High temperature homogenization improves impact toughness of vitamin E‐diffused, irradiated UHMWPE

Diffusion of vitamin E into radiation cross‐linked ultrahigh molecular weight polyethylene (UHMWPE) is used to increase stability against oxidation of total joint implant components. The dispersion of vitamin E throughout implant preforms has been optimized by a two‐step process of doping and homogenization. Both of these steps are performed below the peak melting point of the cross‐linked polymer (<140°C) to avoid loss of crystallinity and strength. Recently, it was discovered that the exposure of UHMWPE to elevated temperatures, around 300°C, for a limited amount of time in nitrogen, could improve the toughness without sacrificing wear resistance. We hypothesized that high temperature homogenization of antioxidant‐doped, radiation cross‐linked UHMWPE could improve its toughness. We found that homogenization at 300°C for 8 h resulted in an increase in the impact toughness (74 kJ/m² compared to 67 kJ/m²), the ultimate tensile strength (50 MPa compared to 43 MPa) and elongation at break (271% compared to 236%). The high temperature treatment did not compromise the wear resistance or the oxidative stability as measured by oxidation induction time. In addition, the desired homogeneity was achieved at a much shorter duration (8 h compared to >240 h) by using high temperature homogenization.