Synergistic Effect of Antioxidants and Anti-Wear Additives for Vegetable Oils

摘要

Vegetable oils are recognized as ecologically acceptable lubricating fluids. Therefore they are expected to be applied to machines where exposure of lubricating oil is a problem. Zinc dialkyldithiophosphates (ZDTP) improve antiwear properties of vegetable oils. The additive performance depends on quality of the base oil. Careful analyses of base oils revealed that peroxide affects the additive response, whereas peroxides themselves do not promote wear. Our attention was also paid to improve antiwear effect of additives by combination of antioxidants. Oxidation test of vegetable oil was performed by tracing peroxide value (POV) to understand the mechanism. We found that POV increases rapidly at the beginning of reaction. It reaches the maximum value of approximately 1500 ppm within 50 hours. Then it decreases to reach an equilibrium value of 400-500 ppm within 200 hours. Antioxidants were examined to prevent the peroxide generation. Phenolic antioxidants and Zinc dibutyldithiocarbamate (ZDTC) exhibit good results in preventing peroxide generation, whereas aromatic amines and vitamin E gave poor results. The synergistic effect of antioxidants with antiwear additives can be confirmed by formulating better lubricants based on vegetable oils.