Industrial Developments

232 Pages·1983·5.124 MB·English

by  G. Henrici-Olivé, S. Olivé (auth.)

51
Advances in Polymer Science
Fortschritte der Hochpolymeren-Forschung
Industrial
Developments
With Contributionsb y
G. D. Bukatov, G. Cecchin,G . Henrici-Oliv6,
S.O livC, E A. Shutov,Y I. Yermakov,
V A. Zakharov,U . Zucchini
With 60 Figures and 52 Tables
Springer-Verlag
Berlin HeidelbergN ew York Tokyo
1983
ISBN-3-540-12189-7 Springer-Verlag Berlin Heidelberg New York Tokyo
ISBN-O-387-12189-7 Springer-Verlag New York Heidelberg Berlin Tokyo
Library of Congress Catalog Card Number 61-642
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Editors
Prof. Hans-Joachim Cantow, Institut fur Makromolekulare Chemie der Uni-
versittit, Stefan-Meier-Str. 31, 7800 Freiburg i. Br., BRD
Prof. Gino Dall’Asta, SNIA VISCOSA - Centro Studi Chimico, Colleferro
(Roma), Italia
Prof. Karel D&k, Institute of Macromolecular Chemistry, Czechoslovak
Academy of Sciences, 16206 Prague 616, CSSR
Prof. John D. Ferry, Department of Chemistry, The University pf Wisconsin,
Madison, Wisconsin 53706, U.S.A.
Prof. Hiroshi Fujita, Department of Macromolecular Science, Osaka Univer-
sity, Toyonaka, Osaka, Japan
Prof. Manfred Gordon, Department of Chemistry, University of Essex, Wiven-
hoe Park, Colchester C 04 3 SQ, England
Dr. Gisela Her&i-Olive, Chemical Department, University of California,
San Diego, La Jolla, CA 92037, U.S.A.
Prof. Joseph P. Kennedy, Institute of Polymer Science, The University of
Akron, Akron, Ohio 44325, U.S.A.
Prof. Werner Kern, Institut fur Organische Chemie der Universitat, 6500 Mainz,
BRD
Prof. Seizo Okamura, No. 24, Minami-Goshomachi, Okazaki, Sakyo-Ku.
Kyoto 606, Japan
Professor Salvador Olive, Chemical Department, University of California,
San Diego, La Jolla, CA 92037, U.S.A.
Prof. Charles G. Overberger, Department of Chemistry. The University of
Michigan, Ann Arbor, Michigan 48 104, U.S.A.
Prof. Takeo Saegusa, Department of Synthetic Chemistry, Faculty of
Engineering, Kyoto University, Kyoto, Japan
Prof. Giinter Victor Schulz, Institut fur Physikalische Chemie der Universitiit,
6500 Mainz, BRD
Dr. William P. Slichter, Chemical Physics Research Department, Bell Tele-
phone Laboratories, Murray Hill, New Jersey 07971, U.S.A.
Prof. John K. Stille, Department of Chemistry. Colorado State University, Fort
Collins, Colorado 80523, U.S.A.
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Table of Contents
The Chemistry of Carbon Fiber Formation from
Polyacrylonitrile
G. Henrici-Oliv6, S. Oliv~ . . . . . . . . . . . . . .
On the Mechanism of Olef'm Polymerization by
Ziegler-Natta Catalysts
V. A. Zakharov, G. D. Bukatov, Y. I. Yermakov . . 16
Control of Molecular-Weight Distribution in Polyolefms
Synthesized with Ziegler-Natta Catalytic Systems
U. Zucchini, G. Cecchin . . . . . . . . . . . . . . 101
Foamed Polymers. Cellular Structure and Properties
F. A. Shutov . . . . . . . . . . . . . . . . . . . 155
Author Index Volumes 1-51 . . . . . . . . . . . . . . 219
Subject Index . . . . . . . . . . . . . . . . . . . . . 226
The Chemistry of Carbon Fiber Formation from
Polyacrylonitrile
G. Henrici-Oliv6* and S. Oliv6*
Monsanto Textiles Company, Pensacola, Florida 32575, U.S.A.
The present status of knowledge with regard to the chemical reactions and physicochemical processes,
taking place during the transformation of a PAN based precursor fiber to carbon fiberi,s discussed.
A large number of precursor fibers has been screened under arbitrarily chosen standard conditions
of spinning, stabilization and carbonization. Included are fibers from binary copolymers, terpolymers
and blends, as well as fibers containing a variety of additives.
The particular case of the AN/VBr precursor, which permits stabilization in 15-20 minutes,
giving carbon fibers with excellent properties (sonic modulus close to 003 GN/m z tensile strength
dose to 3000 MN/m )2 is described in more detail. Chemical and physicoehemical reasons for the
particular situation of this precursor are discussed.
