(435c) Polymer Resin Systems for Precision Direct-Ink-Write Printing of Thermite-Loaded Inks

Additively manufactured sample preparation allows control of the material scale and hierarchical
structure, and can potentially enable unprecedented tailoring of reaction characteristics in energetic
materials. Direct-ink-write 3-dimensional printing offers the simplest test-bed to explore numerous
material classes. However, the inks for such printing require specific, predictable properties such as shear
thinning to accommodate nozzle extrusion, consistent yield stress point and viscosity for predictable flow,
and a rapid transition rate between viscoelastic solid and liquid phases. Most classes of energetic
materials such as explosives, propellants, and pyrotechnics are solids or composites comprised of highly-solids
loaded polymer systems. Optimizing a desired energetic formulation for print quality while also
targeting maximum energy density is problematic due to solid-solid interactions dominating the rheology
of the ink. Solid-solid interactions make the flow and rheological properties less ideal for extrusion-based
printing methods, and require sufficient rheological tunability to be built into the low weight percent
reserved for the resin system. The halting of flow after deposition can be greatly improved by rapid, on
demand chemical curing mechanisms initiated by light or heat, but such systems are poorly suited as
phlegmatizing agents for sensitive energetic materials. An ideal resin system for energetic materials would
have sufficient rheology and yield stress tunability to be precision printed with many types of solids, and
cure on demand to expand the print design space.

We report a general, dual-polymer-based composite resin system with dual-curing mechanisms
that affords extensive adaptability across multiple applications. This resin system allows for precise, omnidirectional
printing of highly solids-loaded inks. Using this resin system, we were able to print single walled
filaments, overhangs, spans, and a freeform helix. Our work on this family of inert ink-composites with
68-80% solids loading exhibited independently tunable (i) cure rate, (ii) rheology, (iii) glass transition
temperature, (iv) print-ability, and (v) tensile/compression properties. Our inks are demonstrated to print
as well as current state-of-the-art inks with little to no solids loading. A reactive ink comprised of Al and
CuO solids forming a thermite was prepared and characterized. Burn characteristics of the Al/CuO
thermite ink as a function of geometry will be discussed.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore
National Laboratory under contract DE-AC52-07NA27344.