Synthesis of New Eco-friendly Biolubricants Based on Oleic Acid, Characterization and Evaluation

Mineral-based lubricants raise significant environmental concerns because of their limited biodegradability and the presence of toxic hydrocarbon fractions. Owing to its excellent lubricating characteristics, oleic acid serves as a promising renewable feedstock for developing sustainable bio-lubricants. In this work, new oleic acid-derived esters were synthesized to enhance physicochemical and tribological performance. A new series of four monoesters (S3-S6) was synthesized through the ring-opening of epoxidized oleic acid (S2) via reaction of epoxidized oleic acid with saturated fatty acids of different chain lengths (C12, C14, C16, and C18) as nucleophiles, The resulting monoesters were then esterified with straight and branched alcohols of varying chain lengths (C3, C4, C16, and C18) to produce a new series of sixteen diesters (S7–S22). The molecular structures were confirmed using Fourier Transform Infrared (FT-IR) and Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopies. The effects of molecular structure, including chain length, branching, and the number of ester groups in individual molecules, on physicochemical and lubricating properties were systematically investigated. The diesters were evaluated for their lubricating efficiency and key physicochemical properties. Diesters exhibited outstanding performance, achieving an acid value of 0.10 mg KOH/g, a pour point of −27.9 °C, and a viscosity index of 133, meeting or surpassing relevant ASTM limits. Their viscosities at 40 °C (23.8 cSt) and 100 °C (4.9 cSt) fall within the SAE 10W viscosity range. These findings confirm the superior performance and environmental compatibility of the synthesized diesters, highlighting their potential as sustainable, high-performance alternatives to conventional mineral lubricants.