Publications
548 results found
Mazlan NM, Marchetti P, Maples HA, et al., 2016, Organic fouling behaviour of structurally and chemically different forward osmosis membranes – A study of cellulose triacetate and thin film composite membranes, Journal of Membrane Science, Vol: 520, Pages: 247-261, ISSN: 0376-7388
The HTI cellulose triacetate (CTA) and novel thin film composite (TFC) membranes are used to study the multifaceted interactions involved in the fouling and cleaning of forward osmosis (FO) membranes, using calcium alginate as a model foulant. Results show that fouling on the TFC membrane was more significant compared to CTA, arising from a variety of factors associated with surface chemistry, membrane morphology and structural properties. Interestingly, it was observed that in FO mode, membrane surface properties dominated over fouling layer properties in determining fouling behaviour, with some surface properties (e.g. surface roughness) having a greater effect on fouling than others (e.g. surface hydrophilicity). In pressure retarded osmosis (PRO) mode, structural properties of the support played a more dominant role whereby fouling mechanism was specific to the foulant size and aggregation as well as the support pore size relative to the foulant. Whilst pore clogging was observed in the TFC membrane due to its highly asymmetric and porous support structure, fouling occurred as a surface phenomenon on the CTA membrane support layer. Besides pore clogging, the severe fouling observed on the TFC membrane in PRO mode was due to a high specific mass of foulant adsorbed in its porous support. It was observed that a trade-off between enhanced membrane performance and fouling mitigation is apparent in these membranes, with both membranes providing improvement in one aspect at the expense of the other. Hence, significant developments in their surface and structural properties are needed to achieve high anti-fouling properties without compromising flux performance. Measured fouling densities on the studied surfaces suggest that there is not a strong correlation between foulant-membrane interaction and fouling density. Cleaning results suggest that physical cleaning was more efficient on the CTA membrane compared to the TFC membrane. Further, they implied that despite diff
De Luca H, Anthony DB, Qian H, et al., 2016, Non-damaging and scalable carbon nanotube synthesis on carbon fibres, ECCM17 - 17th European Conference on Composite Materials
The growth of carbon nanotubes (CNTs) on carbon fibres (CFs) to produce a hierarchical fibre with two differing reinforcement length scales, in this instance nanometre and micrometre respectively, is considered a route to improve current state-of-the-art fibre reinforced composites [1]. The scalable production of carbon nanotube-grafted-carbon fibres (CNT-g-CFs) has been limited due to high temperatures, the use of flammable gases and the requirement of inert conditions for CNT synthesis, whist (ideally) maintaining underlying original substrate mechanical properties. Here, the continuous production of CNT-g-CF is demonstrated in an open chemical vapour deposition (CVD) reactor, crucially, whilst retaining the tensile properties of the carbon fibres. As synthesised CNTs have a diameter of sub 20 nm and length ca. 120 nm, which are predicted to provide ideal fibre reinforcement in composites by retaining optimal composite fibre volume fraction (60%), whilst improving interfacial bonding of the matrix and reinforcement [1, 2]. Mild processing techniques enable this modified CVD process to be fully compatible with industrial practices, and have the potential to generate large volumes of hierarchical CNT-g-CF material.
Anthony DB, Grail G, Bismarck A, et al., 2016, Exploring the tensile response in small carbon fibre composite bundles, ECCM17 - 17th European Conference on Composite Materials
Small composite bundles, AS4 carbon fibre epoxy, with a restricted number of reinforcing fibres, ca. 20, showed a progressive failure when tested in tension. In-situ acoustic emission observations under tensile load reveal that numerous fibres fail before ultimate failure of the small composite bundle, suggesting that isolated and individual fibre failures occur without compromising the integrity of the neighboring fibres or the small composite bundle’s overall mechanical performance. The average strength of the carbon fibres in small composite bundles was 9.6% higher than in standard lab-scale composite specimens using the same fibre type.
