Modern Plastics Handbook 2011 Part 1 pptx

Modern
Plastics
Handbook
Modern Plastics
and
Charles A. Harper Editor in Chief
Technology Seminars, Inc.
Lutherville, Maryland
McGraw-Hill
New York San Francisco Washington, D.C. Auckland Bogotá
Caracas Lisbon London Madrid Mexico City Milan
Montreal New Delhi San Juan Singapore
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0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page iii
Library of Congress Cataloging-in-Publication Data
Modern plastics handbook / Modern Plastics, Charles A. Harper (editor in chief).
p. cm.
ISBN 0-07-026714-6
1. Plastics. I. Modern Plastics. II. Harper, Charles A.
TA455.P5 M62 1999
668.4—dc21 99-056522
CIP
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0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page iv
Contributors
Anne-Marie Baker University of Massachusetts, Lowell, Mass. (CHAP.1)
Carol M. F. Barry University of Massachusetts, Lowell, Mass. (
CHAP.5)
Allison A. Cacciatore TownsendTarnell, Inc., Mt. Olive, N.J. (
CHAP.4)
Fred Gastrock TownsendTarnell, Inc., Mt. Olive, N.J. (

CHAP.4)
John L. Hull Hall/Finmac, Inc., Warminster, Pa. (
CHAP.6)
Carl P. Izzo Consultant, Murrysville, Pa. (
CHAP. 10)
Louis N. Kattas TownsendTarnell, Inc., Mt. Olive, N.J. (
CHAP.4)
Peter Kennedy Moldflow Corporation, Lexington, Mass. (
CHAP. 7, SEC. 3)
Inessa R. Levin TownsendTarnell, Inc., Mt. Olive, N.J. (
CHAP.4)
William R. Lukaszyk Universal Dynamics, Inc., North Plainfield, N.J.
(
CHAP. 7, SEC. 1)
Joey Meade University of Massachusetts, Lowell, Mass. (
CHAP.1)
James Margolis Montreal, Quebec, Canada (
CHAP.3)
Stephen A. Orroth University of Massachusetts, Lowell, Mass. (
CHAP.5)
Edward M. Petrie ABB Transmission Technology Institute, Raleigh, N.C.
(
CHAP.9)
Jordon I. Rotheiser Rotheiser Design, Inc., Highland Park, Ill. (
CHAP.8)
Susan E. Selke Michigan State University, School of Packaging, East
Lansing, Mich. (
CHAP. 12)
Ranganath Shastri Dow Chemical Company, Midland, Mich. (
CHAP.11)

Peter Stoughton Conair, Pittsburgh, Pa. (
CHAP. 7, SEC. 2)
Ralph E. Wright Consultant, Yarmouth, Maine (
CHAP.2)
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page ix
Preface
The Modern Plastics Handbook has been prepared as a third member
of the well-known and highly respected team of publications which
includes Modern Plastics magazine and Modern Plastics World
Encyclopedia. The Modern Plastics Handbook offers a thorough and
comprehensive technical coverage of all aspects of plastics materials
and processes, in all of their forms, along with coverage of additives,
auxiliary equipment, plastic product design, testing, specifications and
standards, and the increasingly critical subject of plastics recycling
and biodegradability. Thus, this Handbook will serve a wide range of
interests. Likewise, with presentations ranging from terms and defin-
itions and fundamentals, to clearly explained technical discussions, to
extensive data and guideline information, this Handbook will be use-
ful for all levels of interest and backgrounds. These broad objectives
could only have been achieved by an outstanding and uniquely diverse
group of authors with a combination of academic, professional, and
business backgrounds. It has been my good fortune to have obtained
such an elite group of authors, and it has been a distinct pleasure to
have worked with this group in the creation of this Handbook. I would
like to pay my highest respects and offer my deep appreciation to all
of them.
The Handbook has been organized and is presented as a thorough
sourcebook of technical explanations, data, information, and guide-
lines for all ranges of interests. It offers an extensive array of property
and performance data as a function of the most important product and

process variables. The chapter organization and coverage is well suited
to reader convenience for the wide range of product and equipment
categories. The first three chapters cover the important groups of plas-
tic materials, namely, thermoplastics, thermosets, and elastomers.
Then comes a chapter on the all important and broad based group
of additives, which are so critical for tailoring plastic properties.
Following this are three chapters covering processing technologies and
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page xi
equipment for all types of plastics, and the all important subject of
auxiliary equipment and components for optimized plastics process-
ing. Next is a most thorough and comprehensive chapter on design of
plastic products, rarely treated in such a practical manner. After this,
two chapters are devoted to the highly important plastic materials and
process topics of coatings and adhesives, including surface finishing
and fabricating of plastic parts. Finally, one chapter is devoted to the
fundamentally important areas of testing and standards, and one
chapter to the increasingly critical area of plastic recycling and
biodegradability.
Needless to say, a book of this caliber could not have been achieved
without the guidance and support of many people. While it is not pos-
sible to name all of the advisors and constant supporters, I feel that I
must highlight a few. First, I would like to thank the Modern Plastics
team, namely, Robert D. Leaversuch, Executive Editor of Modern
Plastics magazine, Stephanie Finn, Modern Plastics Events Manager,
Steven J. Schultz, Managing Director, Modern Plastics World
Encyclopedia, and William A. Kaplan, Managing Editor of Modern
Plastics World Encyclopedia. Their advice and help was constant.
Next, I would like to express my very great appreciation to the team
from Society of Plastics Engineers, who both helped me get off the
ground and supported me readily all through this project. They are

