Orientador: Reinaldo Marchetto / Coorientador: Younés Messaddeq / Banca: Wilton Rogério Lustri / Banca: Rosana Maria Nascimento de Assunção / Resumo: A celulose bacteriana (CB) é um polímero produzido pela bactéria Gluconacetobacter xylinus, e apresenta diversas aplicações biomédicas e tecnológicas. Recentemente foi desenvolvido o método de inserção in situ, que visa a produção de compósitos via adição de materiais no meio de cultura. Neste trabalho tem sido realizada a inserção de colágeno durante a formação da CB no intuito de melhorar as propriedades osteocondutoras do compósito, formando um scaffold visando o uso em regeneração óssea. A produção de celulose bacteriana foi testada via cultivo da bactéria gramnegativa Gluconacetobacter xylinus linhagem ATCC 23769, em diferentes meios de cultura estáticos e agitado à base de distintas fontes de carbono e adição de colágeno in situ, a fim de avaliar tanto a produção, como as propriedades dos materiais produzidos. Foram utilizados meios da literatura, ou com algumas modificações, sendo o meio com melhor resultado foi aquele utilizado no restante do trabalho, ou seja, na produção de compósitos in situ. As membranas sem adição de materiais in situ foram caracterizadas por FT-IR, DRX, MEV, grau de polimerização, intumescimento e análise térmica, apresentando similaridade com o material disponível no mercado para comercialização. O processo de obtenção das mantas de CB foi acompanhado e estudado através da avaliação do crescimento da cepa utilizada, curva de consumo de açúcares, variação do pH e produção de CB em função do tempo de cultivo, para avaliar qual condição seria ideal para a produção de CB. Foram obtidos melhores resultados utilizando-se o manitol como fonte de carbono e um pH inicial de 4,5, ao utilizar a cepa ATCC 23769. O cultivo agitado mostrou-se mais eficiente ao produzir 5,47 g/L. A produção do compósito à base de CB e colágeno (CB+Col) através da adição in situ, variando a... (Resumo completo, clicar acesso eletrônico aba / Abstract: The Bacterial Cellulose (BC) is a polymer produced by Gluconacetobacter xylinus bacteria, and shows many biomedical and technological applications. Recently was developed the in situ method of insertion, that aims to obtain composites materials via addiction of interfering substances in the culture medium. In this work, has been performed the insertion of collagen during the BC formation, aiming to improve the osteoconductive properties of composite, making a scaffold to be used at bone regeneration. The BC production was tested by bacterial culture of gram-negative Gluconacetobacter xylinus strain ATCC 23769, in different culture media static and agitated based on different carbon sources and in situ addiction of collagen, to assess the production and the material properties. Literature mediuns were used, or with some modifications, being the best was that used at rest of the work, i.e., in the in situ composite production. The membranes without addiction of materials in situ were characterized by techniques FT-IR, XRD, SEM, degree of polimerization, swelling and termal analysis, showing similarity with the material available in the market for sale. The obtaining process of the BC blankets was accompanied and studied by evaluation of strain growing, sugar consumption curve, pH variation and BC production versus time of cultivation, to assess whats the ideal for BC production. Thus the better results was obtained using manitol as carbon source and a initial pH of 4,5, using ATCC 23769 strain. The agitated culture showed more efficient leading to a production of 5,47 g/L. The composite materials based on bacterial cellulose and collagen (CB+Col) through in situ addiction, varying from 1 to 5% (v/v) was performed at static culture. The final material was characterized regarding its physical-chemistry properties... (Complete abstract click electronic access below) / Mestre

L'augmentation croissante de la demande en énergie et l'épuisement des combustibles fossiles exigent l'amélioration de l'efficacité de l'utilisation de l'énergie ainsi que la recherche de ressources durables et renouvelables. Les condensateurs sont des systèmes de stockage de l'énergie qui se sont imposés comme une des solutions aux problèmes énergétiques en raison de leurs avantages, tels que le respect de l'environnement, et la charge et la décharge d'énergie très rapides. Des besoins se sont créés pour un système de stockage capacitif à faible coût et à haut rendement, il est donc nécessaire de développer des matériaux avec une forte permittivité diélectrique. A ce propos, les composites diélectriques à matrice polymère suscitent une attention croissante en raison de leurs bonnes performances diélectriques. Des composites à matrice polymère chargée de particules céramiques ont par exemple été utilisés dans certains condensateurs pour le stockage d'énergie. Pourtant, en pratique, l'applicabilité de tels dispositifs est sérieusement entravée par la faible permittivité diélectrique des matériaux d'une part, et par la détérioration des propriétés mécaniques en raison de la forte teneur en particules céramiques rigides dans la matrice polymère flexible d'autre part. En remplaçant ces particules céramiques par des particules conductrices dans la matrice polymère, des composites percolatifs peuvent être réalisés avec une permittivité diélectrique nettement accrue au voisinage du seuil de percolation. Parmi les charges conductrices, les nanotubes de carbone (NTC) ont été les plus étudiés. En effet, du fait de leur facteur d'aspect