Table Of ContentHIGH PERFORMANCE
THERMOPLASTIC RESINS
AND THEIR COMPOSITES
Sylvie B&land
Institute for Aerospace Research
National Research Council of Canada
Ottawa, Canada
NOYES DATA CORPORATION
Park Ridge, New Jersey, U.S.A.
Copyright @ 1990 National Research Council of Canada
Published under licence from the National
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Library of Congress Catalog Card Number: 90-27388
ISBN: O-8155-1278-3
Printed in the United States
Published in the United States of America by
Noyes Publications
Mill Road, Park Ridge, New Jersey 07656
10987654321
Library of Congress Cataloging-in-Publication Data
Bkland, Sylvie
High performance thermoplastic resins and their composites/ by
Sylvie Biland.
p. cm.
Includes bibliographical references and index.
ISBN O-8165-1278-3 :
1. Thermoplastic composites. I. Title.
TA418.9.C6B45 1991
620.1’923--de20 90-27388
CIP
Foreword
This book describes recent developments in high performance thermoplastic resins and their com-
posites and assesses the benefits and limitations of these emerging materials for aerospace and
other applications. Discussions on the performance of neat and continuous fiber reinforced ther-
moplastic resins in terms of their properties and environmental and chemical resistance are pro-
vided. The interrelationships between morphology and properties of semicrystalline thermoplastic
composites are addressed as well as the factors influencing the morphology. The various techniques
to combine fibers and matrix, to produce high quality laminates, to form three-dimensional parts
and to join thermoplastic composite parts are described. One section is devoted to presenting
some examples of aircraft applications of thermoplastic composites. General conclusions and
recommendetions for future research and development work are made.
Recently, a range of commercial composites based on thermoplastic matrix resins have been de-
veloped for high-temperature structural applications. These new thermoplastic composites are
based on aromatic polymers and surmount the major limitations of earlier aliphatic based ther-
moplastic polymers such as low elastic modulus, low glass transition temperature and poor solvent
resistance. The replacement of metallic and fiber reinforced thermoset components with thermo-
plastic based composites is now emerging. Although they are not likely to completely replace
thermosets, at least in the near future, they offer potential advantages over thermosets for de-
manding applications (that reinforce the competition between these two classes of advanced rein-
forced plastics). In general, thermoplastics have an indefinite shelf life, low moisture adsorption,
good thermal stability, high toughness and damage tolerance, short and simple processing cycles,
and potential for significant reductions in manufacturing costs. In addition, they have the ability
to be remelted and reprocessed.
The materials considered here include thermoplastic polymers belonging to various chemical
classes such as polyketones, polyarylene sulfides, polyamides, polyimides, polysulfones, liquid
crystalline polymers, polybenzimidazoles and polyphenylquinoxalines. The main characteristics
of these families are discussed.
The first part of the book reviews the thermal and mechanical properties of the neat thermo-
plastic resins as well as their chemical and moisture resistance and toughness properties.
The second part of the book concerns the performance of advanced thermoplastics reinforced
with continuous carbon fiber. Mechanical properties, interlaminar fracture toughness, damage
tolerance, fatigue and creep behavior, resistance to ionizing radiation and thermal cycling as
well as the mechanisms of failure are presented. Some comparisons with current epoxy, tough-
V
vi Foreword
ened epoxy and bismaleimide based composites are made. A section is devoted to the influence
of morphology of semicrystalline thermoplastics on the properties of the composites, and the
factors influencing the morphology of semicrystalline thermoplastics are addressed as well.
Although the questions of processing techniques, tooling, joining and repairing have not been
fully addressed by researchers and industrial engineers, applications of thermoplastic composites
are increasingly popular. Some primary and secondary structures have been manufactured and
flight tested. Practical experiences in the aircraft and aerospace fields are reviewed to assess the
processing and performance benefits of thermoplastic composites. The book presents conclusions
and recommendations regarding the potential of thermoplastic composites for aircraft structural
applications, especially in comparison with thermoset based composites.
The information in the book is from A Review of High Performance Thermoplastic Resins and
Their Composites, by Sylvie Beland of the Institute for Aerospace Research of the National
Research Council of Canada, for the National Research Council of Canada, February 1990.
The table of contents is organized in such a way as to serve as a subject index and provides easy
access to the information contained in the book.
Advanced composition and production methods developed by Noyes Data
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ACKNOWLEDGMENTS
The author would like to thank Mr. R.F. Scott, Mr. S. Lee and Dr. W. Wallace
from the Institute for Aerospace Research, National Research Council of Canada
for valuable discussions and the proofreading of this report.
