Este trabalho contemplou o estudo do desenvolvimento de amidos termoplásticos (TPS) obtidos a partir da raiz de mandioca bruta e de seus derivados (amido e resíduo). A técnica de preparação deu-se por mistura física dos componentes, via estado fundido, empregando-se o plasticizante glicerol em proporções variadas. Contemplou ainda a busca de alternativas que viessem a melhorar o desempenho mecânico e a resistência à absorção de umidade dos TPS. Foi realizado um estudo inicial de caracterização dos materiais originais e constatou-se que a presença de açúcares na raiz e de fibras no resíduo é o principal diferencial com relação à composição do amido industrial. Os TPS preparados a partir de amido industrial e de raiz apresentaram fraco desempenho mecânico. Por outro lado, as fibras presentes no resíduo foram capazes de gerar TPS com melhores propriedades mecânicas. Os açúcares naturalmente presentes na raiz ocasionaram um efeito adicional de plasticização ao TPS influenciando principalmente nas propriedades de alongamento na ruptura. Os TPS preparados apresentaram comportamentos semelhantes frente à absorção de água. As estratégias empregadas na tentativa de melhorar o desempenho do TPS preparado a partir de amido de mandioca industrial foram: desenvolvimento de blendas de TPS com poli (álcool vinílico) (PVA); adição de látex de borracha natural às blendas TPS/PVA; uso de partículas minerais (alumina e carbeto de silício) aos TPS e uso de nanofibras de celulose (whiskers) como reforço aos TPS. Estas nanofibras foram extraídas a partir das fibras contidas no resíduo da industrialização do amido de mandioca. Em todos os casos foram realizados estudos da morfologia e do desempenho dos materiais resultantes. Os resultados revelaram que as blendas TPS/PVA e TPS/PVA/látex foram, em sua maioria, imiscíveis, porém compatíveis, pois o desempenho mecânico e de resistência à umidade foram aumentados. O látex, empregado em conjunto com o PVA, gerou materiais com módulo elástico cerca de 1330% maior que a combinação TPS/látex, além de reduzir a absorção de água das blendas TPS/PVA em 12%. A alumina (Al2O3) promoveu um efeito de plasticização no TPS ocorrendo um aumento de 68% no alongamento. Em contrapartida, houve uma redução de 70% no módulo elástico e de 40% na tensão de tração na ruptura. O carbeto de silício (SiC) mostrou-se efetivo no aumento do módulo elástico (aumento de 230%). O efeito de reforço acarretado pelos ´whiskers´ foi limitado devido à presença de açúcares decorrentes da hidrólise ácida do amido residual contido no resíduo. Os testes de resistência à tração não foram sensíveis para a completa determinação das propriedades mecânicas. Entretanto, os resultados de análise térmico-dinâmico-mecânica revelaram que houve um aumento de 26% no módulo de armazenamento. A principal contribuição do uso destas nanofibras deu-se na redução de absorção de água (34% em relação ao TPS sem ´whiskers´). Como um todo, os resultados obtidos nesta tese revelaram a possibilidade de obtenção de TPS a partir da mandioca e de seus derivados e que as estratégias adotadas para melhorar o desempenho final dos TPS foram satisfatórias. / In this work it was studied the development of thermoplastic starches (TPS) prepared from raw cassava root and its derivatives, starch and bagasse (residue). The TPS were prepared by melt-processing employing glycerol as plasticizer in distinct proportions. It was searched for alternatives that could improve both, the mechanical performance and resistance to water of the TPS. It was made a previous characterization of the original materials. It was verified that the presence of sugars in the cassava root and of fibres in the bagasse is the main distinction in relation to the composition of industrial starch. The TPS from industrial starch and cassava root presented the poorer mechanical performance. On the other hand, the fibres in the bagasse allowed the obtainment of a more mechanical resistant TPS in relation to the other TPS. The presence of natural sugars in the cassava root promoted an additional effect on the plasticization of TPS, influencing mainly the elongation properties. The prepared TPS presented similar behaviors in relation to water absorption. The strategies adopted to improve the performance of TPS prepared from industrial starch were: the development of TPS blends with polyvinyl alcohol (PVA); addition of latex of natural rubber to TPS/PVA blends TPS/PVA; the use of mineral particles (alumina and silicon carbide) to the TPS and also, utilization of cellulose nanofibres (whiskers), as reinforcement to the TPS. These whiskers were extracted from the fibres contained in the cassava bagasse. For all the cases the morphology and final performance of the resulting materials were investigated. The results revealed that TPS/PVA and TPS/PVA/latex blends were in a greater number immiscible, although, compatibles since, the mechanical performance and water resistance were increased. The latex, employed together PVA, promoted a 1330% increase in the elastic modulus compared to TPS/latex. Also, the water absorption of TPS/PVA blends was reduced in 12%. The alumina (Al2O3) promoted a plasticizing effect in the TPS with an increase of 68% in elongation. On the other hand, the elastic modulus and tensile strength were reduced in 70% and 40%, respectively. The silicon carbide (SiC) was effective to increase the elastic modulus (increase of 230%). The reinforcement effect of the whiskers was limited due to the presence of sugars resultants of the acid hydrolysis of residual starch present in the bagasse. The tensile tests were not sensitive to determine the mechanical properties. However, from dynamicmechanical tests it was verified an increase of 26% in the storage modulus. The main contribution of the use of nanofibers was on the reduction of water absorption in 34% compared to TPS without nanofibers. As a whole, the results obtained in this work revealed the possibility of preparation of TPS from cassava root and its derivatives and that the strategies adopted to improve the final performance of the TPS ware successful.

