Crystallization of polyethylene terephthalate from the glassy amorphous state

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Abstract
The morphology of glassy amorphous PETP is characterized by ball-like structures in which a paracrystalline-type order is present. Movement of the balls is seen at annealing temperatures 5†C or more below Tg as well as at higher temperatures. Crystallization from the glass occurs by the formation of spherulites similar in appearance to those obtained from the melt. They are formed by the two-dimensional alignment of the ball-like structures into the fibrillar ribbons comprising the spherulites. Some merging of the balls occurs at temperatures above Tg. The small-angle X-ray long period is found to increase as expected with the annealing temperature, but it decreases with time at a given annealing temperature. The decrease of long period with time has been accounted for by the regularizing of irregular folds originally present in the ball-like structures.