Neste trabalho foi avaliada a influência do tratamento químico de fibras vegetais nas propriedades mecânicas e dinâmico-mecânicas de resina epóxi reforçada com tecidos de fibras de juta. As fibras foram modificadas a partir de solução de hidróxido de sódio, e caracterizadas por microscopia eletrônica de varredura (MEV), espectrometria no infravermelho com transformada de Fourier (FTIR) e resistência à tração. As análises de FTIR e MEV evidenciaram, respectivamente, que o tratamento alcalino promoveu a remoção parcial da hemicelulose e modificou a morfologia das fibras de juta. Amostras dos compósitos com fibras tratadas e não tratadas foram confeccionadas a partir da laminação manual seguida da moldagem por compressão. Compósitos com fibras tratadas apresentaram propriedades mecânicas e módulo de armazenamento maiores do que as da resina epóxi sem reforço e compósitos com fibras sem tratamento. As micrografias de microscopia eletrônica de varredura (MEV) revelaram que compósitos com fibras tratadas possuem menor quantidade de vazios e menor quantidade de pull-out, sugerindo maior adesão com a matriz polimérica do que os compósitos com fibras sem tratamento.

This study was aimed at evaluating the efficiency of chemical treatment on the dynamic mechanical and mechanical properties of composite materials with jute fibers and epoxy matrix resin. The surfaces of the jute fibers were modified by contact with sodium hydroxide solutions, and characterized through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and tensile strength testing. The FTIR and SEM analysis evidenced that the alkaline treatment promoted removal of the hemicellulose and modification in the morphology of the jute fibers, respectively. Polymeric composites with untreated and treated jute fiber were prepared through hand lay-up process followed by compression molding. The treated jute fiber composites displayed higher mechanical properties and storage modulus values than the epoxy resin and untreated fiber composites. The scanning electron micrographs (SEM) revealed that treated jute fiber composites have less voids and pull-out, suggesting a better adhesion with the polymeric matrix than untreated fiber composites.

The measurement of plasticity in clay bodies is crucial in order to get products free of defects and with less processing time. However, tests which simulate the behavior of the clay during processing and the mathematical modeling of some of its characteristics, particularly the plasticity, become difficult because many variables are involved and there is no consensus on the choice of method to be used. This study aimed to develop a mathematical model based on compression test to evaluate the plasticity of clays. Three types of clays were studied with different levels of moisture and their indices of plasticity were also characterized by the Atterberg's and Pfefferkorn's methods. The experimental data were well fitted by the theoretical curves for a wide range of clay plasticity. Moreover, it was possible to observe a correlation between effective stress of compression and paste moisture within each group of clay.

O presente trabalho diz respeito à investigação do comportamento mecânico de materiais compósitos reforçados com fibras curtas e partículas. É apresentado um modelo simples com o intuito de prever a resistência à ruptura desta classe de materiais compósitos. O modelo consiste na modificação da Lei da Mistura, com a introdução de um termo referente à fase partícula presente no compósito. É introduzido e investigado um fator de correção (gama) nesse termo, para ajustar a magnitude de contribuição efetiva da fase partícula para a resistência do compósito. É desenvolvido, ainda, um equacionamento simplificado para correção do fator beta - de alinhamento de fibras - presente na equação da Lei das Misturas, que é preciso ser feita por causa do alinhamento preferencial das fibras que ocorre durante a etapa de compactação do material durante o processamento. Foram produzidos três materiais compósitos diferentes entre si, empregando as mesmas matérias-primas. Os materiais foram ensaiados pelo método de flexão a três pontos, a fim de determinar suas propriedades mecânicas. A comparação entre as propriedades mecânicas obtidas experimentalmente e as propriedades previstas através do modelo indicam boa concordância do modelo com o comportamento real dos materiais compósitos reforçados com fibras curtas e partículas.

The present work presents the investigation of the mechanical behavior of the composite materials, strengthened with short fibers and particles. A simple model is presented, with purpose for prediction of the breaking stress of this class of composite material. The model consists in the modification of the Rule of Mixture, with the introduction of a term, referring to the particle phase, present in the composite material. It is introduced and investigated a correction factor (gamma), to adjust the magnitude of the phase particle contribution to composite material strength. It is developed, still, a simplified equation to correct the factor (beta) - of fiber alignment - present in the equation of the Rule of Mixtures. This correction needs to be made because of the preferential alignment of the fibers that occurs in the stage of material compaction process. Three different composite materials were produced, varying only the ratios of materials, maintaining the raw materials. The composite materials produced were tested by the three-point flexural method, in order to determine their mechanical properties. The comparison between mechanical properties obtained experimentally and the theoretical results demonstrate good agreement with the real behavior of the composite material strengthened with short fibers and particles.