Etude des propriétés des films préparés par evaporation des solutions d'un polymére dans différents solvants

Films of a plasticized random terpolymer were prepared by evaporation of solutions in several solvents. The glass transition temperatures of the films were determined and were found to follow the Fox's equation. Their tensile modulus, measured just below the glass transition temperature, was found to depend on the residual solvent content of the films.     

Corrections des réponses des détecteurs placés à la sortie d'un CPG

Gel permeation chromatography only fitted with a refractometer is not sufficient for characterization of polymers. In the present study a combination of three detectors, a refractometer, a viscometer, and an IR-spectrophotometer is estimated to be necessary for analyzing polymers showing chemical and molecular heterogeneities. Unfortunately, using the crude results of these detectors for calculations leads to errors, the origins of which are identified and corrected.     

Comparaison des méthodes de fractionnement par chromatographie de perméation et par gradient d'elution pour la détermination des répartitions moléculaires des polypropylénes

Molecular weight distributions for polypropylene samples have been determined by a permeation fractionation method (GPC). Porous silica beads were used as a packing material for the columns. The set of columns allows a good separation of the polypropylene macromolecular chains in a range of molecular weights from 5000 to 1.5 × 10⁶, and the thermal and mechanical stabilities of these beads are very good. The calibration has been carried out with fractions of polypropylene of narrow molecular weight distribution prepared by a large-scale column fractionation. The molecular weights M?_w and M?_n and the ratios M?_w/M?_n calculated from the GPC curves show, in general, good agreement with the ones calculated from the column fractionation curves. However, the M?_w/M?_n ratios are always highter in the case of GPC fractionation. This could be due to diffusion phenomena.     

Propriétés des esters d'énols I. Polymérisation d'acétoxyalcènes et études diélectriques des polymères obtenus

Polymerization of acetoxy-2 styrene, parachloro acetoxy-2 styrene, paramethyl acetoxy-2 styrene and paranitro acetoxy-2 styrene was carried out by means of free radical initiators or by thermic reaction. The polymers therefrom showed molecular weights of about 200 000. Studies on the thermal behaviour reveal that these polymers do not undergo any change of phase, either vitreous or crystalline. Dielectric experiments show losses of about 10^?3 radian; the losses are practically constant within a large scale of temperature and frequency. Over 320°K one notices a relaxation process of small magnitude and the presence of water brings about a marked change in the way the polymer reacts to dielectric treatment.     

Application des chaînes de markov discrétisées à la simulation des réacteurs chimiques

Gibilaro et al have shown that Markov's time discretized process is a simple and general method for simulating unsteady flow systems. The present paper recalls briefly the main features of the original method of Gibilaro et al. It shows how to generalize this method and presents three examples with systems including time delays and systems where chemical reactions occur. Comparisons with other methods of solution (exact solution of Bernoulli's equation, numerical solution by Merson and Runge-Kutta methods indicate the accuracy of the method proposed here.     

Interprétation cinétique des mesures d'ignition dans le cas des systèmes réactionnels gaz-solide

A quantitative interpretation of the ignition phenomenon is proposed which allows the determination of the kinetic parameters of exothermic chemical reactions of the type: gas + solid → gas. Two kinetic methods are presented for the case of unsteady state reaction and their application in practice is discussed. The first method is characterized by a gas-solid heat transfer coefficient different in each experiment, the second one by a constant heat transfer coefficient. The reaction kinetics are determined from the experimental conditions at ignition. Both methods are then applied successfully to a reacting system of complex geometry, hydrodynamics and kinetic mechanism: the catalysed oxidation of carbon black, measured by thermogravimetry.     

Décantation assistée par ultrasons des eaux résiduaires

The impact of ultrasound on settling in water treatment has been studied. The effects already measured of ultrasound on the settling properties of various effluents have been identified and these effects have been observed in a static and a dynamic study. Sonification conditions suitable for optimizing such a process have been determined. The results show the primary role that stationary wave systems have in the settling of effluents (flocculated or not, synthesized or real). With flocculated effluents, a true impact on settling can be observed.     

Caractéristiques rhéologiques des suspensions de tourbe

The flow of peat suspensions in water has been studied in the concentration range of 0.75 to 2.25% by weight on a dry basis; the fibre size was below 3 mesh. The pressure drop has been measured, for an extensive range of flow rates (the Reynolds numbers varying from 10³ to 10⁵), in 3 horizontal tubes, the internal diameter of which was 50.8, 38.1 and 25.4 millimeters, respectively. The results have shown that the deviation from the new-tonian behaviour increased with the concentration and the tube diameter. A comparison with dilute pulp slurries has indicated that the behaviour of both suspension had the same characteristics. The fibre suspensions are non-homogeneous fluids and the conventional rheological models cannot describe their behaviour. The annular ring model, which implies the presence, in a laminar flow, of an entangled-fibre network, explains the experimental results obtained. A size analysis of the particles has shown that the type of pump used had an effect on the fibre degradation.     

