Neste trabalho foram preparados nanocompósitos de polímeros estirênicos com argilas organofílicas. Os polímeros estudados foram o poliestireno (PS), um copolímero tribloco de poliestireno-b-polibutadieno-b-estireno (SBS) e quatro copolímeros tribloco de poliestirenob- poli(etileno-co-butileno)-b-estireno (SEBS), sendo um deles modificado com anidrido maléico. Os nanocompósitos foram preparados por três técnicas de obtenção: mistura no fundido, solução e uma técnica híbrida que combina as duas primeiras. Os materiais obtidos foram caracterizados por difração de raios X (XRD), microscopia óptica (OM), microscopia eletrônica de transmissão (TEM), espalhamento de raios X a baixo ângulo (SAXS) e também foram realizados estudos reológicos através do ensaio de cisalhamento oscilatório de pequenas amplitudes (SAOS). O grau de dispersão de argila em algumas amostras foi avaliado por uma técnica baseada na análise de imagens obtidas por TEM. Os resultados mostraram que na maioria dos casos foram obtidos nanocompósitos intercalados, graças à presença da fase de PS em cada polímero. Amostras preparadas por solução tiveram o melhor grau de dispersão de argila, e o polímero que resultou na estrutura mais exfoliada foi o SEBS maleatado. Estudos reológicos mostraram-se muito sensíveis à formação de reticulados de partículas de argila nos nanocompósitos, que passaram a ter comportamento semelhante ao de sólidos. A combinação de técnicas de SAXS com reologia foi bastante útil para estudar a morfologia de fases ordenadas em copolímeros em bloco, permitindo identificar e distinguir estruturas lamelares, cilíndricas e esféricas em cada copolímero. Foi possível verificar que a presença de argila perturba a ordem das fases dos copolímeros e causa diferentes efeitos nas propriedades reológicas destes materiais. / In this work nanocomposites of styrenic polymers and organoclays were prepared. The polymers studied were polystyrene (PS), a polystyrene-b-polybutadiene-b-polystyrene triblock copolymer (SBS) and four polystyrene-b-poly(ethylene-co-butylene)-polystyrene triblock copolymers (SEBS), with one containing maleic anhydride. The nanocomposites were prepared using three different techniques: melt mixing, solution casting and a hybrid technique combining the former two. The materials obtained were characterized by x-ray diffraction (XRD), optical microscopy (OM), transmission electron microscopy (TEM), small angle x-ray scattering (SAXS) and by rheological studies, through small amplitude oscillatory shear tests (SAOS). The degree of clay dispersion was evaluated in some samples using a TEM image analysis technique. The results have shown that in most cases intercalated nanocomposites were obtained, due to the PS phase present in each polymer. Samples prepared by solution had the highest degree of clay dispersion, and the maleated SEBS was the polymer which originated the most exfoliated nanocomposite. The results have also shown that rheological studies are very sensitive to the formation of clay networks within the nanocomposites, which behave more solidlike. The combination of SAXS techniques and rheology was very useful to study the morphology of ordered phases in block copolymers, allowing to identify and distinguish the different structures of each copolymer, such as the lamellar, cylindrical and spherical phases. It was possible to verify that the presence of clay disturbs the phase order in the copolymers and has different effects on the rheological properties of these materials.

