Influence of Environmental Degradation and Vitamin-E (α-Tocopherol) Addition on the Fatigue Crack Growth Property of Ultra High Molecular Weight Polyethylene

Abstract

Ultra High Molecular Weight Polyethylene (UHMWPE) has been used for the bearing materials of artificial knee joints owing to its superior mechanical properties and chemical resistance. In vivo, however, delamination fracture occurred, because of wear and fatigue of UHMWPE components. Although γ-irradiation and following aging was reported to accelerate the delamination fracture, the effects on the fatigue crack growth behavior have not been revealed yet. On the other hand, the addition of Vitamin-E (α-Tocopherol) was reported to prevent the delamination wear, but the prevention mechanism has not been clarified yet. In this study, in order to understand the influence of γ-irradiation and accelerated aging, and the addition of Vitamin-E on the fatigue crack growth properties of UHMWPE, tensile tests and fatigue crack growth tests of UHMWPE were carried out. After the γ-irradiation and accelerated aging, the specimen surface was oxidized and its crystallinity was increased. However the addition of Vitamin-E reduced the oxidization of the specimen and the increase of its crystallinity. For the tensile tests, the yield stress was increased and the tensile strength was decreased by γ-irradiation and accelerated aging. For the fatigue crack growth tests, the addition of Vitamin-E reduced the decrease of ΔJth by γ-irradiation and accelerated aging. Although the fibrillation and the brittle fracture were observed on the fracture surface of γ-aged specimen, they were not observed on that of Vitamin-E added γ-aged specimen.