Browsing by Author "Kister, Guillaume"
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Item Open Access Andrew Claydon PhD(Cranfield University, 2020-11-27 10:15) Gill, Philip; Claydon, Andrew; Gaulter, Sally; Kister, GuillaumeCurrent Polymer Bonded Explosive (PBX) formulation is limited by a compromise - optimised final properties against processability. While explosive content would ideally be maximised and plasticiser content ideally minimised, the formulation would become too viscous to cast and require arduous mixing processes using conventional techniques. However, with Resonant Acoustic Mixing (RAM), formulation does not have to be constrained. Instead of mixing blades, mixing is achieved using an oscillating platform to impart acoustic pressure waves (vibrations) into the mixture. Mixing is orders of magnitude faster than conventionally achievable, and the added ability to mix in the end use casing (mixing ‘in-situ’) also renders casting obsolete in many scenarios. The research aim of the PhD is to assess how machine control and vessel design can be altered to optimise the mixing mechanism and compare material properties of composites mixed ‘in-situ’ and ‘mixed and cast’.Item Open Access 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, EleftheriaCrystalline 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.Item Open Access Cross-linking of γ-cyclodextrin using non-toxic polyethylene glycol spacer units(Wiley, 2021-08-16) Dossi, Eleftheria; Bolton, Morgan; Kister, Guillaume; Afsar, AshfaqThe crystalline cyclic oligosaccharide γ-cyclodextrin (γCD) is a natural, non-toxic and biodegradable precursor that can be used to prepare innovative polymers. We cross-linked γCD with variable quantities of non-toxic polyethylene glycol diglycidyl ether (PEGDGE) in aqueous NaOH to form 3D structures with tunable physicochemical properties. Mixtures with a 5:1 PEGDGE:γCD molar ratio produced a cross-linked material that was soluble in water and organic solvents, underwent glass transition at –23 °C. The properties of this material were further modified by additional curing with PEGDGE or nitration reaction. Curing produced an insoluble polymeric material with excellent swelling abilities (200% in water) and decreased glass transition temperature to –37 °C. The nitrated cross-linked γCD was soluble in common organic solvents and underwent glass transition at +19 °C, achieving thermal stability below 190 °C. These novel γCD polymers are promising materials for applications in the pharmaceutical and food industries and environmental remediation.Item Open Access Cure monitoring of CFRP composites by dynamic mechanical analyser(Elsevier, 2015-08-29) Kister, Guillaume; Dossi, EleftheriaThe cure characteristics of carbon/MTM44-1 epoxy composite prepreg and neat MTM44-1 epoxy resin are monitored using a dynamic mechanical analyser (DMA). This study also assesses whether the simple containment device recommended by the DMA manufacturer for powder and gel is suitable for prepregs. The device is a disposable 0.1-mm thick stainless steel pocket. The cure behaviour of the packaged materials is compared with that of the unpackaged prepreg. All the samples are cured following the manufacturer's 180°C-isothermal schedule with heating rates of 2 °C/min and 5 °C/min. The tests highlight that: (i) the cure of composite prepregs and resin can be monitored using a DMA; (ii) the stainless steel pocket does not influence the cure of the prepreg and resin; and (iii) the softening and melting of the uncured resin, the resin low viscosity state and the subsequent gelation-vitrification-solidification of the resin are detected with this method.Item Open Access Determination and optimisation of Resonant Acoustic Mixing (RAM) efficiency in Polymer Bonded eXplosive (PBX) processing(Elsevier, 2022-02-07) Claydon, Andrew J.; Patil, Ajay N.; Gaulter, Sally; Kister, Guillaume; Gill, Philip P.An investigation into how the efficiency (time and energy required for homogeneity) of Resonant Acoustic Mixing (RAM) can be determined and optimised was undertaken. An idealised Polymer Bonded eXplosive (PBX) simulant based on glass microbeads (28.3 um D50, 62% v/v in binder and plasticiser) was used for mixing. Mixing evolution was monitored using machine output data, whereby the mixer ‘intensity’ (related to power draw) was plotted against time. Experiments were undertaken with three acceleration settings, three mixer units, and three vessel materials of low, medium, and high surface free energy. Different stages of the mixer ‘intensity’ profiles were found to correspond to discrete stages of mixing, as well as further rheological changes due to continued frictional heating, thus viscosity reduction, beyond homogeneity being achieved. Time to mixing completion was found to be repeatable within a standard deviation of +/- 10%, strongly dependent on acceleration setting, and additionally dependent on vessel material, though additional data is required to confirm this. A significant difference in mixing time was