Observation of a non-radical intermediate in the oxidation pathway of free radicals in gamma-irradiated medical grade polyethylene


Free-radical-depth profile of a large cube (side, 25.4 mm) of UHMWPE was determined following gamma irradiation (25 kGy, 60Co) in air and subsequent aging for 120 days in ringer solution, bovine serum or ethyl alcohol at 37 °C, or in air at room temperature (RT). The initial electron spin resonance (ESR) data showed the presence of predominantly allyl radicals in the core specimens (>6 mm from the surface), alkoxy (PȮ) or peroxy (PO2̇) in the surface (1-3 mm from the surface), but none or very weak radicals in the sub-surface region (3-5 mm from the surface). Ten months later, the same samples, including those in the sub-surface region, produced identical surface radicals. The results of this study led to the conclusion that the transient non-radical species observed, for the first time by ESR technique, could be the well-known hydroperoxy (POOH) group. © 2001 Elsevier Science B.V. All rights reserved.

Publication Title

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms