Made available in DSpace on 2014-10-09T12:52:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:36Z (GMT). No. of bitstreams: 0 / As espumas de polietileno são amplamente utilizadas. Suas aplicações vão de aparelhos domésticos a artefatos médicos, incluindo aplicações nas indústrias de construção civil e automobilística. As propriedades das espumas dependem da densidade e da sua estrutura celular, em outras palavras, da quantidade de células abertas e fechadas, da distribuição e do tamanho das células. Os métodos de produção de espumas de polietileno reticulado são classificados em dois tipos, de acordo com o método de reticulação. Um dos métodos é a reticulação química, que utiliza peróxidos como agente reticulante, O outro método é a reticulação por irradiação, utilizando feixe de elétrons. As espumas obtidas a partir do polietileno reticulado pelo processo de irradiação apresentam superfície lisa e homogênea, e são formadas basicamente por células fechadas. O objetivo deste trabalho foi utilizar a radiação ionizante para a formação de ligações cruzadas entre as moléculas de polietileno de baixa densidade (LDPE), que permitiu a obtenção das espumas. As suas propriedades mecânicas, térmicas e morfológicas foram avaliadas. As amostras de polietileno com densidade de 0,946 g/cm3, contendo 5% de azodicarbonamida (ADCA), agente expansor, foram irradiadas com feixe de elétrons de alta energia com doses de radiação de 10, 20, 30, 40, 50, 60, 80 e 100 kGy. Após a irradiação, as amostras de LDPE foram colocadas em um forno para expansão térmica e formação das espumas. Foi determinado o grau de reticulação das espumas. Algumas amostras também foram envelhecidas termicamente. O desempenho mecânico das amostras de espumas foi avaliado por meio de ensaios de tração e deformação, dureza, deformação permanente por compressão e resiliência. Também foram realizados ensaios de termogravimetria (TGA) e de microscopia eletrônica de varredura (MEV). Os resultados mostraram que no intervalo de doses de radiação estudadas, a resistência à tração aumenta com o aumento do grau de reticulação. Nos ensaios de resistência à compressão, a partir da dose de radiação de 40 kGy, observou-se um decréscimo nos valores obtidos. Já a resiliência sofreu pouca aheração. De acordo com a análise morfológica pode-se concluir que a dose de radiação de 30 kGy foi a que promoveu a formação de espumas com estrutura celular fechada e mais homogênea. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:47:47Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:33Z (GMT). No. of bitstreams: 1 08364.pdf: 6489589 bytes, checksum: 1e73a94458be296353fbd0a5d5f21ab4 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Les matériaux poreux sont omniprésents dans la société grâce à leurs remarquables propriétés provenant de la combinaison de leur structure mésoscopique et de leur nature physico-chimique très versatiles. L’objectif de cette thèse est l’étude du lien entre les propriétés mécaniques de mousses élastomères et leur structure mésoscopique (porosité ouverte ou fermée et diamètre des pores) et la nature physico chimique de matrice élastomère. Pour ce faire il a été nécessaire de synthétiser des matériaux modèles dont il est possible de décorréler les effets dus à la structure et ceux dus à la nature de la matrice polymère. La technique de ‘template’ par émulsion hautement concentrée HIPE (High Internal Phase Emulsion) a été sélectionnée car elle permet de faire varier la structure et la composition chimique de la matrice. Le contrôle des paramètres de l’émulsion (fraction de phase dispersée, nature des monomères et des réticulants, quantité de tensioactif et de réticulant) permet de moduler la morphologie des matériaux. De plus il est possible de changer un des paramètres indépendamment de tous les autres. Cette technique a permis d’obtenir une série de matériaux avec une structure poreuse et une nature physico-chimique contrôlées à façon. Dans le cas particulier des mousses solides élastomères très faiblement réticulées un phénomène d’effondrement des pores peut être observé. Ces mousses sont caractérisées mécaniquement en compression en fonction de trois paramètres physiques : la température de transition vitreuse de la matrice polymère, le taux de réticulation et le diamètre des pores de la mousse. Une étude du module élastique et de la dissipation d’énergie des mousses élastomères a été effectuée dans le but de mieux comprendre le lien avec la nature physico-chimique et la structure mésoscopique des mousses à l’origine des propriétés mécaniques originales. Les réponses temporelles particulièrement lentes de nos élastomères observées lors des essais mécaniques ont conduit à des études de recouvrance des mousses ainsi que la détermination d’un modèle théorique. / Foams are everywhere in the society thanks to their remarkable properties resulting from the coupling of their structure and their physico-chemical nature which are very adaptable. The main goal of this thesis is the study of the relationship between mechanical properties of elastomeric foams and their mesoscopic structure (open or closed-porosity and cells diameter) and their physico chemical nature of elastomeric matrix. In this context, it was necessary to synthesize model porous materials with well-controlled densities and structure. HIPE (High Internal Phase Emulsion) template technique was used thanks to its ability modifying matrix chemical composition and structure. Control of emulsion’s parameters (internal phase ratio, monomers and crosslinker nature, surfactant and crosslinker content) enables tuning foam morphology. Moreover it enables to vary one parameter without changing others. Thanks to this method we were able to synthesize elastomeric foams with well-controlled structure and physico-chemical nature matrix. In the real special case of very low crosslinker content, foam collapsing effect has been detected. Foams are mechanically characterized in compression test depending on tree parameters: glass transition temperature of the polymer matrix, crosslinked ratio and cells diameter of the foam. Elastic modulus and dissipated energy are studied to inverstigate more deeply the relationship with physico-chemical nature and mesoscopic structure. Time behavior response of foams leads us to study recovery ratio of foams and we try to determine a theoretical model.

