " f r o m b a r k as w e l l as the water-soluble t a n n i n s . D u r i n g early phases of s t r u c t u r a l studies o n b a r k p o l y p h e n o l s (15), i t was n o t e d t h a t a l k a l i t r e a t m e n t of isolated t a n n i n p o l y m e r s resulted i n the f o r m a ­ t i o n of a n acidic g r o u p , presumed to be a c a r b o x y l , a n d the loss of f o r m a l d e h y d e r e a c t i v i t y . It was s u r m i s e d t h a t the so-called b a r k phenolic acids were, i n fact, higher m o l e c u l a r weight t a n n i n s t h a t underwent rearrangement d u r i n g i s o l a t i o n . S u p p o r t for t h i s i d e a was g r e a t l y strengthened b y e l u c i d a t i o n of the a l k a l i n e re­ arrangement of catechin to catechinic a c i d (13) —• (14) ( F i g u r e 5) b y Sears, et al. (30). L a k s a n d H e m i n g w a y (31) have c o n t i n u e d to s t u d y the reactions of t a n n i n s w i t h a l k a l i u s i n g p h l o r o g l u c i n o l or p h e n y l m e t h a n e t h i o l as a n u c l e o p h i l e . T h i s w o r k clearly shows o p e n i n g of the p y r a n r i n g , f o r m a t i o n of a reactive site i n the 2 p o s i t i o n , cleavage of interflavonoid b o n d s , a n d f o r m a t i o n of c a r b o n y l groups i n the Α-ring. It is not at a l l s u r p r i s i n g t h a t earlier workers h a d great difficulties i n t r y i n g t o determine b a r k t a n n i n s t r u c t u r e w h e n they used a l k a l i n e e x t r a c t i o n m e t h o d s . F u r t h e r m o r e , the rearrangement of the Α-ring w i t h c o n ­ sequent loss of formaldehyde r e a c t i v i t y s h o u l d be kept i n m i n d w h e n adhesive f o r m u l a t i o n s are m a d e u p f r o m a l k a l i n e e x t r a c t s .

Preparation of Tannin-Based

Adhesives

Interest i n use of condensed t a n n i n s as c o m p o n e n t s of adhesive f o r m u l a t i o n s began a b o u t three decades ago. W h i l e research studies have been c a r r i e d out i n w i d e l y scattered laboratories a r o u n d the w o r l d , three m a j o r areas of a c t i v i t y c a n be d i s t i n g u i s h e d . These are: 1) development of b a r k extracts a n d c o m ­ m e r c i a l p r o d u c t i o n facilities o n the west coast of N o r t h A m e r i c a , 1953 t o 1975; 2) a p p l i c a t i o n of t a n n i n s i n adhesive f o r m u l a t i o n s i n S o u t h A f r i c a based o n i n ­ digenously p r o d u c e d m i m o s a (wattle) t a n n i n , early 1970's t o the present; a n d 3) a resurgence of interest i n pine b a r k as raw m a t e r i a l for t a n n i n - b a s e d adhesives, b e g i n n i n g i n the m i d d l e 1970's. E a c h of these a c t i v i t i e s has been characterized by p a r a l l e l efforts o n s t r u c t u r a l i d e n t i f i c a t i o n of the t a n n i n s a n d development of u n i q u e m e t h o d s for i n c o r p o r a t i n g the isolated t a n n i n s i n t o adhesives.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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F i g u r e 5. A l k a l i n e rearrangement reactions of

(+)-catechin.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Western Conifer B a r k Polyphenols

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F o l l o w i n g W o r l d W a r I I , extensive investigative effort was i n i t i a t e d t o f i n d new uses for the m o u n t a i n s of b a r k generated as b y p r o d u c t s of the W e s t C o a s t forest p r o d u c t s i n d u s t r y i n the U n i t e d States a n d C a n a d a . T h i s w o r k was c a r r i e d o u t at the I n s t i t u t e of P a p e r C h e m i s t r y (sponsored b y the P a c i f i c L u m b e r C o m p a n y of S c o t i a , C a l i f o r n i a ) , the O r e g o n Forest P r o d u c t s L a b o r a t o r y , R a y o n i e r Incorp o r a t e d , the Weyerhaueser C o m p a n y , a n d the Forest P r o d u c t s L a b o r a t o r y o n the U n i v e r s i t y of B r i t i s h C o l u m b i a c a m p u s . W e s t e r n h e m l o c k b a r k was considered t o be a n a t t r a c t i v e m a t e r i a l for t a n n i n p r o d u c t i o n (32), since i t s c h e m i c a l c o m p o s i t i o n was t h o u g h t t o closely p a r a l l e l t h a t of eastern h e m l o c k b a r k , the m a j o r r a w m a t e r i a l for t a n n i n g i n the U n i t e d States at the b e g i n n i n g of the century. M u c h of the h e m l o c k b a r k i n the W e s t was recovered f r o m seawater-floated logs a n d / o r the use of h y d r a u l i c debarkers t h a t d i m i n i s h e d the y i e l d of water-soluble t a n n i n s . Nevertheless, such t a n n i n as c o u l d be o b t a i n e d was f o u n d t o be useful as a n o i l w e l l - d r i l l i n g dispersant or as a n adhesive w h e n m i x e d w i t h f o r m a l d e h y d e , a c c o r d i n g t o the B r i t i s h C o l u m b i a research t e a m (33). Subsequent w o r k showed t h a t m u c h higher y i e l d s of p o l y p h e n o l i c e x t r a c t s c o u l d be o b t a i n e d b y elevated t e m p e r a t u r e e x t r a c t i o n s w i t h s o d i u m b i s u l f i t e , s o d i u m h y d r o x i d e , or a m m o n i a (34-36). Rayonier built two c o m m e r c i a l p l a n t s for the p r o d u c t i o n of such e x t r a c t s , one at H o q i u m , W a s h i n g t o n , a n d the other at V a n c o u v e r , B r i t i s h C o l u m b i a (13). A t t e m p t s t o m a k e adhesive f o r m u l a t i o n s b y direct r e a c t i o n of f o r m a l d e h y d e or i t s equivalent resulted i n p r o d u c t s t h a t were excessively viscous, a n d the w o r k i n g t i m e was t o o short for c o m m e r c i a l a p p l i c a t i o n (37). It was c o n c l u d e d t h a t f o r m a l d e h y d e , a l t h o u g h r e a d i l y reactive w i t h the t a n n i n m o l e c u l e , p r o v i d e d m u c h t o o short linkages t o connect the b u l k y t a n n i n molecules. T h i s p r o b l e m was c i r c u m v e n t e d by the p r e p a r a t i o n of a p o l y m e t h y l o l p h e n o l reagent t h a t , w h e n p u t i n s o l u t i o n w i t h the b a r k e x t r a c t , f o r m e d a c o m b i n a t i o n t h a t was s t a ble for several weeks at r o o m t e m p e r a t u r e . W h e n heated, the p o l y m e t h y l o l p h e n o l a n d b a r k e x t r a c t reacted r a p i d l y t o f o r m a n i n f u s i b l e r e s i n . C o m m e r c i a l t r i a l s were m a d e t o p r o d u c e exterior-grade D o u g l a s - f i r p l y w o o d . W i d e s p r e a d use of the extracts for t h i s purpose, however, was i n h i b i t e d b y a d r o p i n the price of p h e n o l below w h a t the b a r k extracts c o u l d be m a n u f a c t u r e d for. ( T h e best e x t r a c t for adhesive purposes was a n a m m o n i a e x t r a c t of h e m l o c k b a r k converted t o a s o d i u m d e r i v a t i v e p r i o r to s p r a y d r y i n g , a m o r e costly e x t r a c t i o n procedure t h a n s i m p l e 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 of b a r k . ) Subsequent work was, therefore, directed t o s u b s t i t u t i o n of r e s o r c i n o l , a m u c h m o r e expensive p h e n o l , i n c o l d - s e t t i n g , w a t e r p r o o f adhesives (38). Form u l a t i o n s based o n 30 t o 6 0 % of e x t r a c t m i x e d w i t h a r e s o r c i n o l - f o r m a l d e h y d e condensate a n d a d d i t i o n a l f o r m a l d e h y d e m e t p o t - l i f e a n d assembly t i m e requirements for t i m b e r l a m i n a t i o n . Test b o n d s passed requirements of the m a j o r performance s t a n d a r d s i n the U n i t e d States, b u t c o m p e t i t i o n f r o m lower cost, p h e n o l - m o d i f i e d resorcinol resins a n d the lack o f l o n g t e r m c o m m e r c i a l perfor-

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m a n c e records prevented significant acceptance of the p r o d u c t s . Sales o f 300 tons per year d i d not j u s t i f y c o n t i n u e d p r o d u c t i o n , so the effort was t e r m i n a t e d i n 1972. B a r k e x t r a c t i o n b y R a y o n i e r (now I T T R a y o n i e r ) was s t o p p e d i n 1976. P a r t s of the e x t r a c t i o n p l a n t at H o q i u m were subsequently used for m a k i n g products from lignin. A b o u t the same t i m e R a y o n i e r b e g a n m a r k e t i n g b a r k e x t r a c t s f r o m western h e m l o c k , the P a c i f i c L u m b e r C o m p a n y at S c o t i a , C a l i f o r n i a , b u i l t a n e x t r a c t i o n p l a n t t o p r o d u c e a l k a l i n e e x t r a c t s f r o m r e d w o o d b a r k . T h e p r o d u c t s were c a l l e d P a l c o t a n a n d S o d i u m P a l c o n a t e . T h e y m a i n l y f o u n d uses i n o i l w e l l d r i l l i n g . A t t e m p t s t o use the p r o d u c t i n adhesive f o r m u l a t i o n s do not seem t o have been successful, m o s t l y because of v i s c o s i t y p r o b l e m s associated w i t h c a r b o h y d r a t e s c o e x t r a c t e d f r o m the b a r k a l o n g w i t h the p o l y p h e n o l s . W e y e r haeuser p r o d u c e d a l k a l i n e e x t r a c t s of D o u g l a s - f i r b a r k d u r i n g the 1960's. T h e y were s a i d t o be a p p l i c a b l e i n adhesive f o r m u l a t i o n s , b u t there are n o l i t e r a t u r e references a t t e s t i n g t o t h e i r c o m m e r c i a l success. T h e m o s t recent a t t e m p t at t h i s m a r k e t was the p r e p a r a t i o n of finely d i v i d e d D o u g l a s - f i r b a r k , w h i c h h a d been p r e e x t r a c t e d w i t h n o n p o l a r solvents t o remove w a x , as a reactive extender for p h e n o l - f o r m a l d e h y d e adhesives. T h e B o h e m i a L u m b e r C o m p a n y ' s p l a n t for s u c h p r o d u c t s s h u t d o w n i n the e a r l y 1980's. A t t e m p t s were m a d e t o revive interest i n western h e m l o c k b a r k p o l y p h e nols t h r o u g h a research p r o g r a m at the W e s t e r n Forest P r o d u c t s L a b o r a t o r y , F o r i n t e k C a n a d a C o r p . I n t h i s w o r k , i t was c o n c l u d e d (39) t h a t the p h e n o l i c a c i d f r a c t i o n of the b a r k , w h e n i s o l a t e d b y a l k a l i n e e x t r a c t i o n , was insufficiently reactive w i t h f o r m a l d e h y d e t o be o f c o m m e r c i a l value. T h i s i n v e s t i g a t i o n s u g gested e t h a n o l e x t r a c t i o n as the preferred route t o t a n n i n s for adhesive a p p l i c a t i o n . S i n c e e n v i r o n m e n t a l r e s t r i c t i o n s i n the U n i t e d States have l a r g e l y e l i m i n a t e d w a t e r storage of h e m l o c k logs a n d h y d r a u l i c d e b a r k i n g d u r i n g the last decade, q u a n t i t i e s of h e m l o c k b a r k are n o w available t h a t have not been water leached. T h e b a r k is used as f u e l , b u t i t m a y be t i m e l y t o reconsider e x t r a c t i o n of p o l y p h e n o l s p r i o r t o the b u r n i n g process as a higher f o r m o f u t i l i z a t i o n t h a n simple combustion. M i m o s a T a n n i n Adhesives T h e o n l y t a n n i n s i n the w o r l d c u r r e n t l y b e i n g c o m m e r c i a l l y e x p l o i t e d for a d hesive a p p l i c a t i o n s are those i s o l a t e d b y h o t - (or cold-) water e x t r a c t i o n of Acacia meamsii b a r k i n the province of N a t a l , S o u t h A f r i c a . A p p r o x i m a t e l y 100,000 tons of m i m o s a t a n n i n were b e i n g p r o d u c e d a n n u a l l y as r e p o r t e d i n 1980, the latest year for w h i c h p r o d u c t i o n figures were a v a i l a b l e (41)- O f t h i s a m o u n t , a b o u t 10,000 tons were used i n adhesive a p p l i c a t i o n s m a i n l y i n S o u t h A f r i c a , A u s t r a l i a , a n d N e w Z e a l a n d . W h i l e t h i s n u m b e r is n o t large i n l i g h t of the 300,000 t o 400,000 tons o f p h e n o l used a n n u a l l y i n resins, i t does p r o v i d e evidence t h a t b a r k t a n n i n s c a n be e c o n o m i c a l l y used for adhesives. T h i s a p p l i c a t i o n is f a c i l i t a t e d b y the r e l a t i v e l y h i g h cost of p h e n o l a n d resorcinol i n

