Kinetic modelling of the stabilizer consumption and of the consecutive products of the stabilizer in a gun propellant

Diphenylamine is used for the stabilization of solid propellants based on nitrocellulose. It reacts with the autocatalyticly acting decomposition product of nitrocellulose and forms consecutive products, which also stabilize. The kinetics of these stabilizing reactions are described by four reaction models. With respect to DPA and the DPA consecutive products the models have one, two and four steps. The four step model contains the DPA consecutive products up to trinitro-DPA. By approximations an analytical equation for the stabilizer decrease could be derived, which describes the stabilizer consumption very well. The other equation systems have been integrated numerically by a Runge-Kutta procedure and their reaction rate constants have been obtained by a non-linear least squares fit parameter calculation. This allows an evaluation of the reaction kinetic models. Relative reactivities of the DPA consecutive products with respect to DPA are calculable with the obtained reaction rate constants and an effective DPA concentration can be established. The different reactivities of mixed stabilizers as MNA and 2-NO2-DPA can be described with the presented method of modelling.