Polymers for Fibers and Elastomers 9780841208599, 9780841210882

Table of contents :
Title Page......Page 1
Half Title Page......Page 3
Copyright......Page 4
ACS Symposium Series......Page 5
FOREWORD......Page 6
PdftkEmptyString......Page 0
PREFACE......Page 7
1 Instrumental Analyses of Modified Cottons......Page 9
Fabrics......Page 10
Titrations......Page 11
Cold Plasma Treatments......Page 12
Results and Discussion......Page 13
Summary......Page 30
References......Page 31
2 Cross-Polarization/Magic Angle Spinning 13C-NMR Study Molecular Chain Conformations of Native and Regenerated Cellulose......Page 33
Experimental......Page 34
1. Assignments of the Resonance Lines of the Crystalline and Noncrystalline Components.......Page 35
2. Relationships between 13C Chemical Shifts and the Corresponding Torsion Angles.......Page 39
3. Chain Conformation of the Crystalline and Noncrystalline Components of Cellulose.......Page 42
Literature Cited......Page 47
3 Conformational Accessibility of Some Simple Polyglucosides......Page 49
Flexiblity Within the Glucopyranose Ring......Page 50
Flexiblity at the Linkage Between Monomers......Page 52
Results from n-h Map Studies......Page 53
Discussion......Page 59
Literature Cited......Page 64
Comparison of CDIS and FTIR......Page 66
Experimental......Page 67
THPOH-NH3 Treated Cotton......Page 69
DMDHEU Treated Cotton......Page 70
Cotton-Polyester Blends......Page 75
Conclusions......Page 78
References......Page 79
5 Electron Spin Resonance Studies on Oxygen Diffusion In γ-Irradiated Polypropylene Fibers Around the Glassy Transition Temperature......Page 80
Experimental Methods......Page 81
Experimental Data......Page 82
Discussion......Page 87
Mathematical Description......Page 89
Literature Cited......Page 91
Experimental......Page 93
Model Solvate Structure......Page 94
Phase Diagram......Page 96
Discussion......Page 99
References......Page 103
Polymer Preparation......Page 105
Polymer Properties......Page 106
Fiber Preparation and Properties......Page 112
Test Procedures......Page 115
References......Page 116
8 Silicone and Fluorosilicone Elastomers Structure and Properties......Page 117
Discussion......Page 118
Effect of TMPS (B units) Content in Block Copolymers with DMS (A units)......Page 119
Siloxane Elastomer Foams - Structure and Properties......Page 125
Optically Clear Silicone Elastomers From New Silica Technology......Page 128
Summary......Page 137
References......Page 140
9 Phosphazene Elastomers Synthesis, Properties, and Applications......Page 142
The Polymerization Process......Page 143
Poly(organophosphazenes)......Page 145
Alternate Synthesis Approaches Phosphazene......Page 150
Future Trends......Page 153
Literature Cited......Page 154
10 Curing of Vinylidene Fluoride Based Fluoroelastomers......Page 157
Results and Discussion......Page 159
Conclusion......Page 176
Literature Cited......Page 179
11 Rubber Processing Through Rheology......Page 181
Rheology and mixing rubber......Page 182
Rheology and extrusion of rubber......Page 191
Rheology of heterogeneous rubbery materials......Page 198
Conclusions......Page 201
Literature......Page 203
Carbon Yield......Page 205
Orientation......Page 206
References......Page 213
13 Pitch-Solvent Interactions and Their Effects on Mesophase Formation......Page 215
Solvent Selection......Page 217
Characterization of Select Mesophase Forming Samples......Page 223
Effect of Altering Pitch to Solvent Ratio......Page 225
Conclusion......Page 228
Literature Cited......Page 230
14 Molecular Weight Determination and Distribution in Pitches......Page 231
Experimental......Page 232
Results and Discussions......Page 233
References......Page 239
15 Solvent-Extracted Pitch Precursors for Carbon Fiber......Page 240
General Characteristics of Pitches......Page 241
Characteristics of Solvent Extracted Petroleum Pitch......Page 244
Carbon Fiber Characteristics......Page 249
Summary and Conclusions......Page 252
Literature Cited......Page 257
16 Effects of Sulfur and Metals on Mesophase Formation in Coal Liquid Asphaltene and Petroleum Pitch......Page 258
Experimental......Page 259
1. Effect of Elemental Sulfur......Page 261
2. Effect of Dibenzothiophene (DBT)......Page 263
4. Effect of Organometallics with 6% by Wt. Organic Sulfur......Page 265
Conclusions......Page 268
Literature Cited......Page 272
17 Reaction of Formaldehyde Vapor with Water-Wetted Wool......Page 273
Experimental......Page 275
Results and Discussion......Page 278
Literature Cited......Page 285
18 Accelerated UV and Radiation-Induced Grafting of Monomers to Cellulose in the Presence of Additives Applications of These Copolymers in Art Restoration and Preservation......Page 286
Results and Discussion......Page 287
Literature Cited......Page 298
19 The Mechanism of Surface Cavitation in Polyethylene Terephthalate Fibers......Page 300
Experimental Investigations......Page 301
The Mechanism of Cavitation......Page 303
Surface Conditions during Fiber Modification......Page 311
Literature Cited......Page 314
20 Fluorenone Polymers and Fibers......Page 316
Characterization of Polyesters......Page 317
Monomer Synthesis......Page 318
Results and Discussion......Page 319
References......Page 329
21 Polyester Processability in Texturing as a Function of Spun Yarn Morphology......Page 330
Discussion......Page 332
Literature Cited......Page 335
22 Effects of Annealing Below Tg on the Properties of Poly(vinyl chloride)......Page 336
Experiments and Results......Page 337
Discussion......Page 341
Literature Cited......Page 343
23 Modeling the Melt Spinning Process......Page 344
Literature Cited......Page 358
24 Design of Tire Cords Optimization of Viscoelastic Properties......Page 359
Consequences of Mechanical Loss......Page 362
Minimization of Mechanical Loss from the Cord in Running Tires......Page 370
Effect of Excessively Low Mechanical Loss of Cords on Tire Vibration......Page 374
Literature Cited......Page 376
Measurement of Tire Temperature at Strategic Positions in the Tire while Tire is Running on a Test Wheel......Page 377
Iterative Solution of the Heat Transfer Equation by Finite Difference Approximations......Page 378
Relationship between the Mechanical Loss and Standing Wave Formation......Page 380
Critical Speed of Standing Wave Formation......Page 381
Relation Between the Damping Coefficient kr and Mechanical Loss of Tire......Page 383
25 Deformation Profiles Effect on the Properties of High Density Polyethylene Drawn by Solid-State Extrusion......Page 384
DSC Melting Behavior......Page 388
Elastic Shrinkage......Page 390
X-Ray Analysis......Page 392
Morphological Change During Extrusion......Page 393
Literature Cited......Page 400
26 Tailoring Polymer Molecules for Specific Fiber and Ribbon Properties......Page 402
Background......Page 403
Discussion......Page 404
Literature Cited......Page 407
Author Index......Page 408
A......Page 409
C......Page 410
E......Page 411
F......Page 412
L......Page 413
P......Page 414
R......Page 416
S......Page 417
V......Page 418
Y......Page 419

Citation preview

Polymers for Fibers and Elastomers

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

ACS

SYMPOSIUM

SERIES

Polymers for Fibers and Elastomers Jett C. Arthur, Jr.,

EDITOR

Technical Consultant ASSOCIAT

R. J . Diefendorf, T. F. Yen, H . L. Needles, J . R. Schaefgen, M . Jaffe, A. L. Logothetis

Based on a symposium sponsored by the Macromolecular Secretariat at the 186th Meeting of the American Chemical Society, Washington, D.C., August 28-September 2, 1983

American Chemical Society, Washington, D.C. 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

260

Library of Congress Cataloging in Publication Data Polymers for fibers and elastomers. (ACS symposium series, ISSN 0097-6156; 260) "Symposium on Polymers for Fibers and Elastomers"— Pref. Includes bibliographies and indexes. 1. Textilefibers.Synthetic—Congresses. 2. Elastomers—Congresses. 3. Polymers and polymerization—Congresses. I. Arthur, Jett C. II. America Macromolecular Secretariat. III. American Chemical Society. Meeting (186th: 1983: Washington, D.C.) IV. Symposium on Polymers for Fibers and Elastomers ( 1983: Washington, D.C.) V. Series. TS1548.5.P635 1984 677'.4 84-14635 ISBN 0-8412-0859-X

Copyright © 1984 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of thefirstpage 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., 21 Congress Street, Salem, MA 01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of thefirstpage of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

ACS Symposium Series M. Joan Comstock, Series Editor Advisory

Board

Robert Baker U.S. Geological Survey Martin L. Gorbaty Exxon Research and Engineering Co.

Theodore Provder Glidden Coatings and Resins

Herbert D. Kaesz University of California—Los Angeles

James C. Randall Phillips Petroleum Company

Rudolph J. Marcus Office of Naval Research

Charles N. Satterfield Massachusetts Institute of Technology

Marvin Margoshes Technicon Instruments Corporation

Dennis Schuetzle Ford Motor Company Research Laboratory

Donald E. Moreland USDA, Agricultural Research Service W. H. Norton J. T. Baker Chemical Company Robert Ory USDA, Southern Regional Research Center

Davis L. Temple, Jr. Mead Johnson Charles S. Tuesday General Motors Research Laboratory C. Grant Willson IBM Research Department

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

FOREWORD The ACS SYMPOSIUM was founded in to provide a medium for publishin 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 sub­ mitted by the authors in camera-ready form. Papers are re­ viewed 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 since symposia may embrace both types of presentation.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

PREFACE THIS IMPORTANT VOLUME is concerned with giant molecules, polymers, that have been indispensable and abundant since the beginning of human existence. Naturally occurring polymers, such as cellulose, starch, and pro­ teins, sustained human beings and other living things for many centuries. Now we depend upon both The timing of this volume is appropriate. Last year was the 50th anniversary of Gibson and Fawcett's polymerization of ethylene, an acciden­ tal discovery that led eventually to the commercial manufacture of polyethy­ lene by England's Imperial Chemical Industries. Parenthetically, Carl S. ("Speed") Marvel made linear polyethylene with a metal catalyst 54 years ago. However, the opportunity presented by his discovery was not exploited by industry. Several decades ago our knowledge of polymer science was so limited that we could not manufacture even one synthetic polymer fiber. The situation is entirely different today. Tremendous progress has been made in polymer and textile science; we now can make polymers and fibers from almost any raw material, including petroleum, natural gas, corncobs, sand, and pitch. Today, approximately one dozen synthetic fibers are commercially important. A recent addition to the commercial fibers is poly(benzimidazole), a high-temperature and chemical-resistant fiber intended for use in protective apparel. In addition, an incredibly simple method for making carbonfibers,recently discovered, consists in passing natural gas through a hot stainless steel tube. The need to develop syntheticfiberswas recorded as early as the 17th century (Hooke's "Micrographia," 1665): "There might be a way found out to make an artificial glutinous composition much resembling, if not fully as good, nay better, than that excrement or whatever other substance it be out of which the silk-worm wire-draws his clew." This theme was resurrected in 1734 by the French naturalist, de Reaumur, but another 150 years passed before Swann in England and de Chardonet in France produced the first synthetic fibers in which nitrocellulose served as the "artificial glutinous composition" resembling natural silk. Total production of synthetic polymer fibers is high. In 1978, 3.53 billion kg and 11 billion kg of noncellulosic organicfiberswere produced in ix In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

the United States and world, respectively. It has been predicted that produc­ tion of the truly syntheticfiberswill double to about 24.5 billion kg during the next decade. A similar story can be told for synthetic rubbers. Several decades ago we could not even make them. Now, several types of synthetic elastomers, each having special properties and uses, are manufactured in large quantities from various raw materials. The picture is even more exciting when we contemplate the entire synthetic polymer scene. Although polymer science as a distinct field is barely 60 years old, synthetic polymers are ubiquitous in modern life. A recent study sponsored by the National Research Council estimates that at least one-third of all industrial chemists deal with polymers of one kind or another, and that polymer processing accounts for nearly $100 billion of American manufacturing. If the naturalfiberproponents were complacent before the advent of the man-madefibers,they quickly lost their complacency when faced with the new competition. Research on the naturalfiberswas expanded, with special emphasis on efforts to minimize market losses to the man-madefibers.The naturalfiberscientists also enjoyed substantial success in their research. As one result, modified natural fibers were given new properties, for example, wrinkle resistance, flame resistance, enhanced susceptibility to dyeing, and increased resistance to deterioration caused by heat and microorganisms. The natural fibers, particularly those based on cellulose, do have some advantages. For example, cellulose is abundant, annually renewable, inexpen­ sive, and gets its carbon from the air instead of petroleum. In addition, cellulose is amenable to many types of chemical and mechanical treatments. Moreover, cellulose is the most abundant organic material on earth, with some 5 x 1014 kg being formed each year by plants. The Macromolecular Secretariat Symposium upon which this book is based had as its objective interdisciplinary discussions of the topic from the points of view offivedivisions of the American Chemical Society: Cellulose, Paper, and Textile; Colloid and Surface; Polymer; Polymeric Materials Science and Engineering; and Rubber Divisions. The international interest in this topic is evident from the fact that contributions were received from 10 countries. This volume will facilitate further progress in polymers as it will disseminate valuable information on a wide variety of topics. The informa­ tion that this volume provides gives support to the optimistic view of the future of polymer science and technology. CHARLES H. FISHER

Roanoke College Salem, VA 24153

x In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1 Instrumental Analyses of Modified Cottons RUTH R. BENERITO, TRUMAN L. WARD, and OSCAR HINOJOSA Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, LA 70179 Chemically modified celluloses have been ana­ lyzed by conventional wet methods and by various instrumental methods designed to differentiate bulk and surface properties. Electron emission spectroscopy fo alone and in combination with radiofrequency cold plasmas yielded elemental analyses, oxidative states of the element, and distribution of the ele­ ment. Techniques of electron paramagnetic resonance (EPR), chemiluminescence, reflectance infrared spectroscopy, electron microscopy, and energy dispersive X-ray analyses were also used to detect species on surfaces and to obtain depth pro­ files of a given reagent in chemically modified cottons.

Tetraalkylammonium s a l t s , f i r s t synthesized by Hofmann in 1851 by the reaction of a t e r t i a r y amine with an alkyl halide, are soluble in various polar solvents. These salts form c r y s t a l l i n e hydrates that contain large numbers of water of hydration molecules. The unusual physical properties of tetraalkylammonium salts and t h e i r effects on the structure of bulk water have been reported.2,3,4,5 currently, several theories exist as to the effects of the tetraalkylammonium cations on the structure or entropy of bulk water. Yet to be understood are the effects of the anions associated with the tetraalkylammonium ions on the overa l l structure of water. Not only is the theory of interactions of such salts with water of interest to those engaged in basic chemistry, but the salts also are used in various applications. The a b i l i t y of quaternary ammonium cations to attract a variety of dyes and both hydrophilic and hydrophobic microorganisms and part i c l e s of soil has been used to advantage by t e x t i l e chemists. Of interest to the cellulose chemist are surface-active quaternary ammonium salts that have at least one long chain alkyl group and 1

T h i s chapter not subject t o U . S . copyright. P u b l i s h e d 1984, A m e r i c a n C h e m i c a l Society

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4

POLYMERS FOR FIBERS A N D

ELASTOMERS

the chemistry of anion exchange resins that contain quaternary ammonium groups. Boyd and co-workers^ have reported on such anion exchange resins, and we have reported the preparations of various quaternary ammonium cellulose anion exchangers. Our interest has been in the preparation of quaternary cellulose anion exchangers from cotton. Details of preparations of t e r t i a r y amine and quaternary ammonium anion exchange celluloses in aqueous > and in non-aqueous > media have been described. Use of non-aqueous solvents such as methanol for the preparation of the sodium c e l l u l o s a t e s , t e r t i a r y butanol for the preparation of the t e r t i a r y amine, diethylaminoethylcellulose and absolute ethanol for the preparation of quaternary ammonium compounds from the t e r t i a r y amine celluloses has made i t possible to form cellulose anion exchangers in fabric form that contain up to 4.0% nitrogen. Usually, the maximum amount of nitrogen obtained with aqueous preparations i s approximately 0.7%. Recently, we have ammonium celluloses mad variety of instrumental techniques. These techniques have also been used to follow effects of a given anion on the cellulose matrix of a quaternary ammonium cellulose exchanger when the exchanger prepared non-aqueously comes in contact with water. This report i l l u s t r a t e s the importance of using several instrumental methods for the characterization of chemically modified cottons with the majority of specific examples being the anion exchange celluloses prepared non-aqueously. 6

8

7

9

Experimental Reagents Alkyl halides, diahaloalkanes, and t e r t i a r y butanol were reagent-grade chemicals from Eastman Organic Chemicals^ the absolute methanol was from Mallinckrodt Chemical Works , and 3-chloroethyldiethyl amine hydrochloride and dimethylformamide were reagent grade chemicals from Matheson, Coleman, and B e l l . Argon and nitrogen were commercial-grade cylinder gases, purchased from Union Carbide Corporation. Fabrics The nonaqueous preparations of sodium cellulosates in the fabric form (4.4 oz/yd^ cotton sheeting) and t h e i r subsequent reactions at room temperature with 3-chloroethyldiethylamine in t>butanol to form the free amine forms of diethyl aminoethvl (DEAE)cottons of varying nitrogen contents have been r e p o r t e d . w > To prepare a DEAE-cotton of approximately 0.6% N, cotton was reacted with 0.2M sodium methoxide, and the resultant sodium cellulosate was reacted for 5 hr with a 3% by weight solution of 3-chloroethyldiethylamine in t-butanol. The fabric of 3.0% N required a 1.25M 11

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

BENERITO ET AL.

Instrumental Analyses of Modified

Cottons

sodium methoxide solution to prepare the sodium cellulosate and reaction for 24 hr with a solution of 3-chloroethyldiethylamine. Preparation of Monoquaternary and Diquaternary Ammonium Celluloses The DEAE-cottons containing from about 0.6% to 3.0% nitrogen in free amine form were washed free of t-butanol with absolute methanol and then refluxed for about 5 hr in an ethanolic solution of about 10-20% of the alkyl halide or dihaloalkane. Treated fabrics were then washed in ethanol and dried. Storage was in t-butanol. Exchange of Anions Replacement of the halide ion furnished by the original alkyl halide or dihaloalkane used in preparation of the quaternaryammonium exchangers wa some instances the origina exchanged for another halide (chloride) before introduction or exchange with an oxidizing anion (such as super oxide anion). In general, exchange of anions was in absolute alcohol or dried dimethylformamide (DMF). Chemical Analyses Nitrogen contents of a l l modified cottons were determined by the Kjeldahl method and reported as milliequivalents per gram of fabric (meq N/g f a b r i c ) . A l l anion exchange fabrics were analyzed by conventional a n a l y t i c a l procedures for halogen and halide ion and reported as meq X or X per gram of fabric before and after_theijr exchanges with other anions. After each exchange with BrU,SCN, or C^Oy, the fabric was analyzed by conventional wet analyses for the elements B, S, or Cr respectively. Percent of conversionjwith superoxide anions (0o) was calculated from the amount of X ions ions removed during the exchange process. Titrations T i t r i m e t r i c methods reported p r e v i o u s l y ^ r e also used to determine capacities of the anion exchangers. For potentiometric and conductometric t i t r a t i o n s , the anion exchange fabric in salt form was cut in a Wiley mill to pass a 20-mesh screen and then regenerated to the base form in excess 0.05M NaOH. An accurately weighed sample sufficient to furnish approximately one meq of replaceable hydroxide anions was added to s p e c i a l l y designed t i t r a t i o n flasks. In potentiometric t i t r a t i o n s , the flasks contained 50.00 ml of 1 M NaCl solution prepared in conductivity water and kept in a nitrogen atmosphere, and the t i t r a t i o n was a standardized dilute HC1 solution. A l l pH measurements were made to 0.01 pH with a Beckman research pH meter. w e

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

5

6

POLYMERS FOR FIBERS A N D

ELASTOMERS

In conductometric t i t r a t i o n s , the flasks contained 250 ml of conductivity water to which a known amount (approximately 1.5 meq) of HC1 was added. The t i t r a n t was a standardized NaOH solution of approximately 1 M. Measurements were made on a Jones Conductivity bridge under a nitrogen atmosphere. Electron Spectroscopy for Chemical Analyses (ESCA) ESCA spectra were obtained on a Varian spectrometer Model VIEE-15 with a Mg^X-ray source. Spectra were obtained on fabrics and on those fabrics ground in a Wiley mill to pass a 20-mesh screen. A l l binding energies for the nitrogen l , halogens 2p, and metal 2p electrons are reported with reference to carbon l electrons of binding energy of 285.6 eV. A l l spectra were analyzed for r e l a t i v e amounts of nitrogen of low ( t e r t i a r y amine) and of high (quaternized ammonium) binding energies (BE). s

s

Electron Paramagnetic Resonanc Selected samples of anion exchange fabrics containing Op anions or metallic ions capable of forming paramagnetic complexes with t e r t i a r y amine groups were subjected to EPR analyses. Samples were ground to pass a 40 mesh screen, packed in quartz EPR tubes, dried in vacuum oven P2°5> sealed in a nitrogen atmosphere and then analyzed. Spectra were obtained on a Varian 4502-15 EPR spectrometer system. In a few instances spectra were obtained before and after irradiations with UV l i g h t . Chemiluminescence Chemiluminescence (CL) was monitored with a Packard 3255 l i q u i d s c i n t i l l a t i o n spectrometer equipped with low dark-noise photomultiplier tubes (RCA 4501/4V) and a Packard model 585 linear recorder. Experimental details have been described p r e v i o u s l y in a s t a t i s t i c a l report that shows CL values must d i f f e r by 2500 counts per minute to be s i g n i f i c a n t l y different. 13

Infrared Spectra Multiple internal reflectance spectra of fabrics were obtained with a Wilks spectrophotometer Model 8C as described previously. 14

Cold Plasma Treatments The glass reactor with curved external electrodes and with inlets for introduction of gas either downstream from the e l e c trodes or between electrodes has been d e s c r i b e d . The system u t i l i z e s a radio frequency (rf) generator capable of producing up to 100 W of power at a frequency of 13.56 MHz. It can be operated 15

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

BENERITO E T AL.

