Introduction: Our previous study1) suggested that addition of vitamin E(dl-α-Tocopheror) at the grain boundarie of UHMWPE dramatically prevented delamination destruction. This study examined the microscopic and macroscopic mechanical performances of the vitamin E added UHMWPE by using micro indenter testing and high-speed tensile testing.

Methods: UHMWPE powder (GUR1050, Ticona) was directly molded at 10MPa with and without Vitamin E (DL-α-Tocopherol, Wako Pure Chemical Industries. Ltd.) addition. The Vitamin E was compounded to UHMWPE powder in air using a blend mixer. Gamma-ray irradiation (a dose of 25kGy) was performed on each group at room temperature in air, and then, the specimens were aged at 80°C for 23 days. Hardness at grain boundary was measured using dynamic micro indentation testing machine (Shimadzu Dynamic Ultra Micro Hardness Tester, DUH-200) where triangular-pyramid indenter with 115 degrees point angle was used. High-speed tensile testing was performed to dumbbell-shaped test specimens (JIS K7113 No.2, thickness=3mm) with crosshead speed of 1000 mm/min (corresponding strain rates : 0.4/s).

Results and discussion: Results of micro indenter test showed that the dynamic hardness at grain boundary was higher than that in grain and was increased by gamma irradiation. This hardening at grain boundary was reduced by adding vitamin E. Results of high-speed tensile test showed no significant change in Young’s modulus and strength by the vitamin-E addition. However, the elongation at break was increased to more than 10 times as much as that of virgin (aged) UHMWPE.

These results suggest that mechanism for the prevention of delamination by vitamin-E-addition is caused by increased elongation at break by increasing toughness at grain boundary. The addition of vitamin E is a simple and extremely effective method to prevent destruction of UHMWPE joint component.