Preparation of Paraffin-Based Solid Combustible for Hybrid Propulsion Rocket Motor

Abstract

Paraffin stands out as a promising solid combustible grain for the classical hybrid propulsion rocket motor. However, its low mechanical properties increase the risk of grain cracking and rupturing. The purpose of this experimental study is to address the existing drawbacks by formulating paraffin particles within a hydroxyl-terminated polybutadiene binder. Paraffin particles are prepared by crystallization in emulsion, which allows the control of particle size distribution, based on the droplets breakup and coalescence equilibrium. The paraffin particles are suspended in hydroxyl-terminated polybutadiene, and the maximum paraffin loading (62% volume fraction) is attained with the use of bimodal systems. A combustible grain (paraffin particles/hydroxyl-terminated polybutadiene) is cast with the maximum loading and submitted to thermal and mechanical tests. The results are compared to hydroxyl-terminated polybutadiene and paraffin wax counterparts, and they meet the criteria of performance and safety required for this kind of combustible. The crystallization in paraffin-in-water emulsion proves to be an efficient method to prepare spherical paraffin particles with controllable sizes, which may be used to get bimodal systems that improve the packing of paraffin particles. The resulting combustible grain exhibits adequate thermal and mechanical properties (ultimate elongation of 206%) for a hybrid propulsion rocket motor.