Long-term gamma irradiation effects on ultrahigh molecular weight polyethylene

Effects of gamma irradiation, irradiation environment, and long-term postirradiation aging on thermal behavior, crystallinity, mechanical properties, and weight change of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The gamma irradiation was conducted at 2.5 Mrad under four different environments, i.e., air, nitrogen, acetylene, and vacuum. The postirradiation aging effects were monitored over a period of 5.5 years. The results showed that gamma irradiation, irradiation environments, and postirradiation aging significantly changed the properties of UH-MWPE. After gamma irradiation, the melting temperature and crystallinity of UHMWPE were increased in all cases, with the highest increase at longest postirradiation aging time. Gamma irradiation and postirradiation aging caused weight gain of UHMWPE in all conditions. The tensile and flexural properties were significantly affected by gamma irradiation. At 5.5 years postirradiation, tensile-tested UHMWPE specimens fractured in brittle form, indicating dramatic reduction in the material's toughness. This kind of behavior may be detrimental to UHMWPE load-bearing orthopedic devices for their intended long-term applications.