Natural fibres are increasingly being considered as the reinforcement for polymer matrix composites as they are perceived to be sustainable being a renewable resource. However, they suffer from higher variability in mechanical properties and concerns about their long-term durability in a moist environment. In this study the physical properties of the jute fibres were characterised, the fibre length distribution was determined and the fibre cross-section was analysed using digital images. It was observed that the true fibre area followed a log-normal distribution. The fibre area distribution for different geometrical shapes was estimated and the error in the estimated area of assumed fibre cross-section was also determined to assess the applicability of the assumed cross-section. The mechanical properties of the jute technical fibres from a single batch from South Asia were determined; fibre tensile tests were carried out at ten different gauge lengths between 6 mm and 300 mm and the Young’s modulus, strain to failure and ultimate tensile strengths were determined individually. A strong correlation was observed between the fibre strength/fracture strain and fibre gauge length. It was found as the gauge length increases the fibre strength/fracture strain drops. The fibre failure (Strength/Strain) was modelled using Weibull distribution and three statistical models were developed to relate the fibre strength/fracture strain to the fibre gauge length. Examination of tensile test data reveals that the coefficient of variation (CoV) for failure strain is consistently lower than the CoV for fracture stress (strength), as the failure strain is weakly influenced by the fibre cross-section. Hence, failure strain is the more consistent failure criterion and it is recommended to use failure strain as the key design criterion for natural fibre composites in order to improve reliability in the design of these materials. Different authors have tried to model natural fibre reinforced polymer elastic modulus using micromechanical models and have suggested that further study should include fibre angle and length distribution factors to improve the micromechanical prediction. This thesis further seeks to validate a novel methodology for the prediction of the tensile modulus and strength of natural fibre composites through careful consideration of each of the parameters in the rule of mixtures along with consideration of the statistical variation inherent in reinforcements extracted from plants. The tensile modulus and strength of jute fibre reinforced composites manufactured from well characterised fibres was measured experimentally. Six well established micromechanical models were used to predict the composite elastic modulus. Two micromechanical models were used to predict composite strength. For both mechanical properties, the inclusion of a fibre area correction factor to account for the non-circular cross-section of the fibre resulted in an improved prediction of the respective mechanical properties.

The use of asbestos fibres in construction products has been banned in European countries for about two decades due to its effect on human health. At present, many developing countries use asbestos cement board as one of the most important construction products for roofing, cladding and partition walls. The Hatschek process is the most commonly used method to produce asbestos Fibre Cement Board (FCB). There are two major problems for the asbestos FCB manufacturers in replacing their products with non-asbestos FCB. The first one is finding materials and fibres that are available and competitive in price compared to asbestos fibres, and the second is providing inexpensive machines and equipment to produce non-asbestos FCB. In this research, an effort has been made to solve these two major problems. After the initial laboratory investigations on several natural and synthetic fibres some of the fibres with potential use in FCB were chosen for the further investigations. A slurry vacuum dewatering process was then designed and made for the laboratory use. The performance of material selections and mix designs selected from the laboratory studies were subsequently verified with factory Hatschek process in a factory site trial. Many specimens with natural and synthetic fibres incorporating silica fume and limestone powder were made and tested in the laboratory. Silica fume and limestone powder were used for enhancing flexural strength and suppression of alkalinity to reduce breakdown of the cellulose fibres. The results of mechanical, physical and II durability tests were analysed. The microstructure of the fibres and composites was also studied by SEM (Scanning Electron Microscopy). At some stages, mix design optimization was carried out to gain the highest flexural strength. The most suitable mixes were chosen for the factory site trials. A number of full-scale non-asbestos trial boards were made successfully in an asbestos FCB factory and tested in accordance with the current national and international standards. The results indicated that the trial boards fulfilled the requirements of the relevant standards. Based on the outcome of this research, a combination of acrylic fibres and waste cardboard in a mix incorporating silica fume and limestone powder in addition to Portland cement can be used to replace asbestos fibres. Although broadly compatible with the asbestos cement production process, this formulation change will necessitate some changes to the existing production lines in asbestos cement factories to produce non-asbestos FCB.

