Considerando o grande interesse atual em biocompósitos, seja pela utilização de fibras lignocelulósicas como reforço em compósitos poliméricos ou pela produção de matrizes oriundas de fontes renováveis, buscou-se neste estudo a melhora de propriedades do termorrígido fenólico com a inserção de fibras de sisal tratadas com lignosulfonato de sódio. As fibras de sisal, largamente produzidas no Brasil, são provenientes de fontes renováveis, possuem baixa densidade e apresentam boas propriedades mecânicas. Lignosulfonatos são obtidos através do processo de polpação sulfito da madeira, sendo considerado material renovável. As fibras de sisal foram modificadas via adsorção de lignosulfonato via aquecimento a 70 °C/1h e por meio de irradiação com ultra-som em diferentes tempos (1h e 2h) e por 14h de imersão na solução aquosa de lignosulfonato seguindo de 1 h de irradiação com ultra-som. O lignosulfonato também foi utilizado como substituinte do fenol no preparo de resinas fenol-formaldeído, o que é possível devido à presença de anéis fenólicos em sua estrutura. As fibras de sisal, antes e após os tratamentos, foram caracterizadas segundo teor de componentes majoritários, análise elementar, microscopia eletrônica de varredura (MEV), espectroscopia na região do infravermelho (IV), ensaio de tração, análise térmica (TG e DSC) e difração de raios X. Estes resultados revelaram o efeito do ultra-som sobre a superfície da fibra, a presença de lignosulfonato na superfície das fibras e aumento relativo da resistência à tração após as modificações. Os pré-polímeros fenólico e lignosulfonato-formaldeído foram caracterizados por cromatografia de exclusão de tamanho, IV, TG e DSC. Os compósitos preparados em todo trabalho foram caracterizados por ensaio de resistência ao impacto Izod sem entalhe, ensaio de resistência à flexão, análise térmica dinâmico-mecânica, TG, DSC, ensaio de absorção de água e condutividade térmica. O ensaio de resistência ao impacto para os compósitos fenólicos indicaram uma melhora nesta propriedade quando fibras modificadas (à 70 °C/1 h e ultra-som/1 h) foram utilizadas para preparar estes materiais. O ensaio de flexão também indicou melhora de propriedade quando as fibras modificadas por irradiação com ultra-som (1 e 2 h) foram utilizadas em compósitos fenólicos. Os resultados obtidos mostraram que os tratamentos com lignosulfonato de sódio associados a irradiação ultra-som é um tratamento promissor, pois modifica a morfologia da superfície das fibras sem levar à degradação química, sendo que a separação dos feixes de fibra que ocorre permite melhor interação fibra/matriz na interface. O ensaio de absorção de água, mostrou que os tratamentos aplicados à superfícies influenciam pouco na absorção de água dos compósitos fenólicos. Todos os compósitos preparados com matriz lignosulfonato-formaldeído obtiveram valores resistência ao impacto superiores que os compósitos fenólicos, sendo que o compósito preparado com fibra não-modificada alcançou 1000 J.m-1. As modificações nas fibras de sisal, para estes compósitos, não provocaram os efeitos esperados nas propriedades mecânicas destes materiais, embora se tenha observado uma boa adesão na interface fibra/matriz pelas imagens de MEV, resultado da semelhança químico-estrutural entre a matriz e a fibra de sisal. Uma melhora nas propriedades mecânicas dos materiais aqui investigados faz com que estes se tornem atraentes para aplicações nas indústrias automobilística e aeronáutica, visto que na sua produção são utilizados materiais oriundos de fontes renováveis, como as fibras lignocelulósicas e o lignosulfonato, e tratamentos físicos, como o aquecimento e a irradiação de ultra-som, estando de acordo com políticas de sustentabilidade e preservação do meio-ambiente. / Due to the great current interest in biocomposites because of both the use of lignocellulosic fibers as reinforcers of polymer matrices and the production of matrices prepared from renewable raw material, this study has sought to improve the properties of phenolic thermosets using sodium lignosulphonate as a macromonomer, and the insertion of sisal fibers, either treated or not with sodium lignosulphonate, as a reinforcer. Sisal fibers, which are widely produced in Brazil, are renewable, have low density, and present good mechanical properties. Lignosulphonates are obtained by a wood sulphite pulping process, thus using materials from a renewable source. The sisal fibers were modified by lignosulphonate adsorption by heating at 70 °C for 1 h, followed by sonication for different time periods (1 h and 2 h) or by immersion for 14 h in aqueous lignosulphonate solution, followed by sonication for 1 h. Fiber surface treatment by adsorption of a compatibilizing agent rather than by chemical reaction was chosen with the intent of minimizing the reduction of the fiber mechanical properties. The major sisal fiber components were characterized before and after treatment by elemental analysis, scanning electron microscopy, infrared spectroscopy (IR), tensile strength, thermogravimetry (TG) and differential scanning calorimentry (DSC), and X-ray diffraction. The treatments resulted in a significant increase in fiber tensile strength. The phenolic pre-polymers and lignosulphonate-formaldehyde were characterized by size exclusion chromatography, IR, TG, and DSC. The composites were characterized as to Izod impact strength, flexural strength, dynamic mechanic thermal analysis, TG and DSC, water absorption, and thermal conductivity. The phenolic composites reinforced with modified fibers (70 °C/1 h and sonication/1 h) presented improved impact strength. The flexural strength of phenolic composites reinforced with sonication modified fibers (1 and 2 h) improved. The results obtained demonstrate that fiber treatment with sodium lignosulphonate associated with sonication is a promising method, as it modifies the surface morphology of the fibers without drastically changing their properties. The resulting fiber bundle separation allows for a better fiber/matrix interaction. The water absorption assay demonstrated that the fiber surface treatment had little influence on the water absorption of phenolic composites reinforced with these fibers. All the composites prepared with the lignosulphonate-formaldehyde matrix had higher impact strength than phenolic composites; the composite prepared with non-modified fiber reached 1000 J.m-1. The modification of sisal fibers in these composites did not induce effects on the material mechanical properties. However, good adhesion was observed at the fiber/matrix interface, as shown by the SEM images, due to the chemical-structural similarity of the matrix and treated sisal fiber. In this case, the modification of the matrix formulations was the factor that most influenced the material properties. Both the thermosets and the composites had similar thermal conductivity, that is, the presence of untretated or treated sisal fibers did not alter the thermal conductivity of the material. The materials properties that were investigated here show that they may have potential application in the car and aircraft industries (non-structural applications) with the advantage that their production uses renewable resource materials, such as lignocellulosic fibers and lignosulphonate, and physical treatments, such as heating and sonication, meeting the current sustainability and environment preservation policies.

