Influence de la structure sur les propriétés mécaniques dynamiques de quelques polytéréphtalates de polyméthylèneglycol. Relaxations β et γ

The influence of structure, cristallinity and orientation on the β- and γ-relaxation mechanisms of several poly(α,ω-alkandiolterephthalates) has been investigated. The γ-relaxation consists of two main components involving molecular motions in the amorphous phase, and motions of CH₂ groups (glycolic residue) in the gauche or trans form. A third component involves movements of bigger groups. The β-relaxation at low frequencies can be compared with the dilatometric glass transition.     

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.     

Corrélations entre les propriétés viscoélastiques d'un composite verre-epoxy et la présence d'un agent de pontage amino-silane à la surface des fibres

Dynamic, mechanical, and thermal properties were determined for unidirectional glass fibre reinforced resins. By an out axis study, it is possible to show the particular influence of a silane coupling agent on the mechanical and physical properties of composites. This agent increases the modulus of elasticity, the relaxation times, and the apparent activation energy in the rubbery state.     

Application de l'impédancemétrie électrique à l'étude de la réticulation d'un adhésif en film. Cas d'un assemblage métal/métal

Under a thermal treatment, the curing of an adhesive film is associated with changes in rheological and electrical properties of the resin. A non destructive monitoring of the curing process of such a film is performed by using electrical impedance measurements. The interest of such techniques is demonstrated for the determination of the onset and the end of wetting of a prepolymer film (FM96) on a substrate, the gel point and the completion of the curing reaction occurring during the polymerization of the adhesive film sandwiched between two metallic plates (AISI 304 L (Z2 CN 18-10) stainless steel). The results thus obtained show a clear influence of the temperature and cure time. Impedance measurements performed during a subsequent thermal annealing cycle indicate the presence of multiple phases in the crosslinked adhesive. These results were confirmed by using DSC and DTMA.     

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.     

Etude physicochimique et electrochimique de la protection d'un acier au carbone par les monofluorophosphates. II. Influence de l'application d'une couche de peinture sur les surfaces pre-traitees

Résumé A l'aide de méthodes électrochimiques stationnaires (relevé des courbes courant-tension, mesure de la résistance de polarisation) et transitoires (mesure de l'impédance électrochimique) nous avons étudié le comportement en milieu NaCl 3% d'un acier au carbone (XC 38) ayant subi divers pré-traitements avant l'application d'une couche de peinture glycérophtalique.Les mesures d'impédance électrochimique ont permis la détermination de l'évolution au cours du temps des paramètres influant sur les performances de tenue à la corrosion des divers revêtements.On a ainsi mis en évidence — pour de longs temps d'immersion dans le milieu aggressif (>50 h) — l'effet bénéfique des traitements avant peinture et en particulier celui des post-traitements à base de monofluorophosphates, des surfaces ayant subi une phosphatation cristalline.

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XC 38 carbon steel samples pretreated in various ways have been coated with a glycerylphthalate-type paint. The behaviour of the painted samples in 3% NaCl solutions has been investigated by both steady-state (cathodic polarization curves and polarization resistance measurements) and transient (impedance measurements) electrochemical methods.Impedance measurements allow us to follow the evolution, as a function of immersion time, of the parameters influencing the corrosion performance of the different coatings.The favourable effects of prepaint surface treatments have been exhibited for long immersion times in aggressive media, particularly of those based on monofluorophosphate post-treatments applied on zinc phosphated carbon steel.

     

Matériaux composites à base de bois retifié II. Etudes des propriétés mecaniques de differents mélanges

Different composite materials, with retified pine wood as base, were prepared. Their mechanical properties were compared with composite materials prepared using mineral (zinc oxide, talc, glass) or organic (powdered pine wood) constituents and polar (PVC, ABS) or non-polar (PP) resins. The behaviour of the mixtures varied with the nature of the polymer. An improvement in the mechanical properties was observed when retified wood and polar resins were used. Based on the fibre/matrix interactions, a general interpretation of the differences observed in the behaviour, has been proposed. Results obtained from the tests done on the extent of swelling and the gain in weight of the composite materials in humid atmospheres confirm the need in the use of retified wood as an additive of polar resins.     

Synthèse et propriétés de polyuréthannes réticulés par des cycles isocyanurates

The reaction of α-ω-hydroxy-terminated polyethers or polybutadienes and diphenyl methane diisocyanate in presence of a basic catalyst, such as triethylene or dibutyl tin dilaurate gives polyurethane networks. IR spectroscopy shows that the networks contain isocyanurate rings. These rings are stable at high temperature showing a constant rubbery modulus from T_g up to 160°C. It is noted that the modulus varies with the formulation, the nature of the prepolymer and its molecular weight, the rate of diisocyanate and the catalyst as well as the possibility of introducing butanediol into the formulation.     

Synthèse et propriétés de poly(uréthannes-b-diènes hydrogénés)

α-ω hydroxy-terminated oligo-dienes, both butadiene and isoprene, hydrogenated at different ratios, were polymerized with diphenylmethane diisocyanate and 1,4-butanediol. Dynamic and static mechanical studies were made on the segmented polyurethanes. Those synthesized from oligo (1,4-butadiene) show the decrease of damping peak and a second relaxation due to semi-cristalline structure of soft blocks after their hydrogenation. On the other hand, the hydrogenation of oligo (1,2-butadiene) renders polyurethanes with better elastomeric properties, that is, the relaxation of soft blocks at lower temperature, and the good mechanical and thermal properties at higher temperatures. This can be explained by the modification attributed to the better block segregation between the hydrogenated soft blocks and the urethane hard blocks.     