Mautner A, Maples HA, Kobkeatthawin T, et al., 2016, Phosphorylated nanocellulose papers for copper adsorption from aqueous solutions, International Journal of Environmental Science and Technology, Vol: 13, Pages: 1861-1872, ISSN: 1735-2630
Copper is a major problem in industrial wastewater streams, seriously affecting the quality of potential drinking water. Several approaches, including continuous membrane processes or batch-wise application of adsorbents, are in use to tackle this problem. Unfortunately, these processes suffer from their particular drawbacks, such as low permeance or disposal of saturated adsorbents. However, a combination of these processes could constitute a step towards a more efficient copper removal solution. Here, we present a nanopaper ion-exchanger prepared from cellulose nanofibrils produced from fibre sludge, a paper industry waste stream, for the efficient, continuous removal of copper from aqueous solutions. This nanopaper ion-exchanger comprises phosphorylated cellulose nanofibrils that were processed into nanopapers by papermaking. The performance of these phosphorylated nanopaper membranes was determined with respect to their rejection of copper and permeance. It was shown that this new type of nanopaper is capable of rejecting copper ions during a filtration process by adsorption. Results suggest that functional groups on the surface of the nanopapers contribute to the adsorption of copper ions to a greater extent than phosphate groups within the bulk of the nanopaper. Moreover, we demonstrated that those nanopaper ion-exchangers could be regenerated and reused and that in the presence of calcium ions, the adsorption capacity for copper was only slightly reduced.
Blaker JJ, Anthony DB, Tang G, et al., 2016, Property and shape modulation of carbon fibers using lasers, ACS Applied Materials & Interfaces, Vol: 8, Pages: 16351-16358, ISSN: 1944-8244
An exciting challenge is to create unduloid-reinforcing fibers with tailored dimensions to produce synthetic composites with improved toughness and increased ductility. Continuous carbon fibers, the state-of-the-art reinforcement for structural composites, were modified via controlled laser irradiation to result in expanded outwardly tapered regions, as well as fibers with Q-tip (cotton-bud) end shapes. A pulsed laser treatment was used to introduce damage at the single carbon fiber level, creating expanded regions at predetermined points along the lengths of continuous carbon fibers, whilst maintaining much of their stiffness. The range of produced shapes was quantified and correlated to single fiber tensile properties. Mapped Raman spectroscopy was used to elucidate the local compositional and structural changes. Irradiation conditions were adjusted to create a swollen weakened region, such that fiber failure occurred in the laser treated region producing two fiber ends with outwardly tapered ends. Upon loading the tapered fibers allow for viscoelastic energy dissipation during fiber pull-out by enhanced friction as the fibers plough through a matrix. In these tapered fibers, diameters were locally increased up to 53%, forming outward taper angles of up to 1.8°. The tensile strength and strain to failure of the modified fibers were significantly reduced, by 75% and 55%, respectively, ensuring localization of the break in the expanded region; however, the fiber stiffness was only reduced by 17%. Using harsher irradiation conditions, carbon fibers were completely cut, resulting in cotton-bud fiber end shapes. Single fiber pull-out tests performed using these fibers revealed a 6.75 fold increase in work of pull-out compared to pristine carbon fibers. Controlled laser irradiation is a route to modify the shape of continuous carbon fibers along their lengths, as well as to cut them into controlled lengths leaving tapered or cotton-bud shapes.
Maples HA, Smith O, Burgstaller C, et al., 2016, Improving the ply/interleaf interface in carbon fibre reinforced composites with variable stiffness, Composites Science and Technology, Vol: 128, Pages: 185-192, ISSN: 0266-3538
Polystyrene-interleaved carbon fibre reinforced epoxy composites exhibiting controllable stiffness have been manufactured. These composites undergo reductions in flexural stiffness of up to 99% when heated above the glass transition temperature Tg of the interleaf layers. Potential applications for such materials include their use in morphing and deployable structures. Flexural tests at room temperature indicated that improvements in adhesion between the polystyrene and CFRP layers are required to prevent premature failure of the composites at low shear stresses. Here we investigate how modification of the interleaf layer improves the interlaminar shear strength of the laminates without affecting the stiffness loss at elevated temperatures. Two poly(styrene-co-maleic anhydride) (SMA) films with different maleic anhydride content were prepared and used as interleaf films. Thick adherend shear tests showed that the adhesion strength more than doubled, while flexural tests showed that composites containing SMA interleafs had more than twice the apparent flexural strength of composites containing pure polystyrene layers at 25 °C and yet still undergo significant reductions in stiffness at elevated temperature.