et de leur conductivité élevée, ces derniers peuvent conduire à des niveaux de percolation dans les composites pour une très faible quantité de charges. Un des plus grands défis pour l'utilisation des NTC dans les matériaux composites est de séparer les NTC les uns des autres afin de réaliser une dispersion uniforme dans les polymères. Les travaux présentés dans cette thèse ont porté sur l'augmentation de la permittivité diélectrique de matériaux composites à matrice polymère à base de NTC en optimisant à la fois la dispersion des nanotubes ainsi que le contrôle de la microstructure des matériaux composites finaux. L'augmentation de la permittivité diélectrique dans les composites précédents provient de la formation de microcondensateurs au sein du matériau. Toutefois, les NTC ont toujours tendance à s'agglomérer dans le composite, ce qui n'est pas bénéfique à la formation de microcondensateurs. Pour surmonter ce problème, nous avons proposé une microarchitecture hybride SiC-NTC comme charge conductrice. Ces hybrides mulit-échelles ont été produits par dépôt chimique catalytique en phase vapeur assisté par aérosol. L'organisation des NTC sur les particules de SiC peut être efficacement contrôlée en ajustant les différents paramètres de synthèse. Les résultats ont montré que les propriétés de surface asymétriques des micro-particules de SiC étaient plutôt favorables à la croissance des NTC sur SiC selon "une direction unique", alors que certaines conditions expérimentales particulières peuvent aboutir à une croissance "multi-directionnelle". Les particules hybrides de SiC-NTC ainsi obtenues ont également été incorporées dans le PVDF pour préparer des composites percolatifs. Il a été constaté que les hybrides SiC-NTC permettent d'améliorer considérablement la permittivité diélectrique du composite avec un chargement extrêmement faible en NTC. Les NTC sont orientés le long d'un axe sur chaque microplaque de SiC et séparés par une couche mince de polymère, donnant lieu à un réseau de microcondensateurs. Par conséquent, de grandes permittivités diélectriques de plus de 8700 et 2100 à 100 Hz peuvent être obtenues pour un faible taux de chargement de NTC de l'ordre de 2,30% et 1,48% en volume pour les composites à renforts "multi-directionnel" et "unidirectionnel" respectivement. / Ever-increasing energy requirement and exhaustion of fossil fuels demands improving efficiency of energy usage as well as seeking sustainable and renewable resources. Energy storage capacitors are devices that could take this responsibility, and have been the focus of increasing attention due to their advantages such as environment friendliness and very fast energy uptake and delivery. As the requirements grow for a low-cost and high-efficiency capacitive storage system, there is great need for the development of materials with high dielectric permittivity. Polymer composite dielectrics are arousing increasing attention due to their large tunability in dielectric performances. Polymer composites filled with ceramic particles have been used in some energy storage capacitors. Still, their applicability for practical devices is severely hindered by the low dielectric permittivity and deteriorated mechanical and processing properties due to the high content of rigid ceramic particles in the flexible polymer matrix. By replacing ceramic particles with conductive particles in the polymer composites, the percolative polymer composites can be made with the dielectric permittivity dramatically increased in the vicinity of the percolation threshold. Among the conductive fillers, carbon nanotubes (CNTs) have been most intensively studied, as their large aspect ratio coupled with high conductivity can lead to percolation levels in composites at much low loading. One of the greatest challenges for CNT usage in composites is to debundle pristine CNTs and realize uniform dispersion into polymers. This thesis focused on increasing the dielectric permittivity of CNT-based polymer composites by both carefully optimizing the dispersion of nanotubes as well as controlling the microstructure of the composites. The dielectric permittivity increment in the previous composite systems originated from the formation of microcapacitors. However, CNTs were always frizzy in the CNT/polymer composites, which was not beneficial in forming parallel pair electrodes of microcapacitors. To overcome this problem, we proposed a microarchitecture of hybrid SiC-CNT as conductive filler. Such micro/nano hybrids were produced by floating catalytic chemical vapor deposition. The organization mode of CNTs on SiC particles could be effectively tuned by adjusting synthesis conditions. The results showed that asymmetric surface properties of 6H-SiC were prone to led to “single-direction” growth of CNTs on SiC particles, while the competition between the substrate nature and the experimental conditions can resulted in a “multi-directions” hybrid structure. Resultant SiC-CNT hybrids were further incorporated into PVDF to prepare percolative composites. It was found that the SiC-CNT hybrid can significantly improve the dielectric permittivity of SiC-CNT/PVDF composite with an extremely low CNT loading. CNTs on each SiC microplate are oriented along an axis and separated by a thin polymer matrix, giving rise to a network of microcapacitors. As a result, a large dielectric permittivity of more than 8700 and 2100 at 100 Hz could be obtained at a low CNT loading of 2.30 vol% and 1.48 vol% in the “multi-directions” and “single-direction” composites respectively.