Die Verwendung von „klassischen“ Naturfasern als Verstärkungskomponente in Kunststoffbauteilen ist durch ihr besonderes Eigenschaftsspektrum in Kombination mit wirtschaftlichen und ökologischen Vorteilen im gesamten Lebenszyklus begründet. Die Technologien zur Verarbeitung von Naturfasern zu Bauteilen wurden in den vergangenen Jahren kontinuierlich weiterentwickelt, wobei das Hauptaugenmerk auf der Optimierung von Material- und Verfahrensparametern bekannter Technologielösungen lag. Komplexe Anwendungen im Automobilbau erfordern allerdings eine ganzheitliche Betrachtung der gesamten Wertschöpfungskette von der Rohstoffbereitstellung über die Halbzeugfertigung bis hin zur Bauteilentwicklung und -herstellung. In diesem Zusammenhang weisen neuartige Faserverstärkungen aus Ganzpflanzenrohstoffen (GPR) gegenüber den konventionell aufgeschlossenen Naturfasern ein Potenzial für deutlich höhere Material- und Kosteneffizienz auf. Ziel dieser Arbeit ist die Bereitstellung einer werkstoffgerechten Auslegungsstrategie für eine neue durchgängige Prozesskette zur Herstellung von naturfaserverstärkten Bauteilen unter Einsatz von Ganzpflanzenrohstoffen. Am Beispiel der Flachspflanze werden dabei die verketteten Prozessstufen und die zugehörigen Schnittstellen entwickelt, charakterisiert und validiert. Darüber hinaus wird zur Umsetzung von Leichtbauanforderungen der Ansatz verfolgt, funktionale Zusammenhänge zwischen mechanischen Werkstoffkennwerten und lokaler Bauteildichte für eine belastungsgerechte Bauteilauslegung in Leichtbauweise zu erfassen. / The use of „classical“ natural fibres as reinforcing part for plastic components is caused by their particular property range in combination with economical and ecological advantages in the total life cycle. In recent years, technologies for the processing of natural fibres to components were continuously developed, focused on optimising material and process parameters of existing technology solutions. Certainly, complex applications in the automobile industry require an integrated consideration of the total value added chain from material supply to manufacturing of semi-finished products up to component development and production. In this regard novel fibre reinforcements made from whole plant materials possess potential for considerably higher material and cost efficiency compared to conventional natural fibres. The Intention of this work is to provide a material-specific dimensioning strategy for a new integrated process chain to produce natural fibre reinforced components by using raw materials made of the whole plant. Linked process steps and related interfaces were developed, characterised and validated by using the example of a flax plant. Moreover, the approach of realizing lightweight construction requirements is necessary in order to measure functional relations between material parameters and local density for the load-bearing part dimensioning in lightweight structure.

Les fibres végétales utilisées comme renfort dans les matériaux composites présentent des propriétés mécaniques spécifiques concurrentielles par rapport à celles des fibres de verre. De plus, elles ont l'avantage d'être renouvelables et recyclables. Toutefois, leur principal inconvénient est leur sensibilité à l'humidité, ce qui a pour conséquence d'induire une baisse des propriétés mécaniques ainsi d'une décohésion de l'interface fibre/matrice. L'objectif principal de cette thèse est d'étudier l'influence de l'humidité sur le comportement hygro-mécanique de fibres de lin. La première partie de mes travaux a été consacrée à la caractérisation des propriétés hygroscopiques et mécaniques de la fibre et du composite. Dans la deuxième partie, deux modèles multi-échelles, l'un analytique et l'autre numérique, ont été développés pour l'estimation des propriétés hygro-mécaniques des fibres élémentaires de lin. Ils utilisent en partie pour données d'entrée, les propriétés identifiées dans la première partie. / Natural fibres used as reinforcement in composite materials present specific mechanical properties, which are comparable to glass fibres. In addition, they have the advantage of being renewable and recyclable. But, their main drawback is their inherent susceptibility to moisture expansion, which has the effect of inducing a decrease in mechanical properties, and of debonding and fracturing interface in the composite. The main aim of this thesis is to study the influence of humidity on hygro-mechanical behavior of flax fibres. The first part of my work was deal with the characterization of mechanical and hygroscopic properties of the fibre and the composite. The second part is dedicated to the development of two multiscale models, one analytical and one numerical. They have been developed for the estimation of hygro-mechanical properties of elementary flax fibres. Properties identified in the first part of the work are used as input data.

