Friction and Wear Performance of Melt-Processable PTFE/FEP Blends under Dry and Wet Conditions

Polytetrafluoroethylene (PTFE) and perfluoroethylene-propylene copolymer (FEP) were fabricated as test specimens by hot-pressing molding and melt injection molding respectively, and their tribological properties were investigated. The results indicated that PTFE had lower friction coefficient than FEP in both dry and wet circumstance. On the basis of this research, the melt-processable PTFE (M-PTFE)/FEP blends were prepared by melt extrusion and injection molding, and comparatively characterized by x-ray diffration (XRD), differentiall scanning caloriemetry (DSC), and mechanical property measurements, especially tribological properties in both dry and wet states. The XRD and DSC results indicated that the melt-processable PTFE was well miscible with FEP matrix. The tensile strength of the blends increased monotonously with increasing M-PTFE in the studied blending range. The friction coefficient and volume wear rate of the blends, however, performed irregular trends, depending on the M-PTFE addition and testing environments. In dry friction, the friction coefficient decreased with the increase of M-PTFE addition. Whereas, the volume wear rate decreased with the M-PTFE content below 20%, and increased when the M-PTFE addition reached 30% possibly due to the high wear rate of M-PTFE. Different from the results in dry friction, both the friction coefficient and volume wear rate didn’t display a relationship with M-PTFE content under wet friction. It was observed that the friction coefficient and volume wear rate under wet environment were lower than those under dry condition. Scanning electron microscopy observation of worn surface revealed that the transfer film was formed, and became perfection with the increase of M-PTFE content under dry friction. The transfer film, on the other hand, was inhibited to some extent in the presence of water, and only shallow and narrow furrows appeared on the wet worn surface. Based on the investigation, the tribological mechanism of M-PTFE/FEP blends under dry and wet environment was probed.