The role of oleic acid on the structural changes of graphite nanoplatelets in enhancing the tribological performance of a palm oil-based lubricant

The current work investigates the structural changes of graphite (CG) when employed as an additive in palm kernel oil (PKO)-based nanolubricants without and with oleic acid (OA) surfactant. A four-ball tribotester was used to study the tribological performance of PKO + CG nanolubricants. PKO + CG nanolubricants with OA surfactant outperformed others, demonstrating significant reductions in coefficient of friction (20.5%) and wear scar diameter (9.1%) as compared to the PKO base lubricant. Exfoliation of graphite was facilitated during sliding due to the impact of shear force. A transmission electron microscopy structural study showed that the presence of OA surfactant in nanolubricants stimulated the formation of highly exfoliated graphite, resulting in the formation of scrolling graphite. Furthermore, when lubricated with PKO + CG + OA nanolubricants, Raman spectroscopic study of the worn surface reveals the formation of a more ordered tribofilm at the friction contact. The findings highlight graphite structural changes as the major factor in improving tribological performance. These results could help us learn more about the main mechanism of graphite as a lubricant additive and how structural changes affect tribological performance.