observed between different LabRAM units. Partial vacuum application without degassing was beneficial for mixing. Finally, a paradigm linking the ‘movement modes’ of mixing was constructed, based on literature observations and the experimental results.Item Open Access Emily Bagguley PhD(Cranfield University, 2018-09-13 09:13) Gill, Philip; Bagguley, Emily; Kister, Guillaume; Moniruzzaman, MonirSolid Composite Propellants for Improved Safety and Mechanical Properties This work looks to optimise and develop novel composite propellant formulations for use in unconventional rocket motor designs, in particular an integrated ramjet rocket motor. The particular design constraints of such a motor require that the booster propellant, required to get the rocket motor up to operational speed, use the same nozzle as the sustainer propellant and as a result must have the same operational requirements such as low pressure (1.5-2 MPa compared to ~10MPa for conventional rocket motors). In simple terms, this work aims to develop an extremely high burn rate propellant which works at extremely low pressures.Item Open Access Mechanophore-linked hydroxyl-terminated polybutadiene for the remote detection and quantification of mechanical stress(Elsevier, 2018-10-21) Kister, Guillaume; Moniruzzaman, Monir; Khan, M.; Debnath, S.Polymers containing chromophores often exhibit mechanoresponsive behaviour, allowing the remote detection of stress in components such as rocket motors without taking the rockets out of service. Here we describe a polymer comprising a difunctional spiropyran chromophore and methyl methacrylate cross-linked with hydroxyl-terminated polybutadiene (HTPB). This polymer was developed as a sensor for the non-destructive monitoring of mechanical stress by using the force-induced colour changes as a quantitative readout. After about 40 N of load was applied there was a gradual colour changes proportional to the compressive forces on the sample, as revealed by in-situ monitoring using a video camera and UV–Vis spectrometry. The tests highlighted a gradual decrease in the transmitted light intensity at 675 nm with increasing load, due to the opening of the spiropyran rings and their conversion to the coloured merocyanine forms. A reversible change to the initial colour occurred 72 h after the load was removed, but only under artificial fluorescent lighting, confirming that visible light is required for the ring-closing reaction. This new polymer is an ideal candidate for the remote detection of stress-induced damage in inaccessible structures or essential equipment that cannot be withdrawn from service for testing.Item Open Access Resonant acoustic mixing of polymer bonded explosives(2021-01) Claydon, Andrew J.; Gill, Philip P.; Kister, Guillaume; Gaulter, Sally; Flood, NathanCurrent Polymer Bonded Explosive (PBX) formulation is limited by a compromise - optimised final properties against processability. While solid loading (explosive content) would ideally be maximised and plasticiser content would ideally be minimised, this would make the formulation too viscous to cast into its casing and require long and arduous mixing processes using conventional techniques. However, with Resonant Acoustic Mixing (RAM), PBX formulation does not have to be constrained. Instead of traditional mixing blades, mixing is achieved by the use of a vibrating platform to impart acoustic pressure waves (vibrations) into the mixture, agitating it. The added ability to mix in the end use casing (mixing ‘in-situ’) also renders casting obsolete in many scenarios. In order to maximise the benefits of RAM with regards to next generation formulation-optimised PBX manufacture (‘PBneXt’), the underlying mechanisms of how the technique works, how efficiency (time and energy required for homogeneity) can be determined and maximised, and how final material properties may change between casting and ‘in-situ’ processing methods, must be better understood. The research aim of the PhD is therefore to assess how mixing efficiency of RAM can be measured and optimised to maximise its benefits, with a focus on how aspects of machine control and mixing vessel design can be altered to improve the mixing mechanisms on which the technique relies. Areas investigated experimentally include the effects of acceleration and mixer intensity (linked to power draw) setting, mixer model and unit, vessel material (with regards to surface free energy and thermal properties), and vessel surface finish (with regards to roughness). It is found that by modifying these variables, the time and energy required for mixing can be substantially reduced. A comparison between material properties of composites mixed ‘in-situ’ and ‘mixed and cast’ is also undertaken. The findings are then reconciled with wider literature observations and recommendations are made as how to best implement RAM for ‘PBneXt’ manufacture, ultimately allowing for explosive compositions with improved performance, mechanical, safety, and ageing properties.Item Open Access Self-healing in