NOTICE
The materials in this book were prepared as accounts of work spon-
sored by the National Research Council of Canada. On this basis the
Publisher assumes no responsibility nor liability for errors or any
consequences arising from the use of the information contained
herein. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use by the Council
or the Publisher.
Final determination of the suitability of any information or pro-
cedure for use contemplated by any user, and the manner of that
use, is the sole responsibility of the user. The reader is warned that
caution must always be exercised when dealing with potentially
hazardous materials and processes, and expert advice should be
sought at all times.
1. Introduction
The advanced polymer composite market is dominated by composites processed with
thermoset matrix resins such as epoxies, polyimides and bismaleimides. These composites
have already found widespread applications in the aircraft, aerospace and defence
communities. In the last 20 years considerable advancement has been made in perfecting
thermoset based composites. In spite of this progress, certain deficiencies remain including
limited shelf life, insufficient toughness, low strain to failure, long and rigid multi-step
processing and moisture sensitivity.
Recently, a range of commercial composites based on thermoplastic matrix resins have
emerged for high-temperature structural applications. These newer thermoplastic composites
are based on aromatic polymers and surmount the major limitations of early aliphatic based
thermoplastic polymers such as low elastic modulus, low glass transition temperature and
poor solvent resistance. The replacement of metallic and fibre reinforced thermoset
components with thermoplastic based composites is now emerging. Although they are not
likely to completely replace thermosets, at least in the near future, they offer potential
advantages over thermosets for demanding applications (that reinforce the competition
between these two classes of advanced reinforced plastics). In general, thermoplastics have an
indefinite shelf life, low moisture absorption, excellent thermal stability, high toughness and
damage tolerance, short and simple processing cycles and potential for significant reductions
in manufacturing costs. In addition, they have the ability to be remelted and reprocessed and
also damaged aircraft structures can be repaired by the application of heat and pressure.
In the expectation that these high performance thermoplastic resins will find
increasing use in aerospace structures, the Structures and Materials Laboratory at the Institute
for Aerospace Research has completed this literature review in order to identify the most
recent developments in thermoplastic composites and to assess the benefits and limitations of
these materials for aerospace use. This review considers only thermoplastic matrix resins
having the potential to be used with continuous flbre reinforcements in structural aerospace
applications; this is the industry in which much developmental work has occurred. Some
reviews on advanced thermoplastic composites have been reported earlier [ 1, 2. 31. Among
them is a detailed review of thermoplastic composites in structural components that was
completed in 1987 by the National Materials Advisory Board of the U.S. National Research
Council (11.T he present report up-dates these reviews by placing emphasis on the latest
publications. Some aspects discussed in the previous reviews such as short and long fibre
reinforced thermoplastics have been omitted while other aspects have been added or discussed
in greater detail.
2 High Performance Thermoplastic Resins and Their Composites
The materials considered in this work include thermoplastic polymers belonging to
various chemical classes such as polyketones. polyarylene sulfides, polyamides, polyimides.
polysulfones. liquid crystalline polymers, polybenzimidazoles and polyphenylquinoxalines.
The main characteristics of these families are discussed. The first part of this report reviews
the thermal and mechanical properties of the neat thermoplastic resins as well as their
chemical and moisture resistance and toughness properties.
The second part of this review concerns the performance of advanced thermoplastics
reinforced with continuous carbon fibre. Mechanical properties, interlaminar fracture
toughness, damage tolerance, fatigue and creep behavior, resistance to ionizing radiation and
thermal cycling as well as the mechanisms of failure are presented. Some comparisons with
current epoxy, toughened epoxy and bismaleimide based composites are made. A section is
devoted to the influence of morphology of semi-crystalline thermoplastics on the properties of
the composites and the factors influencing the morphology of semi-crystalline thermoplastics
are addressed as well.
Thermoplastic composites have not yet received wide acceptance primarily due to the
limited data available, the lack of processing experience and the unanswered questions
concerning their fatigue and creep behavior and their poor compression properties. Processing
techniques which produce high quality laminates are not as well established as those
developed for advanced thermoset composites. The high melt viscosities and high processing
temperatures are important obstacles to easy processing, although there is considerable
incentive to minimize these processing parameters. Some processes that have been recently
developed for combining fibres and thermoplastic polymers that overcome high melt vicosity
problems are overviewed. The different processing techniques that convert a lay-up of fibres
combined with matrix into either a flat consolidated laminate or a three-dimensional shaped
component are also described. The various methods used to join thermoplastic based
composites including mechanical fastening, adhesive bonding and novel techniques based on
fusion bonding are presented. Since mechanical fastening and adhesive bonding are the
common methods for joining thermoset based composites, emphasis is placed on the
techniques for fusion bonding thermoplastic composites.
