Influence of plane-strain compression on the microstructure and tribological behavior of GUR 1050 UHMWPE

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in orthopedic implants due to its outstanding physical and mechanical properties. Modifications in the structure of the polymer have a direct effect on its wear. In this work, plane-strain compression in a channel die was applied to induce microstructural changes in specimens of UHMWPE GUR 1050. These structural changes were characterized using a combined approach involving Raman spectroscopy and atomic force microscopy. These qualitative and quantitative characterization resulted in a valuable understanding of the changes in the material microstructure when subjected to plastic deformation. A molecular non-uniform alignment of the UHMWPE molecules, with fragmentation and kinking of polymer lamellae, was observed in the direction of material flow, perpendicular to the compressive load direction, following an inhomogeneous strain field generated by the mechanical compression. The microstructural analyses revealed an increased crystalline content and decreased intermediate phase while amorphous phase content remained unchanged, in all the regions of the deformed specimen. The tribological performance, evaluated by the scratch resistance force, decreased along the material flow direction and increased along the load direction in the deformed polymer compared to that of the uncompressed polymer. Plane-strain compression was able to modify the polymer microstructure, introducing directional anisotropy in its tribological behavior that can impact the wear performance of the material.