Dependence of Thermal Crystallization of Poly(ethylene Terephthalate) on Active Mobility of Amorphous Chain Segments

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Abstract
Amorphous poly(ethylene terephthalate) films were stretched in hot water baths at 65 and 80°C to prepare drawn specimens. The specimens were held with fixed dimension in the stretching direction again in a hot water bath at 80°C, in order to study the relationship between thermal crystallization and active mobility of amorphous chain segments. The thermal crystallization rate increased with increasing molecular orientation of the original drawn specimens prior to the annealing, but the final value of crystallinity levelled off and attained a constant value. The corresponding second-order orientation factor showed predominant orientation arising in the annealing process associated with thermal crystallization to form folded-type crystals, and the increase in the factor was dependent on the degree of orientation of the amorphous chain segments in the original drawn films. Further more, spherulitic textures were confirmed by the Hv light scattering technique when the films below the draw ratio of 2.5 were annealed in a hot oven beyond 150°C. Through a series of the experiments, one may conclude that thermal crystallization is strongly affected by the active mobility of amorphous chain segments.