Fabrication of RDX, HMX and CL-20 based microcapsules via in situ polymerization of melamine–formaldehyde resins with reduced sensitivity

• Successful extension of MF resin applications in energetic materials.
• Compact and uniform core–shell coating structure for the microcapsules.
• Significantly reduced impact sensitivity for the energetic composites.
• Visible improved thermal stability after coating and reserved optimal ε-CL-20.

Melamine–formaldehyde resins (MF resins) were selected for the fabrication of three typical nitramine explosives (cyclotrimethylenetrinitramine, RDX; cyclotetramethylenetetranitramine, HMX; and hexanitrohexaazaisowurtzitane, CL-20) based microcapsules, the polymer coating shell could be prepared via a facile in situ polymerization of melamine and formaldehyde on the surface of explosive crystals. Structural characterizations and thermal properties of the core–shell composites were systematically studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), fourier-transform infrared (FT-IR) spectra and differential scanning calorimeter (DSC). The SEM and XPS results indicated that these three energetic cores were mostly well coated. XRD and FTIR analyses showed the combined characteristics of explosives and MF resins, and revealing that the polymorph of CL-20 maintained the optimal ε form during the whole preparing process. After coating, the endothermic polymorphic phase transition as well as the exothermic thermal decomposition temperature of the explosives was visibly increased, attributing to the outstanding heat resistance of MF resin shell. The impact sensitivity of the resultant microcapsules could be reduced from 2 to 3 times, depending on energetic material, after coating by 3 wt% MF resins.

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