Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nos últimos 20-30 anos polímeros biodegradáveis vêm sendo estudados e desenvolvidos e atualmente já são comercializados. Contudo, o custo, a processabilidade e algumas propriedades ainda dificultam a penetração desses polímeros no mercado e a competição com as chamadas commodities. Não são poucos os autores que se dedicam a desenvolver aditivos e formulações para superar essas limitações. Desta forma, esta Tese se dedicou ao desenvolvimento de compósitos de Ecobras, fabricado pela Basf e comercializado pela Corn Products, utilizando como carga mineral resíduo da extração da bauxita, no município de Santa Luzia/PB, o qual consiste em sua totalidade de vermiculita. Esta vermiculita foi quimicamente modificada com sais de alquil fosfônio para melhorar a compatibilidade com a matriz polimérica e também espaçar as camadas de aluminossilicato. De fato, a modificação com o brometo de hexadecil tributil fosfônio resultou na esfoliação da vermiculita tornando-a potencialmente apropriada para a obtenção de nanocompósitos. A preparação dos compósitos foi realizada pelo método de intercalação no estado fundido e foram comparadas a utilização da câmara interna de mistura e da mini extrusora de dupla rosca, sendo esta última mais eficaz na dispersão da vermiculita, conforme revelado pela microscopia eletrônica de varredura, difração de raios-X e reometria de placas. O grau de dispersão também foi influenciado pela estrutura química do modificador da vermiculita e pelo teor dessa carga incorporada à matriz. Teores mais elevados levaram a formação de aglomerados, enquanto a modificação da carga implicou na formação de micro e nanocompósitos. Ainda houve alterações das propriedades térmicas com aumento dos valores da temperatura de transição vítrea, de cristalização e fusão, embora o grau de cristalinidade tenha sido mantido. Nitidamente, foram obtidos materiais mais rígidos, com maior módulo e menor capacidade de deformação. Cerca de 58% de perda de massa foi observada para os micro e nanocompósitos obtidos após 17 semanas de enterro em solo simulado para avaliação da biodegradabilidade, valor bem próximo ao Ecobras puro. De modo geral, a incorporação das diferentes vermiculitas retardou nas primeiras semanas a biodegradação, provavelmente em função de modificações na estrutura cristalina, conforme sugerido pelos maiores valores de temperatura de fusão observados durante o acompanhamento do processo de biodegradação. No entanto, após 7 semanas os perfis de biodegradação dos micro e nanocompósitos se aproximaram bastante do Ecobras puro. Desta forma, foi possível nesta Tese obter um nanocompósito de Ecobras com vermiculita modificada com brometo de hexadecil fosfônio utilizando ferramentas comuns de processamento no estado fundido com biodegradabilidade próxima ao polímero de partida, porém mais rígido e menos deformável / In the last 20-30 years biodegradable polymers have been studied and developed and currently are already commercialized. However, cost, processability and some properties still avoid the penetration of such polymers on the market and the competition with the so-called commodity. There are few authors who are dedicated to developing additives and formulations to overcome these limitations. Thus, this thesis is devoted to the development of Ecobras composites, blend of PBAT and starch manufactured by BASF and commercialized by Corn Products, using as mineral filler a residue of bauxite extraction from Santa Luzia / PB, which consists entirely of vermiculite. The vermiculite was chemically modified with alkyl phosphonium salts to improve compatibility with the polymer matrix, and also to increase the space between aluminosilicate layers. In fact, its modification with hexadecyl tributyl phosphonium bromide promoted the exfoliation of vermiculite making it potentially suitable for obtaining a nanocomposite. The preparation of the composites was performed by the melt intercalation technique. Internal mixing chamber and a twin screw mini-extruder were compared as processing tool, the latter was more effective in dispersing the vermiculite, as revealed by scanning electron microscopy, X-ray diffraction and plate rheometry. The degree of dispersion was also influenced by the amount and chemical structure of the vermiculite. Higher filler levels led to formation of agglomerates, while filler modification led to formation of micro and nanocomposites. There were changes in the thermal properties with increasing temperature values of glass transition, crystallization and melting, although the degree of crystallinity has been