Orientador: Cecília Amélia de Carvalho Zavaglia / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-17T10:45:04Z (GMT). No. of bitstreams: 1 Oliveira_SimoneGoncalvesde_M.pdf: 3805652 bytes, checksum: 8b1a4cc53b1b8005bdadd9b629bab628 (MD5) Previous issue date: 2010 / Resumo: No mundo moderno em que vivemos, devido à acirrada competição no mercado automotivo, surge à necessidade de um motor cada vez mais econômico, necessidade esta agravada pela competição internacional com os mercados asiáticos. Assim, acelera-se não apenas a corrida pelo aumento de qualidade e redução de custo dos produtos, mas também para as questões ambientais, como a redução das emissões de gás carbônico e de consumo de combustível. Sabe-se que, quanto maior o veículo, maior é o seu impacto sobre o consumo de combustível. O peso, por exemplo, é o fator mais importante nas emissões de CO2. Considerando que os metais são mais pesados que os plásticos, existe um grande interesse na substituição de peças metálicas por poliméricas. O objetivo geral deste trabalho foi selecionar plásticos de engenharia ou compósitos de matriz polimérica para aplicação em coletores de admissão de gases de motores a diesel. Para tanto, foi elaborada uma matriz de decisão, onde foram avaliadas as principais características necessárias para essa peça específica, que atualmente é constituída pela liga de alumínio fundida. As seguintes características foram consideradas importantes na montagem da matriz de decisão: resistência mecânica à tração e ao impacto; densidade; resistência ao calor; resistência química aos combustíveis; processabilidade por injeção; custo e disponibilidade. Como substitutos ao alumínio fundido foram escolhidos os seguintes materiais: Poliamida 66 sem reforço (PA 66); Poliamida 66 com reforço de 30% fibras de vidro e sem termoestabilizante (PA 66 30 FV - ST); Poliamida 66 com reforço de 30% fibras de vidro com termoestabilizante (PA 66 30 FV - CT); Poliftalamida com 33% de fibras de vidro (PPA 33 FV) e Acetal (PPO). Uma primeira seleção foi feita com dados obtidos na literatura, restando como candidatos mais promissores o PA 66 30FV ST, PA 66 30 FV com CT e o PPA 33 FV. Para esses três plásticos de engenharia foram realizados ensaios de caracterização como: avaliação das propriedades mecânicas; térmicas; resistência ao calor. Chegou-se à conclusão que o PA66 30FV CT é o material mais adequado para a substituição proposta. Finalmente, foi obtido um modelo da peça estudada (coletor de admissão) por prototipagem rápida, para auxiliar nas etapas posteriores deste trabalho, que será o desenvolvimento da matriz de injeção / Abstract: In the modem world where we live, due to incited competition in the automobilist market, emerges the necessity an engine much more economic and il is worsen by the international competition with the Asian markets. Thus, accelerate not only the race for the raise of the quality and cost reduction of products, but also for the environment topics, such as the reduction of the carbonic gas emissions and fuel consumption. It is known that, as bigger the vehicle is, bigger will be the impact of the fuel consumption. The weight, for example, is the most important factor in the CO2 emissions. Concerning that the metals are heavier than plastics, a great interest in the replacing the metallic parts for polymers exists. The general objective of this work was to select of engineering plastics or composites of polymeries matrix for application in the intake manifold of diesel engines. For this reason, a decision matrix was elaborated where the main necessary characteristics for this specific part had been evaluated, currently is the casting aluminum alloy. The following characteristics had been considered important in the decision matrix: mechanical resistance to the tensile and the impact, density, thermal resistance, chemical resistance to the fuels, injection process, cost and availability. As substitute to casting aluminum the following plastics or composites had been chosen: Polyamide 66 without reinforcement (PA66J, Polyamide 66 with 30% glass fiber reinforcement and without heat stabilizer (PA66 30 GF - CT), Polyamide 66 with 30% glass fiber reinforcement with heat stabilizer (PA 66 30 FV - ST), Poliftalamide with 33% of glass fiber (PPA 33 FV) and Acetal (PPO). A first stage was made with data gotten in literature, remaining as three more promising candidates PA 66 30FV without heat stabilizer, PA 66 30 FV with heat stabilizer and PPA 33 FV. For these three engineering plastics had been carried through characterization tests: evaluation of the mechanical and thermal properties, resistance to the heat. As conclusion, the PA66 30FV with heat stabilizer is the material that more adjusted for the replacement proposal. Finally a model of the studied part (Intake Manifold of Diesel Engine) for rapid prototyping was gotten, to assist the next stage of this work, whit will be the development of the injection matrix / Mestrado / Materiais / Mestre em Engenharia Automobilistica