Ce travail de thèse s’est déroulé dans le cadre du projet de nanolanceur à propulsion hybride PERSEUS du CNES. La performance de ce concept est influencée par l’allègement de la structure du lanceur. La voie de développement qui a été choisie est de supprimer le liner du réservoir composite cryogénique. Elle repose sur trois exigences fonctionnelles : la compatibilité du matériau composite avec l’oxygène liquide (LOX), l’étanchéité du réservoir, et la résistance aux sollicitations thermomécaniques.L’étude de la compatibilité LOX des matériaux composites met en évidence l’importance du transfert de chaleur au sein du composite et plus précisément de la conductivité thermique des fibres. Ce résultat théorique est conforté par l’expérimentation.Le verrou scientifique principal du travail de thèse concerne l'influence de l’endommagement du composite sur la perméabilité de ce dernier. La conception de dispositifs expérimentaux a permis de déterminer l’évolution des endommagements (fissuration transverse, micro-délaminage, ouverture de fissure) et celle de la perméabilité. Un modèle complet de prévision de la perméabilité d’une paroi composite sollicitée thermo-mécaniquement est proposé. Il s’articule autour d’un modèle d’endommagement à l’échelle du pli, d’un modèle de prédiction de l'ouverture des fissures, et d’un modèle d’écoulement en milieu poreux. La pertinence du modèle développé est testée à travers la réalisation d’un démonstrateur technologique sans liner et d’une campagne d’essais d’endommagement et de mesure de perméabilité. / This thesis deals with hybrid propulsion launcher systems studied by the CNES (Centre National d'Etudes Spatiales). The performance of the launcher implies its lightening and in this work, the use of a cryogenic composite linerless tank is evaluated. Three functional requirements must be satisfied: the compatibility between the composite material and the liquid oxygen (LOX), the tank gas-tightness and the strength under pressure.The LOX compatibility of composite materials implies high thermal conductivity of the composite, and consequently of the fiber reinforcement. This theoretical result is confirmed by experiments.The main scientific challenge concerns the damage influence on the composite permeability. Specific experimental devices allow determining the damage evolution (transverse cracking, delamination, opening crack) and the composite permeability. A predictive composite permeability model is applied to a composite wall under thermomechanical load: this model includes a ply-scale damage model, a predictive opening crack model and a model of flow through porous media. The relevance of the model is validated through the realization of a linerless prototype tank and the associated tests which correlate damage and permeability.