Propriétés chimiques et électrochimiques de l'eau dans les carbonates alcalins fondus

After recalling the acid—base and redox properties of the solvent species in fused alkaline carbonates, it is shown through potentiometric and thermogravimetric investigations that the acid—base system exchanging O²⁻ H₂O/2OH⁻ is weak, with an equilibrium constant K_A = p_CO2 × [OH⁻]²/p_H2O with pK_A = 1·5 ± 0·2. This result makes it possible to analyse the chemical transformation of fused carbonates into hydroxides under the influence of water vapour. The redox properties of hydrogen and its derivatives are next discussed with underlying thermodynamic considerations, taking into account the chemical and electrochemical experimental data.

With all of these data in mind, the operation of fuel cells containing fused carbonate electrolytes is explained. A new type of fuel cell is suggested, in which polarization due to proton transport to the electrodes is suppressed by the buffer effect of the acid—base pair H₂O/2OH⁻. Performances of such devices are compared to that of cells designed with a combustive mixture of oxygen and carbon dioxide.

Zusammenfassung

Nach einem Überblick auf das Säure/Basen- und Redox-Verhalten der Komponenten des Lösungsmittels in Schmelzen von Alkali-Karbonaten wird mittels potentiometrischer und thermogravimetrischer Untersuchungen gezeigt, dass das Säure/Basenpaar H₂O/2OH⁻, welches O²-austausct, eine Gleichgewichtskonstante K_A = P_CO2 × [OH⁻]²/P_H2O mit einem pKA = 1·5 ± 0·2 besitzt, also in diesem Lösungsmittel bei 600°C sehr schwach ist. Dieses Ergebnis erlaubt die Aufklärung der chemischen Umsetzung von Karbonaten in Schmelzen zu den entsprechenden Hydroxyden bei Einwirkung von Wasserdampf. Die Redoxeigenschaften des Wasserstoffs und seiner Verbindungen werden im folgenden auf Grund von thermodynamischen Betrachtungen diskutiert, indem von den vorgängig erhaltenen Resultaten und experimentellen chemischen und elektrochemischen Daten Gebrauch gemacht wird. Schliesslich wird die Gesamtheit der Ergebnisse verwendet, um eine Untersuchung des Verhaltens von Brennstoffzellen mit Karbonatschmelzen durchzuführen. Man beschreibt einen neuen Typ dieser Reihe, bei welchem die auf den Protonentransport zurückzuführenden Polarisationserscheinungen infolge des Puffereffektes des vorhandenen Säure/Basenpaares H₂O/2OH⁻ unterdrückt werden. Das Verhalten dieser Zellen wird mit demjenigen von Brennstoffzellen auf der Basis von Sauerstoff und Kohlendioxyd als Brennstoffen verglichen.     

Etude des propriétés viscoélastiques de quelques mélanges polybutène-1 – polypropène

Viscoelastic properties of polybutene-1—polypropene blends were investigated in the β-relaxation range. Those blends show only òne relaxation peak and are assumed to be compatible in the amorphous phase. These results permit to corroborate our former assumption concerning the influence of the relative length of the alkyl group in polyolefin blends.     

Influence de léagitation mécanique sur les transferts thermiques en fluidisation homogène

It is possible, through the use of an agitator with a particular shape which renews in a rapid sequence the matter contacting the column walls, to increase significantly the intensity of the thermal transfer between a liquid fluidized layer and the walls. It is shown experimentally that the rotative speed of the agitator has an important effect on the transfer. The whole results are qualitatively interpreted within the framework of a transiant-state mechanism.     

Influence de la quantité d'un sel de sulfonium sur la coupure des liaisons O?Si et sur la solubilité d'un mélange renfermant le sel et le poly(p-triméthylsiloxystyrène) et irradié par des UV

If coating solutions obtained by dissolving poly(p-trimethylsiloxystyrene) together with one of the salts (C₆H₅)₂(C₆H₅SC₆H₄)SSbF₆ or (C₆H₅)₃SAsF₆ in a solvent such as 3-pentanone are aged, the percentage of O? Si(CH₃)₃ bonds cleaved by irradiation at a given intensity (λ = 254 nm) and after post-annealing depends on the amount of salt introduced. The same result is observed with respect to the solubility of the resist when it is treated with the basic solvent MF-319.     

Influence du molybdène sur la cinétique des réactions de conversion du méthane en présence de H2O et CO2

An experimental study of the catalytic action of molybdenum in the reactions of methane with water vapor and carbon dioxide was performed in a fluidized bed differential reactor. In the experiments, special care was taken to isolate the homogeneous reactions which could have interfered with the catalytic effect. The ratio O₂/CH₄ in the feed and the heterogeneous reactions of oxidation and carbide Mo₂C formation, were shown to have considerable influence on the obtained yields. From kinetic results obtained on carbide and pure metal, a reaction mechanism is proposed, and a rate equation is presented for the conversion of methane by water vapor on molybdenum.