Instrumental Analyses of Modified Cottons

in either a continuous or pulse mode. An impedance matching network, a vacuum pump with a capacity of 150 1/min and appropriate meters and gauges for measuring power output, gas flows, and pressures complete the system. In t h i s investigation, samples were located downstream from the electrodes, but within the glow regions, on glass holders that allowed for suspension of f a b r i c s . In some instances, the plasma generator was attached d i r e c t l y to the ESCA spectrometer c a v i t y . In other instances, samples that were subjected to plasma i r r a d i a t i o n s were immediately removed and stored inert atmosphere before being tested by other techniques. Microscopical Examinations Fibers of the control and selected chemically modified cottons were examined by techniques of optical microscopy described previously. * were subjected to laye methacrylate and to s o l u b i l i t y tests in 0.5 M cupriethylenediamine (cuene) and were examined by the techniques of transmission electron microscopy as previously r e p o r t e d . Scanning electron micrographs of fibers of selected samples before and after subjection to various solvents were also o b t a i n e d . Cross-sections of a few fibers were examined via energy dispersive x-ray analysis (EDAX) t e c h n i q u e s to determine d i s t r i b u t i o n of reagent in the chemically modified cottons. 1

17

18

18

Results and Discussion Surface analyses of unreacted and chemically modified cottons can be used to advantage in t e x t i l e problem solving, provided there is an understanding of the principles and l i m i t s of surface analytical techniques. Surface analyses in combination with other techniques can be used to characterize surfaces, detect changes in composition with depth from surfaces, and even to determine differences in surface and bulk compositions of t e x t i l e samples. Diethyl aminoethylcellulose (DEAE) has been made aqueously and nonaqueously. In an aqueous preparation, even with mercerized f a b r i c , the maximum amount of N is about .8% 10.57 meq/g) and the product is C e l l - O ^ ^ - N ^ r ^ ^ H X, where X i s the anion used in the neutralizing wash water. In the non-aqueous preparation of DEAE c e l l u l o s e , (equations 1 and 2 of Figure 1) the product is a base, C e l l - O ^ ^ - N ( C p H ) . In nonaqueous preparations, various amounts of N (up to 4%) can be added to cotton. The nonaqueously prepared DEAE cottons were reacted with alkyl halides or dihaloalkanes to form mono- and di-quaternary ammonium cellulose anion exchangers according to equations 3 and 4 in Figure 1, where I represents mono- and II the di-quaternary compounds. The DEAE celluloses were also reacted with BI3 and with salts of t r a n s i t i o n 5

2

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1

8

POLYMERS FOR FIBERS A N D

Cell OH + NaOCH

3

CH^OH U ±

- + C e l l - 0 Na

(1)

\

C2

+ Cell-tf Na + ( C H ) 2

5

N c H Cl

2

2

ELASTOMERS

S

Cell-0-C H -N : | C H

4

2

;t-btitanol

(2)

4

2

5

DEAE C H I + Cell-OCoH. N-R X ! 2

CHoOH

DEAE + RX

J

y *

5

C H 2

(3)

5

(I) C H 2

DEAE + X H C - ( C H ) - C H X _ C e n - 0 C H ~* 2

2

n

2

4

2

C H

5

2

5

- N - (CH ) - N - C H 0 - C e l l | n+2 | C H C H (4)

4

2

2

5

2

2

4

5

(ID

C H 2

DEAE + B I

5

_^Cell-0C H j : C H

3

2

^ BI

4

2

(5)

3

5

?2 5 H

DEAE + M e

+2

D M F

>

Cell-0-C

2

H

4

- N : C H 2

^ Me

+2

(6)

5

Figure 1. Equations for non-aqueous preparations of sodium cellulosate (1), diethyl aminoethylcellulose (DEAE) (2), monoquaternary ammonium celluloses (3), where R varies from CH3 to 1 0 2 2 ' diquaternary ammonium celluloses (4), where n varies from 2 to 10, complex formation between DEAE and Lewis base, BI~ (5), and coordination of t e r t i a r y amines of DEAE with a t r a n s i t i o n metal ion (6). C

H

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

I.

BENERITO E TAL.

Instrumental Analyses of Modified Cottons

metal ions that were capable of acting as Lewis acids in reactions with the t e r t i a r y amine groups of DEAE cellulose as indicated in equation 5 and 6 of Figure 1. In Figure 2 are shown the ESCA spectra for a DEAE cotton before and after i t s conversion to the mono-quaternary salt with CH3I that gave a 90% conversion. The N-^ electron binding energy of 402 eV i s characteristic of the more positive quaternary nitrogen and the BE value of 399 eV i s characteristic of the more electronegative t e r t i a r y amine i n DEAE cotton. Reaction of DEAE with longer chain alkyl halides resulted in less conversion to the quaternary. However, a 50% conversion to the mono-quaternary could be realized with C^s 3 7 conversion was obtained with a l l alkyl chlorides and with some dihaloalkanes as shown i n F i g . 3. H

I #

P

o

o

r

The presence of both t e r t i a r y and quaternary groups can be detected in t i t r a t i o n curves as well. In F i g . 4 i s a t i t r a t i o n curve of a cellulose anio The r e l a t i v e amounts o agreement with those amounts indicated by ESCA. The t i t r a t i o n curve for a mono-quaternary ammonium cellulose exchanger that has been t o t a l l y converted with CH3I i s shown in F i g . 5. Confirmation of the type of t i t r a t i o n curve typical of a quaternary ammonium cellulose exchanger was obtained by reacting cotton with trimethylglycidylammonium chloride and then t i t r a t i n g the product: [Cel1-0-CH CH0HCH N(CH ) Cl] 2

2

3

3

+

Its t i t r a t i o n curve i s shown in Figure 6. There was good agreement between the relative amounts of t e r t i a r y and quaternary groups in the cellulose anion exchangers as determined by ESCA and by potentiometric t i t r a t i o n s (Table I). A typical conductometric t i t r a t i o n curve for a DEAE cellulose anion exchanger of 2.58% N i s shown in ( F i g . 7). Distribution of some substituents i n chemically modified cottons can be obtained through depth p r o f i l e s . For example, conventionally applied fluorochemical finishes are concentrated on the surfaces. As a r e s u l t , the intensity of the F i electron peak decreases as the fabric i s etched with an argon colS plasma within the spectrometer cavity. In our analyses of anion exchange c e l l u l o s e s , we were not able to use the r f cold plasma etching method because nitrogen, that we wanted to measure, i s chemically bound to cotton as i t i s subjected to cold plasmas of argon as

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

9

10

POLYMERS FOR

FIBERS A N D

ELASTOMERS

B

i 409

i 402.3

i *

i

BINDING ENERGY

399

Figure 2. ESCA spectra of Nj electrons from a DEAE cotton of 1.7% N before (A) and after (B) i t s Conversion (90%) to a monoquaternary ammonium c e l l u l o s e with C r U I .

Figure 3. ESCA spectra of electrons from a DEAE cotton of 1.7% N before (A) and after (B) i t s p a r t i a l conversion to a diquaternary ammonium c e l l u l o s e with I C r ^ C r ^ ^ C r ^ I .

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

Instrumental Analyses of Modified

BENERITO ET AL.

Meq.

HCI/g

Cottons

Exchanger

Figure 4. Potentiometric t i t r a t i o n curve of a product containing both t e r t i a r y amine and quaternary ammonium groups formed by incomplete conversion of a DEAE c e l l u l o s e of 1.57% N (1.12 meq/g) by i t s reaction with C H B r . (ESCA showed 33% conversion.) 2

5

O 0.2

1.0 MEQ.

2.0

3.0

3.4

TITRANT

Figure 5. Potentiometric t i t r a t i o n curves of a quaternary ammonium c e l l u l o s e formed by complete conversion of a c e l l u l o s e of 2.58% N with CH I. Curve ABC i s for a 0.8043 g sample in base form (1.48 meq) vs 0.1 N HC1. Curve DYEF represents t i t r a t i o n of the chloride form i n excess HC1 (1.72 meq) vs 0.1 N NaOH. In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 3

11

12

POLYMERS FOR FIBERS A N D

(X3 MEQ. Figure

6.

OF

0.5 TITRANT

0.7

ELASTOMERS

0.9

Potentiometric t i t r a t i o n curve of a 1.6400 g sample of the quaternary ammonium c e l l u l o s e , Cell-O-Cl^CHOHCl^N(CH ) 3

2

CT, (0.5001 meq N).

Curve ABC is for

basic

form i n 50 ml of 1 M NaCl vs 0.1 M HC1, Curve DYEF i s for the chloride form in presence of excess HC1 meq) vs 0.1 M NaOH.

(.15

AB and YE represent t i t r a t i o n s of

exchangers.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 0.6

1.6

399

402

4

DEAE + BrC H Br

2

0.3

3.4

399

402

3

0.9

0.9

0.6

End Pt 2

meq/g End Pt 1

DEAE + CH I

N :

0.8

3

0.9

^ / R

NR4

399

, eV

402

s

DEAE

4

x

T i t r i m e t r i c Analyses

NR

N

ESCA Analyses

Relative Amounts of Quaternary and T e r t i a r y Amines

Exchanger

Table I.

1.5

3.0

0.9

14

POLYMERS FOR FIBERS A N D

1.0

2.0

3.0

ELASTOMERS

4.0

Meq. NaOH

Figure

7.

Conductometric t i t r a t i o n curve of a 0.5001 g sample of DEAE cellulose of 2.58% N (0.92 meq) in base form in presence of 1.802 meq HC1 vs. standardized 1.0 M NaOH. XY is neutralization of excess HC1; YZ represents exchange of CT ions of exchanger for Off ions.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

BENERITO ET AL.

Instrumental Analyses of Modified

Cottons

15

well as of nitrogen. Thus f a r , we have been unable to completely eliminate the source of nitrogen in argon plasma. In Figure 8 are ESCA spectra of a purified cellulose before (bottom curves) and after (middle curves) i t s i r r a d i a t i o n for only 20 minutes in an argon plasma within the ESCA spectrometer. Included in t h i s figure are the difference spectra (irradiated unirradiated) for the C^ , 0i and N^ electrons. In addition to showing the increase in 6ound N a f t e r i r r a d i a t i o n , these spectra indicate formation of C having 1 electrons of higher BE and of 0 having l electrons of lower BE than respective control values. Formation of carbon free radicals and carbonyl groups during plasma irradiations account for these new spectra. These d i f f e r ences have been observed in a l l polysaccharides treated in r f cold plasmas and have been discussed in an e a r l i e r r e p o r t . Another method to detect differences in surface and bulk analyses i s to compare ESCA spectra of modified cottons before and after they have been groun spectra of a plasma irradiate to cotton during i t s i r r a d i a t i o n is concentrated at the surface. In Figure 9 are ESCA spectra of the C^ , 0^ and N^ electrons of a cotton fabric that had been irradiated for 90 min in an argon plasma and then analyzed via ESCA in fabric and pulverized forms. These difference spectra show that the N was predominantly on the surface, as were the carbons having highest BE (free radicals) and the oxygens of lowest BE (carbonyl oxygens). Therefore, to see i f N was uniformly distributed in non-aqueously prepared cellulose anion exchangers, we obtained differences in Nj peaks for samples before and after they were ground in a Wiley M i ^ l . Not expected was the fact that the nitrogen was uniformily d i s t r i b u t e d . Uniformity of d i s t r i b u t i o n was also indicated by SEM and EDAX data. A mono-quaternary ammonium cellulose anion exchanger (3.46% N, 31.3% I) was exchanged in non-aqueous media with NaSCN. Wet analyses (4.86% N, 0% I, and 5.70% S) indicated i t was 100% converted to the thiocyanate form. U l t r a - t h i n cross sections of the fibers in the thiocyanate form examined by EDAX revealed that sulfur was uniformly distributed throughout the f i b e r s . The cross-section of the fiber shown in (Fig. 10) (upper) and EDAX scan (lower) are i l l u s t r a t i v e of the uniform d i s t r i b u t i o n of sulfur in a diquaternary ammonium cellulose thiocyanate. _This is typical of a quaternary or diquaternary product in the SCN form. The physical properties of the quaternary ammonium cellulose exchanger varied with the associated anions. A l l fabrics maintained original fabric structure regardless of anion when in non-aqueous media. Usually, anions were exchanged in DMF. Of particular interest was the fact that exchange of chloride for large SCN or BH4 anions resulted in fabrics that were e a s i l y d i s dispersed or almost soluble in water. The effects of the anion on s

s

$

s

1 5

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMERS FOR FIBERS A N D

16

ELASTOMERS

284 532 399 I I I I I 1 • i i i I i » i i I i I I I I I I I I—I—I—I—I—I—I -*

BINDING ENERGY

Figure 8. ESCA spectra o f a p u r i f i e d c e l l u l o s e before (bottom curves) and after i r r a d i a t i o n in argon plasma for 20 min (middle curves) and difference spectra (irradiated-unirradiated) for C-^ , 0^ , and N j electrons.

Figure 9. Difference spectra for C j , 0} , and Ni electrons from cotton. Fabric i r r a d i a t e d for 90 miftin Srgon plasma and then analyzed via ESCA as fabric and pulverized samples. Difference = (fabric - pulverized).

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

BENERITO E T AL.

Instrumental Analyses of Modified

Cottons

17

Figure 10. Scanning electron micrograph of a cross-section (top) of a diquaternary ammonium cellulose prepared by reaction of a DEAE c e l l u l o s e (2.57% N) with diiodopentane and exchanged to thiocyanate form (100% conversion) and EDAX (bottom) showing d i s t r i b u t i o n of S throughout f i b e r .

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

18

POLYMERS FOR FIBERS A N D

ELASTOMERS

the swelling of fibers in water have been followed with the techniques of l i g h t and electron microscopy and w i l l be the subject of another report. For a mono-quaternary anion exchanger of a given N content, those most swollen or_ most easily dispersed in water were those having Oo, BH4 or SCN as anions. The light micrographs of whole fibers of a mono-quaternary of 3.20% N in the I, BH4 and SCN forms before and after being contacted with water are shown in (Fig. 11). These micrographs i l l u s t r a t e the swelling in water of fibers from a l l three exchanges and the partial dissolution in water of the SCN and BH4 forms of the exchangers. Formation of diquaternary ammonium cellulose anion exchangers prevented the dispersion in water of the fibers even when they were in the BH4 or SCN form. Micrographs of whole fibers of diquaternary exchangers of 3.46% N before and after contact with water are shown in Figures 12, 13, and 14 for the I", and SCN forms, respectively. Als of fibers after immersion in 0.5M cuene, a solvent that dissolves cotton, DEAE cottons and mono-quaternary ammonium c e l l u l o s e s . I n s o l u b i l i t y in cuene indicates crosslinking of cellulose chains by the dihaloalkanes. Scanning electron micrographs of cross-sections of the monoand diquaternary exchangers in the BH4 or SCTT form also show that crosslinking decreased the amount of swelling and dispersion or dissolution of fibers when BH4 or SCN i s the associated anion. Use of nonaqueously prepared DEAE celluloses as Lewis bases offers potential for formation of metal ion complexes between t r a n s i t i o n metal ions such as C u and N i , formation of chargetransfer complexes with electron acceptor compounds such as orthoand para-chloranils or bromanils and with other Lewis acid compounds such as BI3. Electron spin resonance spectra of those products that were paramagnetic were used in conjunction with ESCA spectra of the products to gain information on types of bondings. With copper and nickel complexes, the products were paramagnetic and the BE of the Ni electrons shifted to higher BE values as the BE of the CU2 and N i electrons shifted to lower binding energies. Both the Ni a n d C u complexes with DEAE were paramagnetic. Complexing of DEAE with BI3 resulted in an increase of BE of the Ni electrons of DEAE from 399 eV to approximately 402 eV. With charge transfer complexes, formed with ortho- or para-chloranils, the BE of Hi electrons shifted to 401.4 eV (Fig. 15) and the Cl electrons had BE values of 197 for the CI ion and 200.4 for the organic chlorine. These complexes were paramagnetic, as i l l u s t r a t e d by the EPR spectrum for the DEAE-o-chloranil complex shown in Figure 16. The singlet of g-value of 2.0059, indicates + 2

+ 2

2

p

+ 2

p

+2

2 p

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

BENER1TOETAL.

Instrumental Analyses of Modified Cot tons

19

s-

CU

Q. CL

L±J

>>
f0 3 cr i O C

3

CU

Sif-

^ +-> >>.c r- cn tO T 3 S-

o o

E 0) O 3 +-> E oS- C **M- O CD C i— O (O -P

CO

s- -o CD CD CO •

-QS.ES. ro S- 0) M- CL O CU «t- ro •I-

**- S-.

o ojz

5

o c co ^ - o o T -

c o s- rd T D>C\J to o • * sU CO, ^j-cu u^Hi E

CL

(O^

T>

C

E CO

co E *r-

r o

s-

•i-

(D. * +-> co |»—•

»

0)i— cu cu •r 3 £ 5 —I i— 4-> O r— r— CU r-t SH

E 3

H QJ CO+J

CD *r- • ! M— u c o ro 3 O cn E "D -O •r- E c c LL. ro rd ro

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

20 POLYMERS F O R FIBERS A N D E L A S T O M E R S

S i n n n i l V(3.46% i il5 cellulose £fu ,

respeT

l

b

e

r

I " " 1

1

s

6

? prepared « 5 non-aqueously ° l"aternary ammonium from DEAE and diiodoi n mineral o i l , water, and 0.5 M cupri*™ ° " ' ' micrographs, t

l

1

r 0 9 r a p

s

f f i b e r s

f r o m

di£

M N)

i

m

m

e

r

S h

s

e

d

W

i n

t 0 P

m 1 d d l e

a n d

b o t t o m

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

I.

BENERITO ET AL.

Instrumental Analyses of Modified

Cottons

21

Figure 13. Light micrographs of the diquaternary iodide of Figure 12 after i t s conversion to the borohydride (BH^) form and immersion in mineral o i l (top), water (middle), or 0.5 M cupriethylenediamine (bottom).