No description available.

The diploma thesis presents the usability of a new thermosetting material BMC for the construction of a car headlight. In the theoretical part there are described headlights, basic characteristics and properties of plastics focussing on polymer composite materials and material testing. The practical part deals with the processing of test samples for mechanical testing by compression moulding and also with the production of real samples of reflectors and carrier frames by injection moulding. The evaluation is based on comparison of the results of the performed tests of alternative material and the currently used BMC TETRADUR TD 492/2 in HELLA Autotechnik Nova s.r.o. Basic physical-mechanical properties such as strength, stiffness, toughness and hardness are tested and monitored. The reflectors and carrier frames are assembled into the headlight and then tested according to legal and customers´ requirements for climate and vibration resistance and photometry.

Cette thèse consiste en une étude comparative des propriétés thermomécaniques de composites tissés à matrice thermoplastique (PEEK ou PPS) et thermodurcissable (époxy). Une analyse bibliographique a permis la comparaison les comportements des ces stratifies en fonction de la nature de la matrice, de la sollicitation et des conditions environnementales. Une étude expérimentale a conduit à une base de données des trois matériaux sous diverses sollicitations mécaniques (essais monotones élémentaires et structures) et différentes conditions environnementales (température et V.H.). Des essais sur assemblages boulonnes (simple et double recouvrement) ont également été réalisés. Une technique de mesure de champ par corrélation d’images numériques a permis d'étudier le comportement de stratifies troues. Enfin, un modèle de comportement élastoplastique orthotrope de stratifies tisses a matrice thermoplastique a été implémenté dans le code E.F. cast3m et valide pour différentes températures. / This PhD thesis consists in a comparative study of the thermomechanical properties of woven plies composites with a thermoplastic (PEEK or PPS) or a thermosetting (epoxy) matrix. A literature review allowed the comparison between the behaviors of these laminates depending on the matrix nature, the stress state and the environmental conditions. An experimental study led to a database of the three materials for different mechanical loads (monotonic and structural tests) under specific environmental conditions (temperature and wet ageing). Bolted joints tests (single bolt single lap and double lap) have also been performed. A digital pictures correlation technique permitted to study the behavior of circular notched laminates. At last, a model of orthotropic elastoplastic behavior for woven plies laminates with a thermoplastic matrix has been implemented in the F.E. code cast3m and has been validated for different temperatures.

