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REVIEW QUESTIONS

1. During the winter months, the temperature in some parts of Alaska may go as low as -55°c. Of the elastomers natural isoprene, styrene-butadiene, acrylonitrile-butadiene, chloroprene, and polysiloxane, which would be suitable for automobile tires under these conditions? Why?

2. Briefly explain the difference in molecular chemistry between silicone polymers and other polymeric materials.

3. Silicone polymers may be prepared to exist as liquids at room temperature. Cite differences in molecular structure between them and the silicone elastomers.

4. List two important characteristics for polymers that are to be used in fiber applications.

5. Cite five important characteristics for polymers that are to be used in thin-film applications.

6. Cite the primary differences between addition and condensation polymerization techniques.

7. Cite whether the molecular weight of a polymer that is synthesized by addition polymerization is relatively high, medium, or relatively low for the following situations:

a) Rapid initiation, slow propagation, and rapid termination. b) Slow initiation, rapid propagation, and slow termination. c) Rapid initiation, rapid propagation, and slow termination. d) Slow initiation, slow propagation, and rapid termination.

8. Why must the vapor pressure of a plasticizer be relatively low? How will the crystallinity of a polymer be affected by the addition of a plasticizer? Why? Is it possible for a crosslinked polymer to be plasticized? Why or why not? How does the addition of a plasticizer influence the tensile strength of a polymer? Why?

9. What is the distinction between dye and pigment colorants?

SHEET5: POLYMERS TYPES AND FABRICATION

BENHA UNIVERSITY M462 MATERIAL TECHNOLOGY BANHA FACULTY OF ENGINEERING 4TH YEAR MECHANICAL ENGINEERING MECHANICAL ENGINEERING DEPARTMENT DR. SALEH | ENG. ABDALLA MOHAMED

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10. Cite four factors that determine what fabrication technique is used to form polymeric materials.

11. Contrast compression, injection, and transfer molding techniques that are used to form plastic materials.

12. It is desired that some rubber component in its final form be vulcanized. Should vulcanization be carried out prior or subsequent to the forming operation? Why?

13. Why must fiber materials that are melt spun and then drawn be thermoplastic? Cite two reasons.

14. Which of the following polyethylene thin films would have the better mechanical characteristics:

a) Formed by blowing. b) Formed by extrusion and then rolled? Why?

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