retained. Clearly, stiffer materials were obtained, with a higher modulus and low strain capacity. About 58% of weight loss was observed for micro and nanocomposites after 17 weeks of burial in simulated soil for evaluation of biodegradability, very close to pure Ecobras value. Generally, the incorporation of different vermiculite delayed biodegradation in the first weeks, probably due to changes in crystalline structure as suggested by the higher melting temperature values observed during the monitoring of the biodegradation process. However, after seven weeks of the micro and nanocomposites biodegradation profiles approached quite to pure Ecobras. Thus, it was possible in this work obtain a Ecobras nanocomposite with hexadecyl tetrabutyl phosphonium bromide modified vermiculite prepared by melt intercalation technique using common processing tools and with biodegradability close the starting polymer, but more rigid and less deformable

Made available in DSpace on 2015-05-14T13:21:36Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 890995 bytes, checksum: 4c0bc26823987fb8daa080ac8761b740 (MD5) Previous issue date: 2009-11-13 / Fundação de Amparo à Pesquisa do Estado de São Paulo - FAPESP / The interactions between lamellar silicate with dyes have been widely studied for analytical applications that are intended as and electrochemical adsorption. In this work, sodium vermiculite (Vs) and vermiculites exchanged with copper (V/Cu) and cobalt (V/Co) and through controlled leaching (Vac1 and Vac3) were synthesized. The vermiculite reacted with nitric acid at concentrations 1.0 and 3.0 mol/dm3 originating materials named as Vac1 and Vac3. The different solids were characterized by chemical analysis, absorption spectroscopy FTIR, XRD, thermogravimetry and surface area. The solids were used as adsorbents for methylene blue dye (AM) and blue meldola (AD). Leaching of sodium vermiculite originated restructured porous solids with high surface areas whose values were 133 and 673 m2 g-1 for Vac1 and Vac3, respectively. The AM maximum dye quantities retained (Nf) were 0,042, 0,029, 0,00085, 0,020 and 0,021 mmol g-1 para os sistemas for systems Vs, Vac1, Vac3, V/Co and V/Cu respectively. For dye AD, the values of Nf were 0,038, 11.2 and 11.9 mmol g-1 for Vs, V/Cu and V/Co. It was that the adsorption capacity was independent of the nature of the dyes, but was influenced by the interlayer cation. The interactive processes dye/clay reactions involving the insertion and/or ion exchange. Regardless of the solid, it was observed that as the leaching became more pronounced, was deacreased companing with the original vermiculite the reactivity of the activated matrices for the original vermiculite. Solids derived from vermiculite have shown potential adsorbents for species pollutants such as organic dyes in solution. / As interações entre silicatos lamelares com corantes têm sido extensamente estudadas devido aplicações analíticas a que se destinam como eletroquímica e adsorção. Neste trabalho, a vermiculita sódica (Vs) e modificadas por troca iônica com cobre (V/Cu) e cobalto (V/Co) e através de lixiviação controlada (Vac1 e Vac3) foram sintetizadas. A vermiculita foi submetida a tratamento ácido com o ácido nítrico nas concentrações 1,0 e 3,0 mol/L originando os materiais denominados Vac1 e Vac3. Os diversos sólidos foram caracterizados por analise química, espectroscopia de absorção na região do infravermelho, DRX, termogravimetria e área superficial. Os sólidos foram aplicados como adsorventes para os corantes azul de metileno (AM) e azul de meldola (AD). A lixiviação da vermiculita sódica originou sólidos porosos reestruturados com elevadas áreas superficiais cujos valores foram 133 e 673 m2 g-1 para Vac1 e Vac3, respectivamente. Os valores máximos de corante AM retido Nf foram de 0,042, 0,029, 0,00085, 0,020 e 0,021 mmol g-1 para os sistemas Vs, Vac1, Vac3, V/Co e V/Cu respectivamente. Enquanto para o corante AD, os valores de Nf máximos foram de 0,038, 0,015 e 0,011 mmol g-1 para os sistemas Vs, V/Cu e V/Co. Verificou-se que a capacidade de adsorção foi independente da natureza dos corantes, mas foi influenciada pela natureza do cátion interlamelar. Os processos interativos corante/argila envolveram reações de intercalação e/ou troca iônica. Independentemente do sólido, observou-se que a medida que a lixiviação se tornou mais acentuada, não houve um aumento na reatividade frente aos corantes das matrizes ativadas em relação a vermiculita original. Os sólidos derivados da vermiculita se mostraram adsorventes potenciais para espécies poluentes como corantes orgânicos em solução.

