Effects of crystallinity on ageing phenomena in poly(vinyl chloride)

The physical ageing of poly(vinyl chloride) (PVC) is affected by the degree of crystallinity which can be induced by annealing of the sample at temperatures above T_g. Differential scanning calorimetry (d.s.c.) measurements showed that the enthalpy relaxation, induced by sub-T_g annealing, of PVC samples with different crystallinity increases with increasing crystallization temperature (T_c). On the other hand, the enthalpy relaxation decreases with increasing crystallization time (t_c) at a given T_c. These observations cannot be attributed only to the overall crystallinity percentage, but they are attributable mainly to the entire structure of the amorphous phase which depends upon above-T_g annealing conditions (T_c, t_c). The assumptions of different portions of the material crystallized at different T_c and of decreasing extent of disturbed regions as t_c increases seem to explain well the above findings. Solvent sorption experiments served to support our suggestions resulting from d.s.c. experiments.