Radiation-induced crystallinity changes in linear polyethylene: Long-term aging effects in pressure-crystallized ultra-high molecular weight polymer

Abstract

Abstract It has been shown previously that linear polyethylenes undergo increases 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 crystallinity was also found to increase with time after irradiation (aging) up to 112 months, although peak melting temperature declined slowly with aging time. The results were explained in terms of the scission of tie molecules followed by the slow growth of new crystal lamellae. This paper presents similar studies on a single ultra-high molecular weight polyethylene resin which has been crystallized under 5.1 kbar pressure. As before, irradiation causes an immediate rise in crystallinity followed, over a period of 93 months, by further increases. The highest crystallinity achieved by this combination of pressure crystallization, irradiation, and aging is some 82%. This demonstrates that UHMWPE is intrinsically capable of the same degree of crystallinity as normal molecular weight resins.