Characterization of irradiated blends of α-tocopherol and UHMWPE

Adhesive/abrasive wear in ultra-high molecular weight polyethylene (UHMWPE) has been minimized by radiation cross-linking. Irradiation is followed by melting to eliminate residual free radicals and avoid long-term oxidative embrittlement. However, Post-irradiation melting reduces the crystallinity of the polymer and hence its strength and fatigue resistance. We proposed an alternative to post-irradiation melting to be the incorporation of the antioxiclant alpha-tocoplicrol into UHMWPE prior to consolidation. alpha-Tocopherol is known to react with oxygen and oxidized lipids, stabilizing them against further oxidative degradation reactions. We blended GUR 1050 UHMWPE resin powder with alpha-tocopherol at 0.1 and 0.3wt%. and consolidated these blends. Then we gamma-irradiated these blends to 100-kG. We characterized the effect of alpha-tocopherol on the cross-linking efficiency, oxidative stability, wear behavior and mechanical properties of the blends. (1) The cross-link density of virgin. 0.1 and 0.3 wt% alpha-tocopherol blended, 100-kGy irradiated UHMWPEs were 175 +/- 19, 146 +/- 4 and 93 +/- 4mol/m(3), respectively. (II) Maximum oxidation indices For 100-kGy irradiated UHMWPE previously blended with 0, 0.1 and 0.3 wt% alpha-tocopherol that were subjected to accelerated aging at 80 C in air for 5 weeks were 3.32, 0.09. and 0.05, respectively. (III) The pin-on-disc wear rates of 100-kGy irradiated UHMWPE previously blended with 0.1 and 0.3wt% alpha-tocopherol that were subjected to accelerated aging at 80 C in air for 5 weeks were 2.10 +/- 0.17 and 5.01 +/- 0.76mg/million cycles, respectively. (IV) Both accelerated aged, alpha-tocopherol-blended 100-kGy irradiated UHMWPEs showed higher ultimate tensile strength, higher yield strength, and lower elastic modulus when compared to 100-kGy irradiated. virgin UHMWPE. These results showed that alpha-tocopherol-blended 100-kGy irradiated UHMWPEs were not cross-linked to the same extent as the 100-kGy irradiated, virgin UHMWPE. (c) 2005 Elsevier Ltd. All rights reserved.