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The development of a facile method for improvement of interface interaction between rigid particles and coating polymer is of great importance for energetic composite materials, especially for military purpose. In this paper, energetic composites with spherical morphology, toughness property and low sensitivity are firstly fabricated by using Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) as core material and thermoplastic polyester-ether elastomer (TPEE) as shell material via an emulsion solvent evaporation (ESV) method. From the morphology and structure characteristic of as-prepared energetic microspheres, it is found that the HMX@TPEE energetic microspheres have uniform spherical morphologies, narrow size distribution and honeycomb coating structure under the circumstance of compound emulsifiers and appropriate core-shell ratio. The good toughness of HMX@TPEE microspheres in Brazilian test and dynamic mechanical analysis (DMA) demonstrates a new route to enhance interface interaction between HMX particles and TPEE matrix. Moreover, because of the favorable energy-decentralizing property of this exotic honeycomb structure, the sensitivity of HMX@TPEE microspheres measured by BAM impact sensitivity instrument can be markedly decreased and the impact energy ( E li ) can be improved from 3.5 J to 8.0 J at the HMX/TPEE ratio of 5/1. This fabrication of HMX@TPEE microspheres with adjustable coating content via a facile ESV process might provide a promising approach for HMX based energetic composites to enhance the safety and toughness properties when used in advanced weapon system. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) graphene nanoplatelets (GNPs) were adopted to enhance the thermal conductivity of PBX. The results indicated that, the thermal conductivity of PBX was only slightly improved with very low GNP loading (0.05 wt% and 0.15 wt%). However, a remarkable enhanced effect was observed at a relatively high GNP loading (0.5 wt% and 1 wt%). The thermal conductivity of PBX had a nonlinear dependence on the GNPs loading. The nonlinear dependence of the thermal conductivity on GNPs content was fitted by an analytical model which incorporated all the effects. And the thermal conduction mechanism of GNPs based composite could change from series thermal structure to parallel thermal structure with the GNP loading increasing. Additionally, the calculated thermal shock resistance and thermal stress distribution of PBX was both enhanced with the GNP loading. Finally, the sensitivity of sensitive hexanitrohexaazaisowurtzitane (CL-20) based PBX composition could be improved by GNPs due to enhanced thermal conductivity. [ABSTRACT FROM AUTHOR]

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 °C. Moreover, the PDA modification endowed the TPU based composites with excellent mechanical properties. 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 °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. Inspired by the strong chemical adhesion of mussels, the polymerization of dopamine was introduced to coat energetic crystals, which play a vital role in the interfacial interaction and the microstructure evolution of thermoplastic polyurethane (TPU) binder, resulted in mechanical and thermal enhancement for TPU based energetic materials. [Display omitted] • Core-shell structure was constructed through a novel, facile and general route via self-polymerization of dopamine. • CL-20@PDA composites exhibited 11.5 °C higher phase transition (ε.→γ) temperature than that of pure CL-20. • The mechanical enhancement was disclosed based on interfacial interaction and the microstructure evolution of TPU binder. • Theoretical simulations for the interfacial interaction showed good accordance with the experimental observations. [ABSTRACT FROM AUTHOR]

