Studies on a novel thermoplastic polyurethane as a binder for extruded composite propellants

Extruded composite propellant (ECP) is an entirely new thrust area in the development of composite propellants within India. These are based on high-density thermoplastic elastomers as a propellant binder with ammonium perchlorate (AP) as an oxidizer and aluminum (Al) as a metallic fuel. Thus, this class of propellant not only provides higher energy but also yields higher density impulse. There are no pot life problems as with conventional slurry cast composite propellants because the binder used is thermoplastic in nature and hence can be recycled. ECP can take up solid loadings up to 90% and have very good dimensional stability. The present article reports evaluation of a thermoplastic polyurethane, viz. Irostic, as a binder for extruded composite propellants. The polymer was characterized completely before use. The feasibility of propellant processing has been studied and processing parameters have been established. Around 50 propellant formulations are processed for selection and optimization of plasticizer and to investigate the effect of variations in binder content. The results of the propellant characterizations have shown that the binder is capable of imparting significant improvements in mechanical properties and high density. Data generated on burning rate and static evaluation has confirmed that the binder imparts mesa-burning characteristics to the propellant with relatively low temperature sensitivity of burn rate.