Browsing by Author "Mitchell, Geoffrey"
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- Adaptive Platforms and Flexible Deposition System for Big Area Additive Manufacturing (BAAM)Publication . Silva, Ruben; Sereno, Pedro; Mateus, Artur; Mitchell, Geoffrey; José da Silva Carreira, Pedro; Santos, Cyril; Vitorino, João; Domingues, JorgeThe interest around the additive manufacturing is increasing, with more and more solutions at both the industrial and desktop levels. As this is still a relatively recent issue for several industrial areas, there is a clear opportunity to explore in order to optimize the systems in the face of the needs of these same industries, and with increasing times, there are increasing factors to take into ac- count in initial phases of new product development. Presently, there is also a growing ecological awareness, with the concern of implementing a logic of waste reduction and implementation of the circular economy in new products with a view to the valuation of new alternative materials. With the development of solutions aimed at the optimization and feasibility of large additive manufacturing systems, the introduction of new alternative materials will be a reality, presenting in this article a solution and methodology for future tests for new materials. Thus, herein is studied a way of responding to both problems, new ecological materials and BAAM system optimization, presented through a hybrid and flexible solution based on the Pin Bed Forming principle applied to Big Area Additive Manufacturing systems.
- Carbon nanotubes in electrospun polyethylene oxide nanofibres: A potential route to conducting nanofibresPublication . Nazhipkyzy, M; Mohan, S D; Davis, F J; Mitchell, GeoffreyPolyethylene oxide solution containing multi-walled carbon nanotubes have been electrospun onto a rotating collector to produce highly aligned arrays of electrospun nanofibers ranging in diameters from (200 - 360) nanometres. The addition of a surfactant (Triton X-100) is highly effective in dispersing carbon nanotube within an aqueous solution of polyethylene oxide and the resulting mixture can be electrospun without excessive clumping to produce nanofibers containing high loadings of nanotubes; in this case up to 5% wt thereby providing an effective route to electrically conductive nanofibres.
- Controlling Morphology Using Low Molar Mass NucleatorsPublication . Mitchell, Geoffrey; Wangsoub, Supatra; Nogales, Aurora; Davis, Fred J.; Olley, Robert H.Crystallisation is a hugely important process in physical sciences and is crucial to many areas of, for example, chemistry, physics, biochemistry, metallurgy and geology. The process is typically associated with solidification, for example in the purification of solids from a heated saturated solution familiar to all chemistry undergraduates. Crystalline solids are also often the end result of cooling liquids, or in some cases gases, but in order to form require nucleation, in the absence of nucleation supercoiling of liquids well below the melting point is possible (Cava-gna, 2009). The quality of crystals, as gauged by size and levels of order is highly variable, and may depend on factors such as material purity and the rate of cool-ing; rapid cooling may result in poor crystallisation, or even the formation of amorphous materials with no long range order. In geological systems rates of cooling may vary over many orders of magnitude, for example obsidian is a large-ly amorphous material produced when lava is rapidly cooled (Tuffen, 2003), while the gypsum crystals found in the Cueva de los Cristales in Chihuahua, Mexico can reach 10 metres in length (Figure 1) and are formed over hundreds of thousands of years. In this latter case the formation of such large spectacular structures as shown in Figure 1 can only be explained by a low nucleation rate (García-Ruiz, 2007; Van Driessche, 2011).
- Crosslinked nanocomposite sodium alginate-based membranes with titanium dioxide for the dehydration of isopropanol by pervaporationPublication . Premakshi, P. G.; Kariduraganavar, Mahadevappa Y.; Mitchell, GeoffreySodium alginate (NaAlg) based membranes were prepared using a solution technique, crosslinked with poly(styrene sulfonic acid-co-maleic acid) (PSSA-co-MA). Subsequently, the membranes were modified by the incorporation of 0, 10, 20, 30 and 40% w/w of titanium dioxide with respect to sodium alginate. The membranes thus obtained were designated as M, M-1, M-2, M-3 and M-4, respectively. An equilibrium swelling experiment was performed using dfferent compositions of the water and isopropanol mixtures. Subsequently, we used a pervaporation cell fitted with each membrane in order to evaluate the extent of the pervaporation dehydration of isopropanol. Among the membranes studied, the membranes containing 40 mass% of titanium dioxide exhibited the highest separation factor() of 24,092, with a flux(J) of 18.61x10-² kg/m².h at 30ºC for 10 mass%w/w of water in the feed. The total flux and the flux of water were found to overlap with each other, indicating that these membranes can be e ectively used to break the azeotropic point of water–isopropanol mixtures. The results clearly indicate that these nanocomposite membranes exhibit an excellent performance in the dehydration of isopropanol. The activation energy values obtained for the water permeation were significantly lower than those of the isopropanol permeation, underlining that these membranes have a high separation ability for the water isopropanol system. The estimated activation energies for total permeation (EP) and total di usion (ED) values ranged between 10.60 kJ.mol-¹ and 3.96 kJ.mol-¹, and 10.76 kJ.mol-¹ and 4.29 kJ.mol-¹, respectively. The negative change in the enthalpy values for all the membranes indicates that sorption was mainly dominated by Langmuir’s mode of sorption.
