Thermal and Spectroscopic Studies of the Thermal-Oxidation Stabilities of Lubricants

The influence of aromatic antioxidants 2,6-di-tert-butyl-4-methylphenol (BHT) and diphenylamine (DPA) on the thermal-oxidative degradation of base oils 150N was studied by using the hot oil oxidation test (HOOT) with temperatures varying from 100 to 200°C and times ranging from 1–24 h. Qualitative as well as quantitative analyses of the base oils and their fractions were done using gas chromatography–mass spectrometry (GC–MS) and spectroscopic (FTIR, UV–visible) techniques to gain a better understanding of their compositional and structural details. Oxidization processes were also studied and structural changes resulting from thermal oxidation were identified. The results indicate that the addition of antioxidants causes an obvious enhancement in the resistance of base oils to thermal-oxidative degradation. Moreover, the mixture of antioxidants shows better thermal-oxidative resistance than the phenolic or diphenylamine antioxidants alone.