Effect of structural relaxation of glassy PET on crystallization process observed by the simultaneous DSC-XRD and DSC-FTIR

The effect of structural relaxation of the glassy poly(ethylene terephtalate) (PET) caused by annealing below its glass transition temperature (Tg) on the cold-crystallization observed was investigated by the simultaneous DSC-FTIR and DSC-XRD methods. The nucleation and the conformational ordering processes proceeded faster by annealing. From the relationship between the absorbance change and the exothermic heat during the cold-crystallization, the heat of cold-crystallization for the unannealed PET was caused mainly by the conformational ordering. For the annealed PET, the long range ordering contributed to the heat of crystallization in the late stage of cold-crystallization, which was also confirmed by the DSC-XRD method.