Plastic-bonded explosives (PBXs) are critical secondary energetics due to the ability to generate high theoretical maximum density (TMD) materials that are stabilized via elastomeric polymers to increase the insensitive nature of the explosive. PBXs are currently manufactured in significant quantities, generally via slurry or cast-cure processes. However, these processes generate significant amounts of energetically contaminated waste and scrap, which requires some type of remediation to avoid environmental release issues.
The objective of this project is to employ resonant acoustic mixing (RAM) technology to reduce and/or eliminate water and solvents in the generation of pressing powder formulations and enable the ability to mix in-item to eliminate energetic scrap and cleaning solvents and rags for cast-cure formulations.
For production quantities of pressing powder formulations, approximately 6,000 to 7,000 liters of contaminated water are generated per batch. To perform the cleaning of a cast-cure mixing vessel, the sides are scraped down by hand with static and spark resistant scrapers and the residue is removed from the vessel by means of solvent soaked rags. By reducing and/or eliminating energetic scrap and contaminated solvents and rags, environmental, safety and occupational health impacts will be greatly mitigated.
RAM is a new technology that makes use of resonant acoustic energy coupled to the formulation medium to perform the mixing process. RAM is a bladeless process that produces micro-eddies within the medium for rapid and efficient blending that does not generate any “dead zones” and has been effectively utilized to produce both low viscosity pastes and high viscosity / high solids loaded formulations. RAM is uniquely designed for ease of scale-up, as the mixing parameters that are developed in the laboratory setting can be directly applied to both the pilot-scale and production-scale mixing apparatuses with little to no additional parameter optimization.
In this effort, six tasks have been defined, which address both the generation of pressing powder and cast-cure formulations. In Task 1, a design of experiment (DOE) will be performed to develop processes for water slurry generation of pressing powder formulations that optimize solvent concentration and time parameters to allow for minimal water exchanges and examine the use of non-Hazardous Air Pollutant (HAP) solvents. In Task 2, a DOE will be performed to develop processes for the waterless generation of pressing powder formulations that only use small amounts of non-HAP solvents that can be recovered and reused. In Task 3, the optimized parameters developed in Tasks 1 and 2 will be transferred to McAlester Army Ammunition Plant to perform a scale-up analysis to determine scale-up effects from laboratory- to pilot-scale processing. In Task 4, a new cast-cure formulation will be developed to replace the toxic isophorone diisocyanate crosslinker with a much less toxic polyisocyanate crosslinker.
In Task 5, a DOE will be performed to develop processes that enable cast-cure formulations to be mixed in-item of complex geometry munitions to eliminate transfer of the energetic material to the item, thus eliminating the wastes associated with the mixing vessel. In Task 6, the optimized parameters and fixture designs developed in Tasks 4 and 5 will be transferred to McAlester Army Ammunition Plant to perform a scale-up analysis to determine scale-up effects from laboratory- to pilot-scale processing. The end result will be to transition the optimized parameters to McAlester Army Ammunition Plant to validate on the pilot plant-scale 5-gallon RAM5 apparatus, to demonstrate the ease of scale-up for this technology, and to gain a greater understanding of the complexities of scale-up from laboratory- to pilot-scale processing.
A successful effort will provide the Department of Defense with environmentally sustainable PBX-type explosives for use as secondary explosive fills in munitions. Significant reductions in energetically contaminated water and solvents will lead to a reduction in the environmental footprint of explosive formulation facilities. Moreover, in most situations, due to the efficiency and effectiveness of the RAM technology, a greater throughput of material will also be generated, thus increasing the availability of the explosive material for munition fabrication. (Anticipated Project Completion - 2018)