Measurements of free radicals over a period of 4.5 years in gamma-irradiated ultra-high molecular weight polyethylene

Abstract

Gamma irradiation-induced free radicals have been investigated for 4.5 years in medical grade ultra-high molecular weight polyethylene resins, GUR 4120, GUR 4150 and Himont 1900, at room temperature (23 °C) in absence (vacuum) or presence of oxygen (air), and at 75 °C in vacuum. In vacuum, the primary radicals (predominantly allyl) decayed following Y= Y R+ ae− bt and, in 30 days at 75 °C or 100 days at 23 °C, their concentration was reduced from ∼10 17 radical/g (initial) to a minimum Y R∼10 15 radical/g and remained at this level as long as the samples were kept in vacuum. When the samples were exposed to air, at any time during this study, these residual radicals were found to decay to a very stable, polyenyle-type terminal radical.