No abstract

The solid–solid phase transition, poor mechanical properties, and high sensitivity has impeded further practical applications of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) based polymer bonded explosives (PBXs). To address these issues together, a facile and effective route was employed to achieve a coating of polydopamine (PDA) on the surface of explosive crystals via in situ polymerization of dopamine. Additionally, PBXs based on HMX@PDA microcapsules were prepared with a fluoropolymer as polymer binder. Improved storage modulus, static mechanical strength and toughness, and creep resistance has been achieved in as-prepared PDA modified PBXs. The β-δ phase transition temperature of as-obtained PBXs based on conventional HMX (C-HMX)@PDA was improved by 16.3 °C. The friction sensitivity of the C-HMX based PBXs showed a dramatic drop after the PDA coating. A favorable balance proposed in this paper among thermal stability, mechanical properties, and sensitivity was achieved for C-HMX based PBXs with the incorporation of PDA.

The reduction of interfacial interaction and the deterioration of mechanical properties by the introduction of the 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 bioinspired strong adhesive PDA as the exterior shell. The evolution of element states on the surface of energetic microcapsules conducted by X-ray photoelectron spectroscopy indicated 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 (69.8 °C), the HMX@HPW@PDA particles demonstrated a 117% increase of impact energy E BAM from 6 J to 13 J by the Bundesanstalt fur Materialprufung (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 equal 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.