Iso-oleic estolide products with superior cold flow properties

Authors: BIRESAW, GIRMA - Former ARS Employee; CHEN, YUNZHI - South China University Of Technology; CHEN, LI - South China University Of Technology; Ngo, Helen; Wagner, Karen; Vermillion, Karl; Cermak, Steven - Steve

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2022
Publication Date: 4/7/2022
Citation: Biresaw, G., Chen, Y., Chen, L., Ngo, H., Wagner, K., Vermillion, K., Cermak, S.C. 2022. Iso-oleic estolide products with superior cold flow properties. Industrial Crops and Products. 182. Article 114857. https://doi.org/10.1016/j.indcrop.2022.114857.
DOI: https://doi.org/10.1016/j.indcrop.2022.114857

Interpretive Summary: Biolubricants synthesized from vegetable oils usually fail to meet the rigorous demands of industrial lubricants by not having acceptable low temperature properties. Through the use of a material from various sources of vegetable oil, estolides are made. Estolides are unique in that they can be custom-designed to perform under different conditions rather than trying to formulate an unacceptable material into a more acceptable one which is a common practice in the petroleum industry. A series of new compounds, hyper-branched 2-ethylhexyl estolide esters, were developed to help maximize low temperature and viscosity properties of the oil. Having a green biobased industrial fluid that has good cold weather properties would be highly desirable. These new estolide esters required no additives in order to obtain improved low temperature performance, thus limiting our impact on the environment (climate change) and helping reduce our dependence on petroleum sources.

Technical Abstract: One of the drawbacks of using vegetable oils directly as a lubricant is poor low temperature performance, mainly pour and cloud points. Oleic estolides were developed to improve these properties as well as increase the oxidative stability of the oil. However, additional low temperature properties are desirable to increase the field of use of these materials. A new series of iso-oleic estolide free acids and 2-ethylhexyl (2-EH) esters capped with various fatty acids had superior physical properties and cold flow properties, compared to traditional oleic based estolides. The average pour point of the iso-oleic estolide 2-EH esters was -41°C, compared to -23°C of iso-oleic estolide free acids. The iso-oleic-octanoic and iso-oleic-decanoic estolide 2-EH esters had excellent pour points of -60°C. The cold flow properties of iso-oleic estolides decrease with increasing the carbon number of the saturated capping fatty acid, while the viscosity index and oxidation stability were only slightly improved. Therefore, saturated mid-chain fatty acids are more suitable as the capping fatty acid for iso-oleic acid based estolides. Iso-oleic-coconut estolide 2-EH esters exhibited good physical properties, with pour points as low as -45°deg. C. The iso-oleic estolide free acids and 2-EH esters are a new kind of low-cost materials for bio-lubricants with excellent cold flow properties.