The objective of this SERDP Exploratory Development (SEED) project is to demonstrate new energetic binder systems that serve as environmentally conscious replacements for phthalate-containing and isocyanate-based binder systems. Binder systems to be developed have the potential to be used for pyrotechnic, explosives, and propellant applications. Some of the proposed binder systems will be tetrazole-based polymers, while others will be nitro group-based polymers. The cross-linking agents for these polymers will be polyamine curing agents or epoxy-based curing agents, thus side-stepping the use of isocyanate-based curing agents.
One class of energetic binders will consist of novel tetrazole-based polymers, in which the monomers can be synthesized from readily available starting materials utilizing “click chemistry.” Following polymerization of the tetrazole-based monomers, the polymers will be cross-linked with commercially available polyamine-based curing agents. A second class of energetic binders will consist of a novel nitro-based binder system, thus serving as a potential replacement for the glycidyl azide polymer (GAP). GAP is known to be problematic, as the azide functionality can decompose over time, releasing nitrogen gas and cracking the grain of the energetic composition. Epoxy-based cross-linking curing agents will be used, thus mitigating the use of isocyanate curatives in the proposed binder systems.
While it is envisioned that the binder systems can serve as useful replacements for the phthalate-containing Laminac binder-system and bisphenol A-based epoxy binder systems currently found in colored pyrotechnic illuminating compositions, active testing will be performed using these binder systems in explosive and propellant-based formulations. The sensitivities of the binder systems (i.e., impact, friction, ESD, and thermal onset temperatures) will be determined. The new binder systems will be incorporated into formulations, and these new formulations will be measured for their sensitivities and mechanical properties. The formulations will be tested on a small scale and compared to GAP/HMX and GAP/AN control formulations so that an accurate measurement can be obtained on the effect employing the binder systems has on the formulation.
Many binder systems in use today are phthalate-containing and/or consist of toxic isocyanate curing agents. Furthermore, the use of GAP is problematic since the primary azide is not a stable moiety and can decompose over time, releasing nitrogen gas, which affects the performance of pressed energetic compositions. The energetic binder systems to be evaluated will be primarily based on two classes: (1) aromatic tetrazole-based polymers, cross-linked with polyamine curing agents; and (2) aliphatic nitro group-based polymers, cross-linked with epoxy-tetrazole-based curing agents. These binder systems should undergo clean combustion, yielding copious amounts of nitrogen gas and a high level of energy in the process. The higher levels of energy associated with the energetic binder systems, coupled with their high level of nitrogen gas release, should serve to boost the performance of propellant and/or explosive formulations. In addition, the binder systems are likely to have importance from the civilian fireworks perspective, as there is an increased interest in the development of low-smoke pyrotechnics for firework displays. (Anticipated Project Completion - 2015)