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

22

POLYMERS FOR FIBERS A N D

ELASTOMERS

Figure 14. Light micrographs of the diquaternary of Figure 12 after i t s conversion to the SCN form and immersed in mineral o i l (top), water (middle) or 0.5 M cupriethylenediamine (bottom).

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

Figure 16. EPR spectrum obtained at room temperature of a DEAEcotton of 2.58% N after i t s reaction with 2 , 3 , 5 , 6 - t e t r a c h l o r o - p benzoquinone (o-chloranil) i n chloroform, (g-values = 2.0059.)

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

24

POLYMERS FOR FIBERS A N D E L A S T O M E R S

that the complex does not contain a radical cation, as a single electron on nitrogen would generate a t r i p l e t signal. Another technique which can be used in conjunction with EPR spectral changes is chemiluminescence (CL). We have found that certain types of free r a d i c a l s , p a r t i c u l a r l y those formed when cottons or chemically modified cottons are subjected to UV radiations or to r f cold plasmas, react readily with oxygen to produce CL. There i s an inverse linear correlation between CL and EPR i n t e n s i t i e s . The i n t e n s i t i e s of EPR signals decrease as CL increases. Frequently, as EPR signals decrease or as CL increases, the i n t e n s i t i e s of C=0 bonds as determined by multiple internal reflectance IR increase. The e l e c t r o - k i n e t i c properties of DEAE and quaternary ammonium celluloses are also being investigated via techniques of streaming electrode potentials. However, some d i f f i c u l t i e s are encountered, p a r t i c u l a r l y in those products of r e l a t i v e l y high D.S. that form gels whe The drastic change of the anion exchange celluloses with exchange of the associated anion are not yet f u l l y understood. The attraction of the quaternary ammonium cellulose exchanger for neutral * cationic and anionic substances is of great interest to t e x t i l e chemists. Quaternary groups have been used to attract fluorescent w h i t e n e r s , to scavenge anions of heavy m e t a l s , and most recently to scavenge dyes during l a u n d e r i n g s . More i n v e s t i gations using a variety of techniques are needed to f u l l y elucidate the effects of anions as well as the quaternary ammonium cations on the structures of both water and the overall hydrogen bonded network with the cellulose matrix. 19

20

21

22

Summary The materials selected in t h i s report for surface analyses and bulk analyses were nitrogen containing cellulose anion exchangers of the weak-base and strong-base types. The surface analysis technique used (ESCA) has an i n t r i n s i c surface s e n s i t i v i t y to within a range of 50 A. Unfortunately, our Center does not have instrumentation for secondary ion mass spectroscopy (SIMS) which i s the most surface sensitive method. In order to probe deeper than 50 A with ESCA, i t i s necessary to apply ion etching techniques via such methods as radio frequency cold plasmas of argon. This technique has been used to obtain depth p r o f i l e s of various elements with chemically modified c e l l u l o s i c fibers. However, with cellulose anion exchangers used in t h i s d i s cussion, consideration has to be taken of the fact that nitrogen i s bound to cellulose in an amide type of bonding whenever c e l l u lose is subjected to r f cold plasmas of argon, a i r , or nitrogen. The exact BE of core electrons being investigated depends on the nature of the chemical bonding of the element. In some instances,

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

1.

BENERITO E T AL.

Instrumental Analyses of Modified

Cottons

the chemical bonding affects the spectral line shape and the appearance of s a t e l l i t e s . With experience and the use of spectra of known compounds as f i n g e r p r i n t s , i t i s possible to distinguish among oxidation states of a given element in chemically modified cottons. Surface analyses used in conjunction with EPR and CL give some insight into the types of active species formed in chemically modified cottons. Data from a l l of these techniques can be correlated with that from conventional chemical analyses. Once i t i s established that analyses of surfaces correlate with bulk analyses, the s o l i d state analyses are very useful and give more detailed information than conventional chemical analyses. Even in those instances where composition varies with depth from surfaces, the methods of surface analyses can be useful to the cellulose chemist. Acknowledgement The authors wish to thank Jarrel H. Carra, Wilton R. Goynes, J r . and Bruce F. Ingber for the microscopic analyses. Mention of a company and/or product does not imply approval or recommendation by the U.S. Department of Agriculture, to the exclusion of others which may also be suitable.

References 1. 2.

Hofmann, A. W. Ann. Chem. (1851), 78, 253-258. Frank, H. S. and Evans, M. W. J. Chem. Phys. (1945), 13, 507-532. 3. Boyd, G. E., Schwarz, A., and Lindenbaum, S. J. Phys. Chem. (1966), 70, 821-825. 4. Lindenbaum, S. J. Phys. Chem. (1966), 70, 814-821. 5. Diamond, R. M. J. Phys. Chem. (1964), 67, 2513-2517. 6. Soignet, D. M., Berni, R. J., and Benerito, R. R. Textile Res. J. (1966), 36, 978-989. 7. Soignet, D. M. and Benerito, R. R. Textile Res. J. (1967), 37, 1001-1003. 8. Perrier, D. M. and Benerito, R. R. J. Appl. Polym. Sci., (1975) , 19, 3211-3220. 9. Perrier, D. M. and Benerito, R. R. Appl. Polym. Sci. (1976) , 29, 213-221. 10. Berni, R. J., Soignet, D. M. and Benerito, R. R. Textile Res. J. (1970), 40, 999-1006. 11. Soignet, D. M., Berni, R. J. and Benerito, R. R. J. Appl. Polym. Sci. (1971), 15, 155-168. 12. Benerito, R. R., Woodward, B. B. and Guthrie, J., Anal. Chem. (1965), 1693-1699. 13. Jung, H. Z., Ward T. L. and Benerito, R. R., J. Macromol. Sci. Chem. (1979), A13, 1117-1133.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

25

26

POLYMERS FOR FIBERS AND ELASTOMERS

14. 15. 16. 17. 18. 19. 20. 21. 22.

O'Connor, R. T. Instrumental Analysis of Cotton Cellulose and Modified Cotton Cellulose, Marcel Dekker, Inc., New York, (1972), pp 10-11, 441-443. Ward, T. L., Jung, H. Z., Hinojosa, O. and Benerito, R. R. Surface Sci. (1978), 76, 257-273. Tripp, V. W., Moore, A. T. and Rollins, M. L. Textile Research J. (1966), 36, 295. Rollins, M. L. and Tripp, V. W. Methods of Carbohydrate Chemistry (1963) R. W. Whistler, Ed., Academic Press, New York, (1963), p.. 356. Goynes, W. R., Jr. and Carra, J. H. A.C.S. Division of Organic Coatings and Plastics Chemistry, (1976), 36, 9-13. Ward, T. L. and Benerito, R. R. J. Polymer Photochemistry (1983) 3 (4),267-277. Berni, R. J., Benerito, R. R., and Pilkington, M. W. U. S. Patent 3,914,108 (Oct. 21, 1975). Perrier, D. M., Benerito, R. R., and Steele, R. H. U.S. Patent 4,029,533 (Jun Claiborne, J. L. (to Dixie Yarns, Inc.) U.S. Patent 4,380,453 (April 19, 1983).

R E C E I V E D May 3, 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

2 Cross-Polarization/Magic Angle Spinning Study

13

C-NMR

Molecular Chain Conformations of Native and Regenerated Cellulose

F. HORII, A. HIRAI, and R. KITAMARU Institute for Chemical Research, Kyoto University, Uji, Kyoto 611, Japan 13

Quantitative analysis of CP/MAS C NMR spectra has been carried out to characterize molecular chain conformations of crystalline and noncrystalline components of native cellulos and valonia cellulose resonance lines of C1 and C4 carbons in the β-1,4glycosidic linkage and C6 carbon of the CHOH side group are deconvoluted into the crystalline and noncrystalline components. The chemical shifts of the two components of the C1, C4, and C6 carbons as determined by the line deconvolution method are correlated to the torsion angles Фand Ψabout the β-1,4-glycosidic linkage and X about the exo-cyclic C5-C6 bond, respectively. On the basis of these results, the characteristic chain conformations of the crystalline and noncrystalline components of native and regenerated cellulose are discussed. 2

Cellulose, which i s one of the most abundant organic substances found i n nature, has been extensively studied by various techniques such as x-ray s c a t t e r i n g , electron microscopy, IR and Raman spectroscopy, NMR spectroscopy e t c . However, the c r y s t a l structure and noncrystalline state are not yet solved for cotton, ramie, b a c t e r i a l and valonia c e l l u l o s e s which can be e a s i l y obtained i n Dure form. Crosspolarization/magic angle spinning(CP/MAS) NMR spectroscopy i s a promising new method to study these unsolved problems of c e l l u l o s e , because this method i s very sensitive to l o c a l molecular conformations and dynamics. Our recent CP/MAS NMR work(1,2) on native and regenerated celluloses has shown that the resonance l i n e s can be analyzed i n terms of the contribution from the c r y s t a l l i n e and noncrystalline components. The chemical s h i f t s of CI, C4, and C6 carbons thus ascribed to the respective components could be correlated to the torsion angles (> | and ip, which define the conformation about the 61,4-glycosidic linkage, and x about the exo-cyclic C5-C6 bond, 0097-6156/84/0260-0027$06.00/0 © 1984 A m e r i c a n C h e m i c a l Society

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

28

POLYMERS

FOR FIBERS A N D E L A S T O M E R S

respectively(_3,4) . In this paper we review these results and discuss the chain conformations of the c r y s t a l l i n e and noncrystalline components for both native and regenerated c e l l u l o s e samples. Experimental Sample Preparation. Valonia c e l l u l o s e was obtained from the c e l l walls of valonia maorophysa. The valonia c e l l walls were p u r i f i e d as follows. They were washed with water thoroughly, boiled i n a 1% NaOH aquous solution f o r 4 hr, and washed well with water. Then they were immersed i n 0.1% acetic acid to neutralize the trace of the a l k a l i , washed with water, and dried. Aoetobaoter xyUnion, American Type Culture C o l l e c t i o n s t r a i n number 10245, which was kindly supplied by Dr. H. Takai of Hokkaido University, was grown i n a s t e r i l e l i q u i d medium. This consisted o f ( i n g / l i t e r ) : anhydrous glucose 20 yeast extract 5 polypeptons 5 disodium hydrogen phosphate(anhydrous The pH of the mixture wa 15 ml of the l i q u i d medium were simultaneously inoculated with 0.5 ml of inoculum from 2-4 day inoculation culture. Cultures were grown at 30°C f o r 4 days with no a g i t a t i o n . Cellulose membranes which were produced on the surface of the l i q u i d were washed with water, immersed i n 2% NaOH solution f o r more than 7 days at room temperature, then washed again with water. To free the membranes from the a l k a l i they were immersed i n 1% acetic acid f o r 1 day, washed with water and dried. Egyptian cotton, ramie and cupra rayon f i b e r s were p u r i f i e d according to the methods reported previously(_5,j6) . A highly c r y s t a l l i n e cellulose II sample with low molecular weight was prepared using a method based on that of Bulleon and Chanzy(7). Five grams of c e l l u l o s e acetate were mixed with 150 ml dichloromethane, 100 ml acetic anhydride, 45 ml g l a c i a l acetic acid, and 0.2 ml HCIO4(density 1.67 gem" ) and maintained f o r 6 hr at 5 5 ° C The reaction was stopped by adding sodium acetate(2.5 g) suspended i n a small amount of water. The reaction mixture was then poured into 3 I of b o i l i n g 0.1 M aqueous sodium acetate. The p r e c i p i t a t e was f i l t e r e d , washed with water, then s t i r r e d i n methanol to remove oligomers of low molecular weight and the yellow color. The c e l l u l o s e triacetate(1.5g) with low molecular weight thus produced was dissolved i n 1 I of a 40% solution of methylamine i n water. The solution was held at 90°C for 5 hr to e f f e c t deacetylation and c r y s t a l l i z a t i o n of the cellulose. Other c e l l u l o s e and monosaccharides and disaccharides were the same as reported previously(1,_3) . The samples except f o r hydrates and 3-methyl cellobioside«CH30H were well dried at 50°C under vaccum for 2-3 days before and a f t e r packing i n a rotor for CP/MAS measurements. The hydrates and $-methyl cellobioside*CH3OH were used without drying. 3

1 3

1 3

CP/MAS C NMR Spectroscopy. CP/MAS C NMR spectra were recorded on a JEOL JNM FX-100 and FX-200 spectrometers equipped with a CP/MAS unit operating at 25 and 50 MHz f o r respectively. The matched f i e l d strengths V and V m of 71 kHz f o r 25 MHz and 62.5 kHz f o r 50 MHz were applied to 13c and -^-H for 2.0 ms; Vjjj remained on during the s i g n a l a c q u i s i t i o n period. Magic angle spinning was c a r r i e d out l c

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

2.

HORII E T A L .

CP/MAS C-NMR

29

Study

13

at a rate of about 3.2 kHz for 25 MHz and 3.5 kHz f o r 50 MHz by use of a b u l l e t type rotor of poly(chlorotrifluoroethylene), whose volume was about 0.5 cm . Chemical s h i f t s r e l a t i v e to tetramethylsilane( TMS) were determined using a narrow c r y s t a l l i n e resonance l i n e at 33.6 ppm for polyethylene inserted i n a l l samples. 3

Results and Discussion 1. Assignments of the Resonance Lines of the C r y s t a l l i n e and Nonc r y s t a l l i n e Components. Figure 1 shows a 50 MHz CP/MAS NMR spectrum of ramie c e l l u l o s e and a stick-type NMR spectrum of low molecular weight c e l l u l o s e ( DP'VLO) i n deuterated dimethyl sulfoxide solution(DMSO)(8)(The broken and s o l i d l i n e s i n the CP/MAS spectrum w i l l be explained below.). As already reported(9,10), the assignments f o r the CI, C4 and C6 carbons are r e l a t i v e l y easy, base spectrum. However, i t s h i f t downfield by 2.3-9.6 ppm i n the s o l i d state compared to the solution state. The cause of such large downfield s h i f t s ( t o be explained i n the next section) i s attributed to the d i f f e r e n t conformations about the $-l,4-glycosidic linkage and the exo-cyclic C5C6 bond i n which these carbons are involved. Another remarkable feature i s that the resonance l i n e s of the C4 and C6 carbons s p l i t into two components; sharp downfield and broad u p f i e l d components. Similar s p l i t t i n g s have been observed f o r the C4 and C6 resonance lines of cotton, b a c t e r i a l and valonia c e l l u l o s e and for the CI, C4 and C6 resonance l i n e s of regenerated cellulose(1) such as cupra rayon f i b e r s . These spectra and s p l i t t i n g s are shown i n Figure 2. In the case of regenerated c e l l u l o s e ( 1 ) , we have already concluded that the components causing the sharp downfield and the broad u p f i e l d s h i f t s are the c r y s t a l l i n e and noncrystalline components, respectively. Therefore, we have assumed that the s p l i t tings are due to the same components i n native c e l l u l o s e . However, the CI resonance l i n e does not seem e x p l i c i t l y to contain two such components. In order to confirm this assumption, we deconvoluted the C4 and C6 resonance l i n e s into two components by use of a curve resolver and by assuming a Lorentzian l i n e shape as shown by broken and thin s o l i d l i n e s i n Figures 1 and 2. In Figure 3 the integrated f r a c t i o n / of the sharp downfield component of the C4 carbon i s plotted against the degree of c r y s t a l l i n i t y / determined by x-ray analysis based on a modified Hermans' method(l,ll,12). This figure shows also data of hydrocellulose, some regenerated c e l l u l o s e samples(l), and mercerized cotton and ramie. A l i n e a r relationship exists between / and / for a l l the samples. A s i m i l a r relationship was also obtained f o r the case of the C6 resonance l i n e . Therefore, i t i s concluded that the sharp downfield and broad u p f i e l d components of the C4 and C6 carbons of native c e l l u l o s e are also the c r y s t a l l i n e and nonc r y s t a l l i n e components, respectively.*) Recent work(13) reported that the broad u p f i e l d components of C4 and C6 carbons were not attributed to the noncrystalline component but to anhydroglucoses on the surface of elementary f i b r i l s because the spectra of cotton, hydrocellulose, and ramie showed l i t t l e differences i n r e l a t i v e i n t e n s i t y and i n appearance of the broad n

m

x

n

m

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

r

x

r

30

P O L Y M E R S FOR F I B E R S A N D

ELASTOMERS

6

J - I • I . I i I . I . I , 120 110 1 0 0 9 0 80 70 60 ppm

Figure 1. 50MHz CP /MAS C NMR spectrum of ramie and stick-type scalar-decoupled l ^ C NMR spectrum of low molecular weight c e l l u l o s e i n DMSO-dg solution (8). Broken and t h i n s o l i d l i n e s i n the CP/MAS spectrum are for the c r y s t a l l i n e and noncrystalline components, respectively. 1

110

100

3

90 ' 80 ' 70 ' 60 ' ppm

110

1 0 0 ' 90

80

70 60 ppm

1 3

Figure 2. 50 MHz CP/MAS C NMR spectra of b a c t e r i a l c e l l u l o s e , valonia c e l l u l o s e , cotton, and cupra rayon f i b e r s . Broken and t h i n s o l i d l i n e s i n the CP/MAS spectra are for the c r y s t a l l i n e and nonc r y s t a l l i n e components, respectively.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

HORII ET AL.

2.

CP/MAS

C-NMR

13

Study

31

component. However, i t i s very plausible that such differences could not be found among these samples, because their c r y s t a l l i n i t i e s are almost the same. More importantly, they believed that the c r y s t a l l i n i t i e s of these samples were 80-96%. We think that these values are evidently overestimated. According to our quantitative analysis described above i t i s not necessary to consider the contribution of the surface of elementary f i b r i l s to the broad components. On the other hand, the resonance l i n e of the CI carbon i s also assumed to contain c r y s t a l l i n e and noncrystalline components. In order to examine this problem, we measured s p i n - l a t t i c e relaxation times using a pulse sequence as developed by Torchia(16). As a r e s u l t , i t has been found that each resonance l i n e of ramie contains two components with values of 4.6-16s and 65-130s which correspond to the noncrystalline and c r y s t a l l i n e components, respectively(15). On the basis of these d i f f e r e n t values, we were able to record the spectra of the c r y s t a l l i n e and noncrystalline components of native cellulose separately by Figure 4(A) shows th ramie which was obtained under the MAS condition by a pulse sequence for measurements developed by Torchia(16) . The time between the two TT/2 pulses was about 30s. As i s c l e a r l y seen, the broad u p f i e l d components of the C4 and C6 resonance l i n e s disappear and another fine s p l i t t i n g appears i n the CI resonance l i n e which originates only from the c r y s t a l l i n e component. Figure 4(B) shows the spectrum of the noncrystalline component of ramie which was obtained by a conventional TT/2 single pulse sequence with a short waiting time of 4s employing the DD/MAS technique. As the difference i n T-^ between the c r y s t a l l i n e and noncrystalline components i s not very large, a small amount of the downfield c r y s t a l l i n e l i n e s also appears for the C4 and C6 carbons. Although a small amount of the c r y s t a l l i n e component i s also involved i n the CI resonance l i n e , the characteristics of the noncrystalline component of this l i n e can be well observed: the chemical s h i f t of this component i s about 106 ppm from TMS and the l i n e width i s about 90 Hz. By considering the features of the CI resonance l i n e for both components, we deconvoluted the CI resonance l i n e into the c r y s t a l l i n e and noncrystalline components as shown i n Figure 1. Although two Lorentzian l i n e s were used for the c r y s t a l l i n e components based on the r e s u l t i n Figure 4 (A), the CI l i n e could be deconvoluted into the two components. The integrated f r a c t i o n of the c r y s t a l l i n e component was also i n good accord with the f^?Similar deconvolutions were also possible for the CI resonance l i n e s of cotton, b a c t e r i a l and valonia c e l l u l o s e s as shown i n Figure 2. I t shoud be noted that three Lorentzian l i n e s were used for the c r y s t a l l i n e component of the l a t t e r two samples.

