The conformational chain mobility of semi-crystalline poly(ethylene terephthalate),PET,is studied in the glass transition region by thermally stimulated recovery (TSR).The thermal sampling (TS) experiments are analysed according to a simple Voigt-Kelvin model.Both the activation energy (E_a) and the pre-exponential factor follow the usual trends with temperature and present the compensation behaviour,that is discussed in this work.The influence of crystallinity and orientation on the glass transition dynamics is analysed.In particular,the profile of variation of E_a with temperature is found to be very sensitive to these two effects.TSR results are compared with the results obtained by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA).In addition,this technique was successfully applied to the study of the structural relaxation process of semi-crystalline PET and it was found that the characteristic parameters of the TSR curves vary with the ageing temperature and ageing time.These variations are explained on the basis of the changes verified on the distribution of characteristic times with ageing.
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