epoxy thermoset polymer films triggered by UV light(2016-07-26) Moniruzzaman, Monir; Christogianni, Paraskevi; Kister, GuillaumeSelf-healing of damaged structures can occur in three processes: capsule-based healing, vascular healing and intrinsic healing of polymers. The latest concept has a tremendous potential to repair damaged polymers and composite structures. Until now self-healing of composite materials has been addressed using capsule based resin with an initiator that polymerises in the damaged region. In this study, self-healing behaviour of cured epoxy thermoset resins modified with an epoxy-functionalised photoresponsive azobenzene molecule has been addressed by UV light without the use of any resin capsules or other component that is not chemically joined with the composites. The study was executed by nanoindentation and atomic force microscopy (AFM). Artificially damaged thermoset films exhibited good self-healing behaviour under UV irradiation only. This effect is attributed to the intrinsic healing mechanism triggered by UV-induced trans→cis isomerization of the azobenzene chromophore which enables the damaged polymeric matrix to recover.Item Open Access Shaping the structure and properties of HyTemp using polyethylene glycol diglycidyl ether cross-linkers(Wiley, 2024-06-03) Dossi, Eleftheria; Mutele-Nkuna, Khuthadzo Lourate; Wilkinson, Peter; Kister, Guillaume; Patrick, Hugh; Khalili, Mohammad Hakim; Hawi, SaraNovel elastomers are made by reaction of hydroxyl-terminated polyacrylic ester (HyTemp) with polyethylene glycol (PEG, number of ethylene glycol units 1, 3, 6, 9) based cross-linkers. The influence of the cross-linker length, the HyTemp/cross-linker (w/w) ratio and the cross-linking accelerator trifluoromethanesulfonate scandium salt (ScTFMS) on the structure and the properties of the materials are studied. The cross-linker length has not influence on the glass transition (Tg) of the products because of the presence of the flexible PEG units that cancels out the cross-linking effect associated to a shift to higher Tg. A two-domain structure is seen by the presence of a dual Tg in samples cured with ScTFMS. Mathematical analysis of the modulated differential scanning calorimetry curves offers for the first time the possibility to identify/confirm structural differences in complex three-dimensional polymeric structures. Scanning electron microscopy and swelling experiments in ethyl acetate respectively reveal an increase in the pore size (1.13 to 5.48 nm) and in the absorption ability of the elastomers cured with different types and quantities of PEG cross-linker. The new elastomeric materials are exhibiting a rubbery state over a wide temperature range and absorptivity for the potential recovery of pollutants in soil and/or water.Item Open Access Styrene-ethylene/butylene-styrene (SEBS) block copolymer binder for solid propellants(Wiley, 2021-09-20) Wilkinson, Peter J.; Weaver, Matthew C.; Kister, Guillaume; Gill, Philip P.Currently solid composite propellants are manufactured using bespoke, specially manufactured binders. This adds significant cost and obsolescence risks to their development and manufacture. This paper reports on the production of two composite propellants made from a commercially-available-off-the-self polymer as binder by means of a resonant acoustic mixer (RAM) slurry process. The binder consisted of thermoplastic elastomer styrene-ethylene/butylene-styrene (SEBS) block copolymer and the solid filler, either ammonium perchlorate (AP) or 1,3,5-Trinitro-1,3,5-triazinane (RDX). Thermodynamic code demonstrated that SEBS-based propellants exhibited similar theoretical ballistic performance to conventional HTPB-based propellants. Chemical compatibility between SEBS and the solid fillers was shown by the differential scanning calorimetry (DSC) and vacuum stability methods. The novel combination of RAM and slurry coating process produced a propellant moulding powder that was then consolidated by remote hot pressing to simulate an industrial extrusion or rolling process. The propellants exhibited as expected explosive hazard properties and their thermal analysis by DSC-TGA showed typical oxidizer behaviour between AP and SEBS, characterised by two decomposition exotherms (also reported in AP/HTPB compositions), and little or no interaction between RDX and SEBS. The apparent activation energy for decomposition for AP/SEBS (84/16 % w/w) propellant was similar to that for AP/HTPB propellants. This work demonstrates the viability of using SEBS polymer as a binder for solid propellants. The development of propellants using commercially off the shelf, thermoplastic elastomeric binders could add significant benefits in waste reduction through recycling, security of supply, and manufacturing costs.Item Open Access Thermomechanical characterisation of cross-linked β-cyclodextrin polyether binders(Elsevier, 2018-11-26) Luppi, Federico; Kister, Guillaume; Carpenter, Mark; Dossi, EleftheriaCyclodextrins 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.