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Callister - An introduction - 8th edition

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15.13 Melting and Glass Transition Temperatures • 593<br />

Liquid<br />

Figure 15.18 Specific volume versus<br />

temperature, upon cooling from the<br />

liquid melt, for totally amorphous<br />

(curve A), semicrystalline (curve B), and<br />

crystalline (curve C) polymers.<br />

Specific volume<br />

Glass<br />

Semicrystalline solid<br />

A<br />

B<br />

C<br />

Crystalline solid<br />

T g<br />

Temperature<br />

T m<br />

have the same configurations as their ceramic counterparts (Figure 13.6). 5 For the<br />

crystalline material, there is a discontinuous change in specific volume at the melting<br />

temperature T m . The curve for the totally amorphous material is continuous<br />

but experiences a slight decrease in slope at the glass transition temperature, T g .<br />

The behavior is intermediate between these extremes for a semicrystalline polymer<br />

(curve B) in that both melting and glass transition phenomena are observed;<br />

T m and T g are properties of the respective crystalline and amorphous phases in this<br />

semicrystalline material. As discussed earlier, the behaviors represented in<br />

Figure 15.18 will depend on the rate of cooling or heating. Representative melting<br />

and glass transition temperatures of a number of polymers are contained in<br />

Table 15.2 and Appendix E.<br />

Table 15.2<br />

Melting and Glass Transition Temperatures for Some<br />

of the More Common Polymeric Materials<br />

Glass Transition<br />

Melting<br />

Temperature<br />

Temperature<br />

Material [ C<br />

( F)] [ C ( F)]<br />

Polyethylene (low density) 110 (165) 115 (240)<br />

Polytetrafluoroethylene 97 (140) 327 (620)<br />

Polyethylene (high density) 90 (130) 137 (279)<br />

Polypropylene 18 (0) 175 (347)<br />

Nylon 6,6 57 (135) 265 (510)<br />

Poly(ethylene terephthalate) (PET) 69 (155) 265 (510)<br />

Poly(vinyl chloride) 87 (190) 212 (415)<br />

Polystyrene 100 (212) 240 (465)<br />

Polycarbonate 150 (300) 265 (510)<br />

5 No engineering polymer is 100% crystalline; curve C is included in Figure 15.18 to<br />

illustrate the extreme behavior that would be displayed by a totally crystalline material.

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