TSDC study of structural relaxation on polyethylene terephthalate

The influence of physical aging processes on the electrical and thermal properties of amorphous polyethylene terephthalate was investigated by means of the thermally stimulated depolarization current (TSDC), differential scanning calorimetry (DSC) and low frequency dielectric methods. A noticeable decrease in polarization and loss factor corresponding to the main α relaxation was observed with increasing aging times, especially for aging temperatures ranging from 10 to 20 °C below Tg. This behavior is compatible with the free-volume concept, and can be explained by a gradual decrease in segmental mobility following a shift of the relaxation time spectrum of molecular motions to longer time scales. The whole experimental evidence suggests that proper consideration should be given to thermal history and aging effects of polyethylene terephthalate. The thermally stimulated depolarization current was chosen due to its low equivalent frequency, useful to study systems exhibiting multiple relaxations.