Effect of Octa(perfluorodecyl)-Type Polyhedral Oligomeric Silsesquioxanes on Combustion Characteristics of the Mixed Nitrate Ester Gun Propellant

The formation of a burning rate gradient in gun propellant by flame-retardant treatment is one of the effective methods to achieve progressive combustion and thus improve the energy utilization efficiency. In order to reveal the effect of octa(perfluorodecyl)-type polyhedral oligomeric silsesquioxanes (FPS-POSS) on the combustion performance of gun propellants, seven-perforated granular mixed nitrate ester gun propellants containing FPS-POSS of 0, 0.5, 1.0, and 1.5 wt % were prepared by the traditional semisolvent method. The chemical compatibility of FPS-POSS with the gun propellant components, the thermal decomposition properties, and the combustion characteristics of the gun propellants containing FPS-POSS were systematically investigated. The results show that FPS-POSS is well compatible with the components of the mixed nitrate ester gun propellant and does not affect the thermal stability of gun propellant but also reduces the residual weight of the gun propellant after thermal decomposition. Additionally, FPS-POSS can reduce the maximum burning pressure (P_m) and burning rate (u) of the system and prolong the burning time (t_m) for gun propellants to reach the maximum pressure, and this effect tends to increase with the increase of its content. There are two reasons for this. First, FPS-POSS has a lower chemical energy than energy-rich components such as nitrocellulose and nitroglycerin, and its addition to the gun propellant can affect the burning rate at the energy level. The second is that FPS-POSS not only traps reactive radicals in the gas phase by generating fluorine-containing radicals during combustion but also generates porous carbonaceous layer in the condensed phase to hinder the propagation of flames and gaseous products. It suggests that FPS-POSS is an excellent additive in the low burning rate region of gun propellants. When the content of FPS-POSS was 1.5 wt %, FPS-POSS decreased the P_mof the system by 1.83%, increased the tm by 7.57%, and reduced the burning rate by 9.81%. High- and low-temperature experiments showed that FPS-POSS was favorable for reducing the temperature coefficients of gun propellants.