Molecular simulation study on the protective mechanism of three kinds of HTPB propellant antioxidants

Abstract

To investigate the protection mechanism and performance of N-phenyl-1-naphthalenamine (antioxidant A), N-phenyl-2-naphthalene (antioxidant D), and N, N'-diphenyl-1,4-phenylenediamine (antioxidant H) in the HTPB-TDI matrix, quantum chemistry (QC), molecular dynamics (MD), and Monte Carlo (MC) simulation methods were used to calculate the reaction sites, hydrogen dissociation energy, reaction energy barrier, diffusion coefficient, solubility parameters and permeation coefficient of the antioxidants and HTPB-TDI based on the density functional theory (DFT) and transition state theory (TST). The results show that the energy required for the dissociation reaction of N-H bonds in all three antioxidant molecules is less than the dissociation energy of the α-H bonds in the HTPB-TDI, and the reaction energy barriers for the reactions of all three antioxidants with peroxy radicals are also less than the reaction energy barriers for the same type reactions of HTPB-TDI; among the three antioxidants, antioxidant H has the lowest hydrogen dissociation energy and reaction energy barriers; the differences of the solubility parameters between antioxidants and HTPB-TDI are all less than 6.95 (J•cm−3)0.5, and as the temperature increases, the diffusion coefficients of the antioxidants added in the blended system continue to increase; under the same temperature conditions, the diffusion coefficient of antioxidant H is the smallest, and that of antioxidant A is the largest, which indicates that all three antioxidants have relatively good compatibility with HTPB-TDI, and antioxidant H has the best stability in the HTPB-TDI matrix. The order of solubility coefficients of O2 in HTPB-TDI containing different antioxidants is [SHTPB-TDI&A] > [SHTPB-TDI&D] > [SHTPB-TDI&H], indicating that antioxidant H has the strongest oxygen barrier ability. Based on the analysis of the migration, compatibility, oxygen barrier ability, and the difficulty of the reaction of the three antioxidants, it can be seen that the protective performance of the three antioxidants is as follows: [antioxidant H] > [antioxidant D] > [antioxidant A].