Abstract:The thermal oxidation and hydrolysis are the most important reasons for the degradationof the synthetic ester oil,and have a key impact on the useful life of the ester base oil.The continuous aging test on three kinds of synthetic ester base oils was performed in the calorstat oven.The kinematic viscosities and total acid numbers of the oil samples without and with water (copper as the catalyst),and with antioxidants were measured,and combined with their initial oxidation temperatures obtained by the differential scanning calorimetry (DSC),their thermal oxidative and hydrolytic stabilities were compared and judged,the effects of antioxidants on the aging process of the synthetic ester base oils were evaluated.The results show that the thermal oxidative stabilities of the synthetic ester base oils are related to their molecular structuresThe ester base oils containing the aromatics and the alcohol structure without β-H bond have better thermal stabilityPhenol and amine antioxidants have significant antioxidant effects,which can decrease effectively the thermal oxidation rate of the unsaturated polyol ester base oilIn addition,they also have a certain effect to inhibit the hydrolysis of unsaturated polyol ester base oil.