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Some Characteristics of Acrylic Polymers and Fibers . . . . . . . . . . . 4
2.1 Dipole-Dipole Interactions of Nitrile Groups . . . . . . . . . . . . 4
2.2 Relevant Properties of Copolymers . . . . . . . . . . . . . . . . . 6
2.2.1 Solubility . . . . . . . . . . . . . . . . . . . . . . ... 6
2.2.2 Oxygen Permeation . . . . . . . . . . . . . . . . . . . . . 7
2.2.3 Melting Point ~ression . . . . . . . . . . . . . . . . . . 8
2.3 The Effect of Additives . . . . . . . . . . . . . . . . . . . . . . 10
3 The Chemistry of Stabilization and Carbonization . . . . . . . . . . . . 11
3.10ligomerization of Nitrite Groups . . . . . . . . . . . . . . . . . 11
3.1.1 Initiation of CN Oligomerization and Polymerization in Low
Molecular Weight Model Substances . . . . . . . . . . . . . 14
3.1.2 Initiation of CN Oligomerization in PAN and Copolymers .... 17
3.1.3 Intra- versus Intermolecular CN Oligomerization . . . . . . . . 19
3.1.4 The Length of the Cyclized Sequences . . . . . . . . . . . . 22
3.2 Further Reactions During Stabilization . . . . . . . . . . . . . . . 22
3.2.1 The Effect of Oxygen . . . . . . . . . . . . . . . . . . . . 22
3.2.2 Gas Evolution During Stabilization . . . . . . . . . . . . . . 25
3.3 Shrinkage During Stabilization . . . . . . . . . . . . . . . . . . 26
3.4 Characterization of Precursor and Stabilized Fiber . . . . . . . . . . 28
* Present address:
Department of Chemistry
University of California at San Diego,
La Jolla, CA 92037, USA
2 G. Henrici-Oliv6 and S, Oliv~
3.4.1 Orientation Factor from Sonic Modulus . . . . . . . . . . . . 28
3.4.2 X-Ray Scattering Data as Criteria for Complete Stabilization... 29
3.5 Carbonization . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.5.1 The Chemistry of Carbonization . . . . . . . . . . . . . . . 13
3.5.2 The Structure and Properties of Carbon Fibers . . . . . . . . 34
4 Discussion of Specific PAN Based Precursors . . . . . . . . . . . . . . 36
4.1 The Importance of Type and Concentration of Comonomer ..... 36
4.2 Precursor Screening . . . . . . . . . . . . . . . . . . . . . . . 39
4.2.1 Binary Copolymers . . . . . . . . . . . . . . . . . . . . . 40
4.2.2 Terpolymers and Blends . . . . . . . . . . . . . . . . . . . 41
4.2.3 The Effect of Crosslinking Agents . . . . . . . . . . . . . . . 42
4.3 Influence of Spinning and Stabilization Parameters . . . . . . . . . 44
4,3.1 Stretching . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.3.2 Stabilization Profile (Temperature/Time Regime) . . . . . . . . 44
4.4 Correlation between Precursor and Carbon Fiber Properties ..... 46
4.4.1 Molecular Orientation . . . . . . . . . . . . . . . . . . . 46
4.4.2 Molecular Weight of the Polymer . . . . . . . . . . . . . . . 48
4.4.3 Shrinkage Force . . . . . . . . . . . . . . . . . . . . . . 48
4,5 Correlation between Stabilized Fiber and Carbon Fiber Properties... 49
5 The Particular Case of the AN/VBr Precursor . . . . . . . . . . . . . . 50
5.t Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.2 Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.2.1 Polymerization . . . . . . . . . . . . . . . . . . . . . . . 52
5.2.2 Spinning . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.3 Stabilization . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.4 Carbonization . . . . . . . . . . . . . . . . . . . . . . . 55
6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7.1 Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . 56
7.2 Spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
7.3 Stabilization . . . . . . . . . . . . . . . . . . . . . . . . . . 57
7.4 Carbonization . . . . . . . . . . . . . . . . . . . . . . . . . 57
7.5 Carbon Fiber Characterization 57
. . . . . . . . . . . . . . . . . .
7.6 Glossary of Abbreviations . . . . . . . . . . . . . . . . . . . . 58
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
ehT yrtsimehC of nobraC rebiF noitamroF morf elirtinolyrcayloP
1 Introduction
The first carbon fibers ever appear to have been made by Edison ,)1 who used
them as electrical resistance in light bulbs. Prepared by pyrolysis of cellulose threads,
these carbon fibers had but poor mechanical properties.
