Ammonium-nitrate-(AN-) based composite propellants prepared with a hydroxyl-terminated polybutadiene (HTPB)/polytetrahydrofuran (PTHF) blend binder have unique thermal decomposition characteristics. In this study, the burning characteristics of AN/HTPB/PTHF propellants are investigated. The specific impulse and adiabatic flame temperature of an AN-based propellant theoretically increases with an increase in the proportion of PTHF in the HTPB/PTHF blend. With an AN/HTPB propellant, a solid residue is left on the burning surface of the propellant, and the shape of this residue is similar to that of the propellant. On the other hand, an AN/HTPB/PTHF propellant does not leave a solid residue. The burning rates of the AN/HTPB/PTHF propellant are not markedly different from those of the AN/HTPB propellant because some of the liquefied HTPB/PTHF binder cover the burning surface and impede decomposition and combustion. The burning rates of an AN/HTPB/PTHF propellant with a burning catalyst are higher than those of an AN/HTPB propellant supplemented with a catalyst. The beneficial effect of the blend binder on the burning characteristics is clarified upon the addition of a catalyst. The catalyst suppresses the negative influence of the liquefied binder that covers the burning surface. Thus, HTPB/PTHF blend binders are useful in improving the performance of AN-based propellants.
The improvement of the performance of composite propellant has been required due to the development of a wide variety of rockets and missiles. Glycerin has three oxygen atoms in its molecular structure, and it is a safe and low-viscosity material. Therefore, it is expected that glycerin would be one of candidates as a plasticizer of an AP/HTPB based-propellant. The burning characteristics and the mechanical properties of AP/HTPB propellant containing glycerin were investigated in this study. The viscosity of the uncured propellant containing glycerin was lower than that without glycerin. The tensile properties were improved with the small added quantity of glycerin. The burning rate of the propellant at 70%AP increased with the addition of glycerin and the propellant containing glycerin had a plateau burning characteristics. It was found that the addition of glycerin as a plasticizer would be an effective way to improve the burning characteristics, mechanical properties, and processability of the AP/HTPB propellant.
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