Orientadores: Liliane Maria Ferrareso Lona, Paula Forte de Magalhães Pinheiro Bonassi Machado / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-22T16:56:26Z (GMT). No. of bitstreams: 1 Moraes_SamaraBoaventurade_M.pdf: 2271450 bytes, checksum: 53f3a25eef4f92dd7e80b68fe8945abd (MD5) Previous issue date: 2013 / Resumo: O interesse pelos nanocompósitos de matriz polimérica tem crescido acentuadamente nos últimos anos, pois estes materiais apresentam melhores propriedades mecânicas, térmicas, entre outras, quando comparados aos materiais convencionais. Entre os diferentes tipos de nanocompósitos de matriz polimérica, aqueles reforçados com compostos lamelares têm sido amplamente estudados. Os hidroxissais lamelares (HSLs) são exemplos de compostos lamelares e o estudo sobre estes materiais é um assunto novo. Trabalhos na literatura que envolvem os HSLs são relativamente escassos e a maioria está relacionada à sua síntese e caracterização estrutural. Neste trabalho foram sintetizados nanocompósitos de poliestireno utilizando hidroxissais lamelares como agente de reforço. Os nanocompósitos foram produzidos via polimerização in situ utilizando a polimerização em massa e diferentes frações mássicas de HSL. Foram produzidos HSLs intercalados com o ânion dodecilsulfato e o ânion laurato. O polímero puro foi caracterizado pelas análises de cromatografia de permeação em gel, análise gravimétrica, difração de raios-x, espectroscopia no infravermelho por transformada de Fourier, calorimetria exploratória diferencial, termogravimetria e teste de inflamabilidade. Os hidroxissais lamelares foram caracterizados pelas técnicas de inchamento de Foster, difração de raios-x e espectroscopia no infravermelho por transformada de Fourier. Os nanocompósitos poliméricos sintetizados foram caracterizados pelas técnicas de difração de raios-x, espectroscopia no infravermelho por transformada de Fourier, calorimetria exploratória diferencial, termogravimetria e teste de inflamabilidade. Foi escolhido um dos nanocompósitos sintetizados e foi realizada análise gravimétrica para avaliar a influência do HSL na conversão do polímero. Dentre as propriedades do material, os resultados obtidos mostram que os nanocompósitos sintetizados tendem a apresentar melhoras na inflamabilidade quando comparados ao polímero puro e, também apresentam temperatura final de degradação superior ao do poliestireno, além de não influenciarem significativamente na temperatura de transição vítrea do polímero / Abstract: Interest in the nanocomposite polymeric matrix has grown dramatically in recent years because these materials exhibit better mechanical and thermal properties, among others, when compared to conventional materials. Among the different types of nanocomposite polymeric matrix, those reinforced with layered compounds has been widely studied. The layered hydroxides salts (LHSs) are examples of layered compounds and the study of layered hydroxides salts is a new subject. Studies in the literature involving the LHSs are relatively scarce and most of them are related to their synthesis and structural characterization. In this work nanocomposites of polystyrene using layered hydroxides salts as a reinforcing agent were synthesized. The nanocomposites were produced via in situ bulk polymerization. Polymer nanocomposites were synthesized with different mass fractions of LHS. LHSs intercalated with dodecyl sulfate anion and laurate anion was produced. The pure polymer was characterized by analysis of gel permeation chromatography, gravimetric analysis, x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric and flammability test. The layered hydroxides salts were characterized by swelling of Foster techniques, x-ray diffraction and Fourier transform infrared spectroscopy. The synthesized polymer nanocomposites were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric and flammability test. One of the synthesized nanocomposites was chosen and gravimetric analysis was performed to assess the influence of LHS on the conversion of the polymer. Among the material properties, the results obtained show that the nanocompósito synthesized tend to have improved flammability compared to the pure polymer, and also present final temperature higher than the degradation of polystyrene, and do not significantly influence the glass transition temperature of the polymer / Mestrado / Desenvolvimento de Processos Químicos / Mestra em Engenharia Química

