Dans les travaux de cette thèse, des fibres extraites de la plante de chanvre et des agro-composites polypropylène renforcés par des fibres courtes ont été étudiés. Des essais de caractérisations expérimentales alliés à une modélisation numérique ont permis de comprendre et de déterminer leurs comportements mécaniques en tenant compte des considérations géométriques, des défauts naturels ainsi que la taille des fibres. De part leur nature, les fibres unitaires et les faisceaux de chanvre ont une structure, une forme et une composition complexe influençant leur comportement et leurs propriétés mécaniques. Les études menées dans cette thèse ont montré l’influence des conditions de cultures et de la variété de chanvre sur les propriétés des fibres et des agro-composites. Concernant l’agro-composite, d’autres méthodes expérimentales à la fois optique et macroscopique ont été utilisées pour la caractérisation de son comportement. La méthode de corrélation d’images sous diverses sollicitations mécaniques a mis en lumière l’hétérogénéité du comportement local de ces matériaux, montrant ainsi la non-homogénéité des propriétés mécaniques. Une étude complémentaire a montré l’influence de la répartition des fibres et du processus de fabrication des agro-composites sur l’endommagement et la rupture du matériau / In this thesis, fibres extracted from hemp plant and bio-composites polypropylene reinforced by short hemp fibres was investigated. Experimental studies coupled to numerical modelling have enabled to understand and determined their mechanical behaviour taking into account the geometrical shape, the natural defects and the size of hemp fibres. Microscopic experimental method has enabled to characterize the unitary fibre behaviour independently of fibre bundles. Due to their vegetal origins, hemp unitary fibres and bundles present a complex morphology and structure which have an impact on the mechanical properties of composite. Studies carried out the effect of the growing conditions and hemp variety on the fibre behaviour.For the bio-composite material, optical and macroscopic experimental characterization methods were used in order to determine the behaviour of a polypropylene PP reinforced by hemp fibres. The imaging correlation method is also used to analyse the local behaviour showing the heterogeneity of PP/hemp fibres reinforced material. Moreover, complementary work showed the impact of the fibre distribution and the manufacturing process on the composite properties and the damage initiation and growth

[pt] Geopolímeros podem ser descritos como materiais aluminossilicatos estáveis e sintetizados, cujas propriedades apresentadas em estudos anteriores sugerem diversas vantagens quando comparados aos materiais à base de cimento Portland. Como, por exemplo, alta resistência inicial e bom desempenho quando expostos a altas temperaturas. Este trabalho apresenta um estudo experimental acerca do comportamento mecânico de matrizes geopoliméricas reforçadas com tecidos bidirecionais de juta em temperatura ambiente e quando submetidas a temperaturas elevadas. Geopolímeros à base de metacaulim, sílica ativa e escória de alto-forno foram produzidos com diferentes tipos de agregados (areia e chamote). Ensaios de compressão, tração e flexão foram realizados a fim de se determinar a resposta mecânica das diferentes matrizes e compósitos, e seu comportamento de fissuração, antes e depois da exposição a altas temperaturas. A interface fibra-matriz também foi analisada por meio de ensaios de arrancamento. Todos os compósitos exibiram comportamento de strain/deflection-hardening e múltipla fissuração. No geral, as matrizes contendo escória apresentaram maiores resistências, enquanto as matrizes de sílica e as combinações da matriz de metacaulim com agregados alternativos apresentaram aumento na tenacidade dos compósitos, permitindo uma maior tolerância à temperatura. Análises de DRX, TG e MEV foram utilizadas para investigar as características químicas e microestruturais dos materiais estudados. / [en] Geopolymers may be described as stable and synthesized aluminosilicate materials whose properties presented in previous studies suggest several advantages when compared to materials based on Portland cement, such as, high initial strength and good performance when exposed to elevated temperatures. This work presents an experimental study about the mechanical behavior of geopolymeric matrices reinforced with bi-directional jute fabrics under controlled lab conditions and high temperatures. Geopolymers based on metakaolin, silica and blast furnace slag were produced with different types of aggregates (sand and chamotte). Compression, tensile and flexural tests were performed in order to determine the mechanical response of different matrices and composites, along with their cracking behavior, before and after exposure to high temperatures. The fiber-matrix interface was also analyzed by pullout tests. All composites exhibited strain/deflection-hardening and multiple cracking behavior. In general, the matrix containing slag and sand showed higher strengths. Silica matrices and combinations of the metacaulim matrix with alternative aggregates showed an increase in the composites toughness, allowing a higher temperature tolerance. XRD, TGA and SEM were used to investigate the chemical and microstructural characteristics of the studied materials.

