Spherulites and Drawing

Spherulites at the shoulder are pulled apart, and polymer chains are oriented in the direction of stress as they enter the neck. The orientation is permanent, since the new crystalline form is stable. Thus, it is not inconsistent that molded (spherulitic) nylon may be listed as having an elongation at break of about 300%, whereas drawn 

FIGURE 3.16 SpheniUtic stracture of poly(ethylene oxide) seen between crossed polarizing sheets. 

FIGURE 3.17 Successive stages in the drawing (elongation) of a spherulitic polymer. 

The organization of the crystals in a spherulite has been investigated for numerous materials. For example, single crystals have been observed to grow faster in one direction than another with branching so as to assume a sheaflike appearance and ultimately to form the nucleus of a spherulite [30]. The individual arms of the spheruhte 

FIGURE 3.18 The drawing process, (a) Twisted crystal lamellae that make up the spheru-htic structure are pulled into (h) tilted pre-deformed lamellae during the pre-necking period. 

---