Devido à importância industrial e tecnológica dos látices estabilizados com poli(álcool vinílico)/PVA e a dificuldade encontrada na etapa de polimerização em emulsão, na presença de monômeros hidrofóbicos e de PVA\'s com alto grau de hidrólise (>92%), a síntese de novos estabilizantes poliméricos derivados de PVA para utilização em reações de polimerização em emulsão e em miniemulsão se torna muito atraente e desafiadora. O objetivo principal deste trabalho foi sintetizar novos estabilizantes poliméricos do tipo poli(álcool vinílico-co-neodecanoato de vinila)/PVA-VV com alto grau de hidrólise e conseqüentemente com propriedades diferenciadas, para serem utilizados como estabilizantes nas reações de polimerização em emulsão e em miniemulsão do acetato de vinila (VAc) com o neo-nonanoato de vinila (VEOVA-9), visando a obtenção de adesivos com propriedades diferenciadas para colagem de madeiras. Os novos estabilizantes poliméricos foram obtidos em duas etapas: i) copolimerização em solução do VAc com o neo-decanoato de vinila (VEOVA-10); ii) hidrólise alcalina (NaOH/Metanol) do poli(acetato de vinila-coneodecanoato de vinila). As miniemulsões de VAc com VEOVA-9 com diferentes tipos de estabilizantes poliméricos foram preparadas em um homogeneizador de alta pressão do tipo \"Manton Gaulin\". Foi estudado o efeito dos estabilizantes poliméricos (PVA e PVA-VV) na etapa de emulsificação (diâmetro médio das gotas, polidispersão, estabilidade das miniemulsões) e na copolimerização em emulsão e em miniemulsão do VAc com o VEOVA-9, em processo batelada. O efeito do tipo de iniciador (persulfato de amônio/APS e hidroperóxido de tércio butila/TBHP e peróxido benzoato de tércio butila/TBPB, juntamente com o formaldeído sulfoxilato de sódio/SFS) na cinética da polimerização em miniemulsão do VAc com o VEOVA-9 foi estudado em processo semi-contínuo. A distribuição dos estabilizantes poliméricos (PVA e PVA-VV) entre a fase aquosa e a superfície das partículas de polímero (adsorvido/enxertado) foi determinada e correlacionada com a viscosidade e a estabilidade coloidal dos látices. Látices na condição ideal de cópia (1:1) das gotas de monômero para as partículas de polímero foram obtidos via polimerização em miniemulsão, apresentando propriedades diferenciadas, tais como, menores valores de viscosidade, menor concentração de coágulos e maior estabilidade de estocagem, em comparação com os látices obtidos em emulsão. / Due to the technological and industrial importance of latexes stabilized with poly(vinyl alcohol)/PVA and the difficulties related to the emulsion polymerization of hydrophobic monomers and the use of PVA having a high degree of hydrolysis (> 92%), the synthesis of new PVA based polymeric stabilizers for use in emulsion and miniemulsion polymerizations becomes very attractive and challenging. The aim of this work was to synthesize a new class of polymeric stabilizer, poly(vinyl alcohol-co-vinyl neo-decanoate)/PVA-VV, with a high degree of hydrolysis and differentiated properties to be used as stabilizers in the emulsion and miniemulsion copolymerization of vinyl acetate (VAc) with vinyl neo-nonanoate (VEOVA-9), that can be used as adhesive for wood bonding. New PVA based polymeric stabilizers with high degree of hydrolysis (94 - 98%) were synthesized in two steps: i) solution copolymerization of vinyl acetate (VAc) with vinyl neo-decanoate (VEOVA-10) and ii) alkaline hydrolysis (NaOH/Methanol) of poly(vinyl acetate-co-vinyl neodecanoate). Miniemulsions of VAc/VEOVA-9 were prepared using the different polymeric stabilizers in a \"Manton Gaulin\" high pressure homogenizer. The effect of different initiators (ammonium persulfate/APS or tert-butyl hydro peroxide/TBHP and tert-butyl peroxide benzoate/TBPB in the presence of sodium formaldehyde sulfoxylate/SFS) in the polymerization kinetic was evaluated. The effect of the type and concentration of polymeric stabilizer, in the emulsification step (average diameter of drops, stability of miniemulsions) as well in the polymerizations (rate of consumption of monomers, particle size and particles number) was investigated in this work. The partition of the polymeric stabilizers between the aqueous phase and the polymer particle surface (grafted/adsorbed) was determined and correlated with the viscosity and colloidal stability of latexes. Latexes with differentiated properties such as low-viscosity, lower grits content and improved storage stability, were obtained by miniemulsion polymerization with an ideal condition copy (1:1) of the monomer droplets to the polymer particles.

