Investigation of an Approach to Balance Wear Resistance and Mechanical Properties of Crosslinked UHMWPE

In order to produce ultra-high molecular weight polyethylene (UHMWPE) with increased wear resistance for bearing applications, yet minimize degradation in stiffness and oxidation resistance, the authors have proposed irradiation crosslinking of the polymer at moderate radiation doses. It was theorized that this would minimize or eliminate the need for a subsequent stabilization of free radicals, and thus retain a significant proportion of the original stiffness of the crystalline polymer. In this study, four groups of UHMWPE were investigated: (a) non-crosslinked, (b) crosslinked with 50 kGy electron-beam irradiation, thermally stabilized, (c) crosslinked, non-stabilized, and (d) crosslinked, non-stabilized, and exposed to accelerated oxidation to simulate prolonged exposure. Crosslinking and subsequent thermal stabilization significantly reduced the elastic modulus of UHMWPE, while omission of the stabilization step yielded a more moderate reduction in elastic modulus. It was shown that thermal stabilization reduced crystallinity more so than did omission of stabilization. Accelerated aging did not further decrease the storage modulus of UHMWPE over that of non-stabilized, non-aged polymer. Crosslinking showed a significant increase in wear resistance, while aging of the non-stabilized polymer showed no adverse effects on wear. These results suggest the potential for the use of moderate UHMWPE crosslinking without stabilization for industrial and some biomedical applications.