Friction and Wear Behavior of Ultra-High Molecular Weight Polyethylene as a Function of Polymer Crystallinity

In this study the friction and wear behavior of medical grade ultra-high molecular weight polyethylene (UHMWPE) (GUR 1050 resin) were evaluated as a function of polymer crystallinity. Crystallinity was controlled by heating UHMWPE samples to a temperature above its melting point and varying the hold time and cooling rates. Degree of crystallinity of the samples was evaluated using differential scanning calorimetry (DSC). Quantitative friction experiments were conducted at two different scales. A custom-made microtribometer with commercially available spherical Si3N4 probes in dry conditions was used to test friction at the microscale. An atomic force microscope with commercially available Si3N4 probes under dry conditions was used for nanoscale experiments. A higher degree of crystallinity in the UHMWPE resulted in lower friction force and an increase in scratch resistance at both scales. Reciprocating wear tests preformed using the tribometer show that higher crystallinity also results in lower friction, as well as lower wear depth and width.