Mussel-inspired interfacial reinforcement of thermoplastic polyurethane based energetic composites

The interfacial interaction and the microstructure evolution play a vital role in the mechanical properties of thermoplastic polyurethane (TPU) based energetic composites. In this work, inspired by the strong adhesion of mussels, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) energetic crystals were coated with polydopamine (PDA) via in-situ polymerization of dopamine and then dispersed in TPU matrix. The core-shell structure of CL-20@PDA was confirmed by in-depth structural characterizations. The uniform and compact PDA shell gave rise to a high thermal stability with phase transition temperature of CL-20 crystals increased by 11.5 degrees C. Moreover, the PDA modification endowed the TPU based composites with excellent mechanical prop-erties. A striking increase in mechanical properties and creep resistance was achieved with 6 h polymerization time of PDA. Compared with the PBX-Raw with untreated CL-20 crystals, the compressive and tensile strength after PDA coating increased by 115% and 57%, and the compressive and tensile fracture energy increased by 148% and 68%. The storage modulus at 25 degrees C was 40% higher than PBX-Raw. The enhancement effectivity could be ascribed to both interfacial interaction and the microstructure evolution of TPU binder. The theoretical simulations by molecular dynamics demonstrated the strong interfacial interaction mechanism between CL-20 and PDA. Moreover, the abundant hydrogen bonds between the hard segments of TPU and functional groups of PDA facilitated the formation of more hard microdomains which acted as physical crosslinking points to promote the phase separation. This work provides a potential method for the mechanical and thermal enhancement for TPU based energetic materials based on dopamine chemistry.