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S o u t h A f r i c a a n d the p o l i t i c a l strategy t o reduce or e l i m i n a t e i m p o r t s o f strategic m a t e r i a l s such a p e t r o c h e m i c a l s as m u c h as possible. E a r l i e s t a p p l i c a t i o n of m i m o s a t a n n i n s for adhesives came i n the field of p l y w o o d a n d c h i p b o a r d s (41)- E x t e r i o r p l y w o o d adhesives were based o n c o n ­ d e n s a t i o n o f w a t t l e t a n n i n w i t h u r e a f o r m a l d e h y d e c r o s s l i n k i n g agents, a p h e n o l f o r m a l d e h y d e resol, or a p h e n o l - r e s o r c i n o l - f o r m a l d e h y d e p o l y m e r t o w h i c h p a r a ­ f o r m a l d e h y d e was a d d e d to p r o v i d e c r o s s l i n k i n g between the r e s o r c i n o l a n d the Α-ring o f the t a n n i n . F a s t - c u r i n g rates a n d g o o d tolerance t o h i g h m o i s t u r e content veneers characterize these systems. M e t a l c a t a l y s t s s u c h as z i n c acetate have been f o u n d t o be useful for speeding the cure r a t e . P r o b l e m s w i t h viscos­ i t y c a n be a m e l i o r a t e d b y cold-water e x t r a c t i o n o f the b a r k t o reduce p o l y m e r i c c a r b o h y d r a t e content i n the e x t r a c t or b y m i l d s u l f o n a t i o n o f the t a n n i n s . T h e l i t e r a t u r e does n o t i n d i c a t e w h e t h e r these t w o procedures are c u r r e n t l y b e i n g practiced i n mimosa tannin production. E a r l y a t t e m p t s t o use m i m o s a t a n n i n i n p a r t i c l e b o a r d adhesives i n v o l v e d h i g h - t e m p e r a t u r e a l k a l i n e t r e a t m e n t o f the e x t r a c t t o reduce v i s c o s i t y o f the 4 0 % solids level needed (43,44)- Subsequent i m p r o v e m e n t s followed the same course as w i t h p l y w o o d , n a m e l y the use o f p h e n o l - f o r m a l d e h y d e or p h e n o l - r e s o r c i n o l f o r m a l d e h y d e as c r o s s l i n k i n g agents (45) a n d the use of c a t a l y s t s or m i x m o d i f i ­ cations t o reduce press t e m p e r a t u r e requirements a n d t o e x t e n d p o t life. R e c e n t work (46) has s h o w n t h a t exterior c h i p b o a r d adhesives c a n also be p r e p a r e d b y c r o s s l i n k i n g of m i m o s a t a n n i n s w i t h 4 , 4 - d i p h e n y l m e t h a n e d i i s o c y a n a t e . A p p l i c a t i o n s for c o l d - s e t t i n g , w o o d - l a m i n a t i n g adhesives i n i t i a l l y followed the s a m e a p p r o a c h (47) used for l a m i n a t i n g resins f r o m western h e m l o c k (38) (i.e., r e a c t i o n o f t a n n i n w i t h p h e n o l - r e s o r c i n o l - f o r m a l d e h y d e p r e p o l y m e r s ) . I m ­ p r o v e m e n t s resulted t h r o u g h the a p p l i c a t i o n o f K r e i b i c h ' s " H o n e y m o o n " t e c h ­ n i q u e (48 ) w h e r e i n one side o f the m a t e r i a l t o be b o n d e d is t r e a t e d w i t h resin a n d the other w i t h c a t a l y s t . O n e o f the preferred systems (49) was p h e n o l r e s o r c i n o l - f o r m a l d e h y d e or t a n n i n - r e s o r c i n o l - f o r m a l d e h y d e at p H 8 w i t h e x t r a p a r a f o r m a l d e h y d e o n the Α-side a n d t a n n i n at 5 3 % solids or t a n n i n - r e s o r c i n o l f o r m a l d e h y d e at p H 12 o n the B - s i d e . S u c h resin systems are c u r r e n t l y used to l a m i n a t e e u c a l y p t u s or pine i n m o s t S o u t h A f r i c a n t i m b e r - l a m i n a t i n g p l a n t s . Pine B a r k T a n n i n Adhesive Formulations Interest i n p i n e b a r k as a source o f adhesive c o m p o n e n t s b e g a n t o accelerate f o l l o w i n g the o i l crisis o f 1973. S o d i u m h y d r o x i d e e x t r a c t s o f s o u t h e r n p i n e b a r k were successfully used i n r e p l a c i n g u p t o 4 0 % o f the p h e n o l i c resin for b o n d i n g of p a r t i c l e b o a r d s , oriented s t r a n d b o a r d s , a n d composites w i t h a flakeboard core a n d veneer f a c i n g (50,51). S i m i l a r results were o b t a i n e d w i t h e x t r a c t s f r o m p a t u l a p i n e (52). E n c o u r a g e d b y results o f t h i s t y p e , t h e N e w Z e a l a n d Forest Products L t d . C o r p o r a t i o n expanded their r a d i a t a pine bark tannin pilot plant to f u l l - s c a l e o p e r a t i o n i n 1981 t o p r o d u c e a n e x t r a c t t r a d e m a r k e d T a n n a p h e n . T h i s m a t e r i a l was crosslinked w i t h p a r a f o r m a l d e h y d e a n d used as a n adhesive

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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for c h i p b o a r d panels m a r k e t e d p r i m a r i l y as flooring m a t e r i a l i n N e w Z e a l a n d . T h e e x t r a c t i o n p l a n t a n d adhesive f o r m u l a t i o n were d i s c o n t i n u e d recently w i t h out e x p l a n a t i o n . B o a r d s m a d e w i t h T a n n a p h e n were k n o w n t o be m a r g i n a l l y deficient i n m o i s t u r e d u r a b i l i t y . B o a r d s m e e t i n g e x t e r i o r - q u a l i t y s t a n d a r d s c a n be f o r m u l a t e d , however, u s i n g p i n e b a r k e x t r a c t s c o m b i n e d w i t h isocyanate resins (52). S a t i s f a c t o r y exterior p l y w o o d adhesive f o r m u l a t i o n s have also been prepared by combining bark extracts w i t h phenol-formaldehyde prepolymers followed b y the a d d i t i o n o f p a r a f o r m a l d e h y d e . R e c e n t efforts t o develop c o l d - s e t t i n g p h e n o l i c resins f r o m p i n e b a r k have followed p a t h s s i m i l a r t o those used for w a t t l e t a n n i n s . O n e o f these has i n volved the a c i d - c a t a l y z e d cleavage of s o u t h e r n p i n e b a r k u s i n g resorcinol as a n u c l e o p h i l e (53). A second a p p r o a c h has been t o p u r i f y t a n n i n s of c o - o c c u r r i n g c a r b o h y d r a t e a n d use t h e m as resorcinol replacements i n the H o n e y m o o n s y s t e m (48)- O n e surface was s p r e a d w i t h c o m m e r c i a l p h e n o l - r e s o r c i n o l - f o r m a l d e h y d e l a m i n a t i n g adhesive w i t h a d d e d f o r m a l d e h y d e , a n d the other was spread w i t h p i n e t a n n i n i n s o d i u m h y d r o x i d e s o l u t i o n . T h e m o s t recent ( a n d the m o s t econ o m i c a l t o date) a p p r o a c h involves resorcinol replacement b y u s i n g b a r k t a n n i n s e x t r a c t e d w i t h s o d i u m sulfite. M o l e c u l a r weights are reduced d u r i n g the course of the e x t r a c t i o n , a n d the sulfonate f u n c t i o n is a g o o d l e a v i n g group u n d e r c o n d i t i o n s of l a m i n a t i o n . T h e sulfite e x t r a c t s c a n be a p p l i e d as m i x e d syst e m adhesives, w h e r e i n they are c o m b i n e d w i t h c o n v e n t i o n a l p h e n o l - r e s o r c i n o l f o r m a l d e h y d e resins, or i n the H o n e y m o o n s y s t e m . U p t o 5 0 % replacement of s y n t h e t i c resin b y s u l f o n a t e d b a r k t a n n i n s is envisioned b y t h i s process (54). Future Outlook A n u m b e r o f q u i t e s a t i s f a c t o r y adhesive f o r m u l a t i o n techniques i n c o r p o r a t i n g b a r k t a n n i n s have been developed, especially d u r i n g the last decade. U n f o r t u nately, i n m a n y instances, t h e y i n t r o d u c e degrees of c o m p l e x i t y i n t o the b o a r d or l a m i n a t e p r o d u c t i o n l i n e not otherwise experienced w h e n 1 0 0 % p h e n o l or resorcinol-based adhesives are used. I n d u c e m e n t of the b o a r d m a n u f a c t u r e r t o s w i t c h t o b a r k - b a s e d adhesives m u s t involve significant e c o n o m i c incentives (e.g., the use o f b a r k - b a s e d adhesives m u s t be s u b s t a n t i a l l y cheaper t h a n the corres p o n d i n g phenol-based f o r m u l a t i o n ) . T h u s , i t seems a d d i t i o n a l a t t e n t i o n needs t o be p a i d t o finding lower cost, higher y i e l d i s o l a t i o n techniques. P i n e b a r k , i n p a r t i c u l a r , has the p o t e n t i a l t o give higher y i e l d extracts t h a n are r e p o r t e d i n most of the e x p e r i m e n t s m e n t i o n e d i n t h i s review. P o s s i b l y , s u l f o n a t i o n is the answer, b u t m o r e work is r e q u i r e d t o e s t a b l i s h t h i s a p p r o a c h . I n the m e a n t i m e , R & D a n d c a p i t a l c o m m i t m e n t s are needed i n N o r t h A m e r i c a a n d other p i n e g r o w i n g areas f r o m a c o n s o r t i u m of p o t e n t i a l e x t r a c t p r o d u c e r s a n d users s u c h as exists i n S o u t h A f r i c a . T h i s c o u l d w e l l lead t o a m a j o r new business a c t i v i t y d u r i n g the next decade.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

12.

HERGERT

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Tannins in Adhesives: Introduction

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1. Hergert, H. L. In Encyclopedia R.C.,Ed.; 1983, 2, 631.

of American Forest and Conservation

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2. Herrick, F. W.; Hergert, H. L. In Recent Advances in Phytochemistry, 1976, 11, 443. 3. Herrick, F. W. J. Agric. Food Chem., 1980, 28, 228.

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4. Hemingway, R. W. In Organic Chemicals from Biomass; Goldstein, I. S., Ed.; C R C Press: B o c a Raton, F L , 1981, 189. 5. Haslam, E. In The Flavonoids: Recent Advances in Research; Harborne, J. B., and Mabry, J. J., Eds.; Chapman and Hall: New York, 1982, 417. 6. Kreibich, R. E.; Hemingway, R. W. Forest Prod. J., 1985, 35, 23. 7. Roux, D. G.; Ferreira, D.; Botha, J. J. J. Agric. Food Chem., 1980, 28, 216. 8. Rowe, J. W.; Conner, A. H. Gen. Tech. Rep. F P L 18, U.S. Department of Agriculture, Forest Serv., Forest Prod. Lab: Madison, WI, 1979. 9. Weinges, K.; Freudenberg, K. J. Chem. Soc. Chem. Commun., 1965, 220. 10. Porter, L. J. N.Z. J. Sci.,1974, 17, 213. 11. Drewes, S. E.; Roux, D. G.; Eggers, S. H.; Feeney, J. J. Chem.Soc.,C, 1967, 1302. 12. Hergert, H. L. Forest Prod. J., 1960, 10, 610. 13. Hergert, H. L.; VanBlaricom, L. E.; Steinberg, L. E.; Gray, K. R. Forest Prod. J., 1965, 15, 485. 14. Sears, K. D.; Casebier, R. L. Chem. Commun., 1968, 1437; Phytochem., 1970, 9, 1589. 15. Hergert, H. L. Abstracts of Papers, Am. Chem.Soc.,April 13-18, 1958, 7E. 16. Hemingway, R. W.; McGraw, G. W. J. Applied Polym. Sci., Applied Polym. Symp., 1976, 28, 1349. 17. Hemingway, R. W.; Karchesy, J. J.; McGraw, G. W.; Wielesek, R. A. Phytochem., 1983, 22, 275. 18. Porter, L. J. N.Z. J. Sci., 1974, 17, 213. 19. Hemingway, R. W.; Foo, L. Y.; Porter, L. J. J. Chem.Soc.,Perkin Trans. I, 1982, 1209. 20. Drewes, S. E.; Roux, D. G.; Eggers, S. H.; Feeney, J. J. Chem.Soc.,C, 1967, 1217. 21. Roux, D. G., Phytochem., 1972, 11, 1219. 22. Malan, E.; Roux, D. G. Phytochem., 1975, 14, 1835. 23. Roux, D. G.; Ferreira, D.; Botha, J. J. J. Agric. Food Chem., 1980, 28, 216. 24. King, H.G.C.; White, T. J. Soc. Leather Trades Chem., 1957, 41, 368.

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25. Botha, J. J.; Viviers, P. M.; Ferreira, D.; Roux, D. G. J. Chem.Soc.,Perkin Trans. I, 1981, 1235. 26. Viviers, P. M.; Kolodziej, H.; Young, D. Α.; Ferriera, D.; Roux, D. G. J. Chem. Soc., Perkin Trans. I, 1983, 2555. 27. Sears, K. D. J. Org. Chem., 1972, 37, 3546. 28. Foo, L. Y.; McGraw, G. W.; Hemingway, R. W. J. Chem. Soc. Chem. Communica­ tions, 1983, 672.

