Wear and friction resistance of UHMWPE with anisotropic microstructure shaped by mechanical compression

This study investigates the tribological behavior of UHMWPE with an anisotropic microstructure induced by uniaxial compression. Reciprocating sliding tests were conducted under loads exceeding the material's elastic limit to reveal differences in friction and wear when sliding parallel (LD) and perpendicular (FD) to the compression axis. The experiments were conducted under a severe wear regime, exceeding the typical contact stresses in orthopedical prostheses. The results highlight the influence of mechanical deformation on wear resistance and friction, providing insights for optimizing UHMWPE performance in biomedical and industrial applications. The molecular structure of the original and compressed UHMWPE specimens was assessed using AFM images, and the microstructural phases were quantified through Raman spectroscopy. The originally directionless lamellar structure appeared aligned along the FD direction in the compressed specimen. Besides that, the amount of crystalline phase, near 50 % in the original specimen, increased to 57 % when the laser beam is polarized along the FD direction and decreased to 29 % polarized along LD direction in the deformed specimen, indicating permanent anisotropy in the polymeric material due to mechanical compression. The average amount of polymer's microstructural phases clearly changed after sliding process, quite considerably in the compressed specimens. Testing along FD path further increased the crystalline phase in this direction, from 57 % to 66 % after the test. In LD direction the same phase increased from 29 % to 76 % after the test, even reversing the microstructural anisotropy in this case. A larger volume of debris was produced in the plastically deformed polymer specimen in comparison to the original material, independently of the tested direction, and despite the increase in the crystalline phase in the deformed material. The pre-strained material demonstrated more susceptibility of to wear, with no correlation with the crystallinity extent of the material. In conclusion, the results contribute to a better understanding of material deformation mechanics, providing insights into optimizing wear resistance in high-stress environments.