[pt] A pesquisa aborda e métodos e técnicas construtivas e acessíveis, denominadas de fibrobarro, direcionadas as comunidades rurais. Estas técnicas utilizam materiais encontrados na natureza e modos de fazer que não são próprios da região, seguindo a metodologia empírica, traduzida em novos conceitos de design participativo, que determina vivencias que influenciam as relações sociais de ensino e trabalho destas comunidades. O conjunto de métodos e técnicas abordados ajudou no desenvolvimento de uma caixa de água orgânica, servindo de alternativa ao atual modelo de desenvolvimento, no qual o consumo desenfreado dos recursos não renováveis mostrou-de inviável do ponto de vista sustentabilidade. No contexto acadêmico, o LILD (Laboratório de investigação em livre desenho) em seu ambiente de pesquisa é um dos locais para geração de novos materiais e técnicas que substituam as demandas objetivando a sustentabilidade no processo e no uso. Nos últimos 20 anos, o LILD estudou tecnologias limpas de baixo impacto ambiental e o uso de materiais regionais , atendendo a demandas reais na construção de objetos de design e de arquitetura, trabalhando com materiais compósitos de terra crua e fibras naturais. Detalhes sobre essas técnicas e compósitos desenvolvidos em modelos de laboratório e de campo são observados e estudados, no decorrer da pesquisa, apresentando também exemplos de construções feitas em comunidade rural. O Fibrobarro foi usado em experimentos, sendo ele composto de barro agregado a fibras combinadas entre si. Este compósito, quando seco foi impermeabilizado com resina de poliuretano vegetal, extraído do óleo de mamona. Tanto no ensaio com no desenvolvimento dos modelos reduzidos, foram verificadas algumas possibilidades de combinações entre fibras junto ao barro, a fim de se verificar a resistência, durabilidade e impermeabilidade dos novos compósitos oriundos dos ensaios, apropriados á aplicação do material na construção do reservatório de água, bem como em vedações arquitetônicas e em revestimentos. A pesquisa apresenta o resultado do processo de desenvolvimento de um objeto construído com esses compósitos, aplicando-se a metodologia projetual utilizada no LILD, visando o aproveitamento das águas pluviais. / [en] The survey covers constructive and accessible methods and techniques, called Fibrobarro, directed at rural communities. These use materials found in nature and ways of doing that are not from the region, following the empirical methodology, translated into new concepts of participatory design, which determines experiences influencing social relations and education work of these communities. The set of methods and techniques discussed helped in the development of an organic waterbox, serving as an alternative to the current development model, in which unrestrained consumption of non-renewable resources proved to be unviable in terms of sustainability in the process and use. In the last 20 years, the LILD studied clean technologies of low ambient impact and the use of regional materials, taking care of the real demands in the object construction of design and architecture working with composite materials of raw land and natural staple fibers. Details about these techniques and composites developed in laboratory and fields models are observed and studied in the course of research, and also examples of constructions made in the rural community. The Fibrobarro was used in experiments, and he composed of clay added to fibers combined with each other. This composite, when dry polyurethane resin was waterproofed with Vegetable, extracted from castor oil. Both during the tests and in the development of reduced models, some possibilities of combinations had been verified between the fibers along the clay in order to verify the strength, durability and water-resistance of the new composites drawn from the tests, the application of the material in the appropriate construction of the waterbox tank as well as fences and architectural coatings. The survey presents the result of the process of developing an object constructed with these composites, applying the methodology used in the project, with the aim of leveraging LILD rainwater.

