Evaluation of Aromatic Organic Compounds as Additives on the Lubrication Properties of Castor Oil

In the quest for sustainable lubrication solutions, the present research explored the potential of five organic compounds as additives in castor oil (CO) to improve its lubricating properties. The compounds tested were curcumin, eugenol, 1,3-Diphenyl-2-propanone, 1,3-Diphenyl-2-propenone, and 1,3-Diphenyl-1,3-propanedione. The main results showed that each additive enhanced at least one characteristic of CO. Most of the additives lowered the density of the castor oil but increased the viscosity by up to 20%. Curcumin and eugenol were particularly effective in creating thicker lubricant films and higher film thickness ratios. Eugenol and 1,3-Diphenyl-2-propanone significantly reduced the friction coefficient by up to 25%. Wear rate and wear mechanisms were significantly reduced with all the additives, achieving a reduction in wear rate of up to 50% (CO+curcumin). All the additives, except the 1,3-Diphenyl-1,3-propanedione, enhanced the oxidation onset temperature up to 8 °C. The influence of chemical structure was also addressed. The optimal additive combination for a specific application that demands minimal friction and wear, as well as strong oxidation stability, was eugenol, followed by curcumin and 1,3-Diphenyl-2-propanone. Overall, the research contributes to the development of eco-friendly lubricants, aligning with the growing demand for green industrial applications, and highlights the significant tribological benefits of these substances as sustainable additives in biolubricant formulations.