Improvement of Interfacial Adhesion and Tribological Performance of Ultra-High-Molecular-Weight Polyethylene Using Chromic Acid Treatment and Plasma-Functionalized Graphene Nanoplatelets Coatings

Ultra-high-molecular-weight polyethylene is a common choice for wear-resistant applications due to its low friction, high toughness, and chemical stability. However, its chemical inertness and low surface energy limit the adhesion of functional coatings such as graphene nanoplatelets (GNPs). In this study, chromic acid etching and plasma-functionalized GNP coating were used to improve the interfacial adhesion and tribological performance of UHMWPE. Substrates of UHMWPE were etched in chromic acid for 0, 5, 10, and 15 min and then dip-coated with argon plasma-treated GNPs. Etching time significantly impacted surface morphology, coating stability, wettability, and friction behavior. Moderate surface roughness, mechanical interlocking, and homogeneity of the GNP coating were obtained for the 5 min etching condition. This condition achieved the best tribological performance, with the coefficient of friction decreasing to 0.23 and the water contact angle decreasing to 88.17°. Mechanical testing showed that the 5 min etched sample kept most of its bulk properties, with a tensile modulus of 512.8 MPa, tensile strength of 27.71 MPa, and hardness of 67 Shore D. Longer etch times led to over-roughening and generation of micro-defects, causing lower coating uniformity and higher friction. This study shows the potential of controlled chromic acid etching with plasma-functionalized GNP coating to enhance the surface adhesion and tribological characteristics of UHMWPE, and mechanical properties were largely retained.