DIFFERENTIAL SCANNING CALORIMETRY AND THERMOSTIMULATED CURRENT SPECTROSCOPY FOR THE STUDY OF MOLECULAR-ORIENTATION IN POLYMERS

The influence of uniaxial and biaxial orientation on the transition/relaxation of po ethylene) terephthalate (PET) has been investigated. The transitions were studied by differential scanning calorimetry; the corresponding relaxations were studied by thermostimulated current (TSC) spectroscopy. At around 50-degrees-C, a particularly intense TCS peak was observed in the uniaxially oriented sample; this mode is a precursor of the glass transition T(g). The relaxation mode associated with the glass transition is observed at 82-degrees-C in unoriented PET, at 85-degrees-C in uniaxially oriented PET and at 100-degrees-C in biaxially oriented PET. An analysis of the fine structure has shown that it is made up of elementary processes that obey a compensation law: at the compensation temperature T(c), all the relaxation times become equivalent. It is important to note that for amorphous films (unoriented and uniaxially oriented) T(c) - T(g) almost-equal-to 5-degrees-C, whereas for the semi-crystalline film (biaxially oriented) T(c) - T(g) almost-equal-to 15-degrees-C. This result shows that crystallites are strongly coupled to the amorphous phase.