The increase in the price of crude oil, the environmental impact, or the depletion of fossil resources has increased the need for bio-based alternatives. This has led to the search for renewable, biodegradable, and environmentally friendly raw materials to obtain lubricants that meet these characteristics. This review deals with the state of the art of biolubricants along with their most common raw materials and molecular structures, processes of chemical modification of bio-oils, as well as the relationship between their structural features and physicochemical/tribological properties. This review concludes that the production of fatty acid alkyl esters from vegetable oils is the most promising chemical route to produce a wide range of biolubricants through double transesterification reactions. It also highlights the need to explore this route for the production of microalgae-derived biolubricants due to its environmental benefits during cultivation and production processes.

Placing an electric motor (EM) inside the transmission housing of a hybrid electric vehicle (HEV) implies that the automatic transmission fluid (ATF) needs to accomplish additional requirements. Among these requirements, electrical compatibility is of critical significance. This study investigated the influences of the additive concentrations of three commercial ATFs on their electrical compatibilities and tribological performances. Two variations of each ATF with different concentrations of the original additive packages were prepared. The viscosity, electrical conductivity, permittivity, resistivity, dielectric dissipation factor, breakdown voltage, and tribological performance of the nine resulting ATFs were measured. All the ATFs were found to be electrically compatible and showed dissipative performance and sufficiently high breakdown voltage, even at increasing additive concentrations. The tribological performances of the ATFs formulated with the API (American Petroleum Institute) Group III base oils had improved wear reduction at the highest additive concentrations; the better wear performance was related to the formation of iron phosphates and polyphosphates on the worn surface.