EFFECTS OF PHYSICAL AGING ON CREEP IN POLYPROPYLENE

Creep data have been obtained for polypropylene at 23°C over an extensive time range (10-8-106s) as a function of the elapsed time te between quenching from 80°C and the start of the creep experiment. The creep curves have been fitted with empirical functions capable of describing the behavior across the entire β- and α-relaxation regions. Analyses of results from both short-term (t0.1 te) and long-term tests suggest that physical aging produces a decrease in relaxed compliance for the β-(glass-rubber) relaxation together with an increase in average retardation time and broadening of the α-process. Some decrease in magnitude of the α-relaxation also seems to be significant.