The Chemical Degradation of Ester Lubricants

Effect of Temperature on the Chemical Composition and Physicochemical Properties of Diester Aviation Lubrication Oil

High temperature is the main factor responsible for degrading the lubrication and antiwear properties of aero-lubricating oils. Accordingly, this study assessed the effects of thermal treatment of diester aviation lubricating oil and the associated mechanism. Fourier-transform infrared spectroscopy and gas chromatography/mass spectrometry analyses showed that low-molecular-weight compounds, such as monoesters, diesters, alcohols, and olefins, were the primary degradation products. An assessment of the degradation mechanism of bis(2-ethylhexyl)decanedioate showed that pyrolysis, resulting in the cleavage of β-C–H and C–C bonds, was the main process involved. Additional investigation using advanced polymer chromatography showed that the molecular weights of oil samples changed slightly at high temperatures, while the viscosity and viscosity-temperature index values were relatively stable. High-pressure differential scanning calorimetry established that the thermal oxidation stability of these oils decreased above 250°C. Finally, variations in the chemical compositions of the oil samples were found to be highly correlated with changes in physicochemical properties during thermal processing, with the formation of low-molecular-weight polar compounds greatly increasing the acid numbers of the oils.

Synthesis, Characterization, and Performance Evaluation of Sulfur-Containing Diphenylamines Based on Intramolecular Synergism

To obtain novel structural antioxidants that have different antioxidant mechanisms, four 2-(alkylthio)-N-(4-(phenylamino)phenyl)acetamides 2a-d as dual functional antioxidants are designed, synthesized, and confirmed by ¹H-NMR, FTIR, MS, and elemental analysis. The antioxidant behavior of compounds 2a-d as additives of base oil triisodecyl trimellitate (TIDTM) is evaluated by non-isothermal and isothermal DSC analyses. The results showed all compounds can greatly increase the incipient oxidation temperature (IOT) and oxidation induction time (OIT) of TIDTM, especially, compound 2c exhibited an OIT value of 72.5 min at 230 °C, which is almost 28 times the length of TIDTM. Moreover, compounds 2a-d do not affect the tribological performance of TIDTM. The mechanism of antioxidants involved an intramolecular synergism are proposed. This work demonstrates compound 2c can be used as a novel potential antioxidant additive of TIDTM; in addition, it would inspire the emergence of highly potent antioxidants with different antioxidant mechanisms.