Rheological Considerations for Binder Development in Direct Ink Writing of Energetic Materials

Additive manufacturing is a promising approach to prepare highly specifically defined materials with unique dimensions, gradients in material attributes and on-demand properties. For energetic materials applications, it is particularly exciting for its potential to create lattice and cellular structures and gradient solids to focus or dissipate energy. However, there are significant challenges to overcome, particularly in obtaining the very high particle content (>80 vol % particles), while still being manufacturable. This work focuses on the polymer binder used in an energetic materials system and aims to understand how its characteristics affect the viscosity and printability of the suspension. Two different types of polymer binders are examined: (a) high molecular weight polymer in a solvent and (b) polymerizable smaller molecules that were cured via UV light. We show that the suspension viscosity is primarily controlled by the particle volume fraction for the UV curable binder, while both the particle volume fraction and polymer molecular weight influence the response in the case of the polymer/solvent binder. Both binder types can be tuned to provide printable suspensions that result in lines of consistent width and 3D disc-shaped objects, indicating that both paths are good potential directions for future formulations for polymer bonded explosives prepared via additive manufacturing.