Neste trabalho estudou-se o efeito de três diferentes tratamentos químicos utilizando- se soluções aquosas de LiCl, NaCl, e HCl sobre o inchamento, a distribuição de tamanho de partículas e a capacidade de troca catiônica (CTC) de uma vermiculita proveniente da jazida de Paulistana, localizada no Estado do Piauí, visando seu uso em compósitos de matriz polimérica. Para os tratamentos com sais inorgânicos foram utilizadas várias concentrações de LiCl e NaCl a 90°C por 144 horas, permitindo a secagem da solução de tratamento. Para o tratamento ácido foram utilizadas soluções 2M de HCl à temperatura ambiente, utilizando tempos de tratamento de 2 a 10 horas. Após os tratamentos, as amostras foram submetidas a agitação mecânica intensa em dispersor de alta energia de cisalhamento (24000 RPM). Todos os tratamentos empregados resultaram em aumentos nos índices de inchamento e reduçães nos tamanhos de partícula em diferentes graus. Os maiores inchamentos antes da agitação mecânica foram observados nas amostras tratadas com soluções 0,8M de LiCl sem lavagem (4 a 5 vezes a da prova em branco). Após agitação mecânica, os maiores inchamentos foram observados nas amostras tratadas com soluções 2M de HCl por 5 horas (11 vezes a da prova em branco). No entanto, após o processo de secagem não foi possível atingir-se os mesmos valores de inchamento. A diminuição mais importante no tamanho de partícula foi observada nas amostras tratadas com soluções 2M de HCl durante 5 horas, enquanto que as quedas mais significativas nos valores de CTC foram obtidas com as amostras tratadas com soluções 2M de HCl (CTC crescentes com o aumento do tempo de tratamento). Foi analisado o efeito da incorporação de vermiculita tratada acidamente em uma matriz polimérica de polipropileno (PP). A presençaa dessa vermiculita provocou um alto nível de degradação na matriz de PP, com a consequentemente perda de propriedades mecânicas. Esta degradação pode ser atribuída à formação de sítios ácidos nas partículas de vermiculita gerados pelo ataque do HCl, bem como à presença de HCl residual da solução de tratamento. / In the present work, the effect of three different chemical treatments using inorganic solutions of LiCl, NaCl, and HCl on the swelling, particle size distribution, and cation exchange capacity (CEC) of a vermiculite clay was studied. The clay is originary from Paulistana mine, located in the State of Piauí, Northeastern Brazil, and the final purpose of the treatment of the clay was its use in polymer-matrix composites. For the inorganic salts treatments, several solutions of NaCl and LiCl at different concentrations were used, at 90°C for 144 hours, allowing the treatment solution to dry out. For the acid treatment, 2M HCl solutions at room temperature were used, using treatment times of 2 to 10 hours. After the treatments, all the samples were subjected to intense mechanical stirring in the high shear energy disperser (24000 RPM). The results showed that all treatments resulted in increases in the rates of swelling and reduction in the mean particle sizes, in different degrees. The largest swelling before mechanical stirring was observed in samples treated with solutions of 0.8M LiCl without washing (4 to 5 times that of the untreated sample). After mechanical desagglomeration, the highest swelling was observed in samples treated with solutions 2M HCl for 5 hours (11 times that of the untreated sample). However, after drying, it was no longer possible to achieve the same values of swelling. The most significant decrease in particle size was observed in samples treated with solutions 2M HCl for 5 hours, whereas the most significant reduction in the CEC values were also obtained with the samples treated with solutions 2M HCl (CEC increasing with the time of treatment). Finally, the effect of the addition of the acid treated vermiculite to a polymeric matrix of polypropylene (PP) was examined. The evaluation of the resultant composite specimens indicated that the presence of vermiculite caused a high level of degradation of the PP matrix, with the consequent loss of mechanical properties. This degradation can be attributed to the formation of acidic sites on the vermiculite particles, generated by the direct attack of HCl, and the presence of residual HCl from the treatment solution.

