Callister - An introduction - 8th edition

WHY STUDY the Characteristics, Applications, and Processing of Polymers?
There are several reasons why an engineer should know
something about the characteristics, applications, and
processing of polymeric materials. Polymers are used in a
wide variety of applications, such as construction materials
and microelectronics processing. Thus, most engineers
will be required to work with polymers at some point in
their careers. Understanding the mechanisms by which
polymers elastically and plastically deform allows one to
alter and control their moduli of elasticity and strengths
(Sections 15.7 and 15.8). Also, additives may be incorporated
into polymeric materials to modify a host of
properties, including strength, abrasion resistance,
toughness, thermal stability, stiffness, deteriorability,
color, and flammability resistance (Section 15.21).
In the processing/structure/properties/performance
scheme for polymer fibers, reasons for studying the
characteristics, applications, and processing of polymers
are as follows:
• Polymeric materials that are used for fibers in textiles
(i.e., clothing) must be relatively strong. In this
chapter we discuss the mechanical characteristics of
polymers, the mechanisms (on a molecular scale)
by which semicrystalline polymers plastically
deform, and, finally, techniques that are available
to strengthen these materials.
• Several techniques are used to form polymer fibers;
in one fabrication procedure the fibers are spun
from the molten material. This chapter discusses
the phenomenon of melting for polymers, the
concept of melting temperature, and structural
characteristics of polymers that influence melting
temperature. The magnitude of a fiber’s melting
temperature will influence the manner in which it
is processed as well as the maximum temperature at
which it may be used.
Learning Objectives
After studying this chapter you should be able to do the following:
1. Make schematic plots of the three characteristic
stress–strain behaviors observed for polymeric
materials.
2. Describe/sketch the various stages in the elastic
and plastic deformations of a semicrystalline
(spherulitic) polymer.
3. Discuss the influence of the following factors on
polymer tensile modulus and/or strength:
(a) molecular weight, (b) degree of crystallinity,
(c) predeformation, and (d) heat treating of
undeformed materials.
4. Describe the molecular mechanism by which
elastomeric polymers deform elastically.
5. List four characteristics or structural components
of a polymer that affect both its melting and
glass transition temperatures.
6. Cite the seven different polymer application
types and, for each, note its general
characteristics.
7. Briefly describe addition and condensation
polymerization mechanisms.
8. Name the five types of polymer additives
and, for each, indicate how it modifies the
properties.
9. Name and briefly describe five fabrication
techniques used for plastic polymers.
15.1 INTRODUCTION
This chapter discusses some of the characteristics important to polymeric materials
and, the various types and processing techniques.
Mechanical Behavior of Polymers
15.2 STRESS–STRAIN BEHAVIOR
The mechanical properties of polymers are specified with many of the same parameters
that are used for metals—that is, modulus of elasticity and yield and tensile
strengths. For many polymeric materials, the simple stress–strain test is used to
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