Herceg TM, Abidin MSZ, Greenhalgh ES, et al., 2016, Thermosetting hierarchical composites with high carbon nanotube loadings: en route to high performance, Composites Science and Technology, Vol: 127, Pages: 134-141, ISSN: 0266-3538
A wet powder impregnation route to manufacture carbon fibre reinforced thermoplastic composites was adapted to accommodate thermosetting matrices reinforced with high fractions (20 wt%/13.6 vol%) of multiwalled carbon nanotubes (CNTs). The produced carbon fibre prepregs were consolidated into laminates with fibre volume fractions of 50–58% and up to 6.1 vol% CNTs. Microscopic imaging confirmed successful consolidation at intermediate CNT loadings, but some voidage at the highest CNT loading due to the highly viscoelastic uncured matrix. Nonetheless, through-thickness electrical conductivity and Mode I interlaminar fracture toughness were enhanced by as much as 152% and 24% to unprecedented values of σ = 53 S m−1 and GIC = 840 J m−2, respectively. Fractographic characterisation indicated that crack deflection was the mechanism responsible for the improved fracture toughness. The material properties were shown to be strongly dependent on the microstructure of the matrix.
Diao H, Robinson P, Wisnom MR, et al., 2016, Unidirectional carbon fibre reinforced polyamide-12 composites with enhanced strain to tensile failure by introducing fibre waviness, Composites Part A: Applied Science and Manufacturing, Vol: 87, Pages: 186-193, ISSN: 1359-835X
Unidirectional (UD) carbon fibre reinforced polymers offer high specific strength and stiffness but they fail in a catastrophic manner with little warning. Gas-texturing and non-constrained annealing were used to introduce fibre waviness into UD polyamide 12 composites produced by wet-impregnation hoping to produce composites with a more gradual failure mode and increased failure strain. Both methods increased the variation of fibre alignment angle compared to the control samples. The composites containing wavy fibres exhibited a stepwise, gradual failure mode under strain controlled uniaxial tension rather than a catastrophic failure, observed in control samples. Gas-texturing damaged the fibres resulting in a decrease of the tensile strength and strain to failure, which resulted in composites with lower tensile strength and ultimate failure strain than the control composites. Non-constrained annealing of carbon fibre/PA-12 produced wavy fibre composites with ultimate failure strain of 2%, significantly higher than 1.6% of the control composite.
Ferguson A, Khan U, Walsh M, et al., 2016, Understanding the dispersion and assembly of bacterial cellulose in organic solvents, Biomacromolecules, Vol: 17, Pages: 1845-1853, ISSN: 1526-4602
The constituent nanofibrils of bacterial cellulose are of interest to many researchers because of their purity and excellent mechanical properties. Mechanisms to disrupt the network structure of bacterial cellulose (BC) to isolate bacterial cellulose nanofibrils (BCN) are limited. This work focuses on liquid-phase dispersions of BCN in a range of organic solvents. It builds on work to disperse similarly intractable nanomaterials, such as single-walled carbon nanotubes, where optimum dispersion is seen for solvents whose surface energies are close to the surface energy of the nanomaterial; bacterial cellulose is shown to disperse in a similar fashion. Inverse gas chromatography was used to determine the surface energy of bacterial cellulose, under relevant conditions, by quantifying the surface heterogeneity of the material as a function of coverage. Films of pure BCN were prepared from dispersions in a range of solvents; the extent of BCN exfoliation is shown to have a strong effect on the mechanical properties of BC films and to fit models based on the volumetric density of nanofibril junctions. Such control offers new routes to producing robust cellulose films of bacterial cellulose nanofibrils.
