Surface studies of ultra-high molecular weight polyethylene irradiated with high-energy pulsed electron beams in air

Ultra-high molecular weight polyethylene (UHMWPE) was irradiated in air wit h high-energy (9 MeV), pulsed electron beams to doses ranging from 2.5 to 1 00 Mrad and subsequently heat treated at 120 degrees C far a time period of 120 min. Surface characterization of the target side of irradiated UHMWPE samples was carried out both before and after the heat treatment by means o f attenuated total reflection Fourier-transform infrared (FTIR/ATR) spectro scopy and microhardness measurement. The obtained results provided further evidence supporting our earlier observation (Tretinnikov, O. N.; Ogata, S.; Ikada, Y. Polymer 1998, 39, 6115) that thermal decomposition of hydroperox ides formed upon irradiation of UHMWPE with highenergy, pulsed electron bea ms in air leads to surface crosslinking, and the subsequent surface hardeni ng of the irradiated polymer. Importantly we found that this phenomenon has the highest contribution to the surface hardness enhancement of the polyme r when the radiation dose is in the range of 10-30 Mrad. In addition, we fo und that this irradiation and subsequent heat treatment of UHMWPE in air do es not lead to formation of carbonyl-containing products unless the radiati on dose exceeds 20 Mrad. (C) 1999 John Wiley & Sons, Inc.