Experimental evaluation of particle size effect on kaolin additive palm nanolubricants and determination of optimum production parameters using a multi-criteria decision-making method

Nowadays, nanolubricants are attracting increasing attention due to their potential to enhance tribological performance and environmental sustainability. Lubricants containing nanoparticles can extend the lifespan of machine components by reducing friction and wear, while also improving energy efficiency. In this study, to improve the tribological and chemical performance of nanolubricants containing kaolin nanoparticles modified with oleic acid, the optimum nanoparticle size and concentration that minimise friction and wear and increase oxidative and hydrolytic stability were determined. Kaolin nanoparticles of varying sizes (950, 650, and 350 nm) were modified with oleic acid and incorporated into palm oil at various concentrations (0.125%-1.5% by weight). The wear and friction coefficients of the nanolubricants were measured through wear tests, and it was observed that both friction and wear decreased as particle size decreased. Moreover, oxidative and hydrolytic stability tests revealed that small-sized particles increased oxidation and moisture (water) retention resistance. The MOORA multi-criteria decision-making method was used to determine the optimum production parameters. The results indicated that palm lubricant containing 0.125 wt% 350 nm size kaolin nanoparticles showed the best performance.