The main objective of this project was to create a novel Comp B replacement with novel, environmentally favorable ingredients. This was not only achieved, but exceeded in that three potentially viable Comp B replacements were developed: OSX-15, OSX-16 and OSX-17. Four 2,4,6-trinitrotoluene (TNT) alternatives were explored (2,4,6-trinitro-3-bromoanisole [TNBA], 3,4-dinitropyrazole [DNP], 3,5-dinitro-1-methyl-1,2,4-triazole [DNMT], and Picryl propargyl ether [PiPE]) while two were down-selected (TNBA and DNP). Those two were down-selected based on a multitude of factors including projected costs, environmental impact, explosive performance and Insensitive Munitions (IM) properties. Eco-tox modelling suggested TNBA would have the least exo-toxicity of the melt pour candidates. During the course of this effort, concerns arose regarding skin sensitivity of personnel to DNP. Therefore, dermal testing of DNP was performed via direct peptide reactivity assay (DPRA) and human cell line activation test (hCLAT). Both tests confirmed DNP as a probable sensitizer. BAE Systems thus began requiring personnel to wear Tyvek suits and full face respirators while handling DNP in a heated, molten phase and when handling DNP outside of adequate ventilation. TNBA was also tested for skin sensitization via the hCLAT and found to be a probable skin sensitizer as well. Microtox testing was also performed to evaluate the aquatic toxicity of the novel ingredients (Microtox Acute Toxicity assay). DNP was found to be slightly toxic while TNBA was found to be highly toxic to aquatic life. DNP was also found to have a low tendency to bioconcentrate in aquatic life.

Seven Cyclotrimethlyenetrinitramine (RDX) alternatives were explored (1,4-dinitroglycoluril [DNGU], 2,6-Diamino-3,5-dinitropyrazine 1-oxide [LLM-105], 1,3,3,5,7,7-Hexanitrooctahydro-1,5-diazocine [HCO], 1,4-Diamino-3,5-dinitro-1H-pyrazole [DADNP], 1,4,7-Trinitrohexahydro-1H-imidazo[4,5-b]pyrazine-2(3H)-one [HK-56], Bismethylene-3-nitro-1,2,4-triazol-5-one [BiNTO], and N,N-Bis((3-nitro-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)nitramide [NANTO]) while two were down-selected (DNGU and LLM-105). Those two were down-selected based on a multitude of factors including projected costs, environmental impact, explosive performance and IM properties. Eco-tox modelling suggested DNGU would have the least toxicity and exo-toxicity of the crystalline candidates. LLM-105 was also tested for skin sensitization via the hCLAT and found to be a probable skin sensitizer as well. DNGU was evaluated for mutagenic potential using the Ames assay and found to have a low potential for genotoxicity and cytotoxicity, thus not limiting to its continued development. Microtox testing was also performed to evaluate the aquatic toxicity of the novel ingredients (Microtox Acute Toxicity assay). DNGU was found to be non-toxic while LLM-105 was found to be highly toxic to aquatic life.

Of all of the candidate ingredients evaluated in this project, DNGU was found to be the best in terms of environmental or toxicity concerns. DNGU also demonstrates a low cost for large scale manufacture and good IM properties, although the explosive performance is somewhat low for a RDX replacement. DNP was found to be second best in terms of environmental or toxicity concerns although it is a skin sensitizer, which can be mitigated through proper personal protective equipment and engineering controls to protect personnel in manufacturing. DNP also has a distinct advantage of having very high explosive performance although IM properties may not be great. LLM-105 and TNBA were both found to be probably skin sensitizers and to be highly toxic to aquatic life making them both low contenders from an environmental perspective. However, TNBA shows good IM properties and explosive performance and could be a very low cost ingredient as does LLM-105.

Formulation development efforts toward Comp B replacements ultimately afforded three candidate explosives:

1. OSX-15: A mixture of DNP, DNGU and Fluid Energy Milled Cyclotetramethylenetetranitramine (FEM HMX). This explosive contained the most environmentally favorable ingredients and had the best explosive performance, matching or exceeding Comp B in the tests performed in this project. OSX-15 also had the best IM properties with a LSGT shock sensitivity of 119 cards; a 50% improvement over Comp B.
2. OSX-16: A mixture of TNBA, LLM-105 and FEM HMX. This explosive contained the least environmentally favorable ingredients but had very good explosive and IM performance, close to Comp B. OSX-16 also contained the lowest cost TNT replacement and the most thermally stable RDX replacement.
3. OSX-17: A mixture of TNBA and HMX. This explosive contained a lot of HMX which currently poses minimal risks in the environment and is an affordable, mature product. OSX-17 had good explosive performance although shock sensitivity was not improved over Comp B, presumably due to large particles of HMX in the mixture. Also, because of the use of a lot of HMX, this explosive is currently the cheapest to manufacture.

Overall, this project helped not only to develop three novel Comp B alternatives, but also to perform needed environmental and toxicity testing on the ingredients that were developed to go into them. Further in vitro and in vivo testing may be warranted on any of these new ingredients if development is to continue. Further development of the ingredients is recommended including:

• DNP: Further refinement to the purification process to improve yields and purity and reduce waste streams. Continuous chemistry (perhaps through the use of Advanced Flow Reactors or Continuous Flow Reactors) could be a huge benefit to this endeavor.
• DNGU: Further development of synthesis process to reliably get large particles. Also, further development to afford lower surface area crystals for better formulation processing.
• TNBA: Minimal development effort needed.
• LLM-105: Minimal development effort needed.

Since all three of the final formulations are viable as Comp B replacements and each have a list of pros and cons, it is recommended to further the development and scale up of all three. The US Army is highly interested in DNP as a melt pour ingredient as it provides a base for making increased performance explosives. Therefore, continuing this work on OSX-15 to refine the composition to increase the HMX (increasing performance) and optimize viscosity, settling, pouring, etc. is recommended. Also, scaling up the formulation for more IM and performance testing is recommended, most likely in mortar and/or artillery configurations. This would need to be performed alongside further evaluations of strategies to mitigate skin sensitization and exposure in personnel. For the TNBA formulations (OSX-16 and OSX-17), it is recommended to evaluate the use of aluminum to react with the free bromide to afford more energy output of the explosive. Recommended IM testing of any of the formulations includes, slow cook off, fast cook off, bullet impact, fragment impact and sympathetic reaction.