HTPB propellant aging mechanisms and safety characteristics: microscopic structural changes, thermal stability, and self-accelerating decomposition temperature

As hydroxyl-terminated polybutadiene (HTPB) propellant surpasses its intended service life, its performance degrades, necessitating careful disposal to avert potential safety hazards. A thorough understanding of the propellant's safety characteristics before and after aging is crucial to prevent accidents that could result in injuries or fatalities. In this study, Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TG), and Differential Scanning Calorimetry (DSC) were employed to evaluate the microstructural and thermal stability changes in HTPB propellant due to aging. Reaction kinetics models and the Semenov self-heating model were utilized to analyze the activation energy and self-accelerating decomposition temperature ( T SADT ) across various aging stages. The results indicate that aging leads to the fragmentation of ammonium perchlorate (AP) particles and the binder, signifying significant degradation of the microstructure. Thermal analyses reveal a decrease in activation energies during both low-temperature and high-temperature decomposition stages. Additionally, the TSADT decreases from 204.13 °C in unaged samples to 192.89°C after aging, highlighting a reduced thermal safety margin. These findings underscore the impact of aging on the thermal stability and safety of HTPB propellant, emphasizing the need for comprehensive understanding to ensure safe disposal of decommissioned engines.