Afin de protéger les denrées alimentaires, l’industrie d’emballage enduit sur un film une couche très fine de polymère pour augmenter ses propriétés barrière aux gaz. Le problème majeur de ces enduits, généralement faits de poly (chlorure de vinylidène), vient de leur production de gaz toxiques à l’incinération. Les restrictions environnementales mondiales évoluent rapidement et sont de plus en plus strictes. De ce fait, des bioplastiques sont envisagés comme alternative. Dans ce contexte, l’objectif de la présente thèse est d'étudier le revêtement de films poly(téréphtalate d’éthylène) avec un polysaccharide, le chitosane. Ce dernier possède de bonnes propriétés barrières au gaz à sec. Cependant, son application dans l’emballage est limitée à cause de son caractère hydrophile. Le but de notre étude est donc d'améliorer les propriétés barrières à sec du chitosane par l’ajout de nano-charges d’argile et sa résistance à l’humidité par greffage de l’acide palmitique à la chaine du chitosane. L'efficacité d'incorporation de la vermiculite a été confirmée par DLS, DVS et DRX. Un facteur d'amélioration de la barrière (BiF) d’environ 100 pour l'hélium et de plus de 10 pour le dioxygène avec l'addition de 50% de vermiculite a été obtenu à sec. Le greffage de l’acide palmitique a été confirmé par spectroscopie IR-TF, ATG, DSC et RMN. Les résultats de mesures de la perméabilité hélium montrent une amélioration de facteur de la barrière (BIF) de 2 d’une couche de chitosane-g-acide palmitique et vermiculite à 60% en poids par rapport au PET non revêtu à 98% HR. / In order to protect food, the packaging industry performs a film coating with a very thin polymer layer to increase its gas barrier properties. The major problem of these coatings is that they are generally made of poly(vinylidene chloride) which leads to a toxic gas production during incineration. In view of the rapid change of the global environmental restrictions that become quite stringent, bioplastics seem promising alternatives. In this context, this thesis deals with a fundamental study of poly(ethylene terephthalate) films coated with a polysaccharide: chitosan. Chitosan offers good barrier properties in dry conditions. However, its application in the packaging is limited because of its hydrophilic character. Therefore, the main goal of our work is on one hand to enhance the dry barrier properties of the material through adding nanoclays and on the other hand to improve its resistance to moisture by incorporating palmitic acid by grafting it to the chitosane backbone. The incorporation efficiency of vermiculite was confirmed by DLS, DVS and XRD. A barrier improvement factor (BiF) of about 100 for helium and more than 10 for dioxygen with the addition of 50% vermiculite was obtained under dry conditions. The grafting of palmitic acid has been confirmed by FTIR spectroscopy, ATG, DSC and RMN. The results of helium permeability measurements showed an improvement of the barrier factor (BIF) of 2 in the case of a chitosan-grafted-palmitic acid layer with 60 weight% of vermiculite compared to the uncoated PET at 98% RH.

