Wear performances and wear mechanism study of bulk UHMWPE composites with nacre and CNT fillers and PFPE overcoat

Wear of Ultra-High Molecular Weight Polyethylene (UHMWPE) plays an important role in determining the life-span of total hip and knee joint implants. In previous studies, UHMWPE wear has been reduced by improving crystallinity percentage, crosslinking and particle reinforcement, though with varied results. In this research, nacre and three types of Carbon Nano-Tubes (CNTs) were added into UHMWPE bulk, and the composites were overcoated with perfluoropolyether (PFPE), to study the effects on UHMWPE wear in the (aqueous) bovine albumin protein lubricated condition. The wear tests were conducted on a pin-on-disk tribometer. PFPE coated UHMWPE and PFPE coated UHMWPE-nacre composites showed higher wear than that of pure UHMWPE. The three types of CNT-reinforced UHMWPEs also showed higher wear rate. Nevertheless, the worn surfaces and wear debris were studied to understand the wear mechanisms and the reasons for the wear rate increment for the composites in bovine albumin protein lubricated sliding. It is hypothesized that water molecules form hydrogen bond with PFPE lubricant as well as the fillers and thus increase wear of the composite in wet condition. CNTs may also act as third body to increase wear.