Toughening of Plastics. Advances in Modeling and Experiments

256 Pages·2000·26.86 MB·English

by  Raymond A. Pearson, H.-J. Sue, and A. F. Yee (Eds.)

Toughening of Plastics
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.fw001
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.fw001
ACS SYMPOSIUM SERIES 759
Toughening of Plastics
Advances in Modeling and Experiments
Raymond A. Pearson, EDITOR
Lehigh University
H.-J. Sue, EDITOR
TexasA &MU niversity
A. F. Yee, EDITOR
The University of Michigan
American Chemical Society, Washington DC
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.fw001
Library of Congress Cataloging-in-Publication Data
Toughening of Plastics : testing methods and advances in modeling and experiments /
Raymond A. Pearson, editor, H.-J. Sue, Editor, A.F. Yee, editor.
p. cm.—(ACS symposium series , ISSN 0097-6156 ; 759)
Includes bibliographical references and index.
ISBN 0-8412-3657-7
1. Polymers—Additives—Congresses. 2. Polymers—Mechanical properties—
Congresses.
I. Pearson, Raymond A., 1958- . II. Sue, H.-J. (Hung-Jue, 1958- . III. Yee, A. F.,
1945- .IV. Series.
TP142 .T68 2000
68.4´1—dc21 0-26260
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In Toughening of Plastics; Pearson, R., et al.;
Washington, D.C. 20036
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.fw001
Foreword
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A C S B O O K S D E P A R T M E N T
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.fw001
Preface
It is generally accepted that polymers without additives would be
commercial failures. The toughening of polymers involves the use of additives
called toughening agents. The purpose of toughening agents is to impart impact
resistance and to increase damage tolerance. Typically, elastomeric polymers are
used to toughen engineering plastics although rigid polymers and inorganic fillers
can also be used as toughening agents.
The applications of toughened polymers are commonplace today.
Toughened plastics can be found in the cars we drive, in the appliances in our
home, in the electronic devices in our offices, and even in some of the sports
equipment that we use on weekends. The gains made in understanding the
fundamentals of toughening have resulted in new products and new applications.
In summary, the technology of toughening plastics has had a very positive effect
on society.
All of the chapters in this book are based on the papers presented at the
Fall 1998 American Chemical Society (ACS) Meeting in Boston, Massachusetts
and their abstracts can be found in Volume 79 of the Proceedings of the American
Chemical Society: Division of Polymeric Materials: Science and Engineering, Inc.
The abstracts for the Toughening of Plastics Symposium can be found on pages
140 to 217, which contain over 30 contributions. Unfortunately, these papers are
rather brief, hence our motivation for publishing a more comprehensive
compilation of papers.
The papers in this book were chosen because of their significance to the
technology of toughened polymers. Many of the papers are from leading
worldwide experts. We have carefully selected 12 papers that seem to capture the
excitement of the symposium. These papers represent the most recent advances in
synthesis, processing, characterizing, and modeling the toughening of plastics. It is
our belief that the compilation of the modeling efforts has more depth than any
publication to date.
Acknowledgments
The ACS has tracked this important technology for many years and has
organized symposia on "Rubber-Modified Thermoset Resins," "Rubber-
Toughened Plastics," "Toughened Plastics I," and "Toughened Plastics 11".
ix
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.pr001
Therefore, we are indebted to all contributors for their time and patience. We also
thank the ACS Division of Polymeric Materials: Science and Engineering, Inc. for
sponsoring the workshop, the symposium, and this book.
R A Y M O N D A. PEARSON
Department of Materials Science and Engineering
Lehigh University
Bethlehem, PA 18015-3195
H.-J. SUE
Department of Mechanical Engineering
Texas A&M University
College Station, TX 77843-3123
A. F. YEE
Department of Materials Science and Engineering
University of Michigan
Ann Arbor, MI 48109
x
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.pr001
Chapter 1
Introduction to the Toughening of Polymers
Raymond A. Pearson
Department of Materials Science and Engineering,
Lehigh University, Bethlehem, PA 18015-3195
The purpose of this chapter is to provide the background needed for
subsequent chapters on toughened plastics. This chapter introduces
the topic of fracture mechanics, describes the methods used to
quantify toughness, discusses the origin of toughness in terms of
toughening mechanisms, briefly reviews the factors influencing
toughness, and comments on the latest advances in the science of
the toughening of polymers. The main focus is on polymers blends
toughened by a soft rubber phase although several alternative
approaches are briefly mentioned. The purpose of this book is to
present the latest advances in the field of toughened polymers so
that the materials specialist can use these latest concepts to create
new materials with improved toughness.
Introduction
The purpose of this chapter is to provide an introductory review of toughened
polymers. In this section, a brief review of the development of polymer blends is
attempted. It will be revealed that the first toughened polymer blends were binary
mixtures of rubber and plastic, the so called rubber-toughened plastics. Ternary
