Resins for Aerospace

482 Pages·1980·7.81 MB·English

by  Clayton A. May (Eds.)

Resins for Aerospace
Clayton A. May, EDITOR
Lockheed Missiles and Space
Company, Incorporated
Based on a symposium sponsored by
the ACS Division of
Organic Coatings and Plastics Chemistry
at the ACS/CSJ Chemical Congress
(177th ACS National Meeting),
Honolulu, Hawaii,
April 3-6, 1979.
132
ACS SYMPOSIUM SERIES
AMERICAN CHEMICAL SOCIETY
WASHINGTON, D. C. 1980
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
TL 699 .G85A18 1979 copy 1
ACS/CSJ Chemical Congress
(1979 :
Resins for aerospace
Library of Congress CIP Data
ACS/CSJ Chemical Congress, Honolulu, 1979-
Resins for aerospace.
(ACS symposium series; 132 ISSN 0097-6156)
Includes bibliographies and index.
1. Aerospace industries—Materials—Congresses. 2.
Gums and resins, Synthetic—Congresses.
I. May, Clayton Α. II. American Chemical Society.
Division of Organic Coatings and Plastics Chemistry.
III. American Chemical Society. IV. Nippon Kaga-
kukai. V. Title. VI. Series: American Chemical Society.
ACS symposium series; 132.
TL699.G85A18 1979 629.1'028 80-15342
ISBN 0-8412-0567-1 ACSMC8 132 1-501 1980
Copyright © 1980
American Chemical Society
All Rights Reserved. The appearance of the code at the bottom of the first page of each
article in this volume indicates the copyright owner's consent that reprographic copies of
the article 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. 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 new
collective works, for resale, or for information storage and retrieval systems.
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, repro­
duce, use, or sell any patented invention or copyrighted work that may in any way be
related thereto.
PRINTED IN THE UNITED STATES AMERICA
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
ACS Symposium Series
M. Joan Comstock, Series Editor
Advisory Board
David L. Allara W. Jeffrey Howe
Kenneth B. Bischoff James D. Idol, Jr.
Donald G. Crosby James P. Lodge
Donald D. Dollberg Leon Petrakis
Robert E. Feeney F. Sherwood Rowland
Jack Halpern Alan C. Sartorelli
Brian M. Harney Raymond B. Seymour
Robert A. Hofstader Gunter Zweig
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
FOREWORD
The ACS SYMPOSIUM SERIES was founded in 1974 to provide
a medium for publishing symposia quickly in book form. The
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIES except that in order to save time the
papers are not typeset but are reproduced as they are 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 Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
PREFACE
'his book is divided into four sections since the subject matter encom-
passes a variety of technical expertise. Part I is devoted to Resin
Chemistry; Part II, Adhesives, Coatings, and Sealants; Part III, Reinforced
Plastics; and Part IV to Instrumental Characterization Technology. The
aerospace industry has been, and is, contributing much to instrumental
characterization methods as evidenced by Part IV and substantial por
tions of Part III. This activity is based on a need to know as much as
possible about the materials being used to assure high quality hardware.
Aerospace materials an
on our everyday lives. Perhaps the classic example is the early work of
N. A. DeBruyne and co-workers, who developed the Redux bonding sys
tem that played a heavy role in aircraft construction during World War II.
Today we find adhesives everywhere—in the homes where we live, in
the offices and factories where we work, in the automobiles, buses, trucks,
and trains of our surface transportation systems, and in the planes in
which we fly. It is thus fitting that the American Chemical Society and
the Chemical Society of Japan have asked the workers in this industry
to discuss a variety of aspects of their technology.
The editor is deeply grateful to Dr. Dave Kaelble of the Rockwell
Science Center, Mr. George Schmitt of the Air Force Material Laboratory,
and Mr. John Hoggatt of the Boeing Aerospace Company. They not
only served as session chairpersons during the Symposium, but also
helped procure the contributors who made the Symposium a success.
Finally, a special note of thanks is due to Professor Kozo Kawata from
the Institute of Space and Aeronautical Science at the University of
Tokyo. Professor Kawata served as a co-chairperson representing CSJ,
and his vigorous activity during the meeting is appreciated most grate
fully.
Lockheed Missiles and CLAYTON A. MAY
Space Company, Incorporated
Sunnyvale, CA 94086
February 26, 1980
IX
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
1
Status of High-Temperature Laminating Resins and
Adhesives
P. M. HERGENROTHER and N. J. JOHNSTON
National Aeronautics and Space Administration, Langley Research Center,
Hampton, VA 23665
The quest for high temperature polymers for use as functional
resins (e.g., coatings and sealants) and structural resins (e.g.,
adhesives, composite matrices and foams) began in the mid-1950's.
