Tribological Properties and Microstructure Changes of UHMWPE Surface Induced by Water Absorption

Ultra-high molecular weight polyethylene (UHMWPE) has become the preferred material for joint liners due to its excellent wear resistance and chemical stability. This study provides a basic investigation into how water absorption influences the tribological behavior and mechanical characteristics of UHMWPE. The surface plastic deformation layer formed during UHMWPE wear was found to exhibit significant changes after water absorption. Experimental results demonstrate that water absorption not only reduces the friction coefficient of the material by 7.79%, but also exacerbates plastic deformation, resulting in an increase of wear up to 4-fold compared to the control group. Raman spectroscopy analysis further confirmed a notable rise in surface crystallinity after water absorption. Indentation tests show water absorption decreases indentation depth. Molecular simulation results suggest that water absorption in UHMWPE chains tends to reduce the inter-molecular interactions and thereby facilitates the formation of ordered arrangements of surface polyethylene, leading to an anisotropic distribution, i.e., ordered alignment in parallel to the frictional direction, and anisotropic mechanical properties. The anisotropic distribution of surface polymer chains during friction, which was also strengthened after water absorption, in turn increases the resistance to indention. The investigation results of the tribological properties and mechanical characteristics of water-absorbed UHMWPE may provide useful insights for the evaluation and performance of artificial joints.