[pt] A presente tese estuda as propriedades de curta e londa duração de argamassas de cimento reforçadas com fibras de coco e sisal. O trabalho experimental visou a determinação das propriedades físicas e mecânicas do reforço e o estudo da influência do tipo, fração volumétrica e tamanho de fibra, orientação e composição da matriz nas propriedades mecânicas do compósito. Estudos foram executados com o objetivo de se determinar a influência do reforço na retração plástica, com e sem restrições, das matrizes de argamassa. Fissurações resultantes da imposição das restrições e o fenômeno de cicatrização das fissuras foram também investigados. O modo de ruptura e as propriedades de aderência interfacial fibra-matriz foram determinados através de ensaios de arrancamento. As propriedades de longa duração dos compósitos foram determinadas através dos ensaios de fluência, retração e durabilidade. A influência da adição de várias frações volumétricas e tamanhos de fibras na fluência das matrizes de argamassa foi determinada usando-se corpos de prova, selados e não selados, submetidos a uma pressão de 14,4 MPa durante um período de 210-350 dias. Recuperações das deformações elásticas foram monitoradas por um período de 56-180 dias. A influência dos tipos de fibra, fração volumétrica, tamanho de fibra, tipo de cura, traço da argamassa e substituição parcial do cimento Portland por micro-sílica e escória de alto forno na estabilidade dimensional das matrizes de argamassa foi determinada com o uso de ensaios de retração por um período de 320 dias. A durabilidade das fibras de coco e sisal, imersas em soluções alcalinas de hidróxido de cálcio e de sódio e em água de torneira, foi determinada através da realização de ensaios de resistência à tração em idades variando de 30-420 dias. A durabilidade das argamassas reforçadas com fibras naturais após 320-360 dias imersas em água, expostas a ciclos de molhagem e secagem bem como ao ambiente natural foi determinada através de resultados de ensaios de flexão e de observações de imagens obtidas com o uso de microscopia eletrônica. Um mapeamento de elementos químicos foi realizado com o objetivo de se verificar possíveis migrações de produtos da matriz de cimento Portland para o lúmen e paredes das fibras. Tratamentos para garantir a durabilidade dos compósitos foram estudados, a saber: (a) modificações na matriz através da substituição parcial do cimento Portland por micro-sílica e escória de alto orno; (b) carbonatação da matriz de cimento Portland; (c) imersão das fibras em micro-sílica líquida antes de serem incorporadas à matriz de cimento Portand. / [en] This thesis studies both the short-term and long- term behaviour of sisal and coconut fibre reinforced mortar composites.The experimental work involved extensive laboratory testing to determine the physical and mechanical properties of the fibre reinforcement and to study the influence of fibre type, volume fraction, fibre length, fibre arrangement and matrix composition on the mechanical properties of the composite.Studies were also made to determine the influence of fibre reinforcement in controlling free and restrained shrinkage during the early age of mortar mixes. Cracking due to restraint and the phenomenon of crack self-healing were also investigated. The mode of failure and the properties of the resistance to fibre-matrix interfacial bonding were determined using the single fibre pull-out test.The long-term properties of the sisal and coconut fibre reinforced-mortar composites were assessed throughout creep, shrinkage and durability tests. The influence of the addition of sisal and coconut fibres, of various volume fraction and lengths, on the creep of a mortar matrix was determined using sealed and unsealed specimens subjected to a pressure of 14.4 MPa over a period of 210-350 days. Recovery strains were recorded for a period of 56-180 days.The influence of fibre types, volume fraction, fibre lengths, cure types, mix proportions and replacement of OPC by slag and silica fume on the dimensional stability of mortar matrices was determined using drying shrinkage tests for a period of 320 days. The durability of sisal and coconut fibres exposed to alkaline solutions of calcium and sodium hydroxide and stored in tap water was measured as strength loss over a period of 420 days. The durability of fibre-reinforced mortars after 320 to 360 days, stored under water, exposed to cycles of wetting and drying as well as to the natural weather,was assessed from results of flexural tests and from observations of the photomicrographs obtained using backscattered imaging and secondary electron imaging. Dotting maps of chemical elements were obtained in order to verify possible migration of cement products from the matrix to the lumen and voids within of the fibres. Treatments to enhance the durability performance of the composites were studied,including: (a) modifications to the matrix through the replacement of Portland cement by undensified silica fume and by blast-furnace slag; (b) carbonation of the cementitious matrix and (c) immersion of the fibres in slurry silica fume prior to being incorporated into the Portland cement matrix.

