Effects of packaging environments on free radicals in gamma-irradiated UHMWPE resin powder blend with vitamin E.

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) powder (GUR 1020) was blended with high concentration (20%) of vitamin E (alpha-Tocopherol (alpha-T)) for direct detection of alpha-T radicals in presence of PE radicals. Samples were gamma-irradiated in sealed packages filled with N(2), or in open air. Free radicals were measured in open air environment for 71 days using electron spin resonance (ESR) technique. When irradiated in air, both alpha-T and alpha-T-resin produced identical ESR signals characteristics of tochopheroxyl radicals (alpha-T-O(*)), suggesting that PE radicals are quenched by alpha-T. There was no indication of growth of oxygen-induced radicals (OIR) either. However, when alpha-T-resin was irradiated in N(2), presence of both PE and alpha-T radicals were evident in the ESR spectra. And, OIR were produced by the same samples when they were subsequently exposed to air (for 71 days). Oxidation data recorded 85 days after postirradiation aging in air using Fourier transform infra-red (FTIR) spectroscopy, however, did not show any measurable difference between samples irradiated in N(2) and air.