Michael R. Cappelletti, Executive Director, David R. Harper, Past
President, John L. Hull, Honored Service Member, and Glenn L. Beall,
Distinguished Member. In addition, I would like to acknowledge, with
deep appreciation, the advice and assistance of Dr. Robert Nunn and
Dr. Robert Malloy of University of Massachusetts, Lowell for their
guidance and support, especially in selection of chapter authors. Last,
but not least, I am indebted to Robert Esposito, Executive Editor of
the McGraw-Hill Professional Book Group, for both his support and
patience in my editorial responsibilities for this Modern Plastics
Handbook.
It is my hope, and expectation, that this book will serve its reader
well. Any comments or suggestions will be welcomed.
Charles A. Harper
xii Preface
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page xii
Contents
Contributors ix
Preface xi
Chapter 1. Thermoplastics 1.1
1.1 Introduction 1.1
1.2 Polymer Categories 1.4
1.3 Comparative Properties of Thermoplastics 1.79
1.4 Additives 1.79
1.5 Fillers 1.82
1.6 Polymer Blends 1.83
References 1.85
Chapter 2. Thermosets, Reinforced Plastics, and Composites 2.1
2.1 Resins 2.1
2.2 Thermosetting Resin Family 2.2
2.3 Resin Characteristics 2.10

2.4 Resin Forms 2.10
2.5 Liquid Resin Processes 2.13
2.6 Laminates 2.29
2.7 Molding Compounds 2.38
References 2.88
Chapter 3. Elastomeric Materials and Processes 3.1
3.1 Introduction 3.1
3.2 Thermoplastic Elastomers (TPEs) 3.1
3.3 Melt Processing Rubbers (MPRs) 3.24
3.4 Thermoplastic Vulcanizates (TPVs) 3.26
3.5 Synthetic Rubbers 3.33
3.6 Natural Rubber 3.48
3.7 Conclusion 3.49
References 3.50
v
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page v
Chapter 4. Plastic Additives 4.1
4.1 Introduction 4.1
4.2 Scope 4.2
4.3 Antiblock and Slip Agents 4.2
4.4 Antioxidants 4.6
4.5 Antistatic Agents 4.12
4.6 Biocides 4.16
4.7 Chemical Blowing Agents 4.19
4.8 Coupling Agents 4.23
4.9 Flame Retardants 4.26
4.10 Heat Stabilizers 4.36
4.11 Impact Modifiers 4.41
4.12 Light Stabilizers 4.46
4.13 Lubricants and Mold Release Agents 4.49

4.14 Nucleating Agents 4.54
4.15 Organic Peroxides 4.58
4.16 Plasticizers 4.62
4.17 Polyurethane Catalysts 4.66
Chapter 5. Processing of Thermoplastics 5.1
5.1 Material Concepts 5.2
5.2 Extrusion 5.18
5.3 Estrusion Processes 5.55
5.4 Injection Molding 5.84
References 5.121
Chapter 6. Processing of Thermosets 6.1
6.1 Introduction 6.1
6.2 Molding Processes 6.2
6.3 Techniques for Machining and Secondary Operations 6.24
6.4 Postmolding Operations 6.28
6.5 Process-Related Design Considerations 6.29
6.6 Mold Construction and Fabrication 6.34
6.7 Summary 6.37
Chapter 7. Auxiliary Equipment
7.2 Raw Material Delivery 7.5
7.3 Bulk Storage of Resin 7.8
7.4 Bulk Resin Conveying Systems 7.22
7.5 Bulk Delivery Systems 7.28
7.6 Blending Systems 7.35
7.7 Regrind Systems 7.38
7.8 Material Drying 7.43
7.9 Loading Systems 7.50
7.10 System Integration 7.57
vi Contents
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page vi

7.2
Section 1. Material Handling 7.3
7.1 Introduction 7.3
Section 2. Drying and Dryers 7.63
7.11 Why Do We Dry Plastic Materials? 7.63
7.12 Hygroscopic and Nonhygroscopic Polymers 7.65
7.13 Drying Hygroscopic Polymers 7.66
7.14 How Physical Characteristics of Plastics Affect Drying 7.71
7.15 How Dryers Work 7.72
7.16 Critical Dryer Components 7.77
7.17 Monitoring Drying Conditions 7.85
7.18 Drying System Configurations 7.89
7.19 Gas or Electric? 7.93
7.20 Handling Dried Material 7.94
Section 3. CAD, CAM, CAE 7.99
7.21 Introduction 7.99
7.22 Simulation and Polymer Processing 7.101
7.23 The Injection-Molding Process 7.104
7.24 History of Injection-Molding Simulation 7.106
7.25 Current Technology for Injection-Molding Simulation 7.109
7.26 The Changing Face of CAE 7.123
7.27 Machine Control 7.126
7.28 Future Trends 7.129
References on CAD, CAM, CAE 7.131
Chapter 8. Design of Plastic Products 8.1
8.1 Fundamentals 8.1
8.2 Design Fundamentals for Plastic Parts 8.49
8.3 Design Details Specific to Major Processes 8.79
References 8.116
Chapter 9. Finishing, Assembly, and Decorating 9.1

9.1 Introduction 9.1
9.2 Machining and Finishing 9.2
9.3 Assembly of Plastics Parts—General Considerations 9.16
9.4 Methods of Mechanical Joining 9.17
9.5 Adhesive Bonding 9.35
9.6 Welding 9.70
9.7 Recommended Assembly Processes
for Common Plastics 9.80
9.8 Decorating Plastics 9.91
References 9.105
Chapter 10. Coatings and Finishes 10.1
10.1 Introduction 10.1
10.2 Environment and Safety 10.5
10.3 Surface Preparation 10.6
10.4 Coating Selection 10.11
10.5 Coating Materials 10.18
10.6 Application Methods 10.42
Contents vii
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page vii
10.7 Curing 10.55
10.8 Summary 10.58
References 10.59
Chapter 11. Plastics Testing 11.1
11.1 Introduction 11.1
11.2 The Need for Testing Plastics 11.1
11.3 Diverse Types of Testing 11.2
11.4 Test Methods for Acquisition and Reporting of Property Data 11.13
11.5 Uniform Reporting Format 11.66
11.6 Misunderstood and Misused Properties 11.70
11.7 Costs of Data Generation 11.73