This research provides a comprehensive investigation in understanding the effect of the addition of graphene nano-platelets (GNP) on the mechanical, tribological and biological properties of glass/ceramic composites. We investigated two kinds of materials namely amorphous matrices like glasses (silica, bioglass) and polycrystalline matrices like ceramics (alumina). The idea was to understand the effect of GNP on these matrices as GNP was expected to behave differently in these composites. Bioglass (BG) was also chosen as a matrix material to prepare BG-GNP composites. GNP can improve the electrical conductivity of BG which can be used further for bone tissue engineering applications. The effect of GNP on both electrical conductivity and bio-activity of BG-GNP composites was investigated in detail. There were three main problems for fabricating these novel nano-composites: 1) Production of good quality graphene; 2) Homogeneous dispersion of graphene in a glass/ceramic matrix and; 3) Retention of the graphitic structure during high temperature processing. The first problem was solved by synthesising GNP using liquid phase exfoliation method instead of using a commercially available GNP. The prepared GNP were ~1 μm in length with a thickness of 3-4 layers confirmed using transmission electron microscopy. In order to solve the second problem various processing techniques were used including powder and colloidal processing routes along with different solvents. Processing parameters were optimised to fabricate glass/ceramic-GNP composite powders. Finally in order to avoid thermal degradation of the GNP during high temperature processing composites were sintered using spark plasma sintering (SPS) technique. Fully dense composites were obtained without damaging GNP during the sintering process also confirmed via Raman spectroscopy. Finally the prepared composites were characterised for mechanical, tribological and biological applications. Interestingly fracture toughness and wear resistance of the silica nano-composites increased with increasing concentration of GNP in the glass matrix. There was an improvement of ~45% in the fracture toughness and ~550% in the wear resistance of silica-GNP composites with the addition of 5 vol% GNP. GNP was found to be aligned in a direction perpendicular to the applied force in SPS. In contrast to amorphous materials fracture toughness and scratch resistance of alumina-GNP composites increased only for small loading of GNP and properties of the composites decreased after a critical concentration. There was an improvement of ~40% in the fracture toughness with the addition of only 0.5 vol% GNP in the alumina matrix while the scratch resistance of the composite increased by ~10% in the micro-ductile region. Electrical conductivity of the BG-GNP composite was increased by ~9 orders of magnitude compared to pure BG. In vitro bioactivity tests performed on BG-GNP composites confirmed that the addition of GNP to BG matrix also improved the bioactivity of the nano-composites confirmed using XRD analysis. Future work should focus on understanding electrical and thermal properties of these novel nano-composites.

Van der Waals materials and inorganic nanoparticles are two categories of nanomaterials that have been widely investigated in the past two decades. Both of them have been considered to be promising as candidates for the next generation electrical, optical, and mechanical applications. However, both of them have a few limitations that greatly affect the performance of devices, e.g. zero bandgap for graphene; poor contact quality, low mobility and quantum efficiency for MoS2; and poor interparticle conductivity for nanoparticles. This thesis tries to explore a new way of combining these two categories of material into hybrids, so that the intrinsic limitations of materials from each category will be overcome by the other materials that are introduced into the hybrid. This thesis consists of five parts. The first part (Chapter 1) introduces the background and motivation of the thesis. The second part (Chapters 2, 3, 4, and 5) describes the detailed processes and methods, starting from preparing each element to the assembly of these element into a hybrid structure device. This part also includes understanding the mechanisms of 2D and 3D self-assembly of nanoparticles. The third part (Chapter 6 and 7) describes two examples of hybrid structures, including the investigation of electron or molecule transfer inside the hybrid. The fourth part (Chapter 8) introduces other findings and technical innovations, including alternative ways of thin film nanoparticle self-assembly/deposition, and fabrication methods for the band structure analysis of transition metal dichalcogenides by angle resolved photo-electron spectroscopy. The fifth part (Chapter 9) describes several possible future work directions that could be investigated to improve the understanding of the nanoparticle assembly and translating the conceptual device into real applications.

