Sandwich-like interfacial structured polydopamine (PDA)/Wax/PDA: A novel design for simultaneously improving the safety and mechanical properties of highly explosive-filled polymer composites

High melting point paraffin wax (HPW) is a novel desensitizer that has the potential to achieve low sensitivity of energetic crystals, such as 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). However, first-principles calculations confirmed that interface deterioration occurred due to a weak interfacial connection. In this work, the polydopamine (PDA)/HPW/PDA with a sandwich-like interfacial structure was prepared using three simple steps to improve safety performance, thermal stability, and mechanical properties. The theoretical and experimental results suggested that the PDA acted as a double-sided tape to adhere to the adjacent HMX/HPW layer or HPW/polymer binder layer, thus substantially enhancing the interfacial interaction. While maintaining higher safety performance (impact energy: 11∼13 ​J) than that of HMX (5 ​J), the new design improved the β-δ polymorphic transition temperature of HMX to 219.4 ​°C for HMX@PDA@HPW@PDA, which was higher than that of HMX@HPW (202.8 ​°C) and core@double-shell HMX@PDA@HPW (208.9 ​°C). Among the modified energetic composites, polymer-bonded explosives (PBXs) based on HMX@PDA@HPW@PDA exhibited the optimum mechanical performance, including the storage modulus and tensile fracture energy, which were 43.5% and 77.1% higher than those of PBXs based on raw HMX, respectively. The achieved favorable systematical enhancement in thermal stability, mechanical properties, and safety performance shows that such a sandwich-like interfacial structure has great potential for application for HMX-based formulation used in complex environments.