The influence internal stress relaxation on the induction effect of shrinkage in oriented polycarbonate

The measurements of time-dependent thermally stimulated shrinkage forces were employed for investigating the initial stages of shrinkage in oriented and aged polycarbonate (PC). It was found that the observed induction effect results from the high localization of shrinkage processes and that it significantly depends on thermal history of oriented samples. The activation energy of shrinkage, derived on the basis of a simple mechanical model, remains approximately constant during the aging process, indicating that the major effect of aging is confined to the gradual relaxation of internal stresses “frozen-in” after the deformation. A simple relation t₀/t_a ^0.64 = const was found between the induction time t₀ and aging time t_a of oriented PC.