ÉTUDES RHÉOLOGIQUES PRÉLIMINAIRES DE CÉRAMIQUES TECHNIQUES À GRANDE VITESSE DE DÉFORMATION PAR BARRES D'HOPKINSON

Le champ d'application des céramiques techniques s'accroît considérablement. La connaissance de leur comportement dynamique s'avère donc indispensable. Nous présentons ici les premiers résultats d'une étude de comportement à grande vitesse de déformation d'une alumine technique, en vue d'application industrielle. Nous utilisons pour ce faire la technique des barres de Hopkinson en sollicitation de torsion, traction e t compression. Ces dispositifs permettent d'atteindre des vitesses de déformation allant jusqu'à ≃ 103 s-1.The field of application of the engineering ceramics grows more and more. The understanding of their high rate loading behaviour is so necessary. Now, we present the first results of our investigations on this behaviour of engineering alumina for industrial applications. We use the experimental technique of the split Hopkinson bars with compressive, tensile and torsional sollicitations. These apparatus allows us to reach high rate of strain up to 103 s-l

Multi-walled carbon nanotubes as unexpected accelerators of chemical reactions

cited By 0International audienceThe influence of carbon nanotubes on various chemical reactions has been examined. These reactions include epoxy crosslinking, in situ polymerization of copolymers in the presence of carbon nanotubes and thermal degradation of a thermoplastic matrix. The various characterizations were based on different types of analyses, including differential scanning calorimetry, proton nuclear magnetic resonance, size exclusion chromatography and thermogravimetric analysis. In each case, we show that the presence of multi-walled carbon nanotubes accelerates the process. © 2012 Society of Chemical Industry Multi-walled carbon nanotubes can accelerate various chemical reactions: epoxy crosslinking, in situ polymerization of copolymers and thermal degradation of a thermoplastic matrix

Dispersion improvement of carbon nanotubes in epoxy resin using amphiphilic block copolymers

International audienceInterface between Carbon NanoTubes (CNT) and epoxy matrix is admitted to play an important role in the dispersion quality and in the mechanical stress transfer. To improve the interfacial adhesion, we propose to chemically graft molecules onto CNT surface. To achieve this chemical modification, a controlled radical polymerization, named Nitroxide Mediated Polymerization NMP, is used to synthesize a diblock copolymer based on Acrylic Acid (PAA block) and Methyl MethAcrylate (PMMA block). In the present paper, this polymerization is performed "in situ ". The PAA block presents a good affinity with the CNT which enable grafting. The PMMA miscibility with epoxy is expected to give a good adhesion-between the CNT and the matrix-and to bring a better dispersion. In order to compare the chemical modification and the physical adsorption of the copolymers onto CNT dispersion, the same block copolymer was synthesized with and without CNT. The copolymer synthesis was controlled and characterized by different methods as NMR 1H (conversion and composition), SEC (molecular weight) and TGA (grafting density). We show that the better dispersion quality and better physical properties have been obtained with grafted CNT

VISCOPLASTICITÉ DYNAMIQUE DE POLYCARBONATES AUX GRANDES VITESSES DE DÉFORMATION, RELATIONS STRUCTURE-PROPRIÉTÉS

Les comportements rhéologiques de polycarbonates techniques sont étudiés à grande vitesse de distorsion et à grande vitesse de compression (102 s-1 - 5 103 s-1) en fonction de la température (10°C - 150°C) par des dispositifs à barres de Hopkinson. Pour le mode de compression, les résultats sont comparés avec ceux obtenus à très faible vitesse de déformation (10-3 s-1 - 10-1 s-1). On met en évidence dans ce dernier cas l'existence d'une vitesse de déformation critique correspondant à une transition de relaxation ; en outre l'influence d'un prétraitement thermique est aussi abordée.Rheological behaviours of engineering polycarbonates are investigated at high shear strain rates and at high compressive strain rate (102 s-1 - 5 103 s-1) for temperatures ranging from 10°C to 150°C, by means of Hopkinson pressure bar apparati. For the compressive mode, the results are compared to those ones obtained at low strain rates (10-3 s-1 - 10-1 s-1). A critical loading strain rate is pointed out, which is related to a relaxation transition. Moreover the influence of a prethermal treatment is studied

Amphiphilic diblock copolymers with adhesive properties: I. Structure and swelling with water

We study asymmetric block copolymers with the simple diblock AB architecture, in the case where the longer block A is both hydrophobic and "soft", whereas the shorter block B is hydrophilic and "hard". Materials with such a particular combination of physico-chemical and mechanical properties have distinctive advantages, in particular for designing water-compatible adhesive materials. The phase diagram is established, combining NMR and SAXS characterisations of the materials. The swelling with water is monitored through gravimetry and "time-resolved" SAXS. Indications of maintained adhesive properties in a wet environment are given