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|94 Chapter 7 Polymers: Structure, General Properties, and Applications

Salamone, ].C. (ed.), Concise Polymeric Materials Ulrich, H., Introduction to Industrial Polymers, Hanser, 1994.
Encyclopedia, CRC Press, 1999. Ward, I.M., and Sweeny, ]., An Introduction to the
Sperling, L.H., Polymeric Multicomponent Materials: An Mechanical Properties of Solid Polymers, 2nd ed.,
Introduction, Wiley, 1997. Wiley, 2004.
Strong, A.B., Plastics: Materials and Processing, 3rd ed., Young, R.]., and Lovell, P., Introduction to Polymers, 3rd ed.,
Prentice Hall, 2006. CRC Press, 2008.

REVIEW QUESTIONS

7.l. Summarize the important mechanical and physical 7.7. List and explain the additives commonly used in
properties of plastics. plastics.
7.2. What are the major differences between (a) the mechan- 7.8. What is crazing?
ical and (b) the physical properties of plastics and metals? 7.9. What are polyblends?
7.3. List properties that are influenced by the degree of 7.I0. List the major differences between thermoplastics and
polymerization. thermosets.
7.4. What is the difference between condensation polymer- 7.I l. What is an elastomer?
ization and addition polymerization?
7.|2. What effects does a plasticizing agent have on a
7.5. Explain the differences between linear, branched, and polymer?
cross-linked polymers. 7.l3. Define the following abbreviations: PMMA, PVC,
7.6. What is the glass-transition temperature? ABS, HDPE, and LDPE.

QUALITATIVE PROBLEMS

7.l4. Inspect various plastic components in an automobile, 7.26. How can polymers be made to conduct electricity?
and state whether they are made of thermoplastic materials Explain.
or of thermosetting plastics. 7.27. Explain the reasons for which elastomers were
7.l5. Give applications for which flammability of plastics developed.
would be of major importance. 7.28. Give several examples of plastic products or compo-
7.l6. What characteristics make polymers advantageous for nents in which creep and stress relaxation would be impor-
applications such as gears? What characteristics are draw- tant considerations.
backs in such applications? 7.29. Describe your opinions regarding the recycling of
7.l7. What properties do elastomers have that thermoplas- plastics versus the development of plastics that are biode-
tics in general do not have? gradable.
7.l8. Do you think that the substitution of plastics for met- 7.30. Explain how you would go about determining the
als in products traditionally made of metal may be viewed hardness of plastics.
negatively by the public at large? If so, why? 7.3l. Compare the values of the elastic modulus given
7.l9. Is it possible for a material to have a hysteresis behav- in Table 7.1 to the values for metals given in Chapters 2, 5,
ior that is the opposite of that shown in Fig. 7.14, so that the and 6.
two arrows run counterclockwise? Explain. 7.32. Why is there so much variation in the stiffness of
7.20. Observe the behavior of the specimen shown in products made of polymers? Explain.
Fig. 7.13, and state whether the material has a high or a low 7.33. Explain why thermoplastics are easier to recycle than
strain-rate sensitivity exponent, m. (See Section 2.2.7.) thermosets.
7.2l. Add more to the applications column in Table 7.3. 7.34. Give an example of a process where crazing is
7.22. Discuss the significance of the glass-transition temper- desirable.
ature, Tg, in engineering applications. 7.35. Describe the principle behind shrink wrapping.
7.23. Describe how a rechargeable lithium battery works. 7.36. List and explain some environmental pros and cons of
7.24. Explain how cross-linking improves the strength of using plastic shopping bags vs. paper bags.
polymers. 7.37. List the characteristics required of a polymer for (a) a
7.25. Describe the methods by which the optical properties bucket, (b) a golf ball, (c) an automobile dashboard, (d) cloth-
of polymers can be altered. ing, (e) flooring, and (fl fishing nets.