Role of in-situ formed nano- and micro-fibrils in micro-fatigue resistanceof bio-polyethylene

In response to the need for the reduction of micro-debris generation in art ificial human joints for extending the service life, a novel polymer proces s technology, SCORN (shear controlled orientation injection moulding), was employed to manufacture a polyethylene composite reinforced by in-situ form ed nano- and micro-fibrils. Tribological performance of a blend of ultra hi gh molecular weight polyethylene (UHMWPE) and high density polyethylene (HD PE) was evaluated on a pin-on-clisc wear machine. Results indicate a signif icant improvement in micro fatigue wear resistance compared with those moul ded by a conventional injection moulding technology. Scanning electron micr oscopy reveals that a micro-fibril structure forms as an in-situ fibre rein forced composite using SCORIM while an aggregated structure occurs in speci mens moulded by conventional technology. DSC analysis shows the occurrence of a second phase: shish kebab microstructure using SCORIM. Transmission el ectron microscopy reveals the transformation of microstructure from randoml y orientated lamella in the specimens moulded by conventional injection mou lding into nano-fibril shish kebab microstructure, which results in a signi ficant reduction in the possibility of the initiation and development of mi cro-cracks parallel to the contact surfaces using SCORIM. Consequently, the formation of nano-fibril shish kebab and micro-fibril microstructure by us ing the novel SCORIM technology results in a significant reduction in micro -fatigue when using the surface normal to the direction of the orientated m olecular fibril microstructure as a contact surface.