Wear Resistance Of Nanocomposites Based On UHMWPE And Lubricating Fillers

Ultra High Molecular Weight Polyethylene (UHMWPE) and its composites materials are widely used in orthopaedic implants such as hip, knee joint replacement and bearings for its special properties (wear resistance, strength and modulus, toughness, chemical and impact resistance, low moisture absorption, etc..). Highly cross linked polyethylene is the material of choice in contemporary hip arthroplasy procedures. Gamma and electron beam radiation are commonly used to crosslinks UHMWPE and particular treatments need to be performed to avoid material oxidation, such as thermal quenching, thermal annealing or blending with antioxidant molecules (such as Vitamin-E, in an opportune amount). These treatments improve the production process while vitamin E, if can be effective as free radical scavenger, on the other hand it could reduce the cross linking efficiency [1]. In order to improve tribological featurs of UHMWPE, carbon nanofiller can be employed as lubricant to increase the wear resistance of component in friction units [2]. UHMWPE reinforced with carbon nanofibers (CFR-UHMWPE, named Poly II) was used in orthopedic implants in the 1970s for THA/TKA (Total Hip or Knee Arthoplasty) [3]. However, this composite was discontinued due to evidence on reduced crack resistance, rupture of the fibers on the surface, and other issues. The improvement in the incorporation methods developed in the more recent years, the intrinsic properties and cytocompatibility of the carbon nanofiller, let to a reconsideration of these nanocomposites [4]. In this work we we have prepared nanocomposites made by UHMWPE mixed ( by ball milling and twin extrusion) with 1% wt of carbon nano filler (to improve its wear resistance) and 2% wt of PO (to reduce its viscosity, favour its process ability and obtain an optimum filler dispersion). The wear tests were carried out under dry (air) and wet (natural and artificial lubricant), with a normal load of 30 N. Results have highlighted that the mixing technique and the lubricant presence during the wear test, have a greater effect on the specific wear rate, Ws.