<p>Epoxy thermosets have revolutionized the coating, adhesive, and composite industries but the chemicals from which they are synthesized have significant effects on the environment and human health not only pre-cure but also after crosslinking has occurred. Many flame retardants (FR), hardeners, and other additives used in epoxy thermosets are synthesized from petroleum-based monomers leading to significant environmental impacts at the industrial scale. Various bio-based modifiers have been developed to circumvent these environmental concerns; however, dispersing biologically-based molecules into the system without tradeoffs with other properties, especially mechanical properties and the glass transition temperature, has proven challenging. Tannic acid (TA) is a bio-based high molecular weight organic (HMWO), aromatic molecule. Although biologically sourced, TA is a pollutant in industrial wastewater streams, and there is desire to find applications in which to downcycle this molecule after extraction from these streams. The unique properties that make TA applicable in a variety of applications including leather tanning, burn wound treatment, and water purification are desirable in epoxy thermosets. In this study, we propose TA as an alternative additive for epoxy. We will uncover the usefulness of TA as an epoxy hardener and as a FR additive. Previous work uncovered that TA could be dispersed in epoxy with weights up to 37 wt%, the highest loading level achieved in literature for this molecule. Using TA as an epoxy hardener resulted in materials that had glass transition temperatures at and above 200⁰C. Using TA as a FR additive resulted in intumescent-behavior previously unseen with TA in epoxy. Chemical functionalization with acetic anhydride further enhanced the behavior resulting in a reduction of the peak heat release rate of the materials by 80%. Ongoing research in the use of solvent, metal ion complexation, and water-borne epoxy containing TA will additionally be explored. The result of this work indicated that TA showed significant promise as a biologically-based functional additive as a flame retardant and epoxy hardener and could reduce environmental impact of many currently available products.</p>

No description available.

Chancen und Möglichkeiten des Duroplast für MID-Anwendungen

The market is in great need of more environmentally friendly alternatives to fossil-based composite materials to obtain a more sustainable future. Lignin is the second most common biopolymer and is a byproduct in the pulping and paper industry. Fractionation of lignin has made it possible to receive lignin with narrow dispersity and low molecular weight, which is suitable for further applications. Modification of lignin structure yields new reactive sites that can be tailored for specific needs. Because of the aromatic structure of lignin, it is a promising renewable resource for production of thermosets. In this project Kraft lignin is sequentially solvent-fractionated and modified in an allylation process with allyl chloride. The allylated lignin is reacted with a cross-linking agent and used to impregnate carbon fibre mats. The resin-coated material is then cured at 125 oC to achieve a composite material. The project also encompasses characterization of the chemical structure of lignin in the different fractions. The morphology and adhesive properties of the lignin as well as the carbon fibres and the composite material was investigated. Although the production of composite material from lignin and carbon fibres were accomplished, bubble formation in the resin was a problem for all composite samples that were prepared, whether it was during solvent evaporation or during curing. By performing the addition of resin to carbon fibre mats in multiple steps, where pressure is added after the first applied layer, it is suggested that complete adhesion to the carbon fibre can be achieved, whilst maintaining adequate resin to carbon fibre ratio. / Marknaden är i stort behov av mer miljövänliga alternativ till fossilbaserade kompositmaterial för att kunna erhålla en mer hållbar framtid. Lignin är den näst vanligaste aromatiska biopolymeren och framställs som en biprodukt i pappersindustrin. Fraktionering av lignin har gjort det möjligt att erhålla lignin med låg dispersitet och molekylvikt vilket är lämpligt för vidare applikationer. Modifiering av lignins struktur ger upphov till nya reaktiva grupper som kan anpassas för ens behov. Den aromatiska strukturen som lignin besitter resulterar i en lovande förnybar resurs för produktion av härdplast. I detta projekt är Kraft lignin sekventiellt fraktionerat med lösningsmedel och modifierat med hjälp av en allyleringsprocess i närvaro av allylklorid. Det allylerade ligninet reagerar med en tvärbindare och används vidare för att impregnera kolfiber. De impregnerade kolfibermattorna härdades i ugn vid 125 oC för att erhålla kompositmaterial. Projektet omfattar även karaktärisering av den kemiska strukturen i lignin från de olika fraktionerna. Morfologin och vidhäftningsförmåga av lignin, kolfiber och likaså kompositmaterialet undersöktes. Ett kompositmaterial bestående av kolfiber och lignin erhölls med framgång under projektets gång, dock var bubbelbildning ett stort problem under förångningen av lösningsmedel och även under härdningsprocessen. Addition av harts till kolfibermattorna i flera steg, där tryck är adderat efter det första lagret har blivit applicerat, anses vara en lovande metod för att en hög vidhäftningsgrad ska kunna erhållas. Detta medan ett adekvat förhållande mellan harts och kolfiber upprätthålls.

