Alain Ricard

Droplet stabilization in high holdup fraction suspension polymerization reactors

Abstract This paper presents a study on the evolution of the drop size of a methyl methacrylate suspension in an aqueous agitated medium in the absence and in the presence of polymerization reaction. The influence of the impeller speed, of the fraction of monomer and of the surfactant concentration on the Sauter diameter has been determined for the non-reactive system and a correlation between the diameter and these parameters has been established. The evolution of the Sauter mean diameter has been explained by the mean of the variation of the interfacial tension of the system. In the case where a reaction occurs, the properties of the organic phase evolve, that may modify the equilibrium between coalescence and breakage. Consequently, the surfactant concentration has to be higher than without reaction. If this concentration is sufficient, the bead size remains nearly constant during all the reaction. It is defined by the initial properties of the binary system and by the hydrodynamic operating conditions. If the concentration is too low, the bead diameter increases during the reaction especially in the gel effect zone. The final size depends not only on the hydrodynamic factors, but also on the kinetic parameters. Moreover, the hydrolysis ratio of the surfactant has an effect on the bead size due to the quantity adsorbed on the organic surface.

Ion-exchange polymer artificial muscle and actuating system

Chemomechanical transformations are used to produce a mechanical force from a reversible chemical reaction in order to generate artificial muscular contraction, on the model of the biological muscle. The design and experimentation of an original artificial muscle using an ion-exchange polymer which reacts inside a soft envelope, derived from research on pneumatic artificial McKibben muscle, is presented. Then a chemomechanical actuator constituted of two artificial muscles has been conceived: first results are shown on position control in open-loop mode.

Chemical synthesis and microwave properties of polypyrrole dispersed in a polycarbonate matrix

Abstract Conductive composites have been obtained by polymerizing pyrrole with FeCl3 in presence of polycarbonate dissolved in CHCl3 and then precipitating in a non solvent for both polymers. The conductivity of the composite strongly depends on the synthesis conditions : stirring speed, initial pyrrole/matrix ratio, polycarbonate concentration. For composites containing less than 15% of pyrrole, it ranges from 10−2 to 2 S/cm. Also Microwave properties are strongly dependent on the processing (method, temperature). A pressed polypyrrole/polycarbonate composite gives rise to microscopic conduction phenomenon, and its conductivity is stable up to 200°C.

Electrochemical synthesis and characterization of polypyrrole deposited on porous electrode

Abstract Pyrrole has been polymerized by electrooxidation on spherical graphite particles in a pulsed bed reactor. The main characteristics of the reactor are the porous percolated anode and the periodic movement which is set on this particulate electrode. This system gives an homogeneous polymeric deposit which can be used for applications such as modified electrodes or resin exchangers. The influence of the synthesis conditions on the morphology and conductivity of the pellicular phases is presented. In addition the particles covered with polypyrrole film have been used to reduce Ag + ions showing that the polymer has indeed redox properties.

Adsorption of neutral polysaccharides at the silica-water interface role in the formation of a fouling cake at the filtration membrane surfaces used in water treatment

Abstract Membrane fouling is the main drawback of the ultrafiltration process used in water treatment, especially when mineral solids and polymer solutes are both present in the medium to be filtered. We are concerned with the role of the molecular interactions particles/solutes on the formation of a fouling cake. We used model components representative of natural system particles/macromolecular solutes. We worked with two polysaccharides (dextran and pullulan) and with spherical particles of silica. We simulated the fouling deposit accumulated at the membrane surface with a packed bed of silica particles and showed how the adsorption of the polysaccharides at the silica-water interface could induce a great increase of pressure through the bed. The pressure drop after adsorption makes it possible to obtain a hydrodynamic layer thickness of the macromolecules adsorbed on the silica. We compared these calculated values with the viscometric thicknesses determined in a previous study.

Polymerization of pyrrole in a pulsed bed electrode: Mass transfer study

Abstract This paper deals with the preparation of particulate electrodes modified by a deposit of a conducting polymer. Experiments are carried out in an electrochemical reactor containing a pulsed porous bed electrode. The influence of pulsation on the mass transfer is studied. An hydrodynamic correlation between the mass transfer and the dimensionless numbers Re p and Sr is proposed:

Etude cinétique de la synthèse du poly(dibenzo-18-couronne-6) dans un réacteur électrochimique à électrode poreuse percolée pulsée

Abstract This paper reports an experimental study of the synthesis of poly(dibenzo-18-crown-6), a new polymer which can be used to complex the ions contained in industrial effluents, in an electrochemical reactor using a pulsed percolated porous electrode, with the aim of determining the reaction kinetics. Different runs were carried out for monomer concentrations between 0.4×10 −2 and 1.5×10 −2 mol l −1 and temperatures varying from 17 to 29.1 °C. The synthesis rate increases with the concentration but decreases as the temperature increases. A kinetic expression was established as a function of the operating conditions. A reaction order of 1.2 and a global energy factor of −42.0 kJ mol −1 were estimated.