Ferrer J, Bismarck A, Menner A, 2016, 3D-printed macroporous materials, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Kamal NAM, Lee K-Y, Bismarck A, 2016, Bovine biomass based microfibrillated cellulose composites, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Mautner A, Li K, Bismarck A, 2016, Cellulose nanopapers as ion-exchangers for nitrate and heavy metal removal, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Wanasekara N, Zhu C, Eichhorn S, et al., 2016, Molecular deformation in high performance cellulose fibres, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Hakalahti M, Mautner A, Hanninen T, et al., 2016, Cellulose nanofibrils as templates for stimuli-responsive membrane materials, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Lee K, bismarck A, 2016, Single step functionalization of celluloses with differing degrees of reactivity as a route for in situ production of all-cellulose nanocomposites, Nanocomposites, Vol: 1, Pages: 214-222, ISSN: 2055-0332
A method of manufacturing all-cellulose nanocomposites using a single-step functionalization of two different celluloses with differing reactivities is presented. All-cellulose nanocomposites are produced by esterification of microcrystalline cellulose (MCC) in pyridine with hexanoic acid in the presence of bacterial cellulose (BC) followed by solvent removal. Neat MCC is more susceptible to esterification, with an accessible amount of hydroxyl groups of 1.79 compared to BC, with an accessible hydroxyl group content of 0.80. As a result, neat MCC undergoes severe bulk modification, turning into a toluene-soluble cellulose hexanoate (C6-MCC) while BC undergoes surface-only modification. Solution casted C6-MCC films have a tensile modulus and strength of 0.99 GPa and 23.1 MPa, respectively. The presence of 5 wt.% BC in C6-MCC leads to an increase in tensile modulus and strength of the resulting nanocomposites to 1.42 GPa and 28.4 MPa, respectively.
Le Brun N, Markides, Bismarck, et al., 2016, On the drag reduction effect and shear stability of improved acrylamide copolymers for enhanced hydraulic fracturing, Chemical Engineering Science, Vol: 146, Pages: 135-143, ISSN: 0009-2509
Polymeric drag reducers, such as partially hydrolysed polyacrylamide (PHPAAm), are important chemical additives in hydraulic fracturing fluids as they can significantly decrease the frictional pressure drop in the casing (by up to 80%),resulting in an increase of the injection rate that can be delivered to the fracturing point. The incorporation of sodium 2-acrylamido-2-methylpropane sulfonic acid (NaAMPS) moieties in to polyacrylamide (PAAm) can further improve the performance of fracturing fluids by addressing some compatibility issues related to the use of PHPA Am, e.g., the sensitivity to water salinity . In this study, three types of poly(acrylamide-co-NaAMPS) and pure PHPAAm were investigated with respect to polymer induced drag reduction and mechanical polymer degradationin turbulent pipe flow in a pressure-driven pipe flow facility. The test section comprised a horizontal 1” bore circular cross-section pipe. The facility was modified in order to allow, long time/length experiments by automatically recirculating the polymer solution in a closed-loop through the test section.The presence of NaAMPS groups in the copolymer backbone is found to increase the ability of PHPAAm to reduce frictional drag while the vulnerability to mechanical degradation remains unaffected. The drag reduction of NaAMPS copolymer solutions can be described by a modified version of Virk’s correlation (1967), extended to include the effect of Reynolds number. Polymer mechanical degradation is found to proceed until the friction reducer is almost ineffective in reducing drag. This phenomenon is in contrast with the most common correlationfor polymer degradation, which predicts the existence of a n asymptotic(but finite) limit to the reduced drag reduction.
Herceg TM, Yoon S-H, Abidin MSZ, et al., 2016, Thermosetting nanocomposites with high carbon nanotube loadings processed by a scalable powder based method, Composites Science and Technology, Vol: 127, Pages: 62-70, ISSN: 0266-3538
A powder based processing route was developed to allow manufacturing of thermosettingnanocomposites with high (20 wt%) carbon nanotube (CNT) loading fractions. Adaptation ofhigh shear mixing methods, as used in thermoplastic processing, ensured that the CNTs werewell distributed and dispersed even at the highest loadings. By minimising flow distances,compression moulding of powders ensured that the CNTs did not agglomerate duringconsolidation, and yielded a percolated CNT network in a nanocomposite with excellentelectrical and thermal conductivities of 67 S m-1and 0.77 W m-1 K-1, respectively. Unusually,the CNTs provided effective mechanical reinforcement at even the highest loadings;embrittlement is minimised by avoiding large scale inhomogeneities and the maximummeasured Young’s modulus (5.4 GPa) and yield strength (90 MPa) could make thenanocomposite an attractive matrix for continuous fibre composites. The macromechanicalmeasurements were interpolated using micromechanical models that were previouslysuccessfully applied at the nanoscale.
