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Tribological properties of vegetable oils modified by reaction with butanethiol

Biresaw, Girma, Bantchev, Grigor B., Cermak, Steven C.
Tribology letters 2011 v.43 no.1 pp. 17
additives, canola, canola oil, castor oil, corn, corn oil, dissociation, energy, equations, friction, hydrocarbons, hydrogen, oxidation, photochemical reactions, protons, sulfides, vegetable oil, viscosity
Corn, canola, and castor-lauric estolide oils were chemically modified by photochemical direct reaction of butanethiol with the double bonds on the hydrocarbon chains. The effect of chemical modifications on viscosity, viscosity index (VI), pour point (PP), cloud point (CP), oxidation stability (RPVOT), 4-ball anti-wear (AW), and extreme pressure (EP) were investigated. The sulfide modified (SM) corn and canola oils showed increased viscosity, increased RPVOT time (more than one order of magnitude), reduced PP (9–18 °C), and reduced VI. The SM estolide displayed similar trends in VI and RPVOT but showed no change in viscosity or cold flow. The SM oils, along with commercial mono- and polysulfide additives were also investigated as additives, at 0.6% (w/w) S concentration, in corn and polyalphaolefin (PAO) base fluids. In both fluids, the additives resulted in minor changes of PP, CP, coefficient of friction, wear scar diameter (WSD), and weld point (WP). Only the commercial polysulfide EP additive displayed large WP increases in the fluids. The additives resulted in no change of oxidation stability of corn oil, but displayed big improvement in the oxidation stability of PAO (8 to 16-fold increase in RPVOT time). The difference in the effect of the additives on the oxidation stability of PAO versus corn oil was attributed to the difference in the reactive hydrogen contents in the two base fluids relative to those in the additives. An empirical equation, for correlating change in RPVOT time with change in bond dissociation energy of reactive protons before and after chemical modification, is proposed.