Enhanced wear resistance of gamma-irradiated PTFE and FEP polymers and the effect of post-irradiation environmental handling

The wear resistance of bulk polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP) fluoropolymer pin samples when sliding against polished steel countersurfaces is shown to be improved by over two orders of magnitude through the use of gamma irradiation. Wear rates were found to drop monotonically with increasing irradiation dose for both PTFE and FEP, with PTFE having a stronger dose response achieving two order-of-magnitude wear rate reduction within a 5 Mrad dose while FEP required a 30 Mrad dose to achieve similar reductions. Possible wear reduction mechanisms of irradiated fluoropolymers via crosslinking and scission are discussed. Though the effect of environment was less clear for PTFE, post-irradiation heated vacuum storage intended to enhance crosslinking further increased the wear resistance of FEP while accelerated aging potentially causing oxidative scission resulted in partial loss of radiation-induced wear resistance.