Hakalahti M, Mautner A, Johansson L-S, et al., 2016, Direct Interfacial Modification of Nanocellulose Films for Thermoresponsive Membrane Templates, ACS APPLIED MATERIALS & INTERFACES, Vol: 8, Pages: 2923-2927, ISSN: 1944-8244
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Woodward RT, Fam DWH, Anthony DB, et al., 2016, Hierarchically porous carbon foams from pickering high internal phase emulsions, Carbon, Vol: 101, Pages: 253-260, ISSN: 0008-6223
Carbon foams were produced from a macroporous poly(divinylbenzene) (poly(DVB) precursor, synthesized by polymerizing the continuous but minority phase of water-in-oil high internal phase emulsions (HIPEs) stabilized by molecular and/or particulate emulsifiers. Both permeable and non-permeable hierarchically porous carbon foams, or ‘carboHIPEs’, were prepared by carbonization of the resulting macroporous polymers at 800 °C. The carbon yields were as high as 26 wt.% of the original polymer. CarboHIPEs retain the pore structure of the macroporous polymer precursor, but with surface areas of up to 505 m2/g and excellent electrical conductivities of 81 S/m. Contrary to some previous reports, the method does not require further modification, such as sulfonation or additional crosslinking of the polyHIPE prior to carbonization, due to the inherently crosslinked structure of poly(DVB). The use of a pourable, aqueous emulsion-template enables simple moulding, minimises waste and avoids the strong acid treatments used to remove many conventional solid-templates. The retention of the macroporous structure is coupled with the introduction of micropores during carbonization, producing hierarchically porous carboHIPEs, suitable for a wide range of applications as sorbents and electrodes.
Zubairi SI, Mantalaris A, Bismarck A, et al., 2016, Polyhydroxyalkanoates (PHAs) for tissue engineering applications: biotransformation of palm oil mill effluent (POME) to value-added polymers, Jurnal Teknologi, Vol: 78, Pages: 13-29, ISSN: 0127-9696
The study of cancer cell has been hindered by the lack of appropriate ex vivo models, which can mimic this microenvironment. It is hypothesized that the fabrication of porous 3-D scaffolds for the biomimetics growth of cancer cells ex vivo could facilitate the study of the disease in its native 3-D niche. For that reason, biomaterials are used for fabrication of 3-D scaffold, in general, may be natural polymers such as proteins, collagens and gelatin, or synthetic biopolymers. Among the various available biodegradable polymers, polyhydroxyalkanoates (PHAs) have gained significant interest as one of the value-added materials which can be synthesized from abundantly available source of palm oil mill effluent (POME). Down the group of the PHA, poly-3-hydroxybutyrate (PHB) and copolymerizing this PHB that produced PHBVs; these two polymers have the most prevalent polymer used for scaffolds fabrication. A physico-chemical and biological modification has developed to improve wetting, adhesion, and printing of polymer surfaces, generally by introducing a variety of polar groups. These techniques must be tailored to introduce a specific functional group when the surface modification is a precursor to attach a bioactive compound. There are a few methods in order to fabricate porous 3-D scaffolds such as solvent casting, particulate leaching, thermally induced phase separation, gas forming, fiber bonding, electrospinning and also solid free form method. A review of the polyhydroxyalkanoates (PHAs) for tissue engineering applications is presented, beginning with the basic naturally derived polymerization of PHAs, biotransformation of palm oil mill effluent (POME) to the value-added polymers, novel methods of scaffold fabrication capabilities and its physico- chemical and biological surface modifications to increase cell-biomaterial affinity.
Robinson P, Zhang B, Bismarck A, et al., 2016, Interleaving for easy repair of interlaminar damage - Can it be done?
An easy-repair laminate concept is investigated to address the repair problem posed by interlaminar damage due to impact. A carbon epoxy laminate interleaved with PLA is shown to preferentially fail in shear within the interleaf. Good strength recovery is achieved when the laminate is heated and subjected to external pressure.
