Synthesis and Tribological Investigation of Cashew Nutshell Liquid Cardanol Oil Dispersed with Modified Cu–Zn Nanoparticles

The present investigation explores the physicochemical properties, colloidal stability, and tribological characteristics of Cu–Zn nanoparticles (NPs) surface-capped with Oleic acid (OA) in Cashew Nut Shell Liquid Cardanol oil. The functionalized Cu–Zn nanolubricants were formulated with different volume fractions of Cu–Zn NPs viz. 0%, 0.05%, 0.1%, 0.25%, and 0.5% in the synthesized Cardanol oil. The physicochemical properties of the base lubricant and Cu–Zn nanolubricants were evaluated as per ASTM standards. The dispersion stability and functionalization of Cu–Zn/OA nanolubricants were investigated through UV Spectroscopy and FTIR spectroscopy respectively. Further, the tribological behaviour of Cu–Zn NPs in different volume fractions with Cardanol oil was evaluated using a Four-ball tribometer as per ASTM D4172 standards. The results exhibited that the kinematic viscosity of nanolubricants at different temperatures enhanced with the rise in the concentration of nanoparticles. The Cu–Zn NPs surface-capped with OA in base oil exhibited superior stability compared to the unmodified Cu–Zn NPs. Meanwhile, improved dispersion stability was observed for nanolubricants with lower concentrations of Cu–Zn NPs than those with higher concentrations. The outcomes of tribological investigation revealed that the inclusion of 0.1%wt. Cu–Zn NPs exhibited the highest reduction in coefficient of friction and wear scar by 17% and 7% respectively. Moreover, the wear rate declined by 25% for the nanolubricants containing 0.1% wt. Cu–Zn NPs. Further, the surface analysis of worn specimens using SEM / EDS, revealed the lubrication mechanisms that contributed to improving the tribological behaviour of nanolubricants compared to the base lubricants.