Although the questions of processing techniques, tooling, joining and repairing have
not been fully addressed by researchers and industrial engineers, applications of
thermoplastic composites are increasingly popular. Some primary and secondary structures
have been manufactured and flight tested. Practical experiences in the aircraft and aerospace
fields are reviewed to assess the processing and performance benefits of thermoplastic
composites. The report presents conclusions and recommendations regarding the potential of
thermoplastic composites for aircraft structural applications, especially in comparison with
thermoset based composites.
2. Neat Thermoplastic Resins Properties
2.1 Introduction
Plastics are commonly classified into two classes, thermoplastics or thermosets,
depending on their behavior when heated 14, 5, S]. A thermoset polymer undergoes various
degrees of cross-linking when cured by heat (or other means] IS]. The cross-linking reactions
lead to the formation of an insoluble or infusible rigid product, a “set” product, in which chains
are joined together to form a three-dimensional structure 15, 71. In contrast, thermoplastic
polymers do not undergo chemical changes during consolidation: changes are substantially
physical 15, 61. Generally, thermoplastics are melt fusible and can be consolidated by the
application of heat and pressure only. They can be repeatedly softened by heating and
hardened by cooling. There are however some polymers categorized as thermosetting ther-
moplastics or pseudo-thermoplastics [ 1, 6. 81. They are considered as thermoplastic as they
possess true thermoplastic properties but they are produced essentially like thermosets: they
undergo some reaction chemistry during processing cycles. These materials require both
curing and heat treatment for effective consolidation 161.
Thermoplastic polymers are not new: they have been known for a long time. It is only
recently that the newer so-called high temperature or high performance thermoplastics have
been introduced. The early thermoplastic polymers had predominantly aliphatic carbon back-
bones in which flexible carbon chains could be extended and rotated into many configurations
with relative ease [4. 9. 101. Rigidity was obtained by restricting the movement of the backbone
chain either by crystallinity such as in polyethylene and polypropylene or by the introduction
of side groups as in polystyrene or polymethylmethacrylate. The major limitations with these
early thermoplastics which are still on the market are their low elastic modulus, low glass
transition temperature (Tg) and poor solvent resistance. In the past few years, a range of
thermoplastics based on aromatic polymers have been developed which surmount these
limitations. The introduction of rigid aromatic rings instead of aliphatic chains increases the
intermolecular forces, thus restricting the movement of the backbone chain [4, lo]. Hence,
mechanical properties, high temperature capability and solvent resistance are greatly
improved and can be often equivalent or even better than the best thermosets. For ease of
processing, groups such as ether, carbonyl, thioether. amide, methylene. ester, isopropylidine
and sulfone are incorporated between the aromatic rings to render the polymer chain more
flexible 11. 101.
This section presents data on a number of these high performance thermoplastic resins
which have the potential to be used as matrix material in fibre reinforced composites aimed at
aircraft structural applications. The chemical structure, trade name and producers of these
resins as well as their thermal and mechanical properties and solvent resistance are presented.
A brief description of each polymer follows which highlights their important characteristics.
3
4 High Performance Thermoplastic Resins and Their Composites
2.2 Properties of Neat Thermoplastic Resins
2.2.1 Chemical Structure and Some Physical Properties
Table 1 lists the high performance thermoplastic polymers that are discussed in the
present report. Although this list is not exhaustive, it provides a good Indication of the
thermoplastics that have been and are being investigated for use as matrix materials for high
performance composites. Most of these neat resins are either commercially available or nearly
so, in either industrial or developmental quantities. Some of them are provided as a neat resin
or filled with short fibres but not yet reinforced with continuous fibres in a prepreg tape or
fabric form. Although it is included in the present list, polyphenylquinoxaline (PPQ) is not
expected to be available in the form of fibre reinforced matrix because of its low modulus, high
viscosity and its high cost.
