Biolubricants Based on Epoxidized Vegetable Oils: A Review on Chemical Modifications, Tribological Properties, and Sustainability

The growing demand for sustainable and high-performance lubricants has accelerated interest in biolubricants derived from renewable feedstocks. Vegetable oils are attractive candidates due to their biodegradability, low toxicity, and favorable viscosity index. However, their application is limited by poor oxidative and thermal stability. The epoxidation of unsaturated fatty acids offers a versatile route to address these drawbacks by enhancing stability and introducing reactive epoxy groups for further functionalization. This review highlights the advances in the use of epoxidized vegetable oils (EVOs), as platforms for lubricant design. Post-epoxidation modifications, such as ring-opening reactions, crosslinking, hybridization with additives, and click-type chemistries, are critically examined with emphasis on their impact on viscosity, polarity, tribofilm formation, and overall tribological behaviour. Structure–property relationships were discussed to establish design principles linking chemical modifications with lubrication regimes, wear resistance, and film-forming ability. In addition, sustainability aspects, including biodegradability, ecotoxicity, and life cycle assessment, are reviewed to evaluate the trade-offs between performance enhancement and environmental compatibility of these modifications. Current challenges and future perspectives are outlined, including the need for standardized testing protocols, the integration of multifunctional modifications, and predictive modelling tools. By bridging molecular engineering, tribological performance, and sustainability, this review provides a roadmap for the rational design of advanced epoxidized oil-based biolubricants.