Bio-additives Derived from Ricinoleic Acid and Choline with Improved Tribological Properties in Lithium Base Grease

In this study, bio-based ionic liquid prepared from ricinoleic acid and choline was firstly used as additive in lithium base grease. The characterization and tribological performance of the prepared ionic liquid ([cho][ricinoleic]) as additive in grease were studied compared with the traditional ionic liquid such as L-P104. All the concentrations showed promising friction-reducing and anti-wear properties, though a 3% concentration has superior lubricating properties than others. Furthermore, [cho][ricinoleic]) can greatly enhance the lubrication capability of lithium base greaseunder different frequency and load at room temperature. Although L-P104 showed good lubricating performance than [cho][ricinoleic] at 150°C, the chosen formulation (1.5% [cho][ricinoleic] + 1.5% L-P104) could have better synergism at high and room temperature, which could be a good supplement to ionic liquid as grease additive. Thin films formed according to the results of SEM and XPS were attributed to be the main account for the preferable tribological properties of [cho][ricinoleic] in lithium base grease.