Batteries are complex, multidisciplinary, electrochemical energy storage systems that are crucial for powering our society. During operation, all battery technologies suffer from voltage losses due to energetic penalties associated with the electrochemical processes (i.e., ohmic resistance, kinetic barriers, and mass transport limitations). A majority of the voltage losses can be attributed to processes occurring on/in the battery electrodes, which are responsible for facilitating the electrochemical reactions. A major challenge in the battery field is developing strategies to mitigate these losses. To accomplish this, researchers must i) identify the processes limiting the performance of the electrode, ii) characterize the main, performance-limiting processes to understand the underlying mechanisms responsible for the poor performance, and iii) mitigate the voltage losses by developing strategies which target these underlying mechanisms. In this thesis, three studies are presented which highlight the role of electrochemical engineers in alleviating the performance limiting processes in battery electrodes. Each study is focused on a different step of the research approach (i.e., identification, characterization, and mitigation) and analyzes an electrode from a different battery system. The first part of the thesis is focused on identifying the processes limiting the capacity in nanocomposite lithium-magnetite electrodes. To accomplish this, the mass transport processes and phase changes occurring within magnetite electrodes during discharge and voltage recovery are investigated using a combined experimental and modeling approach. First, voltage recovery data are analyzed through a comparison of the mass transport time-constants associated with different length-scales in the electrode. The long voltage recovery times are hypothesized to result from the relaxation of concentration profiles on the mesoscale, which consists of the agglomerate and crystallite length-scales. The hypothesis was tested through the development of a multi-scale mathematical model. Using the model, experimental discharge and voltage recovery data are compared to three sets of simulations, which incorporate crystal-only, agglomerate-only, or multi-scale transport effects. The results of the study indicate that, depending on the crystal size, the low utilization of the active material (i.e., low capacity) is caused by transport limitations on the agglomerate and/or crystal length-scales. For electrodes composed of small crystals (6 and 8 nm diameters), it is concluded that the transport limitations in the agglomerate are primarily responsible for the long voltage recovery times and low utilization of the active material. In the electrodes composed of large crystals (32 nm diameter), the slow voltage recovery is attributed to transport limitations on both the agglomerate and crystal length-scales. Next, the multi-scale model is further expanded to study the phase changes occurring in magnetite during lithiation and voltage recovery experiments. Phase changes are described using kinetic expressions based on the Avrami theory for nucleation and growth. Simulated results indicate that the slow, linear voltage change observed at long times during the voltage recovery experiments can be attributed to a slow phase change from α¬-LixFe3O4 to β¬-Li4Fe3O4. In addition, simulations for the lithiation of 6 and 32 nm Fe3O4 suggest the rate of conversion from α¬-LixFe3O4 to γ-(4 Li2O + 3 Fe) decreases with decreasing crystal size. The next part of the thesis presents a study aimed at characterizing the formation of PbSO4 films on Pb in H2SO4, which has been previously identified as a performance-limiting process in lead-acid batteries. Transmission X-ray microscopy (TXM) is utilized to monitor, in real time, the initial formation, the resulting passivation, and the subsequent reduction of the PbSO4 film. It is concluded with support from quartz-crystal-microbalance experiments that the initial formation of PbSO4 crystals occurs as a result of acidic corrosion. Additionally, the film is shown to coalesce during the early stages of galvanostatic oxidation and to passivate as a result of morphological changes in the existing film. Finally, it is observed that the passivation process results in the formation of large PbSO4 crystals with low area-to-volume ratios, which are difficult to reduce under both galvanostatic and potentiostatic conditions. In a further extension of this study, TXM and scanning electron microscopy are combined to investigate the effects of sodium lignosulfonate on the PbSO4 formation and the initial growth of PbSO4 crystals. Sodium lignosulfonate is shown to retard, on average, the growth of the PbSO4 crystals, yielding a film with smaller crystals and higher crystal densities. In addition, an analysis of the growth rates of individual, large crystals showed an initial rapid growth which declined as the PbSO4 surface coverage increased. It was concluded that the increase in PbSO4 provides additional sites for precipitation and reduces the precipitation rate on the existing crystals. Finally, the potential-time transient at the beginning of oxidation is suggested to result from the relaxation of a supersaturated solution and the development of a PbSO4 film with increasing resistance. The final part of the thesis presents a study aimed at mitigating the ohmic losses during pulse-power discharge of a battery by the adding a second electrochemically active material to the electrode. Porous electrode theory is used to conduct case studies for when the addition of a second active material can improve the pulse-power performance. Case studies are conducted for the positive electrode of a sodium metal-halide battery and the graphite negative electrode of a lithium-ion battery. The replacement of a fraction of the nickel chloride capacity with iron chloride in a sodium metal-halide electrode and the replacement of a fraction of the graphite capacity with carbon black in a lithium-ion negative electrode were both predicted to increase the maximum pulse power by up to 40%. In general, whether or not a second electrochemically active material increases the pulse power depends on the relative importance of ohmic-to-charge transfer resistances within the porous structure, the capacity fraction of the second electrochemically active material, and the kinetic and thermodynamic parameters of the two active materials.

