Research on hot air drying mechanism of double-base propellant and numerical simulation

The drying of double-base propellant involves complex interactions between ethanol/acetone mixed solvents and nitrocellulose/nitroglycerin (NC/NG) matrix. However, the existing studies lack the microscopic mechanism of component migration and the coupled heat-mass transfer model, which seriously constrains the precise optimization of the drying process. Therefore, this study systematically investigated the solvent migration behavior and constructed a prediction model by combining experiments and simulations. Hot air drying experiments at 30–60 °C were conducted, revealing that the drying of double-base propellant is controlled by internal diffusion. The Modified Midilli model could accurately predict the migration kinetics of the propellant as a whole and ethanol/acetone individually. Both the removal rate and the effective diffusion coefficient of ethanol ((3.10–6.31)×10–12 m2/s) is higher than those of acetone ((2.73–4.56)×10–12 m2/s). Molecular dynamics simulations revealed that ethanol binds to NC/NG through hydrogen bonding, with a diffusion activation energy of 22.78 kJ/mol primarily governed by the energy barrier for hydrogen-bond breaking. In contrast, acetone interacts mainly by van der Waals forces (accounting for 65%), resulting in a lower activation energy (17.58 kJ/mol), though its average molecular binding energy is higher. The diffusion coefficient-content curves of ethanol and acetone intersect at approximately 3.43% solvent content: at high contents, acetone diffuses faster due to its plasticizing effect; at low contents, its larger molecular volume and strong interactions become the dominant resistances, leading to a significantly lower diffusion coefficient than that of ethanol. Based on the heat-mass coupling numerical modeling, it was further found that increasing temperature accelerates drying but intensifies the early-stage gradient, and acetone diffusion exhibits pronounced lag. Mechanical tests demonstrate that the sample dried at 40 °C exhibits the best impact strength (36.84 kJ/m2 at 20 °C), owing to its homogeneous fine-pore structure (average pore size 10.58 ± 2.65 μm) and moderate residual solvent content. The study revealed the drying mechanism of double-base propellant for the first time from the perspectives of component diffusion kinetics, molecular mechanism, and temperature/concentration fields, which provides an important theoretical basis and process guidance for the efficient and quality-preserving drying process.