Conclusion
Four novel ricinoleate anion-based ionic liquids were synthesized by metathesis of sodium ricinoleate with bromide salts and were evaluated as green lubricant additives in two base oils EKE and DOS. The synthesized additives exhibited excellent thermal stability and tribological performance. At optimal IL concentration the fatty acid constituted ILs greatly reduced the wear scar diameter and improved the weld point of both base oils. The results obtained from tribological tests confirmed that there is a significant effect of changing the cation on their tribological performance. The ionic liquids BHI-RA and TBA-RA exhibited better tribological performance compared to TPA-RA and CTB-RA under boundary lubrication conditions. Elemental mapping and worn surface morphology studies further confirmed the deposition of tribofilm by ricinoleate constituted ionic liquid. This study illustrates that fatty acid constituted ILs are excellent lubricating oil additives to minimize or replace the use of environmentally hazardous ILs.