Investigating the influence of relative humidity on the hot-air drying mechanism and properties of a double-base propellant

Abstract

A controllable drying process and optimized drying parameters offer an indispensable role in the improvement of the quality and performance of propellant products. However, thus far, the influence of the relative humidity of hot-air on propellants has not been studied. In this study, the influence of relative humidity on drying characteristics of a double-base propellant is investigated for the first time, and the effect of relative humidity on the pore structure and thermal and mechanical properties of the propellant is comprehensively explored. The drying characteristic curve demonstrated that the drying of the propellant belongs to deceleration drying and is controlled by internal diffusion. Five semi-empirical kinetic models were employed to analyze the experimental data, and the results illustrate that the modified Midilli model can well describe the drying behavior of the propellant. The effective diffusion coefficient of volatile matter was calculated using the Fourier number method, the curve of diffusion coefficient varying with the ratio of volatile matter during drying was obtained, and the average effective diffusion coefficient was calculated. The results suggest that high relative humidity is beneficial to improve the drying efficiency of the propellant. The effect of relative humidity on the drying and heat transfer process of the propellant was also studied, and the mechanism of the effect of moisture on the drying rate of the propellant was further analyzed through molecular dynamics simulation. Additionally, the pore structure of the dried propellant was studied via mercury intrusion porosimetry and nitrogen desorption measurements, which indicated that relative humidity has a slight effect on pore size distribution, while the sample density of the propellant obtained at 80% relative humidity was significantly lower than that obtained at 40% and 60% relative humidity. The thermal stability of the samples was studied via DSC and TG analysis, and the mechanical properties were tested, demonstrating that the relative humidity in the drying process of the propellant affects its drying characteristics and subsequently its physical properties. The results showed that the drying of the double-base propellant at 50 °C with 60% relative humidity used shorter drying time and offered better drying quality. Therefore, this study can provide basic theoretical and data support for the control and regulation of relative humidity in the preparation process of a propellant.