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29. Roux, D. G.; Ferreira, D.; Hundt, H.K.L.; Malan, E. J. Appl. Polym. Sci. Polym. Symp., 28, 1975, 335. 30. Sears, K.D.; Casebier, R. L.; Hergert, H. L.; Stout, G. H.; McCandlish, L. E . J. Org. Chem., 1975, 39, 3244. 31. Laks, P.; Hemingway, R. W. J. Chem.Soc.,Perkin 1875-1881. 32. Smoot, C. C ; Frey, W. W. U.S. Dep.

Trans. I, 1987, 465-470; 1987,

of Agriculture, Bull. No. 566, 1937.

33. MacLean, H.; Gardner, J.A.F. Publications V-1009 and V-1010, Western Forest Prod­ ucts Laboratory, Vancouver, B.C., 1950. 34. Scott, D. S. Pulp Paper Mag.

Can., A p r i l 1956, 139.

35. Scott, D. S.; Korach, P. Pulp Paper Mag.

Can., May 1956, 147.

36. Herrick, F. W.; Bock, L. H. U.S. Patent 2 819 295 (1958); U.S. Patents 3 026 250 and 3 053 784 (1962); and U.S. Patent 3 223 667 (1965). 37. Herrick, F. W.; Bock, L. H. Forest Prod. J., 1958, 8, 269. 38. Herrick, F. W.; Conca, R. J. Forest Prod. J., 1960, 10, 361. 39. Fraser, H. S.; Swan, Ε . P. Can. J. Forest Res., 1979, 9, 495. 40. Pizzi, Α., Rev. Macromol. Chem., 1980, C18(2), 247. 41. Pizzi, Α., Wood Adhesives: York.

Chemistry

and Technology, 1983, Marcel Dekker, New

42. Pizzi, A. Adhesives Age, 1977, 27; J. Appl. Polym. Sci., 1978, 22, 1745; ibid, 1979, 23, 2777. 43. Knowles, E.; White, T. Adhesives and Resins, 1954, 10, 226. 44. Parrish, J. R. J. S. African Forest Assoc., 1958, 32, 26. 45. Pizzi, A. Forest Prod. J., 1978, 28, No. 12, 42. 46. Pizzi, A. J. Macromol. Sci. Chem. Ed., 1981, A16(7), 1243. 47. Pizzi, Α.; Roux, D. G. J. Appl. Polym. Sci., 1978, 22, 1945. 48. Kreibich, R. E. Adhesives Age, 1974, 17, 26. 49. Pizzi, Α.; Cameron, F. A. Forest Prod. J., 1984, 34, 61.

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Tannins in Adhesives: Introduction

50. Chen, C. M. Ind. Eng. Chem. Prod. Res. and Dev., 1981, 20, 704. 51. Chen, C. M. Holzforschung, 1982, 3 6 , 109. 52. Pizzi, A. Holz Roh-u. Werkst., 1982, 40, 293. 53. Kreibich, R. E.; Hemingway, R . W . Forest Prod. J., 1985,35(3), 23. 54. Kreibich, R.E.; Hemingway R.W. Forest Prod. J., 1987, 37(2), 43.

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R E C E I V E D September 23, 1988

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171

Chapter 13 Viscosity and Formaldehyde Consumption of Procyanidin Solutions Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

Lawrence J. P o r t e r Chemistry Division Department of Scientific and Industrial Research Petone, New Zealand

The last decade has seen quite remarkable advances in our knowledge of the structure and properties of the proanthocyanidins. Viscosity measurements were made of solutions of procyanidins isolated from Theobroma cacao and Chaenomeles speciosa with number-average degrees of polymerization of 6.1 and 11.8, respectively, in water and 1% sodium hydroxide at 25 °C. Procyanidins are apparently com­ pletely crosslinked by formaldehyde up to a chain length of 6 units, but few units are crosslinked in polymeric procyanidins. T h e sec­ ond order rate constants observed for the formaldehyde reaction with catechin or epicatechin are approximately six times higher than that observed for the C. speciosa polymer. P r o a n t h o c y a n i d i n s are p l a n t p h e n o l i c b i o p o l y m e r s t h a t consist o f flavanoid m o n ­ o m e r u n i t s . T w o m a j o r classes o f p r o a n t h o c y a n i d i n s o c c u r : those t h a t possess a r e s o r c i n o l - p a t t e r n Α-ring ( F i g u r e 1) a n d those t h a t possess a p h l o r o g l u c i n o l p a t t e r n Α-ring. T h e l a t t e r are b y far the m o s t c o m m o n , o c c u r r i n g i n a h i g h p r o ­ p o r t i o n o f m o n o c o t y l e d o n o u s a n d d i c o t y l e d o n o u s p l a n t s (1,2). T h e r e s o r c i n o l p a t t e r n p r o a n t h o c y a n i d i n s are confined t o a few genera o f t r o p i c a l o r s u b t r o p i c a l h a r d w o o d s a n d associated s h r u b b y species (2), b u t are e c o n o m i c a l l y i m p o r t a n t , since the i n t e r n a t i o n a l l y c o m m e r c i a l l y p r e d o m i n a n t w a t t l e (3,4) a n d q u e b r a c h o (5) t a n n i n s are o f t h i s t y p e . Together, they c o n s t i t u t e a p p r o x i m a t e l y t w o - t h i r d s (i.e., a p p r o x i m a t e l y 300,000 tons) o f the w o r l d p r o d u c t i o n o f vegetable t a n n i n s (5). T h e r e s o r c i n o l - p a t t e r n p r o a n t h o c y a n i d i n s are w i d e l y used not o n l y for leather t a n n i n g , b u t also for a range o f other c o m m e r c i a l p r o d u c t s , p a r t i c u l a r l y as adhesives f o r p l y w o o d a n d fiberboard (6,7). W a t t l e t a n n i n i s p r o d u c e d f r o m s u s t a i n e d - y i e l d forests o f Acacia meamsii. l a r g e l y i n s o u t h e r n A f r i c a (6,8). S o m e o f the i m p e t u s a t least t o develop other uses for w a t t l e t a n n i n , a p a r t f r o m 0097-6156/89/0385-0172$06.00/0 ·

1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

PORTER

Viscosity and Formaldehyde

etc F i g u r e 1. S t r u c t u r e a n d n o m e n c l a t u r e o f p r o a n t h o c y a n i d i n s . P h l o r o g l u c i n o l - p a t t e r n Α-ring p r o a n t h o c y a n i d i n s : R = O H ; R = H . Procyanidins. R = R = O H . Prodelphinidins. R e s o r c i n o l - p a t t e r n Α-ring p r o a n t h o c y a n i d i n s : R = R = H . Profisetinidins. R = H ; R = O H . Prorobinetinidins. 2

2

2

2

1

1

2

2

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

leather t a n n i n g , grew o u t o f a w o r l d w i d e t r e n d away f r o m vegetable t a n n i n s i n favor o f s y n t h e t i c a n d c h r o m e t a n n i n g m e t h o d s . Potentially, the phloroglucinol-pattern proanthocyanidins, the procyanidins, a n d p r o d e l p h i n i d i n s ( F i g u r e 1) represent a n enormous resource o f renewable i n d u s t r i a l phenolics. T h e y occur i n h i g h c o n c e n t r a t i o n i n t h e b a r k a n d needles of m o s t conifers, a n d also i n t h e m a j o r i t y o f T e m p e r a t e Zone h a r d w o o d s

(2).

L a r g e q u a n t i t i e s o f t h i s t y p e o f t a n n i n are s t i l l used i n the leather i n d u s t r y - especially i n C h i n a and R u s s i a (Sun Dawang, personal communication) and India (9). A l t h o u g h a c t u a l tonnages are difficult t o a s c e r t a i n , t h e q u a n t i t i e s used for leather t a n n i n g i n these countries are a b o u t h a l f those o f t h e t o t a l p r o d u c t i o n

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

o f w a t t l e a n d quebracho t a n n i n s c o m b i n e d .

A t t e m p t s t o use p r o c y a n i d i n s as

w o o d adhesives a n d other p r o d u c t s , p a r t i c u l a r l y those d e r i v e d f r o m D o u g l a s - f i r , western h e m l o c k , a n d Pinus

radiata (10,11), date back t o t h e 1950V, b u t so f a r ,

no t r u l y successful i n d u s t r i a l process has been developed, l a r g e l y because o f a n u m b e r o f p r o b l e m s associated w i t h t h e i r h i g h c h e m i c a l r e a c t i v i t y a n d r e l a t i v e instability i n solution. M u c h o f t h e p r o b l e m i n f i n d i n g successful i n d u s t r i a l a p p l i c a t i o n s h a s r e v o l v e d a r o u n d a lack o f basic u n d e r s t a n d i n g o f t h e s t r u c t u r e a n d c h e m i s t r y of p h l o r o g l u c i n o l - p a t t e r n p r o a n t h o c y a n i d i n s .

Whereas, South A f r i c a n work-

ers (especially R o u x a n d h i s colleagues) m o u n t e d a concerted

a n d successful

c a m p a i g n b e g i n i n g i n t h e 1950's t o u n d e r s t a n d t h e c h e m i s t r y o f w a t t l e a n d quebracho p r o a n t h o c y a n i d i n s (4,5), s i m i l a r advances i n o u r knowledge o f t h e p h l o r o g l u c i n o l - p a t t e r n p r o a n t h o c y a n i d i n s h a d t o w a i t for the i m p r o v e d c h e m i c a l technology o f the last decade. T h e s e advances s t a r t e d w i t h i s o l a t i o n o f p r o c y a n i d i n oligomers as t h e free phenols u s i n g d e x t r a n gels (12) a n d e l a b o r a t i o n o f t h e i r properties a n d t h e subsequent u n e q u i v o c a l d e m o n s t r a t i o n t h a t p o l y m e r i c p r o c y a n i d i n s a n d p r o d e l p h i n i d i n s consist o f extended chains o f

flavan-3-ol

u n i t s (13), t h e c o m m o n e s t

t y p e b e i n g based o n e p i c a t e c h i n u n i t s ( F i g u r e 2 ) . Subsequent t o these studies, r a p i d advances have been m a d e i n o u r u n d e r s t a n d i n g o f t h e reactions o f p r o c y a n i d i n s i n a c i d i c o r basic s o l u t i o n s a n d t h e i r r e a c t i o n w i t h sulfite, t h i o l s , a n d other phenols. A d v a n c e s i n these areas u p t o t h e present have been considered i n some d e t a i l b y H e m i n g w a y a n d his colleagues (14-17) a n d w i l l n o t be f u r t h e r discussed, except i n context. T h e c u r r e n t s t u d y seeks t o e x t e n d o u r knowledge o f t h e b e h a v i o r o f p r o c y a n i d i n s i n t w o areas i m p o r t a n t t o t h e i r i n d u s t r i a l u t i l i z a t i o n : 1) t h e v i s c o s i t y of p r o c y a n i d i n p o l y m e r s i n aqueous s o l u t i o n s , a n d 2) the s t o i c h i o m e t r y a n d rate of r e a c t i o n o f p r o c y a n i d i n s w i t h f o r m a l d e h y d e . Experimental

Methodolodgy

P r o c y a n i d i n s . C a t e c h i n ( F l u k a ) a n d e p i c a t e c h i n (ex. cacao beans) were r e c r y s t a l l i z e d a n d d r i e d before use. T h e oligomers e p i c a t e c h i n - ( 4 / ? — ^ - e p i c a t e c h i n a n d [epicatechin-(4/?—•8)]3-epicatechin were o b t a i n e d f r o m the e t h y l acetate s o l -

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175

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13.

F i g u r e 2. A n e x a m p l e of a h e x a m e r i c h o m o - o l i g o m e r of e p i c a t e c h i n , c o n t a i n i n g one (4/?—»6) a n d four (4/?—»8) i n t e r f l a v a n o i d linkages, φ = 3 , 4 - d i h y d r o x y p h e n y l .

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u b l e f r a c t i o n of cacao b e a n procyanidin*" b y c h r o m a t o g r a p h y o n Ser. adex L H 20 a n d M C I - g e l a n d identified b y c o m p a i on of t h e i r properties w i t h p u b l i s h e d d a t a (18,19). T h e p e n t a m e r i c a n d h e x a m e r i c p r o c y a n i d i n fractions were o b ­ t a i n e d f r o m the cacao b e a n p o l y m e r f r a c t i o n (see below) b y c h r o m a t o g r a p h y o n F r a c t o g e l H W - 4 0 i n m e t h a n o l (20). T h e m o l e c u l a r weight of a l l oligomers was checked b y negative i o n F A B mass spectroscopy u s i n g a g l y c e r o l m a t r i x (21). T h e p r o c y a n i d i n p o l y m e r s were i s o l a t e d b y acetone-water e x t r a c t i o n a n d S e p h a d e x L H - 2 0 c h r o m a t o g r a p h y as described elsewhere (13). T h e polymers h a d the f o l l o w i n g properties: (1) cacao b e a n (Theobroma cacao): [ α ] § ? = + 1 5 5 ° (c 0.2, w a t e r ) . Analysis. C a l c d . for C i s H ^ O e ^ O : C , 55.4; Η, 5.0. F o u n d : C , 55.4; H , 4.6. N u m b e r - a v e r a g e m o l e c u l a r weight d e t e r m i n e d b y v a p o r pres­ sure o s m o m e t r y i n m e t h a n o l : 1,970; (2) j a p o n i c a fruits (Chaenomeles speciosa) p o l y m e r : [c*]i$ = +149 (1 0.2, w a t e r ) . Analysis. C a l c d . for C i 5 H i 0 6 - 3 H 0 : C , 52.6; H , 5.3. F o u n d : C , 52.9; H , 5.5. N u m b e r - a v e r a g e m o l e c u l a r weight d e t e r m i n e d b y v a p o r pressure o s m o m e t r y i n m e t h a n o l : 4,035.