L’évolution des structures poreuses du graphite et de la vermiculite expansés a été étudiée insitu sous pression uniaxiale. Les propriétés d'un matériau résultant des propriétés intrinsèques à lamatrice et de celles dues à la porosité, les études faites dans ce travail ont porté sur deux échellesdifférentes. Les évolutions structurales de la structure cristalline du graphite et de la vermiculite ontd'abord été étudiées à haute pression en cellule à enclumes de diamant. Cette partie du travail a permisd'établir les équations d'état de la vermiculite et de contribuer, de manière significative, à lacaractérisation de la phase haute pression du graphite: une nouvelle phase, le Carbone Z, a étéproposée après l’analyse des données de la spectroscopie Raman couplée aux simulations. Desdéveloppements techniques ont été particulièrement réalisés pour permettre d’étudier in situl'évolution de la porosité sous pression par diffusion aux petits angles sous pression. L’application dumodèle fractale à l’analyse des données a permis de suivre l’évolution de la dimension fractale et de lasurface spécifique apparente. Les échantillons étudiés sont des formes comprimées de graphite et devermiculite expansés dans lesquelles les plans basaux des cristallites ont une orientation préférentielle.Sous pression uniaxiale, la structure poreuse du graphite expansé comprimé évolue à travers uneffondrement irréversible des pores ou un cisaillement de la matrice suivant l'orientation de la pressionappliquée par rapport à l'orientation préférentielle des plans basaux des cristallites. Des expériencescomplémentaires de mesures électriques et de mesures de la porosité par intrusion de mercure ontpermis de confirmer ces modèles proposés. Dans la vermiculite expansée comprimée, les fissuresapparaissent, de manière générale, sous l’effet de la pression uniaxiale. / The porous structure of expanded graphite and expanded vermiculite has been studied insitu under uniaxial stress. The properties of a porous material being related to the matrix and to theporosity, the in situ evolution under of the crystalline structure (of the matrix) under high pressurehave been first investigated using diamond anvil cell. The equation of state of expanded vermiculitehas been established. This first part of this work allowed giving a particular insight to the study of theunsolved high pressure phase of graphite. Combining Raman scattering data and calculations, a newstructure, called Z-Carbon, has been proposed. Thanks to the specific technical developments of thiswork, the porosities of expanded graphite and expanded vermiculite based systems have been studiedin situ under uniaxial stress. The used of fractal model in data analysis allowed following the evolutionof the fractal dimension and of the apparent specific surface The studied samples were made ofcompressed forms of expanded graphite and expanded vermiculite in which the basal plane of thecrystallites have a preferential orientation. The uniaxial stress was taken perpendicular and parallel tothis preferential direction. The porous structure of the expanded graphite sample was found to undergoan irreversible collapse of the pores or a cracks and creation and propagation. Additional electrical andporosity measurements supported the proposed models. In the expanded vermiculite based systems,the crack apparition was observed under uniaxial stress.

Cette étude s’inscrit dans le projet ANR Célajoas (ComposÉs LAmellaires pour les JOints en Applications Sévères) dont l’objectif est l’étude et l’optimisation de joints d’étanchéité à base de vermiculite exfoliée compactée (VEC). Ces joints d’étanchéité doivent se substituer aux joints à base de graphites pour des applications à hautes températures (800 °C) et à pressions élevées (200 bars). Des essais de mise en œuvre ont permis de mettre en évidence différents paramètres,tels que le type de vermiculite, la pression et la température de compaction sur les performances de ces joints. Les caractérisations expérimentales ont fournis des informations sur la microstructure et les propriétés de joints à base de la VEC. Ainsi, une étude par microscopie électronique à balayage, en compléments de résultats de porosimétrie mercure ont permis d’obtenir certaines caractéristiques du réseau poral. Des caractérisations expérimentales ont fournis les principales propriétés mécaniques anisotropes (modules élastiques, reprise élastique, contrainte à rupture) ainsi que la perméabilité de la VEC et donc le taux de fuite des joints à base de la VEC. Dans un souci de compréhension et d’optimisation des propriétés de ces joints, différents outils de prévisions des propriétés macroscopiques sont proposés. Tout d’abord, un modèle de prévision de la perméabilité,qui se scinde en deux étapes :a) Tout d’abord la construction du réseau poral simplifié en utilisant les résultats des caractérisations expérimentales, b) la résolution, par la méthode des éléments finis, du problème de l’écoulement du fluide à travers le milieu poreux. Les résultats numériques sont confrontés à ceux obtenus par des approches analytiques simples (du type Carman-Kozeny). L’effet de la micromorphologie et du taux de porosité sur la perméabilité sont ensuite examinés. Pour surmonter les difficultés liées à la résolution par la méthode des éléments finis, un modèle semi analytique est ensuite proposé. L’objectif de cette approche est de fournir un outil simple (type bureau d’étude) de prévision de la perméabilité de la VEC, sans avoir recours à un logiciel d’éléments finis. Enfin, pour dimensionner un joint d’étanchéité, il est indispensable de connaître les propriétés mécaniques (modules d’élasticité…) afin de déterminer, par exemple, la pression de serrage du joint. En raison des spécificités du matériau étudié (squelette isotrope transverse, taux