Lubrication properties of trimethylolpropane esters based on palm oil and palm kernel oils

Due to the global drive towards biodegradable products, trimethylolpropane [2-ethyl-2-(hydroxymethyl)-1,3-propanediol] (TMP) esters based on palm and palm kernel oils were synthesized, their lubrication properties evaluated, and their potential as base stock for biodegradable lubricants assessed. Two types of TMP esters were considered: palm kernel (PKOTE) and palm oil (PPOTE) TMP esters, derived from palm oil and palm kernel methyl esters, respectively. Lubrication properties such as viscosity, viscosity index (VI) and pour point (PP) were determined according to methods of the American Society for Testing and Materials. Wear and friction properties were evaluated using a four-ball test machine, while oxidative stability was studied with the Penn State Micro-oxidation thin-film test. High VI ranges between 170 to 200 were recorded for these base stocks. PP were relatively high, between 4 to -1°C, but were improved to at least -33°C in high oleic palm oil TMP esters. The effects of chemical structure and impurities on wear properties and oxidative stability were also studied. The presence of methyl esters was found to improve wear, but hydroxyl groups in mono- and diesters had negative effects at high concentrations. Differences in chemical structures of PKOTE and PPOTE were shown to affect friction and wear results. Both base fluids exhibit oxidative stability comparable to other high oleic base fluids.