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Lipoate ester multifunctional lubricant additives

Girma Biresaw, David Compton, Kervin Evans, Grigor B. Bantchev
Industrial & engineering chemistry research 2016 v.55 no.1 pp. 373-383
additives, alcohols, antioxidants, biolubricants, byproducts, catalysts, engineering, esterification, esters, lipoic acid, nuclear magnetic resonance spectroscopy, oxidation, oxidative stability, solubility, solvents, sunflower oil, temperature, viscosity
Seven lipoate esters were synthesized by esterification of lipoic acid with different structures of alcohols in the presence of a solid acid catalyst and without solvent. The esters were obtained in good yield, characterized using 1H NMR and GPC; and their physical properties investigated. Four of the seven lipoate esters, with good solubility in high oleic sunflower oil (HOSuO) and polyalphaolefin (PAO6) base oils, were further investigated for their lubricant additive property. Additive properties were investigated in HOSuO base oil by varying the additive concentrations in the range 0–20 (w/w %). Properties investigated include: density; kinematic and dynamic viscosity; viscosity index (VI); oxidation stability from onset and peak oxidation temperatures on a PDSC; 4-ball anti-wear (AW); and 4-ball extreme pressure (EP). Neat lipoate esters displayed high oxidation stability and high VI. As additives to HOSuO base oil, lipoate esters displayed good viscosity index improver (VII), good antioxidant (AO), good EP, but poor AW properties. The VI and VII properties were attributed to the preence of low concentrations of polymeric byproducts in the ester product mixtures. This work demonstrates that lipoate esters can be developed into effective mulfi-functional biobased lubricant additives with excellent VII, AO, and EP properties.