This study investigates the rheological and tribological behaviour of modified Calophyllum inophyllum (mCI) oil-based biolubricants enhanced with graphene nanoflakes (GNFs). The transesterification of Calophyllum inophyllum oil was conducted to improve its oxidation stability, thereby ensuring its suitability for high-performance lubrication. Rheological measurements were carried out at 40°C and 100°C, revealing Newtonian behaviour in all mixtures, and providing insight into the stability of GNF in biolubricant. At lower temperatures, the addition of graphene increases the dynamic viscosity, whereas at higher temperatures, a reduction in viscosity was observed. The tribological performance was significantly enhanced at an optimum percentage of GNFs. Coefficient of friction (COF) measurements demonstrated that the addition of GNFs led to a reduction in COF. Wear analysis further confirmed the superior performance of GNF-enhanced biolubricants. FESM images and 3D profilometry of the worn surfaces revealed that the addition of GNFs resulted in smoother wear tracks, indicating reduced wear. The experiments demonstrated that incorporating 0.4 wt% GNFs into the mCI biolubricant significantly enhanced its tribological performance. This improvement was attributed to the formation of a nanoparticle-based tribofilm during the sliding motion.
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