Appendix 11.1 Selected ISO/IEC Standards/Documents 11.77
Appendix 11.2 Selected ASTM Standards 11.84
Appendix 11.3 List of Resources 11.87
Appendix 11.4 Some Unit Conversion Factors 11.92
References 11.92
Suggested Reading 11.94
Chapter 12. Plastics Recycling and Biodegradable Plastics 12.1
12.1 Introduction 12.1
12.2 Overview of Recycling 12.14
12.3 Design for Recycling 12.22
12.4 Recycling of Major Polymers 12.24
12.5 Overview of Plastics Degradation 12.71
12.6 Natural Biodegradable Polymers 12.80
12.7 Synthetic Biodegradable Polymers 12.92
12.8 Water-Soluble Polymers 12.97
12.9 Summary 12.99
References 12.100
Appendix A. Glossary of Terms and Definitions A.1
Appendix B. Some Common Abbreviations Used
in the Plastics Industry B.1
Appendix C. Important Properties of Plastics
and Listing of Plastic Suppliers C.1
Appendix D. Sources of Specifications and
Standards for Plastics and Composites D.1
Appendix E. Plastics Associations E.1
Index follows Appendix E
viii Contents
0267146_FM_Harper_Plastics_MHT 2/24/00 4:39 PM Page viii
1.1
Thermoplastics

A M. M. Baker
Joey Mead
Plastics Engineering Department
University of Massachusetts, Lowell
1.1 Introduction
Plastics are an important part of everyday life; products made from
plastics range from sophisticated products, such as prosthetic hip and
knee joints, to disposable food utensils. One of the reasons for the
great popularity of plastics in a wide variety of industrial applications
is due to the tremendous range of properties exhibited by plastics and
their ease of processing. Plastic properties can be tailored to meet spe-
cific needs by varying the atomic makeup of the repeat structure; by
varying molecular weight and molecular weight distribution; by vary-
ing flexibility as governed by presence of side chain branching, as well
as the lengths and polarities of the side chains; and by tailoring the
degree of crystallinity, the amount of orientation imparted to the plas-
tic during processing and through copolymerization, blending with
other plastics, and through modification with an enormous range of
additives (fillers, fibers, plasticizers, stabilizers). Given all of the
avenues available to pursue tailoring any given polymer, it is not sur-
prising that such a variety of choices available to us today exist.
Polymeric materials have been used since early times, even though
their exact nature was unknown. In the 1400s Christopher Columbus
found natives of Haiti playing with balls made from material obtained
from a tree. This was natural rubber, which became an important
Chapter
1
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.1
product after Charles Goodyear discovered that the addition of sulfur
dramatically improved the properties. However, the use of polymeric

materials was still limited to natural-based materials. The first true
synthetic polymers were prepared in the early 1900s using phenol
and formaldehyde to form resins—Baekeland’s Bakelite. Even with
the development of synthetic polymers, scientists were still unaware
of the true nature of the materials they had prepared. For many years
scientists believed they were colloids—aggregates of molecules with a
particle size of 10- to 1000-nm diameter. It was not until the 1920s
that Herman Staudinger showed that polymers were giant molecules
or macromolecules. In 1928 Carothers developed linear polyesters
and then polyamides, now known as nylon. In the 1950s Ziegler and
Natta’s work on anionic coordination catalysts led to the development
of polypropylene, high-density linear polyethylene, and other stere-
ospecific polymers.
Polymers come in many forms including plastics, rubber, and fibers.
Plastics are stiffer than rubber, yet have reduced low-temperature
properties. Generally, a plastic differs from a rubbery material due to
the location of its glass transition temperature (T
g
). A plastic has a T
g
above room temperature, while a rubber will have a T
g
below room
temperature. T
g
is most clearly defined by evaluating the classic rela-
tionship of elastic modulus to temperature for polymers as presented
in Fig. 1.1. At low temperatures, the material can best be described as
a glassy solid. It has a high modulus and behavior in this state is char-
acterized ideally as a purely elastic solid. In this temperature regime,

materials most closely obey Hooke’s law:
␴ϭEε
where ␴ is the stress being applied and ε is the strain. Young’s modu-
lus, E, is the proportionality constant relating stress and strain.
In the leathery region, the modulus is reduced by up to three orders
of magnitude for amorphous polymers. The temperature at which the
polymer behavior changes from glassy to leathery is known as the
glass transition temperature, T
g
. The rubbery plateau has a relatively
stable modulus until as the temperature is further increased, a rub-
bery flow begins. Motion at this point does not involve entire mole-
cules, but in this region deformations begin to become nonrecoverable
as permanent set takes place. As temperature is further increased,
eventually the onset of liquid flow takes place. There is little elastic
recovery in this region, and the flow involves entire molecules slipping
past each other. Ideally, this region is modeled as representing viscous
materials which obey Newton’s law :
␴ϭ␩
ؒ
ε
1.2 Chapter One
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.2
Plastics can also be separated into thermoplastics and thermosets.
A thermoplastic material is a high molecular weight polymer that is
not cross-linked. A thermoplastic material can exist in a linear or
branched structure. Upon heating a thermoplastic, a highly viscous
liquid is formed that can be shaped using plastics processing equip-
ment. A thermoset has all of the chains tied together with covalent
bonds in a network (cross-linked). A thermoset cannot be reprocessed