Table 2 presents the chemical structure of some of these thermoplastics. The dominant
aromatic character in their polymer backbone is clearly shown. Density, Poisson’s ratio,
Limiting Oxygen Index (L.O.I.) and viscosity are presented in Table 3. Density varies from 1.15
to 1.45 depending on the thermoplastic matrix: the polyamide J-2, a product from E.I. DuPont
de Nemours, has the lowest density while N-polymer, a polyimide from DuPont and Eymyd, a
polyimide from Ethyl Corporation, have the highest.
The melt viscosities of high-molecular weight thermoplaslics are much higher than
most thermosets. At processing temperature. thermosets have viscosities less than 1000 poise
[2]. which is much less than the viscosities presented in Table 3 for thermoplastics. The low
viscosity of epoxy formulations results in high melt flow properties in the uncured state
leading to good wetting of the fibres during prepreg manufacture 111. Figure 1 shows the
relationship between solution viscosity, melt viscosity, number average molecular weight and
the glass transition temperature (Tg) presented in 191.A s shown, the desired high Tg leads
inevitably to high melt viscosity. Unfortunately, the high melt viscosity of thermoplastics
renders processing difficult as high processing temperatures are required to achieve a low melt
viscosity for good consolidation and fibre impregnation: and the viscosity may still be too high
for complete impregnation of continuous fibre bundles. Processing becomes difficult at melt
viscosities above 5500 poise [9]. Melt viscosities of 102 to 104 poise are desirable for the
fabrication of composites [ 11. It is then a question of compromise between processability of
thermoplastic composites and their high temperature performance as reflected by Tg.
L.O.I. numbers found in Table 3 give an indication of the material’s resistance to
burning, which may be very important in certain applications. For example, aircraft interiors
such as sidewall panels, storage bins, partitions. galley doors and ceiling panels have to meet
certain combustibility requirements to comply to the more and more stringent U.S. Federal
Aviation Administration (FAA) cabin safety regulations [57]. “L.O.I. is the minimum
TABLE 1. Selected High-Performance Thermoplastics
GENERIC NAME MANUFACTURER TRADE NAME
POLYKETONES
Polyelherelherketone (PEEK) Imperial Chemical Industries (ICI) Viclrex PEEK
Potyelherkelone (PEK) Imperial Chemical Industries (ICI) Victrex PEK
Polyelherkeloneketone (PEKK) E.I. DuPont de Nemours PEKK (1)
Polyelherketoneelherkeloneketone (PEKEKK) BASF Ultrapek
Polykelone Amoco Performance Products Kadet
POLYARYLENE SULFIDES
Polyphenylene sulfide (PPS) Phillips Petroleum Company Rylon PPS
Polyarytene sulfide (PAS) Phillips Pelroleum Company Ryton PAS-2 (2)
Polyphenylene sulfide sulfone (PPSS) Phillips Petroleum Company Rylon S PPSS (2)
POLYAMIDES
Polyamide E.I. DuPont de Nemours J-2 (1,2)
Polyamideimide (PAI) Amoco Performance Products Torlon
POLYIMIDES
Polyaryleneimide E.I. DuPont de Nemours K-Polymer
Polyaryleneimide E.I. DuPont de Nemours N-Polymer
Polyimide Ethyl Corporation EYMYD
Polyelherimide (PEt) General Electric Company Ultem
Polyelherimide American Cyanamid Cypac
Polykeloimide Milsui Toatsu Chemicals Inc. (MTC) Larc-TPI, New-TPt
Polyketoimide Rogers Corp., Durimid
(1) Is or will be available only as custom finished composite material parts
Ip
(2) Not commercially available but nearly
(3) Not expected to be commercially available as a matrix for composite material (continued) ;
c.
z
TABLE 1. Selected High-Performance Thermoplastics (cont’d)
GENERIC NAME MANUFACTURER TRADE NAME
POLYSULFONES
Polysulfone (PSU) Amoco Performance Products Udel
Polyarylethersulfone Amoco Performance Products Radel A
Polyphenylsulfone Amoco Performance Products Radel R
Polyethersulfone (PES) Imperial Chemical Industries Victrex PES
POLYESTERS
Liquid Crystalline (LCP) Amoco Performance Products Xydar
Liquid Crystalline Hoescht Celanese Vectra
POLYBENZIMIDAZOLES
Polybenzimidazoles (PBI) Hoescht Celanese PBI (1)
POLYPHENYLQUINOXALINES
Polyphenylquinoxalines (PPQ) (3) _ _ _ _ _ - _ _ _ _
(1) Is or will be available as custom finished composite material parts
(2) Not commercially available but nearly so
(3) Not expected to be commercially available as a matrix for composite material