Orientador: José Pissolato Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-20T15:35:10Z (GMT). No. of bitstreams: 1 Silva_DaianaAntonioda_M.pdf: 4722111 bytes, checksum: 375d62ec89d5043ee6edb2f08c980d9d (MD5) Previous issue date: 2012 / Resumo: Sistemas de energia elétrica estão constantemente sujeitos à sobretensões classificadas como internas, decorrentes de operações de manobras e chaveamento no próprio sistema; ou sobretensões decorrentes de agentes externos, por exemplo, descargas atmosféricas. Em ambas as situações, para-raios de óxido de zinco (ZnO) tem sido uma solução eficaz, tanto para os transitórios lentos e oscilatórios quanto para os transitórios rápidos e impulsivos. A utilização de para-raios de óxido de zinco com invólucro polimérico nesses casos é relativamente recente, recorrendo a meados dos anos 80. As informações sobre o desempenho elétrico desses dispositivos ao longo de anos de uso ou quando submetidos a condições críticas de operação são escassas e pouco difundidas na literatura técnica disponível. Dessa forma, uma análise criteriosa é proposta para avaliar o desempenho elétrico de para-raios com invólucro de silicone utilizados nos sistemas de distribuição de energia elétrica, em função da degradação físico-química dos mesmos. São realizados, então, 3 meses de ensaio de imersão/envelhecimento das amostras em água com cloreto de sódio à temperatura de 90 °C, visando representar 20 anos de aplicação do dispositivo em campo. A avaliação do desempenho elétrico é realizada através de medições periódicas da corrente de fuga e da tensão residual, enquanto a avaliação físico-química é obtida através da qualificação do invólucro de silicone utilizado nos para-raios por meio da classificação do grau de hidrofobicidade / Abstract: Electric power systems are constantly subjected to internal overvoltages, i.e. resulting from switching and mechanical operations in the system, or then overvoltages resulting from external causes, e.g. atmospheric surges. In both situations, metal-oxide surge arresters have been an efficacious solution for fast and impulsive electromagnetic transients as well as for slow and oscillatory transients. The use of polymeric metal oxide surge arresters, against atmospheric surges as well as for switching operations, is a relatively recent, dating back to the 1980s. However, the information on the electrical performance of these devices throughout the years of use, or when submitted to critical conditions of operation, is scarce and poorly discussed in the available technical literature. Thus, a thorough analysis is proposed to evaluate the electrical performance of surge arresters with silicone housing, commonly applied in the distribution network, as a function of their physical-chemical degradation. In order to represent 20 years of the field device, 3 months of immersion test/aging in water with sodium chloride at a temperature of 90 degrees will be performed. The evaluation will be through periodic measurements of the leakage current and residual voltage. Another objective is to describe the silicone housing used in surge arresters for classifying the degree of hydrophobicity / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Orientador: Wagner dos Santos Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T20:48:08Z (GMT). No. of bitstreams: 1 FranchinideAlmeida_CarlaCarolinaCaliani_M.pdf: 9851478 bytes, checksum: cba3d3bd5a597c89f24fc14ad1d28c25 (MD5) Previous issue date: 2012 / Resumo: O desenvolvimento e a aplicação de novas propriedades de materiais e de novos materiais propriamente ditos, tem sido um grande objetivo dos pesquisadores. Estamos em uma etapa do conhecimento científico-tecnológico onde a nanotecnologia, em particular, está se tornando presente em todas as áreas da ciência e da tecnologia. Desta forma, os pesquisadores estão investigando maneiras de recorrerem à nanotecnologia em alta escala, determinando suas características a fim de utilizá-las adequadamente, proporcionando novos tipos de materiais. Uma das áreas de P&D em nanotecnologia, importantes nas atividades acadêmicas e industriais, está voltada para os materiais poliméricos, em nanocompósitos. Este trabalho teve como principal finalidade conhecer como a nanotecnologia se faz presente nos materiais poliméricos, recorrendo aos pesquisadores/especialistas na área, e investigar quais as possibilidades futuras de utilização destes novos materiais junto à sociedade como um todo, por meio da de prospecção tecnológica. Todavia, para uma prospecção adequada, neste caso determinado, é necessário a utilização de ferramentas próprias, para se obter uma resposta cujas possibilidades sejam próximas às reais. Recorreu-se aqui, à Metodologia Delphi, que utiliza conhecimento de especialistas em áreas de específicas, afim de obter dados através de questionários capazes de representar cenários futuros, num âmbito de probabilidades subjetivas, cujas respostas possam ser tratadas por métodos matemáticos / Abstract: The development and the applications of new properties of already known materials and new materials properly said, has been researchers' main objective. We are in a phase of scientific and technological knowledge where the nanotechnology is becoming present in all science and technology fields. Thus, the researchers are investigating ways to resort to the nanotechnology