Polymeric binders such as β‐cyclodextrins (βCDs) are used to bind with other constituents of energetic formulations and to prevent accidental ignition. One of the advantages of βCDs is the ability to tune their properties by chemical modification. Here, we synthesised nitrated cross‐linked βCDs (βNCXCDs) to produce new binders for energetic formulations. The cross‐linking of βCD 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 (βCXCDs) 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 βCPCD binder to −20 °C. The analogous nitrated systems (βNCXCDs) 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 °C) and energies (up to 1750 J g−1) comparable to nitrocellulose. Moreover, the glass transition of the inert βCXCDs at low temperatures (<0 °C) was conserved in the corresponding nitrated βNCXCDs, ensuring the desensitisation of energetic compositions even at low temperatures. This is the first time that nitrated derivatives of βCD with glass transition temperatures below 0 °C have been reported, suggesting such derivatives could make suitable replacements for nitrocellulose and other binders in energetic formulations.
Cyclodextrins are promising building blocks for the synthesis of industrial binders. We determined the thermomechanical properties of a new binder prepared by cross-linking β-cyclodextrin with a variable amount of polyethylene glycol diglycidyl ether (40-60% w/w) to produce a soft polyether network that was soluble in water and alcohol. Increasing the amount of cross-linker reduced the glass transition temperature of the binder as determined by differential scanning calorimetry and dynamic mechanical analysis. Cooling experiments revealed sudden stress relief below the glass transition temperature, reflecting the de-bonding of the polymer from the metallic supports. This was prevented by contact with polytetrafluoroethylene tape. Optical microscopy confirmed the stress relief in the form of cracking and revealed self-healing by reptation, promoted by a higher cross-linker content and temperature. The influence of the support medium on the thermomechanical properties of the cross-linked β-cyclodextrins will help to optimise manufacturing and storage methods for new binders.
Crystalline polymers such as b-cyclodextrin( bCD) can be modified with polyethylene glycol (PEG) diglycidyl ether cross-linkers (262, 394, 500 Da). In this work, the authors show that the quantity and length of the PEG soft segments influencet he solubility and malleability of the products, which are water soluble and easily converted to nitrated analoguesu nder standard reaction conditions. Inert and nitrated derivatives containing longer PEG segmentsshowed the ability to self-heal. The degree of cross-linking and de-composition temperatures ande nergies dependedo nt he quantity andl ength of the soft segment. Nitrated crosslinked bCD containingl ongerP EG segmentsd id not ignite following an electrostatic discharge of 4.5 J. The chemical stabilityo fbCD/PEG bindersw as testedb yh eat flow calorimetry at 80 8C. The balanced incorporation of soft PEG and rigid bCD segmentsw as found to improve the processability of cross-linked bCDsa nd desensitised their nitratedd erivatives, offering new solutions for inert and energetic binders.
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