In modern times, the interest in carbon fibers is based mainly on their use as
reinforcement in evpoxy or polyester resins (composites). In the early times of
the development of composites, in the forties, glass fibers were used to provide
tensile strength to the formable matrix, which acts as an agglomerant, and transfers
stress to the fiber .)2 Glass fibers have a high tensile strength, but a relatively poor
elastic modulus, so their use is confined to applications where high modulus is
not required,-e.g, for silos, tanks, boat bodies, etc. As increasingly more demanding
end uses for composites were aspired at, e.g. by the automotive and aeronautic
industry, other fibrous materials had to be developed, which would offer not only
high strength, tensile but also high elastic modulus. consist fibers Such mainly of light
elements such as boron, carbon or beryllium, but also of carbides, nitrides, silicides
and oxides .~3 Among these, carbon fibers are potentially the most interesting
(in particular for the automotive industry) because of their outstanding strength-to-
weight and stiffness-to-weight ratios.
Carbon fibers consist essentially (>99.5% by weight) of carbon. They can, in
principle, be made from many organic, fiber forming materials, however only three
such materials have gained industrial importance: rayon, pitch and polyacrylonitrile
(PAN). Rayon is injured by a relatively high carbon loss during carbonization
(the oxygen contained in rayon fibers tends to be released as CO or CO2); pitch
based carbon fibers have relatively poor tensile properties, unless they are prepared
from extremely purified (expensive) mesophase pitch. At present, PAN appears to be
the most widely used starting material for carbon fibers.
Shindo )4 was the first to obtaicna rbon fibers from PAN. In the meantime, carbon
fiber properties have markedly been improved, largely due to the work of Watt,
Johnson and their co-workers ~5 in England. The high tensile strength and modulus
obtainable with carbon fibers from PAN or copolymers thereof are assumed to
be due to the fact that the high molecular orientation present in stretched fibers from
these materials is, at least in part, maintained through the entire pyrolysis process,
provided the fibers are continuously held under stress. In the course of the
process, the oriented carbon chains quasi coalesce with neighboring chains into
graphitic layers, the extension of which depends mainly on the final temperature
of the treatment.
On the other hand, a slow controlled thermal oligomerization of nitrile groups,
iani r and at moderate temperatures, leads to highly conjugated, crosslinked, oxidized
structures which make the fiber non-flammable and infusible. Such fibers are said
to be "stabilized." They can be further heat-treated in an inert atmosphere to form
the "carbon fibers" (> % 99 carbon).
The stabilization process si crucial for the quality of the final carbon fiber.
Fusion and other damages to the fiber have to be avoided by applying a carefully
balanced regime of time and temperature gradient, For most commercial carbon
fiber precursor fibers, stabilization is a time-consuming and costly procedure,
4 G. 6vilO-icirneH and .S evilO
We presently report on a broad search for specific acrylic carbon fiber precursors,
which should be stabilized in short time (less than one hour), and yet would give
carbon fibers with satisfactory tensile properties. In planning the chemistry of such
precursors, it was necessary to take into account the chemical reactions and physical
processes going on during the heat treatment.
In Section 2, some properties and characteristics of PAN and acrylic copolymers,
as well as of fibers spun therefrom, are discussed, with particular regard to the
stabilization process.
Section 3 treats with the chemical and physical processes during stabilization and
carbonization. Although literature reports have been heavily consulted, and are duely
referenced, the description of the whole process, and of the relative importance of
physical and chemical aspects of it, in many instances represents the authors" present
opinion.
In Section 4 we report on a broad precursor screening with regard to polymer
composition, additives, influence of spinning parameters, stabilization andc arbonizat-
ion conditions.
Section 5, finally, is dedicated to work toward the optimization of the best precursor
fiber developed: fibers from copolymers of acrylonitrile with a few % of vinyl
bromide. The chemical and physicochemical reasons for the particular situation of
this precursor are discussed.
2 Some Characteristics of Acrylic Polymers and Fibers
Most PAN based precursor fibers are made from copolymers, the predominant
component of which, however, is acrylonitrile (in most cases >95 o~ by weight).
Consequently, most physical properties of the fibers are mainly determined by this
highly polar monomer.
In this Section, we review the relationship between intra- and intermolecular forces
in polyacrytonitrile on the one hand, and those macroscopic properties of polymer
and fiber, which are relevant to carbon fiber formation, on the other.
2.1 Dipole-Dipole Interaction of Nitrile Groups
The dominant characteristic of the PAN molecule is the presence of the strongly
polar nitrile groups, at an intramolecular distance of only a few tenths of a nm.
The high dipole moment (3.9 Debye) causes strong attraction or repulsion according
to the orientation.
The energy involved in the interaction of two dipoles, t~ 1 and la2, at a distance r,
is generally given by (see e.g. Ref. 6)):
E = ~ (cos @ -- 3 cos 16 cos 62) (1)
(angles and vectors as defined in Fig. .)1 For parallel side-by-side position,
16 = 2~ = 90°, ~ = 0, and hence the energy has the highest attainable positive