once cross-linked, but a thermoplastic material can be reprocessed by
heating to the appropriate temperature. The different types of struc-
tures are shown in Fig. 1.2.
A polymer is prepared by stringing together a series of low molecu-
lar weight species (such as ethylene) into an extremely long chain
(polyethylene) much as one would string together a series of beads to
make a necklace. The chemical characteristics of the starting low
molecular weight species will determine the properties of the final
polymer. When two different low molecular weight species are poly-
merized, the resulting polymer is termed a copolymer such as ethylene
vinylacetate.
The properties of different polymers can vary widely, for example,
the modulus can vary from 1 MN/m
2
to 50 GN/m
2
. Properties can be
varied for each individual plastic material as well, simply by varying
the microstructure of the material.
In its solid form a polymer can take up different structures depend-
ing on the structure of the polymer chain as well as the processing con-
ditions. The polymer may exist in a random unordered structure
termed an amorphous polymer. An example of an amorphous polymer
Thermoplastics 1.3
Figure 1.1 Relationship between elastic modulus and temperature.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.3
is polystyrene. If the structure of the polymer backbone is a regular,
ordered structure, then the polymer can tightly pack into an ordered
crystalline structure, although the material will generally be only
semicrystalline. Examples are polyethylene and polypropylene. The

exact makeup and details of the polymer backbone will determine
whether or not the polymer is capable of crystallizing. This microstruc-
ture can be controlled by different synthetic methods. As mentioned
previously, the Ziegler-Natta catalysts are capable of controlling the
microstructure to produce stereospecific polymers. The types of
microstructure that can be obtained for a vinyl polymer are shown in
Fig. 1.3. The isotactic and syndiotactic structures are capable of crys-
tallizing because of their highly regular backbone. The atactic form
would produce an amorphous material.
1.2 Polymer Categories
1.2.1 Acetal (POM)
Acetal polymers are formed from the polymerization of formaldehyde.
They are also known by the name polyoxymethylenes (POM). Polymers
prepared from formaldehyde were studied by Staudinger in the 1920s,
but thermally stable materials were not introduced until the 1950s
when DuPont developed Delrin.
1
Homopolymers are prepared from
very pure formaldehyde by anionic polymerization, as shown in Fig.
1.4. Amines and the soluble salts of alkali metals catalyze the reaction.
2
The polymer formed is insoluble and is removed as the reaction pro-
ceeds. Thermal degradation of the acetal resin occurs by unzipping
with the release of formaldhyde. The thermal stability of the polymer
is increased by esterification of the hydroxyl ends with acetic anhy-
dride. An alternative method to improve the thermal stability is copoly-
1.4 Chapter One
Figure 1.2 Linear, branched, cross-linked polymer structures.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.4
merization with a second monomer such as ethylene oxide. The copoly-

mer is prepared by cationic methods.
3
This was developed by Celanese
and marketed under the tradename Celcon. Hostaform is another
copolymer marketed by Hoescht. The presence of the second monomer
reduces the tendency for the polymer to degrade by unzipping.
4
There are four processes for the thermal degradation of acetal
resins. The first is thermal or base-catalyzed depolymerization from
the chain, resulting in the release of formaldehyde. End capping the
polymer chain will reduce this tendency. The second is oxidative
attack at random positions, again leading to depolymerization. The
use of antioxidants will reduce this degradation mechanism.
Copolymerization is also helpful. The third mechanism is cleavage of
the acetal linkage by acids. It is, therefore, important not to process
acetals in equipment used for polyvinyl chloride (PVC), unless it has
been cleaned, due to the possible presence of traces of HCl. The fourth
degradation mechanism is thermal depolymerization at temperatures
Thermoplastics 1.5
Figure 1.3 Isotactic, syndiotactic, and atactic polymer chains.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.5
above 270°C. It is important that processing temperatures remain
below this temperature to avoid degradation of the polymer.
5
Acetals are highly crystalline, typically 75% crystalline, with a melt-
ing point of 180°C.
6
Compared to polyethylene (PE), the chains pack
closer together because of the shorter CᎏO bond. As a result, the poly-
mer has a higher melting point. It is also harder than PE. The high

degree of crystallinity imparts good solvent resistance to acetal poly-
mers. The polymer is essentially linear with molecular weights (M
n
) in
the range of 20,000 to 110,000.
7
Acetal resins are strong and stiff thermoplastics with good fatigue
properties and dimensional stability. They also have a low coefficient
of friction and good heat resistance.
8
Acetal resins are considered sim-
ilar to nylons, but are better in fatigue, creep, stiffness, and water
resistance.
9
Acetal resins do not, however, have the creep resistance of
polycarbonate. As mentioned previously, acetal resins have excellent
solvent resistance with no organic solvents found below 70°C, howev-
er, swelling may occur in some solvents. Acetal resins are susceptible
to strong acids and alkalis, as well as oxidizing agents. Although the
CᎏO bond is polar, it is balanced and much less polar than the car-
bonyl group present in nylon. As a result, acetal resins have relatively
low water absorption. The small amount of moisture absorbed may
cause swelling and dimensional changes, but will not degrade the poly-
mer by hydrolysis.
10
The effects of moisture are considerably less dra-
matic than for nylon polymers. Ultraviolet light may cause
degradation, which can be reduced by the addition of carbon black. The
copolymers generally have similar properties, but the homopolymer
may have slightly better mechanical properties, and higher melting

