Browsing by Author "Luppi, Federico"

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    Chemical modification of β-cyclodextrins: balancing soft and rigid domains in complex structures
    (Wiley, 2019-09-19) Luppi, Federico; Mai, Nathalie; Kister, Guillaume; Gill, Philip P.; Gaulter, Sally; Stennett, Christopher; Dossi, Eleftheria
    Crystalline polymers such as β‐cyclodextrin (βCD) can be modified with polyethylene glycol (PEG) diglycidyl ether cross‐linkers (262, 394, 500 Da). Here we show that the quantity and length of the PEG soft segments influence the solubility and malleability of the products, which are water‐soluble and easily converted to nitrated analogues under standard reaction conditions. Inert and nitrated derivatives containing longer PEG segments showed the ability to self‐heal. The degree of cross‐linking and decomposition temperatures and energies depended on the quantity and length of the soft segment. Nitrated cross‐linked βCD containing longer PEG segments did not ignite following an electrostatic discharge of 4.5 J. The chemical stability of βCD/PEG binders was tested by heat flow calorimetry at 80 °C. We found that the balanced incorporation of soft PEG and rigid βCD segments improved the processability of cross‐linked βCDs and desensitised their nitrated derivatives, offering new solutions for inert and energetic binders.
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    Inert and nitrated cross-linked β-cyclodextrin binders for energetic applications
    (2019-03) Luppi, Federico; Dossi, Eleftheria
    This PhD project focuses on the synthesis of new inert and nitrated cross-linked cyclodextrin systems as binders for energetic formulations. Three diglycidyl ethers with polyethylene glycol segments differing in length were used to crosslink β-cyclodextrin. The physicochemical properties of the compounds were investigated by proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical analysis. The polyethylene glycol chains linked to the rigid β-cyclodextrin conferred low glass transition temperatures (≥ –20 °C) on the inert binders and also on their nitrated derivatives (≥ –14 °C). This is the first time that nitrated βcyclodextrin derivatives have shown viscoelastic behaviour at temperatures below 0 °C. The viscoelasticity of both the inert and nitrated compounds increased with the amount of polyethylene glycol chains in the system. Inert binders with higher polyethylene glycol:β-cyclodextrin units ratios were softer and exhibited self-healing behaviour. The thermo-mechanical characterisation of these binders revealed that the system was exposed to mechanical stress below the glass transition temperature, and the stress was directly related to the proportion of the soft polyethylene glycol segments. The nitrated cross-linked derivatives were characterised by decomposition temperatures of ~200 °C and thermal degradation energies of 1400–2100 J g -1 strictly dependent on the degree of cross-linking and nitration. Self-healing properties were confirmed in nitrated products with a high polyethylene glycol segments content. Nitrated samples with polyethylene glycol segments:β-cyclodextrin units ratios >3.8:1 were safer to handle in the laboratory as determined by small-scale hazard and compatibility tests with various energetic fillers. Additionally, preliminary Energetic Materials Testing Assessment Policy (EMTAP) tests confirmed the samples were not sensitive to electrostatic discharge up to 4.5 J but were sensitive to impact, with a figure of insensitiveness of 29. The nitrated samples were unstable at temperatures >80 °C. The materials developed during this PhD project could facilitate the manufacturing and storage of new binders and may offer a suitable replacement for nitrocellulose and other binders in ii energetic formulations. The stabilisation of the nitrated cross-linked binders should be prioritised in future work
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    Nitrated cross-linked b-cyclodextrin binders exhibiting low glass transition tempratures
    (Wiley, 2018-09-04) Luppi, Federico; Cavaye, Hamish; Dossi, Eleftheria
    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.
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    Thermomechanical characterisation of cross-linked β-cyclodextrin polyether binders
    (Elsevier, 2018-11-26) Luppi, Federico; Kister, Guillaume; Carpenter, Mark; Dossi, Eleftheria
    Cyclodextrins are promising building blocks for the synthesis of industrial binders. A new binder was prepared by cross-linking β-cyclodextrin with variable amounts of polyethylene glycol diglycidyl ether (40–60% w/w) to produce a soft polyether network that was soluble in water and alcohol, and the thermomechanical properties of the binder were determined. 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 information gained on the influence of the support medium on the thermomechanical properties of the cross-linked β-cyclodextrins can be used by industry for optimising manufacture and storage methods for new binders.