Sustainable Alternative to Perchlorate-Based Propellants via Use of Foaming Strategies: Case Study of Porous Solid Rocket Propellants Based on Ammonium Nitrate

This study investigates how porous structure formation influences the properties and safety characteristics of composite rocket propellants. Particular attention was given to approaches that may support more sustainable propellant formulations and processing methods. The work compares the efficiency of different sample-structuring and foaming methods, including a chemical foaming strategy based on two ammonium salts. Additionally, it evaluates the feasibility of generating porosity in propellants containing glycidyl azide polymer through the retention of a low-boiling solvent, remaining from synthesis. This approach is expected to reduce the number of processing steps and simplify them, translating into lessened environmental impact. Propellants incorporating this polymer were found to exhibit consistent low-level porosity and improved performance compared to other ammonium nitrate-based propellants, constituting a potential sustainable alternative to perchlorate-based propellants. The investigation encompassed decomposition kinetics (including decomposition activation energy), combustion product analysis, and exploratory nitrogen porosimetry. From a sustainability perspective, the investigated approach addresses key limitations of perchlorate-based propellants by eliminating chlorine-containing oxidising agents and reducing the need for auxiliary chemicals. In particular, the physical foaming strategy enables pore formation using residual solvent, which is already present in the system, supporting waste minimisation and inherently safer processing. These aspects are discussed in the context of selected principles of Green Chemistry and fundamental properties–sustainability trade-offs. Overall, the results highlight how foaming method selection affects not only propellant behaviour but also opportunities for more resource-efficient and environmentally conscious manufacturing routes.