Early work on high temperature polymers concentrated primarily on
thermal stability and paid little or no attention to cost, pro
cessability, performance or actual use temperature. As work pro
gressed, it was quickly recognized that a successful polymer must
exhibit a favorable combination of price, processability and per
formance and also that thermal stability differed from dimensional
stability or heat resistance.
Work on most of the more exotic and costly polymers was soon
discontinued as a result of this realism and the more current
emphasis has generally been restricted to the development of mate
rials for specific applications. In fact, this review will be
confined to those high temperature polymers currently being de
veloped as adhesives and composite matrices. The term "high
temperature" in this context refers to the ability of a structural
material to perform properly in air for thousands of hours at
232°C, hundreds of hours at 3l6°C and/or minutes at 538°C.
The ideal high temperature polymeric system for use as a
production-line adhesive or laminating resin would exhibit a vari
ety of desirable features such as the following: easy tape and
prepreg preparation, good shelf-life, acceptable tack and drape,
acceptable quality control procedures, low processing temperature
and pressure, no volatile evolution, dense glueline or matrix (no
voids), good mechanical performance over the desired temperature
range, time, and environmental conditions, acceptable repaira-
bility and cost-effectiveness. Ironically, no commercially avail
able system exists which actually offers any reasonable combina
tion of these features. Instead, the few commercially available
materials represent a compromise of these properties.
0-8412-0567-l/80/47-132-003$05.00/0
© 1980 American Chemical Society
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
4 RESINS FOR AEROSPACE
Historical Development of High Temperature Structural Resins
To place the current status of high temperature polymers in
proper perspective, a brief chronological review on each of the
more popular high temperature polymers is appropriate. In '1955 *
Ε. I. DuPont de Nemours and Company, Inc., was awarded the first
of several patents (2) on aromatic polyimides (PI) considered to
be the first family of high temperature polymers. Several
companies such as Westinghouse, Monsanto, General Electric,
Amoco and DuPont devoted a significant effort to PI development.
In fact, more effort has gone into PI development than a l l of the
other high temperature polymers combined and, now that the DuPont
PI patents are expiring, i t will be interesting to see i f com­
panies who are basic i certai PI (e.g. Gulf Oil
Chemicals Company who sell
acid dianhydride) will ente
tion of the earlier PI work involved the preparation of soluble
precursor poly ami c acids from the reaction of aromatic tetra­
carboxylic acid dianhydrides and aromatic diamines and their
subsequent cyclodehydration to PI (Eq. l ) .
Precursor polyamic acids exhibit severe problems i n shelf life
and processing due to hydro lytic instability, water released
during the cyclodehydration and general lack of melt flow. In
spite of these problems, several PI made by this general syn­
thetic route became commercially available about i960, such as
Pyre ML lacquers, Vespel molding materials and m-3h
adhesive.
Concurrent with the development of PI, the polybenzimida­
zoles (PBI) as initially reported by Marvel (3) were being
evaluated. Polybenz imidazoles are generally prepared by the
poly c on dens at i on of aromatic bis (o^-di amines ) with diphenyl esters
of aromatic dicarboxylic acids (Eq. 2).
C0<t> -2n H 0
2 2
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
1. HERGENROTHER AND JOHNSTON High-Temperature Laminating 5
Considerable amounts of phenol and water are evolved which
caused pronounced fabrication problems during the processing of
composites and adhesives. PBI was commercially available in the
mid I9601 s (e.g. , Imidite 850 from Narmco Materials) and is
currently being evaluated for use as hollow fibers in water
purification, flame resistant fibers and low density foams.
During the I960's a variety of new polymers were reported
as high temperature materials primarily on the basis of their
weight loss performance as measured by thermogravimetric analysis
(^,5)« Few of these new materials were investigated as structural
resins. One of several systems which did receive considerable
attention, however, was the polyphenylquinoxalines (PPQ). These
materials, as first reported in 1967 (0 > are readily prepared
from the polycyclocondensatio aromati bis(o-diamines
aromatic dibenzils (Eq
thermoplastics. Althoug y display potentia
high temperature structural resins, particularly as adhesives,
COCO φ -4nH 0
2
m
the PPQ are relatively expensive, require high temperature pro­
cessing and at present are not commercially available.