Le projet Européen UNIfHY a vu le jour dans une optique de production d’hydrogène à partir de biomasse pour le remplacement des énergies fossiles. La purification des gaz produits par la gazéification de la biomasse permet l’obtention d’hydrogène pur pour une utilisation dans les piles à combustible. Cette thèse s’inscrit dans ce projet avec pour but le développement de catalyseurs Fe/CeO2 et Cu/CeO2 déposés sur des supports de mousse céramique pour la réaction de conversion du gaz à l’eau à haute et basse températures, de manière à augmenter la production d’hydrogène et diminuer la perte de charge dans le système. Les principaux objectifs de la thèse sont la synthèse et les caractérisations des catalyseurs à base de fer et de cuivre, l’optimisation des conditions réactionnelles dans la limite du cadre fixé par le projet, la modélisation cinétique en présence des catalyseurs Fe/CeO2 et Cu/CeO2 et la transposition à grande échelle des catalyseurs pour une utilisation en réacteur pilote. / The UNIfHY European project was launched in an optic of producing hydrogen from biomass to replace fossil fuels. Purification of gases produced by biomass gasification allows obtaining pure hydrogen which can be used in fuel cells. This thesis takes part in this project with the development of Fe/CeO2 and Cu/CeO2 catalysts deposited on ceramic foam supports for high temperature and low temperature water gas shift reaction to increase the production of hydrogen and decrease the pressure drop in the system. The main objectives of this thesis are the synthesis and characterizations of iron and copper based catalysts, the optimization of reaction conditions within the limits of the framework set by the project, the kinetic modeling of the reaction in the presence of Fe/CeO2 and Cu/CeO2 catalysts and the scale-up of catalysts to use them in a pilot reactor.

Polystyrene (PS) nanocomposite foams were prepared using supercritical fluid (SCF) CO2 as a solvent and blowing agent. PS was first in-situ polymerized with a range of concentrations of montmorillonite layered silicate (MLS). The polymerized samples were then compression molded into 1 to 2mm thick laminates. The laminates were foamed in a batch supercritical CO2 process at various temperatures and pressures from 60°-85°C and 7.6-12MPa. The resulting foams were analyzed by scanning electron microscopy to determine effect of MLS on cellular morphology. Differential scanning calorimetry was used to determine the impact of nanocomposite microstructure on glass transition of the foamed polymer. X-ray diffraction spectra suggested that the PS/MLS composite had an intercalated structure at both the 1% and 3% mixtures, and that the intercalation may be enhanced by the foaming process.

Recently developed mathematical tools for the modelling of contact problems on thin film structures are adapted to allow the investigation of arbitrarily mixed purely isotropic and transversally isotropic laminate structures. The new tool is applied to model a variety of load problems resulting in the failure of windsurfing boards consisting of a relatively thin laminate shell and a soft polymer foam core. It is shown that local impact and distributed bending loads due to “bad landing” after high jumps or contact with parts of the sailing gear (the so called rig) especially the front part of the boom are leading to the most critical stress distributions resulting in failure. So most of the investigated boards were damaged because the rider (windsurfer) landed flat and thus produced a sudden impact force under his feet (impact defect). Other overloading occurred due to overturning of so called loop movements or the landing of the board exactly on respectively between two waves and this way producing high bending moments. Some of those typical loads are analysed in detail and the stresses occurring in the complex structure of the windsurfing boards are evaluated.

