Radical photoinduced cationic frontal polymerization in porous media

Two different interpenetrating phase composites were produced using a radical photoinduced cationic frontal polymerization process. The composites were based on polyurethane (PU) and aluminium open-cell foams impregnated with a formulation of a cycloaliphatic epoxy with different concentrations of a cationic photoinitiator and a thermal initiator. The influence of both types of initiators on the frontal polymerization features was systematically evaluated for the PU foam. It was found to occur only when the concentration of both initiators was greater than 0.5 wt%, leading to full conversion of the epoxy in the whole volume of the 15 mm thick composite samples within less than 100 s. The maximum temperature reached by the propagation front was in the range 275–305 °C depending on the type of formulation, leading to pores in the epoxy phase and extensive degradation of the PU phase. In the case of the opaque aluminium foam, an additional layer of pure resin was required on the UV-exposed surface, which corresponded to a critical mass of a few grams to ensure sufficient heat generation and trigger the front propagation. © 2020 Society of Chemical Industry

Analysis Of Failure Mechanisms In Platelet-Reinforced Composites

The short-term mechanical strength of platelet-reinforced polymer composites was modeled using classical two-dimensional stress-transfer analysis. The stress field in the platelet and at the platelet/matrix interface was described in the presence of a matrix crack perpendicular to the interface. Modeling takes into account the tensile strength of the platelet, its adhesion to the matrix, and also considers the internal stress state resulting from processing. Platelet rupture and interface delamination were considered to be the two key failure mechanisms, depending on the ratio of platelet strength to interface strength. The transition between the two failure events was predicted to occur at a critical platelet length, the value of which depends on the elastic properties of the platelet and matrix, on the platelet geometry and strength, on the platelet/matrix adhesion, and on the internal stress state. The approach was applied to the case of low volume fraction silicon oxide platelets/poly(ethylene terephthalate) composites, where the size of the platelets was accurately controlled either below or above the predicted critical length. Compression molded composites, with perfect alignment of the platelets, and injection molded composites, were prepared and tested. The toughness of the compression molded composites was found to be accurately predicted by the strength model, with a 100% increase in the case of platelets smaller than the critical length compared to larger platelets. Injection molded composites with platelets larger than the critical length were found to fail without yielding. By contrast, when the platelets were smaller than the critical length, the injection molded composites exhibited excellent ductility. The general agreement obtained between the predicted and observed toughening transition shows the importance of filler size and stress state on the strength of platelet-reinforced composite

Time-intensity transformation and internal stress in UV-curable hyperbranched acrylates

The photocuring of three different highly functional acrylates—Di-pentaerythritol penta/hexaacrylate (DPHA) and two hyperbranched molecules (HBP), one with a stiff polyester and one with a more flexible polyether structure—was investigated by means of photorheology, photo differential scanning calorimetry, and beam bending. Special attention was paid to the influence of the composition of DPHA/HBP reactive blends and UV intensity on gelation and vitrification and the resulting dynamics of the internal stress. It was found that adding HBPs to DPHA did not influence gelation significantly, but shifted the onset of vitrification to higher conversions and thus caused lower internal stresses in the material. Increasing UV intensity increased both the conversion at vitrification, thus retarding the build-up of internal stresses, and the ultimate conversion, thus increasing the final stress level. The obtained conversion, gelation, and vitrification data were assembled into time-intensity transformation diagrams, thus providing a useful tool for optimizing photocurin

Durability of Nanosized Oxygen-Barrier Coatings on Polymers

Research on silicon oxide thin films developed as gas-barrier protection for polymer-based components is reviewed, with attention paid to the relations between (i) coating defects, cohesive strength and internal stress state, and (ii) interfacial interactions and related adhesion to the substrate. The deposition process of the oxide from a vapor or a plasma phase leads in both cases to the formation of covalent bonds between the two materials, with high adhesion levels. The oxide coating contains nanoscopic defects and microscopic flaws, and their respective effect on the barrier performance and mechanical resistance of the coating is analyzed. Potential improvements are discussed, including the control of internal stresses in the coating during deposition. Controlled levels of compressive internal stresses in the coating are beneficial to both the barrier performance and the mechanical reliability of the coated polymer. An optimal coating thickness, with low oxygen permeation and high cohesive strength, is determined from experimental and theoretical analyses of the failure mechanisms of the coating under mechanical load. These investigations are found relevant to tailor the interactions and stress state in the interfacial region, in order to improve the reliability of the coating/substrate assembly

Du patrimoine musical. Le concours de chants nationaux de 1848

Pas de résumé disponible actuellementNo abstract available by no

De l'utopie comme lieu commun

Pas de résumé disponible actuellementNo abstract available by no

Esteban BUCH, La neuvième de Beethoven, une histoire politique, Bibliothèque des histoires, Paris, Éditions Gallimard, 1999 ; Joël-Marie FAUQUET et Antoine HENNION, La grandeur de Bach — l'amour de la musique en France au XIXe siècle, Les chemins de la musique, Paris, Librairie Arthème Fayard, 2000.

Deux livres fort différents sont parus récemment, l'un concernant Beethoven, l'autre Bach. Ils traitent tous deux de l'histoire de la musique à travers des représentations. Le livre d'E. Buch traite plutôt de la culture politique de l'Europe, à travers le destin de l'œuvre la plus connue et la plus emblématique de Beethoven, tandis que celui de J.-M. Fauquet et Antoine Hennion concerne le statut de Bach dans la musique au XIXe siècle. Pour comprendre comment la IXe symphonie s'est imposée non..