Boundary lubrication performance of free fatty acids in sunflower oil

Free fatty acids are released over time in vegetable oils, primarily through the hydrolysis of the triglyceride base. In mineral oils, fatty acids are considered to be one of the classical boundary lubrication additives, but they may not have the same impact in vegetable oils, due to the vast difference in chemistry between the base oils. The purpose of this study was to evaluate the influence of free fatty acids on the boundary lubrication performance of sunflower oil, with particular focus on the impact of unsaturation within the fatty acid and assessing the effect of elevated temperatures. The results obtained suggest stearic acid can effectively reduce both the wear and friction of sunflower oil formulations under boundary lubrication conditions, although performance is limited when bulk oil temperatures approach 150degreesC.