de porosité de l’ordre de30 %), un modèle d’homogénéisation itératif, basé sur des approches analytiques classiques, est proposé pour évaluer l’influence de certains paramètres de la micro géométrie (rapport de forme des porosités, leur orientation…) sur les propriétés élastiques de la VEC. / This study deals with the study and optimization of gaskets made from compacted exfoliated vermiculite(VEC). It is a response to the need to replace gaskets made from graphite for high temperature (800 °C) and high pressure (200 bars) applications. In this work [in the aim of providing information on the microstructure and properties of VEC gaskets] experimental characterization have been conducted. The influence of different parameters such as the type of vermiculite, pressure and temperature of compaction on the performance of these gaskets has been studied. From scanning electron microscopy and mercury porosimetry results, some characteristics of the porous network have been identified. The anisotropic mechanical properties (elastic properties, elastic recovery, tensile stress), the permeability and the leakage rate of the VEC have also been characterized. Based on experimental data, a finite element (FE) predicting model for permeability evolution has been developed. This model is divided in two steps:a) using the results of the experimental characterization, the pore network is constructed; b) the problem of fluid flow through the porous media is solved by finite element method. The numerical results have been confronted with analytical models (Carman-Kozeny). The effect of micromorphology and porosity is discussed. Due to meshing problems, a semi-analytical model is also proposed. The aim of this approach is to provide a simple tool (type design office) for predict the permeability of VEC, without have recourse to finite element software. The mechanical properties are necessary to design a gasket. Eventually, thanks to specificities of the studied material (skeleton transverse isotropic, porosity of around 30%), a model of iterative homogenization is proposed to evaluate the influence of some parameters of the micro geometry (porosities ratio, orientation ...) on the elastic properties of the VEC. This work is supported by the French research national agency (ANR) through the Célajoas project (ComposÉs LAmellaires pour les JOints en Applications Sévères).

Le processus d'aluminisation dans les sols acides, conduit à la formation de minéraux argileux hydroxy-alumineux (HIMs). La fixation d'aluminium dans l'espace interfoliaire diminue la réactivité des feuillets expansibles (feuillets HI). La caractérisation des HIMs issus d'un Alocrisol a été réalisée par modélisation des diffractogrammes de rayons X (raies 00l) de la fraction <2 µm et de ses sous-fractions (<0.05, 0.05-0.1, 0.1-0.2 et 0.2-2 µm). Cette étude a montré que les HIMs sont des minéraux interstratifiés à deux ou trois types de feuillets (HI, illites et/ou expansibles). La proportion relative de feuillets HI par rapport à celle des feuillets expansibles diminue avec la taille des particules. La persistance de feuillets illitiques a été observée dans la fraction fine (<0.05 µm). Afin de tester l’effet de la taille des particules sur l'aluminisation, des expériences d'auto-aluminisation de vermiculites saturées K ou Ca séparées en trois fractions (0.1-0.2, 1 2 et 10-20 µm) ont été tentées. Toutes montrent l'importance du couple taille-cation interfoliaire sur le contrôle de l'échange et de la dissolution qui sont les processus de premier ordre pour l'aluminisation. C'est dans les expériences mettant en jeu les K vermiculites que la compétition entre ces deux processus conduit à la formation de minéraux interstratifiés aluminisés à trois composantes similaires à ceux identifiés dans les sols. L'effet de la taille des particules se marque par la persistance de feuillets illitiques comme cela avait été observé dans les fractions infra-micrométriques des sols. La compétition entre échange et dissolution sont donc très probablement le moteur des évolutions minérales dans les sols. / The aluminization process of clay minerals in acidic soils, leads to the formation of hydroxyl interlayered minerals (HIMs). It decreases the reactivity of the clay fraction by the fixation of aluminium in the interlayer space of expandable layers (HI). The characterization of HIMs from an Alocrisol was investigated through X-Ray Diffraction profile modeling (00l reflections) of the <2 µm size fraction and its sub-fractions (<0.05, 0.05-0.1, 0.1-0.2 and 0.2-2 µm). The results obtained highlight the mixed layer structure of HIMs which is composed of two or three different layers (HI, illites and/or expendables). The relative proportion of HI layers compared to that of expandable ones decreases with the particle size. In addition, the persistence of illite layers has been observed in the <0.05 µm size fraction. Auto aluminization experiments of K-or Ca- vermiculite separated in three-sized fraction (0.1-0.2, 1-2 and 10-20 µm) have been conducted in order to test the influence of the particle size on the aluminization process. These experiments exhibit the key role played both by the interlayer cation and the particle size on the cationic exchange and the crystal dissolution. The competition between of ion-exchange reactions and that of mineral dissolution on the K-vermiculite experiment, leads to the formation of 3 component MLMs (HI, illite and expandable) similar to those found in acidic soils. A similar effect of particle size leading to the persistence of illite layers was observed between the experiment products and the infra-micrometric particles of soils. Consequently, it is highly probable that both cation exchange and dissolution are the main processes governing the mineral evolutions in soils.

