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When subjected to complicated thermal alternation, the low thermal conductivity (k) of polymerbonded explosives (PBXs) will induce high thermal stress, which will undermine the safety and reliability of the explosives by causing cracks or damage. However, it has been proven to be a challenge to efficiently increase the k of PBXs due to the high interfacial thermal resistance (ITR) and intrinsic defects of their conductive nanofillers. By introducing AgNWs with a high aspect ratio into graphene, this study constructed a novel multi-dimensional high-k nanofiller composed of one-dimensional (1D) silver nanowires (AgNWs) and two-dimensional (2D) graphene, namely gra@AgNWs. The AgNWs decorated could remedy the intrinsic defects of graphene by passing through the interspaces within graphene nanosheets to form connections as bridges. Consequently, the k of energetic polymer composites increased significantly by 89% from 0.425 ​W ​m−1 ​K−1 to 0.805 ​W ​m−1 ​K−1 at ultralow filler loading of 0.5 ​wt%. Furthermore, the temperature gradients and thermal stress in the composite cylinder decreased significantly under complicated thermal changes owing to the enhanced k. As quantitatively demonstrated through the fitting of experimental data using a theoretical model, AgNWs significantly decreased the ITR, paving highways” for phonon transfer between adjacent graphene nanosheets. Hence an expected synergistic effect of heat transfer was produced in the composites. This study provides new insights into the design and preparation of highly thermally conductive composites.

Under complex temperature variations, the irreversible thermal expansion of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) based polymer bonded explosives (PBXs) results in decreased shape stability, directly impacting mechanical properties, safety performance during storage and use. In recent years, extensive and thorough researches have seen carried out on the thermal expansion characteristics of TATB based explosives. This paper summarizes the thermal expansion characteristics of TATB based PBXs, the influencing factors, as well as their suppression methods. Starting with the distinctive crystal structure of TATB, the thermal expansion mechanism of TATB based PBXs is introduced, the microstructural evolution during the thermal expansion process is summarized, and the effects of thermal expansion on comprehensive performance are analyzed. More attention to the influencing factors of thermal expansion and control methods are paid. Existing challenges are summarized with the recommendation for further exploration into the irreversible expansion mechanism of TATB based PBXs. It point out several key directions for future development: design and control of TATB crystal structure, construction and development of novel composites with integrated structural-functional properties, as well as the application of negative thermal expansion functional materials.

To improve the mechanical properties of 2,4,6-trinitrobenzene-1,3,5-triamine (TATB)-based polymer bonded explosives (PBXs), four kinds of polythiourea binders, namely the polyetherthiourea (P1), aliphatic polythiourea (P2), aromatic polythiourea (P3) and silane polythiourea (P4), were prepared and used in the PBXs. These four polythioureas were synthesized via the copolymerization of carbon disulfide (CS2) and diamines with various structures under mild conditions. They were then characterized using nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR). The interfacial binding energy between polythioureas and TATB was calculated via molecular dynamics simulations. The tensile and compression mechanical properties of various PBXs (PBX-Pn, n ​= ​1–4) were studied through Brazilian and compression tests and were then compared with those of the PBX with a conventional fluoro polymer binder (PBX-FP). The results show that the PBX-P1 possessed the strongest interfacial interaction energy and the best mechanical properties among all the prepared PBXs. Its Brazilian strength and strain was 11.0 ​MPa and 0.56%, which was 89% and 256% higher than those of the PBX-FP with the same binder proportion, respectively. Furthermore, PBX-P1 showed excellent compression mechanical properties, with a compression strength of 40.7 ​MPa and a compression strain of 3.53%. Moreover, its Brazilian and compression fracture energy was 600% and 101% higher than those of PBX-FP, respectively, which was beneficial for improving the PBX stability. The results of this study provide a new idea for designing TATB-based PBX with improved mechanical properties using polyetherthiourea binders.

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.

Abstracts: The mechanical strength was influenced by the quality of the crystal and interfacial interaction between energetic particles and polymeric binders. In this work, rod-like and hairy-spherical 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) with a high crystal quality was modified by polydopamine (PDA) and hyperbranched polymers (HBP) grafting. The morphology of modified LLM-105 changed into a rough surface, resulting in the obvious enhancement of surface energies and adhesion work with the fluoropolymer. Further, the thermal behavior was slightly affected after surface modification due to the decomposition latent of PDA and HBP. Owing to the combined e chemical bonding of PDA and interlocking interaction of HBP, the creep resistance and mechanical strength of the modified LLM-105-based polymer bonded explosives (PBXs) were significantly improved, assisted by quantitative analysis of the interfacial strength. This strategy may provide insights to other composites requiring high mechanical performance.

The safety properties and desirable detonation performance of energetic materials (EMs) are mutually exclusive, therefore, various strategies including the coating, doping, crystallization, and co-crystallization, are applied to achieve high-energy insensitive explosives with well-balanced energy and safety level. Among these strategies, the crystallization is the most commonly method owing to its low cost and facile process, through which the tuning of the particle size and morphology, adjust sensitivity of EMs by tailoring the processes conditions. As the control of the crystal particle size is difficult, the ultrasound and electrospray are introduced, and by use of the spray drying or spray-assisted electrospray methods, the spherical RDX, HMX, and CL-20 crystals with less defects is obtained. Moreover, the perfect spherical crystals are gained without agglomeration through employing polymeric additives in the crystallization process. In general, the crystallization with spray drying, electrospray, and ultrasound-assisted solvent/antisolvent are the optimal crystals preparation methods. The nano-crystals with narrow particle size distribution are less sensitive to external stimuli than irregular microcrystals, and defects are associated with hot spots, the safety and energy performance of EMs could be well balanced by crystallization.