*) Garroway et al.(14) have recently pointed out that the r e l a t i v e i n t e n s i t i e s of resonance l i n e s of CP/MAS -^C NMR spectra are proport i o n a l to the number of carbons, when the time constant T q for -4113 cross p o l a r i z a t i o n i s much shorter than the s p i n - l a t t i c e relaxation times T]Jp and T ^ p i n the rotation frames of ^-H and -^C n u c l e i , respectively. Since this condition has been found to be f u l f i l l e d under our experimental condition(15), such a quantitative analysis as shown i n the text can be reasonably carried out for c e l l u l o s e samples. H

C

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

32

POLYMERS

F O R FIBERS

A N D

ELASTOMERS

1.0

Ol 0

i

0.5

I 1.0

fx

Figure 3

Integrated f r a c t i o

C4 resonance l i n e v s . degree of c r y s t a l l i n i t y / analysis.

determined by x-ray

•: native c e l l u l o s e , o: regenerated c e l l u l o s e ,

Q: mercerized cotton and ramie.

(The data of regenerated c e l l u l o s e

samples except f o r cupra rayon fibers were reproduced from Ref. 1.)

120 ' 110 ' 1 0 0 ' 9 0 " 8 0 ' 7 0 ' 6 0 ppm

Figure 4

P a r t i a l l y relaxed 2 5 MHz

C NMR spectra of the c r y s t a l -

l i n e and noncrystalline components of ramie which were separately measured by a pulse sequence f o r CP T^ measurements developed by Torchia(16) and a single TT/2 pulse sequence, respectively.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

2.

HORII E T A L .

CP/MAS

13

C-NMR

Study

33

The pulse techniques employed for the s e l e c t i v e observation of the c r y s t a l l i n e and noncrystalline components f o r native c e l l u l o s e are also useful for regenerated c e l l u l o s e . Figure 5 shows the spectrum of the c r y s t a l l i n e component of cupra rayon f i b e r s together with that of a regenerated c e l l u l o s e sample(JL) of high c r y s t a l l i n i t y . The good agreement of the two spectra confirms that very sharp l i n e s of the c r y s t a l l i n e component are involved i n the respective l i n e s of the whole spectrum of the rayon f i b e r s which i s r e l a t i v e l y broad as shown i n Figure 2. The chemical s h i f t s of CI, C4, and C6 carbons of the c r y s t a l l i n e and noncrystalline components of native and regenerated c e l l u l o s e s are tabulated i n Tables I and I I , respectively. Table I I shows also the l i n e width Av of each resonance l i n e . Before we discuss these r e s u l t s , l e t us consider the meanings of the s o l i d - s t a t e -^C chemical s h i f t s i n the next section. 2. Relationships betwee Torsion Angles. 1 3

The C i s o t r o p i c chemical s h i f t s obtained by CP/MAS technique are also determined by the magnetic shielding of electrons surrounding concerned carbons just as i n s o l u t i o n . Nevertheless, MAS can produce high-resolution l i n e s without any a i d of molecular motions. Therefore, the respective states of electron shielding fixed i n the s o l i d state are r e f l e c t e d on the respective chemical s h i f t s of a given carbon, whereas such states are usually averaged out i n solution by rapid inner molecular motions. This suggests that the s o l i d - s t a t e chemical s h i f t s provide important information of the l o c a l conformations and alignments of molecules i n the s o l i d state which possibly determine the extent of the electron s h i e l d i n g . However, the s o l i d - s t a t e chemical s h i f t s are not well understood at present. The main e f f e c t s which have been pointed out hitherto are the e f f e c t s of packing, hydrogen bonding, and torsion angles about chemical bonds involving concerned carbons. In r e l a t i o n to the packing e f f e c t , VanderHart(17) has found that the resonance l i n e of CH2 carbons of t r i c l i n i c c r y s t a l s of W-C20H42 i s shifted 1.31"0.4 ppm downfield i n comparison to that of n-paraffins of other c r y s t a l forms. As for the hydrogen bonding e f f e c t s , Terao et al.(18-20) have reported that large downfield s h i f t s appear for the carbons bonded chemic a l l y to hydroxyl groups which form strong hydrogen bonds. F i r s t we have examined these two e f f e c t s for the c r y s t a l s of monosaccharides and disaccharides which are compounds related to c e l l u l o s e . Table I I I compares the C CP/MAS chemical s h i f t s i n the s o l i d state and the corresponding s h i f t s i n D2O. The comparison i s made only for carbons not associated with exo-cyclic C-C bonds and $-1,4glycosidic linkages. The respective resonance l i n e s of the s o l i d state spectra of a-glucose and $-glucose and of the solution spectra of a l l the samples were assigned according to the results of Pfeffer et al.(21,22) In the table are also shown the 0«»»0 distances of the hydrogen bonds i n the s o l i d state(23-26). The difference A6 i n chemical s h i f t between the two states ranges from -1.51 ppm to 2.43 ppm and are independent on the 0»««0 distances. Therefore, the hydrogen bonding seems not to s i g n i f i c a n t l y a f f e c t the chemical s h i f t s i n these carbohydrates. However, the somewhat large 1 3

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

34

POLYMERS

FOR FIBERS A N D

ELASTOMERS

120" 110 ' 100" 90 ' 80 ' 70 ' 60 ' ppm

Figure 5

50 MHz

1 3

CP/MAS C

NMR

spectrum

(A) of highly c r y s t a l l i n e 13

c e l l u l o s e II sample and p a r t i a l l y relaxed 25 MHz

C NMR

spectrum

(B) of the c r y s t a l l i n e component of cupra rayon f i b e r s which was separately measured by the pulse sequence for CP T

measurements.

Table I 'C Chemical Shifts of the C r y s t a l l i n e Components of Native and Regenerated Cellulose

chemical shift/ppm C6

C4

CI

sample native c e l l u l o s e valonia

107.0

106.4

105.3

91.3

90.1

66.5

105.3

91.0

90.1

66.4

bacterial

107.3

cotton

107.1

105.4

89.9

66.5

ramie

107.2

105.0

89.7

66.0

cupra rayon

108.0

106.3

89.5

88.2

64.1

high-crystalline cellulose II

108.1

106.3

89.6

88.4

63.7

106.3

regenerated c e l l u l o s e

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

2.

HORII E T A L .

CP/MAS

"C-NMR

Study

35

Table I I 13

C

Chemical Shifts and Line-Widths of the Noncrystalline Components of Native and Regenerated Cellulose

CI

C4

C6

6/ppm

Av/Hz

6/ppm

Av/Hz

6/ppm

Av/Hz

valonia

106.2

114

85.2

249

63.4

185

bacterial

106.6

120

85.0

242

63.4

163

cupra rayon

105.3

284

85.1

327

62.8

185

amorphous

105.2

284

81.6

284

62.8

284

sample

native c e l l u l o s e

cotton ramie regenerated c e l l u l o s e

Table I I I 13 Comparison of C Chemical S h i f t s of Monosaccharides and Disaccharides i n the S o l i d State and i n Solution

6/ppm Sample

Carbon

A6/ppm Solid

a-D-glucose

0•••0 distance/A

solution

1 2 3 4

93.54 71.22 73.75 73.36

93.30 72.73 74.05 70.93

0.24 -1.51 -0.30 2.43

2.847 2.776 2.707 2.773

1 2 3 4

97.34 76.39 76.39 70.34

97.15 75.46 77.17 70.93

0.19 0.93 -0.78 -0.59

2.666 2.686, 2, 2.772 no

$-D-cellobiose

1'

98.02

97.05

0.97

2.776

b

Ot-D—lactose monohydrate

1'

93.50

93.15

0.35

2.790

c

$-D-lactose

1'

99.00

97.10

1.90

2.772

d

$-D-glucose

a.

Ref. 23 b. Ref. 24

c. Ref. 25

a

a

a

a

b

b

b

d. Ref. 26

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

36

POLYMERS

FOR FIBERS A N D

ELASTOMERS

difference A6 may originate from t o t a l intermolecular effects such as packing and hydrogen bonding e f f e c t s . In Table IV the s o l i d - s t a t e chemical s h i f t s of the carbons of ramie which are involved i n the 3-1,4-glycosidic linkages and i n the exo-cyclic C-C bonds are compared with the corresponding values of low molecular weight c e l l u l o s e i n DMSO solution(8). In this case the A6 values are as large as 2.3-9.8 ppm, suggesting that such larger differences may stem from the difference i n the torsion angles , determined from x-ray analyses(24-28) , for d i f f e r ent disaccharides of the $-l,4-glycosidic linkages(4). The chemical s h i f t s of the c r y s t a l l i n e components of d i f f e r e n t c e l l u l o s e samples which are shown i n Table I are also plotted against the corresponding ((> values (29-32) . In the l a t t e r case two or three d i f f e r e n t s h i f t values are plotted agains ramie where two d i f f e r e n analysis(31) . Although the data are somewhat scattered., the chemical s h i f t of CI carbon seems to be correlated to the torsion angle ((). Figure 7 shows the similar plot of the chemical s h i f t s of C4 carbon against the torsion angles \p determined by x-ray analyses. As a l i n e a r relationship also exists between them, the chemical s h i f t of the C4 carbon seems to be dependent on the torsion angles ip. In Figure 8, the C chemical s h i f t s of C6 carbon are plotted against the torsion angles x about C5-C6 bonds for glucose and glucose residues of d i f f e r e n t disaccharides and c e l l u l o s e ( 3 ) . In this case there exists also a l i n e a r relationship between the two parameters. According to a recent survey(33) of the rotations about the C-C bonds i n low molecular weight glucosides, gauche-gauche and gauche-trans are the two favored conformers. In agreement with t h i s f a c t , no data of monosaccharides and disaccharides are included i n this figure which correspond to the x values around 300°. On the other hand, the conformation of the CH2OH groups of the c r y s t a l l i n e component of native c e l l u l o s e i s found to be trans-gauche(29,31) against the expectation from the data of low molecular weight glucosides. Figure 8 shows that these three preferred conformations are well correlated to the chemical s h i f t s of "the C6 carbon; gauchegauche, gauche-trans, and trans-gauche correspond to the chemical s h i f t s of about 62 ppm, 62.7-64.5 ppm, and about 66 ppm,respectively. It i s concluded that the s o l i d - s t a t e chemical s h i f t s of the CI, C4, and C6 carbons are mainly correlated to the torsion angles (j>, i[>, and x> respectively. However, the intermolecular e f f e c t s such as packing and hydrogen bonding produce t o t a l l y the downfield or u p f i e l d s h i f t of 0.2-2.4 ppm f o r the carbohydrates studied here. Therefore, when the downfield or u p f i e l d s h i f t of such an order appears even i n the s o l i d - s t a t e l^C NMR spectra, the intermolecular e f f e c t s must be also considered. 1 3

3. Chain Conformation of the C r y s t a l l i n e and Noncrystalline Components of Cellulose. F i r s t we discuss the chemical s h i f t s of the c r y s t a l l i n e components shown i n Table I. The CI and C4 resonance l i n e s of valonia and

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

2.

HORII E T A L .

CP/MAS

"C-NMR

Study

37

Table IV Comparison of Chemical Shifts of CI, C4 and C6 Carbons of Ramie i n the Solid State with Those of Low Molecular Weight Cellulose i n Solution

6/ppm

A6/ppm

Carbon Crystalline J

®on,. Solution crystalline

1

107.2, 105.0

105.8

4

89.9

84.

6

66.0

63.0

a.

i n deuterated dimethyl

20

a

Crystalline J

102.7

4.5,

60.6

n

^° -. crystalline

2.3

5.4

n

3.1

2.4

sulfoxide(8).

40

60

80

^/degree 13 Figure 6 .

C chemical s h i f t s of the CI carbons vs. torsion angles

a: $-D-cellobiose, b: $-D-methyl cellobioside'CH^OH, c:

a-D-

lactose monohydrate, d: 3-D-lactose, e: c e l l u l o s e I (29), f: c e l l u l o s e I (31), g: c e l l u l o s e II (30), h: c e l l u l o s e II (32). (Data a-d, g-h; Ref.

4.)

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

38

POLYMERS

F O R FIBERS A N D

ELASTOMERS

t|V degree Figure 7 . chemical s h i f t s of the C4 carbons v s . torsion angles a: /3-D-cellobiose, b: 0-D-methyl cellobioside-CI^OH, c: Qf-Dlactose monohydrate, d: j3-D-lactose, e: c e l l u l o s e I ( 2 9 ) , f : c e l l u l o s e I ( 3 1 ) , g: c e l l u l o s e I I ( 3 0 ) , h: c e l l u l o s e II ( 3 2 ) . (Data a-e, g-h; Ref. 4 . ) 68

1

i

i

i

i

g

••

66-

*

E

c /

CL CL

-

•

if) o 62

-

e

E >>

4

I n e q u a t i o n (2) a n d (3) R 0 r e p r e s e n t s t h e n u m b e r o f peroxy r a d i c a l s , whereas R0 « i s associated t o t n e s . s . of peroxy r a d i c a l s . A s e . s . r . d a t a a r er e l a t e d t o R 0 t e q u a t i o n (4) becomes: 2

2

2

RO**(T)

= RO**(l

- exp(-K

• K ^ T 3 F T

t(exp

}

}

)

#

( < >) F

T

w h e r e f (T) g i v e s s . s . d e p e n d e n c e o n t e m p e r a t u r e . f(T) may have t h e f o l l o w i n g expression: f (T) = C / t T - T - , )

(5

>

Usual (6)

where

C i s a constant T represents t h e asymptotic temperature. T = 0 for a pure paramagnetic peroxy r a d i c a l . F o r ferromagnetic coupling T i s p o s i t i v e whereas f o r an antiferromagnetic coupling T i s negative. However, T i s s m a l l i n many s i tuations, analogous t o o u rone. F i n a l l y , t h e temperature dependence o f t h e double i n t e g r a l o f e . s . r . spectrum (R0 «) i s : 1

n

1

n

1

2

(1 RO .(T) a

= CR0 . 2

-

exp(-Kt(exp ^

T

^

j

E/K (T-T )))) B

"

Q

2

(

7

)

E q u a t i o n (7) g i v e s a s a t i s f a c t o r i l y d e s c r i p t i o n o f t h e a n o m a l y o b s e r v e d b y u s i n gamma i r r a d i a t e d polypropylene, f o r various types o f i r r a d i a t i o n . Analogous behav i o u r f o r a c t i v e centers h a s been e x p e r i m e n t a l l y reported

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

P O L Y M E R S FOR FIBERS A N D

86 in (16). The theoretical g e s t e d i n (17) .

description

f o r t h i s

ELASTOMERS

case

i s

sug-

Conclusions A n a n o m a l y i n s . s . o f p e r o x y r a d i c a l s a r o u n d T , i n gamma i r r a d i a t e d PF f i b e r s i s related. The e n v i r o n m e n t a l c o n d i t i o n s under w h i c n t h i s anomaly is observed a r e carefully investigated (by experiments) and e x t e n s i v e l y discussed. It i s proved that t h i s anomaly i s r e l a t e d t o t h e g l a s s y t r a n s i t i o n phenomenon. A phenomenological d e s c r i p t i o n o f t h i s anomaly i s suggested. I t i s supposed that t h e anomaly concerns t h e conversion of R e e n t e r s i n peroxy r a d i c a l s . Accordingly, i s proposed that t h i s reaction occurs i n two steps, d i f f u sion and chemical reaction t i o n i s controlled b that t n e d i f f u s i o n depends on temperature according t o a W.L.F. l a w . A mathematical d e s c r i p t i o n o f t h i s anomaly i s sugg e s t e d . The agreement between theory and experiments i s satisfactory. G

Literature Cited 1. F. Bovey, "The effects of ionizing radiation on natu­ r a l and synthetic polymers "Interscience Press, New York, 1958 2. Malcolm Dole (Editor) "The radiation chemistry of ma­ cromolecules" Academic Press, New York, 1973 3. N. Zolotova, T. Denisov, J . Polym. S c i . , 1971, A - l , 9, 3311 4. H.P. Frank, Polypropylene, Gordon & Breach, 1968 5. P.B. Ayscough, K.J. Ivin, J.O. Donell, Proc. Chem. Soc., 1961, 71 6. H. Fisher, K. Hellwege, J . Polym. S c i . , 1962, 56, 33 7. B.R. Loy, J. Polym. S c i . , 1963, 1, 2251 8. L . J . Forrestal, W.G. Hodgson, J . Polym. S c i . , 1972, A - l , 2, 1275 9. S. Ohnishi, Y. Ikeda, M. Kashiwagi, M. N i t t a , Polymer, 1961, 2, 119 10. B. Ranby, J . F . Rabek, "E.S.R. Spectroscopy in Polymer Research" Springer-Verlag, B e r l i n , 1977 11. M. Iwasaki, T. Ichikawa, T. Ohmori, J . Chem. Phys., 1969, 50, 1991 12. P.O. K i n e l l , B. Ranby (Editors) "E.S.R. Applications to polymer Research"; Proceedings of the XXII n d Nobel Symposium, John Wiley & Sons, New York, 1973 13. S. Nara, H. Kashiwabara, J . Sohma, J. Polym. S c i . , 1968, A-2, 6, 1435 14. R. Baican, M. C h i p a r ă , Proc. XXth Congress AMPERE, T a l l i n n , 1978, Springer Verlag B e r l i n , 1979, p. 214

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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CHIPARA E T AL.

ESR Studies on Oxygen Diffusion

87

15. R. Baican, M. Chipară, Rev. Roum. Phys. , 1978 , 23, 9, 1079 16. S. Pivovarov, A . I . Poljakov, Yu. A. Rjabikin, N.L. Philippov, M.I. Bitenbaev Rad. Effects, 1982, 59, 179 17. M.I. Chipară, S. Turbatu, L. Georgescu, L. Cojocaru, M. Velter-Stefănescu, VIIth Int. Congress of Radiation Research (I.C.R.R.) , Amsterdamm, 1983 R E C E I V E D F e b r u a r y 28, 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

6 A Partial Phase Diagram and Crystal Solvate for the Poly(p-Phenyleneterephthalamide)/Sulfuric Acid System K. H. GARDNER, R. R. MATHESON, P. AVAKIAN, Y. T. CHIA, and T. D. GIERKE Central Research and Development Department, E. I. du Pont de Nemours and Company, Experimental Station, Wilmington, DE 19898 It is now well established that certain aromatic polyamides form ordered complexes with their solvents (i.e., crystal solvates). A solvates has been compile and Papkov1. Among the crystal solvates that have been identified are poly(m-phenylene isophthalamide) with N-methylpyrrolidone and with hexamethylphosphortriamide ; poly(p-benzamide) with sulfuric acid ; and poly(p-phenylene terephthalamide) (PPTA) with sulfuric acid and with hexamethylphosphortriamide . These solvates are all characterized by a discrete melting point and a crystalline diffraction pattern. 2

2

3

4

5

Although the presence of solvate phases has been established and qualitative phase diagrams have been published, to our knowledge, a detailed model for a polymer solvate and its phase behavior has not been presented. At this time we would like to present a partial phase diagram for the poly(p-phenylene terephthalamide) (PPTA)/sulfuric acid system and a model for the crystal solvate formed. In addition the structure of a model complex will be described. Experimental Experiments were carried out with low molecular weight poly(p-phenylene terephthalamide) (PPTA) produced by the acid ^ degradation of commercial Kevlar aramid fibers (6N H C l , 20 hr) . The inherent v i s c o s i t y of the degraded polymer was ca. 1.0 which, based on an empirical correlation between molecular weight and inherent v i s c o s i t y , corresponds to a molecular weight of ca. 7000. Solutions of PPTA i n 99.7% s u l f u r i c acid were prepared with concentrations ranging from 2% 24% (w/w) under ^ i n a dry box. Homogeneous solutions were obtained by intensive mixing at

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POLYMERS FOR FIBERS A N D E L A S T O M E R S

50-70°C for short times. This low molecular weight polymer was chosen for the study because of i t s ( r e l a t i v e l y ) easy d i s s o l u t i o n behavior and low solution v i s c o s i t i e s as compared to those of higher molecular weight polymer. D i f f e r e n t i a l Scanning Calorimetry (DSC) of the PPTA/ s u l f u r i c acid system was carried out i n order to establish the melting behavior of the system. Samples (5-10 mg) were sealed i n gold-coated aluminum pans under N2 and cooled at 10°C/min to -150°C. Subsequently the samples were heated to 100°C at 10°C/min and the melting thermograms were recorded. The d i f f r a c t i o n patterns of various PPTA/sulfuric acid solutions as a function of temperature were obtained using a Rigaku Theta-Theta Diffractometer run in the horizontal mode (CuK« r a d i a t i o n ) . D i g i t a l data were taken at intervals of 0.02° in 2®. The 2 scale wa temperature was measure sample. e

RESULTS Model Solvate Structure In order to determine the manner i n which s u l f u r i c acid interacts with PPTA we are investigating the structure of PPTA oligomers complexed with s u l f u r i c acid. We have recently determined the structure of a N,N'-(p-phenylene)dibenzamide (PPDB)/sulfuric acid complex using single c r y s t a l x-ray methods and similar studies with longer PPTA oligomers are underway now. We expect that the general p r i n c i p l e s for the interaction of s u l f u r i c acid and PPTA w i l l become apparent from these studies. The PPDB/sulfuric acid complex c r y s t a l l i z e s i n a t r i c l i n i c unit c e l l with dimensions a_ = 9.75A, b_ = 10.31A, c^ = 7.88A, a_ = 108.7°, 6_ = 111.4° and jy = 89.2°. The space group i s PI and the c e l l contains one PPDB molecule and four s u l f u r i c acid moieties. A view of the molecule together with the four nearest 2 4 groups i n the plane of the phenyl groups i s presented i n Figure 1. Two of the s u l f u r i c acid molecules can be seen to have protonated the carbonyl oxygens of the amide groups, thus the structure i s actually a s u l f u r i c acid/bisulfate salt of PPDB. H

S 0

The neutral compound PPDB exists i n twg phases, and structural studies have been reported for each. ' A comparison with these two structures and with the structure of N,N -diphenylterephthalamide (DPTA) i s presented i n Table 1. The protonated oxygens cause an expected lengthening of the C-0 bonds from 1.22A (avg) i n the neutral compound to 1.30A (avg) i n the s u l f u r i c acid s a l t . In addition the C-N amide bond i s shortened from 1.36A (avg) to 1.30A (avg), indicating a substantial increase of double bond character i n this bond. f

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

6.

