Tribological characterization of nanoparticle filled PTFE: Wear-induced crystallinity increase and filler accumulation

The present research aims to clarify the friction and wear behavior, the transfer layer formation, and the wear mechanism of mono-filled polytetrafluoroethylene (PTFE). A well-known limitation of PTFE is the low wear resistance, which can be surpassed with the use of micro- or nanoparticles. The applied fillers were graphene, alumina (Al2O3), boehmite alumina (BA80), and hydrotalcite (MG70). The samples were produced by room temperature pressing - free sintering method. All specimens were tested with a pin-on-disc tribo-tester in dry contact condition against 42CrMo4 steel disc counterface with 3 MPa contact pressure and 0.1 mm/s sliding speed. PTFE filled with 4 wt% Al2O3 achieved the highest wear resistance; the increase was more than two orders of magnitude compared to the neat PTFE. This improvement comes from the protective transfer layer formation due to the Al2O3 and the iron-oxide accumulation on the polymer contact surface. Significant wear-induced crystallinity was also registered, which originated from the mechanical chain scission of the PTFE molecular chains during the wear process.