point, but poorer thermal stability and poorer alkali resistance.
11
Along with both homopolymers and copolymers, there are also filled
materials (glass, fluoropolymer, aramid fiber, and other fillers), tough-
ened grades, and ultraviolet (UV) stabilized grades.
12
Blends of acetal
with polyurethane elastomers show improved toughness and are avail-
able commercially.
Acetal resins are available for injection molding, blow molding, and
extrusion. During processing it is important to avoid overheating or the
production of formaldehyde may cause serious pressure buildup. The
polymer should be purged from the machine before shutdown to avoid
excessive heating during startup.
13
Acetal resins should be stored in a
1.6 Chapter One
CH
2
H
2
COO
n
n
Figure 1.4 Polymerization of formaldehyde to polyoxymethylene.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.6
dry place. The apparent viscosity of acetal resins is less dependent on
shear stress and temperature than polyolefins, but the melt has low
elasticity and melt strength. The low melt strength is a problem for
blow molding applications. For blow molding applications, copolymers

with branched structures are available. Crystallization occurs rapidly
with postmold shrinkage complete within 48 h of molding. Because of
the rapid crystallization it is difficult to obtain clear films.
14
The market demand for acetal resins in the United States and
Canada was 368 million pounds in 1997.
15
Applications for acetal
resins include gears, rollers, plumbing components, pump parts, fan
blades, blow-molded aerosol containers, and molded sprockets and
chains. They are often used as direct replacements for metal. Most of
the acetal resins are processed by injection molding, with the remain-
der used in extruded sheet and rod. Their low coefficient of friction
make acetal resins good for bearings.
16
1.2.2 Biodegradable polymers
Disposal of solid waste is a challenging problem. The United States
consumes over 53 billion pounds of polymers a year for a variety of
applications.
17
When the life cycle of these polymeric parts is complet-
ed they may end up in a landfill. Plastics are often selected for appli-
cations based on their stability to degradation, however, this means
degradation will be very slow, adding to the solid waste problem.
Methods to reduce the amount of solid waste include either recycling
or biodegradation.
18
Considerable work has been done to recycle plas-
tics, both in the manufacturing and consumer area. Biodegradable
materials offer another way to reduce the solid waste problem. Most

waste is disposed of by burial in a landfill. Under these conditions oxy-
gen is depleted and biodegradation must proceed without the presence
of oxygen.
19
An alternative is aerobic composting. In selecting a poly-
mer that will undergo biodegradation it is important to ascertain the
method of disposal. Will the polymer be degraded in the presence of
oxygen and water, and what will be the pH level? Biodegradation can
be separated into two types—chemical and microbial degradation.
Chemical degradation includes degradation by oxidation, photodegra-
dation, thermal degradation, and hydrolysis. Microbial degradation
can include both fungi and bacteria. The susceptibility of a polymer to
biodegradation depends on the structure of the backbone.
20
For exam-
ple, polymers with hydrolyzable backbones can be attacked by acids or
bases, breaking down the molecular weight. They are, therefore, more
likely to be degraded. Polymers that fit into this category include most
natural-based polymers, such as polysaccharides, and synthetic mate-
rials, such as polyurethanes, polyamides, polyesters, and polyethers.
Thermoplastics 1.7
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.7
Polymers that contain only carbon groups in the backbone are more
resistant to biodegradation.
Photodegradation can be accomplished by using polymers that are
unstable to light sources or by the use of additives that undergo photo-
degradation. Copolymers of divinyl ketone with styrene, ethylene, or
polypropylene (Eco Atlantic) are examples of materials that are sus-
ceptible to photodegradation.
21

The addition of a UV-absorbing mate-
rial will also act to enhance photodegradation of a polymer. An
example is the addition of iron dithiocarbamate.
22
The degradation
must be controlled to ensure that the polymer does not degrade pre-
maturely.
Many polymers described elsewhere in this book can be considered
for biodegradable applications. Polyvinyl alcohol has been considered
in applications requiring biodegradation because of its water solubil-
ity. However, the actual degradation of the polymer chain may be
slow.
23
Polyvinyl alcohol is a semicrystalline polymer synthesized
from polyvinyl acetate. The properties are governed by the molecular
weight and by the amount of hydrolysis. Water soluble polyvinyl alco-
hol has a degree of hydrolysis 87 to 89%. Water insoluble polymers
are formed if the degree of hydrolysis is greater than 89%.
24
Cellulose-based polymers are some of the more widely available, nat-
urally based polymers. They can, therefore, be used in applications
requiring biodegradation. For example, regenerated cellulose is used in
packaging applications.
25
A biodegradable grade of cellulose acetate is
available from Rhone-Poulenc (Bioceta and Biocellat), where an addi-
tive acts to enhance the biodegradation.
26
This material finds applica-
tion in blister packaging, transparent window envelopes, and other

packaging applications.
Starch-based products are also available for applications requiring
biodegradability. The starch is often blended with polymers for better
properties. For example, polyethylene films containing between 5 to
10% cornstarch have been used in biodegradable applications. Blends
of starch with vinyl alcohol are produced by Fertec (Italy) and used in
both film and solid product applications.
27
The content of starch in
these blends can range up to 50% by weight and the materials can be
processed on conventional processing equipment. A product developed
by Warner-Lambert, called Novon, is also a blend of polymer and
starch, but the starch contents in Novon are higher than in the mate-
rial by Fertec. In some cases the content can be over 80% starch.
28
Polylactides (PLA) and copolymers are also of interest in biodegrad-
able applications. This material is a thermoplastic polyester synthe-
sized from the ring opening of lactides. Lactides are cyclic diesters of
lactic acid.
29
A similar material to polylactide is polyglycolide (PGA).
1.8 Chapter One
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.8
PGA is also a thermoplastic polyester, but one that is formed from gly-
colic acids. Both PLA and PGA are highly crystalline materials. These
materials find application in surgical sutures, resorbable plates and
screws for fractures, and new applications in food packaging are also
being investigated.
Polycaprolactones are also considered in biodegradable applications
such as films and slow-release matrices for pharmaceuticals and fer-