Nesta tese, apresentamos três estudos envolvendo técnicas de ressonância paramagnética eletrônica (RPE) de onda contínua e pulsada nas bandas X e Q em vidros e nanocompósitos dopados com íons de metais de transição. O objetivo geral deste texto é evidenciar a complementariedade destas técnicas no estudo destes materiais. Os dois primeiros estudos focam-se em vidros e vitro-cerâmicas dopados com íons de metais de transição. O objetivo destes estudos é analisar o efeito dos tratamentos térmicos no espectro de RPE das amostras. O primeiro estudo trata de vidros fosfo-germanato dopados com íons de vanádio e os resultados de RPE de onda contínua mostram que, para a amostra sem tratamento térmico e para a amostra tratada em temperaturas menores do que 470 °C, apenas um sítio de vanádio é observado enquanto que, para as amostras tratadas com temperaturas acima de 470 °C, um segundo sítio de vanádio, mais distorcido do que anterior, aparece. Experimentos de ESEEM e HYSCORE observaram a interação entre os íons de vanádio e núcleos 31P próximos e pudemos estimar a máxima densidade de spin transferida pelo mecanismo through-bond e máxima distância média entre o íon paramagnético e os núcleos 31P. O segundo estudo trata de um vidro fluorosilicato dopado com íons Cu2+ e os resultados de RPE de onda contínua não mostram alterações relevantes no sítio paramagnético devido ao tratamento térmico. Experimentos de ESEEM e HYSCORE mostraram picos devido a interação desse íon com núcleos 19F, 207Pb, 111Cd e 113Cd. O terceiro estudo foca-se numa argila natural laminar contendo íons Cu2+ e moléculas de polioxietileno (PEO). O objetivo deste estudo é analisar a complexação do íon Cu2+ com as moléculas de PEO e moléculas de água no espaço interlaminar da argila. Os resultados de RPE de onda contínua não evidenciaram alterações na coordenação do íon Cu2+ através dos dois métodos de preparação propostos. Os experimentos de ESEEM E HYSCORE mostraram que, para o método onde o complexo PEO-Cu é inserido no espaço interlaminar da argila, o íon Cu2+ interage apenas com prótons em, pelo menos, duas conformações diferentes. Nossa hipótese é que observamos prótons tanto da molécula de PEO quanto de moléculas de água. No método onde moléculas de PEO são inseridas no espaço interlaminar da argila previamente preenchido com íons Cu2+, tal hipótese não pode ser feita. Ainda, observamos outro centro paramagnético nas amostras oriundo de vacâncias de oxigênio nas lâminas da argila. / This thesis contains three studies where X- and Q-Band continous-wave electron paramagnetic resonance (CW-EPR) and pulsed EPR techniques were applied in glasses and nanocomposites doped with transition metal ions. Our general goal is to show the complementarity of these techniques for the study of this materials. The first two studies focus on glasses and glass-ceramics doped with transition metal ions and the main goal is to analyse the effect of sample heat treatments on the EPR spectra. The first study focuses on phospho-germanate glasses and the CW-EPR results show that, for non-treated samples or for heat-treated samples at temperatures below 470°C, only one vanadium site is observed, while for samples heat-treated at higher temperatures a second, more ditorted site is produced. ESEEM and HYSCORE experiments observe the interaction between vanadium ions and near 31P nuclei. The maximum spin density transfer by the through-bond mechanism and maximum average distance between the two species could be estimanted. The second study focuses on fluorosilicate glasses doped with Cu2+ and the CW-EPR results show no relevant changes in the paramagnetic site upon heat treatment. ESEEM and HYSCORE experiments display peaks due to the interaction between Cu2+ ions and 19F, 207Pb, 111Cd e 113Cd nuclei. The third study focus on a natural bentonite clay containing copper ions and polioxiethilene (PEO) molecules. The main goal of this study is to analyze the complexation of the Cu2+ ions with the PEO and water molecules in the interlaminar space of the clays. CW-EPR results does not show any changes in the Cu2+ coordination caused by the two preparation methods proposed. ESEEM and HYSCORE experiments, however, showed that, for the method where the PEO-Cu complex is inserted in the interlaminar space, the paramagnetic ion interacts only with protons in at least two different conformations. Our hypothesis is that both protons from the PEO chain and water molecules are being observed. In the method where PEO molecules are inserted in the material, which was previosly filled with Cu2+ ions, no such assignment could be made. In addition, another paramagnetic center is observed and associated with oxigen vacancies in the sheets of the clay.