Submitted by VINICIUS SOUZA MORAIS null (vinicius.souza.morais@gmail.com) on 2016-08-19T14:49:52Z No. of bitstreams: 1 Tese Vinicius Souza Morais.pdf: 8282472 bytes, checksum: 64f0af45a29590e87cec66a93963523a (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-08-19T19:01:21Z (GMT) No. of bitstreams: 1 morais_vs_dr_ilha.pdf: 8282472 bytes, checksum: 64f0af45a29590e87cec66a93963523a (MD5) / Made available in DSpace on 2016-08-19T19:01:21Z (GMT). No. of bitstreams: 1 morais_vs_dr_ilha.pdf: 8282472 bytes, checksum: 64f0af45a29590e87cec66a93963523a (MD5) Previous issue date: 2016-06-24 / Desde a antiguidade os seres humanos vêm buscando aprimorar o uso de materiais em seu favor, buscando conferir vantagens de aspectos diversos. Aliado à necessidade de experimentação de novos materiais os softwares simuladores foram impulsionados e conferiram uma poderosa ferramenta da atualidade. A partir desta premissa, a inserção de conhecimento, princípios de estudo e aprendizado, principalmente no que tange a modelagem de ensaios mecânicos como o de tração e de impacto destrutivo Charpy foram realizados. Posteriormente uma máquina de ensaio destrutivo do tipo Charpy foi confeccionada e instrumentada analógico-digitalmente. De posse de bons resultados da máquina, a mesma foi utilizada no comparativo entre teoria e prática a partir de diferentes materiais, possibilitando que tais dados em forma de tabelas e gráficos serem confrontados com resultados obtidos através de simulações com o software comercial. Ensaios de Tração foram realizados em máquinas universais em diferentes materiais metálicos e compósitos (fibras naturais e sintéticas), coletados seus devidos dados e posteriormente confrontados com a literatura e software comercial. Os resultados oriundos das fibras naturais, principalmente do bambu, surtiram efeitos interessantes proporcionando uma maior resistência, leveza e redução no custo para sua produção. / Since ancient times humans have sought to improve the use of materials in their favor, seeking to confer advantages in many aspects. Together with the need to experiment with new materials simulators were driven software and gave a powerful tool today. From this premise, the inclusion of knowledge, study and learning principles, especially regarding the modeling of mechanical tests such as tensile and Charpy destructive impact were performed. Later, a destructive test machine Charpy type was made and analog-digitally instrumented. Possession of good results of the machine, it was used in the comparison between theory and practice from different materials, enabling such data in tables and graphs are faced with results obtained through simulations with commercial software. Tensile tests were performed on machines in different metal materials and composites (natural and synthetic fibers) collected their proper data and subsequently confronted with the literature and commercial software. The results derived from natural fibers, mainly bamboo, have heightened interesting effects providing greater strength, light weight and reduced cost for production.

