Abstract
Abstract The ester base oil of dioctyl adipate (DOA) was oxidized in an oven at 200 °C for 30 h, and variations in the physicochemical and tribological properties were studied. To investigate the thermal-oxidation mechanism, the thermal-oxidation products were analyzed by gas chromatography–mass spectrometry (GC−MS), and the thermal-oxidation process was simulated using visual reactive force field molecular dynamics (ReaxFF MD). The results indicated that the total acid number (TAN) increased significantly because of the presence of 14% carboxylic acids and low molecular weight monoesters. The tribological properties were improved by the formation of the strongly polar carboxylic acids. Additionally, the increase in kinematic viscosity was limited due to the formation of high molecular weight polymerization products and low molecular weight degradation products. Thermal-oxidative degradation and polymerization mechanisms were proposed by combining ReaxFF MD simulations and GC−MS results.
Highlights
Dioctyl adipate (DOA), a synthetic ester oil, is prepared by the esterification of adipic acid and 2-ethyl hexanol [1]
Based on the relative contents, it can be seen that the thermal-oxidative degradation products mainly consist of low molecular weight carboxylic acids, monoesters, and diesters, whereas the polymerization products mainly consist of carboxylic acids and diesters
The thermal-oxidation products of DOA were analyzed by gas chromatography–mass spectrometry (GC−MS), and the total acid number (TAN), kinematic viscosity, and tribological properties of oxidized DOA were measured
Summary
Dioctyl adipate (DOA), a synthetic ester oil, is prepared by the esterification of adipic acid and 2-ethyl hexanol [1] It has been widely used in the aerospace and automotive industries, as well as under extreme working conditions, due to its high thermal-oxidation stability, low production of carbon residue, excellent viscosity index, good thermal conductivity, and large specific heat capacity [2−4]. CL can be used to evaluate the degrees of thermal-oxidation of ester oils at the macro level, but it cannot elucidate the chemical components and molecular structure information of the thermal-oxidation products. Similar to PDSC and CL, infrared spectroscopy cannot completely identify the chemical components and molecular structures of thermal-oxidation products. The thermaloxidation mechanism was studied through ReaxFF MD simulations coupled with GC−MS, and could provide important supporting data for the use of DOA base oil
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