Graphene Nanoplatelets (GNP) was incorporated into polyamide 6 (PA6) matrix by melt compounding method and the enhancements in the properties of the nanocomposites were studied. Response Surface Methodology (RSM) was employed to assist in the study of processing conditions in melt compounding. RSM analysis revealed that the GNP concentrations to be the most significant term to affect the tensile modulus and crystallinity followed by the screw speed whereas the residence time was found to be non-significant. GNP with 5 Î1⁄4m (G5) and 25 Î1⁄4m (G25) were used in the GNP aspect ratio study. The average flake size of G5 and G25 to was measured to be 5.07 Î1⁄4m and 22.0 Î1⁄4m, respectively with the G5 distributed narrowly whereas the G25 exhibit broad distribution. TGA analysis shown that HT25 is more thermally stable compared to G25 due to some remnants lost during thermal treatment and this was confirmed by EDX and CHNS analysis. XRD profiles of the PA6-G-NC illustrate typical peaks of PA6 crystals phase as well as pure graphite characteristic peak. PA6-G25-NC observed to exhibit slightly higher peak intensity compared to PA6-G5-NC suggesting more formation of PA6 crystals. Similar improvement was observed on PA6-HT25-NC compared to PA6-G25-NC indicating more formation of PA6 crystals due improved dispersion of HT25. DSC on PA6-G25-NC showed higher cooling temperature and crystallinity compared to PA6-G5-NC due to larger surface area of the G25. Similarly, PA6-HT25 showed better improvement in crystallinity over PA6-G25-NC due to increase nucleation sites by the HT25. The thermal conductivity of PA6-G25-NC is slightly higher than the thermal conductivity of PA6-G5-NC but not significant considering the G25 is 5 times larger than G5. Instead, no significant difference was observed between PA6-HT25-NC and PA6-G25-NC. Addition of GNP increased the thermal stability of the PA6-G-NC systems under both nitrogen and air atmospheres regardless of the GNP aspect ratio. The viscoelastic properties showed insignificant difference between PA6-G5-NC and PA6-G25-NC. The inefficient improvement by G25 might be due to agglomeration formed during processing. The storage modulus and tan Î ́ of PA6-HT25-NC decreased but the Tg significantly improved compared to PA6-G25-NC. This was assumed to be because of improved dispersion of HT25 but reduced interfacial interaction after the heat treatment. The shear storage modulus, G’ and complex viscosity, |η*| were observed to increase with increasing GNP content with more pronounced improvement seen on PA6-G25-NC compared to PA6-G5-NC. However, no network percolation threshold was observed until 20 wt.% of GNP. The poor interfacial interaction of HT25 resulted in lower G’ and |η*| compared to G25. Tensile test results showed typical improvement with PA6-G25-NC having higher tensile modulus compared to PA6-G5-NC. Further enhancement was obtained with PA6-HT25-NC suggesting improved dispersion and volume of constrained chains mobility despite the poor surface interaction. Comparison with Halphin-Tsai modulus revealed that the effective modulus to be 150 GPa for G5 and 200 GPa for G25. The water uptake measurement results showed that GNP reduced the water uptake percentage and diffusion coefficient especially with G25. The test conducted on saturated PA6-G-NC results in improved thermal conductivity due to the high thermal conductivity of water but the viscoelastic and tensile properties severely reduced due to plasticisation effect.

