Développement d'un matériau de liner pour réservoir cryogénique de lanceur

Le développement de structures de plus en plus légères et présentant des rapports performances/coût toujours plus élevés est un enjeu permanent dans le domaine des transports. Les matériaux polymères présentent des caractéristiques particulièrement bien adaptées à ces besoins. Ce travail de thèse repose sur le développement d un matériau polymère destiné à être utilisé en tant que liner de réservoir de stockage d oxygène liquide (LOX). L objectif est de démontrer une réduction des masses de l ordre de 20 à 30%, en comparaison avec des structures métalliques. Pour les besoins de l application, le matériau à développer se doit de présenter une bonne compatibilité au LOX, une faible perméabilité aux gaz, des propriétés mécaniques suffisamment élevées à basse température ainsi qu une bonne aptitude à la mise en forme par rotomoulage. La première partie de ces travaux a porté sur la compatibilité au LOX des polymères. En tenant compte des théories proposées dans la littérature, des nanocomposites à matrice polyamide 6 (PA6) ont été élaborés et caractérisés afin d atteindre les performances recherchées. L influence de différents paramètres supposés régir la tenue à l oxygène liquide des matériaux polymères a ensuite été déterminée. Les nanocomposites obtenus présentent globalement une bonne compatibilité avec le LOX. Cette étude a également permis de mettre en évidence que les résultats sont fortement dépendants des paramètres liés à l échantillonnage. Dans un second temps, la processabilité par rotomoulage de ces nanocomposites PA6 a été évaluée. Les propriétés rhéologiques et de stabilité thermique ont notamment été étudiées. Quelques essais de rotomoulage sur les systèmes les plus pertinents ont également été réalisés et ont démontré des résultats encourageants. Dans une dernière partie, les propriétés barrière aux gaz de ces systèmes PA6 ont été étudiées. Les perméabilités mesurées ont été interprétées en tenant compte de la morphologie des mélanges. En particulier, cette étude montre que les nanocomposites à base de PA6 et de graphite lamellaire présentent des performances adaptées pour l application en raison de l effet de tortuosité induit par la charge. Les propriétés mécaniques en traction uniaxiale des systèmes élaborés ont finalement été déterminées et confrontées aux spécifications requises. Les résultats obtenus montrent que les caractéristiques mécaniques sont tout à fait adaptées pour une utilisation en tant que liner de réservoir de stockage d oxygène liquide.In the field of transport, the development of lighter, cheaper and more efficient structures is a recurrent challenge. Polymer materials are good candidates for these applications due to their characteristics quite suitable for requirements. This Phd work aims at developing a thermoplastic material which will be used as an internal liner of a liquid oxygen (LOX) storage tank. The objective is to demonstrate a 20 % to 30 % weight saving, compared to metallic structures. To be used in this kind of application, the thermoplastic material must be LOX compatible, processable by rotational moulding and display a low gas permeability as well as good mechanical properties at low temperatures. In a first part, LOX compatibility of polymers was studied. Taking into account theories proposed in the literature, polyamide 6 (PA6) nanocomposites based on LCP, fluoride and graphite fillers were processed and characterized in order to reach desired properties. The influence of several parameters having an impact on LOX behaviour of polymers was then investigated. The nanocomposites show overall good compatibility with liquid oxygen. This study also demonstrates that LOX sensitivity largely depends on the preparation of samples. The processability of nanocomposites by rotational moulding has then been investigated. Rheological properties and thermal stability have especially been studied. Some rotational moulding trials were carried out on the most relevant systems and demonstrate promising results. Finally, the gas transport properties of PA6 nanocomposites were studied. Measured gas permeability was discussed as a function of the morphology of blends. In particular, this study shows that PA6 nanocomposites filled with lamellar graphite present convenient performances which are due to the tortuosity effect induced by the filler. Mechanical properties of filled systems were finally determined and compared with set requirements. The results show that mechanical characteristics are quite relevant for use as internal liner of LOX storage tank.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

IonicLiquids as new multifunctional agentsfor design of polymer materials with enhancedphysical properties