on a large scale, determining its characteristics in order to use them properly, providing new types of materials. One of the R&D fields in nanotechnology is focused on polymeric materials, in nanocomposites, which are present in academic and industrial activities. This study had as main objective to acquire the knowledge of how the nanotechnology is present in polymeric materials, resorting to researchers/ specialists in the field, to know which are the future possibilities of these new materials in the society, as a whole, through technological prospection. However, in order to obtain a prospection of the future in this determined case, it is necessary to use the appropriate tools, in order to obtain an answer which possibilities are close to the real ones. It was used the Delphi Method, which uses the specialists' knowledge in a specific area, in order to obtain data through questionnaires that may represent future scenarios, in an ambit of subjective probabilities, whose answers can be treated by mathematical methods / Mestrado / Ciencia e Tecnologia de Materiais / Mestra em Engenharia Química

No description available.

Low density polyethylene (LDPE) and Hytrel (a thermoplastic elastomer) were used as polymeric matrices in polymer + metal composites. The concentration of micrometric (Al, Ag and Ni) as well as nanometric particles (Al and Ag) was varied from 0 to 10 %. Composites were prepared by blending followed by injection molding. The resulting samples were analyzed by scanning electron microscopy (SEM) and focused ion beam (FIB) in order to determine their microstructure. Certain mechanical properties of the composites were also determined. Static and dynamic friction was measured. The scratch resistance of the specimens was determined. A study of the wear mechanisms in the samples was performed. The Al micro- and nanoparticles as well as Ni microparticles are well dispersed throughout the material while Ag micro and nanoparticles tend to form agglomerates. Generally the presence of microcomposites affects negatively the mechanical properties. For the nanoparticles, composites with a higher elastic modulus than that of the neat materials are achievable. For both micro- and nanocomposites it is feasible to lower the friction values with respective to the neat polymers. The addition of metal particles to polymers also improves the scratch resistance of the composites, particularly so for microcomposites. The inclusion of Ag and Ni particles causes an increase in the wear loss volume while Al can reduce the wear for both polymeric matrices.

Over the past years, research efforts have focused on adding highly conductive nanoparticles, such as carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), into polymers to improve their electrical conductivity or to tailor their piezoresistive behavior. Resultant materials are typically described by the weight or volume fractions of their nanoparticles. The weight/volume fraction alone is a very global quantity, making it a poor evaluator of a doping configuration. Knowing which particles actually participate in improving electrical conductivity can optimize the doping strategy. Additionally, conductive particles are only capable of charge transfer over a very short range, thus most of them do not form part of the conduction path. Thus, understanding how these particles are arranged is necessary to increase their efficiency. First, this work focuses on polymers loaded with CNTs. A computational modeling strategy based on a full morphological analysis of the CNT network is presented to systematically analyze conductive networks and show how particles are arranged. A definition of loading efficiency is provided based on the results obtained from this morphology analysis. This study provides useful guidelines for designing these types of materials based on important features, such as representative volume element, nanotube tortuosity and length, tunneling cutoff distance, and efficiency. Second, a computational approach is followed to study the conductive network formed by hybrid particles in polymer nanocomposites. These hybrid particles are synthesized by growing CNTs on the surfaces of GNPs. The objective of this study is to show that the higher electrical conductivity of these composites is due to the hybrids forming a segregated structure. Polymers loaded with hybrid particles have shown a higher electrical conductivity compared with classical carbon fillers: only CNTs, only GNPs or mixed CNTs and GNPs. This is done to understand and compare the doping efficiency of the different types of nanoparticles. Finally, some parameters of the hybrid particle are studied: CNT density on GNPs, and CNT and GNP geometries. Recommendations to further improve the composite’s conductivity based on these parameters are presented. It is noted that this work is the first time the hybrid particle is studied through a computational approach.

