Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 12, 2005
Publication Date: February 28, 2006
Citation: Cermak, S.C., Brandon, K.B., Isbell, T.A. 2006. Synthesis and physical properties of estolides from lesquerella and castor fatty acid esters. Industrial Crops and Products. 23:54-64. Interpretive Summary: While you are shopping for oil in your local department store have you ever wondered how good that oil really is? You have a 40K dollar truck in the lot and you are spending about 6 dollars for an oil change. If you had the opportunity to purchase a biobased material with better properties at only a slight price increase; would you put that superior product in your new truck? We feel most consumers would make that slight investment to protect their larger investments. Thus, our lab is creating these new biodegradable vegetable-based lubricants and fluids from lesquerella estolides, which are easier on our environment than petroleum products and have much favorable low temperature properties without the addition of additive packages. Lesquerella is a developing new rotation crop for the desert Southwestern United States that produces a seed containing 30% oil rich in hydroxy fatty acids. We have compared these lesquerella estolides to other estolides made from castor oil as well as commercially available materials. The lesquerella and castor estolides had very similar properties for most all cases studied, indicating that lesquerella will be suitable in many applications where castor oil is currently used which will result increased production for lesquerella. Estolides from lesquerella are therefore a renewable U.S.-based crop oil that will help ease the dependence on imported, petroleum-based oils while helping the U.S. farmer.
Technical Abstract: Biodegradable, vegetable oil-based lubricants must have better low temperature properties as well as comparable cost to petroleum oil before they can become widely acceptable in the marketplace. The low temperature property usually measured is the pour point (pp), the minimum temperature at which the material will still pour. Viscosity and viscosity index also provide information about a fluid's properties where a high viscosity index denotes that a fluid has little viscosity change over a wide temperature range. Lesquerella oil is a good candidate for its development into a biodegradable lubricant. Lesquerella is being developed as an alternative crop for the southwestern region of the U.S. The hydroxy site on the fatty acid (FA), from the oil, makes a suitable site for esterification to yield estolides. Castor and lesquerella FA esters were combined with different types of saturated, unsaturated, and branched FAs to produce estolides. Castor and lesquerella estolide esters had the best cold temperature properties when capped with oleic (pp = -54 deg C for castor and pp = -48 deg C for lesquerella) or capped with a branched material, 2-ethylhexanoic acid (pp = -51 deg C for castor and pp = -54 deg C for lesquerella). As saturation was increased in the estolide pour and cloud points also increased. The increased saturation such as in stearic capped estolides allowed for sufficient alkyl stacking of these long saturated chains producing higher pour points. Oxidative stability of the estolides was compared for the oleic-castor 2-ethylhexyl estolide ester and the saturated oleic-castor 2-ethylhexyl estolide ester by RBOT. The RBOT times for both estolides were low with a similar time of about 15 min. However, when anti-oxidant (3.5 wt%) was added the RBOT times increased to 403 min for the saturated based castor while still retaining outstanding cold temperature properties, (pp = -36 deg C and cp = -<36 deg C). The viscosity index ranged from 164 to 200 for these new hydroxy FA derived 2-ethylhexyl estolide esters. These oleic-castor and lesquerella estolide esters have displayed far superior low temperature properties (pp = -54 deg C) than any other estolides reported to date. Due to the lack of need for solvent and any catalysts these estolides should be of reasonable cost, and were more suitable as a base stock for biodegradable lubricants and functional fluids than current commercial materials.