Investigation of a Low-Toxicity Energetic Binder for a Solid Propellant: Curing, Microstructures, and Performance.

In this work, a promising propellant binder using the energetic branched glycidyl azide polymer (B-GAP) as a matrix and the low-toxic dimer acid diisocyanate (DDI) as a curing agent was prepared, under the catalysis of dibutyl tin dilaurate. The curing kinetics considering the thermal diffusion effect and the reaction endpoint of B-GAP/DDI were investigated by the thermal analysis method and a newly proposed variance method, respectively. Moreover, the buildup of microstructures during curing and the tensile and dynamic mechanical performance of this binder were respectively explored. Results show that there exists an obvious induction period in the beginning of the curing reaction, and the autocatalytic model shows that thermal diffusion can effectively describe the curing process. Shore A hardness of sample stabilizes around 40.78 in the end of curing, and the reaction endpoint of B-GAP/DDI is in the time range of 156-168 h. There exist cross-linking, suspension, and free chains during the whole curing process, and the cross-linking density of the binder reaches approximately 4.0 × 10 mol·cm when the curing completes. Hydrogen bonding (H-bond) is found to be a strong binder: 53.3% of the carbonyls participates in forming the H-bond. Furthermore, this binder has better mechanical performance and lower glass-transition temperature than the GAP/N100 binder.