<p>In this doctoral thesis work, the impacts of alternative constituent material’s impact on low-cost prepreg manufacturing for high volume applications will be considered. Unidirectional prepregs offer the potential for significant increase of specific-properties and thereby weight savings. Hence the automotive industry is seeking to utilize composite components in their design, in order to meet new fuel economy ratings and global emissions targets imposed by governments. New resin formulations to achieve 3-minute cycle times or low-cost carbon fiber manufacturing have been created to address the needs of the automotive and other cost-sensitive industries, however these innovations have led to challenges in the composites manufacturing process. Quality control issues may include variations in resin saturation of the fiber bed, consolidation, porosity, and fiber volume fraction. These quality issues arise in the part forming step or from the initial resin infiltration during prepregging.</p> <p> </p> <p>Some low-cost carbon fiber has a kidney-bean shaped cross-section which has implications on the compaction and permeability of the fiber bed. The kidney-bean shaped fibers were shown in this work to follow a different compaction trend compared to circular fibers. Furthermore, these fibers required an order of magnitude larger force to compact than circular fibers to achieve similar fiber volume fraction, which had implications on the infiltration and consolidation step. A shape correction factor based on the fiber cross-sectional aspect ratio was proposed to extend the existing compaction model to fibers with irregular cross-sectional shapes. Additionally, permeability simulations were performed on the kidney-bean shaped carbon fiber in various fiber packing unit cells. Since the kidney-bean shaped fiber had some degree of asymmetry, there are two valid hexagonal packing arrangements. At a minimum, the hexagonal packed unit cell orientation caused a 17% reduction in permeability for the same unit cell and fiber volume fraction between the <u>+</u>90° and 0° orientations. In the most extreme case, a 47% reduction in the permeability was observed between the <u>+</u>90° and 0° orientations. Depending on the fiber orientation, comparable permeabilities to circular fibers were attained or up to a 74% reduction in permeability. This means a selection of low-cost carbon fiber could cause the infiltration time to be up to 3.86 longer than for a traditional carbon fiber.</p> <p> </p> <p>The low-cost carbon fiber was paired with a rapid cure epoxy resin which contained internal mold-release to further improve part cycle times to 3-minutes and reduce part costs. The effect of polar and non-polar internal mold-release was studied for its potential influence on cure kinetics. The polar internal mold-release caused a 20 second delay in the 3-minute part cycle, which increased the cycle time by 10% and would therefore influence part production schedules. This prepreg system was reported to have prepreg quality issues related to solids filtering during infiltration. A hot-melt prepregging process was modeled for S-wrap and nip-roller configurations. The S-wrap process was found to better suited for prepregging multi-phase resins since lower pressures were used. Additionally, a general rule was established when working with multi-phase resins was established, particle diameters should not exceed fiber radii.</p> <p> </p> <p>The general design principles from the thermoset hot-melt prepregging were used to develop a thermoplastic prepreg tape line. Thermoplastic composites lend themselves to efficient manufacturing processes such as hybrid overmolding which is suitable for the automotive industry. polyamide-66/Kevlar^® prepreg tapes were manufactured at various line tensions. Neat, rubber toughened, and glass bead filled polyamide-66 based resins were considered. The neat polyamide-66 resin provided a baseline and was able to consistently saturate the fiber bed up to 400µm regardless of manufacturing conditions. The addition of rubber particles did reduce the infiltration distances from the base resin by 20% with significant a significant 50% reduction when the fiber volume fraction reached 0.70. While the addition of glass particles significantly reduced the infiltration distances by up to 70% across all manufacturing conditions. The reduction in flow distance resulted in poor infiltration in thicker fiber beds.</p>