The crystallization of oriented poly(ethylene terephthalate)

The rate of crystallization of oriented poly(ethylene terephthalate) has been measured at 100°, 120° and 150°C using carefully prepared amorphous fibre samples. The samples were held to length during crystallization so that shrinkage did not occur, and the course of crystallization was followed by measuring the changes in density and boiling water shrinkage of the samples. The results show that the rate of crystallization is strongly dependent on the degree of orientation. Nucleation and initial growth of crystallites occur in times of the order of milliseconds at 120°C in samples of birefringence 0.08 compared with times of several minutes in isotropic material. It was found that crystallization in oriented material cannot be described by the Avrami equation.