On the thermooxidative degradation of polyethyleneterephtalate

The thermal degradation in air of PET within the glass transition range is a complex phenomenon. According to mechanical data it might be concluded that the thermooxidative degradation of PET is described by a single first order process. Due to the thickness of the sample and as the degradation temperatures were above T_A, the thermooxidative degradation process is homogeneous. Thermal analysis have revealed the presence of a weak liquid-liquid transition. Both the liquid-liquid transition and the glass transition depends on degradation time and temperature. From the effect of the thermooxidative degradation on T_G, it is possible to conclude that at low degradation temperatures the polymer crosslinks. At 150°C, a transition from crosslinking to chain scissions at large degradation times (above 500 h) is noticed. Hence T_c depends on the degradation time and temperature. Dc electrical conduction measurements have revealed two competing first order relaxation processes, ascribed to crystalline and amorphous domains. Further studies are in course, in order to elucidate this behaviour