blends were developed soon after the simple binary mixtures and also contain a
rubbery phase for toughness. Most recently, toughr igid-rigidp olymer alloys have
been developed in an attempt to improve toughness without sacrificing strength.
© 2000 American Chemical Society 1
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.ch001
2
The history of polymer blends and alloys is described in detail in a book by
Utracki [1], For introductory purposes a brief description of polymer blends is
contained below.
The first modern thermoplastic blend is often identified as a PVC/NBR blend
which, in early 1942, NBR was discovered to permanently plasticize PVC. A co-
polymerized polystyrene-polybutadiene blend was introduced by Dow later that same
year. Soon after the introduction of PS-PB blends, mechanical mixtures of NBR and
SAN were developed thus ABS blends were born. ABS-type blends dominate the
blend market and, on average, 80 new blends of ABS are introduced to the US market
place each year [1].
Toughened engineering polymer blends were developed as early as 1960 when it
was discovered that polystyrene (PS) was miscible with poly-2,6-dimethyl-l,4-
poryphenyleneether (PPE). Polystyrene-butadiene copolymers were added to improve
impact resistance. These ternary blends, known in the industry as the NoryP blends,
were commercialized by the General Electric company. A number of other toughened
engineering polymer blends soon followed including super tough nylon, rubber-
toughened PBT/PET, and rubber-toughened polycarbonate (PC). Ternary blends of
PC/PBT/ rubber and PPE/ PA/ rubber were also commercialized. The most
frequently claimed property contained in patents during this period was high impact
strength.
In the early 1980s it was discovered that epoxy resins could be toughened by the
addition of a rigid thermoplastic phase, thus ther igid-rigidp olymer alloy concept was
born [2]. The advantage of using ar igidt hermoplastic phase over a soft rubbery
phase is that there is not a drop in modulus or strength. Such behavior is critical for
matrices used in advanced composites. Polyether sulfone, poly sulfone,
polyetherimide, polyphenylene ether, and polybutylene terephthalate have been
evaluated as toughening agents for a wide variety of memosetting plastics [3] and in
some cases, significant increases int oughnessh as been achieved.
Of course, the use of inorganicf illerst o modify the properties of polymers has
been around for many years. However, much of the focus on filled-polymers has
been on the reinforcing effect, yet it has long been recognized that fracture toughness
is also improved [4,5]. Perhaps the lack of attention given to inorganicf illersa s
toughening agents is due to their poor response to impact situations and the sharp
surfaces generated by an impact event However, the fact remains that the addition of
inorganic spheres, platelets or shortf ibersc an improve the static fracture toughness of
many polymers.
The main reasons for blending, compounding and reinforcing plastics are
economy and r^rformance. If a material can be generated that will lower the overall
cost while maintaining or improving performance of a particular product then the
manufacturer must use it to remain competitive. The purpose of this book is to
present the latest advances in thef ieldo f toughened polymers so that the materials
specialist can use these latest concepts to create new materials with improved
toughness.
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.ch001
3
Measurements of Toughness
The toughness of a material can be measured using a variety of techniques. Tensile
testing (ASTM D638) is perhaps the simplest technique. The area under the stress
strain curve is often used to quantify toughness. However, the mechanical behavior
of polymers is extremely rate and stress-state dependent [6]. Therefore, more
complicated tests have been derived to predict the performance of plastic products.
For example, the ASTM D 3763 puncture test and the ASTM D256 Izod test utilize
biaxial and triaxial stress states at impact velocities. Unfortunately, the values
provided by these impact tests cannot be used in directly in design. Preliminary
screening of materials can be accomplished by looking at ductile-brittle transition
temperatures of the appropriate impact test The qualitative nature of the impact tests
make them better-suited for quality control purposes than for design For quantitative
measures of toughness, most researchers employ the use of fracture mechanics.
Linear Elastic Fracture Mechanics (LEFM) is now widely used to quantify the
toughness of polymers (ASTM D5045). Two test geometries are covered by the
ASTM test method for plane-strain fracture toughness and strain energy release rate
of plastic materials. See Figure 1. Fracture toughness is often quantified using a
stress intensity approach but strain energy release rates can also be used. There are
numerous textbooks on fracture toughness testing and it is recommended to review
the books written by Broek [7], Hertzberg [8], and Kinloch and Young [9].
(a) (b)
Figure 1: Schematic diagrams of the a) compact tension (CT) and b) Single-Edge-
Notched, 3-PointBend (SEN-3PB) specimens, which are often used to determine the
fracture toughness ofp olymers.
The stres intensity factor, K, is a parameter used to relate the applied stres, c
and the flaw size, a:
K = GY4a (1)
In Toughening of Plastics; Pearson, R., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
August 15, 2012 | http://pubs.acs.org
Publication Date: August 8, 2000 | doi: 10.1021/bk-2000-0759.ch001