tilizers.
30
Polycaprolactone is produced through ring opening polymer-
ization of lactone rings with a typical molecular weight in the range of
15,000 to 40,000.
31
It is a linear, semicrystalline polymer with a melt-
ing point near 62°C and a glass transition temperature about Ϫ60°C.
32
A more recent biodegradable polymer is polyhydroxybutyrate-
valerate copolymer (PHBV). These copolymers differ from many of
the typical plastic materials in that they are produced through bio-
chemical means. It is produced commercially by ICI using the bacte-
ria Alcaligenes eutrophus, which is fed a carbohydrate. The bacteria
produce polyesters, which are harvested at the end of the process.
33
When the bacteria are fed glucose, the pure polyhydroxybutyrate
polymer is formed, while a mixed feed of glucose and propionic acid
will produce the copolymers.
34
Different grades are commercially
available that vary in the amount of hydroxyvalerate units and the
presence of plasticizers. The pure hydroxybutyrate polymer has a
melting point between 173 and 180°C and a T
g
near 5°C.
35
Copolymers with hydroxyvalerate have reduced melting points,
greater flexibility and impact strength, but lower modulus and ten-
sile strength. The level of hydroxyvalerate is 5 to 12%. These copoly-

mers are fully degradable in many microbial environments.
Processing of PHBV copolymers requires careful control of the
process temperatures. The material will degrade above 195°C, so
processing temperatures should be kept below 180°C and the pro-
cessing time kept to a minimum. It is more difficult to process
unplasticized copolymers with lower hydroxyvalerate content
because of the higher processing temperatures required. Applications
for PHBV copolymers include shampoo bottles, cosmetic packaging,
and as a laminating coating for paper products.
36
Other biodegradable polymers include Konjac, a water-soluble nat-
ural polysaccharide produced by FMC, Chitin, another polysaccharide
that is insoluble in water, and Chitosan, which is soluble in water.
37
Chitin is found in insect exoskeletons and in shellfish. Chitosan can be
formed from chitin and is also found in fungal cell walls.
38
Chitin is
used in many biomedical applications, including dialysis membranes,
bacteriostatic agents, and wound dressings. Other applications
include cosmetics, water treatment, adhesives, and fungicides.
39
Thermoplastics 1.9
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.9
1.2.3 Cellulosics
Cellulosic polymers are the most abundant organic polymers in the
world, making up the principal polysaccharide in the walls of almost
all of the cells of green plants and many fungi species.
40
Plants produce

cellulose through photosynthesis. Pure cellulose decomposes before it
melts, and must be chemically modified to yield a thermoplastic. The
chemical structure of cellulose is a heterochain linkage of different
anhydroglucose units into high molecular weight polymer, regardless
of plant source. The plant source, however, does affect molecular
weight, molecular weight distribution, degrees of orientation, and
morphological structure. Material described commonly as “cellulose”
can actually contain hemicelluloses and lignin.
41
Wood is the largest
source of cellulose and is processed as fibers to supply the paper indus-
try and is widely used in housing and industrial buildings. Cotton-
derived cellulose is the largest source of textile and industrial fibers,
with the combined result being that cellulose is the primary polymer
serving the housing and clothing industries. Crystalline modifications
result in celluloses of differing mechanical properties, and Table 1.1
compares the tensile strengths and ultimate elongations of some com-
mon celluloses.
42
Cellulose, whose repeat structure features three hydroxyl groups,
reacts with organic acids, anhydrides, and acid chlorides to form
esters. Plastics from these cellulose esters are extruded into film and
sheet, and are injection-molded to form a wide variety of parts.
Cellulose esters can also be compression-molded and cast from solu-
tion to form a coating. The three most industrially important cellulose
ester plastics are cellulose acetate (CA), cellulose acetate butyrate
(CAB), and cellulose acetate propionate (CAP), with structures as
shown below in Fig. 1.5.
These cellulose acetates are noted for their toughness, gloss, and
transparency. CA is well suited for applications requiring hardness

and stiffness, as long as the temperature and humidity conditions
don’t cause the CA to be too dimensionally unstable. CAB has the best
environmental stress cracking resistance, low-temperature impact
1.10 Chapter One
TABLE 1.1 Selected Mechanical Properties of Common Celluloses
Tensile strength, MPa Ultimate elongation, %
Form Dry Wet Dry Wet
Ramie 900 1060 2.3 2.4
Cotton 200–800 200–800 12–16 6–13
Flax 824 863 1.8 2.2
Viscose rayon 200–400 100–200 8–26 13–43
Cellulose acetate 150–200 100–120 21–30 29–30
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.10
Figure 1.5 Structures of cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate.
OCOCH
3
OCOCH
3
OCOC
4
H
9
OCOC
4
H
9
H
9
C
4

