Effect of Boron‐Aluminium Particles on Rheological Properties of AP/HTPB Based Bi‐Curative Composite Solid Propellants

Abstract Propellants with Boron‐Aluminium fuels are of interest as they exhibit high energy densities when compared to various other fuels. The effect of aluminium (Al) and aminopropyl triethoxy silane functionalized amorphous micron‐sized boron (APTES−B) on the rheological properties of ammonium perchlorate (AP) and hydroxyl terminated polybutadiene (HTPB) based bi‐curative composite solid propellant (CSP) has been investigated in the present work. Numerous CSP formulations were prepared in which Al contents were reduced from 21% to 10%, while APTES−B contents were increased from 0% to 11%. The major constituents include AP as oxidizer, HTPB as binder fuel, TDI and IPDI as curing agents, MAPO as bonding agent, PPD as antioxidant and TBFE as burning rate modifier. The CSP slurry exhibited non‐Newtonian, shear‐thinning flow behaviour. Scanning electron microscopy (SEM) and laser particle size analyzer were used to analyse the size, shape and surface morphology of Al, raw amorphous B and APTES−B particles. Fourier transform infrared spectroscopy (FTIR) provided insights into the surface functionalization of B with APTES. The rheological properties were evaluated using a rotational rheometer. The effects of B−Al particle loading on the viscosity, shear stress and shear rate were investigated. The CSP formulation code P6, with an Al content of 16% and B content of 5%, emerged as the most optimal mix due to its optimal processability. The results are expected to provide useful inputs for optimizing the propellant composition and processing characteristics to obtain enhanced performance in terms of rheology of propellant.