GARDNER ET AL.

Figure 1.

PPTA/Sulfuric

Acid System

93

f

Molecular structure of N,N -(p-phenylene) dibenzamide (PPDB) and the four nearest s u l f u r i c acids; (a) atomic numbering, (b) with hydrogens.

Table 1

Structure

9

PPDB

PPDB

DBTA

1.222 1.355 28.9 35.7 64.4

1.229 1.356 23.8 55.4 79.2

1.226 1.359 30.7 30.4 60.9

8

10

present

o

C-0 distance(A) O N distance(A) amide...outer ring angle(°) amide...central ring angle(°) outer...central ring angle (°)

1.30, 1,293 1.301, 1.303 36.6, 37.9 -41.2, -44.4 5.7, 8.2

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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94

A pronounced flattening of the protonated PPDB structure i s observed i n comparison to the unprotonated compound. In the neutral compound the phenyl rings are rotated by 64° and 79° from each other, while i n the present structure the phenyl rings are nearly coplanar. However, i n a l l cases, the amide groups are severely rotated out of the plane of the phenyl groups. The torsional angles about the amide groups are ca. +30, +30 i n the neutral compound and ca. +30, -30 i n the acid s a l t . These conformers would be iso-energetic i n the neutral state and, i t would seem, of close i f not i d e n t i c a l energy i n the protonated form. Both previous studies of the neutral compound indicate a s i g n i f i c a n t influence of c r y s t a l packing on the conformation (see Table 1). It i s possible that the conformer found i n the acid s a l t was directed by c r y s t a l packing considerations which may not be a factor i n the PPTA/sulfuric acid complex. In the c r y s t a l , the s u l f u r i c acid and b i s u l f a t e groups are arranged i n sheets with an extensive networ sheets alternate with molecules with p i - p i * ring interactions (allowed by the planarity of the molecule). The sheets are inter-connected by strong amide to sulfate hydrogen bonds. A l t e r n a t i v e l y , the structure can be thought of as the close-packing of hydrogen bonded sheets containing PPDB and s u l f u r i c acid/bisulfates (Figure 3). We believe a sheet structure of this or similar nature i s the structural unit of the PPTA/sulfuric acid solvate phase. Phase Diagram The phase diagram for the (quasi-binary) PPTA-sulfuric acid system was compiled based on the melting point/composition information gathered from DSC-melting thermograms. In Figure 4, melting thermograms of a number of polymer-acid mixtures are presented. These thermograms were recorded for the temperature range -150° to 100°C at 10°C/min. The various thermograms were used to construct the melting point/composition diagram, which i s shown i n Figure 5. It can be seen that we are dealing with an apparent eutectic polymer-diluent system with a eutectic composition of 11-12% (w/w) of PPTA and a eutectic temperature of -8°C. The clearing temperature of the solutions as determined by o p t i c a l microscopy have been indicated i n Figure 5. Figure 6 shows the d i f f r a c t i o n pattern of a 22% PPTA/sulfuric acid solution as a function of temperature. The d i f f r a c t i o n patterns can be seen to consist of two components sharp d i f f r a c t i o n peaks superimposed on a broad component. This pattern i s consistent with a two phase system containing semicrystalline PPTA/sulfuric acid solvate and disordered components. As the temperature i s raised the portion of the d i f f r a c t i o n patterns attributable to the solvate phase decreases and f i n a l l y disappears at temperatures consistent with the melting endotherm observed by DSC. This d i f f r a c t i o n pattern agrees wjtjj that previously reported for the PPTA/sulfuric acid solvate. '

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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GARDNER ET AL.

Figure 2.

Figure 3.

PPTA I Sulfuric Acid System

95

In the c r y s t a l , the s u l f u r i c acids are arranged i n sheets with an extensive network of hydrogen bonding. These sheets alternate with sheets of PPDB.

A l t e r n a t i v e l y , the complex can be viewed as sheets consisting of PPDB molecules alternating with s u l f u r i c acids. Sheets of this nature are believed to exist i n the PPTA solvate.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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P O L Y M E R S FOR FIBERS A N D E L A S T O M E R S

Figure 5.

Phase diagram f o r PPTA/I^SO^. Experimental points were obtained by DSC (m) and o p t i c a l microscopy ( c ) .

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

6.

PPTA/Sulfuric

G A R D N E R E T AL.

Acid System

97

Solvate Structure The c r y s t a l l i n e component o f the d i f f r a c t i o n pattern can be indexed by a m e t r i c a l l y orthorhombic unit c e l l with dimensions £ = 16.35A, _b = 9.59A and £ = 12.9A. The c e l l contains two chain fragments and ca. 9 s u l f u r i c acid molecules per chemical repeat of the polymer. The quantity and organization of the s u l f u r i c acid i n the c e l l w i l l be d i s c u s s ^ below. Projections down the chain axis of the PPTA unit c e l l and the proposed solvate structure are shown i n Figure 7. Both structures have PPTA chains located at the corner and center of their respective unit c e l l s . In the neutral structure, the chains form hydrogen bonded sheets p a r a l l e l to the be plane. The c r y s t a l solvate can be thought of as a "swollen form of the neutral structure. The hydrogen bonded sheets p a r a l l e l to the bc_ plane have been preserved but now s u l f u r i c acid molecules participate i n the sheet while other acid molecule hydrogen bonded sheets s u l f u r i c acids per amide as was found i n the PPDB/sulfuric acid complex. [The chain-chain separation distance i n the polymer sheet is 9.59A as compared with 9.75A i n the model structure.] However, with this chain-chain separation distance i t i s also possible to construct a plausable sheet structure with one s u l f u r i c acid molecule per amide where a single s u l f u r i c acid molecule bridges two amide groups (N-H...0-S-O...H...0-C). In both models the s u l f u r i c acids between the sheets are not d i r e c t l y attached to the PPTA molecules. 77

°3 The volume of the solvate unit c e l l i s 2006A . If we assume that the volume occupied by the PPTA chains in the solvate i s tlje same as i t would be i n the pure PPD-T c r y s t a l , i . e . , 526A , and the volume of the s u l f u r i c acid molecules i n the hydrogen bonded s^eet i s the same as that i n the PPDB/sulfuric acid complex (78A ) we can calculate the volume of the intersheet s u l f u r i c acid molecules. These volume considerations and density measurements on undegraded samples (unpublished data) lead us to conclude that ( i ) there i s a nonstoichiometric amount of s u l f u r i c acid between the sheets and ( i i ) the acid i s disordered with a m o l e c u l a r volume equivalent to that of l i q u i d s u l f u r i c acid (ca. 87A ). These observations lead us to believe that the space group of the solvate i s a c t u a l l y monoclinic (or even t r i c l i n i c ) and the structural unit i s a sheet. Discussion Our present understanding of the phase diagram i n Figure 5 i s at a semiquantitative l e v e l . If the e u t e c t i c - l i k e pattern of the points labeled m are interpretable as such, then the l e f t hand branch r e f l e c t s the freezing point depression of s u l f u r i c acid (mp * 10°C). The fjope of this branch might then be expected to obey the familiar equation ,

AT =

km f

l

(1)

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMERS FOR FIBERS A N D E L A S T O M E R S

15

25 35 SCATTERING ANGLE

45

D i f f r a c t i o n pattern of a 22% (w/w) solution of PPTA/H SO^ as a function of temperature. 2

ab Projections of the PPTA and PPTA/IUSO. solvate unit cells. (a) PPTA structure using Northolt coordinates, molecules ^orm hydrogen bonded sheets p a r a l l e l to the bc_ plane. (b) Proposed structure for the PPTA/^SO^ solvate. Sulfuric acid molecules have been incorporated i n the hydrogen bonded sheets and between the sheets (not shown).

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

6.

GARDNER ET AL.

PPTA / Sulfuric Acid System A

in the l i m i t of m * 0. Here, T i s the difference i n melting points between the pure acid and a solution of^molarity m; and i s th^ cryoscopic constant. For^ s u l f u r i c acid k^ = 68.1 [K*10 g acid*(moles of solute) ]. When the low concentration points i n Figure 5 are f i t with eq. 1 and this value of k^, the desired number average molecular weight of the PPD-T solute i s only ca. 500. This value i s much smaller than the molecular weight derived from an empirical c o r r e l a t i o n between molecular weight and inherent v i s c o s i t y ; ca. 7000. We believe that this d i s p a r i t y r e f l e c t s , in part, the e l e c t r o l y t i c character of the dissolved PPTA . The r i g h t hand branch of the locus of 'm' points in F i g . 5 i s also interpretable as a freezing point depression. In this case, the most that we can say i s that the data are consistent with plausible values for the heat of fusion and melting points of a stoichiometric sheet-lik l i m i t i n g slope of the dat to the sheet melting point], and presume that the sheet s t o i c h i o metry i s 2 acids/amide as suggested by the x-ray observations on PPDB (see Figure 3), then the sheets are computed to melt at 162°C with a heat of fusion of ca. 5.0 kcal/mole of amides. Assumed stoichiometries of 1 to 1 and 3 to 1 r e s u l t i n melting points of 205°C or 126°C and heats of fusion of ca. 4 or ca. 8 kcal/mole, respectively. A l l three sets are p l a u s i b l e . Their exact quantitative significance i s questionable, since they are based on the i m p l i c i t assumption that a l l of the PPTA present i s incorporated into sheets. This assumption i s suspect on the general grounds of inevitable imperfections in these quite viscous solutions, and the rather long extrapolation required; as well as on the s p e c i f i c grounds discussed in the next paragraph. The points marked as 'c' i n Figure 5 correspond to observed clearing points. We cannot claim that they are equilibrium c l e a r i n g points; but, rather, indicate the temperature at which s i g n i f i c a n t quantities^of an i s o t r o p i c solution phase form on the time scale of 10 -10 seconds. Nevertheless, the biphasic character of the solutions lying near the locus of 'c'-points i s indisputable. Conse^engly, i t i s of interest to ask about the predictions of theory * for nematic-isotropic biphasic s t a b i l i t y . The appropriate equations have been published. The appropriate m o ^ l i s one of polydisperse chains of s p e c i f i e d Kuhn length i n a nonathermal solvent. The r e s u l t s of some i l l u s t r a t i v e calculations are presented i n Figure 8a and 8b, with the r e q u i s i t e parameters noted i n the legends of that figure. It i s important to note that the Flory-Huggins solvation parameter x has been treated as a disposable parameter. The intention here i s to merely demonstrate the q u a l i t a t i v e correspondence between theory and observation; no claim i s made for the actual value of x« There i s c l e a r l y predicted to be a biphasic regime i n the concentration range corresponding to Figure 5. This i s a d i r e c t consequence of the PPTA polydispersity, and i s subject to only a minor degree to

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100

P O L Y M E R S FOR FIBERS A N D

1

e.e ——— e.e

•

"

. WEIGHT FRACTION

Figure 8a.

«

——i .3

POLYMER

The isotropic fraction of the t o t a l solution volume i s plotted versus the o v e r a l l polymer-concentration (w/w). Parameters used i n the c a l c u l a t i o n are: most probable d i s t r i b u t i o n of chain lengths with p = 0.9881; the longest a x i a l ^ r a t i o of the system, n = 100; the 1956 approximation , C = 0; and solvation parameters, X = X' of (a) +0.005, (b) 0.0, (c) -0.005.

WEIGHT FRACTION

Figure 8b.

1 .2

.1

ELASTOMERS

POLYMER

The same plot as i n Figure 8a but with x = 0 and the longest a x i a l r a t i o of the system, n = (a) 200, (b) 100, (c) 50.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

6. G A R D N E R E T A L .

PPTA I Sulfuric Acid System

the influence of the somewhat arbitrary parameterization of the calculations. It i s not unreasonable that the isotropic phase w i l l act d i f f e r e n t l y than the predominent nematic phase at the freezing point. This v i t i a t e s the exact v a l i d i t y of the estimates of sheet melting parameters based on the data presented i n Figure 5 and analyzed i n the preceding paragraph. In summary, a l l of the qualitative features of the phase diagram are explicable i n terms of established physical p r i n c i p l e s . A quantitative description of the data i s tentative, because the PPTA-sulfuric acid solution i s very complicated. However, with plausible values for the various parameters a satisfactory semiquantitative description i s attainable.

References 1. M. M. Iovleva and 233 (translated in Polymer Sci. U.S.S.R. (1982) 24, 236). 2.

Yu. A. Tolkachev, O. P. Fialkovskii and Ye. P. Krasnov, Vysokomol. soyed. (1976) B18, 563.

3.

S. N. Pankov, M. M. Iovleva, S. I. Banduryan, N. A. Ivanova, I. N. Andreyeva, V. D. Kalmykova and A. V. Volokhina, Vysokomol. soyed. (1978) A20, 658. (translated in Polymer Sci. U.S.S.R. (1978) 20, 742).

4.

M. M. Iovleva, S. I. Banduryan, N. I. Ivanova, V. A. Platonov, L. P. Milkova, Z. S. Khanin, A. V. Volokhina and S. P. Papkov, Vysokomol. soyed. (1979) B21, 351.

5.

T. Takahashi, H. Iwamoto, K. Inoue and I. Tsujimoto, J. Polym. Sci., Polym. Phys. Ed. (1979) 17, 115.

6.

M. Panar, et al., J. Polym. Sci., Polym. Phys. Ed. (in press).

7.

J. Calabrese and K. H. Gardner - publication in preparation.

8.

S. Harkema and R. J. Gaymans, Acta. Cryst. (1977) B33, 3609.

9.

W. W. Adams, A. V. Fratini and D. R. Wiff, Acta Cryst. (1978), B34, 954.

10.

S. Harkema, R. J. Gaymans, G. J. van Hummel and D. Zylberlicht, Acta Cryst. (1979) B35, 506.

11. M. G. Northolt, Eur. Polym. J. (1974) 10 , 798-804. 12.

J. H. van't Hoff, Z. Physik. Chem. (1887) 1, 481.

13.

International Critical Tables (1928) IV, 214.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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102

14.

D. G. Baird and J. K. Smith, J. Polym. Sci., Polym. Chem. Ed. (1978) 16, 61.

15.

P. J. Flory, Proc. Roy. Soc. (London) (1956) A239, 73.

16.

P. J. Flory and A. Abe, Macromolecules (1978) 11, 1119.

17.

R. R. Matheson, Jr., and P. J. Flory, Macromolecules (1981) 14, 954.

R E C E I V E D M a y 4, 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

7 Aromatic Azomethine Polymers and Fibers PAUL W. MORGAN1, TERRY C. PLETCHER, and STEPHANIE L. KWOLEK Textile Fibers Department, E. I. du Pont de Nemours and Company, Experimental Station, Wilmington, DE 19898

An aromatic polyazomethine structure is shown in the first line of Table 1. The literature of polyazomethines is voluminous but in general these material bility and to be unmeltable, and therefore difficult to characterize (1-9). On the other hand, mono and bisazomethines with appropriate terminal groups were among the early substances found to exhibit a liquid crystalline state. We set out to prepare tractable, high molecular weight, aromatic polyazomethines by depressing the melting points through ring substituents, flexible chain units, and/or copolymerization, as Schaefgen and co-workers (10) had done with aromatic polyesters. Since our work was published in patents in 1976 to 1978 (11), Millaud and co-workers (12) have examined several of these polymers, particularly the polymer from 2-methyl-l,4-phenylenediamine and terephthaldehyde, for viscosity-light scattering molecular weight relationships, persistence length, light absorption spectra, and the formation of lyotropic solutions in sulfuric acid. Polymer Preparation Table 1 shows four reactions for the preparation of polyazomethines. The diamine-dialdehyde reaction proceeds r a p i d l y at room temperature or above without c a t a l y s t s and the reactions of a diamine with a b i s a c e t a l or a bisazomethine proceed well at elevated temperature. We have used primarily the f i r s t and t h i r d reactions. Table 2 outlines several procedures using these reactions. For the low temperature procedures, equivalents, or near equivalents, of the reactants are combined quickly i n an anhydrous solvent. I f water i s to be removed, arrangement i s made f o r d i s t i l l a t i o n . After a short time the polymer usually p r e c i p i t a t e s . 1

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P O L Y M E R S F O R FIBERS A N D

ELASTOMERS

Some further gain i n molecular weight may be attained i n the precipitated state. Monoamines or monoaldehydes may be added to control molecular weight i n the preparation and i n subsequent processing steps. The polymers from solution preparation can be further polymerized thermally i n the s o l i d state or as a melt. Of course, any of the preparative reactions can be carried out as a melt system with appropriate care i n i n i t i a t i n g the reaction. A well-controlled polymerization i s obtained by melting together a diamine with a b i s azomethine. An i l l u s t r a t i o n of that process appears i n Table 3 for the reaction of 2-methyl-l,4-phenylenediamine with the bisazomethine from a n i l i n e and terephthalaldehyde. The reaction was carried out i n a small f l a s k under nitrogen with s t i r r i n g and d i s t i l l a t i o n of byproduct a n i l i n e . Time was counted from the point when the i n g r e d i ents were melted. The reaction was proceeding slowly a f t e r about forty minutes. The progres a n i l i n e removal and woul Polymer Properties Table 4 shows the inherent v i s c o s i t i e s and melting temperatures of some mono-substituted polyazomethines. The unsubstituted polymers do not melt up to 400°C. One finds that the methyl group i s more e f f e c t i v e than the chloro group i n lowering the melting point and that a substituent on the diamine r i n g has a somewhat greater melting point lowering e f f e c t than the same substituent on the aldehyde r i n g . The larger naphthalene and biphenylene units, s u r p r i s i n g l y , y i e l d polymers melting close to that from terephthalaldehyde. A l l of the polymers described i n Table 4 and i n Tables 5 and 6 y i e l d l i q u i d c r y s t a l l i n e melts. The diphenyl ether unit had a v a r i a b l e e f f e c t on melt temperature. The f i r s t polymer (Table 5) melted 32° higher than the 255° value for the phenylene polymer (Table 4} whereas the t h i r d polymer (Table 5) melted 30° lower than the corresponding phenylene polymer i n Table 4. F l e x i b l e chain units, such as ethylene or dioxyethylene, lower the melting temperature and, i n general, lengthening such segments increases the melting point lowering. A wide v a r i e t y of copolymers which give l i q u i d c r y s t a l l i n e melts were prepared. Three are shown i n Table 6. In the t h i r d example a high proportion of hexamethylene units greatly depressed the melting point, yet the melted polymer was l i q u i d c r y s t a l l i n e . Up to t h i s point the melting temperature has been described as though i t were an exact property. And i t may be for a given polymer sample and testing method. However, we have found that the melting temperature may vary with inherent v i s c o s i t y , the preparative method, the thermal history and the testing method. Differences i n molecular weight, molecular weight d i s t r i b u t i o n and i n polymer c r y s t a l l i n i t y probably account f o r some of t h i s v a r i a t i o n .