Le remplacement des tissus mous du système ostéo-articulaire par des implants synthétiques en hydrogels est souvent limité par un faible ancrage avec le tissu osseux. Une approche pour renforcer l’interface os/implant consiste à fonctionnaliser la surface de l’implant par un revêtement biocéramiques. Dans cette thèse, nous étudions deux approches pour revêtir des hydrogels d’alcool polyvinylique (APV) avec des particules biocéramiques d’hydroxyapatite (HA). Dans une première approche, basée sur le procédé d’enduction, des substrats d’hydrogel ont été revêtus par des particules d’HA enchâssées dans une matrice d’hydrogel d’APV non-dégradable. Dans ce procédé, le contrôle de la composition de la solution de trempage permet d’ajuster finement l’épaisseur, la cohésion et l’adhérence du revêtement, ainsi que le taux d’exposition d’HA à la surface du revêtement. La biocompatibilité avec la pratique chirurgicale et l’ostéointégration de ces revêtements ont été évaluées par une étude in vivo sur un modèle de cicatrisation de tunnel osseux chez le lapin. Ces premiers travaux nous ont menés à la découverte d’une nouvelle approche pour gélifier des films d’hydrogel par un procédé auto-entretenu, qui consiste à utiliser la déplétion de solvant créée à la surface d’un substrat gonflant dans une solution de polymère pour induire la gélification sans action extérieure. Dans ce procédé, la croissance de ces films dépend de la concentration de la solution, du temps de trempage et de la cinétique de gonflement du substrat. Le caractère doux de ce procédé de gélification a été vérifié en encapsulant des fibroblastes, qui restent viables durant 48h. Avec un second procédé plus énergétique, des substrats d’hydrogels d’APV ont été revêtus de couches denses de particules d’HA submicroniques par cold spray. Les paramètres de projection (température, pression, distance de projection) ont été variés systématiquement pour déterminer des conditions de projection appropriées. Un schéma de formation du revêtement est proposé, basé sur les observations microscopiques. Chacun de ces procédés et leur combinaison ouvrent de nouvelles voies dans la conception de système hydrogel-céramique ayant des propriétés microstructurales, mécaniques et biologique contrôlées. / The replacement of soft osteoarticular tissues by synthetic hydrogel implants is often limited by a weak anchorage to bone tissues. One approach to strengthen the bone-implant interface consists in functionalizing the surface of the implant by a coating of bioceramics. In this thesis, we investigate two approaches to coat hydrogels of poly(vinyl alcohol) (PVA) with ceramic particles of hydroxyapatite (HA). In a first “soft” process, based on dip-coating, hydrogel substrates were coated with hydroxyapatite particles embedded in a non-degradable PVA hydrogel matrix. In this process, the control of the soaking solution composition allows to finely tune the thickness, the cohesion and the adhesion of the coating, as well as the HA exposure at the coating surface. The biocompatibility with surgical handling and the osteointegration of these systems were assessed by an in vivo study in a rabbit model of bone tunnel healing. This first approach led to the discovery of a new approach to grow physical hydrogel films by a self-sustained process, consisting in using the solvent depletion created at the surface of a swelling polymer substrate immersed in a PVA solution to induce the gelation of hydrogel films without external action. In this process, the growth of these hydrogel films depends on the solution concentration, the soaking time and the swelling kinetics of the substrate. We verified the gentle character of this process by encapsulating fibroblasts, which remain viable for 48h. In a second more “energetic” process, dense coatings of submicronic HA particles were produced on PVA hydrogel by cold spray. Spraying parameters (temperature, pressure and stand-off distance) were varied systematically to determine efficient spraying condition. Based on microscopic observations, a picture explaining the formation of the coating is proposed. Both processes and their combination open new routes for the design of ceramic-hydrogel systems having controlled microstructural, mechanical and biological properties.

Year 2019, football, rugby, netball and skiing had most occurring ACL injuries, listed by United Kingdom National Ligament Report (NLR). The standard procedure treatment of complete laceration of the ACL, is performed by tissue autograft implantation designed from a patellar tendon, for replacement of damaged tissue using orthopaedic surgery. The aim of this thesis is to design and fabricate an ACL graft, attempting to mimic the natural ACL, for the purpose of tissue reconstruction. The desired graft analogues exhibited properties imitating native connective tissue, reducing pain through drug delivery with great biocompatibility and enhance suture mechanical strength. Various biomaterials were implemented into this study, utilising strategies; polymer solution fabrication, electrospinning, hydrogel synthesis, mechanical braiding and graft assembly to fabricate an ACL graft. The polymeric material poly (E- caprolactone) (PCL) was researched, utilising its ability to fabricate scaffolds. Results showed, three analogue ACL grafts (Braided PCL-BP, Braided PCL + Hydrogel-BPH & Braided PCL + Sutures-BPS) created utilising the properties of braiding, hydrogels and sutures, ultimately improving the versatility of electrospinning for tissue engineering and reconstruction. Graft analogues were tested and compared against patellar tendons producing similar tensile properties. Poly vinyl alcohol (PVA) hydrogels successfully held ibuprofen, revealing drug delivery characteristics, polyester threads improved mechanical properties of electrospun grafts and dry degradation showed that PCL did not lose significant mass over two months. Conclusion, tensile strength of patella tendon was 395x, 790x & 56x of analogue grafts (BP, BPH & BPS) respectively, having potential for improvement of tensile parameters for ligament reconstruction.

<p>Radiotherapy is used in many clinics to deliver a sufficient and uniform dose to the cancerous tumours while the dose to normal tissues is minimized. However, there is a possibility of missing the target volume due to patient set up/motion errors, or any fluctuation in treatment delivery. Therefore, accurate dose verification tools are essential to evaluate the delivered dose distribution of the designed treatment plan under realistic treatment conditions.</p> <p>Current research is focused on developing 3D dose verification tools to record the complex dose distributions for quality assurance purposes and the evaluation of new treatment techniques. New and novel materials and read-out techniques suitable for use in hospitals are desirable. The objective of this research is to fabricate a transparent radiochromic gel dosimeter that may be used as quality assurance tool. Also, the fabricated gel must be analyzed using a simple optical read-out technique.