Chemical, physical and tribological investigation of polymercaptanized soybean oil

Authors: Biresaw, Girma; LANSING, JAMES - Orise Fellow; Bantchev, Grigor; Murray, Rex; Harry O Kuru, Rogers

Submitted to: Tribology Letter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2017
Publication Date: 5/24/2017
Publication URL: http://handle.nal.usda.gov/10113/5852200
Citation: Biresaw, G., Lansing, J.C., Bantchev, G.B., Murray, R.E., Harry-O'Kuru, R.E. 2017. Chemical, physical and tribological investigation of polymercaptanized soybean oil. Tribology Letters. 65:87.

Interpretive Summary: Development of fully biobased lubricants requires the blending of biobased base oils with biobased additives. Such a blend, with 100% biobased components, will provide the maximum economic, environmental, safety and health benefits from application of biobased products. Currently, there are very few commercial biobased base oils, but no commercial biobased additives. As a result, formulation of biobased lubricants requires the use of commercially available petroleum-based additives, which will produce partially biobased formulations with partial benefits. In order to remedy this, a variety of research is being pursued by tribologists worldwide to develop and commercialize biobased additives. In the work described here, scientists at the National Center for Agricultural Utilization Research, Peoria, IL, investigated polymercaptanized soybean oil (PMSO) for its chemical, physical and potential multi-functional lubricant additive properties using high oleic sunflower oil (HOSuO) as the base oil. Tribological investigations showed that PMSO has multi-functional additive properties. Thus, blending of PMSO in HOSuO resulted in: improved oxidation stability; improved friction and wear in 4-ball anti-wear tests; and improved extreme pressure (EP) properties in 4-ball EP tests. This result indicates that cost-competitive biobased lubricant additives can be developed from commodity soybean oil. Successful commercialization of such products will increase the utilization of farm products, while at the same time replacing environmentally unfriendly petroleum-based additives from lubricant formulations.

Technical 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.