MODULATED DIFFERENTIAL SCANNING CALORIMETRY .2. STUDIES OF PHYSICAL AGING IN POLYSTYRENE

Physical ageing in polystyrene (PS) has been studied by means of modul ated differential scanning calorimetry (m.d.s.c.). The results show th at there exists a characteristic annealing temperature at which relaxa tion enthalpy has a maximum value. When annealing below 65 degrees C, another relaxation peak has been found. The position of this relaxatio n peak, which changes with annealing temperature, lies approximately b etween 54 and 64 degrees C. It has been postulated previously in the l iterature that the relaxation behaviour involves phenyl ring relaxatio n. As measured from heat capacity curves, this transition is evident a s a shoulder on the glass transition. With increasing annealing temper ature, the glass transition of PS increased slightly.