Rhéocinétique lors de la polymérisation avec séparation de phase dans un système thermoplastique/thermodurcissable.

4 p.Pour les matériaux polymères, la combinaison de l'écoulement et de la réaction chimique dans un outillage de transformation permet de générer in situ des structures ou des morphologies particulières à l'origine de nouvelles propriétés. Le contrôle du procédé requiert alors la connaissance de l'évolution de la rhéologie du système pendant la réaction chimique (rhéocinétique). Le travail exposé s'attache à décrire l'évolution des modules dynamiques d'un système complexe thermoplastique/thermodurcissable (polystyrène/époxy-amine) lors de la polymérisation du thermodurcissable. Les précurseurs du réseau sont initialement miscibles à haute température mais une séparation de phase sous forme de nodules sphériques intervient en cours de polymérisation. Des mesures microcalorimétriques de l'évolution de la transition vitreuse du thermoplastique et des observations en microscopie de la séparation de phase ont été réalisées. L'évolution des modules du système complexe au cours du temps a été suivie en rhéométrie dynamique. Sur cette base expérimentale, un modèle rhéocinétique prédictif des modules de perte et de conservation a été développé. Il intègre les phénomènes de séparation de phase, de variation de la température de transition vitreuse, de dilution des enchevêtrements de la phase TP dans le cadre d'un modèle d'émulsion généralisé à partir des modules dynamiques du TP et du TD en cours de polymérisation. La généralisation du modèle d'émulsion est réalisée en prenant en compte les interactions entre les particules de phase dispersée au delà du seuil de percolation mécanique sous la forme d'une loi de mélange

Synthesis of branched poly(butylene succinate): Structure properties relationship

International audience; A series of branched poly(butylene succinate) (PBS) were synthesized with several branching agents namely trimethylol propane (TMP), malic acid, trimesic acid, citric acid and glycerol propoxylate. The structure of the branched polymers was analyzed by SEC and H-1-NMR. The effect of branching agent structure on crystallization was also investigated and played a significant role. Isothermal studies showed that glycerol propoxylate could act as a nucleating agent. By contrast high content of TMP disturbed the regularity of the chain and hindered the crystallization of PBS. From the non-isothermal kinetic study, it was found that glycerol propoxylate increased noticeably the crystallization rate due to the flexible structure of the branching agent. A secondary nucleation was observed with glycerol propoxylate attributed to the crystallization of amorphous fraction included between crystallites formed at the primary crystallization. Chain topology was obtained through rheological investigations and the synthesized polymers showed a typical behavior of a mixture of linear and randomly branched PBS. The incorporation of branches improved the processability of PBS for film blowing application and the modulus and the stress at break of the resulting film were significantly increased

Rheological study of mixing in molten polymers: 1-mixing of low viscous additives

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Rheological study of mixing in molten polymers: 2-mixing of reactive systems

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Formation of a fibrillar morphology of crosslinked epoxy in a polystyrene continuous phase by reactive extrusion

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Reaction and Morphology Development Influenced by Diffusion in a Thermoplastic/Thermoset Blend

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The morphology of rigid polyurethane foam matrix and its evolution with time during foaming – New insight by cryogenic scanning electron microscopy

International audienceThis paper presents an investigation of the morphology of growing polyurethane (PU) rigid foams during the very first seconds of the process by cryogenic scanning electron microscopy (cryoSEM) performed at -150°C. The heterogeneous nature of the initial mixture has been revealed withthe presence of sub-micron size physical blowing agent droplets (isopentane), micron size dispersed phase nodules, and large air bubbles dispersed in a continuous matrix. Following the evolution of the microstructure during foaming by cryo-SEM suggested that the isopentane liquid droplets (undissolved part of the physical blowing agent) did not vaporize to create their own bubbles. These observations were confirmed by showing that the number of air bubbles per unit volume (~10^6 bubble/cm3) was similar to the cell population density of the final foam (~10^6 cell/cm3), while the number of isopentane droplets initially present was found to be six orders of magnitude higher (~10^12 droplet/cm3). This all means that isopentane molecules initially dissolved in the continuous phase diffuse into the pre-existing air bubbles with no energy barrier to overcome (non-classical nucleation) whereas the isopentane droplets simply act like reservoirs. Finally, despite our best efforts, there is still some doubt whether polymeric 4,4-diphenylmethane diisocyanate (PMDI) is dispersed in the polyol phase, or polyol dispersed in PMDI

Thermal Polymerization of Methyl Methacrylate at High Temperature

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Polymerization of methyl methacrylate at high temperature with 1-butanethiol as chain transfer agent

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