Direct Writing of a 90 wt% Particle Loading Nanothermite

• Published in: Advanced materials (Weinheim) 2019-06, Vol.31 (23), p.e1806575-n/a
• Main Authors: Wang, Haiyang, Shen, Jinpeng, Kline, Dylan J., Eckman, Noah, Agrawal, Niti R., Wu, Tao, Wang, Peng, Zachariah, Michael R.
• Format: Article
• Language: English
• Subjects: 3D printing; direct writing; Energetic materials; Flame temperature; Heat flux; high loading; Materials science; Modulus of elasticity; nanothermites; Packing density; Polyvinylidene fluorides; Rheological properties; Thickening agents; Vinylidene fluoride
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201806575

The additive manufacturing of energetic materials has received worldwide attention. Here, an ink formulation is developed with only 10 wt% of polymers, which can bind a 90 wt% nanothermite using a simple direct‐writing approach. The key additive in the ink is a hybrid polymer of poly(vinylidene fluoride) (PVDF) and hydroxy propyl methyl cellulose (HPMC) in which the former serves as an energetic initiator and a binder, and the latter is a thickening agent and the other binder, which can form a gel. The rheological shear‐thinning properties of the ink are critical to making the formulation at such high loadings printable. The Young's modulus of the printed stick is found to compare favorably with that of poly(tetrafluoroethylene) (PTFE), with a particle packing density at the theoretical maximum. The linear burn rate, mass burn rate, flame temperature, and heat flux are found to be easily adjusted by varying the fuel/oxidizer ratio. The average flame temperatures are as high as ≈2800 K with near‐complete combustion being evident upon examination of the postcombustion products. Particle loading is a critical parameter that is routinely used for benchmarking the energy density and energy release rate of nanoenergetic materials, including propellants, explosives, and pyrotechnics. An ink formulation is developed with only 10 wt% of polymers, which can bind a 90 wt% nanothermite using a simple direct‐writing approach.