</p> <p>Gel dosimeters are gels that undergo some chemical changes upon irradiation as a function of absorbed dose. The absorbed dose may be recorded in three dimensions depending on the type of gel dosimeter. Radiochromic gels are dosimeters that change colour upon irradiation. A radiosensitive dye, leucomalachite green (LMG) is dissolved in a matrix material to record the dose distribution in 3D. LMG changes its colour upon irradiation, and has an absorbance band of 629nm.</p> <p>In this research two different matrix materials were investigated: poly (vinyl alcohol) and gelatin. PVA was studied as the primary agent due to its adjustable mechanical strength and high transparency. PVA has also been studied to have a low diffusion rate when it was used as the matrix material in Fricke gel dosimeters [41]. Even though PVA had all the desired characteristics, fabricating a PVA based radiochromic dosimeter was not successful. Consequently, gelatin was used as the matrix material to fabricate a gelatin-based radiochromic dosimeter.</p> <p>Using gelatin, highly transparent radiosensitive gels were successfully fabricated. The absorbencies of the irradiated gels were measured as a function of absorbed dose, using a 1D set up. After, the gels were formed into 5mm thick films and used as two-dimensional dose verification tools. The relationship between absorbance and absorbed dose for 1D measurement was obtained to be 0.00241± 0.00004 , and 0.0022 ± 0.00007 for 2D gels scaled to a thickness of 1 cm.</p> <p>In all of the experiments the absorbance-dose relationships were similar in slopes, but there was an offset between different batches. The offset was 20% between the different experiments. Moreover, there was less than 5% error associated with the physical set up; the major source of error was due to the production and handling of the mixture, possibly due to the effects of inconsistent heating and UV light exposure.</p> <p>The 2D gels were used to verify the dose distribution for the purpose of quality assurance. Six different complicated beams were delivered to the gels and their dose distributions were compared to their respective Pinnacle Calculated Planar (PCP) dose maps. The difference was found to be about 35% at worst; however, this error may be reduced by utilizing more sophisticated data processing methods. Nevertheless, the images were quite similar above 20Gy. Furthermore, the dose distributions recorded by the gels are qualitatively and quantitatively similar to the (PCP) dose map. Although the fabricated gel dosimeters show some promise as future tools for quality assurance purposes, they must go through many more stages of research to be used clinically.</p> / Master of Science (MSc)

In recent years, electrochemical capacitors have emerged as devices with the potential to enable major advances in electrical energy storage. Electrochemical capacitors (ECs) are akin to conventional capacitors but employ higher surface-area electrodes and thinner dielectrics to achieve larger capacitances. This helps ECs to attain energy densities greater than those of conventional capacitors and power densities greater than those of batteries. Akin to conventional capacitors, ECs also have high cycle-lives and can be charged and discharged rapidly. But ECs are yet to match the energy densities of mid to high-end batteries and fuel cells. On the basis of mechanism involved in the charge-storage process, ECs are classified as electrical double-layer capacitors (EDLCs) or pseudocapacitors. Charge storage in EDLCs and pseudocapacitors is brought about by non-faradaic and faradaic processes, respectively. Faradaic process, such as an oxidation-reduction reaction, involves the transfer of charge between electrode and electrolyte. By contrast, a non-faradaic process does not use a chemical mechanism and charges are distributed on surfaces by physical processes that do not involve any chemical reaction. ECs employ both aqueous and non-aqueous electrolytes in either liquid or solid form, the latter providing the advantages of freedom from leakage of any liquid component, compactness, reliability and large operating potential-window. In the literature, polymer electrolytes are the most widely studied solid electrolytes. Complexation of functional-groups of certain polymers with cations results in the formation of polymer-cation complexes commonly referred to as solid-polymer electrolytes (SPEs). Mixing a polymer with an alkali metal salt dissolved in an organic solvent result in the formation of a polymer gel electrolyte. Organic solvents with low molecular-weights, such as ethylene carbonate and propylene carbonate, employed in polymer gel electrolytes are commonly referred to as plasticizers. When water is used as a plasticizer, the polymer electrolyte is called a polymer hydrogel electrolyte. Part I of the thesis is directed to studies pertaining to Polymer Hydrogel Electrolytes for Electrochemical Capacitors and comprises four sections. After a brief survey of literature on polymer hydrogel electrolytes employed in ECs in Section I.1, Section I.2 of Part I describes the studies on electrochemical capacitors employing cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration. Acidic poly (vinyl alcohol) hydrogel membrane electrolytes (PHMEs) with different perchloric acid concentrations are prepared by cross-linking poly (vinyl alcohol) with glutaraldehyde in the presence of a protonic acid acting as a catalyst under ambient conditions. PHMEs are characterized by scanning electron microscopy and temperature-modulated differential scanning calorimetry in conjunction with relevant electrochemical techniques. An optimised electrochemical capacitor assembled employing PHME in conjunction with black pearl carbon (BPC) electrodes yields a maximum specific capacitance value of about 96 F g-1, phase angle value of about 79o and a discharge capacitance value of about 88 F g-1. Section I.3 of Part I describes the studies on cross-linked poly (vinyl alcohol)/ploy (acrylic acid) blend hydrogel electrolytes for electrochemical capacitors. Acidic poly (vinyl alcohol)/poly (acrylic acid) blend hydrogel electrolytes (BHEs) have been prepared by cross-linking poly (vinyl alcohol)/poly (acrylic acid) blend with glutaraldehyde in presence of perchloric acid. These acidic BHEs have been treated suitably to realize alkaline and neutral BHEs. Thermal characteristics and glass-transition behavior of BHEs have been followed by differential scanning calorimetry. Ionic conduction in acidic BHEs has been found to take place by Grötthus-type mechanism while polymer segmental motion mechanism is predominantly responsible for ion motion in alkaline and neutral BHEs. Ionic conductivity of BHEs has been found to range between 10-3 and 10-2 S cm-1 at 298 K. Electrochemical capacitors assembled with acidic PVA hydrogel electrolyte yield a maximum specific capacitance of about 60 and 1000 F g-1 with BPC and RuOx.xH2O/C electrodes, respectively. Section I.4 of Part I describes the studies on gelatin hydrogel electrolytes and their application to electrochemical capacitors. Gelatin hydrogel electrolytes (GHEs) with varying NaCl concentrations have been prepared by cross-linking an aqueous solution of gelatin with aqueous glutaraldehyde under ambient conditions, and characterized by scanning