Résumé -Perméabilité, diffusion et solubilité des gaz dans le polyéthylène, le polyamide 11 et le polyfluorure de vinylidène -Les coefficients de transport de gaz, c'est-à-dire la perméabilité, la diffusion et la solubilité, sont déterminés par la méthode du temps retard sur une cellule de perméabilité spécifique. Trois polymères semi-cristallins, le polyéthylène (PE), le polyamide 11 (PA11) et le polyfluorure de vinylidène (PVDF) sont étudiés en présence d'hélium (He), d'argon (Ar), d'azote (N 2 ), de méthane (CH 4 ) et de dioxyde de carbone (CO 2 ) pour des températures de 40 à 80°C dans le cas du PE et de 70 à 130°C pour les deux autres matériaux. Les pressions appliquées sont dans la majorité des tests de 10 MPa pour He, Ar, N 2 et CH 4 et de 4 MPa pour le CO 2 , sauf dans quelques cas particuliers où nous avons regardé l'influence de la pression. Dans le cas du PE, l'influence de la fraction volumique de phase amorphe, comprise entre 0,21 et 0,70, de la température et de la nature du gaz sur les processus de transport de gaz est étudiée. L'indépendance de ces phénomènes vis-à-vis de la pression et de l'épaisseur de l'échantillon, comprise entre 0,5 et 6 mm, est également démontrée. En ce qui concerne le PA11, après avoir déterminé l'influence de la température et de la nature du gaz, nous regardons l'effet de l'incorporation de molécules plastifiantes dans cette matrice polymère. Au niveau du PVDF, mis à part les paramètres classiques que sont la température et le type de gaz utilisé, une comparaison des coefficients de transport du CH 4 et du CO 2 dans du PVDF mis en oeuvre par extrusion et par moulage en compression est effectuée. Pour chaque polymère étudié, la dépendance de la perméabilité, de la diffusion et de la solubilité peut s'exprimer à partir de lois d'Arrhenius. Il semble également que la diffusion soit liée de façon très étroite à la taille des molécules et que la solubilité puisse être reliée au paramètre ε/K des gaz. La comparaison des résultats obtenus avec les données disponibles dans la littérature apparaît satisfaisante.Mots-clés : perméabilité, diffusion, solubilité, gaz, PE, PA11, PVDF.Abstract -Permeability, Diffusion and Solubility of Gases in Polyethylene, Polyamide 11 and Poly(vinylidene fluoride) -The gases transport coefficients, permeability, diffusion and solubility, are determined by the time lag method on a specific permeation cell. Three semicrystalline polymers, polyethylene
Résumé -Méthodes de mesure des coefficients de transport de gaz dans les polymères -La perméabilité aux gaz des polymères est une propriété inhérente à leur structure, qui résulte de la solubilisation des fluides dans la matière, puis de la diffusion de ces produits à travers la matrice polymère. L'aptitude d'un gaz à pouvoir traverser plus ou moins rapidement un matériau peut être mise à profit dans de nombreux domaines industriels. Des polymères très peu perméables sont par exemple recherchés dans des domaines aussi divers que la production pétrolière, l'emballage alimentaire ou le domaine automobile. Dans les applications pétrolières, la fonction principale des polymères est d'assurer l'étanchéité des structures telles que les conduites. Dans ce cas, les matériaux sont au contact de gaz à haute température et sous forte pression et les informations concernant les coefficients de transport dans ces conditions extrêmes ne sont généralement pas disponibles dans la littérature. C'est pourquoi certains appareillages susceptibles de donner accès à ces valeurs ont été développés. Après quelques rappels théoriques des méthodes de calcul pour l'obtention des coefficients de transport et une brève revue bibliographique des différentes techniques expérimentales existantes, les différents montages expérimentaux étudiés sont décrits précisément.Mots-clés : perméabilité, diffusion, solubilité, polymères, gaz, méthodes expérimentales. Abstract -Transport Properties of Gases in Polymers: Experimental Methods -The permeability of gases in polymers is a property inherent to their structure, which results, firstly, from the absorption of fluids by the material, then, from the diffusion of these products through the polymer matrix. The capacity of a gas to cross more or less fast a material can be used in numerous industrial
Endothelial precursor cells (EPCs) cultured from adult bone marrow (BM) have been shown to mediate neovasculogenesis in murine models of vascular injury. We sought to directly compare umbilical cord blood (UCB)- and BM-derived EPC surface phenotypes and in vivo functional capacity. UCB and BM EPCs derived from mononuclear cells (MNC) were phenotyped by surface staining for expression of stromal (Stro-1, CXCR4, CD105, and CD73), endothelial (CD31, CD146, and vascular endothelial [VE]-cadherin), stem cell (CD34 and CD133), and monocyte (CD14) surface markers and analyzed by flow cytometry. The nonobese diabetic/severe combined immunodeficiency murine model of hind-limb ischemia was used to analyze the potential of MNCs and culture-derived EPCs from UCB and BM to mediate neovasculogenesis. Histologic evaluation of the in vivo studies included capillary density as a measure of neovascularization. Surface CXCR4 expression was notably higher on UCB-derived EPCs (64.29%+/-7.41%) compared with BM (19.69%+/-5.49%; P=.021). Although the 2 sources of EPCs were comparable in expression of endothelial and monocyte markers, BM-derived EPCs contained higher proportions of cells expressing stromal cell markers (CD105 and CD73). Injection of UCB- or BM-derived EPCs resulted in significantly improved perfusion as measured by laser Doppler imaging at days 7 and 14 after femoral artery ligation in nonobese diabetic/severe combined immunodeficiency mice compared with controls (P<.05). Injection of uncultured MNCs from BM or UCB showed no significant difference from control mice (P=.119; P=.177). Tissue samples harvested from the lower calf muscle at day 28 demonstrated increased capillary densities in mice receiving BM- or UCB-derived EPCs. In conclusion, we found that UCB and BM-derived EPCs differ in CXCR4 expression and stromal surface markers but mediate equivalent neovasculogenesis in vivo as measured by Doppler flow and histologic analyses.