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8

8

2

2

V i s c o s i t y M e a s u r e m e n t s . These were c a r r i e d o u t o n s o l u t i o n s of the p r o ­ c y a n i d i n p o l y m e r s u s i n g a F e r r a n t i - S h i r l e y cone viscometer at 25.0 ± 0.1 ° C w i t h a 3 . 5 - c m - r a d i u s cone. T h i s viscosity was measured at several r o t a t i o n rates t o check for shear dependence. T h e results were constant over the ranges used (20 t o 500 r e v o l u t i o n s per m i n u t e , d e p e n d i n g o n the v i s c o s i t y ) , a n d the r e s u l t i n g viscosity values were averaged t o o b t a i n the results i n the test. Formaldehyde Reaction Rate and Consumption Experiments. Solu­ t i o n s of a p p r o x i m a t e l y 1% w / v f o r m a l d e h y d e were p r e p a r e d b y s u i t a b l e d i ­ l u t i o n of a 3 8 % w / v f o r m a l i n s o l u t i o n ( B D H ) a n d were s t a n d a r d i z e d b y the c h r o m o t r o p i c a c i d m e t h o d (22). T h e k i n e t i c a n d r e a c t i o n s t o i c h i o m e t r y e x p e r i m e n t s were c a r r i e d o u t i n a m a g n e t i c a l l y s t i r r e d , water-jacketed, 70 m L - c a p a c i t y closed glass beaker e q u i p p e d w i t h four p o r t s for a condenser, c o m b i n e d glass a n d c a l o m e l electrode, n i t r o ­ gen i n l e t , a n d s a m p l e w i t h d r a w a l . T h e l a t t e r three were a l l sealed w i t h s e p t a . T h e k i n e t i c r u n s were c a r r i e d o u t b y t r a n s f e r r i n g a n a p p r o p r i a t e a m o u n t of a c c u r a t e l y weighed flavanoid t o the vessel together w i t h 50 m L of p H 8.0 b o r a t e / h y d r o c h l o r i c a c i d ( M e r c k ) buffer. T h e vessel was assembled a n d allowed t o come t o t e m p e r a t u r e (30 ° C m a i n t a i n e d v i a water c i r c u l a t e d f r o m a t h e r m o s t a t e d w a t e r b a t h ) u n d e r a slow s t r e a m of n i t r o g e n . T h e flavanoid caused a d o w n w a r d shift of buffer p H , a n d t h i s was carefully readjusted t o p H 8.0 b y d r o p wise a d d i t i o n of 0 . 1 M s o d i u m h y d r o x i d e . T h e n , the r e a c t i o n was i m m e d i a t e l y i n i t i a t e d b y a d d i t i o n of 0.5 m L of 1% formaldehyde s o l u t i o n , a n d the r e s i d u a l f o r m a l d e h y d e c o n c e n t r a t i o n was measured b y r e m o v a l at t i m e d i n t e r v a l s of 0.5 m L a l i q u o t s , d i l u t i o n of these a l i q u o t s to 5.0 m L w i t h p H 6.0 c i t r a t e - s o d i u m h y d r o x i d e ( M e r c k ) buffer, a n d transfer of two 1.0 m L samples o f the d i l u t e d so­ l u t i o n t o 8 m L - c a p a c i t y screw-top glass v i a l s e q u i p p e d w i t h teflon-lined l i d s . A 3.0 m L a l i q u o t of a s o l u t i o n of 1 m L of acetylacetone a n d 0.6 m L of g l a c i a l acetic a c i d i n 100 m L of 2 M a m m o n i u m acetate was a d d e d t o each v i a l , w h i c h were

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c a p p e d a n d the contents a g i t a t e d o n a v o r t e x m i x e r ; the v i a l s were t h e n heated at 60 ° C for 40 m i n u t e s . T h e f o r m a l d e h y d e c o n c e n t r a t i o n was t h e n m e a s u r e d s p e c t r o p h o t o m e t r i c a l l y f r o m the i n t e n s i t y of the a b s o r p t i o n b a n d at 412 n m b y reference t o a s t a n d a r d curve (23). T h e t o t a l c o n s u m p t i o n o f f o r m a l d e h y d e for each r e a c t i o n was e s t i m a t e d b y r e m o v i n g t w o 7 m L a l i q u o t s o f the r e a c t i o n m i x t u r e a n d h e a t i n g these at 60 ° C for 2 h o u r s i n screw-top glass v i a l s a n d a n a l y z i n g r e s i d u a l f o r m a l d e h y d e b y the above m e t h o d .

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Results and Discussion V i s c o s i t y M e a s u r e m e n t s . T h e viscosity results o b t a i n e d for the t w o p r o c y a n i d i n p o l y m e r s were as follows, the percentage values b e i n g the s o l u t i o n concentrations ( w / w ) :

Polymer

20%

Theobroma cacao Chaenomeles speciosa

4.5 6.4

V i s c o s i t i e s (mPa-s0 40% (NaOH) 40% 192 159 441 897

30% 18.0 45.7

T h e lower viscosities observed for the T. cacao p o l y m e r are e x p e c t e d as its number-average degree of p o l y m e r i z a t i o n is a b o u t h a l f t h a t of the C. speciosa p o l y m e r , the values b e i n g 6.1 a n d 11.8, respectively. T h e degrees o f p o l y m e r i z a t i o n were c a l c u l a t e d b y d i v i d i n g the number-average m o l e c u l a r weights b y the h y d r a t e d m o n o m e r m o l e c u l a r weight as i n d i c a t e d b y m i c r o a n a l y s i s (24). T h e s e results m a y be c o m p a r e d w i t h viscosities o b t a i n e d i n a s i m i l a r w a y f r o m conifer b a r k e x t r a c t s w h i c h , w h i l e heterogeneous, c o n t a i n p o l y m e r i c p r o c y a n i d i n s or m i x e d p o l y m e r i c p r o c y a n i d i n s a n d p r o d e l p h i n i d i n s as t h e i r p r e d o m i n a n t c o m p o n e n t s (2). F o r e x a m p l e , W e i s s m a n (25) r e p o r t e d a v i s c o s i t y of 65 m P a - s for a 3 0 % s o l u t i o n of the water e x t r a c t f r o m Pinus oocarpa b a r k , a n d D i x a n d M a r u t s k y (26) o b t a i n e d a value of 31 m P a - s for a s i m i l a r s o l u t i o n f r o m P t c e a abies b a r k . T h e s e viscosities are s i m i l a r t o those observed for the 3 0 % p r o c y a n i d i n p o l y m e r s o l u t i o n s . T h e y i n d i c a t e t h a t the viscosities of these b a r k e x t r a c t s o l u t i o n s are d o m i n a t e d b y the p r o a n t h o c y a n i d i n s a n d t h a t there is l i t t l e influence f r o m any a c c o m p a n y i n g p o l y s a c c h a r i d e s - a s a l r e a d y suggested b y W e i s s m a n n (25)-m contrast t o w a t t l e e x t r a c t s where g u m s p l a y a n i m p o r t a n t role i n d e t e r m i n i n g s o l u t i o n viscosities ( 7 ) . A y l a (27) r e p o r t e d a v i s c o s i t y of 65 m P a - s for a 4 0 % s o l u t i o n o f the b a r k e x t r a c t f r o m Pinus brutia. T h i s is very m u c h lower t h a n t h a t o b t a i n e d for the T. cacao p r o c y a n i d i n p o l y m e r , even t h o u g h A y l a ' s (27) e s t i m a t e o f 7-8 for t h e number-average degree of p o l y m e r i z a t i o n was a p p a r e n t l y higher t h a n the value of 6.1 o b t a i n e d for the T. cacao p o l y m e r . However, i t has r e c e n t l y been s h o w n t h a t the P. brutia p o l y m e r is a c t u a l l y a p r o c y a n i d i n - 0 - g l u c o s i d e (28). When

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allowance is m a d e for t h i s , the degree of p o l y m e r i z a t i o n of the P. brutia is reduced t o 4 t o 5, w h i c h p r o b a b l y accounts for the lower viscosity.

polymer

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

I n c o n t r a s t , Y a z a k i a n d H i l l i s (29) o b t a i n e d a v i s c o s i t y of 8,500 m P a - s for a 4 5 % s o l u t i o n of the aqueous e x t r a c t f r o m Pinus radiata b a r k . T h i s is a l m o s t a n order of m a g n i t u d e higher t h a n t h a t expected o n the basis of the p r o c y a n i d i n p o l y m e r results. V i s c o s i t i e s of the m e t h a n o l - s o l u b l e p o r t i o n a n d the u l t r a f i l t e r e d p o r t i o n s o f t h i s e x t r a c t were 500 a n d 90 m P a - s , respectively. T h e former value is a b o u t t h a t expected for a p r o a n t h o c y a n i d i n p o l y m e r , b u t the l a t t e r i n d i c a t e s t h a t m o s t o f the p o l y m e r has been e x c l u d e d b y the filter, a n d i t f u r t h e r i m p l i e s t h a t m o l e c u l a r sizes of p r o a n t h o c y a n i d i n s based o n u l t r a f i l t r a t i o n measurements are often m i s l e a d i n g . W h e n P. radiata b a r k is e x t r a c t e d b y s u l f i t e - c a r b o n a t e , the s o l u t i o n v i s c o s i ­ ties are m u c h lower. F o r e x a m p l e , W o o (30) r e p o r t e d a v i s c o s i t y of 1,600 m P a - s for a 4 5 % s o l u t i o n o f " T a n n a p h e n , " a c o m m e r c i a l t a n n i n e x t r a c t f r o m P. radi­ ata b a r k t h a t contains a p p r o x i m a t e l y 7 0 % p r o a n t h o c y a n i d i n s . W h e n e x t r a c t e d w i t h s u l f i t e - c a r b o n a t e , the p r o a n t h o c y a n i d i n s w i l l be p a r t l y d e p o l y m e r i z e d (31), w h i c h w i l l cause a f a l l i n viscosity. W h e t h e r the very h i g h viscosities observed for aqueous e x t r a c t s b y Y a z a k i a n d H i l l i s (29) are due t o the P. radiata p r o a n t h o ­ c y a n i d i n s b e i n g of m u c h higher m o l e c u l a r weight t h a n other conifer t a n n i n s or due t o c o m p l e x a t i o n o f the p r o a n t h o c y a n i d i n s w i t h the p o l y s a c c h a r i d e f r a c t i o n (32) r e m a i n s t o be s h o w n . T h e v i s c o s i t y measurements i n alkaline s o l u t i o n are m o r e difficult t o i n ­ terpret. H e m i n g w a y a n d his colleagues (15,17) have s h o w n t h a t , i n s t r o n g l y alkaline s o l u t i o n s , p r o c y a n i d i n p o l y m e r s are r a p i d l y converted at a m b i e n t t e m ­ peratures t o species where most m o n o m e r s c o n t a i n a rearranged Α-ring, such as s h o w n i n F i g u r e 3. O n t h i s basis, p r o c y a n i d i n s are converted t o chains w i t h a greater degree of r i g i d i t y t h a n the o r i g i n a l p o l y m e r . It is possible t h a t t h i s m a y e x p l a i n the increased v i s c o s i t y (33). H o w e v e r , the p r o c y a n i d i n results are very different f r o m those o b t a i n e d b y W e i s s m a n n (25) for a l k a l i n e e x t r a c t s f r o m Pinus oocarpa b a r k . O n the basis o f 3 0 % w / w s o l u t i o n s at 25 ° C , the w a t e r - s o l u b l e m a t e r i a l was f o u n d t o have a v i s c o s i t y of 65 m P a - s , whereas, the m a t e r i a l soluble i n 1% s o d i u m h y d r o x i d e h a d a v i s c o s i t y of 1,294 m P a - s . I n l i g h t of the results of the c u r r e n t s t u d y , t h i s o b s e r v a t i o n is o n l y e x p l i c a b l e i f the viscosity of the s o d i u m h y d r o x i d e e x t r a c t is due t o n o n t a n n i n components. R e a c t i o n o f P r o c y a n i d i n s w i t h F o r m a l d e h y d e . O u r knowledge of the k i n e t i c s a n d s t o i c h i o m e t r y of the r e a c t i o n of p r o a n t h o c y a n i d i n p o l y m e r s w i t h f o r m a l d e h y d e t o p r o d u c e crosslinked resins is based m a i n l y o n three studies of the r e a c t i o n of m o d e l phenols or c a t e c h i n w i t h f o r m a l d e h y d e (34-36). These studies showed t h a t , at lower t e m p e r a t u r e s a n d p H values between 2 a n d 9, the s t o i c h i o m e t r y of the r e a c t i o n was near e q u i m o l a r i n c a t e c h i n a n d f o r m a l d e h y d e . K i a t g r a j a i et a l . (36) s t u d i e d the k i n e t i c s o f the r e a c t i o n o f c a t e c h i n w i t h f o r m a l d e h y d e over a range of stoichiometries, p H values, a n d t e m p e r a t u r e s , a n d o b t a i n e d the a c t i v a t i o n energies for the r e a c t i o n . T h e y i n t e r p r e t e d t h e i r d a t a i n

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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F i g u r e 3.

