EFFECTS OF GAMMA-IRRADIATION, GAS ENVIRONMENTS, AND POSTIRRADIATION AGING ON ULTRAHIGH MOLECULAR-WEIGHT POLYETHYLENE

The effects of low-dose (1 to 5 Mrad) gamma irradiation in different g as environments on thermal and tensile properties, and mass of melt-cr ystallized ultrahigh molecular weight polyethylene (UHMW-PE) have been investigated. The gamma irradiation was conducted under four differen t environments, air, nitrogen, acetylene, and vacuum. Thermal paramete rs were investigated using differential scanning calorimetry. The resu lts showed that both irradiation dose and environments affected the th ermal and tensile properties. Gamma irradiation significantly increase d the melting temperature of UHMW-PE in all cases. However, the oxidat ion temperatures of irradiated polyethylene was lowered in all cases e xcept those associated with acetylene environment. The crystallinity o f the polymer was increased upon irradiation. Tensile yield strength a nd modulus of irradiated UHMW-PE increased for all cases except those treated at 1.25 and 2.5 Mrad, and in nitrogen environment that showed a decrease in the modulus, Gamma irradiation caused a weight gain of U HMW-PE in all conditions. To further the study, the postirradiation ag ing effect on the irradiated polymer was examined during a period of 1 year, and the results showed that the thermal and tensile properties of UHMW-PE were, indeed, affected. The data suggests that irradiation in acetylene affects mainly the crosslinking of the polymer. (C) 1995 John Wiley & Sons,Inc.