Methyl Oleate-Alkylated Tetralin with Dual-Functional Groups as Base Oil with PAO to Improve the Performance of Lithium-Based Grease

A novel dual-functional group base oil was synthesized by alkylation of methyl oleate from biomass and tetralin from coal chemical industry. Interestingly, the monoalkylated product (MOAT) exhibited low pour point, high flash point, and viscosity index compared with the traditional alkyl aromatic lubricating oil (AN5), owing to the combination of the naphthenic aromatic (tetralin) and the methyl oleate framework. MOAT as co-base oil with PAO8 was studied to prepare lithium-based greases for the first time, and their rheological and tribological properties were evaluated in detail. The microstructure of the MOAT-based grease displayed high entanglement of lithium fiber. The 20% MOAT-based grease markedly reduced friction and wear compared with PAO8-based grease and 20% AN5-based grease. The excellent tribological performances were attributed to the strong interaction between the ester group and the soap fiber that provides more relative elasticity of grease and improves tribological behavior. Our finding clearly demonstrated that MOAT had the potential as a new class of base oil for obtaining high-performance lithium grease.