Lee WJ, Clancy AJ, Kontturi E, et al., 2016, Nanocellulose/poly vinyl alcohol fibres : A green renewable high performance composite
© 2016, European Conference on Composite Materials, ECCM. All rights reserved.Cellulose nanocrystals (CNC) are promising candidates as stiff fillers in green, renewable, high performance composites, owing to their intrinsic high strength and stiffness. However, historically CNC materials have had low mechanical properties due to CNC aggregation, poor alignment, and low loading fractions. Here, high loadings of water-soluble CNCs are well dispersed in poly vinyl alcohol (PVOH) to form coagulation spinning dopes for composite fibres. The final fibres contain high CNC loading (up to 60 wt. %) while mechanical behaviour is heavily dependent on CNC loading, with tensile strengths approaching the GPa scale at high loadings. The alignment and crystallinity of CNCs and PVOH along the fibre axis was measured by 2D X-ray scattering to account for these differences. This work provides a possible strategy to the challenging question of preparing practical, high performance, green and renewable composites.
Mautner A, Lee KY, Wan Nawawi WMF, et al., 2016, Cellulose nanopaper composites: Influence of nanopaper characteristics on composite properties
Nanocellulose, cellulose in the form of nanofibrils (CNF), has gained considerable attention in recent years as reinforcement agent for the production of composite materials due to its excellent mechanical and chemical properties, with the Young's modulus even outperforming glass fibres. One promising approach to produce nanocomposites based on nanocellulose is to utilize nanopapers as reinforcement in laminated composites, enabling better exploitation of the outstanding mechanical properties of CNF compared to composites in which CNF are introduced in a different way. Accordingly, the characteristics of the nanopapers also influence the properties of the composites. One parameter that is anticipated to influence the final properties of composites a lot is the porosity of the nanopaper employed. A low porosity shows high resistance for the resin to enter into the nanopaper structure hence resulting in lower mechanical properties as potentially possible. Our approach was to alter the porosity of the nanopapers by solvent-exchanging the CNF suspension with different types of organic solvents prior to papermaking to allow for a better infiltration of the resin.
Lee KY, Bismarck A, 2016, Single step functionalisation of celluloses with differing degrees of reactivity as a route for in-situ production of all-cellulose nanocomposites
A method of manufacturing all-cellulose nanocomposites using a single step functionalisation of two different celluloses with differing reactivities is presented. All-cellulose nanocomposites are produced by esterification of microcrystalline cellulose (MCC) in pyridine with hexanoic acid in the presence of bacterial cellulose (BC) followed by solvent removal. Neat MCC is more susceptible to esterification. As a result, neat MCC undergoes severe bulk modification, turning into a toluene-soluble cellulose hexanoate (C6-MCC) whilst BC undergoes surface-only modification. The solution casted C6-MCC films have a tensile modulus and strength of 0.99 GPa and 23.1 MPa, respectively. The presence of 5 wt.-% BC in C6-MCC leads to an increase in tensile modulus and strength of the resulting nanocomposites to 1.42 GPa and 28.4 MPa, respectively.
De Luca F, Bismarck A, Shaffer MSP, 2016, Anisotropic nanostructure inspired by nature for energy abosrbing composite interfaces
The "brick-and-mortar" structure of natural nacre is well known for its combination of high stiffness, strength and toughness thanks to well organised hard inclusions, experiencing pull-out within a soft organic matrix rather than fracture upon loading. Mimicking the structure of nacre while maintaining the same phase proportions and aspect ratio, but at a smaller length scale, opens up the possibility to create composite materials with high performance and large energy absorption properties through interface deformation. Therefore, Layered Double Hydroxide (LDH) nanoplatelets and poly(sodium 4-styrene sulfonate) (PSS) polylelectrolyte were assembled together with a high degree of alignment using Layer-by-Layer (LbL) assembly, resulting in a dense and well organized nanostructure similar to that of nacre. The mechanical properties of the nacre-nanomimetics were comparable to those of natural nacre while the plastic deformation was found amplified. The amplification of the proportion of plastic deformation can be explained by an increase in the volume of platelet interfaces per unit volume at the nanometer length scale. The known toughening mechanisms of nacre, such as platelet sliding and interlocking as well as crack deflection, were also found to occur in the reduced length scale embodiment.