As more potential applications developed for high temperature
structural resins, alternate synthetic routes to PI were investi­
gated to improve processability. These routes concentrated on
alleviating the evolution of the volatiles responsible for fabri­
cation problems. In the late I960's TRW (j) developed a route to
nadic end-capped imide oligomers which could be thermally polymer­
ized through the unsaturation (Eq. k). This technology became
known as P13N with the Ρ standing for polyimide, the 13 repre­
senting an average oligomeric molecular weight of 1300, and the Έ
Ο Ο o
AMIC ACID
A~200°C -5.34H-0
THERMOSET
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
6 RESINS FOR AEROSPACE
referring to nadic end-caps. The thermal chain extension, often
referred to as pyrolytic polymerization, apparently occurs
through a combination of addition reactions involving the vinyl
groups of the nadimide moiety and maleimide/cyclopentadiene
products formed from a reverse Diels-Alder reaction of the
nadimide. This process is accomplished -with the evolution of a
small amount of cyclopentadiene. A significant improvement in
processing over the polyamic acids was realized but the resultant
resin was brittle. The P13N patents were purchased by the Ciba-
Geigy Corporation who was unsuccessful in developing a P13N
product line.
Work at Rhone-Poulenc on polyimides resulted in the develop
ment of maleimi de end-capped oligomers which could be chain ex
tended thermally and/o
(Eq. 5) (8*)· The Kerimi
Rhodia in the U. S. evolved from this technology. They exhibit
excellent melt flow properties and easily form void-free parts.
Although these materials are used in certain applications such
(5)
RESIN FROM ADDITION THROUGH DOUBLE BOND AND THROUGH
MICHAEL REACTION OF AMINE WITH DOUBLE BOND
as circuit boards, they have not received acceptance as high
temperature structural resins because of their limited thermal
stability.
Current High Temperature Structural Resins
The P13N chemistry was extended at NASA-Lewis Research
Center to the development of PMR-15, PMR standing for Polymeri
zation of Monomeric Re act ant s (£). The chemistry is the same as
in P13N except the average oligomeric molecular weight was in
creased to 1500 and the material initially used for prepreg
formation is a mixture of monomers. The dianhydride of 3,3**+, V-
benzophenone tetracarboxylic acid and nadic anhydride are
separately reacted with an excess of methanol to form the half-
methyl esters. hk*-Methylene di aniline is added to a methanolic
9
solution of the two half-esters. The resultant varnish is used
to impregnate the reinforcement. Tack and drape are obtained in
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
1. HERGENROTHER AND JOHNSTON High-Temperature Laminating 7
the prepreg through residual methanol which frequently evaporates
and leaves the prepreg boardy. Esterifi cation beyond the half-
ester stage has been observed and has been the source of process
ing problems. Residual volatiles are removed during a B-stage
cycle with additional cure occurring through the nadimide end-
caps. PMR-15 has shown considerable potential for use i n high
temperature structural composites and is currently under evalua
tion in many laboratories. PMR-15 prepreg i s commercially avail
able.
In an attempt to improve process ability and introduce tack
and drape character into a PI prepreg without using solvent,
work was initiated at NASA-Langley Research Center i n the mid-
19701 s which climaxed i n the development of LARC-l60 (Eq. 6)(l0).
A mixture of nadic anhydrid h,V
carboxylic acid dianhydrid
X / NH " „ . ;
2 V
-H 0, -EtOH
2 (6)
THERMOSET^JL B-STAGED IMIDE FORM
esters using essentially a stoichiometric quantity of ethanol.
A liquid oligomeric amine, Jeffamine AP-22 or Ancamine-DL, i s
then blended with the two half-ethyl esters with the stoichio-
metry adjusted to provide an oligomer with an average molecular
weight of l600. The resultant mixture of monomers i s a viscous
liquid at room temperature and contains no residual solvent. The
monomeric mixture i s amenable to melt impregnation to provide
prepreg with tack and drape without the use of residual solvent.
In composite fabrication, the condensation volatiles are removed
during a B-stage cycle to form imide oligomers which exhibit
excellent flow. These are then thermally chain-extended and
cross-linked through the nadimide end-groups. Composites of
LARC-I60 exhibit good performance at high temperatures. Both
neat resin and prepreg can be obtained commercially. Because of
its enhanced processability, LARC-I60 i s currently being evalua
ted as a matrix material i n many laboratories. Fabrication
development activities on both PMR-15 and LARC-160 are being
sponsored by NASA-Langley at Boeing Aerospace Company and
Rockwell International, respectively.
In Resins for Aerospace; May, C.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1980.