electron microscopy, temperature-modulated differential scanning calorimetry, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic chronopotentiometry. Glass transition temperatures for GHEs range between 340 and 377 K depending on the dopant concentration. Ionic conductivity behavior of GHEs is studied with varying concentrations of gelatin, glutaraldehyde and NaCl, and conductivity values are found to vary between 10-3 and 10-1 S cm-1 under ambient conditions. GHEs have a potential window of about 1 V with BPC electrodes. The ionic conductivity of pristine and 0.25 N NaCl-doped GHEs follows Arrhenius behavior with activation energy values of 1.9×10-4 and 1.8×10-4 eV, respectively. Electrochemical capacitors employing GHEs in conjunction with black pearl carbon electrodes are assembled and studied. Optimal values for capacitance, phase angle, and relaxation time constant of about 81 F g-1, 75o, and 0.03 s are obtained for 3 M NaCl-doped GHE, respectively. EC with pristine GHE exhibits continuous cycle life for about 4.3 h as against 4.7 h for the electrochemical capacitor with 3 M NaCl-doped GHE. Unlike electrochemical capacitors, fuel cells do not store the charge internally but instead use a continuous supply of fuel from an external storage tank. Thus, fuel cells have the potential to solve the most challenging problem associated with the electrochemical capacitors, namely their limited energy-density. A fuel cell is an electrochemical power source with advantages of both the combustion engine and the battery. Like a combustion engine, a fuel cell will run as long as it is provided with fuel; and like a battery, fuel cells convert chemical energy directly to electrical energy. As an electrochemical power source, fuel cells are not subjected to the Carnot limitations of combustion (heat) engines. A fuel cell operates quietly and efficiently and, when hydrogen is used as a fuel, it generates only power and potable water. Thus, a fuel cell is a so called ‘zero-emission engine’. In the past, several fuel cell concepts have been tested in various laboratories but the systems that are being potentially considered for commercial developments are: (i) Alkaline Fuel Cells (AFCs), (ii) Phosphoric Acid Fuel Cells (PAFCs), (iii) Polymer Electrolyte Fuel Cells (PEFCs), (iv) Solid-Polymer-Electrolyte-Direct Methanol Fuel Cells (SPE-DMFCs), (v) Molten Carbonate Fuel Cells (MCFCs) and (vi) Solid Oxide Fuel Cells (SOFCs). Among the aforesaid systems, PEFCs that employ hydrogen as fuel are considered attractive power systems for quick start-up and ambient-temperature operations. Ironically, however, hydrogen as fuel is not available freely in the nature. Accordingly, it has to be generated from a readily available hydrogen carrying fuel such as natural gas, which needs to be reformed. But, such a process leads to generation of hydrogen with some content of carbon monoxide, which even at minuscule level is detrimental to the fuel cell performance. Pure hydrogen can be generated through water electrolysis but hydrogen thus generated needs to be stored as compressed / liquefied gas, which is cost-intensive. Therefore, certain hydrogen carrying organic fuels such as methanol, ethanol, propanol, ethylene glycol, and diethyl ether have been considered for fuelling PEFCs directly. Among these, methanol with a hydrogen content of about 13 wt. % (specific energy = 6.1 kWh kg-1) is the most attractive organic liquid. PEFCs using methanol directly as fuel are referred to as SPE-DMFCs. But SPE-DMFCs suffer from methanol crossover across the polymer electrolyte membrane, which affects the cathode performance and hence the cell performance during its operation. SPE-DMFCs also have inherent limitations of low open-circuit-potential and low electrochemical-activity. An obvious solution to the aforesaid problems is to explore other promising hydrogen carrying fuels such as sodium borohydride, which has a hydrogen content of about 11 wt. %. Such fuel cells are called direct borohydride fuel cells (DBFCs). Part II of the thesis includes studies on direct borohydride fuel cells and comprises three sections. After a brief introduction to DBFCs in section II.1, Section II.2 describes studies on an alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant. A peak power density of about 150 mW cm-2 at a cell voltage of 540 mV could be achieved from the optimized DBFC operating at 70oC. Section II.3 describes studies on poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells. This DBFC employs a poly (vinyl alcohol) hydrogel membrane as electrolyte, an AB5 Misch metal alloy as anode, and a gold-plated stainless steel mesh as cathode in conjunction with aqueous alkaline solution of sodium borohydride as fuel and aqueous acidified solution of hydrogen peroxide as oxidant. The performance of the PHME-based DBFC in respect of peak power outputs, ex-situ cross-over of oxidant, fuel, anolyte and catholyte across the membrane electrolytes, utilization efficiencies of fuel and oxidant as also cell performance durability under ambient conditions are compared with a similar DBFC employing a Nafion®-117 membrane electrolyte (NME). Peak power densities of about 30 and 40 mW cm-2 are observed for the DBFCs with PHME and NME, respectively. The PHME and NME-based DBFCs exhibit cell potentials of about 1.2 and 1.4 V, respectively, at a load current density of 10 mA cm-2 for 100 h. Publications of Nurul Alam Choudhury 1. Gelatin hydrogel electrolytes and their application to electrochemical supercapacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Electrochem. Soc., 155 (2008) A74. 2. Cross-linked polymer hydrogel electrolytes for electrochemical capacitors, N. A. Choudhury, A. K. Shukla, S. Sampath, and S. Pitchumani, J. Electrochem. Soc., 153 (2006) A614. 3. Hydrogel-polymer electrolytes for electrochemical capacitors: an overview, N. A. Choudhury, S. Sampath, and A. K. Shukla, Energy and Environmental Science (In Press). 4. Cross-linked poly (vinyl alcohol) hydrogel membrane electrolytes with varying perchloric acid dopant concentration and their application to electrochemical capacitors, N. A. Choudhury, S. Sampath, and A. K. Shukla, J. Chem. Sc. (Submitted) 5. An alkaline direct borohydride fuel cell with hydrogen peroxide as oxidant, N. A. Choudhury, R. K. Raman, S. Sampath, and A. K. Shukla, J. Power Sources, 143 (2005) 1. 6. Poly (vinyl alcohol) hydrogel membrane as electrolyte for direct borohydride fuel cells, N. A. Choudhury, S. K. Prashant, S. Pitchumani, P. Sridhar, and A. K. Shukla, J. Chem. Sc. (Submitted). 7. A phenyl-sulfonic acid anchored carbon-supported platinum catalyst for polymer electrolyte fuel cell electrodes, G. Selvarani, A. K. Sahu, N. A. Choudhury, P. Sridhar, S. Pitchumani, and A. K. Shukla, Electrochim. Acta, 52 (2007) 4871. 8. A high-output voltage direct borohydride fuel cell, R. K. Raman, N. A. Choudhury, and A. K. Shukla, Electrochem. Solid-State Lett., 7 (2004) A 488. 9. Carbon-supported Pt-Fe alloy as a methanol-resistant oxygen-reduction catalyst for direct methanol fuel cells, A. K. Shukla, R. K. Raman, N. A. Choudhury, K. R. Priolkar, P. R. Sarode, S. Emura, and R. Kumashiro, J. Electroanal. Chem., 563 (2004) 181.