Made available in DSpace on 2014-12-17T15:42:13Z (GMT). No. of bitstreams: 1 FrancielAB_DISSERT.pdf: 3637529 bytes, checksum: 50d6de8b3a00a0b045a5b17d540f59d2 (MD5) Previous issue date: 2014-01-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Catalytic processes are widely present in everyday life. This results in large number of studies seeking materials that may combine the low cost catalytic efficiency. Based on this assumption, the clays have long been used as catalysts, with its huge availability, diversity and possibility of improving their properties from structural changes, primarily responsible for this great use. Among the natural clays, vermiculite due to their characteristic properties (high cation exchange capacity and expansion), is suitable for various applications including as catalysts and catalyst supports. In this work, the acid leaching of clay vermiculite was performed, coming from Santa Luzia-PB, with nitric acid (2, 3 and 4 mol / L) and subsequent calcination of the materials obtained. The materials were named as Vx/400, where x is the acid concentration employed and 400 used in calcination temperature. The effectiveness of changes made was determined by XRD techniques, FT-IR, EDS, TG/DTG, nitrogen physisorption and DTP of n-butylamine. Acid leaching has improved some properties of the clay - specific area and acidity - but the control of the acid concentration used is of vital importance, since the highest concentration caused the partial destruction of vermiculite entailing a decline in their properties. For analysis of the catalytic activity of the modified clay was made a comparative study with the SBA -15 mesoporous materials, synthesized via hydrothermal method, using the pyrolysis of low density polyethylene (LDPE). The results showed that the acid plays a fundamental role in the conversion of the polymer into smaller molecules, the material V3/400 was more selective for the source monomer (ethylene) due to their increased acidity, which promotes more breaks bonds in the polymeric chain, while materials and V0/400 V2/400, lower acidity, showed higher selectivity to light hydrocarbons, the range of fuel (41.96 and 41.23%, respectively), due to less breakage and secondary condensation reactions chains; already V4/400 SBA-15/550 and resulted in lower percentages of light hydrocarbons and the partial destruction of the structure and low acidity, respectively, responsible for the inefficiency of materials / Os processos catal?ticos est?o largamente presentes no cotidiano. Isso resulta no grande n?mero de pesquisas buscando materiais que possam aliar baixo custo ? efici?ncia catal?tica. Partindo desse pressuposto, as argilas t?m sido muito utilizadas como catalisadores, sendo sua grande disponibilidade, diversidade e possibilidade de melhoria de suas propriedades, a partir de modifica??es estruturais, os principais respons?veis por esse grande uso. Entre as argilas naturais, a vermiculita devido ?s suas propriedades caracter?sticas (alta capacidade de troca cati?nica e de expans?o), ? apta para diversas aplica??es, entre elas, como suportes catal?ticos e catalisadores. Neste trabalho, foi realizada a lixivia??o ?cida da argila vermiculita, oriunda de Santa Luzia-PB, com ?cido n?trico (2, 3 e 4 mol/L) e posterior calcina??o dos materiais obtidos. Os materiais foram nomeados como Vx/400, onde x corresponde ? concentra??o ?cida empregada e 400 ? temperatura usada na calcina??o. A efici?ncia das modifica??es realizadas foi determinada pelas t?cnicas de DRX, FT-IR, EDS, TG/DTG, fisissor??o de nitrog?nio e DTP de n-butilamina. A lixivia??o ?cida melhorou algumas propriedades da argila ?rea espec?fica e acidez , por?m o controle da concentra??o ?cida empregada ? de vital import?ncia, visto que a maior concentra??o provocou a destrui??o parcial da