Viscometric Properties of Polyethylene Glycol di‐Esters of Estolides

Abstract

AbstractPolyethylene glycol (PEG) diesters from estolides of oleic acid, ricinoleic acid, and 12‐hydroxy stearic acid were used up to 5 wt% additive in petroleum‐derived base oils: 100 N, 220 N, 600 N, PAO 2cSt, PAO 4cst, and PAO 8cSt. The viscosity indices of the petroleum base oils were the lowest (VI = 104–108); the polyalpholefin (PAO) synthetic petroleum‐derived base oils were better (VI = 124–136) and the vegetable‐derived oils were the best (VI = 111–205). 12‐Hydroxystearic estolide PEG 400 diester gave the largest increase in viscosity index in 5% w/w admixtures with PAO 2cSt, 4cSt, 220 N, and 600 N base oils with a 12.3–16.3% increase in viscosity index. Single fatty chain esters had the least impact on viscosity index. As the molecule bulk increased, the viscosity index also increased. This viscosity index effect was demonstrated for the series of monomer to oleic estolide to oleic estolide PEG‐200 diester, which gave viscosity indices of 110, 111–122, respectively, in 5% admixtures with 100 N base oil. The larger the size of the molecule coupled with the polar PEG moiety gave the largest impact on viscosity index improvement where a 5 wt% admixture of 12‐hydroxystearate estolide PEG‐200 diester gave a 25.8% increase in 100 °C viscosity in PAO 2cSt. Incorporation of a dihydroxyl moiety into the molecule at a central side chain location in laurate‐capped ricinoleate estolide PEG‐200 diester did not increase viscosity index of the base oil but greatly reduced its solubility to less than 0.5 wt%.