High crystallinity makes excellent wear resistance in crosslinked UHMWPE

Abstract

Nowadays, irradiation crosslinking is still a primary method to improve the wear resistance of ultrahigh molecular weight polyethylene (UHMWPE). As a semi-crystalline polymer, crystalline structure of UHMWPE will also significantly affect the abrasion performance. Due to the difficulty in obtaining a wide range of crystallinity (Xc), there is less knowledge on the synergistic enhancement of crosslinking and crystallization to wear resistance. Herein, a combination of using low entanglement nascent powder and adjusting thermal history of sinter molding causes the Xc of UHMWPE varied in a range of 44%∼56%, and then γ-ray irradiation is utilized to form crosslinking between molecular chains. The significances of crystallization on the wear resistance of crosslinked UHMWPE are manifested as follows. (1) When Xc maintains almost constant, the wear rate per 105 cycles doesn't decrease continuously with the increase of molecular weight (MW), indicating the effect of MW on abrasion performance is limited. (2) For the crosslinked samples with same MW but different Xcs, the wear rate reduces monotonously as increasing Xc. It drops for −41% at the highest Xc, which means the wear resistance is susceptible to the amount of crystalline phase. (3) By exposing to γ-irradiation, the wear rate of the low-Xc sample (44%) reduces for −12%, while it reaches −21% for the counterpart with Xc∼56%. Obviously, crosslinking at high Xc is more effective in tailoring wear resistance. In addition, the fact that among the samples with similar Xc the wear rate changes faintly regardless of distinct variations in crystalline microstructure, suggests Xc plays a vital role on anti-abrasive behavior rather than other structural factors. According to these results, we propose an effective strategy to improve the wear resistance of crosslinked UHMWPE by utilizing high crystallinity, which has potential for developing high-performance artificial joint prosthesis materials.