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

7.

Aromatic Azomethine Polymers & Fibers

MORGAN ET AL.

Table 1.

HN

Reactions f o r Preparation of Polyazomethines

NH + OCH

2

105

CHO —> [=N

2

N = CH - < § > " C H = ] + 2 H0 n

Diamine + (RO) CH

CH (OR)

2

Diamine + R-N = CH RCH = N

> Polymer + ROH

2

CH = N-R

> Polymer + RNH

2

N = CHR + Dialdehyde

Table 2.

> Polymer + RCHO

Procedures f o r Polyazomethine Preparation Diamine and Dialdehyde Amide solvent plus LiCI Ethanol, hot Methylene chloride, azeotropic removal of water Melt with distillation of water Diamine and Bisazomethine Melt with distillation of monoamine

Table 3.

Melt Preparation of a Polyazomethine

H N^)-NH + 2

2

CH

-

N= C H - ^ ) - C H = N-(g)

>

3

[ = N ^ N CH

= C H ^ C H = ]

n

3

w

Reaction T8me Min

*inh dL/g in cone. H SQ 2

13

1.55

20

1.73

30

2.71

40

3.50

50

3.77

60

3.93

90

4.11

4

a) Equivalents of intermediate at 260°C and 760 torr with aniline removal.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

2

n

POLYMERS

106

Table 4. Diamine Component

CH

Aromatic Polyazomethines

Dialdehyde Component

?inh dUg in H SQ 2

Table 5.

Polymer MeK Temperature, °C

2.0

255

0.66

310

0.70

270

0.56

350

3

0.60

l6lOl

245

3

^KQ>-

- Q -

4

3

CH

CH

FOR FIBERS A N D ELASTOMERS

1.22

250

Aromatic Polyazomethines with Angular and F l e x i b l e Units

Diamine Component

^ 0 - < g ^

7

Dialdehyde Component

inh dL/g in HJSQ*

- Q -

Polymer Melt Temperature, °C

0.78

287

0.64

305

0.51

320

1.9

175

CI " ® CH

^>-CH CH Hg>2

s

3

^Q)-CHCH-J

0.70

2

CI -2

2

1-67

260 253

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

7.

Aromatic Azomethine Polymers & Fibers

M O R G A N ET AL.

Table 6. Diamine Components

CH

Aromatic Azomethine Copolymers Dialdehyde Components

3

107

* inh dL/g in H SQ 2

4

Polymer Melt Temperature, °C

1.9

260

0.60

272

0.70

150

80/20

50/50

^

/-(CH ) 2

6

--

CH / 3

50/50

Figure 1 shows the type of v a r i a t i o n that was observed for a series of copolymers from 2-methyl-l,4-phenylenediamine, 1,4phenylenediamine and terephthalaldehyde. The methyl-substituted homopolymer i s at the l e f t with decreasing amounts of substitution toward the r i g h t . The samples were from d i f f e r e n t preparations and had d i f f e r i n g inherent v i s c o s i t i e s . The spread i n melting temperatures i s greatest i n the middle range of compositions. There appears to be a r i s e i n average melting temperature at low modification and then the usual depression i n melting f o r copolymers with non-isomorphous u n i t s . With less than forty percent substitution of repeat units the polymers do not melt before decomposition. The r e s u l t s f o r another copolymer series i s presented i n a d i f f e r e n t way i n Figure 2. The p a r t i a l plots show melting points based on DTA determinations and the temperature at which f i b e r s could be pulled from the melt. The horizontal scale i s the proportion of Y-component. In t h i s series a l l of the polymers were prepared i n a melt system by reaction of the diamines with a bisazomethine. There was some v a r i a t i o n i n inherent v i s c o s i t y which appears not to have affected the r e g u l a r i t y of the data. As was stated e a r l i e r , the aromatic polyazomethines described form l i q u i d c r y s t a l l i n e melts. The presence of l i q u i d c r y s t a l l i n i t y can be determined by observing the high l i g h t transmittance of the melt and i t s texture on the hot stage of a microscope with crossed p o l a r i z e r s . For a more quantitative examination the microscope can be equipped with a photometer and a recorder for p l o t ting the transmitted l i g h t and the temperature of the sample on the hot stage (15). Because of the tendency of the polyazomethines to

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

108

POLYMERS FOR FIBERS A N D E L A S T O M E R S

375

= N

0(2)

-^O)- N = CH

o is arithmetical mean ( ) is number of samples

3

350

= N - ^ N

= 325

CH

CH =

f(5)

x+ y i 300

1

(3)

275

250 -

?(4) (7)

225 0

Figure 1

10 20 30 40 50 60 Mol Percent 1,4-Phenylenediamine in Diamine Fraction

Relation of polymer melt temperature and composition f o r a series of copolyazomethines from 2-methyl-l,4-phenylenediamine, 1,4-phenylenediamine and terephthalaldehyde.

polymerize further at high temperatures, i t was found desirable to pre-press t h i n films f o r t h i s test and use a high heating rate. Figure 3 provides a t y p i c a l plot with an anisotropic melt range, followed by a sharp decline i n l i g h t transmittance. This l a t t e r region can be a nematic-isostropic phase t r a n s i t i o n , although at the high temperatures one must be careful to observe whether there i s polymer decomposition. Most of the polymers have been examined by t h i s method of thermal o p t i c a l analysis. The aromatic polyazomethines are colored yellow, orange, red or brown but not black as has been reported i n some e a r l i e r studies. Burgi and Dunitz (13) have examined the structure of benzylideneaniline by X-ray d i f f r a c t i o n and determined the bond angles and r i n g arrangement i n the s o l i d state (see Figure 4). The angles at the trans azomethine unit are such that there i s only a 2.8° deviation from p a r a l l e l extension of the bonds to the phenyl r i n g s . The phenyl r i n g attached to nitrogen i s twisted out of the plane of the azomethine unit by 55.2° and the other r i n g has a 10.3° twist i n the opposite d i r e c t i o n . Substituents have an e f f e c t on these angles. By analogy the polymers would be expected to have a moderate degree of color because of the l i m i t e d range of conjugation brought about by the out-of-plane twist of the aromatic r i n g s .

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

109

Aromatic Azomethine Polymers & Fibers

7. MORGAN ET AL.

350 = N^O)-CH -CH ^O^N= ?

o Melting with fiber formation A DTA melting

?

^-o—6

300

"=N^O^-N=J

/

=CH, ^ C H = | CI Jx

+

/

//

250 CH Br + CF3CF2CFCF3

(3)

3

With this information in hand, we investigated the curing process of these fluoroelastomers by examining the amount and

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

10.

ill

Fluoroelastomers

SCHMIEGEL AND LOGOTHETIS

TABLE 3 POST CURE EFFECT ON PROPERTIES PEROXIDE

BISPHENOL PRESS CURE POST CURE

PROPERTIES

5.0

7.9

5.0

7.9

10.0

13.8

9.7

15.9

225

175

165

150

85

0

52

Miooi MPa T , MPa B

PRESS CURE POST CURE

E % B

COMPRESSION SET (70 HRS/200°C) 0-RIN6S PELLETS PRESS CURE POST CURE

10 MINS at 177°C

- 24 HRS at 232°C

Reproduced with permission from Ref. 6 c . Copyright 1982 Rubber Chem. Technol.

A - "DIAK" 1 B - PEROXIDE C - BISPHENOL

0

I 0

1 5

204°C, under N GUM STOCKS

1 10 HOURS

2

1 15

J 20

Figure 1 1 . The c r o s s l i n k density of various cure systems plotted as a function of post-cure time at 2 0 4 °C under nitrogen. Reproduced with permission from Ref. 6 c . Copyright Chem. Technol.

1982 Rubber

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

178

P O L Y M E R S F O R FIBERS A N D

ELASTOMERS

nature of the volatile by-products generated during a peroxide cure. Fully compounded stocks containing the fluoroelastomers, carbon black, metal oxide, peroxide, and radical trap were used. Hie total amount of volatile materials i s proportional to the amount of peroxide present. A typical analysis i s shown in Table 4. Among organic fragments, acetone i s the largest component. Surprisingly, methane and, especially, methyl bromide are present in the gas mixture in relatively low concentrations. Hie water formed comes from the calcium hydroxide and from water dissolved in the polymer. When the radical trap, triallylisocyanurate, i s omitted, the methyl bromide concentration increases by 100% but s t i l l remains relatively low. If the peroxide i s omitted, water i s the only volatile product. I f the peroxide i s retained and the metal oxide and the triallylisocyanurate are both omitted, the isobutene concentration increases dramatically. Hie isobutene i s formed by dehydration of t-butanol reactions taking plac The primary decomposition product i s the t-butoxy radical which may abstract a hydrogen atom to give T-butanol (minor reaction) or decompose into acetone and a methyl radical (major reaction). Hie methyl radical, in turn, can abstract a bromine atom from the polymer to give methyl bromide (a minor reaction) or add to the triallylisocyanurate to give a more stable radical intermediate. These intermediate radicals abstract bromine from the polymer to generate polymeric radicals (see Figure 13). The driving force for the chain reaction during propagation i s the transfer of a bromine atom from the electron-poor fluoropolymer to an electron-rich hydrocarbon radical on the coagent. Crosslinking takes place when the polymeric radicals add to the a l l y l i c bonds of the trifunctional coagent. Hie coagent, therefore, becomes the crosslinker and in order to give optimum properties i t should be (a) an efficient radical trap, (b) multifunctional, and (c) thermally and oxidatively stable. Conclusion Peroxide-curability of vinylidene fluoride-based fluoroelastomers becomes possible by incorporating a bromine or iodinecontainng monomer. An organic peroxide, coagent, and an acid acceptor are necessary to obtain good cures. These results support the following cure mechanism: Initiation: Generation of position. Propagation: Generation of reaction in which a bromine Crosslinking: Addition of functional coagent.

alkyl radicals via peroxide decomradicals on the polymer via a chain or iodine atom i s abstracted. the polymeric radicals to the t r i -

Since the crosslinking molecule i s the coagent, i t s structure determines how effective i t i s as a radical trap and how stable the network w i l l be to thermal and oxidative attack.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

10.

Fluoroelastomers

S C H M I E G E L A N D LOGOTHETIS

OFF-GAS ANALYSIS

TABLE 4

RECIPE:

POLYMER

100 (5.6 mmoles BROMINE)

MT BLACK Ca(0H)

179

30 4

2

2,5-DIMETHYL-2,5-Di-tBUTYL PEROXY HEXANE

4 (5.5 mmoles)

TRIALLYL ISOCYANURATE VOLATILES- ACETONE, mmoles

9.45

tBuOH

0.78

CH Br

0.18

3

CH

2.68

4

C H 2

0.26

4

C H + C H mmoles

0.41

C H

0.39

3

6

3

8

mmoles

H

CONDITIONS - 40°C/MIN TO 190°C, HELD AT 190°C/10 MINS UNDER HELIUM ATMOSPHERE

Reproduced with permission from Ref. 6c. Copyright 1982 Rubber Chem. Technol. CH CH I I CH3—C—CHgCHg—C C H 3 3

3

—

CH, I CH,-C-0« I CH,

(MAJOR)

3

0 1 0 1 CH3-C-CH3 CH,

CH I CH -C-0» I CH,

0 I 0 I CH3-C-CH3 CH,

0

3 3

3

3

CH « + CH3-C-CH3

(MAJOR)

( C H ) C - 0 H + R»

(MINOR)

3

RH 3

3

= COAGENT

Figure 12. The most probable reactions r e s u l t i n g from peroxide decompo s i t ion. Reproduced with permission from Ref. 6c. Copyright 1982 Rubber Chem. Technol.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

180

POLYMERS FOR FIBERS A N D

ELASTOMERS

PROPAGATION

RADICAL TRAP

Figure 13.

POLYMERIC RADICAL

CROSSLINKED NETWORK

The main reactions of the proposed c r o s s l i n k i n g mechanism.

Reproduced with permission from Ref. 6c. Chem. Technol.

Copyright 1982 Rubber

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

10.

Fluoroelastomers

SCHMIEGEL AND LOGOTHETIS

181

Curing with nucleophiles does not require any specific cure site. As i t was shown i n the case of bis-phenols, curing requires the additional presence of an accelerator and a metal oxide base. Hie results described i n this paper support the following mechanisms: Step 1 - Reaction between bis-phenol, phosphonium accelerator and metal oxide to give R P OArOH. Step 2 - Attack by R»»P OArOH on the polymeric backbone to generate double bonds. Step 3 - Nucleophilic attack by R*P OArOH on the unsaturated sites to form crosslinks. H

The selection of the bis-phenol i s important because i t s structure determines the cure rate and the stability of the resultant network.

Literature Cited 1. 2. 3.

4. 5. 6.

7. 8. 9. 10. 11. 12. 13.

D. C. Thompson and A. L. Barney, Kirk-Othmer Encyclopedia of Polymer Science and Technology, 1971, 14, 611. R. G. Arnold, A. L. Barney and D. C. Thompson, Rubber Chem. Technol., 1973, 46, 169. J. F. Smith, Rubber World, 1960, 142, 103; J. F. Smith and G. T. Perkins, J. Appl. Polym. Sci., 1961, 5, 460; K. L. Paciorek, L. C. Mitchell, and C. T. Lenk„ J. Polym. Sci., 1960, 45, 405; K. L. Paciorek, W. G. Laginess, and C. T. Lenk, J. Polym. Sci., 1962, 60, 141; D. K. Thomas, J. Appl. Sci., 1964, 8, 1415; T. L. Smith, J. Polym. Sci., Part A-2, 1972, 10, 133. A. L. Moran and D. B. Patterson, Rubber Age, 1971, 103, 37. W. W. Schmiegel, Kaut. Gummi Kunst., 1978, 31, 137; Angew. Makromol. Chem., 1979, 76/77, 39. (a) J. W. Finlay, A. Hallenbeck, and J. D. MacLachlan, J. Elastomers Plast., 1978, 10, 3. (b) D. Apotheker and P. J. Krusic, U.S. Patent 4 035 565, 1977; U.S. Patent 4 214 060, 1980. (c) D. Apotheker, J. B. Finlay, P S. Krusic and A. L. Logothetis, Rubber Chem. Technol., 1982, 55, 1004. P. Tarrant and J. P. Tandon, J. Org. Chem., 1979, 34, 864; A. H . . Fainberg and W. T. Miller, Jr., J. Am. Chem. Soc., 1957, 79, 4170. G. E. Decker, R. W. Wise, and D. Guerry, Rubber Chem. Technol., 1963, 36, 451. P. J. Krusic and J. K. Kochi, J. Am. Chem. Soc., 1971, 93, 846. K. S. Chen, P. J. Krusic, and J. K. Kochi, J. Phys. Chem., 1974, 78, 2030. (a) A. W. Pogiel, J. Polym. Sci. Symp., 1975, 53, 333. (b) U. Flisi, G. Giunchi and S. Geri, Kaut. u. Gummi Kunst., 1976, 29, 118. D. B. Pattison, U.S. Patent 3 876 654, 1975. R. C. Ferguson, J. Am. Chem. Soc., 1960, 82, 2416.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMERS FOR FIBERS A N D E L A S T O M E R S

182

14. 15. 16.

S. H. Kalfayan, R. H. Silver, and S. S. Liu, Rubber Chem. Technol., 1976, 49,, 1001. S. H. Kalfayan, R. H. Silver and A. A. Nazzeo, Rubber Chem. Technol., 1975, 48, 944. P. Meakin and P. J. Krusic, J. Am. Chem. Soc., 1973, 95, 8185; B. E. Smart, P. J. Krusic, P. Meakin, and R. C. Bingham, J. Am. Chem. Soc., 1975, 96, 7385; K. S. Chen, P. J. Krusic, P. Meakin, and J. K. Kochi, J. Phys. Chem., 1974, 78, 2036; P. J. Krusic and R. C. Bingham, J. Am. Chem. Soc., 1976, 98, 230.

R E C E I V E D F e b r u a r y 6, 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

11 Rubber Processing Through Rheology JEAN L. LEBLANC Monsanto Europe S.A., 270-272, Avenue de Tervueren, B-1150Bruxelles, Belgium

This paper gives some insights into the growing under­ standing of the particular flow phenomena associated with rubber processing particular operations extrusion. Using simple capillary rheometry experimen­ tal results, the importance of elongational flow and energy absorption processes is demonstrated in the mixing of natural rubber. The rôle played by the converging zone at the entrance of short extrusion dies is underlined and estimated using experimental data. In addition, some particular effects typical of heterogeneous rubbery materials are presented and their significance in rubber processing discussed. The discussion i n rheological terms of the problems associated with rubber processing i s r e l a t i v e l y recent and results from theoretical and experimental progress i n understanding flow properties of pure polymers, and p a r t i c u l a r l y thermoplastics. However the rheology of elastomers i s further complicated by the necessary presence of f i l l e r s , p l a s t i c i z e r s and other ingredients. These lead to peculiar flow properties associated with heterogeneous matter and therefore not yet well understood. The aims of this presentation are to give some insights into the growing understanding of the p a r t i c u l a r flow phenomena involved i n rubber processing. Rather than give a general survey of the numerous flow situations i n rubber processing, attention w i l l be focused on two p a r t i c u l a r operations, i . e . internal mixing and extrusion. Using experimental r e s u l t s , the main rheological effects associated with rubber processing w i l l be demonstrated and their significance underl i n e d . In addition, some p a r t i c u l a r effects t y p i c a l of heterogeneous rubbery materials, such as thermoplastic elastomers, w i l l be presented and their significance i n rubber processing discussed. Most of the results discussed i n this paper have been obtained through a suitable use of the Monsanto P r o c e s s a b i l i t y Tester, and therefore this paper w i l l also consist i n an i m p l i c i t demonstration of the usefullness of this v e r s a t i l e instrument. 0097-6156/ 84/ 0260-0183S07.00/ 0 §> 1984 A m e r i c a n C h e m i c a l Society

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

184

POLYMERS

FOR FIBERS A N D

ELASTOMERS

Rheology and mixing rubber Preparing rubber compounds by blending of raw elastomers and mixing f i l l e r s , o i l s and other ingredients into rubbers i s a fundamental operation i n the rubber industry which, s u r p r i s i n g l y , has been the object of l i t t l e work u n t i l recently. The aims of mixing are to incorporate and uniformly disperse the various ingredients within the elastomer matrix, i n such a way that easy processing, e f f i c i e n t curing and adequate end-use properties w i l l be obtained. This operation i s generally achieved i n internal mixers which are thoroughly described elsewhere (1, 2). Physics of mixing. The mixing of rubber compounds i s a very complex operation about which i t i s d i f f i c u l t to have an o v e r a l l and clear understanding (3-5). However, i t i s useful to consider that four basic physical operations take place during the mixing cycle (1). For the sake of discussion described with respect t Figure 1: 1. The incorporation of ingredients, either s o l i d or l i q u i d , i n the elastomer takes place at the beginning of the mixing cycle. More s p e c i f i c a l l y , this operation concerns the 'wetting of s o l i d particles which, according to Tokita and P l i s k i n (6) and Nakajima (8), can occur following two mechanisms: (i) large deformation of the elastomer increases the contact area with f i l l e r p a r t i c l e s and seals them inside, ( i i ) the elastomer breaks down into small pieces, mixes with the f i l l e r agglomerates and once again sealing occurs. If the former mechanism can e a s i l y be observed i n an open m i l l , the l a t t e r i s not necessarily apparent because these phenomena occur on a micro-scale. The incorporation involves a decrease i n the s p e c i f i c volume of the mix (6). 2. The dispersion results i n progressive spreading of f i l l e r p a r t i c l e s . This operation involves a reduction i n size of f i l l e r agglomerates, possibly to their ultimate p a r t i c l e size and, generally takes place between the two power peaks. An attempt i n t h e o r e t i c a l l y predicting the dispersive mixing process from fundamental considerations has recently been published (7). 3. The p l a s t i c i z a t i o n modifies the rheological properties of the mix mainly a v i s c o s i t y decrease by mechano-chemical degradation of the polymer and modification of i t s v i s c o e l a s t i c properties. 4. The d i s t r i b u t i o n or simple mixing involves the moving of p a r t i c l e s throughout the compound, without changing their physical shape, i n order to increase the randomness of the s p a t i a l d i s t r i b u t i o n and therefore the entropy of the mix. This elementary physical process takes place during the whole mixing cycle. To describe p r a c t i c a l mixing with a set of four basic physical operations i s c l e a r l y an o v e r s i m p l i f i c a t i o n since, to a c e r t a i n extent, a l l actions occur simultaneously. This description helps however i n introducing the rheology of mixing. 1