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R e p r e s e n t a t i o n of the general s t r u c t u r e of a p r o c y a n i d i n p o l y m e r

c h a i n t h a t has undergone alkaline rearrangement. R = H , or a c o n t i n u a t i o n of the same t y p e of s t r u c t u r e [after reference

(15)].

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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RESOURCES

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

t e r m s of first-order k i n e t i c s , w h i c h was s t a t e d to be observed over the first h a l f of the r e a c t i o n , followed b y a slower rate process. T h i s was e x p l a i n e d b y a s s u m i n g different r e a c t i v i t y of C - 6 a n d C - 8 t o w a r d f o r m a l d e h y d e . T h e s e observations were a l i t t l e s u r p r i s i n g i n v i e w of the fact t h a t M c G r a w a n d H e m i n g w a y (37) h a d observed t h a t 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 at C - 6 or C - 8 lacked regioselectivity for a s m a l l a t t a c k i n g s p e c i e s - s u c h as f o r m a l d e h y d e . T h e r e a c t i o n k i n e t i c s were reinvestigated, therefore, for c a t e c h i n , e p i c a t e c h i n , a n d t w o p r o c y a n i d i n s . T h e progress of the r e a c t i o n was followed b y m o n i t o r i n g the decrease i n f o r m a l d e h y d e c o n c e n t r a t i o n w i t h t i m e . P r e v i o u s studies used the h y d r o x y l a m i n e h y d r o c h l o r i d e m e t h o d o f a n a l y s i s (34-36), b u t t h i s was avoided i n the c u r r e n t s t u d y as i t requires tedious p H t i t r a t i o n s . I n s t e a d , a c o l o r i m e t r i c m e t h o d was used t h a t was first developed b y N a s h (23), i n v o l v i n g f o r m a t i o n of 3 , 5 - d i a c e t y l 1 , 4 - d i h y d r o l u t i d i n e , b y 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 a m m o n i a a n d acetylacetone at n e u t r a l p H . T h e cyclic p r o d u c t absorbs at 412 n m w i t h a m o l a r e x t i n c t i o n coefficient of 8,000 (23). O t h e r c o l o r i m e t r i c m e t h o d s cannot be used as they a l l involve very s t r o n g l y a c i d i c or basic m e d i a (22), w h i c h w o u l d force the phenol-formaldehyde reaction to completion. T h e reactions were c a r r i e d out i n a b o r a t e - h y d r o c h l o r i c a c i d buffer at p H 8.0, the p H b e i n g readjusted, i f necessary, b y a d d i t i o n of 1 M s o d i u m h y d r o x i d e s o l u t i o n after the a d d i t i o n of p r o c y a n i d i n . T h e above p H was chosen t o o b t a i n a convenient r e a c t i o n rate w h i l e m i n i m i z i n g catechinic a c i d f o r m a t i o n (36). It was f o u n d t h a t , i f water r a t h e r t h a n buffer was used for the r e a c t i o n , a n d the p H was s i m p l y adjusted t o p H 8.0 as described b y K i a t g r a j a i et a l . (36), the observed p H was u n s t a b l e a n d subject to d r i f t . T h e e x p e r i m e n t a l values for the k i n e t i c s a n d s t o i c h i o m e t r y of f o r m a l d e h y d e c o n s u m p t i o n are s u m m a r i z e d i n T a b l e I. T h e e x p e r i m e n t a l values for r e a c t i o n s t o i c h i o m e t r y i l l u s t r a t e t h a t , at least u p to a h e x a m e r , p r o c y a n i d i n s f o r m c o m p l e t e l y c r o s s l i n k e d p r o d u c t s i n d i l u t e s o l u t i o n , whereas, very l i t t l e c r o s s l i n k i n g occurs for the C. speciosa p r o c y a n i d i n p o l y m e r . I f the values of X for the hexamer a n d the T. cacao p o l y m e r are c o m p a r e d , i t m a y be seen t h a t , a l t h o u g h they have s i m i l a r degrees of p o l y m e r i z a t i o n , the h e x a m e r obeys the crosslinked m o d e l w e l l , whereas, the p o l y m e r consumes m o r e f o r m a l d e h y d e t h a n p r e d i c t e d by t h i s m o d e l . T h e difference is a p p a r e n t l y due t o the presence of longer c h a i n l e n g t h species i n the polydisperse (24) T. cacao p r o c y a n i d i n p o l y m e r ( w h i c h contains oligomers f r o m t r i m e r s to greater t h a n heptamers as i n d i c a t e d by c h r o m a t o g r a p h y - F A B mass s p e c t r o m e t r y ) . T h i s result i m p l i e s t h a t the a b i l i t y of p r o c y a n i d i n oligomers to f o r m s u b s t a n t i a l l y crosslinked p r o d u c t s must s t a r t to f a i l at somewhere a r o u n d a c h a i n l e n g t h o f 8 or 9 u n i t s . T h e s e results s u p p o r t the thesis t h a t t o achieve h i g h degrees of c r o s s l i n k i n g i n p r o a n t h o c y a n i d i n chains, b r i d g i n g species larger t h a n f o r m a l d e h y d e m u s t be used to s p a n the increased i n t e r m o l e c u l a r distances due to unfavorable steric d i s p o s i t i o n s ( 7 ) . However, the above results show t h a t f o r m a l d e h y d e is able to achieve s u b s t a n t i a l c r o s s l i n k i n g at a s u r p r i s i n g l y h i g h degree of p o l y m e r i z a t i o n . These results also e x p l a i n the success of u t i l i z i n g P. brutia b a r k extracts for w o o d

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PORTER

181

T a b l e I. S t o i c h i o m e t r y a n d K i n e t i c s of the R e a c t i o n B e t w e e n F o r m a l d e h y d e a n d Some F l a v a n - 3 - o l s ( p H 8.0 a n d 30 ° C )

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

(a) S t o i c h i o m e t r y Compound

X (observed)

Epicatechin Dimer Tetramer Pentamer Hexamer Theobroma cacao p o l y m e r Chaenomeles speciosa p o l y m e r

1.0 0.79 0.70 0.54 0.59 0.73 0.96

3

4

5

5

(b) K i n e t i c s

1

X

(predicted) 1.0 m o d e l 0.5 m o d e l 2

2.00 1.50

1.0 0.75 0.62 0.60 0.58 0.58 0.54

1.25 1.20 1.17 1.17 1.08

6

Compound

kziM-^ec" )

Catechin Epicatechin Dimer Chaenomeles

0.23 0.22

1

0.095 0.036

3

speciosa

polymer

X = moles of f o r m a l d e h y d e consumed per e p i c a t e c h i n u n i t . P r e d i c t e d values of X a s s u m i n g either 0.5 or 1.0 molecules of f o r m a l d e h y d e reacts w i t h each Α-ring site. I f the 0.5 m o d e l is o b e y e d , t h e n a l l h y d r o x y m e t h y ­ lene groups w i l l have c r o s s l i n k e d . Epicatechin-(4/3—•8)-epicatechin. [Epicatechin-(4/?—•δ)]3-epicatechin. U n f r a c t i o n a t e d m i x t u r e s of e p i c a t e c h i n p e n t a m e r s or hexamers o b t a i n e d chrom a t o g r a p h i c a l l y f r o m the T. cacao p o l y m e r . C o n c e n t r a t i o n of f o r m a l d e h y d e was 3.6 χ 1 0 ~ m o l a r a n d the r a t i o of f o r m a l d e ­ h y d e per Α-ring r e a c t i o n site was 0.5 i n each r u n . 1

2

3

4

5

6

3

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

adhesives (27) since, w i t h a degree of p o l y m e r i z a t i o n o f 4 t o 5, they are o b v i o u s l y well w i t h i n the established range for s u b s t a n t i a l c r o s s l i n k i n g . A l t e r n a t i v e l y , a p r o c y a n i d i n p o l y m e r w i t h a h i g h degree of p o l y m e r i z a t i o n m u s t be cleaved w i t h reagents s u c h as sulfite o f resorcinol to reduce the average c h a i n lengths p r i o r t o r e a c t i o n w i t h f o r m a l d e h y d e (38,39). K i n e t i c s . D a t a were collected for c a t e c h i n , e p i c a t e c h i n , epicatechin-(4/?—>8)e p i c a t e c h i n a n d the C. speciosa p o l y m e r . T h e r a t i o o f react ants was chosen so t h a t the c o n c e n t r a t i o n o f f o r m a l d e h y d e a n d r e a c t i o n sites was e q u i m o l a r , a s s u m i n g complete c r o s s l i n k i n g (i.e., 0.5 molecule of f o r m a l d e h y d e per react i o n site converts t o one molecule p e r r e a c t i o n site after c r o s s l i n k i n g , as each f o r m a l d e h y d e m o l e c u l e reacts w i t h t w o sites). T h e c o n c e n t r a t i o n o f f o r m a l d e hyde was kept the same for each c o m p o u n d so as t o p r o v i d e a consistent basis for c o m p a r i s o n . P l o t s of ( a b s o r b a n c e ) versus t i m e were l i n e a r for greater t h a n 9 0 % of the r e a c t i o n for each s y s t e m s t u d i e d . T h e s e observations m a y be i n t e r p r e t e d i n t e r m s o f the r e a c t i o n o b e y i n g second-order k i n e t i c s where the reactants are e q u i m o l a r (40). Second-order or m o r e c o m p l e x k i n e t i c s are t y p i c a l of p h e n o l f o r m a l d e h y d e condensations under alkaline c o n d i t i o n s ( 7 ) . A s expected, k2 for c a t e c h i n a n d e p i c a t e c h i n are the same, since the react i o n r a t e w o u l d be expected t o be independent o f C - r i n g stereochemistry. T h e c o m p a r a t i v e l y s m a l l e r rate constants observed for the t w o p r o c y a n i d i n s c o u l d be e x p l a i n e d b y the fact t h a t t h e y possess fewer r e a c t i o n sites p e r m o n o m e r u n i t t h a n c a t e c h i n or e p i c a t e c h i n a n d also b y steric effects. - 1

Conclusions T h e current s t u d y confirms t h a t f o r m a l d e h y d e is too s m a l l a b r i d g i n g g r o u p to s u b s t a n t i a l l y crosslink extended p r o a n t h o c y a n i d i n c h a i n s , extensive c r o s s l i n k i n g a p p a r e n t l y s t a r t i n g t o f a i l at c h a i n lengths of greater t h a n 6 u n i t s . T h e s t u d y also defines the v i s c o s i t y range c h a r a c t e r i s t i c o f p r o c y a n i d i n p o l y m e r s a n d i l l u s t r a t e s t h a t the v i s c o s i t y o f aqueous extracts f r o m some conifer b a r k s is d o m i n a t e d b y p r o a n t h o c y a n i d i n s , whereas, h i g h viscosities c h a r a c t e r i s t i c of n o n t a n n i n s or t a n n i n - p o l y s a c c h a r i d e complexes are c h a r a c t e r i s t i c o f the aqueous e x t r a c t s i n other cases. Literature Cited

1. Hemingway, R. W . In Natural Products Extraneous to the Lignocellulosic Cell Wall of Woody Plants; Rowe, J . W . , E d . ; Springer: New York, Chapter 6.6 (in press). 2. Porter, L . J. In Natural Products Extraneous to the Lignocellulosic Cell Wall of Woody Plants; Rowe, J . W . , E d . ; Springer: New York, Chapter 6.7 (in press). 3. Roux, D . G . ; Ferreira, D . ; Botha, J. J. J. Agric. Food Chem. 1980, 28, 4. Roux, D . G . ; Ferreira, D . Pure Appl. Chem. 1982, 54, 2465.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

216.

13.

PORTER

Viscosity and Formaldehyde

183

5. Viviers, P. M.; Kolodziej, H.; Young, D. Α.; Ferreira, D.; Roux, D. G. J. Chem. Soc., Perkin Trans. 1 1983, 2555. 6. Porter, L. J.; Hemingway, R. W. In Natural Products Extraneous to the Lignocellulosic Cell Wall of Woody Plants; Rowe, J. W., Ed.; Springer: New York, Chapter 9.3 (in press). 7. Pizzi, A. In Wood Adhesives, Chemistry and Technology; Pizzi, Α., Ed.; Marcel Dekker: New York, 1983; Chapter 4, pp. 177-246. 8. Roux, D. G. Phytochemistry 1972, 11, 1 2 1 9 . 9. Santappa, M.; Sundara Rao, V. S. J. Sci. Ind. Res. 1982, 41, 7 0 5 . 10. Herrick, F. W. J. Agric. Food Chem. 1980, 28, 2 2 8 .

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

11. Jenkin, D. J. J. Adhesion 1984, 16, 2 9 9 . 12. Thompson, R. S.; Jacques, D.; Haslam, E.; Tanner, R.J.N. J. Chem. Soc., Perkin Trans. 1. 1972, 1 3 8 7 . 13. Czochanska, Z.; Foo, L. Y.; Newman, R. H.; Porter, L. J. J. Chem.Soc.,Perkin Trans. 1. 1 9 8 0 , 2 2 7 8 .

14. Hemingway, R. W.; Laks, P. E.; McGraw, G. W.; Kreibich, R. E . Proc. F.P.R. International-Achievements and the Future 1985, 16, 17-11. 15. Laks, P. E.; Hemingway, R. W. Holzforschung 1987, i n press. 16. Laks, P. E.; Hemingway, R. W. J. Chem.Soc.,Perkin Trans. 1 1987, 4 6 5 . 17. Laks, P. E.; Hemingway, R. W.; Conner, A. H. J.Chem.,Soc.,Perkin Trans. 1. 1 9 8 7 , 1875.

