Tribological performance of trimethylolpropane ester bio-lubricant enhanced by graphene oxide nanoparticles and oleic acid as a surfactant

One of the issues of nanoparticle additives is the tendency to agglomerate. The presence of a surfactant may help reduce this issue. In this study, trimethylolpropane (TMP) ester was used as a base lubricant, graphene oxide (GO) as a nanoparticle additive, and oleic acid (OA) as a surfactant. Tribological testing was carried out using a four-ball tribotester at various concentration ratios. The results showed that the TMP + GO + OA demonstrated increased dispersion stability compared to TMP + GO alone. Furthermore, the presence of OA reduced the coefficient of friction of the samples containing 0.05 wt%, 0.1 wt%, and 0.5 wt% GO by 22.9%, 21.1%, and 23.6%, respectively. Surface roughness and physical wear conditions were also observed and discussed.