Tailoring Binder Melting Temperature to Study the Binder Melt Layer Flow in Ammonium Perchlorate Composite Propellants

ABSTRACT

Understanding the melt layer of composite solid propellants is crucial to theoretically model the combustion mechanism. Numerous studies on the melt layer flow have determined that the melting temperatures of the binder govern the burning rate dependence on pressure. Previous investigations discovered that using curatives and using different binders alter the binder melting temperature. The authors have developed a process to tailor the melting temperature through a functionalization process on the hydroxyl-terminated polybutadiene (HTPB) polymer. This study presents the analysis on the impacts of the melt layer dynamics of an ammonium perchlorate (AP)/HTPB-based propellant with tailorable melting temperatures. Pyrolysis measurements observed increased binder melt layer flow, resulting in lower pyrolysis rates. Propellants made with similar melting temperatures to the traditional R45M had similar burning rates but introduced more scatter due to the hardness of the propellant. Additional propellant samples containing 17 wt% aluminum (Al) and 70 wt% AP were made with a range of melting temperatures to study the impact of melting temperature on the melt layer. A rheological study on the cured propellant mixtures with tailored melting properties identified the melting temperatures for the level of HTPB functionalization. Those mixtures were burned, and the burning rates varied based on the melting temperature. The results suggested that a lower melting temperature produces a plateau propellant.

KEYWORDS:

• HTPB/AP
• melting temperature
• viscosity

Acknowledgments

The authors wish to thank the NAVAIR ILIR program, managed at ONR and administered by Alan Van Nevel.