Evaluation of molybdate ester as a synergist for arylamine antioxidant in lubricants

An oil-soluble additive molybdate ester (ME) was synthesized. The antioxidation properties of p,p′-dioctyldiphenylamine (DODPA)- and ME-containing poly-α-olefin (PO)-derived lubricants were evaluated by differential scanning calorimetry (DSC) to measure and hot oil oxidation (HOO) tests. DSC test measures incipient oxidation temperature (IOT) and oxidation induction time (OIT) of the lubricant at high temperatures and the oxidation stability of oil viscosity increase is measured by HOO test. DSC test shows that IOT and OIT of DODPA-containing PO were improved significantly by ME addition. HOO test indicates that when combining with DODPA antioxidants, ME can also effectively reduce the increase in viscosity of the mineral oil 150 SN. These results suggest that the ME shows a good oxidative synergism with DODPA antioxidant. In addition, the changes occurring to DODPA in 150 SN oxidation with and without ME were observed by GC/MS analysis. The proposed mechanism of the inhibition involves a synergy between ME and DODPA.