Molecular simulation study of the stabilization process of NEPE propellant

Abstract

In this reported study, the density functional theory (DFT) was used at the (U)B3LYP/6-311G(d,p) level to investigate the stabilization process of the nitrate ester plasticized polyether propellant (NEPE). Molecular simulations were conducted of the reaction that generates NO2, the autocatalytic and aging reaction triggered by the NO2, and the nitrogen dioxide absorption reaction of the stabilizers during the propellent stabilization process. These simulations were derived using the transition-state theory (TST) and variational transition-state theory (VTST). The simulation results suggested that the stabilization of the NEPE propellant consisted of three stages. First, heat and NO2 were generated during the denitrification reaction of nitroglycerine (NG) and 1,2,4-butanetriol trinitrate(BTTN) in the NEPE propellant. Second, nitroso products were generated by the reactions of N-Methyl-4-nitroaniline (MNA) and 2-nitrodiphenylamine (2NDPA) with NO2. Third, the stabilizers were exhausted and the autocatalytic reaction of NG and BTTN and the aging reaction of polyethylene glycol (PEG) were triggered by the heat and NO2 generated in the first stage. By comparing the energy barriers of the various reactions, it was found that the NO2 generated from the denitrification reaction significantly reduced the reaction energy barrier to 105.56–126.32 kJ/mol, also increased the reaction rate constant, and decreased the thermal stability and energetic properties of the NEPE propellant. In addition, the NO2 also weakened the mechanical properties of the NEPE propellant by attacking the –CH2 groups and the O atoms in the PEG molecular chain. The energy barriers of the reactions of MNA and 2NDPA with NO2 (94.61–133.61 kJ/mol) were lower than those of the autocatalytic and decomposition reactions of NG, BTTN, and the aging reactions of PEG (160.30–279.46 kJ/mol). This indicated that, by eliminating NO2, the stabilizer in the NEPE propellant can effectively prevent NO2 from reacting with the NG, BTTN, and PEG in the NEPE propellant. Consequently, this would help maintain the energy and mechanical properties of the NEPE propellant, thereby improving its thermal stability.