Orientador: Newton Luiz Dias Filho / Resumo: Desde a antiguidade os seres humanos vêm buscando aprimorar o uso de materiais em seu favor, buscando conferir vantagens de aspectos diversos. Aliado à necessidade de experimentação de novos materiais os softwares simuladores foram impulsionados e conferiram uma poderosa ferramenta da atualidade. A partir desta premissa, a inserção de conhecimento, princípios de estudo e aprendizado, principalmente no que tange a modelagem de ensaios mecânicos como o de tração e de impacto destrutivo Charpy foram realizados. Posteriormente uma máquina de ensaio destrutivo do tipo Charpy foi confeccionada e instrumentada analógico-digitalmente. De posse de bons resultados da máquina, a mesma foi utilizada no comparativo entre teoria e prática a partir de diferentes materiais, possibilitando que tais dados em forma de tabelas e gráficos serem confrontados com resultados obtidos através de simulações com o software comercial. Ensaios de Tração foram realizados em máquinas universais em diferentes materiais metálicos e compósitos (fibras naturais e sintéticas), coletados seus devidos dados e posteriormente confrontados com a literatura e software comercial. Os resultados oriundos das fibras naturais, principalmente do bambu, surtiram efeitos interessantes proporcionando uma maior resistência, leveza e redução no custo para sua produção. / Abstract: Since ancient times humans have sought to improve the use of materials in their favor, seeking to confer advantages in many aspects. Together with the need to experiment with new materials simulators were driven software and gave a powerful tool today. From this premise, the inclusion of knowledge, study and learning principles, especially regarding the modeling of mechanical tests such as tensile and Charpy destructive impact were performed. Later, a destructive test machine Charpy type was made and analog-digitally instrumented. Possession of good results of the machine, it was used in the comparison between theory and practice from different materials, enabling such data in tables and graphs are faced with results obtained through simulations with commercial software. Tensile tests were performed on machines in different metal materials and composites (natural and synthetic fibers) collected their proper data and subsequently confronted with the literature and commercial software. The results derived from natural fibers, mainly bamboo, have heightened interesting effects providing greater strength, light weight and reduced cost for production. / Doutor

Orientador: Lucia Helena Innocentini Mei / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T05:07:51Z (GMT). No. of bitstreams: 1 Jesus_RodolfoCardosode_M.pdf: 2937094 bytes, checksum: 406428b06b411d967d625ec5cff8fa13 (MD5) Previous issue date: 2008 / Resumo: O problema do acúmulo de lixo urbano tem aumentado nas últimas décadas e o grande consumo de plásticos é um dos responsáveis por esta situação. Estes materiais possuem a capacidade de permanecer no ambiente por muitos anos o que dificulta ainda mais a sua destinação correta. Este problema foi a principal motivação do trabalho aqui apresentado. O PHB é um material termoplástico biodegradável produzido por bactérias que se alimentam de sacarose, tais microorganismo convertem a sacarose em PHB. O Brasil é hoje um dos maiores produtores de PHB, entretanto este material possui baixas propriedades mecânicas quando comparados' a plásticos mais usados industrialmente. Algumas propriedades mecânicas foram melhoradas com a adição de triacetina como agente de plastificação, mas a resistência ao impacto diminui com este aditivo. Fibras são materiais utilizados em compósitos de matriz plástica para conferir resistência e flexibilidade a estes materiais. Fibras naturais têm sido empregadas com sucesso na tentativa de diminuir custos de compósitos e gerar reforço estrutural, além de diminuir o impacto ambiental dos plásticos. Neste trabalho foram obtidos compósitós de PHB, Triacetina e Fibras de Coco ou de Sisal, acetiladas e não-acetiladas, através de processos de extrusão e injeção. Os compósitos foram caracterizados por Análises Térmicas, Mecânicas, Espectroscópicas, Microscópicas e de Biodegradação. Os compósitos obtidos apresentaram vantagem em relação a matriz de PHB nos desempenhos mecânicos e de biodegradação devido a adição das fibras naturais e da triacetina. A reação de acetilação aparentemente melhorou a interação entre a superficie fibra-matriz e aparentemente foi mais bem sucedida na fibra de sisal / Abstract: The problem of urban waste accumulation has increased in recent decades and the large consumption of plastics is one of those responsible for this situation. These materiaIs have the ability to remain in the environment for many years making it difficult further to provide its correct destination. This problem was the main motivation of the work presented here. The PHB is a biodegradable thermoplastic material produced by bacteria feeding on sucrose, such microorganisms