Mixing rheology - l u b r i c a t i o n theory. When considering only the nip region, i t i s possible to develop a rheological approach based on the l u b r i c a t i o n theory (11). Analyses by Bernhardt (3), Bolen and

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

Rubber Processing Through Rheology

LEBLANC

Mechanisms

of

filler

incorporation

(i)

(

In f a c t , as seen i n the previous section (see Figure 6), the o v e r a l l extrusion pressure AP consists of several components, i . e . AP - AP + AP,. + P . (15) ent die exit where A P , AP^^g and it Pressure drop, the pressure gradient within the die and the exit pressure respectively. Since P £ i s generally very small, i t can be neglected i n f i r s t approximation and i t follows that: AP . = AP (16) die en And since the Bagley correctio entrance pressure drop effects (and the n e g l i g i b l e exit e f f e c t s ) , i t can be written that: p

e n t

e x

a

e

r

e

t l i e

e

n

t

r

a

n

c

e

x

t

A

AP

4 -

+

l

V

4i

AP - AP _

4i

Equation (17)allows an estimation of the entrance pressure drop, A P , to be calculated, knowing the extrusion pressure and the Bagley correction, as follows: ent

(—) . o ent D

AP

AP

ent

1 •

D

(18)

«o ent

o

At the entrance of a die, there i s a converging f i e l d which produces a strong extensional flow. Cogswell (24) has suggested a procedure for c a l c u l a t i n g an 'apparent extensional v i s c o s i t y , ^ E C * from measurements of entrance flow. Since neither the l o c a l normal stresses nor the l o c a l extension rate can be calculated d i r e c t l y from measurable quantities, i t i s necessary to make a number of assumptions about the flow. Cogswell assumes that the entrance pressure drop, A can be represented as a sum of two terms, one related to shear and the second to extension. He further assumes that the f l u i d follows streamlines that r e s u l t i n the minimum pressure drop, and for a f l u i d having a power law v i s c o s i t y function, he derived the following equation for an 'apparent extensional 1

p

e

v i s c o s i t y ' , TI Q E

z

9(n+l) (AP_J ent "EC

32 n

(19)

1

where n i s the flow index, and n « .the apparent v i s c o s i t y at shear rate Y . a^ #

Y

a

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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Using experimental r e s u l t s obtained with the three Santoprene grades studied, the entrance pressure drop and the apparent extensional v i s c o s i t y were calculated according to equations (18) and and (19). Results are given i n graphical terms i n Figures 11 and 12 respectively. Figure 11 shows that, as expected, the entrance pressure drop increases with increasing shear rate. In addition, the AP vs y curves of the three samples are s i g n i f i c a n t l y d i f f e r e n t , obviously related to the rubber p a r t i c l e content. The lower the hardness the higher the entrance pressure loss. As f a r as entrance effects are i n d i c a t i v e of the magnitude of melt e l a s t i c i t y , i t i s e a s i l y understood that the higher the rubber p a r t i c l e content, the higher the melt e l a s t i c i t y . This r e s u l t associated with the fact that the extrudate swell of Santoprene decreases with increasing rubber content indicates the l i m i t s of the analogy between OTV's and highly f i l l e d polymer. Indeed, the analogy can only be correct i f ' e l a s t i c f i l l e r s ' are considered seem to converge at ver rheological behaviour of OTV's i s controlled by the existence of a connective structure of rubber p a r t i c l e s , progressively destroyed when shear increases, as suggested by Goettler, Richwine and Wille (32). As far as Cogswell's approach i s correct i n estimating elongational v i s c o s i t y from entrance pressure drop, Figure 12 presents very interesting r e s u l t s . As can be seen, the 'extensional v i s c o s i t y ' increases with decreasing hardness of the material. This can be explained using the connective structure model pointed out above. These p a r t i c l e associations however are more l i k e l y to form while the melt i s not under shear and therefore, the 'apparent elongational v i s c o s i t y ' at die entrance i s decreasing when shear rate increases. As the connective structure i s destroyed, the entrance flow resistance i s weaker. In addition, i t seems that the r w v s Y curves exhibit a maximum, depending upon the rubber content. The higher the rubber content, the lower the shear rate for this maximum. As can be seen i n Figure 12, the 40D grade exhibits an increasing elongational v i s c o s i t y below 30-40 s ~ l and a decreasing n £ at higher shear rate. Lower hardness grades probably exhibit the same behaviour but with the maximum a r i s i n g at lower shear rate. Whilst not yet f u l l y understood these r e s u l t s c l e a r l y demonstrate that the processing rheology of Santoprene thermoplastic rubbers i s dominated by singular e f f e c t s associated with the connective structure of rubber p a r t i c l e s . a

E

Conclusions The rheological approach to rubber processing allows a better understanding of the flow behaviour of elastomers to be achieved. Obviously the picture i s f a r from being complete and due to their complexity, rubber compounds are exhibiting phenomena not yet completely understood. The s p e c i f i c examples presented i n t h i s paper, either i n mixing rubber compounds, or i n shaping through short dies or when considering the melt rheology of thermoplastic elastomers, demonstrate c l e a r l y that one has to pay as much attention to elongational flow as to shear flow i n rubber processing s i t u a t i o n s .

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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POLYMERS F O R FIBERS A N DE L A S T O M E R S

500 Elongational, viscosity T = 204°C

100 kPa.s

SANTOPRENE®

10 201-87

3 1D

1

I

• 2

10 Apparent shear

1

io rate

3

>^

•

S"

203-40 . i

• i i i i 1

4

10

Figure 11 :Entrance pressure drop versus shear rate f o r Santoprene thermoplastic elastomers at 204°C

Apparent

shear

rate

Figure 12 :Apparent elongational v i s c o s i t y versus shear rate f o r Santoprene thermoplastic elastomers at 204°C

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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Correct and imaginative use of suitable rheological equipment, such as the Monsanto P r o c e s s a b i l i t y Tester, allows pertinent information to be obtained at lower cost than the c l a s s i c a l t r i a l and-error approach. Furthermore, better cost e f f i c i e n c y can be achieved when interpreting c a p i l l a r y rheometer results i n terms of processing and selecting the best operating conditions with respect to material flow properties. Acknowledgements The author wishes to thank Dr. M. Bristow of Malaysian Rubber Producers Research Association - Brickendonbury, U.K. who kindly supplied various grades of natural rubber. He i s grateful to Dr. L.A. Goettler and Mr. J . Sezna from Monsanto Polymer Products Company, Akron, Ohio, f o r the experimental data on Santoprene thermoplastic rubbers used i n this paper.

Literature (1) H. PALMGREN - Rubb. Chem. Technol. 48, 462 (1975) (2) J.M. FUNT - "Mixing of Rubbers" - RAPRA, Shrewsbury, England (1977). (3) E.C. BERNHARDT - "Processing of thermoplastic materials" van Nostrand Reinhold, New York, pp 424-446 (1959). (4) J.M. McKELVEY - "Polymer Processing" - chap.12, Wiley, New York (1962). (5) P.S. JOHNSON - Elastomerics, 115 (1), 9, January 1983. (6) N. TOKITA and T. PLISKIN - Rubb. Chem. Technol.,46, 1166 (1973). (7) I. MANAS-ZLOCZOWER, A. NIR and Z. TADMOR - Rubb. Chem. Technol., 55 (5), 1250 (1982). (8) N. NAKAJIMA - Rubb. Chem. Technol.,53, 1088 (1980). (9) W.M. WIEDMANN and H-M. SCHMID - Rubb.Chem.Techno1. 55, 363(1982) (10) P.K. FREAKLEY and W.Y. VAN IDRIS - Rubb.Chem.Technol.,52, 134 (1979) (11) H. LAMB - "Hydrodynamics" - chap. XI, pp 583, Dover Publ., New York (1945). (12) W.R. BOLEN and R.E. COLWELL - SPE Antec, 14, 1004 (1958). (13) J.L. WHITE and N. TOKITA - J . Appl. Polym. Sc., 12 1589 (1968). (14) J.L. WHITE - Polym. Eng. Sc., H) (11), 818 (1979). (15) K. ODA, J.L. WHITE and E.S. CLARK - Polym. Eng. Sc., 18, 25 (1978). (16) G.R. COTTEN - Plastics and Rubber : Processing, 4 (3),89 (1979). (17) J . MEISSNER - Trans. Soc. Rheol., 26, 405 (1972). (18) N. NAKAJIMA - Polym. Eng. Sc., 19, 215 (1979). (19) G.M. BRISTOW - NR Technology, 10 (3), 53 (1979). (20) J.L. LEBLANC - Plastics and Rubber Processing and Applications, Vol.1, No 2, 187 (1981) (21) G.M. BRISTOW and A.G. SEARS - NR Technology, 11 (3), 45 (1980); ibid, 11 (4), 77 (1980); ibid, 12 (2),36 (1981) (22) S. MONTES and J.L. WHITE - Rubb. Chem. Technol, 55, 1354 (1982) (23) E.B. BAGLEY - J. Appl. Phys., 28, 624 (1957) (24) F.N. COGSWELL - Trans. Soc. Rheol., 16, 383 (1972) (25) J.M. McKELVEY - "Polymer Processing" - Chap. 2, sec. 2-7, p 51, Wiley, New-York (1962)

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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(26) (27) (28) (29)

C.D. HAN and M. CHARLES - Trans. Soc. Rheol., 15, 371 (1971) J.L. WHITE and A. KONDO - J . Non-Newtonian Fluid Mech.,3,41(1978) J.L. LEBLANC - Rubb. Chem. Technol., 54, 905 (1981) E.B. BAGLEY, S.M. STOREY and D.C. WEST - J. Appl. Polym. Sc., 7, 1661 (1963) (30) J.L. WHITE; A.P. PLOCHOCKI and h. TANAKA - Polym. Eng. Rev., Vol. 1, N° 3, 218 (1981) (31) A.Y. CORAN and R. PATEL - Rubb. Chem. Technol.,53, 141 (1980) (32) L.A. GOETTLER, J.R. RICHWINE and F.J. WILLE - Rubb. Chem. Technol., 55, 1448 (1982)

RECEIVED February 6, 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

12 Mesophase Formation in Polynuclear Aromatic Compounds A Route to Low Cost Carbon Fibers R. J. DIEFENDORF Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12181 P i t c h precursor carbon f i b e r s have the potential of providing good mechanica The high preferre planes that is necessary hig by forming a d i s c o t i c l i q u i d c r y s t a l p i t c h . Requirements for l i q u i d c r y s t a l l i n i t y are discussed for model compounds. These considerations are generalized and expanded to describe l i q u i d c r y s t a l formation i n pitches. The element carbon i n the form of graphite has the highest s p e c i f i c s t i f f n e s s (stiffness/kg) and highest t h e o r e t i c a l , t e n s i l e strength. While graphite i s s t i f f and strong i n the basal plane networks, i t i s compliant and weak normal to the planes. Furthermore, the layer planes can e a s i l y shear over each other i n perfect graphite. A problem to be solved i n producing a high performance carbon f i b e r i s how to a l i g n the graphite basal planes roughly p a r a l l e l to the f i b e r axis, and have a high defect structure such that basal plane shear i s d i f f i c u l t . Since graphite can not be dissolved and only melts at very high temperature under pressure, the f i b e r must be made from a precursor which can be converted subsequently to carbon. Desired c h a r a c t e r i s t i c s of the precursor are that i t : 1) develops an oriented structure which i s carried through to the carbon f i b e r , 2) has a high y i e l d of carbon, 3) i s cheap, and 4) i s easy to handle through the various processing steps such as spinning and carbonization. Pitch materials appear to be able to meet a l l four of these c r i t e r i a . Carbon Y i e l d The carbon y i e l d from pitches can be understood by studying the y i e l d s of the generic components of p i t c h using the method of corbett (1,2). The amounts of saturates, napthene-aromatics, polar aromatics & asphalentenes can be determined for d i f f e r e n t pitches for various 0097-6156/ 84/0260-0209S06.00/0 © 1984 A m e r i c a n C h e m i c a l Society

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

P O L Y M E R S FOR FIBERS A N D E L A S T O M E R S

210

heat treatment temperatures and times, Figure 1. Saturates and napthene-aromatics are observed to evaporate during heat treatment leaving the less v o l a t i l e polar aromatics and asphaltenes, Figure 2. The carbon y i e l d at 800°C i s found to be l i n e a r l y related to the amount of polar aromatics and asphaltenes i n the precursor p i t c h , Figure 3. Although y i e l d depends upon more than molecular weight, the carbonization of model polynuclear aromatic compounds indicates that a minimum molecular weight of 400 i s needed to prevent v o l a t i l i z a t i o n before molecular weight increasing, condensation reactions occur. Figure 4. From these r e s u l t s an asphaltene p i t c h would give a high y i e l d and would be low cost. Orientation Liquid c r y s t a l l i n i t y i s determined by the length to diameter r a t i o , L/d, for rod-like molecules, and diameter to thickness, D/h, for d i s c - l i k e molecules c r y s t a l l i n i t y i n rod-lik and i n d i s c - l i k e molecules with D/h r a t i o s greater than 3.5 (4,5) . Liquid c r y s t a l l i n i t y i s observed i n the rod-like para polyphenylene series when the L/d r a t i o approaches or exceeds 6.3, Figure 5. While both quinque- and s e x i - paraphenyl have s u f f i c i e n t l y high L/d r a t i o s to form r o d - l i k e l i q u i d systems, no d i s c - l i k e polynuclear aromatic compounds are available with a high enough D/h r a t i o to form a l i q u i d c r y s t a l . Ovalene, which has ten fused rings, i s close (D/h=3.0-3.2), but l i q u i d c r y s t a l l i n i t y has not been observed for i t or for the binary system of ovalene/coronene, Figures 5. Ovalene has a melting point of 472°C. Presumably, fused ring systems with higher D/h would have higher melting points, and thermal decomposition would occur before the crystalline/mesophase t r a n s i t i o n temperature i s reached. Brooks and Taylor (6) showed that heat treatment of coal tar and petroleum p i t c h forms a l i q u i d c r y s t a l (mesophase) with d i s c o t i c symmetry. Generally, mesophase formation was assumed to occur by polymerization and condensation of smaller p i t c h molecules to form large planar aromatics. I t i s true that the molecular weight increases upon heat treatment, but our studies on carbon y i e l d indicates that v o l a t i l i z a t i o n might be more important than polymerization and condensation. I f so, the o r i g i n a l i s o t r o p i c p i t c h already may contain the mesogenic species. Mesophase can be observed i n pitches which have a higher molecular weight than ovalene yet can have a softening point well below the melting point of ovalene. Several factors cause t h i s . F i r s t l y , a wide range of species with d i f f e r i n g molecular weights and structures are present i n a p i t c h . Melting point depression w i l l occur, and mesophase regions may be uncovered. For example, i n a binary eutectic system, two nonmesogenic compounds often w i l l "uncover" a l i q u i d c r y s t a l l i n e region near the eutectic composition where the melting point depression i s greatest, Figure 6. Secondly, the wide range of species makes c r y s t a l l i z a t i o n sluggish, so that the systen can be supercooled and mesophase may form before c r y s t a l l i z a t i o n occurs or the glass t r a n s i t i o n temperature i s reached. Thirdly, mesophase pitches often appear to consist of f l e x i b l y linked polynuclear aromatics with three to s i x rings with a number average molecular weight of 1000 or more. By analogy with calculated e f f e c t s of adding f l e x i b l e l i n k s to r i g i d - r o d molecules, the softening point i s more

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

12.

Mesophase Formation in Polynuclear Aromatics

DIEFENDORF

saturates

saturates

naphthene aromatics

naphthene aromatics

saturates

naphthene aromatics

naphthene aromatics

polar aro.

211

naphthene aromatics polar aro.

polar aromatics

asphaltene

asphaltene

polar aro. polar grornatics

asphaltene

Carbon Black Oil R

Carbon Black Oil B

Figure 1 .

Dau Bottom

Ashland 240

CTP

Ashland

240

260

The saturate, napthene-aromatic, polar aromatic, and asphaltene content of valious pitches and heavy o i l s .

CARBON BLACK OIL B 4 2 5 «fc

ABSOLUTE

saturates

FRACTIONATION

naphthene aromatics

naphthenes I—naphthenes———* M—napiimeiieo Jj--polar a r o m a t i c s — — polars — polar aromatics asphaltenes

asphaltenes

asphaltenes

asphaltenes

asphaltenes mesophase

- mesophase-

AS RECEIVED Figure 2.

38

MIN

68MIN

117MIN

256MIN

The generic fractions for a c a t a l y t i c cracker o i l upon heat treatment at 425C.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

212

POLYMERS

F O R FIBERS A N D

ELASTOMERS

100

200

Molecular Figure 4.

400

600

800

Weight

The carbon y i e l d of polynucleat aromatic compounds upon heating to 800C.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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Mesophase Formation in Polynuclear Aromatics

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depressed than the mesophase/isotropic t r a n s i t i o n temperature. Fourthly, short a l k y l side arms on the polynuclear aromatic cores may enhance mesophase formation s i m i l a r l y to the effects of a l k y l t a i l s on rod-like l i q u i d c r y s t a l s . F i n a l l y , mesophase pitches have many of the c h a r a c t e r i s t i c s of lyotropic l i q u i d c r y s t a l systems. In t h i s case, low molecular weight nonmesogenic species act as solvents or p l a s t i c i z e r s for the high molecular weight mesogenic species. Without these low molecular weight p l a s t i c i z e r s , the high molecular weight species would decompose before a sample could be heated hot enough to form f l u i d mesophase. These f i v e factors which enhance formation of mesophase are hard to study independently. Chemical reactions are occuring at the temperatures required to study p i t c h mesophase such that the system c h a r a c t e r i s t i c s are continuously changing. V i s c o s i t y i s also f r e quently high, and o p t i c a l microstructures can be misleading as e v i dence for mesophase formation. Quenched and slow cooled specimens may appear i s o t r o p i Pitches are not very idea altered by s o l u b i l i t y considerations, which considerably clouds interpretation of experimental data. F i n a l l y , the complexity of a pitch makes the a n a l y t i c a l characterization very d i f f i c u l t (10,11). Simple averages such as number average molecular weight are just i n s u f f i c i e n t , and even these values may be hard to measure properly (12). These problems make for ambiguities i n the interpretation of experimental data. A gross s i m p l i f i c a t i o n i s to c l a s s i f y p i t c h molecules into two general groups. One group consists of mesogens with r e a l mesophase/ i s o t r o p i c t r a n s i t i o n temperatures (T&), Figure 7. Generally, the higher molecular weight, more aromatic species would belong to t h i s group. Mesogenic species where the mesophase/isotropic transition temperature i s just above the softening point would be e a s i l y d i s rupted by small additions of non-mesogenic species. Larger mesogenic species would have higher mesophase/isotropic t r a n s i t i o n temperatures, and would require larger amounts of non-mesogenic species to destroy the mesophase. The second group consists of nonmesogens which have v i r t u a l t r a n s i t i o n temperatures (Ty), e.g., the mesophase/isotropic t r a n s i t i o n temperature i s below the softening point and only an i s o t r o p i c l i q u i d i s observed. Nonmesogens which have v i t r u a l transi t i o n s temperatures close to the softening point w i l l not be very disruptive to a mesophase, while a nonmesogen with a low v i r t u a l t r a n s i t i o n temperature would be very d i s r u p t i v e . Also, an i s o t r o p i c pitch may contain an appreciable quantity of mesogens. The only requirement i s that the t r a n s i t i o n temperature (range) be v i r t u a l , e.g., below the softening point. S i m i l a r l y , a mesophase p i t c h may contain appreciable quantities of nonmesogenic species. In a two phased, i s o t r o p i c & mesophase pitch, both phases w i l l contain mesogeni c & nonmesogenic species but with d i f f e r e n t r e l a t i v e concentrations. The proof that an i s o t r o p i c p i t c h can contain an appreciable mesogenic component can be obtained by removing a s u f f i c i e n t amount of the nonmesogenic species. V o l a t i l i z a t i o n has been successfully used to reduce the lower molecular weight nonmesogenic species. However, appreciable chemical reaction occurs at the temperatures required to remove the less v o l a t i l e nonmesogens. Hence, the chemical reactions may be the cause for mesophase formation rather than v o l a t i l i z a t i o n . Solvent fractionation of pitches circumvents t h i s problem as the

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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Figure 5.

