Paraffin-based Solid Fuels for Hybrid Propulsion Filled with Lithium Aluminum Hydride: Thermal, Mechanical and Ballistic Characterization

A chemical, thermal, mechanical, and ballistic investigation of paraffin-based solid fuels filled with lithium aluminum hydride [(LAH) LiAlH4] for hybrid propulsion is presented in this paper. Two different formulations containing 5% and 10% of polystyrene-block-poly(ethylene-ran-butylene)-block- polystyrene, a styrene-based thermoplastic elastomer [i.e., styrene-ethylene-butylene-styrene grafted with maleic anhydride (SEBS-MA)], were investigated to strengthen paraffin waxes. Two LAH mass fractions were considered for each paraffin-based blend (5% and 10%), for a total of four fuel formulations. The paraffin-based blends filled with LiAlH4 were found to be stable when exposed to air. The rheological properties were investigated using a parallel-plate rheometer giving evidence of the link between the elastic modulus (G′) evolution and the thermal behavior of LAH. The thermal properties were studied using differential scanning calorimetry in order to obtain data on the typical transitions of paraffin waxes (solid/solid and solid/liquid) and also on the thermal decomposition of the added energetic filler. A manufacturing technique for the production of homogeneous blends strengthened with SEBS-MA and filled with LAH is described. Firing tests were performed in a laboratory-scale hybrid motor using gaseous oxygen; the local and instantaneous regression rates were measured using a fiber-optic technique. The behavior of paraffin waxes blended with the selected SEBS-MA thermoplastic elastomer and filled with LAH is discussed.