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 b efore and after introduction of oxygen into the sample chamber. The free ra dicals (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-dispersi on 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) occu rred 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 Sci ence B.V. All rights reserved.