Enhancing the rheological and processing properties of PBX explosives containing boron through surface modifications and compatibilization with the binder

Abstract. Besides commonly used aluminium or magnesium, boron is one of the attractive metal powders for thermobaric PBX explosive formulations, particularly due to its high gravimetric and volumetric heat of oxidation. However, there are some important challenges such as compatibility issues with the most often used hydroxy-terminated polybutadiene (HTPB) binders and high suspension viscosity of these formulations. Mitigation strategies like particle phlegmatization and the addition of compatibilizing agents may improve the processing characteristics of the PBX formulations. This study investigates the influence of boron powder particles on the rheological behavior of polymeric binders used in cast-cured PBX formulations and possible options to improve the castability of these explosive compositions. In the first part of the research, suspensions were prepared: boron powder in HTPB, boron powder in carboxyl-terminated polybutadiene (CTBN), boron pre-passivated with HTPB in HTPB, and boron with the addition of octadecylamine as a compatibilizer in HTPB. In the second part of the study, two HMX-based thermobaric explosive formulations were manufactured, with boron powder and HTPB-pre-passivated boron. Morphology of B powder and phlegmatized B particles was examined by scanning electron microscopy and particle size analyses, to observe particle size and shape. Differential thermal analyses were performed to estimate the extent of compatibility between boron and the binders. The rheological characteristics were determined of pre-polymer suspensions based on HTPB/CTBN containing boron powder, phlegmatized boron powder, or boron powder with octadecyl amine. These analyses included viscosity-shear rate dependencies, dynamic rheological properties, and deformation amplitude-frequency responses, tracked by a rheometer. The obtained results will contribute to a deeper understanding of the rheological behavior of boron-containing PBX formulations, offering insights into the potential optimization of their processing properties.