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(工学) / 乙第12460号 / 論工博第4042号 / 新制||工||1497(附属図書館) / 28070 / (主査)教授 岩田 博夫, 教授 伊藤 紳三郎, 教授 辻井 敬亘 / 学位規則第4条第2項該当

[ES] Las pilas de combustible de hidrógeno o bioalcohol son una tecnología prometedora para la generación de energía limpia y eficiente en el intento actual de revertir los severos efectos causados por el cambio climático. No obstante, para lograr generalizar su uso, esta tecnología debe optimizarse. Concretamente, la membrana de intercambio de protones es un componente crucial para mejorar su rendimiento general. Esta línea de investigación, entre otras, está incluida en la mayoría de las actuales líneas estratégicas nacionales y europeas con el objetivo de implantar estos sistemas de producción de energía sostenibles en un futuro próximo. En la presente tesis doctoral se presenta un procedimiento robusto y fiable que permite el diseño de membranas de intercambio de protones mediante la caracterización y análisis de varios materiales poliméricos con la intención de predecir su comportamiento en condiciones operativas. En ese sentido, se analizan cuatro tipos diferentes de microestructuras. En el Capítulo 4 se analizan dos series de membranas basadas en copolímeros en bloque sulfonados de estireno-etileno-butileno-estireno (SEBS). La microestructura se ha ajustado para su idoneidad en aplicaciones de pilas de combustible. Posteriormente, se aplica a las muestras un proceso de sulfonación, fotorreticulación UV e hibridación. En el Capítulo 5 se analiza una serie de membranas de poli(alcohol vinílico) (PVA) convenientemente modificadas para su idoneidad como membranas de intercambio de protones en celdas de combustible de metanol directo (DMFC). El análisis se centra en si la reticulación y la sulfonación mediante el uso de SSA mejoran la estabilidad y aumentan la conducción de protones en la estructura de PVA tal y como se esperaba inicialmente. Además, se evalúa el efecto de la adición de óxido de grafeno (GO) en los espectros dieléctricos y la conductividad protónica. En el Capítulo 6 se analizan dos series de membranas a base de copolímero de poli (epiclorhidrina) (PECH) y poli (epiclorhidrina-co-óxido de etileno) (PECH-co-EO). Ambas membranas están modificadas con unidades de 3,4,5-tris[4-(n-dodecan-1-iloxi)benciloxi]benzoato. El análisis se centra en la capacidad de estas membranas para formar canales, promovidos por la orientación térmica, lo que mejora los mecanismos de transferencia de carga y la conductividad de los protones. En el Capítulo 7 se realiza el análisis de una membrana sintetizada a partir de una red adaptable covalente (CAN). La característica más importante de este tipo de polímeros es la presencia de enlaces reversibles en la estructura que les permite mostrar propiedades físicas como la autoreparación, la soldabilidad y la reciclabilidad. Estas propiedades podrían mejorar el ciclo de vida de las membranas de intercambio protónico. El análisis realizado incluye una evaluación de las dos temperaturas más importantes desde el punto de vista viscoelástico, es decir, la transición vítrea Tg y la temperatura de transición de congelación de la topología Tv, y su impacto en la conductividad protónica. Como resultado de este estudio, se desarrolla una metodología para analizar diversas membranas poliméricas con diferentes microestructuras mediante Análisis Térmico Dieléctrico (DETA). En consecuencia, el estudio de las propiedades dieléctricas, en términos de la permitividad compleja (ε∗), junto con el análisis de la conductividad compleja (σ∗), permite obtener información sobre la dinámica molecular que favorece eficientemente los mecanismos de transferencia de carga. La conductividad protónica (σprot) se estimará a partir de los datos dieléctricos, lo que permitirá evaluar las membranas poliméricas ensayadas para su aplicación como membranas de intercambio protónico. En consecuencia, se puede optimizar el funcionamiento de las membranas de intercambio de protones, y se promueve su implementación masiva. / [CA] Les piles de combustible d'hidrogen o bioalcohol són una tecnologia prometedora per a la generació d'energia neta i eficient en l'intent actual de revertir els severs efectes causats pel canvi climàtic. No obstant això, per a aconseguir generalitzar el seu ús, aquesta tecnologia ha d'optimitzar-se. Concretament, la membrana d'intercanvi de protons és un component crucial per a millorar el seu rendiment general. Aquesta línia d'investigació, entre d'altres, està inclosa en la majoria de les actuals línies estratègiques nacionals i europees amb l'objectiu d'implantar aquests sistemes de producció d'energia sostenibles en un futur pròxim. En la present tesi doctoral es presenta un procediment robust i fiable que permet el disseny de membranes d'intercanvi de protons mitjançant la caracterització i anàlisi de diversos materials polimèrics amb la intenció de predir el seu comportament en condicions operatives. En aqueix sentit, s'analitzen quatre tipus diferents de microestructures. En el Capítol 4 s'analitzen dues sèries de membranes basades en copolímers en bloc sulfonats d'estiré-etilé-butilé-estiré (SEBS). La microestructura s'ha ajustat per a la seua idoneïtat en aplicacions de piles de combustible. Posteriorment, s'aplica a les mostres un procés de sulfonació, fotorreticulació UV i hibridació. En el Capítol 5 s'analitza una sèrie de membranes de poli(alcohol vinílic) (PVA) convenientment modificades per a la seua idoneïtat com a membranes d'intercanvi de protons en cel·les de combustible de metanol directe (DMFC). L'anàlisi se centra en si la reticulació i la sulfonació mitjançant l'ús de SSA milloren l'estabilitat i augmenten la conducció de protons en l'estructura de PVA tal com s'esperava inicialment. A més, s'avalua l'efecte de l'addició d'òxid de grafé (GO) en els espectres dielèctrics i la conductivitat protònica. En el Capítol 6 s'analitzen dues sèries de membranes a base de copolímer de poli (epiclorhidrina) (PECH) i poli (epiclorhidrina-co-òxid d'etilé) (PECH-co-EO). Totes dues membranes estan modificades amb unitats de 3,4,5-tris[4-(n-dodecan-1-iloxi)benciloxi] benzoato. L'anàlisi es centra en la capacitat d'aquestes membranes per a formar canals, promoguts per l'orientació tèrmica, la qual cosa millora els mecanismes de transferència de càrrega i la conductivitat dels protons. En el Capítol 7 es realitza l'anàlisi d'una membrana sintetitzada a partir d'una xarxa adaptable covalent (CA). La característica més important d'aquesta mena de polímers és la presència d'enllaços reversibles en l'estructura que els permet