vermiculita, acarretando em um decr?scimo das suas propriedades. Para an?lise da atividade catal?tica das argilas modificadas fez-se um estudo comparativo com o material mesoporoso SBA-15, sintetizado via m?todo hidrot?rmico, empregando-os na pir?lise de polietileno de baixa densidade (PEBD). Os resultados mostraram que a acidez exerce papel fundamental na convers?o do pol?mero em mol?culas menores; o material V3/400 foi o mais seletivo para o mon?mero de origem (eteno), devido ? sua maior acidez, que promove mais cis?es nas liga??es da cadeia polim?rica; enquanto os materiais V0/400 e V2/400, de menor acidez, apresentaram maior seletividade para hidrocarbonetos leves, da faixa dos combust?veis (41,96 e 41,23%, respectivamente), em virtude de menos cis?es e rea??es secund?rias de condensa??o nas cadeias; j? V4/400 e SBA-15/550 resultaram nos menores percentuais de hidrocarbonetos leves, sendo a destrui??o parcial da estrutura e baixa acidez, respectivamente, respons?veis pela inefici?ncia dos materiais

Résumé : L'évolution des structures poreuses du graphite et de la vermiculite expansés a été étudiée in situ sous pression uniaxiale. Les propriétés d'un matériau résultant des propriétés intrinsèques à la matrice et de celles dues à la porosité, les études faites dans ce travail ont porté sur deux échelles différentes. Les évolutions structurales de la structure cristalline du graphite et de la vermiculite ont d'abord été étudiées à haute pression en cellule à enclumes de diamant. Cette partie du travail a permis d'établir les équations d'état de la vermiculite et de contribuer, de manière significative, à la caractérisation de la phase haute pression du graphite: une nouvelle phase, le Carbone Z, a été proposée après l'analyse des données de la spectroscopie Raman couplée aux simulations. Des développements techniques ont été particulièrement réalisés pour permettre d'étudier in situ l'évolution de la porosité sous pression par diffusion aux petits angles sous pression. L'application du modèle fractale à l'analyse des données a permis de suivre l'évolution de la dimension fractale et de la surface spécifique apparente. Les échantillons étudiés sont des formes comprimées de graphite et de vermiculite expansés dans lesquelles les plans basaux des cristallites ont une orientation préférentielle. Sous pression uniaxiale, la structure poreuse du graphite expansé comprimé évolue à travers un effondrement irréversible des pores ou un cisaillement de la matrice suivant l'orientation de la pression appliquée par rapport à l'orientation préférentielle des plans basaux des cristallites. Des expériences complémentaires de mesures électriques et de mesures de la porosité par intrusion de mercure ont permis de confirmer ces modèles proposés. Dans la vermiculite expansée comprimée, les fissures apparaissent, de manière générale, sous l'effet de la pression uniaxiale.

Phosphorus (P), a necessary plant and animal nutrient, can also lead to eutrophication of fresh waters when in excess. Appropriate P management is necessary to prevent fresh water pollution. Mineralogy of soil clays has been shown to affect P adsorption, desorption, and movement through soils. Specifically, hydroxy-interlayered minerals have been shown to adsorb and retain inorganic P in soil systems. This study was designed to determine the sorption and desorption characteristics of inorganic, organic, and mixed forms of P interacting with soil hydroxy-interlayered vermiculites (HIV) and smectites (HIS), and compare the findings to sorption and desorption processes of natural aluminum (Al) and Iron (Fe) hydroxide minerals. Results indicate natural Al and Fe hydroxide minerals sorbed and retained P more strongly than hydroxy-interlayered minerals in our samples and inositol hexakisphosphate was more highly sorbed and retained than inorganic P.