Deep Eutectic Solvents as Green and Novel Lubricant Additives for Castor Oil with High Tribological Performance

This research reveals the anti-friction and anti-wear performance of lubricants using a castor oil base and a deep eutectic solvent (DES1) as an additive. To this end, DES1 was synthesized in a successful manner using DL-menthol and dodecanoic acid as components. Mass concentrations from 0.1 wt% up to 5 wt% of DES1 additives were chosen to formulate the lubricants. Friction experiments were conducted, yielding friction enhancements up to 4% compared to the castor oil base. Notably the greatest reduction was achieved for the lubricant with 0.1 wt% of DES1. In terms of the wear generated, the best anti-wear performance was achieved for the 0.5 wt% DES1 lubricant (with a wear reduction of 17%). Furthermore, by means of the profilometry of worn surfaces, it can be observed that the tribofilm formation of DES1 on steel surfaces is a potential lubrication mechanism.