In order to reduce over-dependency on fossil fuels and to create an environment that is free of non-degradable plastics, and most importantly to reduce greenhouse gas emission, bio-based products are being developed from renewable resources through intense research to substitute conventional petrochemical-based plastics with renewable alternatives and to replace synthetic fibers with natural fibers. Many authors have done quite a lot of work on synthesizing polymers from renewable origin. Polylactic acid (PLA) has been developed and characterized, and it was found that it has enormous potential and can serve as an alternative to conventional thermoplastics in many applications. Modification of the plant oil triglycerides has been discussed by many authors, and research is still going on in this area. The challenge is how to make these renewable polymers more competitive in the market, and if possible to make them 100% bio-based. There is also a major disadvantage to using a bio-based polymer from plant oils because of the high viscosity, which makes impregnation of fibers difficult. Although natural fibers are hydrophilic in nature, the problem of compatibility with the hydrophobic matrix must be solved; however, the viscosity of the bio-based resin from plant oils will complicate the situation even more. This is why many authors have reported blending of the renewable thermoset resin with styrene. In the process of solving one problem, i.e reducing the viscosity of the renewable thermoset resin by blending with reactive diluents such as styrene, another problem which we intended to solve at the initial stage is invariably being created by using a volatile organic solvent like styrene. The solution to this cycle of problems is to synthesize a thermoset resin from plant oils which will have lower viscosity, and at the same time have higher levels of functionality. This will increase the crosslinking density, and they can be cured at room temperature or relatively low temperature. In view of the above considerations, the work included in this thesis has provided a reasonable solution to the compounded problems highlighted above. Three types of bio-based thermoset resins were synthesized and characterized using NMR, DSC, TGA, and FT-IR, and their processability was studied. The three resins were subsequently reinforced with natural fibers (woven and non-woven), glass fibers, and Lyocell fiber and the resulting natural fiber composites were characterized by mechanical, dynamic mechanical, impact, and SEM analyses. These composites can be used extensively in the automotive industry, particularly for the interior components, and also in the construction and furniture industries. Methacrylated soybean oil (MSO), methacrylic anhydride-modified soybean oil (MMSO), and acetic anhydride-modified soybean oil (AMSO) were found to be suitable for manufacture of composites because of their lower viscosity. The MMSO and MSO resins were found to be promising materials because composites manufactured by using them as a matrix showed very good mechanical properties. The MMSO resin can completely wet a fiber without the addition of styrene. It has the highest number of methacrylates per triglyceride and high crosslink density. / Akademisk avhandling för avläggande av teknologie doktorsexamen vid Chalmers Tekniska högskola försvaras vid offentlig disputation, den 6:e maj, Chalmers, KE-salen, Kemigården 4, Göteborg, kl. 10.00.

