Ravendra Kumar Pal, Amit Suhane
Abstract The increasing global demand for sustainable and high-performance lubricants has accelerated the transition from petroleum-based products to biodegradable alternatives. Among these, bio-lubricants derived from vegetable oils have gained attention due to their low toxicity, inherent lubricity, and renewability. However, limitations such as low oxidative stability, poor cold-flow behavior, and susceptibility to degradation hinder their practical application. This review critically examines both edible and nonedible vegetable oils as potential base stocks, with a focus on their tribological and physicochemical characteristics. Various chemical modification techniques—including epoxidation, transesterification, hydrogenation, and estolide formation—are evaluated for their ability to improve low-temperature fluidity, viscosity, and thermal-oxidative stability. Furthermore, recent advancements in nano-enhanced lubrication are explored, with emphasis on waste-derived nanoparticles (WDNPs) synthesized from agro-industrial residues such as waste rubber (carbon soot), eggshell (CaO), rice husk (SiO2), and grape pomace [zinc oxide (ZnO)]. These eco-friendly nano-additives not only demonstrate tribological performance comparable to conventional mineral-based additives but also contribute to circular economy goals. By integrating nanotechnology, green synthesis methods, and sustainable feedstocks, this review outlines a promising pathway toward the development of environmentally friendly, high-performance lubricants. Future research should focus on enhancing nanoparticle dispersion stability, synthesis scalability, and long-term tribological validation under real-world conditions to support industrial adoption.