THEORETICAL AND EXPERIMENTAL PACKING DENSITY STUDY OF HYDROXYL TERMINATED POLYBUTADIENE-AMMONIUM PERCHLORATE BASED PROPELLANT AND ITS INFLUENCE ON BURNING RATE

Abstract

A model that gives the particulate composition with maximum packing density and minimum viscosity for highly loaded trimodal hydroxyl terminated polybutadiene-ammonium perchlorate (HTPB-AP) based composite propellant was developed by using the packing density concept. The theoretical model developed by Furnas was utilized to predict particulate composition for maximum packing density. The apparent density of each component of trimodal propellant was determined by tapped density analyzer. The void fractions of the components were calculated from the apparent volumes of the component sizes and pre-known particle densities. Using the void fractions of AP components, the optimum size distribution was gathered by Furnas' method. Least-squares technique was used to test the closeness to the optimum size distribution. The fractions of solid components were calculated for the maximum packing and minimum viscosity. The model was tested by rheological characterization of uncured propellant with the predetermined fractions of components. The variation of viscosity with overall void fraction of the propellant was obtained. For trimodal concentrated suspension of two propellants containing the same mean particle size and size distribution of AP particles from different suppliers, different mix viscosity values were obtained due to different shape and surface characteristics of particles shown by scanning electron microscopy analysis. The effect of both packing density and viscosity on the burning rate of propellant was also explored. It was realized that not only average particle size, but also void fraction of AP particles, were important parameters affecting burning rate and better packing changed ballistic properties of propellant.