Polymer Testing (Nov 2024)
Analysis and prediction for dynamic migration behavior of NEPE propellant/liner interface layer full components
Abstract
The migration behavior of nitrate ester-plasticized polyether (NEPE) propellant components significantly impacts safety. Experimentally observing the migration process is challenging and time-consuming. This study employed molecular dynamics (MD) methods to simulate a molecular model of the NEPE propellant/liner interface layer, enabling the prediction of component migration behavior. We visualized the migration process of all propellant components and studied the interface layer components' migration patterns, diffusion coefficients, and concentration gradient distributions. The contents of migrated components of the propellant and liner at different accelerated aging times at 70 °C were determined using high-performance liquid chromatography (HPLC), and the simulation patterns were compared with experimental observations. The results indicate that the migrated components in the propellant mainly consist of nitrate esters (Nitroglycerin, abbreviated as NG, and Butanetriol Trinitrate, abbreviated as BTTN), stabilizers (NMethylnitroaniline, abbreviated as MNA, and 2-Nitrodiphenylamine, abbreviated as 2-NDPA), and solid component (Hexahydro-1,3,5-trinitro-1,3,5-triazine, abbreviated as RDX). The migration process is primarily dominated by the substantial migration of nitrate esters, which is a key factor contributing to the degradation of propellant performance during storage. The migration process can be divided into three stages: swift migration, steady slow migration, and migration equilibrium. The diffusion coefficients are ranked from most significant to most minor as NG > BTTN > RDX > MNA > 2-NDPA. Three migration stages consistent with the simulation process were observed using HPLC, and the migration behavior of nitrate esters aligned with simulation patterns. Our designed full-component model can qualitatively predict component migration behavior. Additionally, a faster diffusion coefficient does not necessarily lead to a greater amount of migration. We employed MD simulations combined with density functional theory (DFT) calculations to explain this phenomenon and found that intermolecular interactions may influence the diffusion coefficient. At the same time, the migration amount is highly correlated with molecular polarity. Therefore, increasing the molecular polarity difference between easily migrating components and liner materials is a beneficial strategy for slowing the migration process and enhancing the storage safety of propellants.
