Propellants Explosives Pyrotechnics, Vol.43, No.10, 1023-1031, 2018
Nitrated Cross-linked beta-Cyclodextrin Binders Exhibiting Low Glass Transition Temperatures
Polymeric binders such as beta-cyclodextrins (beta CDs) are used to bind with other constituents of energetic formulations and to prevent accidental ignition. One of the advantages of beta CDs is the ability to tune their properties by chemical modification. Here, we synthesised nitrated cross-linked beta CDs (beta NCXCDs) to produce new binders for energetic formulations. The cross-linking of beta CD with non-toxic triethylene glycol diglycidyl ether (TEGDGE, X=T) and poly(ethylene glycol) diglycidyl ethers (PEGDGE, X=P) yielded soft, water soluble oligomeric compounds (beta CXCDs) which can improve the processability of energetic formulations and contribute to their desensitisation. When the PEGDGE cross-linker was used, lower glass transition temperatures were achieved, which extended the operative range of the beta CPCD binder to -20 degrees C. The analogous nitrated systems (beta NCXCDs) were therefore synthesised using a 1:1 (v/v) ratio of 98% sulfuric acid/100% nitric acid or 100% fuming nitric acid, increasing their solubility in acetone and tetrahydrofuran. The nitrated derivatives were characterised by decomposition temperatures (200 degrees C) and energies (up to 1750 Jg(-1)) comparable to nitrocellulose. Moreover, the glass transition of the inert beta CXCDs at low temperatures (< 0 degrees C) was conserved in the corresponding nitrated beta NCXCDs, ensuring the desensitisation of energetic compositions even at low temperatures. This is the first time that nitrated derivatives of beta CD with glass transition temperatures below 0 degrees C have been reported, suggesting such derivatives could make suitable replacements for nitrocellulose and other binders in energetic formulations.