L'objectif de ce travail est de développer l'utilisation de la biomasse ligno-cellulosique dans le domaine des matériaux. Ce travail explore trois voies différentes d'utilisation de la ligno-cellulose afin de balayer un large spectre de constituants et de matériaux finaux. La première voie concerne l'incorporation de fibres naturelles dans la fabrication de panneaux utilisant la lignine comme adhésif. Des améliorations dans la fabrication de ces panneaux de fibres ont été apportées, par traitement chimique ou ajout de nouveaux compatibilisants, permettant un renforcement des propriétés mécaniques. La seconde voie a consisté à développer un procédé original de mise en forme sous haute pression testé et mis en place sur du coton dans le but d'obtenir des objets tridimensionnels sans étape de dissolution/régénération de la cellulose. Une fois le protocole défini, les effets des paramètres de mise en forme et de la variété de coton sur la microstructure et les propriétés mécaniques des objets en coton compressé ont été étudiés. Enfin, une troisième voie à consisté à élaborer des matériaux nanocomposites à partir d'hydroxydes double lamellaire modifiés par la lignine (HDL/LS). L'utilisation de cette nanocharge dans l'amidon a montré une capacité de renforcement pour un faible taux de charge. Ce composite amidon-(HDL/LS) a ainsi été utilisé avec une matrice polyéthylène afin d'augmenter la part renouvelable de la matrice sans diminuer significativement ses propriétés mécanique. Ce travail permet d'envisager des développements futurs pour ces différents matériaux développés et offre ainsi de nouvelles possibilités d'utilisation de la biomasse ligno-cellulosique dans l'élaboration de matériaux techniques. / This work aims at developing new ligno-cellulosic biomass based materials as a way for giving added value to this raw material. This study aimed at developing three different new ways of using ligno-cellulosic components to get a large overview of the possible technical materials. The first way deals with the preparation of natural fibres filled lignin fibreboard panels. Improvements in panels forming have been achieved by using either chemical treatment or novel compatibilisation to improve the strength of the prepared fibreboards. In a second way, an original forming process by high pressure has been tested and carried out on cotton fibres in order to produce 3D objects without dissolution/coagulation processes of cellulose. After setting up the forming procedure, effects of process parameters and cotton variety on microstructures and mechanical properties of highly compressed cotton have been studied. Finally, a third way was the study of new nanocomposites made of layered double hydroxide modified by lignin (LDH/LS). Using such nanofillers into thermoplastic starch turned out to be an efficient solution to reinforce mechanical properties with low nanofillers loading. This starch-(LDH/LS) nanocomposite was also blended with polyethylene to increase the bio-content without a degradation of the mechanical properties. This study is an advanced basis for a further development of these three different materials and offers a broad range of applications suitable for the preparation of new technical materials.

[pt] O aproveitamento sustentável de fibras naturais na construção de membranas estruturais arquitetônicas constitui a questão principal desta dissertação. A conjugação entre os Sistemas Modulares Têxteis e o estudo das interações entre as fibras naturais, tecnologias e o meio permite incorporar técnicas artesanais têxteis e parâmetros ambientais de sustentabilidade às estratégias de concepção e confecção de objetos de Arquitetura & Design. Impactos ambientais e sociais percebidos, tecnologias artesanais e industriais de aproveitamento de fibras naturais e suas relações com o meio físico e social, e as estratégias aprendidas na Natureza e reproduzidas através de experiências em Arquitetura & Design, são aqui investigados. A metodologia experimental com a realização de protótipos permitiu elaborar os princípios que fundamentaram as bases dos Sistemas Modulares Têxteis. As investigações realizadas contribuem para o aperfeiçoamento e adequação de tecnologias artesanais têxteis e fibras naturais disponíveis e pouco padronizadas, adaptando-as a diversos contextos através dos Sistemas Modulares Têxteis. / [en] The natural fibers sustainable use in architectonic structural membranes construction is the main question of this dissertation. The association between the Textile Modular Systems and the inter-actions studies between natural fibers, technologies, and environment, aloud to incorporate into conception and manufacturing strategies of Architecture & Design objects , textile craftsmanship technologies and sustainable environment parameters. Social and environment footprints perceived, industrial and craftsmanship technologies of natural fibers uses, their relations to the social and material environment, and the strategies learned from Nature and reproduced through experiences in Architecture & Design, are investigated here. The consumation of the Experimental Methodology through prototypes aloud to elaborates the principles that conceived the basis of the Textile Modular Systems. The investigations accomplished contribute to improve and adequate the textile craftsmanship technologies and the available non-patterned natural fibers, adapting them to several contexts through the Textile Modular Systems.

