Effect of polyhedral oligomeric silsesquioxane on combustion performance of HTPB propellants

HTPB-based (hydroxyl‑terminated polybutadiene) propellants containing aluminum and ammonium perchlorate (AP) were prepared with 1 wt% polyhedral oligomeric silsesquioxanes (POSS) and Fe₂O₃, respectively. The influences of POSS compounds on combustion performance of HTPB propellants were investigated. Four POSS compounds, octa (phenyl) silsesquioxane (OPS), octa (nitrophenyl) silsesquioxane (ONPS), octa (dinitrophenyl) silsesquioxane (ODNPS) and octa (aminophenyl) silsesquioxane (OAPS) were used. Their compatibility with the HTPB propellant components were tested by DSC analysis. Their combustion heats of and sensitivities were measured by oxygen bomb calorimeter and friction and impact tests, respectively. The results show that ODNPS and ONPS belong to low sensitive energetic compounds. The POSS compounds have good compatibility with the components of HTPB propellant. The burning rates of the HTPB propellants were measured in combustion chamber with transparent window under pressure. The combustion behaviors of the propellants under atmospheric pressure were recorded using high-speed camera. The condensed-phase combustion products were collected and studied through the SEM observation, XRD analysis and particle size measurements. The POSSs can increase the burning rates of HTPB propellants. With the ODNPS, the burning rate of HTPB propellant is similar to that of Fe₂O₃. The addition of the OPS, OAPS and Fe₂O₃ reduces the combustion heats of propellants, while with ONPS and ODNPS, the combustion heats are close to that of the HTPB propellant. POSS compounds can promote the combustion of aluminum in the propellants, inhibit the agglomeration of aluminum particles in the combustion process, and reduce the size of condensed phase products. These should correlate to the formation of the nano carbon layers from the POSS compounds in combustion of the propellants.