Nanothermites (also called metastable intermolecular composites), composed of nanoscale metals and metal oxides, have drawn increasing interests as energetic materials over the past two decades. Nanothermites have twice the energy density of 2,4,6-trinitroluene, and their nanostructures, functions, energy release, and reaction performance are continuously being improved. However, these materials suffer from low pressure because of low gas expansion from the reaction and incapability of deflagration to detonation transition (DDT). Fast DDT is necessary to substantially improve the reaction velocity and output pressure not only of nanothermites but also of other monomolecular organic energetic materials, such as cyclotrimethylene trinitramine (RDX) and octogen. Accordingly, this study aims to produce energetic composites material that are safe, green, and free from heavy metals. A strategy of rapid DDT acceleration is proposed by fabricating quasi-core/shell structured materials of RDX@Fe 2 O 3 –Al based on Fe 2 O 3 –Al nanothermites. A surface modifying and ultrasonic synthesis technology is also demonstrated. Scanning electron microscopy and X-ray photoelectron spectroscopy characterizations prove that the material comprises an RDX core and an Fe 2 O 3 –Al nanothermite shell. Results of closed vessel combustion tests show that the RDX@Fe 2 O 3 –Al combustion velocity accelerates to an average pressurization rate of 2.527 MPa/μs. DDT tube tests further confirm that DDT accelerates to a primer explosive level in which the run-to-detonation distances of DDT is below the test-condition limitation (<15 mm). Sensitivity tests also reveal that the RDX@Fe 2 O 3 –Al composite has low sensitivity to impact, friction, and electric spark. Therefore, the RDX@Fe 2 O 3 –Al composite with a quasi-core/shell structure is a potential green and safe fast DDT energetic material that is easy to synthesize and applicable to other quasi-core/shell structures. [ABSTRACT FROM AUTHOR]

Polymer bonded explosives (PBXs) have weak strength and toughness, as well as they are prone to fracture under stress. To overcome these disadvantages, inspired by the strong adhesion of mussels and the hierarchical structure of nacre, we designed and fabricated novel PBX composites by coating three explosive crystals (2,6-diamino-3,5-dinitropyrazine-1-oxide, LLM-105; 1,3,5-triamino-2,4,6-trinitrobenzene, TATB; and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane, HMX) with polydopamine (PDA), respectively. The results of mechanical analysis and in situ small angle neutron scattering measurements showed that these novel PBX composites exhibited higher strength, stronger toughness, and higher creep resistance, and higher microstructural thermal stability simultaneously, compared to PBXs without multiple bio-inspired designs. Contact angles measurements indicated that the interfacial interaction intensities between energetic crystals and polymer binder could be largely enhanced by PDA coating on energetic crystals. Theoretical calculations revealed that PDA-modified PBX-LLM-105 achieved the most increment in mechanical strength, which were well consistent with the experiments. An enhancement mechanism combining the van der Waals forces, π–π interaction, and hydrogen bonds, as well as surface roughness was proposed to account for the variety of mechanical properties and microstructural thermal stability of PDA-modified PBXs. The results revealed in this study are commonly significant to interfacial modification and performance enhancement of materials. [Display omitted] • Multiple bio-inspired designs were applied successfully to balance the strength and toughness ofPBXs. • The bio-inspired designs have significantly enhanced the mechanical strength, creep resistance, and thermal stability of PBXs. • The molecular structures and surface roughness of energetic materials have great effect on the interfacial interaction. • The inter-facial interaction enhancement mechanism of polydopamine on different explosive crystals were detailedly revealed. [ABSTRACT FROM AUTHOR]

The interfacial strength usually plays a key role for exhibiting great effects on mechanical performances. In this work, typical energetic crystal 1,3,5-triamino-2,4,6-trintrobenzene (TATB) was firmly coated by the strong adhesion of polydopamine (PDA), then two HBPs with fatty and aromatic structure were grafted onto the surface of TATB, by using the hydroxyl groups of the PDA layer as secondary reaction platform. Four highly-loaded polymer based energetic composites (solid loading was 95%) were prepared with fluoropolymer binders as substrate. The results showed that the surface of grafted samples with 0.5 wt% HBP was more easily wetted by non-polar liquid. Improved storage modulus and creep resistance properties were exhibited in polymer bonded explosives (PBXs). The static mechanical properties of tensile and compressive strength were increased significantly by 26.5% and 19.8%, respectively, due to the strong interfacial reinforcement of HBPs. • Successfully grafting hyperbranched polyester to energetic crystal for the first time. • Mechanical properties of PBX effectively enhanced by hyperbranched polyester grafting. • Interfacial reinforcement strategy can be extended to other highly loaded composites. [ABSTRACT FROM AUTHOR]