Optimization of Graphene Additive Concentration in Used Cooking Oil-Based Lubricating Grease to Minimize Friction Coefficient

Abstract

Abstract:
Waste cooking oil (WCO) is a household waste that has the potential to cause environmental pollution; however, it can be utilized as a renewable base material for eco-friendly lubricating grease. One approach to improving the performance of WCO-based grease is the addition of graphene as an additive due to its excellent tribological properties. This study aims to investigate the effect of graphene concentration on the coefficient of friction (COF) of waste cooking oil-based grease and to determine the optimum graphene concentration to achieve the best lubrication performance. Grease samples were synthesized using waste cooking oil as the base oil, fumed silica as a thickener, and graphene additives at concentrations of 0%, 1%, 2%, and 3%. Tribological performance was evaluated using the Pin-on-Disk method in accordance with the ASTM G99 standard to measure the coefficient of friction. The results showed that the addition of graphene significantly reduced the coefficient of friction compared to the grease without graphene. The average COF values were 0.0738, 0.0347, 0.0443, and 0.0400 for graphene concentrations of 0%, 1%, 2%, and 3%, respectively. Optimal performance was achieved at a graphene concentration of 1%, yielding a 52.98% reduction in the coefficient of friction compared to the plain grease. Increasing the graphene concentration above 1% provided no further improvement, which was likely due to particle agglomeration. These findings demonstrate that a 1% graphene addition is the optimal concentration to enhance the tribological performance of waste cooking oil-based lubricating grease.
Keywords: coefficient of friction, graphene, lubricating grease, tribology, waste cooking oil.