Sulfurized Methyl Esters of Soya Fatty Acids: Synthesis and Characterization

Soy-based fatty acid methyl ester disulfide (FAME-S-2) was synthesized in good yield by oxidation of polymercaptanized soybean oil fatty acid methyl ester (PM-FAME). The chemical structure of FAME-S-2 is of interest because of its potential as a biobased multi-functional additive in lubricant formulations. Neat FAME-S-2 and their blends (1-10% w/w) in polyalphaolefin (PAO-6) and high oleic sunflower oil (HOSuO) were characterized for its chemical, physical and tribological properties. Blends of FAME-S-2 in HOSuO relative to similar blends of PM-FAME displayed higher oxidation onset temperature (> 15 degrees C) that remained constant with increasing concentration. Evaluation of FAME-S-2 as an extreme pressure (EP) additive on a 4-ball tribometer showed increasing weld point (WP) with increasing concentration to a maximum of 220 and 180 kgf in HOSuO and PAO-6, respectively, at 10% w/w concentration. The results indicate that FAME-S-2 has both anti-oxidant and EP properties and can be applied as a multi-functional biobased additive in lubricant formulation. This work demonstrates an encouraging progress towards the development of effective biobased lubricant additives.