Materiais naturais nanoestruturados, tipo smectita, têm sido amplamente usados em nanocompósitos poliméricos, com ganhos expressivos em muitas propriedades. Porém, devido a sua natureza polar, seu uso em nanocompósitos de poliolefinas apresenta uma série de problemas. Entre esses problemas está a dificuldade de esfoliação na matriz, o que geralmente resulta um sistema não nano-estruturado e, por conseqüência, com pouco ou nenhum ganho em propriedades. Para tentar resolver esse problema, materiais tipo esmectita têm sido modificados com sais de amônio quartenário. Esses, por sua vez, possuem características tóxicas, impedindo seu uso em embalagens de alimentos. Com o objetivo de estudar uma nova alternativa que contorne esses problemas, dois materiais lamelares nano-estruturados, tipo esmectita, contendo grupos alquila ligados por ligação sigma com a rede inorgânica, foram sintetizados. Ambos apresentaram excelente ordem mesoestrutural. Um dos materiais sintetizados, formado por um Alsilsesquioxano lamelar, contendo alto teor de cadeia alquila entre as lamelas inorgânicas, foi usado na formação de compósito de polietileno. Comparativamente, uma argila natural, modificada com sais de amônio quaternário (Cloisite 15A), foi usada para fins comparativos. Os compósitos, então obtidos, foram caracterizados para avaliar diferenças microestruturais, morfológicas e mudanças em suas propriedades mecânicas e reológicas. Comparativamente à argila comercial Cloisite 15A, os compósitos contendo os materiais sintéticos apresentaram reologia diferenciada, melhor resistência ao impacto e ao Tensofissuramento Acelerado pelo Ambiente (ESCR). / Nanostructured natural materials, as smectites, have been widely used in polymeric nanocomposites, with significant gains in many properties. However, due to its polar nature, the use in nanocomposites of polyolefins presents a series of drawbacks. Among these problems, its difficulty exfoliation in the matrix, which generally results in a system not nanostructured and, consequently, with little or no gain on properties. To try to resolve this problem, materials type smectite have been modified with quaternary ammonium salts. These salts, in turn, have toxic characteristics, preventing its use in food packaging. In order to study a new alternative that bypasses these problems, two lamellar nanostructured materials, like smectite, with alkyl groups containing sigma links connected to lamellar inorganic network, were synthesized. Both materials had excellent mesostructural order. One of the synthesized materials, formed by a lamellar Al-silsesquioxane, containing high levels of alkyl chain between the inorganic lamella, was used in the formation of a polyethylene composite. Commercial natural clay, modified with quaternary ammonium salts (Cloisite 15A), was used for comparative purposes. The composites then obtained, were characterized to assess microstructural differences, morphological change, and its mechanical and rheological properties. Comparatively to commercial clay (Cloisite 15A), the composites containing synthetic materials, showed differented rheologics properties, better impact resistance and better Environmental Stress Cracking Resistance (ESCR).

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

Nanocompósitos poliméricos foram preparados por meio da incorporação de 1, 2, 5 e 10% das argilas montmorilonita organofílicas Cloisite 15A e 30B em poliamida-6, pelo método de fusão numa extrusora dupla rosca. Em seguida, foram reprocessados numa extrusora mono-rosca gerando folhas pelo método balão e caracterizados por meio de técnicas espectroscópicas, de análise térmica e difração de raio-X. Os estudos mostraram a formação de nanocompósitos com uma boa dispersão e esfolheamento, principalmente em concentrações de argila inferiores a 5%. Nas amostras com 5 e 10%, nanocompósitos intercalados também foram observados. Portanto, quando a concentração de argila aumenta no nanocompósito, fica cada vez mais difícil obter nanocompósitos totalmente esfoliados. Além disso, verificou-se que a incorporação de 1% da Cloisite 15A ou 30B induzem a cristalização do polímero, predominando a fase γ nos filmes. Entretanto, a medida que a concentração de argila aumenta a fração de fase amorfa tende a aumentar, provavelmente em decorrência da diminuição da velocidade do processo de recristalização em torno de 194 ºC, que gera a fase cristalina γ. Foi demonstrado a presença de um excesso de surfactante em uma das argilas organofílicas, tanto na parte exterior dos tactóides como na região interlamelar, aumentando o espaçamento basal e facilitando o processo de intercalação/esfolheamento. Todavia, o excesso de surfactante interfere nos processos de incorporação pois sofrem decomposição em temperaturas relativamente baixas (200 ºC) enquanto o cátion amônio intercalado se decompõe a 240 ºC. De fato, os estudos realizados comprovam que o surfactante tem influência