Radiation-sterilization and subsequent oxidation of medical grade polyethylene: an ESR study

Oxidation processes of irradiated ultra-high molecular weight polyethylene (medical grade, GUR 415) was examined by making free radical measurements before and after introduction of oxygen into the sample chamber. The free radicals (predominantly, alkyl and allyl), produced by X-irradiation at 45 K, remained frozen in the temperature regime 45-150 K. They, however, decayed rapidly (6 x 10(-3)/K) in the temperature regime 150-190 K (gamma-dispersion region) and slowly (2 x 10(-3)/K) in the beta-dispersion region, 190-300 K. The oxidation of the remaining radicals (about 50% of the initial) occurred in presence of oxygen at 300 K. While the presence of oxygen-centered radicals (PO2. or PO.) could not be confirmed, evidences of vinyl type and polyenyl radicals of various conjugations were found. (C) 1999 Elsevier Science B.V. All rights reserved.