mostrar propietats físiques com l'autoreparació, la soldabilitat i la reciclabilitat. Aquestes propietats podrien millorar el cicle de vida de les membranes d'intercanvi protònic. L'anàlisi realitzada inclou una avaluació de les dues temperatures més importants des del punt de vista viscoelàstic, és a dir, la transició vítria Tg i la temperatura de transició de congelació de la topologia Tv, i el seu impacte en la conductivitat protònica. Com a resultat d'aquest estudi, es desenvolupa una metodologia per a analitzar diverses membranes polimèriques amb diferents microestructures mitjançant Anàlisi Tèrmic Dielèctric (DETA). En conseqüència, l'estudi de les propietats dielèctriques, en termes de la permitivitat complexa (ε∗), juntament amb l'anàlisi de la conductivitat complexa (σ∗), permet obtindre informació sobre la dinàmica molecular que afavoreix eficientment els mecanismes de transferència de càrrega. La conductivitat protònica (σprot) s'estimarà a partir de les dades dielèctriques, la qual cosa permetrà avaluar les membranes polimèriques assajades per a la seua aplicació com a membranes d'intercanvi protònic. En conseqüència, es pot optimitzar el funcionament de les membranes d'intercanvi de protons, i es promou la seua implementació massiva. / [EN] Hydrogen or bioalcohol fuel cells are a promising technology for clean and efficient energy generation in the current attempt to reverse the severe effects caused by climate change. However, in order to achieve its general use, this technology must be optimized. Specifically, the proton exchange membrane is a crucial component to improve your overall performance. This line of research, among others, is included in most of the current national and European strategic lines with the aim of implementing these sustainable energy production systems in the near future. In this doctoral thesis, a robust and reliable procedure is presented that allows the design of proton exchange membranes through the characterization and analysis of various polymeric materials with the intention of predicting their behaviour under operating conditions. In this sense, four different types of microstructures are analysed. In Chapter 4, two series of membranes based on sulfonated block copolymers of styrene-ethylene-butylene-styrene (SEBS) are discussed. The microstructure has been adjusted for its suitability in fuel cell applications. Subsequently, a sulfonation, UV photocrosslinking, and hybridization process are applied to the samples. In Chapter 5, a series of polyvinyl alcohol (PVA) membranes suitably modified for their suitability as proton exchange membranes in direct methanol fuel cells (DMFC) are discussed. The analysis focuses on whether crosslinking and sulfonation using SSA improve stability and increase proton conduction in the PVA structure as initially expected. In addition, the effect of the addition of graphene oxide (GO) on the dielectric spectra, and proton conductivity is evaluated. In Chapter 6 two series of membranes based on copolymers of poly (epichlorohydrin) (PECH) and poly (epichlorohydrin-co-ethylene oxide) (PECH-co-EO) are analysed. Both membranes are modified with 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate units. The analysis focuses on the ability of these membranes to form channels, promoted by thermal orientation, which improves the charge transfer mechanisms and the proton conductivity. In Chapter 7, the analysis of a membrane synthesized from a covalent adaptive network (CAN) is performed. The most important characteristic of this type of polymer is the presence of reversible bonds in the structure that allows them to display physical properties such as self-healing, weldability, and recyclability. These properties could improve the life cycle of proton exchange membranes. The analysis carried out includes an evaluation of the two most important temperatures from the viscoelastic point of view, that is, the glass transition Tg and the freezing transition temperature of the topology Tv, and their impact on the proton conductivity. As a result of this study, a methodology is developed to analyse various polymeric membranes with different microstructures by means of Dielectric Thermal Analysis (DETA). Consequently, the study of the dielectric properties, in terms of the complex permittivity (σ∗), together with the analysis of the complex conductivity (ε∗), allows us to obtain information on the molecular dynamics that efficiently favour the charge transfer mechanisms. The proton conductivity (σprot) will be estimated from the dielectric data, which will allow the evaluation of the tested polymeric membranes for their application as proton exchange membranes. Consequently, the functioning of proton exchange membranes can be optimized, and their massive implementation is promoted. / Pascual José, B. (2023). Design and Characterization of Polymeric Materials for their Application as Electrolytes in Fuel Cells [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/196863

L’alcool polyvinylique a été fonctionnalisé avec des aldéhydes et des acides boroniques dans le but d’obtenir des polymères pouvant apporter de la brillance tout en étant solubles dans les formulations de rouges à lèvres ou de vernis à ongles. De bons taux de fonctionnalisation ont été obtenus permettant d’avoir une bibliothèque de poly(vinyl acétals) et de poly(vinyl esters boroniques) d’une cinquantaine de polymères. Une multi-fonctionnalisation du PVA a été effectuée pour obtenir des polymères alliant ces deux propriétés. Cinq poly(vinyl acétals) ont ainsi permis d’apporter une forte brillance à des rouges à lèvres. La E-poly-L-lysine a également été fonctionnalisée avec diverses cétones afin d’obtenir de nouvelles poly-4-imidazolidinones. Ces polymères sont prometteurs pour des applications dans des produits cosmétiques tels que des soins. Ils ont également été utilisés en catalyse organique asymétrique. / Poly(vinyl alcohol) has been functionalized with aldehydes and boronic acids to obtain polymers with high shining and being soluble in cosmetic formulations as lipsticks or nail polishes. Good grafting rates have been obtained permitting to have a library of about fifty poly(vinyl acetals) and poly(vinyl boronic esters). Multi-functionalization has been developped to obtain polymers having these both properties. Five polymers gave strong shining to lipsticks. E-poly-L-lysine was also functionalized with several ketones to obtain new poly-4-imidazolidinones. These polymers are promising for cosmetic applications as skincare products. They were also used for organocatalysis.

