Post electron-beam irradiation oxidation of orthopaedic UHMWPE

The mechanisms and products of the oxidation process induced by electron-beam irradiation of UHMWPE were thoroughly investigated in the present study. The e-beam technique has the peculiarity of dispensing the whole radiation dose in a very short time and it allows following the post-irradiation oxidation process at room temperature, which represents a major advantage for the present purpose. Thin sections of orthopaedic grade UHMWPE GUR 1050 were irradiated at doses ranging from 5 to 100 kGy in vacuum, air or pure oxygen, depending on the aim of the following analyses. After irradiation, the samples were stored in liquid nitrogen until the measurements began. Chemical and physical changes caused to the polymer by irradiation were investigated by FTIR, derivatisation techniques and spectral subtractions. As reported in the literature, secondary hydroperoxides and ketones were found to be the main oxidation products, along with carboxylic acids and alcohols. Nevertheless, in our case, the kinetics of formation of oxidation products were inconsistent with previously reported mechanisms. An alternative oxidation mechanism, including the simultaneous formation of hydroperoxides and ketones, is proposed. The thermal stability of hydroperoxides is also discussed in detail and the similarities between the post-irradiation oxidation process and the thermal oxidation process are highlighted. (C) 2008 Elsevier Ltd. All rights reserved.