Boundary lubrication performance of fatty acid and its derivatives using energy dissipation method

This study evaluates the performance of various fatty acids including undecylenic, oleic, erucic, ricinoleic and 12-hydroxystearic acid, their estolides and estolide ethanolamides in the boundary lubrication regime. The influence of molecular structure variation in terms of functional groups, branching and molecular weight on the frictional behavior of these Organic Friction Modifiers (OFMs) at elevated temperatures (40°C, 70°C, and 100°C) has been studied. A custom-built Force-Controlled Pendulum Tribometer (FCPeT) was used to evaluate the friction of the OFMs at a concentration of 0.1% w/w in group III (32 cSt) base oil. The results demonstrated repeatable frictional response which varied significantly with temperature. At 40°C, the stability of adsorbed film was found to be eminent, leading to lower friction for molecules with higher packing efficiency. At 70°C, the molecular weight was found to be critical, owing to its inverse relation with desorption rate, leading to stronger adsorbed films. For a higher temperature of 100°C, the ability to chemisorb was found to be important to achieve lower friction. Erucic acid and its estolide and estolide ethanolamide derivatives were found to perform efficiently across the range of temperatures studied. The study concludes that the molecular structure significantly influences the efficiency of the OFMs, with the ability to chemisorb onto the metal surface, higher molecular weight and low branching being the desired features for optimal performance of OFMs.