18. Hemingway, R. W.; Foo, L. Y.; Porter, L. J. J. Chem. Soc.,Perkin Trans. 1. 1 9 8 2 , 1209.

19. Morimoto, S.; Nonaka, G.; Nishioka, I. Chem. Pharm. Bull. 1986, 34, 6 3 3 . 20. Derdelinckx, G.; Jerumanis, J. J. Chromatog. 1984, 285, 2 3 1 . 21. Karchesy, J. J.; Hemingway, R. W.; Foo, L. Y.; Barofsky, E.; Barofsky, D. F. Anal. Chem. 1986, 58, 2563. 22. Pickard, A. D.; Clark, E. R. Talanta 1984, 31, 7 6 3 . 23. Nash, T. Biochem. J. 1953, 55, 4 1 6 . 24. Porter, L. J. Aust. J. Chem. 1986, 39, 557. 25. Weissmann, G. Int. J. Adhesion Adhesives. 1983, 31. 26. Dix, B.; Marutzky, R. J. Appl. Pol. Sci.: Appl. Pol. Symp. 1984, 40, 9 1 . 27. Ayla, C. J. Appl. Pol. Sci.: Appl. Pol. Symp. 1984, 40, 6 9 . 28. Porter, L. J.; Foo, L. Y.; Furneaux, R. H. Phytochemistry 1985, 24, 5 6 7 . 29. Yazaki, Y.; Hillis, W. E. Holzforschung 1980, 34, 1 2 5 . 30. Woo, J. K. Paper presented at the International Symposium on Adhesion and Adhesives for Structural Materials, 28-30 September 1982, Washington State University, Pullman, Washington. 31. Foo, L. Y.; McGraw, G. W.; Hemingway, R. W. J. Chem. Soc. Chem. Commun. 1983, 672.

32. Rahman, M. D.; Richards, G. N. Carbohydrate Res. 1987, (in press). 33. Vollmert, B. In Polymer Chemistry; Springer: New York, 1973, P 3 7 8 . 34. Hillis, W. E.; Urbach, G. J. Appl. Chem. 1957, 9, 4 7 4 .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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35. Hemingway, R. W.; McGraw, G. W. J. Liquid Chromatog. 1978, 1, 163. 36. Kiatgrajai, P.; Wellons, J. D.; Gollob, L.; White, J. D. J. Org. Chem. 1982, 47, 2913. 37. McGraw, G. W.; Hemingway, R. W. J. Chem.Soc.,Perkin Trans. 1. 1982, 973. 38. Kreibich, R. E.; Hemingway, R. W. Forest Prod. J. 1987,37, 2, 43. 39. Kreibich, R. E.; Hemingway, R. W. Forest Prod. J. 1985,35, 3, 23. 40. Gould, E . S. In Mechanism and Structure in Organic 1959, p. 161.

Chemistry; Holt: New York,

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch013

R E C E I V E D June 2, 1988

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Chapter 14 Reactions of Tannin Model Compounds with Methylolphenols G . Wayne M c G r a w Louisiana College Pineville, LA 71360 Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

Seiji O h a r a

1

and R i c h a r d W. H e m i n g w a y

Southern Forest Experiment Station Forest Service, U . S . Department of Agriculture Pineville, LA 71360

Most formulations of tannin-based adhesives employ phenol-formaldehyde prepolymers as crosslinking agents. These condensations were modeled by reacting equimolar proportions of o- and p-hydroxybenzyl alcohols with resorcinol, phloroglucinol, or (+)-catechin in various combinations over a p H range of 3.0 to 11.0 at 100 °C. The H - and C-NMR spectra of peracetate derivatives of reaction products show that: 1) similarities in rates of condensation of o- and p-hydroxy benzyl alcohols with resorcinol, phloroglucinol, or (+)-catechin suggest that the stabilities of carbocations/quinone methides rather than the nucleophilicity of the phenol are rate controlling; 2) the nucleophilicity of the phenol is significant in determining product ratios when the phenols are competing for the same electrophile; 3) that condensations are selective, favoring those of p-hydroxybenzyl alcohol; 4) because of the dominance of condensation with p-hydroxybenzyl alcohol, there is little regioselectivity in the condensations at the C-6 or C-8 positions of (+)-catechin; 5) rearrangements are important in the reaction of (+)-catechin at alkaline p H , epimerization to (+)-epicatechin being prominent at p H ≤ 9.0, and formation of catechinic acid being dominant in reactions at p H 10.0 or 11.0; 6) because of the slow rate of condensation of hydroxybenzyl alcohols with phloroglucinol or (+)-catechin and rearrangement at alkaline p H , practical applications of these reactions in development of tannin-based adhesives are limited. 1

13

On study leave from Forestry and Forest Products Research Institute, Tsukuba, DanchiNai, Ibaraki, Japan 1

0097-6156/89/0385-0185$06.00A>

c

1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

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ADHESIVES F R O M RENEWABLE RESOURCES

M a c L e a n a n d G a r d n e r (1) first d e m o n s t r a t e d the i m p o r t a n c e of c r o s s l i n k i n g condensed t a n n i n s w i t h p o l y m e t h y l o l phenols r a t h e r t h a n w i t h f o r m a l d e h y d e i n the f o r m u l a t i o n o f p l y w o o d adhesives based o n conifer b a r k e x t r a c t s . T h e need t o use p o l y m e t h y l o l phenols arose because of the e x t r e m e l y r a p i d c o n d e n s a t i o n r a t e o f conifer b a r k t a n n i n s w h e n reacted w i t h f o r m a l d e h y d e over a w i d e range o f r e a c t i o n p H c o n d i t i o n s . H e r r i c k a n d B o c k (2) were able t o successf u l l y develop e x t e r i o r p l y w o o d glues based o n western h e m l o c k b a r k t a n n i n s b y c r o s s l i n k i n g t h e m w i t h s p e c i a l l y f o r m u l a t e d p o l y m e t h y l o l phenols. S i n c e t h e i r w o r k , m o s t o f the a t t e m p t s t o develop p l y w o o d or p a r t i c l e b o a r d adhesives based o n condensed t a n n i n s have i n v o l v e d t h e i r reactions w i t h p h e n o l - f o r m a l d e h y d e p r e p o l y m e r s ( 3 ) . I m p r o v e d properties o f the cured p o l y m e r s are t h o u g h t t o arise f r o m a h i g h e r frequency o f m o r e flexible crosslinks (4 ) w h e n u s i n g these p h e n o l - f o r m a l d e h y d e resins. S u r p r i s i n g l y l i t t l e is k n o w n a b o u t the reactions o f condensed t a n n i n s w i t h p h e n o l - f o r m a l d e h y d e p r e p o l y m e r s despite w i d e s p r e a d a t t e m p t s t o use these condensations i n f o r m u l a t i o n of t a n n i n - b a s e d adhesives. M c G r a w a n d H e m i n g w a y (5,6) first e x a m i n e d the reactions o f (-f ) - c a t e c h i n w i t h either o- or ph y d r o x y b e n z y l a l c o h o l t o m o d e l the c o n d e n s a t i o n o f p h e n o l - f o r m a l d e h y d e resins w i t h condensed t a n n i n s . I n reactions o f c a t e c h i n w i t h p - h y d r o x y b e n z y l a l c o h o l , s u b s t i t u t i o n o c c u r r e d at the C - 6 a n d C - 8 p o s i t i o n s o f the p h l o r o g l u c i n o l rings i n a p p r o x i m a t e l y e q u a l p r o p o r t i o n s . However, significant regioselectivity was seen i n the reactions o f c a t e c h i n w i t h o - h y d r o x y b e n z y l a l c o h o l . S u b s t i t u t i o n at the C - 8 p o s i t i o n was preferred over t h a t at C - 6 b y a factor o f a b o u t 2.5 t o 1. T h e rate of c o n d e n s a t i o n o f either o- or jp-hydroxybenzyl a l c o h o l w i t h ( + ) - c a t e c h i n was slow i n c o m p a r i s o n w i t h the reactions of f o r m a l d e h y d e w i t h p h l o r o g l u c i n o l or ( - f ) - c a t e c h i n . Recent w o r k o n the use of condensed t a n n i n s for the f o r m u l a t i o n of c o l d - s e t t i n g p h e n o l i c adhesives (7,8) has p o i n t e d out the need for u n d e r s t a n d i n g m o r e a b o u t the reactions o f condensed t a n n i n s w i t h p o l y m e t h y l o l phenols u n d e r a v a r i e t y o f c o n d i t i o n s . Therefore, either r e s o r c i n o l , p h l o r o g l u c i n o l , or (-f ) - c a t e c h i n was reacted w i t h e q u i m o l a r a m o u n t s of o- a n d p - h y d r o x y b e n z y l alcohols at 100 ° C over a p H range o f 3.0 t o 11.0. Experimental

Methodology

Reaction Conditions.

E q u i m o l a r q u a n t i t i e s o f o - h y d r o x y b e n z y l a l c o h o l , p-

h y d r o x y b e n z y l a l c o h o l a n d either r e s o r c i n o l , p h l o r o g l u c i n o l , or

(-h)-catechin

were dissolved i n p-dioxane-water (1:2, v / v ) a n d the s o l u t i o n p H a d j u s t e d to 3.0, 5.0, 7.0, 9.0, 10.0, or 11.0 b y a d d i t i o n o f acetic a c i d or 5 . 0 M N a O H . A n a l i q u o t was freeze-dried i m m e d i a t e l y ( 0 - T i m e ) , a n d the r e m a i n d e r was d i v i d e d a n d a d d e d t o a series o f sealed v i a l s , flushed w i t h N 2 , a n d heated for t i m e p e r i o d of 1, 2, or 6 h o u r s i n a b o i l i n g water b a t h . A f t e r the a p p r o p r i a t e r e a c t i o n p e r i o d , the samples were transferred t o r o u n d - b o t t o m e d flasks a n d freeze-dried.

In a

s i m i l a r m a n n e r , e q u i m o l a r q u a n t i t i e s o f two c o m p e t i n g phenols were reacted w i t h one equivalent o f either 0- or p - h y d r o x y b e n z y l a l c o h o l .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

14.

MCGRAW E T AL.

187

Tannin Compounds and Methylolphenoh

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

T h e freeze-dried residues were a c e t y l a t e d w i t h acetic a n h y d r i d e - p y r i d i n e (1:1, v / v ) at a m b i e n t t e m p e r a t u r e o v e r n i g h t . T h e samples were t h e n a d d e d t o water i n a s e p a r a t o r y f u n n e l a n d the peracetates e x t r a c t e d i n t o d i c h l o r o m e t h a n e . T h e d i c h l o r o m e t h a n e - s o l u b l e f r a c t i o n was d r i e d over a n h y d r o u s s o d i u m sulfate a n d t h e n e v a p o r a t e d t o a n o i l o n a r o t a r y e v a p o r a t o r at -hydroxybenzyl p h l o r o g l u c i n o l C-6 C-2 C-2 C-2 C-2 C-8 C-6 C-6

in in in in in in in in

di-(p-hydroxybenzyl) phloroglucinol resorcinol o - h y d r o x y b e n z y l resorcinol d i - ( p - h y d r o x y b e n z y l ) resorcinol d i - ( o - h y d r o x y b e n z y l ) resorcinol 8-(o-hydroxybenzyl) catechin 6-(o-hydroxybenzyl) catechin 6,8-di-(o-hydroxybenzyl) catechin

C-8 i n 6,8-di-(o-hydroxybenzyl) catechin C - 6 i n 4-( o - h y d r o x y b e n z y l ) resorcinol C - 4 a n d C - 6 i n 4 , 6 - d i - ( o - h y d r o x y b e n z y l ) resorcinol

