Abstract
The progress of physical ageing has been followed spectroscopically in thin films of polyethylene terephthalate, stress relieved to eliminate the effect of orientation. The changes observed are ascribed to the temperature dependent conformational changes of liquids interrupted by the onset of the glass formation. On physical ageing, there is progressive relaxation of the glass, determined by the temperature, towards the equilibrium conformation as defined by extrapolation of the liquid temperature dependence, and there is no necessity to assume structure formation within the glass to account for the spectroscopic changes. Physical ageing has no effect on the subsequent rate of crystallization at temperatures above the glass transition. Heating above the glass transition immediately eliminated physical ageing effects.
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