Friction and Wear Performance of Soybean-Based Oils + Protic Ionic Liquid and Graphene Biolubricants

A novel class of high-performance soybean-based biolubricants has been developed through the incorporation of a protic ionic liquid, graphene nanoplatelets, or both, resulting in improved lubrication and wear reduction performance. These biolubricants were studied in a severe metal-ceramic tribopair under pin-on-disk configuration using low-volume lubrication. The best tribological performance was obtained for epoxidized soybean oil containing 1 wt% ionic liquid, which reduced the friction coefficient by up to 72%. Wear rate decreased by as much as 91% with the addition of 0.1 wt% graphene to the ionic liquid modified oil. All the biolubricants presented Newtonian behavior; the addition of graphene and protic ionic liquid to neat epoxidized oil markedly increased its viscosity, indicating strong interactions and improving load-carrying capacity. Furthermore, the thermo-oxidative resistance of these vegetable biolubricants increased significantly when the epoxidized oils were evaluated, showing that chemical modification strongly influenced degradation pathways under the applied testing conditions. The presence of ionic liquid and epoxidized-oil tribofilms within the wear tracks was confirmed by X-ray photoelectron spectroscopy. This study demonstrates the potential of a synergistic protic ionic liquid–graphene system as an antiwear additive for biolubricant formulations.