[pt] O presente trabalho tem como objetivo o estudo do comportamento mecânico, os mecanismos de fissuração e a autocicatrização de compósitos cimentícios reforçados com fibras de curauá. Desenvolveram-se três tipos de compósitos distintos, cada um reforçado com uma, três ou cinco camadas de tecido unidirecional de curauá. O comportamento mecânico foi avaliado por meio de ensaios de tração direta e flexão a quatro pontos. Estudaram-se os mecanismos de fissuração por meio de fotografias obtidas ao longo dos ensaios, além de análises por correlação digital de imagens (Digital Image Correlation - DIC). Estágios de carregamento foram identificados e associados com o espaçamento entre as fissuras formadas. Os corpos de prova de flexão foram instrumentados com strain gauges nas faces inferior e superior, a fim de medir as deformações de tração e compressão. Dessa forma, foi possível realizar um estudo sobre o desenvolvimento da linha neutra e correlacionar as deformações com espaçamento entre fissuras. A capacidade de autocicatrização dos compósitos foi avaliada por meio de ensaios mecânicos cíclicos e de carregamento contínuo, e também por acompanhamento da evolução das fissuras. Estas foram monitoradas com o auxílio de microscópio estereoscópico. As amostras foram expostas a diferentes ambientes (seco, ciclos de água borrifada, imersão em água) e a influência deles foi avaliada. Todos os compósitos apresentaram strain/deflection hardening com formação de múltiplas microfissuras. Fissuras na presença de água apresentaram cicatrização total e parcial, demostrando que o material desenvolvido é promissor para a ocorrência de autocicatrização. / [en] The present work aims to study the mechanical behavior, cracking mechanisms and the autogenous healing capability of cementitious composites reinforced with curauá fabric. Composites with one, three and five fabric layers were produced. Their mechanical behavior was evaluated through direct tensile and four point bending tests. The cracking mechanisms were studied using image analysis of both photographs took during the tests and Digital Image Correlation (DIC). Various stages of loading were identified and associate with the crack formation. The effect of flexural cracking on the composite neutral axis position was analyzed using strain-gages and correlated with the crack spacing. The autogenous healing capability of the three layered composite system was analyzed by means of the mechanical behavior, in cyclic bending and constant load tests. The crack evolution was follow with microscope stereoscope. The samples were subject to several conditions (RH of 55 percent, cycles of spayed water, water immersion) and their influence was evaluated. All the composites presented strain/deflection hardening behavior with multiple microcrack formation. Cracks exposed to water were partially or totally healed, demonstrating that three layered composite is a promising material for autogenous healing.

[pt] Fibras naturais vêm sendo utilizadas desde a antiguidade, mas, a partir do século XX, foram amplamente substituídas por fibras sintéticas, que apresentam diversas vantagens, tais como grande uniformidade de suas propriedades. Com a preocupação de se ter um desenvolvimento sustentável, voltou-se a substituir os materiais sintéticos por materiais naturais. Algumas das vantagens de utilizar fibras ligno-celulósicas incluem biodegrabilidade, a fixação de carbono, baixo custo e baixa abrasividade. Nos últimos anos, entre diversas aplicações, os setores de construção civil e automobilística estão utilizando fibras naturais como reforço de compósitos termoplásticos, assim como para interiores de cabines de automóveis e caminhões e em capacetes usados em EPI. Este trabalho visa realizar uma caracterização de fibras naturais existentes no mercado brasileiro, a saber: Bastão do Imperador, Costus e Helicônia bihai. O principal uso dessas três espécies se dá como flores ornamentais e como plantas medicinais, mas há um grande potencial no reaproveitamento dos rejeitos dos caules dessas plantas. Para isto foi realizada uma caracterização das fibras, visando medir a verdadeira seção transversal destas utilizando microscopia digital e análise de imagens. Alem disto foi desenvolvida uma metodologia própria para a preparação de amostras de fibras naturais. Foi realizado caracterização por MEV, DRX e TGA. / [en] Natural fibers have been used since ancient times, but since the 20th century they have been largely substituted by synthetic fibers, which offer several advantages such as their homogeneous properties. However, in light of the growing concerns about sustainable development, natural materials have once again started to substitute synthetic ones. A few of the advantages of utilizing lignocellulosic fibers include biodegradability, low cost, and low abrasiveness. In recent years, among many applications, the civil construction and automotive industries are using natural fibers as reinforcement in thermoplastic composites, as well as interior cabins of cars and trucks and helmets used in PPE. Over the past years, areas such as civil construction and the automotive industry have used natural fiber-reinforced thermoplastic composites in car and truck interiors, as well as in helmets used in constructions. This work intends to characterize fibers available in the brazilian market, in particular: Etlingera elatior, Costus, Helicônia bihai. These three species are mainly used as medicinal plants or ornamental flowers, but there is a great potential to reutilize the discarded stems of these plants. Furthermore, these fibers will be characterized using digital microscopy and image analysis, aiming to measure their real transversal section. A method for preparing natural fiber samples will be developed for this purpose. For this was a characterization of the fibers was done in order to measure the true cross section of these using digital microscopy and image analysis. Besides it has been developed a methodology for the preparation of samples of natural fibers. Characterization was performed by SEM, XRD and TGA.