OCO
OCOC
3
H
7
OCOC
3
H
7
H
7
C
3
OCO
H
3
COC O
CH
CH CH
CH
CH
CH
CH
CH
CH CH
CH
CH
OCH
OCH
O

O
OCH
O
1.11
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.11
strength, and dimensional stability. CAP has the highest tensile
strength and hardness. Comparison of typical compositions and prop-
erties for a range of formulations are given in Table 1.2.
43
Properties
can be tailored by formulating with different types and loadings of
plasticizers.
Formulation of cellulose esters is required to reduce charring and
thermal discoloration, and typically includes the addition of heat sta-
bilizers, antioxidants, plasticizers, UV stabilizers, and coloring
agents.
44
Cellulose molecules are rigid due to the strong intermolecu-
lar hydrogen bonding which occurs. Cellulose itself is insoluble and
reaches its decomposition temperature prior to melting. The acetyla-
tion of the hydroxyl groups reduces intermolecular bonding, and
increases free volume depending upon the level and chemical nature of
the alkylation.
45
Cellulose acetates are thus soluble in specific sol-
vents, but still require plasticization for rheological properties appro-
priate to molding and extrusion processing conditions. Blends of
ethylene vinyl acetate (EVA) copolymers and CAB are available.
Cellulose acetates have also been graft-copolymerized with alkyl
esters of acrylic and methacrylic acid and then blended with EVA to

form a clear, readily processable, thermoplastic.
CA is cast into sheet form for blister packaging, window envelopes,
and file tab applications. CA is injection-molded into tool handles,
tooth brushes, ophthalmic frames, and appliance housings and is
extruded into pens, pencils, knobs, packaging films, and industrial
pressure-sensitive tapes. CAB is molded into steering wheels, tool
handles, camera parts, safety goggles, and football nose guards. CAP
is injection-molded into steering wheels, telephones, appliance hous-
ings, flashlight cases, screw and bolt anchors, and is extruded into
1.12 Chapter One
TABLE 1.2 Selected Mechanical Properties of Cellulose Esters
Cellulose Cellulose acetate Cellulose acetate
Composition, % acetate butyrate propionate
Acetyl 38–40 13–15 1.5–3.5
Butyrl — 36–38 —
Propionyl — — 43–47
Hydroxyl 3.5–4.5 1–2 2–3
Tensile strength at fracture,
23°C, MPa 13.1–58.6 13.8–51.7 13.8–51.7
Ultimate elongation, % 6–50 38–74 35–60
Izod impact strength, J/m
notched, 23°C 6.6–132.7 9.9–149.3 13.3–182.5
notched, Ϫ40°C 1.9–14.3 6.6–23.8 1.9–19.0
Rockwell hardness, R scale 39–120 29–117 20–120
Percent moisture absorption
at 24 h 2.0–6.5 1.0–4.0 1.0–3.0
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.12
pens, pencils, tooth brushes, packaging fim, and pipe.
46
Cellulose

acetates are well suited for applications which require machining and
then solvent vapor polishing, such as in the case of tool handles, where
the consumer market values the clarity, toughness, and smooth finish.
CA and CAP are likewise suitable for ophthalmic sheeting and injec-
tion-molding applications which require many postfinishing steps.
47
Cellulose acetates are also commercially important in the coatings
arena. In this synthetic modification, cellulose is reacted with an
albrecht halide, primarily methylchloride to yield methylcellulose or
sodium chloroacetate to yield sodium cellulose methylcellulose
(CMC). The structure of CMC is shown in Fig. 1.6. CMC gums are
water soluble and are used in food contact and packaging applica-
tions. Its outstanding film-forming properties are used in paper siz-
ings and textiles and its thickening properties are used in starch
adhesive formulations, paper coatings, toothpaste, and shampoo.
Other cellulose esters, including cellulosehydroxyethyl, hydrox-
ypropylcellulose, and ethylcellulose, are used in film and coating
applications, adhesives, and inks.
1.2.4 Fluoropolymers
Fluoropolymers are noted for their heat-resistance properties. This
is due to the strength and stability of the carbon-fluorine bond.
48
The
first patent was awarded in 1934 to IG Farben for a fluorine-con-
taining polymer, polychlorotrifluoroethylene (PCTFE). This polymer
had limited application and fluoropolymers did not have wide appli-
cation until the discovery of polytetrafluorethylene (PTFE) in
1938.
49
In addition to their high-temperature properties, fluoropoly-

mers are known for their chemical resistance, very low coefficient of
friction, and good dielectric properties. Their mechanical properties
are not high unless reinforcing fillers, such as glass fibers, are
added.
50
The compressive properties of fluoropolymers are generally
superior to their tensile properties. In addition to their high-
Thermoplastics 1.13
OCOCH
2
CO
-
Na
+
O
O
CH
CH
CH CH
HO OH
OCH
Figure 1.6 Sodium cellulose methyl-
cellulose structure.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.13
temperature resistance, these materials have very good toughness
and flexibility at low temperatures.
51
A wide variety of fluoropoly-
mers are available, PTFE, PCTFE, fluorinated ethylene propylene
(FEP), ethylene chlorotrifluoroethylene (ECTFE), ethylene tetraflu-

oroethylene (ETFE), polyvinylindene fluoride (PVDF), and polyvinyl
fluoride (PVF).
Copolymers. FEP is a copolymer of tetrafluoroethylene and hexa-
fluoropropylene. It has properties similar to PTFE, but with a melt
viscosity suitable for molding with conventional thermoplastic pro-
cessing techniques.
52
The improved processability is obtained by
replacing one of the fluorine groups on PTFE with a trifluoromethyl
group as shown in Fig. 1.7.
53
FEP polymers were developed by DuPont, but other commercial
sources are available, such as Neoflon (Daikin Kogyo) and Teflex
(Niitechem, formerly USSR).
54
FEP is a crystalline polymer with a
melting point of 290°C, which can be used for long periods at 200°C
with good retention of properties.
55
FEP has good chemical resistance,
a low dielectric constant, low friction properties, and low gas perme-
ability. Its impact strength is better than PTFE, but the other mechan-
ical properties are similar to PTFE.
56
FEP may be processed by
injection, compression, or blow molding. FEP may be extruded into
sheets, films, rods, or other shapes. Typical processing temperatures
for injection molding and extrusion are in the range of 300 to 380°C.
57
Extrusion should be done at low shear rates because of the polymer’s

