Effects of Dimeryl Diisocyanate Content on the Rheological Behavior and Mechanical Properties of an HTPB Based Solid Propellant

Several parameters affect the rheological and mechanical properties of solid composite propellants. Among them, the molar ratio of isocyanate (NCO) to hydroxyl (OH) groups (i.e. R value) is one of the important factors. In this research, the effects of changing the weight ratio of dimeryl diisocyanate (DDI) curing agent related to hydroxyl terminated polybutadiene on different properties of a HTPB based solid composite propellant such as end of mix viscosity, time depending behavior of viscosity, tensile stress, elongation, elastic modulus and hardness is investigated. For this purpose, five propellant formulations were prepared with various R value in the range of 0.755 to 0.815. Results showed that as the R value increased, end of mix viscosity is reduced at the first due to the wetting effect resulting from DDI addition and then is increased because of progressing of curing process. Furthermore, the mechanical properties are enhanced by increasing the R value, whereas elongation at maximum stress is reduced about 20%.