Location: Bio-oils Research Unit
Title: Tribological properties of vegetable oils modified by reaction with Butanethiol Authors
Submitted to: Tribology Letter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2011
Publication Date: June 5, 2011
Citation: Biresaw, G., Bantchev, G.B., Cermak, S.C. 2011. Tribological properties of vegetable oils modified by reaction with Butanethiol. Tribology Letters. 43(1):17-32. Interpretive Summary: Starches, proteins, oils and fats from farm products have the potential to be used as raw materials for a number of products currently manufactured from petroleum, including lubricants. Successful development of consumer and industrial products from these raw materials will reduce the huge crop surplus, improve the income of farmers and grow the rural economy. It will also lead to sustainable economic growth by shifting the manufacturing raw material base from dwindling petroleum to renewable and abundant farm-based components. However, development of lubricants and other products from farm-based raw materials requires overcoming a number of serious and inherent weaknesses of biobased raw materials such as inadequate oxidation stability and unacceptably high pour point and cloud point. Several approaches are being explored to counter these inherent weaknesses of farm-based raw materials, including modification of their chemical structures by chemical, thermal, genetic, and/or enzymatic methods. In the work described here, corn, canola, and castor-lauric estolide oils were chemically modified and their properties investigated. The chemical modifications resulted in improved oxidation stability and cold flow properties. The investigation also showed that the chemically modified materials, when used as additives, improved the oxidation stability and cold flow properties of synthetic oils. This finding shows that chemical modification can be used to upgrade the properties of vegetable oils, so that they can be used to formulate bio-based lubricants that effectively compete against petroleum-based products currently dominating the market.
Technical Abstract: Corn, canola and castor-lauric estolide oils were chemically modified by 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 (OS), rotating pressure vessel oxidation test (RPVOT), 4-ball anti wear (AW), and extreme pressure (EP) were investigated. Sulfurization resulted in increased viscosity, increased RPVOT time (more than one order of magnitude), and reduced PP (9-18ºC). Sulfurization reduced VI but caused no change in CP. The sulfur modified oils, along with commercial mono- and polysulfide additives were also investigated as additives in corn and poly-alpha-olefin (PAO) based fluids. In these investigations, the sulfur content of all the blends was kept constant at 0.6 % (w/w). In corn oil, these additives resulted in: no change in RPVOT or PP; slight improvement (2–6ºC) in CP; slight increase in AW coefficient of friction (COF) and wear scar diameter (WSD); and no change in EP weld point (WP) (except for the commercial polysulfide EP additive which displayed a large WP increase). The results in PAO based fluid were: no change in PP, CP, AW (COF or WSD), EP WP (except for the commercial polysulfide EP additive),but a big improvement in OS (8 to 16-fold increase in RPVOT time). The difference in the effect of the additives on the OS of PAO vs. corn oil was attributed to the difference in the reactive hydrogen contents in the two based fluids relative to those in the additives. An empirical equation was developed for predicting change in RPVOT time from the change in bond dissociation energy of reactive protons before and after chemical modification. The equation was capable of predicting the relative change in RPVOT time of corn vs. canola oils as a result of chemical modification.