Ce travail vise à étudier le comportement mécanique des composites renforcées par des fibres de lin ainsi que le comportement mécanique et hydrique des composites hybrides. Un taux de porosité élevée observée chez ces matériaux conduit à une dégradation des propriétés mécaniques. Des essais de traction et de flambement avec suivi par émission acoustique ont permis d’identifier les mécanismes d’endommagements qui règnent dans ces matériaux et à mettre en évidence leur chronologie d’apparition. Des observations microscopiques des faciès de rupture ont permis de valider ces résultats. Une optimisation des propriétés mécaniques et notamment en termes de réduire le taux de porosité a été testée et ceci en insérant des fibres de carbone dans la structure. Les résultats ont montré que la position des fibres de carbone est primordiale dans l’amélioration des propriété hydrique et mécaniques. / This work aims to study the mechanical behavior of composites reinforced by flax fibers as well as the mechanical and water behavior of hybrid composites. A high porosity rate observed in these materials leads to a degradation of the mechanical properties. Tensile and buckling tests with acoustic emission monitoring have identified the mechanisms of damage that reign in these materials and highlight their chronology appearance. Microscopic observations of fracture facies validated these results. An optimization of the mechanical properties particularly in terms of reducing the porosity rate has been tested by inserting carbon fibers in the structure. The results showed that the position of carbon fibers is essential in the improvement of water and mechanical properties.

[pt] O desenvolvimento, caracterização mecânica e fluência de compósitos cimentícios têxteis reforçados com fibra de sisal foram realizados neste trabalho. Os compósitos foram fabricados utilizando uma matriz com baixo teor de hidróxido de cálcio, obtida pela substituição parcial do cimento por cinza volante e metacaulim. Foram desenvolvidos três tipos de compósitos, cada um com três ou cinco camadas de tecido unidirecional de sisal. Os compósitos com três camadas foram reforçados variando a condição das fibras em saturadas e com umidade natural. O comportamento mecânico foi avaliado por meio de ensaios de tração direta e flexão a quatro pontos. Estudaram-se os mecanismos de fissuração por meio de fotografias obtidas ao longo dos ensaios, além de análises por correlação digital de imagens - DIC. Todos os compósitos apresentaram comportamento strain/deflection hardening com formação de múltiplas fissuras. Ensaios de fluência à tração e à flexão foram realizados nos compósitos pré-fissurados a fim de estudar as respostas dependentes do tempo. As amostras reforçadas com fibras saturadas apresentaram deformações superiores na tração devido às propriedades da interface fibra-matriz e níveis de deflexão inferiores, além da diminuição da tensão máxima resistida e redução da capacidade de deflexão/deformação. A evolução das fissuras foi monitorada durante todo o ensaio de fluência com o auxílio de um microscópio estereoscópico. Para uma melhor compreensão do mecanismo de fluência dos compósitos, foram realizados ensaios de tração de uma única fibra sob carga sustentada. Além disso, ensaios de fluência à compressão e retração da matriz com diferentes níveis de substituição do cimento por metacaulim foram realizados para entender o seu efeito ao longo do tempo. / [en] In the present work, the development, mechanical characterization and creep of textile reinforced cementitious composites reinforced with sisal fiber were investigated. The composites were manufactured using a matrix with a low calcium hydroxide content, obtained by partially replacing the cement by fly ash and metakaolin. Three types of composites were developed, each with three or five layers of unidirectional sisal fabric. The composites with three layers were reinforced varying the condition of the fibers in saturated and with natural humidity. The mechanical behavior was evaluated through direct tension and four-point flexural tests. Cracking mechanisms were studied through photographs obtained during the tests, as well as analyzes by digital image correlation - DIC. All composites presented strain/deflection hardening behavior with formation of multiple cracks. Tensile and flexural creep tests were performed on pre-cracked composites in order to study time-dependent responses. The samples reinforced with saturated fibers showed higher strain in tension due to the properties of the fiber-matrix interface and lower deflection levels, in addition to the reduction of the ultimate stress and deflection/deformation capacity. The evolution of cracks was monitored throughout the creep test with a stereoscopic microscope. For a better understanding of creep mechanism of the composites, tensile tests of a single fiber were carried out under sustained load at different levels of loading. In addition, compression creep and shrinkage tests of the matrix with different levels of cement replacement with metakaolin were performed to understand its effect over time.

