Fatty acid based phosphite ionic liquids as multifunctional lubricant additives in mineral oil and refined vegetable oil

Ionic liquids (ILs) are highly attractive lubricant additives for their nonflammability, low vapor pressures, structural diversity and reasonable tribological properties. A convenient synthesis route to oil-dispersible ILs has been presented in this paper. Phosphite binds to aliphatic acid as anion and triethylbenzylammonium serve as a cation, which could be applied as lubricant additives in mineral oil (5CST) and refined vegetable oil (RSO). Results demonstrated that these ILs could effectively enhance the antiwear, friction-reducing and extreme pressure properties of 5CST and RSO. The chain length and unsaturation of fatty acid is significant in improving the tribological properties of base oil. TEY and FY mode K-edge XANES analysis of the formed tribofilms showed that the improvement of anti-wear and friction-reducing properties was closely related to the content of phosphate species on the near surface. •Fatty acid based phosphite ionic liquids were synthesized and applied as lubricant additives in RSO and 5CST.•The synthesized ILs have reasonable thermal stability, dispersion and tribological properties. The tribological properties of ILs is related to the carbon chain length, phosphorous content and polarity of IL molecular.•The content of FePO4/FeP2O7 is proportional to the improvement of tribological properties. Additionally, the thick adsorption film may lead to relatively large COF.