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

methylenes g a i n e d were based u p o n changes i n the n u m b e r o f p r o t o n s a c t u a l l y f o u n d between 0- a n d X - T i m e o f r e a c t i o n . A s s i g n m e n t s f o r the H - N M R s p e c t r a o f ( + ) - c a t e c h i n derivatives are given i n T a b l e I . T h e s e d a t a are based o n results p u b l i s h e d earlier {5,12). T h e H N M R s p e c t r a o f the c a t e c h i n r e a c t i o n p r o d u c t s were n o r m a l i z e d b y a s s i g n i n g 11 p r o t o n s t o the b r o a d b a n d o f signals a t 6.75 t o 7.50 p p m . T h e c a r b o n s p e c t r a were o b t a i n e d u s i n g a 45° pulse a n d a n 0.8 second a c ­ q u i s i t i o n t i m e w i t h n o pulse delay. A c o m p a r i s o n o f these s p e c t r a w i t h those o b t a i n e d b y q u a n t i t a t i v e m e t h o d s (i.e., a 45° pulse, n O e suppressed, a n d a 14 second pulse delay) (IS) i n d i c a t e d t h a t accurate estimates o f the r a t i o s o f o- o r p - m e t h y l o l s , t h e r a t i o s o f o- a n d p-methylenes, a n d t h e u n s u b s t i t u t e d , m o n o s u b s t i t u t e d , a n d d i s u b s t i t u t e d resorcinol o r p h l o r o g l u c i n o l C - 2 c a r b o n s c o u l d be o b t a i n e d u s i n g a fast pulse sequence. T h e C - N M R s p e c t r a were, therefore, used t o c o m p u t e : 1) the r e l a t i v e a m o u n t s o f r e s i d u a l o- a n d p - m e t h y l o l s ; 2) t h e relative a m o u n t s o f o-o, o-p, a n d p-p methylenes t h a t m a y have been p r o d u c e d by self-condensation o f the b e n z y l alcohols; 3) t h e relative a m o u n t s o f o- a n d p-methylenes f o r m e d b y r e a c t i o n w i t h r e s o r c i n o l , p h l o r o g l u c i n o l , o r c a t e c h i n , and 4) the relative proportions o f unsubstituted, monosubstituted, a n d disub­ s t i t u t e d r e s o r c i n o l o r p h l o r o g l u c i n o l derivatives. T h e r a t i o o f p- t o o - m e t h y l o l c a r b o n signals averaged 0.87 t o 1.0, respectively, i n samples a t 0 - T i m e u s i n g these N M R p a r a m e t e r s . I t is possible t h a t the differences observed i n the i n t e n ­ sity o f these c a r b o n signals were d u e t o differences i n t h e extent o f h y d r a t i o n of the t w o b e n z y l alcohols used for t h e reactions. O n average, 9 1 . 4 % o f the loss o f p - m e t h y l o l was accounted for b y a n increase i n the i n t e n s i t y o f the p-o-o m e t h y l e n e c a r b o n s i g n a l s , a n d 8 5 . 6 % o f t h e loss o f o - m e t h y l o l was a c c o u n t e d for b y increases i n the o-o-ο m e t h y l e n e b r i d g e c a r b o n signals i n reactions w i t h p h l o r o g l u c i n o l . S i m i l a r results were o b t a i n e d i n reactions w i t h r e s o r c i n o l a n d w i t h ( + ) - c a t e c h i n i n reactions a t a c i d i c t o n e u t r a l p H . 1

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

1

1 3

A s s i g n m e n t s for the C - N M R s p e c t r a o f ( + ) - c a t e c h i n derivatives are given i n T a b l e I I . M o s t o f these assignments were p r e v i o u s l y p u b l i s h e d (5,12). W h e n a 45° pulse a n d a n 0.8 second a c q u i s i t i o n t i m e are used, t h e signals f o r C 6 a n d C - 8 o f the c a t e c h i n >i-ring, as w e l l as those for t h e C - 2 , C - 3 a n d C - 4 o f the h e t e r o c y c l i c r i n g , are a l l o f a p p r o x i m a t e l y e q u a l area. T h e signals for the o- a n d ]>-hydroxybenzyl C H are a p p r o x i m a t e l y 5 0 % o f the i n t e n s i t y o f the c a t e c h i n C - 2 a n d C - 3 c a r b o n s . Therefore, the C - N M R s p e c t r a were i n t e r p r e t e d t h r o u g h reference t o the average o f the c a t e c h i n h e t e r o c y c l i c C - 2 a n d C - 3 c a r b o n signals. T h e p r o p o r t i o n s o f A-nng c a r b o n s lost a n d m e t h y l e n e c a r b o n s g a i n e d were c o m p u t e d d i r e c t l y f r o m the relative i n t e n s i t y o f these peaks. T h e estimates for the n u m b e r o f o- o r p - m e t h y l o l c a r b o n s lost were o b t a i n e d b y m u l t i p l y i n g the changes i n s i g n a l i n t e n s i t y b y a factor o f 2. R e s u l t s o b t a i n e d i n t h i s w a y were r e a s o n a b l y consistent w i t h those o b t a i n e d f r o m the H - N M R s p e c t r a b u t u s u a l l y i n d i c a t e d a higher degree o f c o n d e n s a t i o n . 1 3

2

1 3

1

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

14.

McGRAW ET A L .

191

Tannin Compounds and Methyblphenols

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

Results and Discussion o- a n d p - H y d r o x y b e n z y l A l c o h o l s w i t h R e s o r c i n o l . T h e c o n d e n s a t i o n of e q u i m o l a r p r o p o r t i o n s o f o- a n d p - h y d r o x y b e n z y l alcohols w i t h r e s o r c i n o l was m o s t r a p i d at p H 3.0. A t t h i s p H , c o n d e n s a t i o n was a b o u t 5 0 % complete after 1 h o u r a n d over 7 5 % complete after 6 hours at 100 ° C . T h e reactions were m u c h slower at p H 5.0 a n d p H 7.0 a n d s o m e w h a t slower at p H 9.0, 10.0, a n d 11.0. T h e r e were o n l y s m a l l differences i n the extent o f c o n d e n s a t i o n i n reactions m a d e at i n i t i a l p H c o n d i t i o n s o f p H 9.0, 10.0, a n d 11.0. A t these p H values, i n i t i a l rates o f c o n d e n s a t i o n were less t h a n h a l f t h a t o b t a i n e d at p H 3.0 ( F i g u r e 1). E s t i m a t e s o f the degree o f c o n d e n s a t i o n o b t a i n e d b y m e a s u r i n g the loss o f m e t h y l o l s or the g a i n i n methylenes f r o m H - N M R s p e c t r a a n d f r o m the p r o p o r t i o n o f u n s u b s t i t u t e d , m o n o s u b s t i t u t e d , a n d d i s u b s t i t u t e d r e s o r c i n o l f r o m the C - N M R s p e c t r a u s u a l l y gave s i m i l a r results ( T a b l e I I I ) . 1

1 3

C o m p a r i s o n s o f the r a t i o s o f o- t o j>-methylol s i g n a l intensities i n C-NMR s p e c t r a i n d i c a t e d s t r o n g s e l e c t i v i t y i n the c o n d e n s a t i o n o f t h e p - m e t h y l o l s at either extreme o f r e a c t i o n p H (i.e., i n i t i a l p H o f 3.0 or 11.0). However, as the r e a c t i o n p H a p p r o a c h e d n e u t r a l i t y , there was s i g n i f i c a n t l y less difference i n the rates o f loss o f o- a n d p - m e t h y l o l s ( F i g u r e 2). S e l e c t i v i t y i n c o n d e n s a t i o n w i t h p - m e t h y l o l s was also evident f r o m c o m p a r i s o n s o f the intensities o f o-p a n d o-o m e t h y l e n e signals i n the C - N M R s p e c t r a . A t m o r e a c i d i c or m o r e a l k a l i n e p H , the o-p methylenes d o m i n a t e d e a r l y i n the r e a c t i o n ( T a b l e I I I ) . A s the degree o f c o n d e n s a t i o n increased, the o-o methylenes increased i n r e l a t i v e p r o p o r t i o n as w o u l d be e x p e c t e d because o f low r e s i d u a l c o n c e n t r a t i o n s o f p - m e t h y l o l s . I n reactions at p H 7.0, t h e o-p m e t h y l e n e signals were m o r e d o m i n a n t t h a n w o u l d have been expected f r o m the change i n o- a n d p - m e t h y l o l s , b u t the relative p r o p o r t i o n s o f the o-p a n d o-o methylenes d i d not change m u c h after longer r e a c t i o n t i m e s . T h i s also w o u l d be expected because o f the c o m p a r a t i v e l y larger a m o u n t s o f r e s i d u a l j>-methyols. 1 3

1 3

o- a n d p - H y d r o x y b e n z y l A l c o h o l s w i t h P h l o r o g l u c i n o l . T h e s e results closely p a r a l l e l those f r o m r e a c t i o n o f these alcohols w i t h r e s o r c i n o l . T h e o v e r a l l rates o f c o n d e n s a t i o n w i t h p h l o r o g l u c i n o l were also sensitive t o i n i t i a l r e a c t i o n p H . A t p H 3.0, c o n d e n s a t i o n was over 7 0 % complete after 6 hours o f h e a t i n g at 100 ° C . T h e degree o f s u b s t i t u t i o n decreased w i t h i n c r e a s i n g i n i t i a l r e a c t i o n p H t o a m i n i m u m at p H of 9.0 where o n l y a b o u t 4 0 % o f the t o t a l m e t h y l o l h a d reacted after 6 hours at 100 ° C . T h e rates of c o n d e n s a t i o n increased at m o r e alkaline p H where a p p r o x i m a t e l y 6 0 % a n d 5 5 % o f the m e t h y l o l reacted after 6 h o u r s at 100 ° C , at p H 10.0 a n d p H 11.0, respectively. E s t i m a t e s of the r e l a t i v e p r o p o r t i o n s of u n s u b s t i t u t e d , m o n o s u b s t i t u t e d , a n d d i s u b s t i t u t e d p h l o r o g l u c i n o l derivatives, o b t a i n e d by i n t e g r a t i o n of the C - 2 p h l o r o g l u c i n o l c a r b o n signals at 112.5, 114.0, a n d 115.7 p p m , respectively, were r e a s o n a b l y consistent w i t h results o b t a i n e d f r o m i n t e g r a t i o n of the m e t h y l o l a n d m e t h y l e n e signals i n the H - N M R s p e c t r a ( T a b l e I V ) . 1

A s was observed i n reactions w i t h r e s o r c i n o l , the

1 3

C - N M R s p e c t r a showed

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

192

adhesives f r o m r e n e w a b l e r e s o u r c e s

+ &-

+ jp -

hydroxybenzyl

alcohols

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

resorcinol

reaction

time

(hrs.)

F i g u r e 1. Degree o f s u b s t i t u t i o n o n t o resorcinol at various p H values p l o t t e d against r e a c t i o n t i m e .

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

14.

McGRAW E T A L .

Tannin Compounds and Methylolphenols

193

T a b l e I I I . M e t h y l o l , M e t h y l e n e , a n d Degree of S u b s t i t u t i o n per M o l e of R e s o r c i n o l after R e a c t i o n w i t h o- a n d p-Hydroxybenzyl Alcohols

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

Reaction Time (Hrs)

Methylols ρ ο

Methylenes o-p o-o pH

-

3.0

-

0 1 2 6

0.82 0.20 0.04 0.00

0.86 0.70 0.63 0.30

0 1 2 6

0.77 0.71 0.62 0.40

0.83 0.87 0.82 0.62

0 1 2 6

0.74 0.73 0.61 0.43

0.81 0.79 0.81 0.59

0 1 2

0.79 0.61 0.51 0.30

0.83 0.81 0.77 0.47

0.85 0.56 0.42 0.13

0.87 0.87 0.72 0.43

0.69 0.48 0.28 0.11

0.78

0.09 0.18 0.46 P H 11.0 0.19 -

0.80 0.70 0.53

0.23 0.37 0.66

0.60 0.75 0.79 pH

nm 0.12 0.34 H P

6 0 1 2 6 0 1 2 6

0.11 0.15 0.29 pH

-

0.21 0.32 0.52

0.12 0.24 0.50 5.0

-

nm 0.06 0.17 7.0

-

0.04 0.09 0.16 9.0

-

0.07 0.14

0.46 P H 10.0

-

Substitution unsub mono disub

-

0.27 0.44 0.64

0.09 0.16 0.33

-

-

1.00 0.33 0.21 0.14

0.39 0.42 0.32

0.28 0.37 0.54

1.00 0.81 0.74 0.46

0.19 0.19 0.34

-

1.00 0.72 0.73 0.45

0.28 0.27 0.35

1.00

-

-

0.07 0.20

-

0.19

-

0.63 0.35 0.17

0.37 0.51 0.32

1.00 0.63 0.35 0.17

0.37 0.51 0.32

0.87

0.13

-

0.48 0.32

0.43 0.45 0.37

0.10 0.23 0.43

0.19

-

0.14 0.52

-

-

0.52

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

194

adhesives f r o m r e n e w a b l e

resources

REACTION WITH RESORCINOL pHII

I

0

%

1

50

pH7

I

100

SL- AND £ -

I

I

0

50

pH3

I

100

I

I

I

0

50

100

HYDROXYBENZYL ALCOHOL LOST

F i g u r e 2. P e r c e n t o f o- a n d p - h y d r o x y b e n z y l a l c o h p l r e a c t i n g w i t h r e s o r c i n o l as a function of time.

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

McGRAW E T A L .