direta sobre as propriedades das argilas organofílicas e grande importância no processo de incorporação. Melhorias significativas foram observadas nas propriedades de barreira a gases e mecânicas, principalmente com relação a resistência a tração, que aumenta a medida que se aumenta a concentração de argila. As propriedades de perfuração não foram significativamente modificadas, mas também verificou-se um aumento significativo da estabilidade mecânica em função da temperatura. Porém, a absorção de umidade interfere negativamente tanto nas propriedades mecânicas quanto na de barreira a gases, sendo que a Cloisite 15A é menos suscetível que a Cloisite 30B, provavelmente devido ao cátion de amônio quaternário ser mais hidrofóbico. Assim, os filmes de nanocompósitos de poliamida- 6/argila devem ter aplicações diversas na indústria de embalagens / Polymeric nanocomposites were obtained by incorporation of 1, 2, 5 e 10% of the organophilic clays Cloisite 15A e 30B in polyamide-6, using a twin-screw extruder and the melting process. Then, the pellets were reprocessed as films in a single-screw extruder coupled with the blow method, and those materials were characterized by means of spectroscopic, thermal and X-ray difraction techniques. The results were consistent with the formation of nanocomposites with excellent dispersion and exfoliation, especially when the concentration of clay was below 5%. In the samples containing 5 e 10%, the presence of tactoids were observed showing the formation of intercalated nanocomposites as well. Thus, as the concentration of organophillic clay increases, the fraction of completely exfoliated clay decreased. Furthermore, the incorporation of clays (Cloisite 15A or 30B) in concentrations as low as 1% induced the crystallization of polyamide-6, such that it was found in the films predominantly in the γ phase. However, as the concentration of clay increases there is a steady increase of the amorphous phase, probably due to the decrease of the rate of the recrystallization process at 194 ºC, responsible for the formation of the γ phase. Also, the presence of an excess of surfactant was confirmed for both, Clositite 15A and 30B, around the tactoids and in the interlamelar space also, increasing the basal distance and facilitating the intercalation/exfoliation process. However, such an excess interfere in the nanocomposite preparation process since decomposes at relatively low temperatures (200 ºC) while the intercalated quaternary ammonium cation decomposes at 240 ºC. In fact, we showed that the structure of the surfactant directly influences the properties of the organophilic clays, and has strong influence on the nanocomposite preparation process. Significant improvements in the barrier effect to gases and in the mechanical properties were noticed for the nanocomposites, particularly on the resistance to traction and on the mechanical stability as a function of temperature, but the resistance to perforation didnt change significantly as the concentration of clay increased. The absorption of water by the nanocomposites influenced negatively the mechanical properties and the barrier effect as well. However, the nanocomposites prepared with Cloisite 15A were less susceptible than those obtained with Cloisite 30B, probably because the quaternary ammoniun salt in the first one is more hydrophobic and repels more effectively the water molecules

Ao contrário de muitos polímeros, as resinas fenólicas se caracterizam por possuir um grande número de aplicações por conta de sua superior resistência ao fogo e baixa emissão de fumos e ao seu excelente nível de resistência térmica e química, além de seu baixo custo. No entanto, devido à sua estrutura tridimensional, caracterizada pelo alto grau de reticulação, este tipo de resina apresenta baixas tenacidade e resistência à fratura. Com isso, para garantir seu bom desempenho, faz-se necessário promover modificações em sua formulação ou acrescentar agentes de reforço de modo a compensar essas deficiências resultantes de sua estrutura. São inúmeros os materiais que, usualmente, são incorporados à matriz fenólica. Além da preparação de blendas poliméricas em que uma das fases consiste em um elastômero ou um termoplástico, a introdução de agentes de reforço como materiais fibrosos também são utilizados. São exemplos de agentes de reforço: fibras vegetais, fibras de vidro e de carbono, negro de fumo, argilas entre outros. A mistura de polímeros e argilas pode levar à formação de nanocompósitos de modo a obter excelentes combinações de resistência à fratura, tenacidade, condutividade, resistência ao calor e redução da permeabilidade a gases e líquidos quando comparados com o polímero puro. Neste trabalho, argilas do tipo montmorilonita modificadas foram utilizadas como agente de reforço na preparação de filmes de nanocompósitos de matriz fenólica com o objetivo de melhorar as propriedades mecânicas deste material polimérico