Systematic evaluation of additive loading effects on burn rate, density, and mass flow in PVC/AP composite solid propellants

Solid composite propellants continue to play a key role in space and defense propulsion due to their high energy density, ease of handling, and manufacturing scalability. While several studies have investigated the effect of individual additives on propellant performance, most are limited to a fixed weight percentage or particle size, making it difficult to derive comprehensive design guidelines. This study presents a systematic comparative investigation into the influence of various additives (Al, Fe₂O₃, CuCr₂O₄, and thermite combinations) and their particle sizes/loadings on the performance of polyvinyl chloride (PVC)/ammonium perchlorate (AP)-based composite propellants. Over 30 distinct formulations were experimentally characterized for burn rate, density, adiabatic flame temperature (AFT), and mass flow rate to establish comprehensive performance trends and trade-offs. The results demonstrate that smaller metal particle sizes and higher additive loadings generally enhance burn rate and mass flow, indicative of catalytic effects. Thermochemical analysis supports the significant exothermic contribution of the Al–Fe₂O₃ thermite reaction (–851.5 kJ/mol) to increased combustion energy. Furthermore, calculated oxidizer-balance percentages correlate with AFT and burn rate, with near-stoichiometric formulations exhibiting peak performance. The highest theoretical thrust (∼73 N) was predicted for a Fe₂O₃-rich formulation aligning with high energy and burn rate. While the catalytic mechanisms of these additives are known, the key contribution of this work lies in the extensive, comparative dataset across a wide range of propellant compositions. This broad dataset serves as a valuable resource for optimizing propellant formulations, validating combustion models, and guiding future propellant design.