Exploration on thermal behavior of synthetic ester with antioxidant based on thermodynamic analysis and molecular...

Synthetic ester is a high-quality lubricating base oil, and its antioxidant stability and high-temperature service life are greatly affected by antioxidants. For a considerable period, a significant number of researchers have utilized a variety of conventional methodologies, including the rotating oxygen bomb test, for the selection and evaluation of antioxidants. However, there is little systematic research on the thermal stability and antioxidant performance of these antioxidants through a combination of experiments and calculations. In this study, a range of investigative approaches, including experimental, calculation, and molecular simulation methods, were employed to assess the impact of synthetic esters (PE5) with antioxidants (1010, L57, and hybrid). Compared with PE5 base oil, the thermodynamic analysis showed the value of activation energy for PE5 samples was probably PE5 + 2% L57 ≥ PE5 + 1% 1010 + 1% L57 > PE5 + 2% 1010 ≥ PE5. These results were in consistent with the acid number changes and viscosity changes for PE5 samples. The IOT results obtained from PDSC also proved the validity of this trend. Especially, PE5 containing 1% 1010 and 1% L57 showed good antioxidant properties, indicating that the hybrid antioxidants have excellent high-temperature antioxidant performance. The molecule simulation results show L57 can effectively and quickly reach the protected point without rapid volatilization and loss, thereby achieving excellent antioxidant performance. In addition, the movement rate of the hybrid antioxidant system (1wt% 1010 + 1wt% L57) can also achieve similar results compared with L57.

The thermal stability of antioxidants was investigated by TG/DTG analysis, and the corresponding decomposition kinetic parameters were evaluated by Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. The optimization of the geometry of related molecules was performed via Gaussian 16 package at B3LYP/def2-SVP level. The single point energy was then calculated at B3LYP/def2-TZVP level. The ACPEPY script was employed to obtain the GAF force field topology file of them. Molecular dynamics simulations were performed using the GROMACS software package.