The chemical structures of quinque parapolyphenylene and ovalene.

ISOTROPIC

LIQUID

NONMESOGEN A

Figure 6.

NONMESOGEN B

A schematic binary phase diagram of two nonmesogens which show mesophase formation near the eutectic composition.

Molecular Weight

Figure 7.

A schematic i l l u s t r a t i n g that an i s o t r o p i c p i t c h can be considered to consist of mesogens and nonmesogens.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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separation can be carried out at ambient temperature. The wide range of a v a i l a b l e solvents allows a t a i l o r i n g of the separation process (13). This technology i s a c r i t i c a l factor i n producing low cost carbon f i b e r s as i t allows a 100% mesophase p i t c h to be made which can be spun at temperatures where chemical reactions occur slowly. (The 100% mesophase structure produces high modulus i n the carbon f i b e r . ) E a r l ier p i t c h precursor carbon f i b e r s were made from pitches containing only 55% mesophase to allow a suitable, lower spinning temperature. Solvent separations depend on solvent/solute i n t e r a c t i o n s , and the mesogen/nonmesogen separation obtainable with solvents may not be very good as solvent/solute interactions are not controlled by mesogenicity. However, the toluene insoluble f r a c t i o n of a commercial p i t c h , Ashland A240, d i r e c t l y forms mesophase upon heating. The gel permeation chromatogram for the whole p i t c h and the toluene soluble portion shows, by difference, that the toluene insoluble molecular, weight d i s t r i b u t i o n i s quite broad, Figure 8. Although the toluene soluble portion of the p i t c of mesogens, they do no without including too high an amount of nonmesogens. A f i n a l proof that mesophase formation i s mainly due to the physical separation of nonmesogenic species rather than chemical reactions was performed by adding 25% of Ashland A240 p i t c h back to the toluene insolubles of A240 mesophase p i t c h . Almost a l l the mesophase was destroyed upon heating even for t h i s r e l a t i v e l y minor addition of v i r g i n p i t c h (14). Grouping p i t c h molecules into mesogenic and nonmesogenic f r a c t i o n s allows construction of a "pseudo" binary phase diagram, Figure 9. Transition temperatures become broadened to t r a n s i t i o n temperature ranges because of the d i s t r i b u t i o n s . Conventional heat treatment of i s o t r o p i c pitches would increase the temperature to the heat treatment temperature with l i t t l e change i n composition. As the nonmesogens evaporate, the composition moves towards the mesophase region. I f the temperature i s s u f f i c i e n t l y high and the time s u f f i c i e n t l y long, the composition w i l l change u n t i l mesophase i s formed. By contrast, s o l vent f r a c t i o n a t i o n removes the nonmesogens and the composition w i l l be in the mesophase region. Heat treatment need only be severe enough to cause softening and s u f f i c i e n t domain growth to produce microscopically observable mesophase. In general, the mesophase/isotropic t r a n s i t i o n i s not observed i n mesophase pitches because of molecular weight increases at higher temperatures and coking. There are many types of natural and synthetic pitches. Some consist of large polynuclear aromatic cores with a large number of r e l a t i v e l y long a l k y l side arms which s o l u b i l i z e and soften the species. Others with similar softening points consist of r e l a t i v e l y small polynuclear cores with no or at most a few methyl groups attached. The structures for a solvent fractionated, c a t a l y t i c cracker mesophase p i t c h are i l l u s t r a t e d i n Figure 10, (15). The lowest molecular weight species are nonmesogenic but p l a s t i c i z i n g . The highest molecular species won't soften by themselves, but s t a b i l i z e the mesophase structure. The most probable molecule has a molecular weight of about 1000. Molecular structures are constructed by combining r e s u l t s from IR, UV/VIS, NMR, VPO, GPC, HPLC and elemental analysis (16). These structures are only based on the average a n a l y t i c a l r e s u l t s . Even for averages, a wide range of structures, only one of which i s i l l u s t r a t e d , can be drawn. Since molecules can deviate from these average r e s u l t s , a much wider range of structures w i l l exist with

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

216

POLYMERS FOR

FIBERS A N D

ELASTOMERS

A 240

Elution

Figure 8.

Time

—•

The gel chromatogram for Ashland A240 p i t c h and toluene soluble (TS) f r a c t i o n .

the

LU QC D QC UJ CL LU

SOLID

Mesogen

Figure 9.

Nonmesogen

A pseudo binary phase diagram which explains mesophase formation i n a p i t c h . MESOPHASE

MW=230

Figure 10.

MW= 950

PITCH

MW *

1400

Typical average chemical structures for the toluene insoluble f r a c t i o n of a c a t a l y t i c cracker pitch.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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217

the only requirement being that the d i s t r i b u t i o n must give the average analytical results. Processability Mesophase p i t c h can be melt spun into f i b e r s . Major requirements are that the p i t c h i s : 1) thermally stable at spinning temperatures, 2) free from p a r t i c u l a t e s , and 3) rheologically acceptable. Solvent fractionated mesophase pitches can be made which meet these three requirements. As spun strength of p i t c h f i b e r s i s low but i n the same range as some other commercially produced t e x t i l e f i b e r s . Subsequent processing to carbon f i b e r i s similar to that used for polyacrylonitrileprecursor carbon f i b e r . A more complete description of this process and f i b e r properties are presented i n the paper of Riggs & Diefendorf i n t h i Conclusions Calculation and model compounds show that a length to diameter r a t i o of 6.3 i s s u f f i c i e n t to form a r i g i d rod l i q u i d c r y s t a l . Similarly, c a l c u l a t i o n indicates that a diameter to thickness r a t i o of at least 3.5 i s required to form a d i s c o t i c l i q u i d c r y s t a l . Mesophase formation i n pitches i s enhanced by the broad molecular weight d i s t r i b u tions, f l e x i b l e l i n k s between polynuclear aromatic elements and a l k y l side groups. Generically, pitches can be considered to consist of two species: mesogenes and nonmesogens. Solvent fractionation can be used to p a r t i a l l y separate the two types of species. F i n a l l y , a 100% mesophase p i t c h can be produced which can be melt spun and processed into a carbon f i b e r with high mechanical properties. Acknowledgment The author i s indebted to h i s students, p a r t i c u l a r l y : S.H. Chen, D.M. Riggs, W.C. Stevens, and J . Venner. Special thanks should be given to S.H. Chen for the artwork and D. Ruddy for typing the manuscript.

References 1. 2. 3. 4. 5.

Riggs, D. M. ; Diefendorf, R. J. "Factors Controlling the Thermal Stability and Liquid Crystal Forming Tendencies of Carbonaceous Materials", Preprint, CARBON '80, Baden-Baden, 1980, pp. 330-333. Corbett, L. W. "Relationship Between Composition and Physical Properties of Asphalt" presented at the Assoc. of Asphalt Paving Technologists, Kansas City, Missouri, Feb. 1970. Riggs, D. M.; Diefendorf, R. J. "Thermal Stability of Aromatic Compounds", Extended Abstracts, 14th Biennial Conf. on Carbon, Pennsylvania State Univ., June 1979, pp. 350-351. Flory, P. J.; Ronca, G. "Theory of Rod-like Particles - Part II: Thermotropic Systems with Orientation-Dependent Interactions", Mol. Cryst. Liq. Cryst., 1979, Vol. 54, pp. 311-330. Alben, R., Phy. Rev. Lett. 24, p. 1041, 1970.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMERS FOR FIBERS AND ELASTOMERS

218 6.

Brooks, J. D.; Taylors, G. H. "Chemistry and Physics of Carbon", P. L . Walker, Jr. and P. A. Thrower, Eds., Marcel Dekker, New York, 1968, Vol. 4, pp. 243-268. 7. Smith, G. W. "Phase Behavior of Some Condensed Polycyclic Aromatics", Mol. Cryst. Liq. Cryst., Vol. 64, Letts., pp. 15-17. 8. Chen, S. H.; Diefendorf, R. J. "Mesophase Formation in Polynuclear Aromatic Compounds", Extended Abstracts, 16th Biennial Conf. on Carbon, U.C. San Diego, July, 1983, pp. 28. 9. Riggs, D. M.; Diefendorf, R. J., This volume. 10. Greinke; O'Conner, L. H. "Determination of Molecular Weight Distributions of Polymerized Petroleum Pitch by Gel Permeation Chromatography with Quinoline Eluent", Anal. Chem., 52, 1980, pp. 1877-81. 11. Chen, S. H., Stevens, W. C. and Diefendorf, R. J. "Molecular Weight and Molecular Weight Distributions in Pitches" International Symposium on Carbon, Toyohashi, Japan, 1982, pp. 59-72. 12. Chen, S. H.; Diefendorf of Pitches", Extende U. C. San Diego, July, 1983, p. 433. 13. Venner, J.; Diefendorf, R. J., This volume. 14. Riggs, D. M.; Diefendorf, R. J. "A Phase Diagram for Pitches", Preprint, CARBON '80, Baden-Baden, 1980, pp. 326-329. 15. Chen, S.H.; Diefendorf, R. J. Unpublished data. 16. Chen, S. H.; Diefendorf, R. J., This volume. 17. Riggs, D. M.; Diefendorf, R. J., This volume. RECEIVED January 17, 1984

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

13

P i t c h - S o l v e n t Interactions a n d T h e i r Effects on Mesophase Formation 1

J. G. VENNER and R. J. DIEFENDORF Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12181 High performance pitch carbon fiber can only be manufactured from mesophase forming pitches Generally commercially availabl heat-treatment to increas pitch by removing or condensing the low end species, prior to the mesophase formation. A selective solvent can also be used to remove the low molecular weight, mesophase-inhibiting species. The multidimensional solubility parameters of a solvent provide qualitative information as to the type of molecular interactions a solvent is capable of undergoing, and the suitability of a solvent for separating a mesophase-forming fraction from the pitch. The effects of varying the selective solvent and altering the pitch to solvent ratio are reported in this paper. High strength, high modulus, pitch based carbon fiber can be made from a precursor pitch which forms an anisotropic phase, or a mesophase. The aligned pitch molecules in the mesophase provide the fundamental structural elements of graphitizable carbons (1,_2). Unfortunately, commercially available pitches, such as Ashland A-240, are complex mixtures of mesophase forming species and mesophase disrupting species(3). A commercial pitch must be processed to remove the low molecular weight mesophase inhibiting species to provide a pitch fraction that will form a coalesced mesophase rapidly upon melting (Figure 1). Formerly, it was thought that a pitch could not form 100% coalesced mesophase without undergoing extensive heattreatments to increase molecular weight and aromaticity(4). The nonmesophase forming species were thought to react to form larger, planar molecular blocks more capable of alignment. Recently, however, Riggs and Diefendorf(5) patented the use of selective solvent as an alternative to extensive heat-treatments. A selective solvent can 'Current address: Exxon Enterprises Materials Division, Fountain Inn, SC 29644. 0097-6156/84/0260-0219S06.00/0 §> 1984 American Chemical Society

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

73

m Three-dimensional pseudo-phase diagram of a t y p i c a l p i t c h . Figure 1.

c/5

mr >

α

>

C/5

53 m73

73

C/5

*n Ο

m73

"0

Ο ζ

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

VENNER AND

13.

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Pitch-Solvent Interactions

221

dissolve many of the lower molecular weights, disordering species leaving the larger, more orientable species, insoluble. The i n s o l uble d i s t r i b u t i o n s are capable of forming a 100% coalesced structure rapidly upon melting provided enough of the low molecular weight species have been removed, and the insolubles have the proper structure to form a mesophase. The mesophase forming tendencies of a p i t c h f r a c t i o n depend l a r g e l y on the structure of the precursor p i t c h , and on the extraction c a p a b i l i t y of the solvent. Therefore, the selection of an extracting solvent and extraction conditions are c r i t i c a l . This research focused on answering three fundamental questions: 1. What solvents can be used to extract a f r a c t i o n from a commercial p i t c h (such as A-240) which i s capable of forming a coalesced mesophase r a p i d l y upon melting, and what c r i t e r i a w i l l predict their effectiveness? 2. What extraction conditions are c r i t i c a l ? 3. Can the extraction b fractions? Solvent

Selection

The regular d i s s o l u t i o n of a s o l i d i n a n o n - e l e c t r o l y t i c solvent has been described i n d e t a i l by Hildebrand(6) who showed that mole f r a c tion of s o l i d dissolved depends on the molecular weight of the s o l i d , (which a f f e c t s i t s enthalpy of fusion), i t s melting temperature, the system temperature, and the difference between the s o l b i l i t y parameter of the solvent and the solute. 4.575

F

•

L O g

1 x

=

AH m(Tm-T) 4.575TmT

ACD. Tm^T ACp log Tm 4.575 ( T )T7y87 T

2 ^ l

}

2

1

x^

= mole f r a c t i o n of s o l i d soluble i n solvent

(1)

AHm Tm ACp

= heat of fusion at the melting point = melting point of the s o l i d = the difference between the heat capacities of the s o l i d l i q u i d solute - molar volume of solute

and

V^ 6^,

6^ = s o l u b i l i t y parameters of solvent and

and $

= volume f r a c t i o n of the

solute

solvent

If the solute, the concentration, and the system temperature are kept constant, then differences i n s o l u b i l i t y depend s o l e l y on the difference between the s o l u b i l i t y parameter of the s o l i d and the solvent. Riggs showed the s o l u b i l i t y of a p i t c h i n a series of solvents with increasing s o l u b i l i t y parameters followed a b e l l shaped curve, with maximum s o l u b i l i t y occurring when the s o l u b i l i t y parameter of the solute and solvent were equal(5). In general, non-polar solvents with t o t a l s o l u b i l i t y parameters ranging from 8.0-9.5 were desirable for extracting mesophase forming fractions from pitches. In t h i s

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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work, A-240 p i t c h was dissolved i n 38 solvents, both dispersive and polar (Table I ) . A plot of weight percent dissolved versus solub i l i t y parameter shows that A-240 s o l u b i l i t y i n dispersive solvents does follow the t y p i c a l b e l l shaped curve, however, the t o t a l parameter s o l u b i l i t y f a i l s to describe A-240 s o l u b i l i t y i n polar solvents (Figure 2). Alcohols, aldehydes, a c e t o n i t r i l e , acetone, dioxane, and other non-dispersive solvents dissolve less than the predicted percentage of A-240. As Hildebrand's s o l u b i l i t y parameter was intended for use i n dispersive systems, t h i s i s not surprising. The inadequacy of using the t o t a l s o l u b i l i t y parameter to describe the behavior of polar and hydrogen bonded solvents i n polymer systems led Charles Hansen(7) to generalize Hildebrand's parameter. The t o t a l s o l u b i l i t y parameter was broken down into three components representing the three types of interactions possible between molecules: dispersive, polar, and hydrogen bonding.

AE

Vm

=

Vm

Vm

Vm

+ 6

(3)

Although generalizing the s o l u b i l i t y parameter into three dimensions i s not e n t i r e l y rigorous (as the geometric mean expression i s used to describe hydrogen bonding i n t e r a c t i o n s ) , the three dimensions provide an improved q u a l i t a t i v e understanding of solute-solvent interactions, and should be useful i n predicting s o l u b i l i t y of pitches. A solub i l i t y map can be created by p l o t t i n g the weight percentage of p i t c h dissolved as a function of dispersive and polar components of the s o l u b i l i t y parameter. Symbols or contours are used to highlight regions of reduced or enhanced s o l u b i l i t y . A s o l u b i l i t y plot i s shown i n Figure 3 where s o l u b i l i t y i s indicated by the shape of the symbol used to show l o c a t i o n on the p l o t . Strong dispersive solvents with moderate polar character are most able to dissolve A-240, while solvents with small dispersive parameters or large polar parameters, are generally incapable of d i s s o l v i n g an appreciable percentage of the p i t c h . In between these two regions exists an area of p a r t i a l s o l u b i l i t y . Solvents, such as benezene, dioxane, toluene, xylene, carbon tetrachloride, DMF, or DMA, dissolve between 75 and 96% of A-240. Because many of the lower molecular weight species can be removed by these solvents, their insoluble fractions should be ideal candidates for forming mesophase. The mesophase forming tendencies of the insoluble fractions were investigated by encapsulating samples under vacuum, then heat-soaking to 375°C for two hours. A l i s t of the mesophase forming fractions i s presented i n Table I I . As expected, solvents with s o l u b i l i t y parameters located at the outer edge of the enhanced s o l u b i l i t y region extract A-240 fractions capable of forming coalesced mesophase. These solvents range i n t o t a l s o l u b i l i t y parameter from 8.65 to 12.14 ( g l ) l / 2 , with dispersive parameters ranging from 8.7 to 9.3. Solvents, such as DMF and acetaldehyde, show appreciable polar parameter while DMF and dioxane are strongly hydrogen bonded. MeCl, c

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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223

Pitch-Solvent Interactions

TABLE I E f f e c t o f S o l u b i l i t y Parameter on Weight % A2**0 Dissolved

, . Solvent e

1,2,1* Trichlorobenzene Bromobenzene Acetophenone Nitrobenzene Tetrahydrofuran Quinoline Pyridine Chlorobenzene Tetramethylurea Ethylene bromide Trichloroethylene Carbon d i s u l f i d e Ethylene d i c h l o r i d e Chloroform Methylene chloride Dimethyl acetamide Benzene Xylene Dioxane Toluene Dimethyl formamide Carbon t e t r a c h l o r i d e Decalin Diethyl amine Acetaldehyde Benzyl alcohol Nonane Decane Acetone Dimethyl sulfoxide Octane Nitromethane Hexane Pentanol Acetonitrile Propanol Ethylene g l y c o l Methanol

* v v • +4 Abbreviation

S o l u b i l i t y Parameter ( «l/cc)* c

Wt.? A2**0 Dissolved*

TCB Bb A Nb Tf

10.U5 10.60 10.60 10.62 9.52

99.8 99.8 99.8 99.7 99.7

y Cb Tmu Eb Tee Cd Ed Cf Mc DMA B X D T DMF Ct DI Da Aa Ba Nn Dn Act DMS On Nm Hn Pol Acn Ppl EG M

9.57 10.60 11.70 9.20 10.00 9.80 9.2 9.93 11.10 9.15 8.80 10.00 8.91 12. ll* 8.65 8.80 7.97 9.86 11.6U 7.70 7.70 9.77 12.93 7.60 12.90 7.30 10.61 11.90 11.97 16.30 ll*.28

98.9 98.9 98.6 98.0 97.5 97.3 96.7 96.0 95.0 88.8 88.6 87. k 86.8 86.1 82.8 66.1 63.6 1*9.8 1*8.0 1*1*.8 1*1*.7 1*0.5 36.6 36.3 31.8 31.1 22.7 19.5 16.0 7.1 2.5

*Room temperature l g pitch/100 ml solvent.

In Polymers for Fibers and Elastomers; Arthur, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

224

POLYMERS FOR FIBERS AND ELASTOMERS

T

100

Tee

C

B

Tf .^CfT.-A Cf i M c

Py Tmu A Bb Nb x • Eb |D\EA •

•

\ \

\-

• Ct

ESTIMATED

DMF

80h

\

1

Da •DI

Q W

60h

5

O co to M Q O CM