Preparation and Tribological Study of Novel Amide-Based Organic Friction Modifiers

Energy saving and emission reduction are the two most important driving forces to promote the advancement of internal combustion engine technology, and the requirements of energy saving and emission reduction promote the development of engine oil to the direction of low viscosity, low sulfate ash, low phosphorus and low sulfur (SAPS). Low viscosity engine oil can reduce friction during engine operation to a certain extent and play a role in energy saving, but with the reduction of viscosity, its anti-friction performance will also be affected to a certain extent. Low SAPS will also limit the use of some anti-wear additives containing sulfur, phosphorus and other elements, resulting in a decline in the tribological properties of engine oil. In order to solve this problem, the organic friction modifiers with low sulfur and phosphorus content and no ash content were studied in this paper. At present, the widely used organic friction modifiers were prone to desorption at high temperature, which led to their tribological properties becoming unstable at high temperature. Therefore, this paper studied the amide type organic friction modifiers adsorbed at multiple sites. Two novel amide type organic friction modifiers (DAO and DMO) were prepared by keto amine condensation reaction with oleo amine and diacetone acrylamide, N,N-dimethylacetylacetamide. The prepared organic friction modifiers had good solubility in PAO6. The tribological properties of DAO and DMO at different temperatures (25, 80 and 135 ℃) and the tribological properties of organic friction modifier combined with zinc dialkyldithiophosphate (ZDDP) were studied. The results showed that DAO and DMO had good anti-friction and anti-wear properties in PAO6 at different temperatures, and both of the two organic friction modifiers showed good synergistic anti-friction effects with ZDDP. At the same time, scanning electron microscopy was used to analyze the wear surface after friction. The analysis results showed that when the friction modifiers DAO, DMO and ZDDP were combined, they played a synergistic role in anti-wear, making the wear surface smoother and flat, and the wear marks formed on the surface sharer and narrower. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis showed that the synergistic effect between the two organic friction modifiers and ZDDP was mainly due to the interaction between the organic friction modifiers and ZDDP molecules. During the friction process, a frictional chemical reaction occurred, resulting in a dense frictional chemical reaction film containing wear-resistant compounds such as phosphates and sulfides. At the same time, the organic friction modifiers adsorbed on the surface of the ZDDP friction film. The boundary lubrication film and the adsorption film worked together to achieve the effect of reducing friction an anti-wear at high temperature. The amide type organic friction modifier prepared in this paper could expand the temperature range of the organic friction modifier in the actual working condition to a certain extent, and the combination with anti-wear additives had a better effect. Meanwhile, the analysis of its lubrication mechanism provided a theoretical basis for the action mechanism of the same type of organic friction modifier.