Thermoanalytical and rheological characterization of automotive mineral lubricants after thermal degradation

This work aims to characterize thermal degradation process of automotive mineral lubricants, in relation to its rheological and thermoanalytical properties. Lubricants were degraded at temperatures varying from 150 to 210 °C, and times of 1–48 h. After degradation, oils were characterized by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), rheologic measurements and thermal analysis (TG/DSC). IR and NMR spectra indicated oxidation reaction products. TG curves indicated a decrease in the temperature of decomposition start after degradation. DSC curves indicated a decrease in the peak related to hydrocarbon combustion after degradation. In general, the increase in degradation temperature led to an increase of the lubricants viscosity, besides thixotropy appearance for some samples.