Radiation Induced Crystallinity Changes in Linear Polyethylenes: Long Term Aging Effects

It has been shown previously that linear polyethylenes undergo an increase in crystallinity and peak melting temperature after irradiation, the magnitude of the effects being dependent upon the dose and the molecular weight of the polymer. The effects were also found to change with time after irradiation (aging) up to 31 months. These changes have now been followed up to aging times of 112 months. The heats of fusion (thus the crystallinities) continue to increase over this extended time-span, but the peak melting temperatures rise to a maximum immediately after irradiation and then fall progressively with the passage of time. The results are attributed to tie molecule scission with the consequent relaxation of local stresses, followed by the slow growth of new crystal lamellae.