Change of Micromechanical Properties of Polyethylene Induced by a Tribological Process in Polymer/Metal System

The influence of a tribological process in the polymer/metal system on changes in microhardness (H) and Young’s modulus (E) of the surface under friction and UHMWPE volume has been studied. Twelve samples of polyethylene characterized by a different degree of initial plastic deformation and different electron irradiation dose were analyzed. For four of the samples a decrease by 5÷10 times in polyethylene degradation has been found. This result is promising in that a prolonged durability can be expected in case of application for endoprostheses acetabular cups. It has been found also that a polyethylene material irradiated after initial prestraining only once shows enhanced micromechanical properties after friction. It has been found that this result was due to reorientation of lamellas on the friction surface taking place during deformation which accompanies the tribological process. It has been proved that the increase of H and E values in the layers situated at a depth of 1.5 mm÷7.5 mm is due to a decrease of the free volume centers in the UHMWPE polyethylene and to an increase of the degree of spatial arrangement of the structure (absorption in crystallinity band of FTIR spectrum).