Study on the mechanisms of the lubricating oil antioxidants: Experimental and molecular simulation

Abstract The oxidation of lubricating oils seriously affects the operation of machinery, the O2 in the air has a strong impact during the oxidation process. Here, in ester-based lubricating oil, i.e. with the trimethylolpropane trioleate (TMPTO) as the main component, the mobility and activity of the hindered phenolic antioxidants, and the permeability of O2 were investigated by molecular simulation methods and then confirmed by experiments. The mobility of antioxidants is related to their compatibility and binding energy with lubricating oils. The antioxidant molecules with larger molecular weights and longer alkyl chain will show lower mobility and better physical resistance to the permeability of O2. Besides, the antioxidant molecules with longer phenolic hydroxyl para-alkyl chains possess higher activity to scavenge the free radicals. Therefore, according to the experimental analysis, the antioxidant molecules with larger molecular weights and longer phenolic hydroxyl para- alkyl chain do show better oxidative resistance, which is consistent with the simulation predictions. The present study hopes to supplement and explain the anti-aging mechanisms of lubricating oils and provide a new approach for designing of antioxidants.