- Design, synthesis and thermo‑chemical properties of rosin vinyl imidazolium based compounds as potential advanced biocompatible materialsPublication . Zaoui, Aniss; Mahendra, Vidhura; Mitchell, Geoffrey; Cherifi, Zakaria; Harrane, Amine; Belbachir, MohammedRosin is a natural material extracted from the pine tree that is vastly used as an adhesive in the construction industry. It chemically consists of cyclic carboxylic structure that is known as rosin acids or abietic acid and other isomers. The abietic acid or/and its isomers can structurally be altered to design for different applications. Herein we envisage the potentials of altering the rosin structure to investigate its thermal and physicochemical properties for advanced material applications. In this regard we have utilised the potassium rosinate (rosin soap) also known as the saponified rosin. Saponified rosin is reacted through an anion exchange metathesis process promoted by ultrasound, with either an ionic liquid or a poly(ionic liquid), namely the 3-octyl-1-vinylimidazolium bromide and the poly (3-octyl-1-vinylimidazolium bromide) as a scope to improve thermal and mechanical applications. The structures of these new compounds were determined using fourier transform infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance spectroscopy (NMR). The rosin/ionic liquid based compound found to be a better fitting candidate for advanced material applications, due to significant improvement in the thermal stability compared to the crude rosin (up to 70 °C raise in the thermal degradation) and promising mechanical characters such as elasticity and malleability.
- Development of composite anion-exchange membranes using poly(vinyl alcohol) and silica precursor for pervaporation separation of water–isopropanol mixturesPublication . Premakshi, H. G.; Kariduraganavar, M. Y.; Mitchell, GeoffreyComposite anion-exchange membranes were prepared using sol-gel techniques with poly(vinyl alcohol) (PVA) and anion-exchange silica precursor (AESP). Ammonium functionality was created on the AESP through a ring opening reaction between 2-(3-aminoethylamino)propyltrimethoxysilane and glycidyltrimethylammonium chloride under mild heating conditions. The resulting membranes were subjected to physico-chemical investigations using various techniques. The pervaporation performance of the membranes was systematically investigated based on the effects of feed composition and the mass% of AESP. Among the membranes studied, the membranes containing 4 mass% of AESP exhibited the highest separation factor of 2,991 with a flux of 10.76 × 10-2 kg/m2h at 30 °C for 10 mass% of water in the feed. The trade-off phenomenon which exists between the flux and the separation factors was overcome by the incorporation of AESP in PVA matrix. We find that the overlap between the total flux and flux of water, suggests that these membranes could be used effectively to break the azeotropic point of water-isopropanol mixtures. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The Ep and ED values ranged between 18.36 and 7.94, and 18.68 and 8.09 kJ/mol, respectively. The negative heat of sorption ( Hs) values was obtained for all the membranes, indicating that Langmuir’s mode of sorption is predominant in the transport process.
- Development of novel 3D scaffolds using BioExtruder by varying the content of hydroxyapatite and silica in PCL matrix for bone tissue engineeringPublication . Pattanashetti, Nandini A.; Viana, Tânia; Alves, Nuno; Mitchell, Geoffrey; Kariduraganavar, Mahadevappa Y.Polycaprolactone (PCL) is considered as a most widely used biodegradable polymers in tissue engineering. But, PCL is also associated with certain limitations like, low stiffness, hydrophobic nature and limited cell affinity. These drawbacks are addressed in the present study by incorporating different wt% of silicon dioxide (SiO2) and hydroxyapatite (HAp) in the PCL matrix. 3D scaffolds were developed using a novel BioExtruder. The physicochemical properties, thermal stability and wettability of the composite scaffolds were studied systematically. Optical and Scanning Electron Microscopic images were analysed for morphological evaluation of the scaffolds. The pore size of the developed scaffolds increased from 290 to 315 μmwith increasing SiO2 content, as examined by scanning electron microscope. An improved compressive modulus of 68.82 MPa was observed for 15 wt% SiO2 incorporated composite scaffold. The in-vitro degradation study of the composite scaffolds demonstrated an increase in the degradation rate for PCL/HAp scaffolds, while no significant change was observed for SiO2 incorporated scaffolds. Further, the cytotoxicity and cell proliferation studies were carried out using L929 Mouse Fibroblasts and MG-63 Osteoblasts respectively. The developed scaffolds revealed no toxic effects towards the cellular response and an increase in cell proliferation of ≥90% was observed during 7 days of cell culture. Thus, the scaffolds were proved to be potential candidate for bone tissue engineering application, particularly the scaffold with 10 wt% SiO2 incorporation into PCL/HAp (75/15) composite has resulted into higher cell proliferative % and improved mechanical strength.
