Synthesis and physical properties of new estolide esters

Vegetable oil-based oils usually fail to meet the rigorous demands of industrial lubricants by not having acceptable low temperature properties, pour point (PP) and/or cloud point (CP). Oleic estolide was produced from oleic fatty acid and a catalytic amount of perchloric acid. The oleic estolide was then esterified with a series of 16 different alcohols that were either branched or linear-chained. The new estolide esters physical properties were recorded and evaluated as a potential industrial lubricant. The linear-chain esters had higher low temperature properties (PP = −9 to −33 °C) but still compete well with other commercial bio-based materials. The oleic estolide ethyl ester yielded the best PP at −33 °C for the linear-chain series. The branched alcohol produced the best PP (−24 to −39 °C) and CP (−30 to <−50 °C) with the best PP performers being a 2-hexyldecanol (Jarcol I-16) sample, a 16 carbon-chained branched material, and 2-octyldodecanol (Jarcol I-20), a 20 carbon branched material, with a PP at −39 °C. The best CP performers from the same series were the 2-octyldodecanol, with a CP lower than −50 °C followed by the 2-hexyldecanol at −42 °C. The viscosities (55–209 cSt @ 40 °C) and viscosity indexes (VIs) (169–192) performed well. The iso-stearyl alcohol (Oxocol 180) sample had the highest viscosity at 40 °C of 209.3 cSt which was higher than all other materials tested. Finally, these new estolide esters required no additives in order to obtain the improved performance in low temperature physical properties, thus limiting our impact on the environment and replacing fluids that are based on non renewable resources.

► The oleic estolide was esterified with a series of 16 different branched or straight-chained alcohols.
► The straight-chain esters had higher low temperature properties (pour point = −9 to −33 °C).
► The branched alcohol produced the best pour point (−24 to −39 °C) and cloud point (−30 to <−50 °C) with the best pour point performers being a 2-hexyldecanol.
► The iso-stearyl alcohol sample had the highest viscosity at 40 °C of 209.3 cSt which was higher than all other materials tested.