The effect of water absorption on the physical ageing of amorphous poly(ethylene terephthalate) film

Amorphous poly(ethylene terephthalate) (PET) films with different thermal h istories were annealed at 30 degrees C in a desiccator, in a humid atmosphe re and in liquid water respectively, for investigation of enthalpy relaxati on by differential scanning calorimetry (DSC). For the quenched sample anne aled in a humid atmosphere, the evolution of the endothermic peak near the glass transition temperature (Tg) with annealing time is remarkable. For th e aged samples further annealed in the humid atmosphere and water, the shap e of the endothermic peak changed from a single peak into broad double peak s with annealing time. However no such change of the endothermic peak can b e observed for both the quenched and the aged samples further annealed in t he desiccator. The experimental results showed that the change of the DSC c urve was reversible, involved only with the physical process. The results m ay indicate that some ordered structure formed during the physical ageing p rocess. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.