Title: Study of cooperative dislocation phenomena in solids by the acoustic emis- sion technique Author: Michal KNAPEK Department: Department of Physics of Materials Supervisor: doc. RNDr. František Chmelík, CSc., Department of Physics of Materials Abstract: Plastic deformation of micron-scale crystalline materials differs con- siderably from bulk specimens, as it is characterized by random strain bursts. Three categories of metallic samples were investigated in this thesis: micron- scale copper micropillars with varied geometries, submillimeter-scale aluminum microwires, and aluminum and aluminum-magnesium salt-replicated foams. Very precise fabrication methods and sensitive measurement set-ups consisting of uni- axial compression and tensile tests with concurrent acoustic emission (AE) record- ing were developed. These fine methods allowed for investigations of effects re- lated to plastic deformation at micrometer scales, i.e. the dislocation dynamics associated with the stress drops. Size effects in plastic deformation, as well as clear correlations between the stress drops and the AE events, were found in mi- crosamples, confirming that dislocation avalanches are indeed responsible for the stochastic character of deformation processes also at microscales. Open-cell pure aluminum and aluminum-magnesium...

Manufacturing of Mechanical Supporting Foamed Sheets by processing Free Flowing Phenolic Molding Compounds with the Foam Extrusion and its Characterization

The limiting current technique has widely been used to study liquid-solid mass transfer in various reactor configurations. In the present contribution several underlying physical aspects have been investigated in order to improve the design of mass transfer experiments. Experimentally, the significant influence of electrolyte composition and hydrodynamic conditions have been studied and quantified to ensure conditions of high reproducibility. In the course of single phase COMSOL simulations, different electrode configurations have been examined with emphasis on concentration fields and electric current distribution showing a large sensitivity of the experimental configuration on the absolute current values.

Kolmaterial, såsom kolfibrer och kolskum, används som värmeisolatorer i applikationer vid höga temperaturer. För närvarande härleds dessa material från fossilbaserade källor, vilket tyder på ett behov av att hitta alternativa kandidater baserade på förnybara källor. Detta examensarbete undersökte möjligheten att använda kraftlignin som ett förnyelsebart startmaterial för framställning av kolskum med värmeisoleringsegenskaper. Två kraftligniner av barrträd med olika molekylvikter och ett kraftlignin av lövträd användes. De tre kraftligninerna karboniserades vid 1000°C efter att ha blandats i olika förhållanden och kombinationer (formuleringen av råmaterialet). Formuleringen av råmaterialet påverkade densiteten och porositeten hos de erhållna materialen, vilket i sin tur ledde till skillnader i kompressionsstyrkan och värmeledningsförmågan hos de erhållna kolskummen. Kolskummen hade olika värmeledningsförmåga (0,11-0,35 W/mK), porositet (80,55-97,53%) och densitet (0,08-0,42 g/cm3). För skummet med den högsta densiteten uppskattades krossstyrkan till cirka 10,03 MPa vilket är jämförbart med kommersiellt använda kolskum för högtemperaturisolerande applikationer. Kolskummens värmeledningsförmåga var inom omfånget för kommersiellt använda kolskum för högtemperaturapplikationer. Detta arbete visar möjligheten att tillverka kolskum från 100% kraftlignin som har liknande egenskaper som kommersiellt tillgängliga termiska isoleringsmaterial för högtemperaturapplikationer. / Carbon materials, such as carbon fibres and carbon foams, are used as thermal insulators in high-temperature applications. At present, these materials are derived from fossil-based sources, which suggests a need of finding alternatives candidates based on renewables. This thesis work investigated the possibility of using kraft lignin as a renewable starting material for the preparation of carbon foams with thermal insulation properties. Two softwood kraft lignins with different molecular weights and a hardwood kraft lignin were used. The three kraft lignins were carbonized at 1000°C after being mixed in different ratios and combinations (precursor formulation). The precursor formulation affected the density and porosity of the obtained materials, which in turn led to differences in compression strength and thermal conductivity of the carbon foams derived. The obtained carbon foams had different thermal conductivities (0.11-0.35 W/mK), porosity (80.55-97.53%) and density (0.08-0.42 g/cm3). For the foam with the highest density, the crushing strength was estimated to approximately 10.03 MPa which is comparable to commercially used carbon foams for high-temperature insulating applications. The thermal conductivity of the prepared carbon foams was in the range of commercially used carbon foams for high-temperature applications. This work demonstrates the possibility of preparing carbon foams from 100% kraft lignin which has properties similar of commercially available insulating materials for high-temperature applications.