DSC

dynamic mechanical properties and density measurement have been performed for PET samples heat treated or stretched at different conditions. It was found that the position of the exothermal peak is obviously dependent on the degree of crystallization and orientation of the samples. The amount of heat calculated from the exothermal peak is not uniquely determined by the density of the sample

but is linearly dependent on tan 6 at 70℃

which can be used as a measure of the amount of amorphous state within a sample. At this stage of crystallization imperfect crystalline regions are formed and an abrupt increase of density is observed.