Influence of particle size on the thermal-mechanical properties of composite propellants

Abstract. Composite propellant consists of an energetic filler and polymeric binder which are intimately mixed, the interaction between the filler and binder affects the propellant rheology and mechanical properties, which are mainly influenced by the size of the particles and the packing fraction. This project aims to study the effect of the particle size on the thermal-mechanical properties of an inert model by mixing an HTPB binder with a filler of spherical glass beads using a resonant acoustic mixer, cast inside a square mold, and cured under vacuum. The main objective is to thoroughly study and analyze how different particle sizes influence the material's overall properties. By understanding these interactions, the aim is to optimize the formulation for potential applications in developing high-performance rocket motors. Four bimodal systems of coarse and fine glass beads were mixed for high solid loading. The density of the cured systems was studied by gas pycnometry, and it was observed that the density was slightly decreasing towards the top of the sample due to glass bead settling. The thermal properties were evaluated using differential scanning calorimetry, and the mechanical properties were assessed by dynamic mechanical analysis, the results suggested that glass transition temperature decreased as the particle size get finer, the storage modulus values increased with decreasing bead size in the systems, tan delta curves showed samples with larger particles have more damping characteristic.