Tribological behavior of biolubricant base stocks and additives

Biolubricants are gaining popularity and acceptance globally due to their sustainable and environmentally friendly properties; being derived from feedstocks from vegetable oils. Indeed, the potential for biolubricants to eventually replace conventional lubricants is currently viewed in the literature as a real possibility. This study will provide valuable information pertaining to the formulation of biolubricants, by assessing and evidencing the tribological performances of various types of biolubricant base stocks and their related additives. This study begins with a presentation of the basic tribological parameters in lubrication. Following that, the criteria for the molecular structure of biolubricant base stocks for high tribological performance are discussed, based both on the tabulation of the friction coefficient and on the measurement of wear scar from experimental studies. The biolubricant base stocks under review in this study include vegetable oils (VO), epoxidized VO, ring-opened products from epoxidized VO, estolides, and polyol esters. This review also discusses recent advances in eco-friendly tribological additives such as plant-derived compounds and polymers, particulate and layered materials, and ionic liquids. The performance and various applications of these additives are also reviewed.