International audienc

Exchange of Functional Modifications on the Clay Surface

Polymer nanocomposites revolutionized the research in this field owing to the tremendous improvement in the composite properties at very low filler volume fraction. The surface modification of the filler, generally layered silicate montmorillonite clay, is required to compatibilize the organic and inorganic phases. The inorganic clay was modified conventionally with alkyl ammonium ions and the exfoliated nanocomposites with polar polymers could be formed where the clay could be dispersed at nanometer scale. During the initial phase of nanocomposite developments, only ammonium ions of fixed chain length were exchanged on the clay surface. However, this technology suffered when polyolefins and other non-polar polymers were used owing to the difficulties in dispersion of polar clay in the hydrophobic matrices. At best, only partially exfoliated composites could be formed by using these ammonium modified clays. To circumvent these limitations, two possible routes have been followed. By polarizing the polymer matrix (e.g. by addition of compatibilizers or surfactants), one can achieve compatibilization between the organic-inorganic phases. However, this technology leads to deterioration of nanocomposite properties even though better delamination is achieved. On the other hand, one can also focus on the more efficient modification of the filler surface so that the residual polarity after modification of the surface with conventional ammonium ions is also eliminated. A number of new clay surface modification techniques have been developed in the recent years which help in the generation of more exfoliated polymer nanocomposites. These techniques do not rely on the ion exchange of fixed chain length ammonium ions, but lead to generation/exchange of long and polydisperse polymer chains. These techniques include grafting of polymers to the clay surface, grafting of polymers from the clay surface, controlled living polymerization from the clay surface, in situ generation of polyolefins from the clay surface and clay surface reactions etc. and form very robust technologies for the complete organophilization of the clay surface. The generation of thick brushes around the clay surface owing to the better surface modification leads to better coverage of the electrostatic forces binding the clay platelets together and also leads to higher basal plane spacing between them. As a result, the modified platelets are more susceptible to exfoliation when compounded with the polymer matrices

Design of Interfacial Agents Tethered on Lamellar Silicates for Tailoring Morphology and Properties of Nanofilled Polymers : Different Routes

International audienc

Functionalization of Polymer Surfaces

International audienc

Les Liquides Ioniques dans les polymères : où en est on ?

International audienc

IonicLiquids as new multifunctional agentsfor design of polymer materials with enhancedphysical properties

International audienc

Key Role of the Dispersion of carbon nanotubes (CNTs) within Epoxy Networks on their ability to Release

International audienceCarbon nanotubes (CNT) reinforced nanocomposites represent an unique opportunity in terms of designing advanced materials with mechanical reinforcement and electrical and thermal conductivities improvements. However, toxic effects of these composites on human health still have been studied and very soonly some regulations on CNT and on composites based on CNT will be enacted. That is why CNT releasing during nanocomposites lifecycle must be controlled. As the releasing depends on the interfacial strength that is stronger between CNT and polymer compared to CNTs in a CNTs agglomerate, two dispersion states, one poorly dispersed versus another well dispersed are generated and finely described. So the main aim of this study is to check if CNT dispersion state has an influence on the CNT potential releasing in the nanocomposite. To well tailor and characterize the CNT dispersion state in the polymer matrix, the electronic microscopies (SEM and TEM) but also the rheological analysis are carried out to well identify if CNTs are isolated, in bundles or in agglomerates. When the dispersion state is known and controlled, its influence on the polymerization kinetic and on mechanical properties is discussed. It appears clearly that in the case of good dispersion state, strong interfaces are generated linking the isolated nanotubes with the polymer whereas the CNT cohesion in an agglomerate seems much more weak and it does not provide any improvement to the polymer matrix. Raman spectroscopy is relevant to analyze the interfacial properties and allows the relationship with the releasing ability of nanocomposites, i.e. CNTs poorly dispersed in the matrix are more readily released when compared to well dispersed nanocomposites. The tribological tests confirm from released particles granulometry and observations that a CNT dispersion state sufficiently achieved in the nanocomposite avoids single CNT releasing under those solicitations

Key Role of the Dispersion of carbon nanotubes (CNTs) within Epoxy Networks on their ability to Release

International audienceCarbon nanotubes (CNT) reinforced nanocomposites represent an unique opportunity in terms of designing advanced materials with mechanical reinforcement and electrical and thermal conductivities improvements. However, toxic effects of these composites on human health still have been studied and very soonly some regulations on CNT and on composites based on CNT will be enacted. That is why CNT releasing during nanocomposites lifecycle must be controlled. As the releasing depends on the interfacial strength that is stronger between CNT and polymer compared to CNTs in a CNTs agglomerate, two dispersion states, one poorly dispersed versus another well dispersed are generated and finely described. So the main aim of this study is to check if CNT dispersion state has an influence on the CNT potential releasing in the nanocomposite. To well tailor and characterize the CNT dispersion state in the polymer matrix, the electronic microscopies (SEM and TEM) but also the rheological analysis are carried out to well identify if CNTs are isolated, in bundles or in agglomerates. When the dispersion state is known and controlled, its influence on the polymerization kinetic and on mechanical properties is discussed. It appears clearly that in the case of good dispersion state, strong interfaces are generated linking the isolated nanotubes with the polymer whereas the CNT cohesion in an agglomerate seems much more weak and it does not provide any improvement to the polymer matrix. Raman spectroscopy is relevant to analyze the interfacial properties and allows the relationship with the releasing ability of nanocomposites, i.e. CNTs poorly dispersed in the matrix are more readily released when compared to well dispersed nanocomposites. The tribological tests confirm from released particles granulometry and observations that a CNT dispersion state sufficiently achieved in the nanocomposite avoids single CNT releasing under those solicitations