Effect of Platelet Thickness on Wear of Graphene–Polytetrafluoroethylene (PTFE) Composites

Abstract

Under conditions of dry sliding against polished stainless steel, the steady-state wear rates of composites of polytetrafluoroethylene (PTFE) filled with graphene platelets with typical platelet thickness varying between 1.25 and 60 nm were measured. The fraction of the graphene platelets was varied between 0.02 and 30 wt%, also including 0 % unfilled PTFE. With 4 % loading of the 1.25 and 1.6 nm thick graphene platelets, the measured steady-state wear rates approached ~4 × 10⁻⁷ mm³/Nm levels which are roughly three orders of magnitude lower than that measured for unfilled PTFE, decreasing further to 10⁻⁷ mm³/Nm at 10 % loading. In addition, among all the tested graphene platelets, the thinnest graphene platelets already imparted considerable wear resistance even at a low 0.32 % loading. The thicker graphene platelets also started providing some slight resistance to sliding wear but not until a greater filler loading of 1.1 %. For a given graphene platelet, there appears to be a lowest achievable steady-state wear rate, while the filler loading is gradually increased. For the 8 nm thick graphene platelets, this minimum was found to be about 3 × 10⁻⁷ mm³/Nm at a filler loading of about 20 %. When the wear rates are plotted as a function of the filler loading on log–log axes, for each of the graphene platelets, the wear rates are found to decrease linearly beyond a threshold filler loading up to at least 10 % filler loading. Wear rates corresponding to each type of graphene platelet fall on its own line on such a plot. However, when the wear rates are instead plotted as a function of the filler surface area available per unit mass of the composite, the data (with the exception of the thickest 60 nm platelets) collapse around a master line with slope of about −1.73.