- Direct Digital Manufacturing and PolymersPublication . Mitchell, Geoffrey; Alves, Nuno; Mateus, Artur Jorge dosPreface: This special issue contains selected papers presented at the second edition of the International Conference on Direct Digital Manufacturing and Polymers held in Marinha Grande, Portugal. The conference is heldbiannually and takes place in India(University of Karnatak)and Portugal(Institute Polytechnic of Leiria)on an alternating basis. In 2017 was held in Marinha Grande, an important industrial area of Portugal and home of the Centre for Rapid and Sustainable Product Development, Institute Polytechnic of Leiria. The conference coincided with the 10thanniversary of the foundation of the Centre and a special celebratory gala dinner was held at the Hotel Mar e Sol. Director of the Centre, Professor Nuno Alvespresented to ProfessorPramod Gai, the Vice-Chancellorthe University of Karnatak, the “International Institutional Collaborator2017” award. Other awardswere presented and the Director, Professor Alves acknowledged the strong support received by CDRSP from the President of the Marinha Grande MunicIpality.
- Fabrication of Poly(𝜀-caprolactone) Scaffolds Reinforced with Cellulose Nanofibers, with and without the Addition of Hydroxyapatite NanoparticlesPublication . Morouço, Pedro; Biscaia, Sara; Viana, Tânia; Franco, Margarida; Pereira Malça, Cândida Maria dos Santos; Mateus, Artur; Monteiro de Moura, Carla Sofia; Ferreira, Frederico C.; Mitchell, Geoffrey; Alves, Nuno M.Biomaterial properties and controlled architecture of scaffolds are essential features to provide an adequate biological and mechanical support for tissue regeneration, mimicking the ingrowth tissues. In this study, a bioextrusion system was used to produce 3D biodegradable scaffolds with controlled architecture, comprising three types of constructs: (i) poly(𝜀-caprolactone) (PCL) matrix as reference; (ii) PCL-based matrix reinforced with cellulose nanofibers (CNF); and (iii) PCL-based matrix reinforced with CNF and hydroxyapatite nanoparticles (HANP). The effect of the addition and/or combination of CNF and HANP into the polymeric matrix of PCL was investigated, with the effects of the biomaterial composition on the constructs (morphological, thermal, and mechanical performances) being analysed. Scaffolds were produced using a single lay-down pattern of 0/90∘, with the same processing parameters among all constructs being assured. The performed morphological analyses showed a satisfactory distribution of CNF within the polymer matrix and high reliability was obtained among the produced scaffolds. Significant effects on surface wettability and thermal properties were observed, among scaffolds. Regarding the mechanical properties, higher scaffold stiffness in the reinforced scaffolds was obtained. Results from the cytotoxicity assay suggest that all the composite scaffolds presented good biocompatibility.The results of this first study on cellulose and hydroxyapatite reinforced constructs with controlled architecture clearly demonstrate the potential of these 3D composite constructs for cell cultivation with enhanced mechanical properties.
- Green nanocomposites from rosin-limonene copolymer and algerian clayPublication . Derdar, Hodhaifa; Mitchell, Geoffrey; Mahendra, Vidhura; Benachour, Mohamed; Haoue, Sara; Cherifi, Zakaria; Bachari, Khaldoun; Harrane, Amine; Meghabar, RachidGreen nanocomposites from rosin-limonene (Ros-Lim) copolymers based on Algerian organophilic-clay named Maghnite-CTA+ (Mag-CTA+) were prepared by in-situ polymerization using di erent amounts (1, 5 and 10% by weight) of Mag-CTA+ and azobisisobutyronitrile as a catalyst. The Mag-CTA+ is an organophilic montmorillonite silicate clay prepared through a direct exchange process; the clay was modified by ultrasonic-assisted method using cetyltrimethylammonuim bromide in which it used as green nano-filler.The preparation method of nanocomposites was studied in order to determine and improve structural, morphological, mechanical and thermal properties ofsin.The structure and morphology of the obtained nanocomposites(Ros-Lim/Mag-CTA+) were determined using Fourier transform infrared spectroscopy, X-ray di raction, scanning electronic microscopy and transmission electronic microscopy. The analyses confirmed the chemical modification of clay layers and the intercalation of rosin-limonene copolymer within the organophilic-clay sheets. An exfoliated structure was obtained for the lower amount of clay (1% wt of Mag-CTA+), while intercalated structures were detected for high amounts of clay (5 and 10% wt of Mag-CTA+). The thermal properties of the nanocomposites were studied by thermogravimetric analysis (TGA) and show a significant improvement inthe thermal stability of the obtained nanocomposites compared to the purerosin-limonene copolymer (a degradation temperature up to 280ºC).
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