Recent advancements in synthesis, rheological characterization, and tribological performance of vegetable oil-based lubricants enhanced with nanoparticles for sustainable lubrication

Energy and material conservation is an important global issue. In conventional practice, lubricants were selected based on cost, performance, and life, and concern was not given to the impact of lubricants on humans, animals, plants, and the environment. Vegetable oil-based lubricants are gaining more significance in the industrial lubrication market because of their biodegradability, renewability, minimal environmental impact, excellent tribological performance, and stringent environmental regulations. This review paper highlights the most recent advancement in the synthesis, rheological characterization, and tribological performance of biolubricants under different lubrication conditions. Biolubricants are produced from edible and non-edible vegetable oils with limitations such as low thermo-oxidation stability, low hydrolytic stability, and poor low-temperature properties. It can be overcome by modifying vegetable oils chemically and by blending additives in a base oil. The review provides various aspects of biolubricants, such as the chemical composition of various vegetable oils, chemical modification methods used to synthesize biolubricant, physicochemical and rheological properties of biolubricant, tribological performance of biolubricant under various conditions, and various nanoparticles used to enhance the performance of biolubricant. Numerous studies reported that the blending of additives containing nanoparticles enhances the tribological performance of biolubricant and the results obtained from the various researchers have been observed and analyzed in the review. Nanoparticles have gained importance in engineering lubricants because of their shape, size, and other lubrication properties. The properties of biolubricant enhanced with nanoparticles, the dispersion stability of nanoparticles in various biolubricants, the effect of shape, concentration, and morphology of nanoparticles on tribological properties, nanolubrication mechanism, and surface topology and morphology analysis of rubbing surface are emphasized in the review. The research suggests that vegetable oil has a significant prospective to be used as sustainable lubricating oil with nanoparticle additives. The issues limiting the use of biolubricant have also been highlighted with feasible solutions. Additionally, this comprehensive review is highly significant, as it provides new direction and valuable insights to researchers and practitioners towards sustainable lubricants.