Synthesis, Characterization, Tribological and Rheological Properties of Di (2-Butyloctyl) Dicarboxylate Esters for Environmentally Friendly Biolubricant Applications

Abstract

The passion for replacing petroleum-based lubricants with renewable and sustainable alternatives has encouraged the development of plant-based biolubricants. In this work, a synthesis of di (2-butyloctyl) dicarboxylate esters for biolubricant base oil was carried out through esterification between selected dicarboxylic acids (succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, and dodecanedioic) with branched alcohol (2-butyl-1-octanol) catalyzed by sulphuric acid. The synthesized dicarboxylate esters showed high yield percentages in the range of 88 – 98 %. The chemical structures were confirmed using FTIR and NMR (1H and 13C) spectroscopies. The lubrication results show that the synthesized dicarboxylate esters have very good low-temperature properties with pour points less than −70°C. Furthermore, the esters' flash point, oxidative stability, and viscosity indices increased with their molecular weight. Tribological results have indicated that the tested dicarboxylate esters have good lubrication properties with a low friction coefficient (µ) range of 0.18-0.34 at 40 and 100°C. Rheological analysis showed that the di (2-butyloctyl) dicarboxylate esters were non-Newtonian. The synthesized products were categorized as ISO VG 32 and compatible with some selected commercial lubricants. These make them plausible to be used hydraulic fluids for various industrial applications such as gear, hydraulic, and transmission fluids in heavy machinery usage.