polymerization for energetic material binder without isocyanate – POLIMESI

The formulation of energetic materials is a key step in the manufacturing process of final composite objects in the military and civil fields:
- cast Plastic Bonded Explosives used for military applications for all types of munitions: bombs, penetrators, missile warheads, shells
- composite propellants used for civil applications such as the propellants of the ARIANE launchers
The current formulation of composite objects uses explosive fillers, oxidants, reducers up to mass levels of 90% and a polymeric binder, often of the HTPB type, a plasticizer, additives and an isocyanate type cross-linking agent. The latter presents acute toxicity and ecotoxicity, which could lead to a limitation of use in the near future.
Producers and end-users are still looking for an energetic composition with improved performance and sensitivity, as well as a low environmental impact to reduce exposure to health and safety risks. Several advances have been made in the field of new energetic materials, in particular:
- 5,5'-bis-tetrazole-1,1'-diolate dihydroxylammonium (TKX-50), which has better energy performance and sensitivity. However, during the formulation phase, incompatibility with the cross-linking agent (isocyanate) was noted, which makes their use more complicated.
- ADN (Ammonium dinitramide) is an alternative to ammonium perchlorate, which is an oxidant widely used in space propulsion but unfortunately is a suspected endocrine disruptor. Its incompatibility with isocyanates is an obstacle to its industrial development.
As a result, new cross-linking agents compatible with the new fillers must be identified, as well as the development of a new formulation route that would limit the incompatibility between the filler and the other reagents.
Taking into account all the regulations in force in the field of chemistry (REACh...) and in order to anticipate the obsolescence of isocyanate in the formulation of energetic materials as well as the implementation of new fillers, solutions for replacing cross-linking agents with a low environmental impact will have to be sought, which could require the change of the PBHT polymeric binder matrix.
To this end, Eurenco and the CNRS (Charles Sadron Institute) are combining their expertise to develop a research strategy based on two concepts:
- Medium-term concept for the substitution of the PBHT/isocyanate matrix by less toxic and REACh-compatible matrices in order to limit the environmental impact:
o epoxy resins prepared from an epoxy prepolymer and a hardener based on primary amines (reduced toxicity) to which agents such as plasticizer and other additives can be added
o vinylester resins obtained by radical polymerization of an unsaturated vinyl ester type prepolymer and a vinyl monomer (usually styrene)
- Long-term concept with the development of customised functional acrylic elastomers based on a chain copolymerization reaction of at least two acrylic comonomers allowing the chemical nature of the matrix to be adapted to the load while reducing the environmental impact.
Both concepts will be tested and validated on Eurenco explosive formulations. This includes
- A validation of the concept (acrylic polymerization and epoxy and vinylester resins): preparation of polymers on a laboratory scale
- Small-scale inert formulation
- Small-scale energetic formulation and mechanical characterization of the manufactured objects.