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A refinabilidade de pastas químicas papeleiras: um contributo para a sua avaliação utilizando o refinador Valley
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O objectivo desta tese é o estabelecimento de uma metodologia que permita relacionar as propriedades da suspensão fibrosa, nomeadamente as morfológicas e físicas, assim como as do papel, designadamente as estruturais, ópticas e de resistência, com as variáveis operacionais de refinação e as características físicas e químicas da matéria-prima. Visa-se assim efectuar um contributo para a análise da refinabilidade de pastas químicas para papel. As refinações realizaram-se num refinador Valley laboratorial, tendo-se utilizado como variáveis de estudo a carga sobre o cilindro, a velocidade de rotação do rotor e a energia específica aplicada. Para a sua consecução adaptou-se ao equipamento um variador de velocidade no rotor, um sensor para medição da distância entre o rotor e o estator e um medidor de potência eléctrica. Estudaram-se estes efeitos para diferentes matérias-primas, tendo-se incluído na análise três pastas Kraft branqueadas, uma de pinho silvestre, uma de eucalipto e outra de bétula. Ao nível da fibra, analisou-se a sua morfologia por análise de imagem, especificamente o seu comprimento médio e a sua distribuição, a sua largura, massa linear, curvatura, teor em dobras, fibrilação e proporção de finos; determinou-se ainda a sua resistência intrínseca, o seu nível de hidratação e a sua flexibilidade em estado húmido. Ao nível do papel analisou-se a massa volúmica das folhas, a resistência à tracção, a resistência ao rebentamento, a resistência ao rasgamento, a brancura, a opacidade e os coeficientes de dispersão e absorção da luz. Implementaram-se metodologias para a medição da área relativa de ligação e para estimar a energia de ligação entre as fibras da folha de papel através de métodos ópticos e mecânicos. Fez-se igualmente a análise hidromecânica das condições de refinação para estas três matérias-primas. Desta forma estudou-se o efeito das condições de refinação sobre a carga específica de aresta, estimaram-se as forças tangenciais e forças normais desenvolvidas, determinou-se a viscosidade aparente da pasta ao longo da refinação, quantificou-se a distância entre o rotor e o estator (ou seja, o entreferro) e a eficiência energética do processo. Consequentemente, estabeleceu-se uma relação entre a viscosidade aparente da pasta e o valor do entreferro, assim como entre a primeira variável e o gradiente de velocidade. Os resultados experimentais são explorados de forma a desenvolver relações de controlo das propriedades das pastas para a produção do papel. Foi possível tentarse uma optimização das condições de refinação para cada uma das matérias-primas estudadas para tipos específicos de papéis industriais, respectivamente em termos das propriedades do papel e do consumo de energia no refinador Valley. Pode-se concluir que a suspensão de pasta apresenta um comportamento reofluidificante e que a viscosidade aparente da pasta diminui com o progresso da refinação. Observaram-se igualmente diferentes comportamentos reológicos das diversas pastas, o que permite inferir que do ponto de vista de uma análise hidrodinâmica é preferível a refinação de pastas com diferentes características morfológicas em separado. As equações de ajuste obtidas para as diferentes propriedades estudadas permitem que se comparem as diferentes pastas e que se estude os efeitos das condições operatórias sobre as mesmas. Desta forma, foi possível comprovar que o pinho silvestre exibe melhores propriedades mecânicas, enquanto que o eucalipto apresenta as melhores propriedades ópticas. No entanto, a bétula supera o eucalipto em termos de desempenho mecânico. Relativamente à análise das condições operatórias, pode-se verificar que a velocidade de rotação tem um efeito preponderante sobre as propriedades da suspensão e do papel. Pode-se ainda aferir que a bétula revela um comportamento inverso do pinho e do eucalipto face à velocidade de rotação e da carga específica de aresta.