Optimisation de l'hydrolyse des protéines du lactosérum en utilisant des détergents commerciaux enzymatiques et non-enzymatiques

The main aim of this study is to characterize the effect of some commercial detergents on whey proteins in order to select an efficient detergent to clean inorganic membranes fouled during the process of whey proteins fractionation. The influence of such variables such as time, pH, temperature, type and detergent concentration on the rate of protein hydrolysis has been established. Also, the nature and size of produced peptides have been determined. The most efficient values of cleaning parameters have been obtained by using the enzymatic detergent P3-Ultrasil 62.     

Influence des copolymères greffés sur les propriétés mécaniques des alliages de polyéthylène avec polystyrène

The use of graft copolymers polyethylene-graft-polystyrene (P(E-g-S)) in blends of low-density polyethylene and polystyrene is studied. The copolymers P(E-g-S) are prepared by polymerisation of styrene in the presence of hydroperoxylated polyethylene. Addition of 2,5 wt.-% P(E-g-S) to polyethylene-polystyrene blends considerably increases its breaking strength σ_R but much less so its elongation at break ε_R. A comparison of graft and block copolymers used as emulsifiers in polyethylene-poly-styrene blends at present shows that P(E-g-S) is intermediate between the former graft and block copolymers with regard to their influence on the mechanical properties of blends. Photographs of fractures in the blends show a tenfold smaller phase size upon adding P(E-g-S) to the blends.     

L'électrolyseur dans l'optique de la dynamique des procédés

This article written for the non-specialists reviews the various methods for modeling electrolyzer behavior. Deterministic and stochastic models are discussed and the adaptation of process dynamic to electrolysers is emphasized.     

Etude des propriétés rhéologiques de mélanges fondues de polybutène-1 et de polypropène à des cisaillements élevés

The viscoelastic behaviour of polybutene-1-polypropene blends has been studied in the molten state with respect to temperature, shear stress and shear rate. The corrections of experimental data have been carried out and the influence of the radius of capillary on these corrections was studied. The elasticity was investigated by means of Barus factor and the variation of viscosity versus composition of blends shows a minimum which might be interesting for the technology of plastic materials.     

Précipitations sélectives des métaux solubilisés biologiquement de boues aérobies d'épuration

The selective and successive precipitation resulting from the biological solubilization (Thiobacillus ferrooxidans) of sewage sludge metals was studied. At the same time, theoretical diagrams representing the solubility of hydroxides and metal carbonates (Ca, Mg, Fe, Al, Cu, Zn, Ni, Cd, Mn) and their complexes are compared to the experimental values. The pH was progressively increased by means of Ca(OH)₂- The iron hydroxide precipitate, which was the least contaminated, was obtained at pH of 3.5. The theoretical pH's for acceptable metal precipitation were identified as: Fe⁺³ at pH 3.2, Al⁺³ at pH 4.7, Cu⁺² at pH 6.9, Zn⁺² at pH 8.15, Ni⁺² at pH 8.4 and Mn⁺² at pH 9.1, and were closed to theoretical values. The hydroxide ion controls Ca, Mg and Cu solubilities. A precipitate with about 20% of Cu can be obtained at a pH of 7 after iron hydroxide was precipitated. Recovery of other metals than iron is thus possible.     

Analyse par résonance magnétique nucléaire des polycondensats urée–formol

The oligomer reaction products between urea and formaldehyde were preliminarily studied by 60-MHz NMR spectroscopy. This analytical method was extended to urea–formaldehyde copolymers and provided means to attempt to determine their molecular stucture. Prior to NMR analysis, dilution water was removed by freeze drying in order to avoid degradation and advancement of the resin. Lithium chloride was found to enhance polycondensate solubility in deuterated dimethylsulfoxide and to improve resolution of the spectra by reducing overlapping of the signals. It was then possible to proceed to a qualitative and quantitative analysis of urea–formaldehyde copolymer structure. Structural differences appeared between one-step synthesized resins and those involving a second urea addition; in the latter case, the percentage of unreacted urea was calculated. The shape of the unresolved broad signal assigned to the various methylene groups yielded further information on the resins. A particular shoulder on the methylene signal gives evidence for polyoxymethylene sequences occurring in polycondensates synthesized from concentrated aqueous formaldehyde solutions.