Enhancement in micro-fatigue resistance of UHMWPE and HDPE processed by SCORIM

Abstract

The tribological performance of UHMWPE and HDPE polymers, processed by a novel polymer process technology SCORIM (Shear-Controlled ORientation TEChnology) in injection moulding, shear controlled orientation in injection moulding (SCORIM) was evaluated against a through-hardened steel under different test conditions and compared with those processed by conventional injection moulding. Results indicate a significant improvement in the wear resistance using the SCORIM technology as a result of an increase in the mechanical properties. SEM microscopy shows a change of wear mechanisms dominated by micro-fatigue when using conventional injection moulding, compared to mild abrasive wear when using the SCORIM technology under the same test conditions. Examination of microstructure reveals the random aggregation of polymer molecules in the samples processed by a conventional injection moulding. Using the SCORIM technology, the molecules were sheared and orientated and a fibril microstructure formed as an in situ fibre reinforced composite. DSC analysis shows an increase in a second phase shish kebab structure in the samples processed by SCORIM technology. The fibril microstructure with an increase in shish kebab structure results in a significant improvement in wear resistance. Using the surface normal to the direction of the orientated molecular fibril microstructure as a contact surface, the possibility of the initiation and development of micro-cracks was reduced, especially the micro-cracks parallel to the contact surfaces.