Litchi-like Core-Shell HMX@HPW@PDA Microparticles for Polymer-Bonded Energetic Composites with Low Sensitivity and High Mechanical Properties.

The reduction of interfacial interaction and the deterioration of mechanical properties by the introduction of the indispensable paraffin wax is a long-standing problem. To address it, a novel litchi-like core-shell 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)@paraffin wax@polydopamine (PDA) structure was constructed with a new high melting point paraffin wax (HPW, 101.9 °C) as the inner shell and the bio-inspired strong adhesive PDA as the exterior shell. The evolution of element states on the surface of energetic microcapsules conducted by X-ray photoelectron spectroscopy (XPS) indicated that the successful introduction of paraffin wax and PDA to form the core@double shell structure. Compared with the core@double shell particles based on the conventional low melting point paraffin wax (LPW, 69.8 °C), the HMX@HPW@PDA particles demonstrated a 120% increase of impact energy EBAM from 5 J (raw HMX) to 11 J by Bundesanstalt für Materialprüfung (BAM) method. Attributed to the stronger interfacial interaction, the litchi-like core-shell HMX@paraffin wax@PDA based energetic composites also exhibited much superior mechanical properties than that of the corresponding HMX@paraffin wax based ones and could be equaled to or even higher than that of the raw HMX based ones. In addition, the β-δ phase transition temperature of HMX in HMX@HPW@PDA crystals was improved by 11.3 °C than that of raw HMX. The simplicity and scalability of the described approach provided a creative opportunity for design and fabrication of energetic composites with high safety performance and mechanical properties.