Combined microwave assisted extraction/degradation of technical lignin in green solvents was successfully employed to generate polyphenolic oligomers with lower Mw than the starting material. For Lignoboost, the highest liquid yield (65 %) was obtained in 20 min at 160 °C using ethanol as solvent. This is an increase in ethanol soluble yield with 38 % compared to solvent extraction. The highest yield for Lignosulfonate was obtained with methanol as solvent, at 160 °C for 20 min. Obtained liquid fractions were analysed by SEC, FT-IR, DSC, TGA, 31P-NMR and 2D-HSQC NMR in order to explain the mechanism of the increased yield, and to study the structural changes after microwave extraction/degradation. 2D-NMR indicates cleavage of β-O-4 inter-unit linkages, but also that some modification around the bond could take place. Lignin based thermosets were synthesised employing the polyesterification between lignin, citric acid and poly(ethylene glycol) (PEG). It was concluded that introduction of PEG into the system was crucial for a homogenous thermoset synthesis with a high gel content. From TGA analysis it could be concluded that the thermoset based on original Lignoboost had a lower thermal stability than the counterparts prepared from lower molecular weight fractions. This implies that the esterification reaction between original Lignoboost and the other co-monomers is obstruct by sterically hindrance, which means that pre-conditioning is positive for the final material properties. / I denna studie utnyttjades en mikrovågsbaserad teknik, för att framgångsrikt extrahera och bryta ner lignin till polyfunktionella oligomerer med lägre molekylvikt än ursprungsmaterialet. Både lignin extraherat genom sulfat- och sulfitprocessen, d.v.s. kraft lignin (Lignoboost) och lignosulfonat, undersöktes. Det högsta lösliga utbytet för Lignoboost (67 %) kunde uppnås efter 20 min vid 160 °C genom att använda etanol som lösningsmedel, vilket är en ökning med 38 % jämfört med enbart extraktion i etanol. Under samma förhållanden uppnåddes även det högsta lösliga utbytet för Lignosulfonat, fast genom att använda metanol som lösningsmedel. De erhållna lösliga fraktionerna analyserades med hjälp av SEC, FT-IR, DSC, TGA, 31P-NMR samt 2D-HSQC NMR, med syftet att förklara ökning i lösligt utbyte samt studera eventuella strukturella förändringar efter bearbetning i mikrovågsugnen. Resultat från 2D-NMR indikerar på nedbrytning av β-O-4 bindningar, men även på att modifikationer kring bindningen kan ha uppkommit. Tvärbundna, ligninbaserade material syntetiserades genom att nyttja polykondensationsreaktionen mellan lignin, citronsyra och polyetylenglykol (PEG), vilket resulterade i esterbindningar. Det var möjligt att dra slutsatsen att introducering av PEG in i systemet var avgörande för att nå homogena material med hög andel tvärbindningar. Genom TGA analyser kunde det fastslås att tvärbundna material baserade obehandlad Lignoboost hade lägre termisk stabilitet än dess motsvarigheter baserade på fraktioner med lägre molekylvikt. Detta tyder på att esterreaktionen mellan obearbetad Lignoboost och de två andra monomererna försvåras genom steriskhindring, vilket innebär att bearbetning av ligninet medför positiva effekter på egenskaperna hos det slutgiltiga materialet.