THERMALLY STIMULATED CURRENT AND CREEP IN POLY(ETHYLENE-TEREPHTHALATE)

Two thermal stimulation techniques (thermally stimulated current and creep) have been used to study the dielectric and mechanical retardation modes observed in poly(ethylene terephthalate) between liquid-nitrogen temperature and the glass transition temperature. From the data acquired, the dielectric and mechanical energy losses have been calculated: they are found to be in good agreement with those derived from other dielectric and mechanical techniques. The high resolving power of the thermal stimulation methods has allowed us to distinguish three modes in both bioriented and amorphous PET. In the bioriented sample, the three modes correspond to a discrete distribution of retardation time τ, while in the amorphous sample, they correspond to a continuous distribution of τ. In amorphous PET, the distributions of dielectric and mechanical retardation times are reduced to a single τ - 5×10 -4 and 7×10-3 sec - for a converging temperature of 233 and 277 K, respectively.