Energetic ionic liquids have been gathering attention and are now considered to be an interesting form of energetic materials, and the use of bio-renewable compounds is one of the most promising approaches for the fabrication of such materials.
A team of Researchers from Sichuan University, China have now created ionic bio-energetic materials (IBEMs) from a sustainable source of naturally occurring amino acids.
Energetic materials are a class of materials which contain a high amount of stored chemical energy. The controlled release under given conditions is a major benefit for many high-energy applications, such as explosives, propellants and pyrotechnics.
TNT is one of the most widely known energetic materials and its use in explosive devices is widespread. However, TNT and other high energy neutral compounds require many steps to produce, often in which the intermediates themselves are explosive.
In addition, many of the common energetic materials are produced from non-renewable precursors and large strides to make energetic materials from renewable resources has been made.
Biomolecules have been studied as a renewable alternative to conventional energetic materials and have been shown to possess great properties. However, to date, research has only focused on neutral bio-renewable compounds as they are closest in electronic structure to conventional energetic materials.
The Researchers from China have now explored the possibility of non-neutral bio-renewable energetic materials by using amino acids with charged groups. Despite amino acids themselves being used in fuels and propellants, the energetic properties of materials derived from amino acids molecules have rarely been studied, opening a potential new area of energetic materials research.
The Researchers studied sixteen potential naturally sustainable amino acid salts/ionic liquids including those with nitrate (NO3–) and perchlorate (ClO4–) groups to produce ionic bio-energetic materials (IBEMs).
The energetic materials were formed through a direct and simple acidification process from the amino acids and corresponding acids in water, before evaporating and vacuum drying the materials.
To test the efficiency and properties of the materials for energetic applications, the Researchers tested the impact sensitivity, friction sensitivity, detonation pressure, detonation velocity and the heat of combustion.
The Researchers also used a combination of Fourier-transform infrared (FTIR) spectroscopy (NEXUS 670), nuclear magnetic resonance spectroscopy (NMR, Bruker 400MHz), elemental analyses (Elementar Vario MICRO CUBE), thermogravimetric analysis (TGA, NETZSCH TG 209F1), differential thermal analysis (DTA, NETZSCH TG 209F1), differential scanning calorimetry (DSC, TA Q20), bomb calorimetry (Parr 6725) and X-ray diffraction (New Gemini, Dual, EosS2) to characterize both the amino acid precursors and the formed energetic materials.
The Researchers also employed MP2 simulations using Gaussian09 software to determine the heat of combustion.
The novel bio-renewable energetic materials showed fundamental characteristics expected of high energy materials, including combustibility, high density and good thermal stability.
In addition, the materials were formed through a simple one-step simple preparation method, preserved the benign environment from the natural source and possessed excellent hypotoxicities and low sensitivities.
The combustion properties of these materials were found to be more intense than many conventional neutral energetic materials. Moreover, the energetic properties of [Gly]ClO4, [Pro]ClO4, [Val]NO3 and [Ile]NO3 were found to be the highest and comparable to that of TNT and other commonly used explosives.
The simple procedure showcases that bio-renewable materials have an advantage towards energy conservation, in addition to being produced from an abundant renewable source. The production of the materials is low-cost and simplistic compared to many conventional energetic materials and shows that these IBEMs are promising candidates as novel frameworks for safer bio-based energetic materials.
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“Insensitive ionic bio-energetic materials derived from amino acids”- Zhang L., et al, Scientific Reports, 2017, | DOI:10.1038/s41598-017-12812-7