Abstract.The statement that a knot K has Property P means that (1) if C is a cube with a ^-knotted hole, and M3 is a simply connected 3-manifold obtained by sewing a solid torus onto C, then M3^S3, and (2) any piecewise linear homeomorphism of a cube with a Ä-knotted hole into S3 can be extended to a piecewise linear homeomorphism of S" onto S3. In this paper it is shown that many familiar classes of knots have Property P.1. Introduction. The 3-dimensional Poincaré conjecture is that a compact, connected, simply connected 3-manifold without boundary is topologically a 3-sphere S3. Despite efforts to prove the conjecture, it has withstood attack [4].Since no solution has been found, some believe that the conjecture is false, and that there is a counterexample.In attempting to construct a counterexample to the Poincaré conjecture, the first hurdle seems to be that of showing that the proposed example has a trivial fundamental group. This is difficult in that the information about the fundamental group usually appears as an exotic presentation of the group. Having somehow verified that this group is indeed trivial, one encounters the second hurdle of somehow showing that the example is topologically different from S3.It is known that every orientable 3-manifold may be obtained by removing a collection of disjoint solid tori from S3 and sewing them back differently [14], [22], [12]. In this paper we examine some of the possibilities for constructing a counterexample to the Poincaré conjecture by removing a single solid torus from S3 and sewing it back differently. Actually, we examine not only this process but one analogous to it which we call "attaching a pillbox to a cube with a knotted hole".We find it useful to consider two sorts of surgery which are inverses of each other. If Ma is a 3-manifold with boundary, A2 is an annulus on Bd M3 and P3 is a 3-cell such that M3 n P3 = A2 = BdP3 r\ Bd M3, then we say that M3 u P3 was obtained by sewing a pillbox P3 to M3 along A2. Suppose that H3 is a 3-cell in M3 such that H3 n Bd M3 is the union of two disjoint disks D\ and D\, and N3 = C\ (M3 -H3) is a 3-manifold with boundary. We say that N3 was obtained by boring a hole in M3.
ABSTRACT:The knowledge of chemical equilibria in {gas-polymer} systems plays an essential role as regards the safety of transport of petroleum products in polymer-made pipes. Thermophysical properties of thermoplastic semicrystalline polymers are key data for the development of several engineering applications. These applications require the investigation of the behavior of a polymer, in the solid state i.e., between glass-transition temperature T g and melting-transition temperature T m , submitted to the triple thermal, barometric, and chemical constraint. The chemical stress results from supercritical fluid sorption. The relatively high temperature and pressure, industrial operating conditions, require for laboratory investigations the use of sophisticated experimental instrumentation in which such extreme conditions can be reproduced. In this context, coupling gas solubility and swelling techniques (VW-PVT) on the one hand, calorimetry and PVT techniques (PCSC) on the other hand, over extended temperature and pressure ranges, provide a wide spectrum of thermophysical and thermomechanical properties like solubility and isobaric thermal expansion, in absence or in presence of solubilized gases.
Thennoplastic polymers are used in the field of petroleum where they may encounter very severe conditions. So we are induced to study the ageing behaviour and the effect of rapid decompressions in a gaseous environment. In the latter case our aim is to define the limits of use and to identify the parameters influencing degradations. Such damaging is essentially of two types : (1) local in the form of blisters and (2) under extreme conditions, more homogeneous microscopic damage of the "foaming" type. Damage of the blistering type may threaten the integrity of the polymer part, and the microscopic damage does not necessarily affect the mechanical behaviour, for example the impact strength.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.