The goal of this thesis is to set up a methodology to establish a relationship between pulp properties, namely morphological and physical, and paper properties, specifically structural, optical and strength, with the operating variables of refining and the physical and chemical properties of the raw material. The goal is to contribute to the analysis of the beatability of chemical pulps for paper production. The beatings took place in a laboratory Valley beater, and the studied variables were the charge on the roll, the rotor speed of rotation and the specific applied energy. For its feasibility, one fitted the following adaptations to the Valley: a rotor speed of rotation variation controller, a sensor to measure the distance between rotor and stator and an electrical power consumption meter. The effects for three different bleached Kraft pulps were studied, one being pine and the others Portuguese eucalyptus and birch. At the fibre level, its morphology was analysed by image analysis, such as the average fibre length and distribution, its width, coarseness, curl, kinks, fibrillation and fines proportion; the intrinsic fibre resistance was evaluated, such as its water retention value and wet flexibility. At the paper level, one measured its density, tensile strength, burst strength, tear strength, brightness, opacity and its scattering and absorption coefficients. One implemented methodologies to evaluate the relative bonded area and the bond strength in the paper structure using optical and mechanical methods. The hydromechanics of the beating was analysed for the three pulps. So the beating effects on the specific edge load was studied, the normal and tangential forces were evaluated, the pulp apparent viscosity evolution during refining was determined, the distance between rotor and stator was measured and also the energetic efficiency was quantified. One obtained relationships between the apparent viscosity and the rotor-stator gap, and another between the first one and the rate of shear. One explored the experimental results in order to develop control relationships for the pulp properties to paper production. One essayed an optimization of the refining conditions for each pulp for specific types of industrial papers, namely in terms of paper properties and the energy consumption in the Valley beater. The pulp suspension presents rheofluidificant behaviour and the apparent viscosity diminishes along the refining. The different pulps reveal different rheological behaviour, which leads to the inference that from the hydrodynamical point of view one should treat pulps with different morphological characteristics separately. The obtained adjustment equations for the different studied properties permit the comparison between the pulps and the study of the effects of the operating conditions. As expected, the pine revealed the best strength performance, the eucalyptus showed the best optical properties, and the birch showed a better mechanical performance relatively to the other hardwood. In what concerns the analysis of the operating conditions, one verified that the rotor speed of rotation has a major influence on the pulp and paper properties. One also inferred that the birch reveals an opposite behaviour comparatively to the pine and the eucalyptus, from the standpoint of the sped of rotation and the specific edge load.
The goal of this thesis is to set up a methodology to establish a relationship between pulp properties, namely morphological and physical, and paper properties, specifically structural, optical and strength, with the operating variables of refining and the physical and chemical properties of the raw material. The goal is to contribute to the analysis of the beatability of chemical pulps for paper production. The beatings took place in a laboratory Valley beater, and the studied variables were the charge on the roll, the rotor speed of rotation and the specific applied energy. For its feasibility, one fitted the following adaptations to the Valley: a rotor speed of rotation variation controller, a sensor to measure the distance between rotor and stator and an electrical power consumption meter. The effects for three different bleached Kraft pulps were studied, one being pine and the others Portuguese eucalyptus and birch. At the fibre level, its morphology was analysed by image analysis, such as the average fibre length and distribution, its width, coarseness, curl, kinks, fibrillation and fines proportion; the intrinsic fibre resistance was evaluated, such as its water retention value and wet flexibility. At the paper level, one measured its density, tensile strength, burst strength, tear strength, brightness, opacity and its scattering and absorption coefficients. One implemented methodologies to evaluate the relative bonded area and the bond strength in the paper structure using optical and mechanical methods. The hydromechanics of the beating was analysed for the three pulps. So the beating effects on the specific edge load was studied, the normal and tangential forces were evaluated, the pulp apparent viscosity evolution during refining was determined, the distance between rotor and stator was measured and also the energetic efficiency was quantified. One obtained relationships between the apparent viscosity and the rotor-stator gap, and another between the first one and the rate of shear. One explored the experimental results in order to develop control relationships for the pulp properties to paper production. One essayed an optimization of the refining conditions for each pulp for specific types of industrial papers, namely in terms of paper properties and the energy consumption in the Valley beater. The pulp suspension presents rheofluidificant behaviour and the apparent viscosity diminishes along the refining. The different pulps reveal different rheological behaviour, which leads to the inference that from the hydrodynamical point of view one should treat pulps with different morphological characteristics separately. The obtained adjustment equations for the different studied properties permit the comparison between the pulps and the study of the effects of the operating conditions. As expected, the pine revealed the best strength performance, the eucalyptus showed the best optical properties, and the birch showed a better mechanical performance relatively to the other hardwood. In what concerns the analysis of the operating conditions, one verified that the rotor speed of rotation has a major influence on the pulp and paper properties. One also inferred that the birch reveals an opposite behaviour comparatively to the pine and the eucalyptus, from the standpoint of the sped of rotation and the specific edge load.
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Palavras-chave
Ciência e Tecnologia do Papel Refinação Refinabilidade Pastas químicas Avaliação de pastas Valley Hidromecânica Propriedades das fibras Propriedades da pasta Propriedades do papel