Chemical, Physical and Tribological Investigation of Polymercaptanized Soybean Oil

Abstract

Polymercaptanized soybean oil (PMSO) was investigated for its chemical, physical and tribological properties relative to soybean oil (SO) and also as a potential multi-functional lubricant additive in high oleic sunflower oil (HOSuO). Analytical investigations showed that PMSO is obtained by conversion of 76% of double bonds in SO into thiol (–SH) and sulfide (R–S–R′) groups. PMSO product mixture comprised 70% monomer and 30% oligomers, versus 99.6 and 0.4%, respectively, for SO. Relative to SO, PMSO displayed higher density, viscosity and oxidation stability; similar cold flow properties; and lower viscosity index. PMSO displayed good solubility in HOSuO (>10% w/w), but poor solubility in polyalpha olefin-6 (<1% w/w). Investigation of PMSO as a lubricant additive in HOSuO showed that it had multi-functional properties. Thus, blending of PMSO in HOSuO resulted in improved oxidation stability; improved friction and wear in 4-ball anti-wear tests; improved extreme pressure (EP) properties in 4-ball EP tests; and no effect on cold flow properties.