Synthesis and Physicochemical Properties of New Estolide Esters as Potential Biolubricant Base Oil

Abstract

In this study, plant oil-derived oleic acid was modified chemically to generate estolide esters that displayed low pour points and good oxidation stability. Specifically, oleic acid was reacted with hydrogen peroxide (H 2 O 2 ) to yield estolide with hydroxyl groups, which were then end-capped with various organic acids of different chain lengths and structures, while the carboxylic acid group of estolide was esterified with 2-ethylhexanol (2EH). Analysis results revealed that products end-capped with lauric acid (C12) and 2-ethylhexanoic acid, respectively recorded the best pour point at -36°C, while other products made with shorter or longer chain length organic acids showed higher pour points. Additionally, product end-capped with longer chain length organic acid exhibited better anti-wear properties and lower kinematic viscosity than product made with shorter chain length organic acid. Furthermore, the oxidation stability of products end-capped with linear organic acid were higher than those end-capped with branched organic acids and the oxidation onset temperature (OOT) of products were between 193°C-200°C, which is an improvement in comparison with starting material. Physicochemical properties evaluation revealed that most of the prepared estolides esters have lubricant properties comparable to commercial product, which suggested that they are suitable to be used as base oil for lubricants.