[pt] Apresenta-se o estudo experimental sobre o comportamento de um solo arenoso reforçado e não reforçado com fibras de coco, através da realização de ensaios físicos e mecânicos (ensaios triaxiais isotropicamente drenados). A fibra de coco utilizada foi cortada nos comprimentos de 25 e 50 mm, sabendo que seu diâmetro não é constante, por se tratar de uma fibra natural. Busca-se estabelecer padrões de comportamento que possam explicar a influência da adição de fibras de coco, relacionando-a com os parâmetros de resistência ao cisalhamento e deformação do solo arenoso. Os ensaios foram realizados em amostras compactadas na densidade relativa de 50 por cento e umidade de 10 por cento, variando os teores de fibra na proporção de 0,25; 0,50; e 0,75 por cento em relação ao peso seco do solo. Constatou-se que a adição de fibra não modifica bruscamente as propriedades físicas na areia pura. Com relação ao comportamento mecânico comprovou-se a existência de um incremento na resistência ao cisalhamento em todas as misturas solo-fibra, uma vez que se observou um expressivo aumento do intercepto coesivo das misturas, e um discreto aumento do ângulo de atrito, em comparação aos resultados obtidos para a areia pura. Selecionou-se a mistura que apresentou os melhores resultados de resistência e submeteu-se as fibras a um processo de impermeabilização, com o objetivo de aumentar a vida útil do compósito, onde foi conferido que os parâmetros de resistência não se alteraram quando comparados a mistura com fibras sem impermeabilização. Os resultados se mostraram satisfatórios para aplicação da areia-fibra em camadas de aterros sanitários e aterros sobre solos moles, dando assim uma destinação mais sustentável a esse resíduo, garantindo soluções temporárias e mais econômicas. / [en] We report the experimental study on the behavior of a reinforced sandy soil and not reinforced with coir fibers, by conducting physical and mechanical tests (isotropic drained triaxial tests). Coir used was cut in lengths of 25 and 50 mm, knowing that its diameter is not constant, because it is a natural fiber. The aim is to establish behavior patterns that might explain the influence of the addition of coir fibers, relating it to the shear strength parameters and deformation of sandy soil. The tests were performed on specimens compressed in relative density of 50 percent and 10 percent moisture, varying fiber contents in the proportion of 0.25; 0.50; and 0.75 percent on the dry weight of the soil. It was found that the presence of the fiber does not change the physical properties of pure sand. With regard to mechanical behavior proved the existence of an increase in shear strength in all soil-fiber mixtures, since it was observed a significant increased cohesive intercept of mixtures, and a modest increase in friction angle, compared to the results obtained for the pure sand. The fibers of the mixture showed the best strength results were subjected to a sealing process with the aim of increasing the useful life of the composite, where the strength parameters have not changed compared to the mixture without sealing fibers.The results were satisfactory for use in sand-fiber landfill layers and embankments on soft soils, thus giving a more sustainable destination to this waste, ensuring temporary and more economical solutions.