Fluoro-polymer functionalization for enhanced interfacial adhesion and mechanical properties in polymer bonded explosives

Abstract

The poor interfacial adhesion between energetic crystals and polymer matrices results in undesirably low mechanical properties, limiting the application of energetic composites. Surface engineering has been widely implemented in materials science to regulate the mechanical properties. However, to achieve strong interfacial adhesion with precise control of interfacial structure is attractive and highly challenging for polymer bonded explosives. To address this issue, a covalent functionalization strategy were developed via the self-polymerization of dopamine on the surface of the energetic crystals, followed by the covalent grafting of fluoro-polymers using toluene-2,4-diisocyanate (TDI) as a bridging molecule. In-depth characterizations, combined with molecular dynamics simulation, have been systematically adopted to investigate the interfacial interaction and mechanical performance after covalent grafting of fluoro-polymers. Remarkably, both experimental results and numerical simulations revealed that the covalent functionalization and fluorine-containing binder system significantly increased the number of hydrogen bonds and interfacial interactions, thereby enhancing the interfacial adhesion between energetic crystals and the polymer matrix. Energetic composites with fluoro-polymer functionalization exhibited substantial interfacial enhancement effects. The mechanical properties of the composites improved with increasing grafted fluoro-polymer content. The composites based on energetic crystals with 2 wt% grafted fluoro-polymer exhibited optimal performance, with compressive and tensile fracture energies increased by 97.7 % and 182.0 %, respectively, compared to the unmodified composites. Additionally, computational simulations provided fundamental insights into how the interfacial structure affects the mechanical properties of energetic composites, confirming that the covalent functionalization and fluorine-containing binder system enhance interfacial adhesion by increasing hydrogen bond numbers and interfacial interactions.