Expanding Fluorinated-Energetic Feedstock for Fused Deposition Modeling

To probe reaction kinetics and polymer decomposition, energetic filaments composed of aluminum (Al) and poly(vinylidene fluoride) (PVDF) with varying hexafluoropropylene (HFP) content are tested for processability and combustion characteristics. Rheological and crystallization findings indicate that the Al-binder interfacial interactions are disrupted by HFP content. Thermal analysis shows that fuel consumption scales with Al particle size due to the diffusion-driven Al-fluoropolymer reaction regardless of HFP concentration. Char yield analysis shows that more solid product is retained in samples with smaller particle diameters, which further reflects the diffusive nature of both Al-PVDF and Al-P(VDF-HFP) reactions. Burn rates reveal two competing mechanisms for reaction efficiency: 1) accelerated binder decomposition through Al-PVDF interactions and 2) more energetic fluorination due to higher fluorine content in the P(VDF-HFP) binders. Finally, powder X-ray diffraction (PXRD) patterns show that AlF3 is the primary product from self-propagating burns. However, in larger Al particle sizes, filaments are unable to burn completely and result in high levels of Al2O3 and Al4C3 formation, which indicates that these binders are not amenable with low surface area, metallic fuels. These findings aim to improve fluorinated feedstock selection for potential binder candidates in energetic additive manufacturing (AM).