quando comparado com o material puro. A resina fenólica utilizada neste trabalho é a do tipo resol, utilizada comercialmente para a formulação de vernizes para revestimento de embalagens metálicas. No estudo foram utilizadas três argilas comerciais: Cloisite® sódica (Na) e argilas Cloisite® modificadas com sais quaternários de alquilamônio, de códigos 15A e 30B, objetivando verificar qual apresentaria melhor compatibilidade com a matriz fenólica. Para a preparação de filmes poliméricos uniformes, isentos de defeitos como bolhas, foi feita, de forma preliminar, a seleção de um ciclo de cura apropriado. Como a formação de bolhas é intrínseco à cura da resina fenólica resol, a definição de um esquema de tratamento térmico de cura apropriado constituiu-se em etapa crítica no processo de preparação dos compósitos de resina fenólica/argila montmorilonita modificada. Os filmes curados isentos de defeitos foram caracterizados por difração de raios X, análise termomecânica dinâmica (DMA) e calorimetria exploratória diferencial (DSC). Os resultados das análises de DRX mostraram para os compósitos preparados com as argilas modificadas 15A e 30B manutenção e até mesmo redução do espaçamento basal da estrutura cristalina das argilas, indicando não ter ocorrido intercalação do polímero nessas argilas; enquanto que para a argila Cloisite® Na ocorreu aumento do espaçamento basal. Os resultados de DMA mostraram para a maioria das amostras aumento no módulo de armazenamento em baixa e alta temperatura. Por último, a análise de DSC mostrou redução na temperatura de transição vítrea nos compósitos preparados com as argilas modificadas 15A e 30B, e elevação na composição de 5% da argila Cloisite® Na. Os resultados indicam o potencial de reforço mecânico de resinas fenólicas com argilas lamelares do tipo montmorilonita sem a necessidade de modificação química. / Unlike most polymers, phenolic resins are characterized by having a large number of applications because of its superior fire resistance and low emission of smoke and its excellent level of thermal and chemical resistance, and low cost. However, due to its three dimensional structure, characterized by a high degree of crosslinking, this type of resin has low toughness and fracture resistance. Thus, to ensure their good performance, it is necessary to make enhancements in their formulation or adding strengthening agents so as to compensate for these deficiencies due to its structure. There are numerous materials that usually are incorporated into the phenolic matrix. Besides the preparation of polymer blends in which one phase consists of an elastomer or a thermoplastic, the introduction of agents such as fibrous reinforcement is also used. Examples of reinforcing agents: vegetable fibers, glass and carbon fibers, carbon black, clay and others. The mixture of polymer clays may cause the formation of nanocomposites in order to obtain excellent combination of fracture strength, toughness, conductivity, heat resistance and reduced permeability to gases and liquids when compared with the pure polymer. In this work, modified montmorillonite clays were used as a reinforcing agent in the preparation of nanocomposite films of phenolic matrix with the aim of improving the mechanical properties of polymer materials when compared with the pure material. The phenolic resin used in this work is that of the resol type, used commercially for the formulation of varnish for coating metal containers. The study used three types of commercial clay: Cloisite® sodium (Na) and Cloisite® clays modified with quaternary alkylammonium salts, codes 15A and 30B in order to verify which present better compatibility with the phenolic matrix. For the preparation of uniform polymeric films, free of defects such as bubbles, was preliminarily selected a suitable cure cycle. As the bubble formation is intrinsic to the cure of resol phenolic resin, the definition of a heat treatment scheme is a critical step in the process of preparing composites of phenolic resin/montmorillonite clay. The cured films free of defects were characterized by X-ray diffraction (DRX), dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The results of XRD analysis showed the composites prepared with the modified clays 15A and 30B maintained and even reduced the basal spacing within the clay crystal structure, indicating not having occurred polymer intercalation of the clay; for the Cloisite® Na clay DRX has shown increased basal spacing. DMA results showed for most of the samples increase in storage modulus at low and high temperatures. Finally, DSC analysis showed a reduction in glass transition temperature of the composites prepared with the modified clays 15A and 30B, and an increase in the composition of 5% in the Cloisite® Na clay. The results indicate the potential of enhancement of phenolic resins mechanical properties with layered clays of montmorillonite without chemical modification.