CRYSTALLIZATION KINETICS FOR POLY(ETHYLENE-TEREPHTHALATE) ORIENTED BY SOLID-STATE COEXTRUSION

A series of uniaxially drawn films has been prepared from isotropic, amorphous poly(ethylene terephthalate) (PET) by using solid-state coextrusion below its T//g. The cold-crystallization temperature T//c, crystallization rate constant, k, and activation energy E//a has been studied as a function of extrusion draw temperature and draw ratio. The rapid crystallization of highly oriented amorphous PET in extrudates was followed by a temperature-programmed DSC technique. This avoids the marked precrystallization often found in samples brought to appropriate isothermal temperatures. With increasing extrusion draw ratio, T//c shifts to lower temperatures, the first-order crystallization rate constant k increases markedly (by two or three orders of magnitude) and E//a decreases markedly. In contrast, for extrusion-drawn PET, both T//c and E//a increase with draw temperature.