convert the sucrose in PHB. Brazil is today one of the largest producers of PHB, however this material has low mechanical properties compared to most plastics used industrially. Some mechanical propérties were improved with the addition of triacetin as agent for plasticization, but the resistance to the impact decreases with this additive. Fibers are used materiaIs in plastic matrix composite to give strength and flexibility to these materiaIs. Natural fibers have been used successfully in the attempt to reduce costs, and generate structural reinforcement composites, in addition to reducing the environmental impact of plastics. In this study were obtained from composites PHB, triacetate and Fibers of Coconut or Sisal, acetylated and non-acetylated through extrusion ~d injection, processes. The composites were characterized by Thermal Analysis, Mechanical, Spectroscopics, Microscopics and biodegradation. The composites obtained showed advantage over the array of PHB in the mechanical and performance degradation due to the addition of natural fibers and triacetate. The acetylation reaction apparently improved the interaction between the surface fiber-matrix and apparently was more successful in the sisal fiber / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

Les fibres naturelles sont une alternative aux fibres de verre pour renforcer les polymères. Lors de la mise en œuvre par injection, la taille, l'orientation et la distribution de fibres évoluent en fonction de l'écoulement, et cela conditionne les propriétés des pièces injectées. L'objectif de cette thèse est de caractériser la microstructure de composites à base de deux types de fibres, le lin et Tencel®, et d'établir une corrélation avec leurs propriétés. Les fibres et matrice ont été mélangées en extrusion bivis et les composites obtenus injectés. La rupture de fibres est plus importante lorsque leur concentration augmente. La casse est principalement pendant la phase de mélange. Une nouvelle approche de caractérisation permettant la quantification des orientation, distribution et courbure de fibres a été développée. Les composites présentent une structure cœur-peau dans l'épaisseur de la pièce injectée. Les propriétés rhéologiques des composites ont été étudiées en modes dynamique et capillaire. Les fibres Tencel®, qui sont les plus flexibles, conduisent à une augmentation plus grande des viscosités, modules et seuil d'écoulement. Les propriétés mécaniques en traction et au choc ont été déterminées dans des éprouvettes prélevées dans des boites injectées avec différentes orientations par rapport à l'axe d'écoulement. Les propriétés d'impact des composites à fibres Tencel® sont supérieures à celles à base de lin et de verre. Des modèles ont été testés en prenant en compte l'orientation de fibres. Lors des campagnes d'injection, les pressions sur des capteurs situés dans la cavité ont été mesurées. Les pressions calculées avec le logiciel Rem3D sont en assez bon accord avec la mesure. Le modèle d'orientation de fibre rigide utilisé dans Rem3D donne des résultats corrects pour les fibres de lin, mais il s'est avéré inapproprié pour prédire l'orientation des fibres Tencel® extrêmement flexibles. Ce travail est réalisé dans le cadre de la Chaire Industrielle Bioplastiques financée par Mines ParisTech et Arkema, l'Oréal, Nestlé, PSA et Schneider Electric / Natural fibres are an alternative to glass fibres for reinforcing polymers. During injection, fibre size, orientation and distribution evolve as a function of flow and determine composite properties. The goal of this thesis is to characterize the microstructure of composites based on two types of fibres, flax and Tencel®, and to correlate with composite properties.The composites were prepared by extrusion and injection. Fibre rupture was higher at higher fibre concentrations. There was practically no breakage during injection. A new approach allowing quantification of fibre orientation, distribution and curvature was developed. The composites with cellulosic fibres have core-skin structure along the part thickness. The rheological properties of composites were studied in dynamic and capillary modes. Tencel® fibres, which are the most flexible, showed the highest viscosity, moduli and yield stress. Tension and impact were measured for samples cut from the moulded part at different orientations towards the main flow direction. Impact properties of Tencel®-based composites were the highest compared to flax and glass fibre composites. Models taking into account fibre orientation were tested. Pressure in the mould during injection was recorded. Pressure calculated with Rem3D software showed a reasonable agreement with the experiment. Modelling of fibre orientation with Rem3D gave results comparable with experiment for flax but turned out to be not applicable for Tencel® which are flexible.The work was performed within the Industrial Chair in Bioplastics supported by MINES ParisTech and Arkema, L'Oréal, Nestlé, PSA and Schneider Electric.