Assessment of the Migration of Combustion Moderator in Nitrocellulose-Based Propellant

The impregnation in surface with combustion moderator (also called deterrent) is usually applied to improve the ballistic properties, for example in the case of deterred spherical propellant which is largely employed in defense applications. The disadvantage of this surface impregnation is the migration of the deterrent toward the center of the grains. The knowledge of the diffusion coefficient of deterrent into grain core during the lifetime of the propellant is of significant importance because it is a fitting factor for the estimation of the shelf life. Diffusion coefficient has been determined by various techniques. In the most recent articles, we find that the most employed method is infrared (IR) microscopy; however, this method is highly time consuming. Therefore, the aim of this work is to explore the possibility to obtain an efficient procedure needing less time to be achieved. In this paper, we present an improved procedure based on well-known experimental technique namely high pressure liquid chromatography (HPLC). It is composed of the following steps: (1) the preparation of propellant grains that have cylindrical shape and double base chemical composition (around 11% nitroglycerin) using extrusion process, (2) known quantities of deterrent (dibutylphthalate; DBP) are deposited on the surfaces perpendicular to the axis of the grains before the conditioning at constant temperature (85 ℃) for 04 h. After that, each grain was sliced by a microtome into little pieces of a thickness equal to 20 μm. The last step comprises the determination of the concentration in DBP of each slice by HPLC. The results permit the establishment of the concentration profile and the migration coefficient of DBP in grain matrix by both infrared (IR) microscopy improved procedure. The obtained values of the diffusion coefficient according to infrared (IR) microscopy and improved procedure are equal to 6.9 × 10−16 m2/s and 8.7 × 10−12 m2/s, respectively.