Tannin Compounds and Methylolphenols

T a b l e I V . C o m p a r i s o n of M e t h y l o l L o s s , M e t h y l e n e F o r m a t i o n , a n d P h e n o l S u b s t i t u t i o n as Percentage of M e t h y l o l C o n s u m e d after 6 H o u r s a n d 100 ° C at V a r i o u s p H Methylol Lost

Initial p H

1

Methylene Gained 1

Phenol Substitution

Average 2

Resorcinol 3.0 5.0 7.0 9.0 10.0 11.0

82.5 35.7 33.5 52.5 67.4 56.5

76.0 31.2 28.4 55.6 65.7 67.3

70.0 37.0 36.5 59.3 79.1 83.7

76.2 34.7

67.5 50.0 44.5 34.9

72.2 49.2 42.1 40.4

67.5 68.5

60.7 55.9

32.8 55.8 70.7 69.2

Phloroglucinol 3.0 5.0 7.0 9.0

82.0 58.7 49.7 48.7

10.0 11.0

58.3 49.6

67.0 39.0 32.0 37.5 56.3 49.6

B a s e d o n H - N M R d a t a a n d n u m b e r of m e t h y l o l s at 0 - t i m e . B a s e d on C - N M R data and assuming equimolar proportions. D o e s not account for possible t r i s u b s t i t u t e d p r o d u c t . 1

1

2

1 3

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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ADHESIVES F R O M RENEWABLE RESOURCES

t h a t the extent o f s e l e c t i v i t y i n reactions o f o- a n d p - m e t h y l o l s was h i g h l y de­ pendent o n i n i t i a l r e a c t i o n p H . C o n d e n s a t i o n o f the p - m e t h y l o l d o m i n a t e d i n reactions at p H 3.0, p H 10.0, a n d p H 11.0, b u t there was less s e l e c t i v i t y i n reactions m a d e at i n i t i a l p H o f 7.0 t o 9.0 ( T a b l e V ) . T h i s same preference for c o n d e n s a t i o n w i t h p - h y d r o x y b e n z y l a l c o h o l was evident i n the h i g h p r o p o r t i o n of p-methylenes i n r e a c t i o n p r o d u c t s o b t a i n e d at a c i d i c p H . o- a n d p- H y d r o x y b e n z y l A l c o h o l s w i t h ( + ) - C a t e c h i n . The H - N M R s p e c t r a o f p r o d u c t s o f the r e a c t i o n of c a t e c h i n w i t h a p p r o x i m a t e l y e q u i m o l a r p r o p o r t i o n s o f o- a n d p - h y d r o x y b e n z y l alcohols i n d i c a t e d t h a t (-f-)-catechin reacts w i t h these phenols at rates s i m i l a r t o those f o u n d for r e s o r c i n o l a n d p h l o r o g l u c i n o l . I n reactions at p H 3.0, a b o u t 5 0 % of the c a t e c h i n y l - r i n g p r o ­ tons were lost due t o s u b s t i t u t i o n after 1 h o u r . O n l y a b o u t 1 5 % o f the y l - r i n g p r o t o n s r e m a i n e d after 6 hours o f r e a c t i o n at p H 3.0 a n d 100 ° C . A s was o b ­ served i n the reactions w i t h p h l o r o g l u c i n o l , the rates o f c o n d e n s a t i o n o f o- a n d p - h y d r o x y b e n z y l alcohols w i t h (-f ) - c a t e c h i n are dependent o n the i n i t i a l reac­ t i o n p H . T h e c o n d e n s a t i o n r a t e decreases w i t h a n increase i n r e a c t i o n p H t o a m i n i m u m at p H 7.0.

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

1

I n reactions at p H 9.0, there is significant e p i m e r i z a t i o n o f (-f)-catechin t o ( + ) - e p i c a t e c h i n . T h i s was best seen i n the C - N M R s p e c t r a where there are large differences i n the c h e m i c a l shifts o f the C - 2 a n d C - 3 c a r b o n signals ( T a b l e I I ) . R e d u c t i o n s i n the i n t e n s i t y o f Α-ring p r o t o n s , losses o f m e t h y l o l p r o t o n s , a n d gains i n m e t h y l e n e p r o t o n s were reasonably consistent, suggesting t h a t the m a j o r r e a c t i o n was c o n d e n s a t i o n w i t h the h y d r o x y b e n z y l alcohols i n a d d i t i o n t o t h i s e p i m e r i z a t i o n . A f t e r 1 h o u r at 100 ° C a n d p H 9.0, the r a t i o o f c a t e c h i n t o e p i c a t e c h i n was 3 t o 1 ( F i g u r e 3). T h e loss of ^4-ring carbons was s l i g h t l y higher t h a n the loss o f m e t h y l o l s or the increase i n m e t h y l e n e c a r b o n s , suggest­ i n g t h a t a b o u t 1 0 % o f the flavan-3-ols m a y have been lost b y b a s e - c a t a l y z e d rearrangement t o catechinic a c i d . I n reactions at i n i t i a l p H of 10.0 or 11.0, there is significant loss o f the p h l o r o g l u c i n o l A - r i n g f u n c t i o n a l i t y t h r o u g h rearrangement o f c a t e c h i n t o cate­ c h i n i c a c i d (14-16). T h i s was evident i n the large loss o f Λ-ring p r o t o n signals i n c o m p a r i s o n w i t h the m u c h s m a l l e r increase i n the m e t h y l e n e or loss of m e t h y l o l p r o t o n s . R e a r r a n g e m e n t o f c a t e c h i n to c a t e c h i n i c a c i d d o m i n a t e s over c o n d e n ­ s a t i o n w i t h h y d r o x y b e n z y l alcohols w h e n reactions are m a d e at p H of 10.0, since o n l y a b o u t h a l f o f the >l-ring c a r b o n s lost c o u l d be a c c o u n t e d for b y losses i n m e t h y l o l or gains i n m e t h y l e n e b r i d g e carbons. T h e C - N M R s p e c t r a o f peracetates recovered f r o m reactions at p H 10.0 a n d 11.0 for 1 h o u r showed intense signals at c h e m i c a l shifts expected for a m i x t u r e of o- a n d p - h y d r o x y b e n z y l a l c o h o l . M u c h s m a l l e r signals o c c u r r e d at c h e m i c a l shifts f o u n d for c a t e c h i n . A l t h o u g h a n u m b e r of other s m a l l signals was e v i d e n t , none of these c o u l d be r e a d i l y assigned t o catechinic a c i d or other l o g i c a l p r o d u c t s o f ( + ) - c a t e c h i n . I n reactions at p H 11.0, no p h l o r o g l u c i n o l A-i'mg can be detected after o n l y 1 h o u r at 100 ° C , a n d there is l i t t l e change i n the a m o u n t o f m e t h y l o l or f o r m a t i o n of m e t h y l e n e b r i d g e after 6 hours o f h e a t i n g . T h e m e t h y l e n e signals t h a t are 1 3

1 3

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

14.

MCGRAW ET AL.

197

Tannin Compounds and Methylolphenols

T a b l e V . M e t h y l o l , M e t h y l e n e , a n d Degree of S u b s t i t u t i o n p e r M o l e o f P h l o r o g l u c i n o l after R e a c t i o n w i t h ο- a n d p - H y d r o x y b e n z y l A l c o h o l s Reaction Time

Methylols

Methylenes o-o

Substitution

o-o-ο

unsub.

mono

-

1.00 0.32 0.22 0.16

0.37 0.36 0.33

ρ

ο

o-p

0 1 2 6

0.88 0.16 0.08 0.00

0.78 0.70 0.52 0.30

0.05 0.08 0.04

0 1 2 6

0.77 0.64 0.48 0.18

0.87 0.75 0.78 0.50

0.04 0.04 0.05

0 1

0.78 0.59

0.84 0.81

-

-

-

0.24

0.24

6

0.40 0.28

0.73 0.53

0.03 0.06

0.51 0.22

0.78 0.62

0.74

--

di

(Hrs) Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

pH

0 1 2 6 0 1 2 6 0 1 2 6

-

0.59 0.27

0.76 0.67 0.51

0.65 0.65 0.46 0.08

0.81 0.80 0.69 0.55

0.69

0.72

0.53 0.41 0.12

0.74

0.04

0.61 0.60

0.06 0.06

3.0

-

0.12 0.58 0.69 0.26 0.44 0.70 p H 5.0

-

-

0.04 0.13 0.09 0.19 0.23 0.50 p H 7.0

0.12

0.17 0.40 p H 9.0

-

-

-

0.17 0.06 0.17 0.04 0.33 0.20 p H 10.0

0.08 0.09 0.07

-

0.05 0.06

-

0.03 0.08 0.19 0.23 0.55 p H 11.0 0.02 0.20 0.34 0.49

0.07 0.09 0.16

1.00 0.62 0.56 0.32 1.00 0.79 0.55 0.37 1.00 0.87 0.68 0.57 0.92 0.76 0.62

-

0.28 0.35 0.38

-

-

0.10 0.10 0.31

-

0.21 0.34

.00 0.11

0.37

0.26

-

-

0.13 0.29 0.33

0.23

0.08 0.24 0.32 0.52

0.98

0.02

0.68 0.54

0.28 0.36 0.46

0.28

-

0.31 0.42 0.51

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

0.03 0.10

0.06 0.25

-

0.04 0.10 0.26

198

adhesives f r o m r e n e w a b l e r e s o u r c e s

seen after 6 hours o f h e a t i n g at p H 11.0 are p r e d o m i n a n t l y at δ 3.80 t o 3.90 p p m , suggesting t h a t t h e c o n d e n s a t i o n t h a t does o c c u r is p r i m a r i l y due t o selfc o n d e n s a t i o n o f the h y d r o x y b e n z y l alcohols. It was suspected t h a t the c a t e c h i n i c a c i d f o r m e d b y rearrangement was not recovered after a c e t y l a t i o n . Therefore, p r o d u c t s o f these b a s e - c a t a l y z e d reac­ t i o n s were e x a m i n e d b y C - N M R i n the free p h e n o l i c f o r m ( F i g u r e 4). C o m p a r ­ i s o n o f the s p e c t r u m t o the C - N M R c h e m i c a l shifts g i v e n i n T a b l e I I i n d i c a t e t h a t the m a j o r p r o d u c t , i s o l a t e d f r o m the r e a c t i o n of c a t e c h i n w i t h e q u i m o l a r p r o p o r t i o n s o f a- a n d p - h y d r o x y b e n z y l a l c o h o l at p H 10 or 11, was the s o d i u m salt o f c a t e c h i n i c a c i d . I n t h i s r e a c t i o n p r o d u c t , there are n o signals a p p a r e n t for the C - 6 a n d C - 8 o f c a t e c h i n (95.5 t o 96.0 p p m i n the p h e n o l ) , yet the catechol r i n g resonances are p r o m i n e n t as are those for the h y d r o x y b e n z y l alcohols. If r e t a i n i n g some o f the p h l o r o g l u c i n o l r e a c t i v i t y o f the t a n n i n for subsequent re­ a c t i o n w i t h aldehydes i n c o l d - s e t t i n g adhesive a p p l i c a t i o n s (7,8) is desired, i t is i m p o r t a n t t h a t the i n i t i a l c o n d e n s a t i o n w i t h p h e n o l - f o r m a l d e h y d e prep o l y m e r s be c a r r i e d o u t u n d e r a c i d i c p H c o n d i t i o n s . 1 3

Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch014

1 3

T h e h i g h degree o f s e l e c t i v i t y i n r e a c t i o n o f ( + ) - c a t e c h i n w i t h p - h y d r o x y b e n z y l a l c o h o l is r e a d i l y seen i n the C - N M R s p e c t r a . A l l o f the p - m e t h y l o l h a d reacted after o n l y 1 h o u r at p H 3.0 a n d 100 ° C . A t t h i s same t i m e , the r a t i o o f p- t o o-methylenes f o r m e d was a b o u t 2 t o 1. I n reactions at p H 5.0, the average r a t i o o f p- t o o-methylols lost a n d methylenes f o r m e d was a b o u t 1.8 t o 1. A s was observed i n reactions w i t h p h l o r o g l u c i n o l , t h e s e l e c t i v i t y i n reactions o f the p - h y d r o x y b e n z y l a l c o h o l decreased w i t h a n increase i n r e a c t i o n p H . T h e average r a t i o o f p- t o o-methylols lost a n d methylenes g a i n e d decreased t o a b o u t 1.4 t o 1 i n reactions m a d e at p H 7.0. Because o f the preference for r e a c t i o n w i t h p - h y d r o x y b e n z y l a l c o h o l , there was no evidence for s e l e c t i v i t y i n the s u b s t i t u t i o n at C - 8 over t h a t at C - 6 . T h i s result is i n agreement w i t h earlier work t h a t showed n o significant regioselectivity i n the reactions of ( - f ) - c a t e c h i n w i t h p - h y d r o x y b e n z y l a l c o h o l (5,6) . 1 3

o- o r p - H y d r o x y b e n z y l A l c o h o l w i t h R e s o r c i n o l a n d P h l o r o g l u c i n o l . R e s o r c i n o l a n d p h l o r o g l u c i n o l were reacted w i t h either o- or p- h y d r o x y b e n z y l a l c o h o l at p H 3.0 a n d p H 11.0. C o n d e n s a t i o n proceeded m o s t r a p i d l y at p H 3.0 w i t h the p - h y d r o x y b e n z y l a l c o h o l . Less t h a n 6 5 % o f the o - h y d r o x y b e n z y l a l c o h o l was condensed after 6 h o u r s at 100 ° C a n d p H 3.0, w h i l e less t h a n 3 5 % reacted u n d e r s i m i l a r c o n d i t i o n s at p H 11.0. I n c o n t r a s t , the p-isomer was a l m o s t 9 0 % reacted after 6 h o u r s at 100 ° C a n d p H 11.0 a n d was c o m p l e t e l y c o n s u m e d before 2 h o u r s o f r e a c t i o n t i m e at p H 3.0. I n a l l o f the reactions, m o s t o f the c o n d e n s a t i o n t o o k place w i t h p h l o r o g l u c i ­ n o l , y i e l d i n g four t o s i x t i m e s m o r e o f t h a t c o n d e n s a t i o n p r o d u c t . A s o m e w h a t higher r a t i o o f p h l o r o g l u c i n o l versus resorcinol c o n d e n s a t i o n o b t a i n e d w i t h the p - h y d r o x y b e n z y l a l c o h o l c o m p a r e d t o the o-isomer seems t o i n d i c a t e t h a t steric factors d o influence t h e p r o d u c t r a t i o s , b u t n o t s i g n i f i c a n t l y . A l t h o u g h t h e over­ a l l r e a c t i o n rates o f resorcinol or p h l o r o g l u c i n o l w i t h the h y d r o x y b e n z y l alcohols

In Adhesives from Renewable Resources; Hemingway, R., el al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

14.

McGRAW E T A L .

13

199

Tannin Compounds and Methylolphenols

C-NMR

(O-Catechin *