Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 2006
Publication Date: March 6, 2007
Citation: Cermak, S.C., Skender, A.L., Deppe, A.B., Isbell, T. 2007. Synthesis and physical properties of tallow-oleic estolide 2-ethylhexyl esters. Journal of the American Oil Chemists' Society. 84(5):449-456. Interpretive Summary: While you were standing at the gas pump paying for a premium price for foreign oil, have you ever wondered what you can do to decrease your need for this foreign oil? Your vehicle does not only require fuel but also oil for engine lubrication and almost everyone is using petroleum oil. We are willing to spend $30-40K for a vehicle that will last 8-10 years, but are not willing to spend a few dollars more for a biobased material as a lubricating oil so that we can extend our limited supply of petroleum oil for future generations. Thus, our lab is creating new biodegradable vegetable-based lubricants and fluids from tallow estolides, which are easier on our environment than petroleum products and have equal or better low temperature properties without the addition of additive packages. The U.S. produces about 10 million tons of tallow which contains a 50-50 mixture of saturated and unsaturated fatty acids. Estolides from tallow are the cheapest estolides that can be produced and compared them to commercially available materials. Estolides from tallow are therefore a renewable U.S.-based oil that will help ease the dependence on imported, petroleum-based oils while helping the U.S. farmer.
Technical Abstract: Tallow-oleic estolide 2-ethylhexyl esters were synthesized in a one pot process from tallow and oleic fatty acids, while varying the ratio of tallow and oleic fatty acids, with 0.05 equivalents of perchloric acid at 60°C with the esterification process incorporated into an in situ second step to provide a functional fluid at a very reasonable cost. Estolide number (EN), the average number of fatty acid units added to a base fatty acid, varied with reaction conditions but averaged about 1.25. Viscosity for a 100% tallow estolide 2-EH ester was 57.8 cSt @ 40°C and 10.8 cSt @ 100°C, while the other tallow estolide 2-EH esters ranged from 67-80 cSt @ 40°C and 12-14 cSt @ 100°C. The viscosity index ranged from 169 to 185 cSt for the tallow-oleic estolide 2-EH esters. The 100% tallow estolide 2-EH ester had modest low temperature properties (pp = -15°C and cp = -14°C), while the 50:50 mixture of oleic and tallow fatty acids produced an estolide that had better low temperature properties (pp = -21°C and cp = -21°C) without a large negative effect on the oxidative stability. The oxidative stability increased as the amount of saturation increased (RBOT times 165-274 min). The tallow-oleic estolide 2-EH esters have shown remarkably low evaporative losses of only 1% loss versus 15-17% loss for commercial materials. These tallow-oleic estolide 2-EH esters had acceptable low temperature properties, oxidative stability, evaporative losses, and low cost that should provide a specialty niche for this potential lubricant.