The thesis describes the synthesis of PbS nano-, micro-structures by colloidal and hydrothermal techniques. Size and morphology dependent luminescence studies were carried out in detail. Application oriented studies like ion sensing and modulation of luminescence are carried out on colloidal PbS QDs. Photoelectrical studies are carried out on various morphologies of PbS microstructures. We observe the persistent photoconductivity, growth and quenching of photocurrent, and a few novel phenomena in flower shaped PbS microstructures. This work is presented in eight chapters inclusive of summary and directions for future work. CHAPTER 1 provides a brief introduction to optical and photoelectrical properties of semiconductor quantum dots and hydrothermal technique in preparation of quantum structures. A review of PbS nanostructures and its technological applications are discussed. CHAPTER 2 provides the experimental techniques used in this work. First, the synthesis of PbS nano-, micro-structures by various methods, and characterization tools used in this work are briefly presented. CHAPTER 3 deals with the synthesis of PbS quantum dots in poly vinyl alcohol with various precursor concentrations to identify the surface states by temperature dependent photoluminescence (PL) measurements. Average bandgap value calculated from absorption measurements was 2.1 eV. We have observed that high-energy PL bands (>1.3 eV) are due to electron traps (Pb dangling bonds) and low-energy bands (<1 eV) are due to hole traps (S dangling bonds). By capping with thiol compounds (mercaptoethanol-C2 H5OSH), absence of the 1.67 eV band indicates the passivation of Pb dangling bonds. To explain above observed results, we propose a band diagram with distributed shallow to deep states and attributed them to the specific surface related defects (Pb or S). CHAPTER 4 discusses the ion sensing applications of PbS quantum dots. We found that the sulfur related dangling bonds are quite sensitive to different metallic ions (since mercaptoethanol passivates only Pb atoms). Sulfur related PL band (~ 1 eV) have shown an order of magnitude improvement in its intensity for Hg, Ag ions and relatively low enhancement for Zn, Cd ions at 1 µmol concentrations. However Cu quenches the luminescence. An important distinction may have to be made between PbS and Cd related quantum structures. The PbS QDs can distinguish between Cu & Hg, however Cd related QDs couldn’t distinguish between these two ions. Photo-brightening and photo-darkening is an interesting phenomena indicative of photo-induced ionic migration that either helps in enhancing the emission of sulfur related defect emission or degrades the emission properties depending on the ion concentration. This report is the first of its kind in ion sensing applications using PbS QDs. CHAPTER 5 discusses the results of duel beam excitation on trap luminescence of PbS QDs. By using different lasers simultaneously (514 nm and 670 nm), we have observed the reversible luminescence quenching of trap emission. The high-energy PL band (1.67 eV) has double the quenching effect compared to low-energy PL band (1.1 eV). The luminescence quenching mechanism is attributed to the re-emission of the charge carriers from the traps (photo-ionization) due to the simultaneous excitation with the second beam. The dependence of the temperature, the effect of two beam excitation intensities and modulation frequency dependent quenching mechanism are primarily focused in this chapter. The quenching mechanism is considered to be quite useful in the optical modulation devices. CHAPTER 6 discusses the PL results on various morphologies of PbS nano-, microstructures. Interestingly, after protecting the surface with organic ligands such as mercaptoethanol (C2 H5OSH), dendrite structures have shown high-energy bands (~ 1.0 eV) in the PL spectra, which indicate the existence of various quantum confinement regimes in different branches of dendrites. The anomalous temperature dependent behavior of PL intensity is attributed to the size distribution. CHAPTER 7 discusses the results of photoconductivity measurements on various morphologies of PbS nano-, micro-structures. Flower shaped structures have shown persistent photoconductivity (PPC). This observed PPC is attributed to the presence of potential barriers, which are created by the different confinement regimes or due to the lattice relaxation, which occurs due to the carrier trapping at surfaces. In PPC, the estimated time constants of both build up and decay transients using the stretched exponentials are of the order of few tens of seconds. In PPC measurements, we observe the PC quenching below 40 K and growth above this temperature. PC quenching is attributed to the transfer of photo-excited carriers to a metastable state. The presence of metastable state is supported by the dark conductivity measurements in flower shaped structures. CHAPTER 8 presents the summary and directions for the future work.