Maples HA, James T, Bismarck A, 2016, Manufacturing high performance composites using solid epoxy resins
We aim to lower the cost of composite manufacturing by formulating solid epoxy resins. Cured solid epoxies are typically used as protective coatings e.g. in marine applications, and are in general much cheaper than the liquid epoxy resins used in composite production. The development of a cost effective composite manufacturing technique using cheaper starting materials, such as solid epoxy resins, will increase the likelihood of composite uptake in sectors where cost and feasibility have previously limited their adoption. Powdered, uncured solid epoxy resins were formulated by mixing solid epoxies, hardeners and accelerators at elevated temperature. The resulting mixtures were then ground into powders that were applied directly onto carbon fibres. The fibres were then heated, infused with the melted resin system and subsequently cured. The following laminates have competitive mechanical properties when compared against other high performance composites. The laminates have a flexural strength and modulus of 919 MPa and 70 GPa, respectively. Using the same fibre format with a liquid epoxy resin results in a composite with a flexural strength and stiffness of 940 MPa and 80 GPa, respectively. Demonstrator 3D composite panels have been produced showing that is possible to mould the laminates during manufacturing.
Lee WJ, Clancy AJ, Kontturi E, et al., 2016, Nanocellulose/poly vinyl alcohol fibres : A green renewable high performance composite
Cellulose nanocrystals (CNC) are promising candidates as stiff fillers in green, renewable, high performance composites, owing to their intrinsic high strength and stiffness. However, historically CNC materials have had low mechanical properties due to CNC aggregation, poor alignment, and low loading fractions. Here, high loadings of water-soluble CNCs are well dispersed in poly vinyl alcohol (PVOH) to form coagulation spinning dopes for composite fibres. The final fibres contain high CNC loading (up to 60 wt. %) while mechanical behaviour is heavily dependent on CNC loading, with tensile strengths approaching the GPa scale at high loadings. The alignment and crystallinity of CNCs and PVOH along the fibre axis was measured by 2D X-ray scattering to account for these differences. This work provides a possible strategy to the challenging question of preparing practical, high performance, green and renewable composites.
Zhang B, Robinson P, Bismarck A, et al., 2016, Modelling the shape memory capability of an interleaved composite
A composite, consisting of carbon fibre reinforced epoxy laminae and polystyrene interleaf layers, has been developed which exhibits controllable stiffness and a shape memory capability upon heating. This paper investigates finite element modelling of the shape memory capability of this composite. Such modelling could be useful in the design of deployable structures made of this shape memory composite.
Bismarck A, Maples HA, Tridech C, et al., 2016, Controllable stiffness composites: An overview
Composites with controllable stiffness have a number of potential applications including their use as skin materials in morphing aerostructures. Much work has focused on the development of such materials, which are required to withstand aerodynamic loads but also deform on demand at relatively low actuation forces. We provide an overview of the work carried out at Imperial College London on the development of high performance controllable stiffness composites. Two composite designs were explored, 1) composites containing thermoplastic interphases and 2) composites containing thermoplastic interleaf layers. Large reductions in stiffness of up to 99% were achieved when the composites were heated above the glass transition temperatures of the polymer interphase or interleaf layer. At these temperatures the composites could be deformed significantly and would retain their shape when cooled to room temperature. The process was completely reversible as the composites would return to their original configuration when reheated without an applied load. Self-deploying structures have also been manufactured from the controllable stiffness materials using the shape memory effect of the composites.
Menner A, Jiang Q, Bismarck A, 2016, Spring elements for rewod energy harvesters: Printing emulsion templates to manufacture macroporous polymers
We aim to develop an energy harvesting device that allows charging a battery of e.g. a smart phone while jogging simply by converting mechanical energy into electrical energy using the "REWOD" (Reverse-Electrowetting-On-Dielectric) effect. A vital part of such an energy harvester are highly interconnected and flexible macroporous polymer springs which are required to improve the harvesting efficiency. We use emulsion templates as inks and syringe print them on the harvester's dielectric in any desired shape and dimension (e.g. cages having dimensions ranging from 2mm x2mm down to 0.5mmx0.5mm which are up to 400 μm high). UV-polymerisation of the polyurethane diacrylate/ethylhexyl acrylate based continuous phase of the emulsion templates and subsequent removal of the internal phase yields in highly flexible macroporous polymer springs: cyclic compression tests confirmed that they can repeatedly be compressed by 70% without experiencing permanent plastic deformation. Furthermore, we will present a REWOD energy harvesting prototype achieving a capacity change of up to 1000pF upon mechanical deformation.
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