high melt viscosity and melt fracture at low shear rates. Applications
for FEP include chemical process pipe linings, wire and cable, and
solar collector glazing.
58
A material similar to FEP, Hostaflon TFB
(Hoechst), is a terpolymer of tetrafluoroethylene, hexafluoropropene,
and vinylidene fluoride.
ECTFE is an alternating copolymer of chlorotrifluoroethylene and
ethylene. It has better wear properties than PTFE along with good
flame resistance. Applications include wire and cable jackets, tank lin-
ings, chemical process valve and pump components, and corrosion-
resistant coatings.
59
ETFE is a copolymer of ethylene and tetrafluoroethylene similar to
ECTFE, but with a higher use temperature. It does not have the flame
1.14 Chapter One
CC
FF
FF
n
CC
FCF
3
FF
Figure 1.7 Structure of FEP.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.14
resistance of ECTFE, however, and will decompose and melt when
exposed to a flame.
60
The polymer has good abrasion resistance for a flu-

orine-containing polymer, along with good impact strength. The polymer
is used for wire and cable insulation where its high-temperature proper-
ties are important. ETFE finds application in electrical systems for com-
puters, aircraft, and heating systems.
61
Polychlorotrifluoroethylene. Polychlorotrifluoroethylene (PCTFE) is
made by the polymerization of chlorotrifluoroethylene, which is pre-
pared by the dechlorination of trichlorotrifluoroethane. The polymer-
ization is initiated with redox initiators.
62
The replacement of one
fluorine atom with a chlorine atom, as shown in Fig. 1.8, breaks up the
symmetry of the PTFE molecule, resulting in a lower melting point and
allowing PCTFE to be processed more easily than PTFE. The crys-
talline melting point of PCTFE at 218°C is lower than PTFE. Clear
sheets of PCTFE with no crystallinity may also be prepared.
PCTFE is resistant to temperatures up to 200°C and has excellent
solvent resistance with the exception of halogenated solvents or oxygen
containing materials, which may swell the polymer.
63
The electrical
properties of PCTFE are inferior to PTFE, but PCTFE is harder and has
higher tensile strength. The melt viscosity of PCTFE is low enough that
it may be processing using most thermoplastic processing techniques.
64
Typical processing temperatures are in the range of 230 to 290°C.
65
PCTFE is higher in cost than PTFE, somewhat limiting its use.
Applications include gaskets, tubing, and wire and cable insulation.
Very low vapor transmission films and sheets may also be prepared.

66
Polytetrafluoroethylene. Polytetrafluoroethylene (PTFE) is polymer-
ized from tetrafluoroethylene by free radical methods.
67
The reaction
is shown in Fig. 1.9. Commercially, there are two major processes for
the polymerization of PTFE, one yielding a finer particle size disper-
sion polymer with lower molecular weight than the second method,
which yields a “granular” polymer. The weight average molecular
weights of commercial materials range from 400,000 to 9,000,000.
68
PTFE is a linear crystalline polymer with a melting point of 327°C.
69
Thermoplastics 1.15
n
CC
FF
FCl
Figure 1.8 Structure of PCTFE.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.15
Because of the larger fluorine atoms, PTFE assumes a twisted zigzag
in the crystalline state, while polyethylene assumes the planar zigzag
form.
70
There are several crystal forms for PTFE, and some of the
transitions from one crystal form to another occur near room temper-
ature. As a result of these transitions, volumetric changes of about
1.3% may occur.
PTFE has excellent chemical resistance, but may go into solution near
its crystalline melting point. PTFE is resistant to most chemicals. Only

alkali metals (molten) may attack the polymer.
71
The polymer does not
absorb significant quantities of water and has low permeability to gas-
es and moisture vapor.
72
PTFE is a tough polymer with good insulating
properties. It is also known for its low coefficient of friction, with values
in the range of 0.02 to 0.10.
73
PTFE, like other fluoropolymers, has excel-
lent heat resistance and can withstand temperatures up to 260°C.
Because of the high thermal stability, the mechanical and electrical
properties of PTFE remain stable for long times at temperatures up to
250°C. However, PTFE can be degraded by high energy radiation.
One disadvantage of PTFE is that it is extremely difficult to process
by either molding or extrusion. PFTE is processed in powder form by
either sintering or compression molding. It is also available as a dis-
persion for coating or impregnating porous materials.
74
PTFE has a
very high viscosity, prohibiting the use of many conventional process-
ing techniques. For this reason techniques developed for the process-
ing of ceramics are often used. These techniques involve preforming
the powder, followed by sintering above the melting point of the poly-
mer. For granular polymers, the preforming is carried out with the
powder compressed into a mold. Pressures should be controlled as too
low a pressure may cause voids, while too high a pressure may result
in cleavage planes. After sintering, thick parts should be cooled in an
oven at a controlled cooling rate, often under pressure. Thin parts may

be cooled at room temperature. Simple shapes may be made by this
technique, but more detailed parts should be machined.
75
Extrusion methods may be used on the granular polymer at very low
rates. In this case the polymer is fed into a sintering die that is heat-
ed. A typical sintering die has a length about 90 times the internal
1.16 Chapter One
F
2
CCF
2
n
n
CC
FF
FF
Figure 1.9 Preparation of PTFE.
0267146_Ch01_Harper 2/24/00 5:01 PM Page 1.16