Changes in the tribological behavior of an epoxy resin by incorporating CuO nanoparticles and PTFE microparticles

Different amounts of CuO nanoparticles are incorporated into both a neat epoxy resin and into an epoxy resin containing PTFE microparticles. The content of CuO is varied in the range of 0–10 vol.% while the PTFE content is fixed at 7.5 vol.%. The dispersion state of added particles is examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which show a relatively good dispersion of both kinds of particles. Differential scanning calorimetry (DSC) and Vickers hardness measurements show no clear changes in glass transition temperature or hardness as a function of the nano-CuO content. However, both parameters are reduced when PTFE is added. Friction and wear data is collected using a custom-made tribotester of the pin-on-disk type. Measurements are performed under dry-sliding conditions against smooth steel counterfaces. When a pressure–velocity (pv) condition of 0.25 MPa, 6.0 m/s is applied the following is found: without PTFE, the coefficient of friction (μμ) is roughly independent of the nano-CuO content. When PTFE is added, an average reduction in μμ of 35% is found in the CuO range of 0–0.4 vol.%. At higher CuO concentrations the friction lowering effect of PTFE deteriorates. Addition of CuO increases wear relative to the neat epoxy at all concentrations. When nano-CuO is added to epoxy with PTFE incorporated, the wear rate decreases slightly up to a CuO content of 0.4 vol.% after which it increases. The measurements are repeated for some of the composites using a smoother counterface. This gives rise to significantly less wear, which for composites without PTFE is attributed to formation of a protective transfer film. At a pv condition of 1.16 MPa, 1.0 m/s the following is found: composites without PTFE generally show an unsteady behavior with high average wear rates whereas composites with PTFE generally show a good friction and wear performance. The best results are seen at a CuO content in the range of 0.1–0.4 vol.%. The latter shows a positive synergistic effect of adding a small amount of nano-CuO together with PTFE into the epoxy resin.