Le glissement à la paroi d'un mélange de caoutchouc naturel

National audienceLa condition de non-glissement à la paroi est l'hypothèse de départ de nombreux calculs d'écoulements dans les procédés de mise en forme. Si cette condition n'est pas remplie, il en découle des erreurs dans la détermination des grandeurs rhéologiques. Le phénomène de glissement à la paroi est fréquemment rencontré pour les mélanges d'élastomères, pour lesquels ce glissement est souvent assimilé à un glissement apparent, résultant de la formation d'une fine couche de fluide de faible viscosité à la paroi. Dans cette étude, la caractérisation rhéologique d'un mélange à base de caoutchouc naturel est effectuée sur un rhéomètre capillaire à pré-cisaillement et la méthode de dépouillement adoptée est la méthode de Mooney. Cette méthode est toutefois prise en défaut aux fortes contraintes de cisaillement à la paroi. Une interprétation est proposée pour expliquer ce résultat

Etude rhéocinétique d'un système polyuréthane

International audienceL'étude cinétique et rhéocinétique d'un système polyuréthane est réalisée pour déterminer les modèles théoriques les mieux adaptés, l'objectif final étant la simulation du remplissage d'un moule par injection. Le paramètre le plus important est la viscosité et son évolution avec le temps et la température. Pour un système réactif, l'évolution de la réaction entraîne la formation de liaisons covalentes et par conséquent un dégagement de chaleur. Une étude de la cinétique de réaction s'avère donc nécessaire pour prédire les profils de température à l'intérieur du moule. Les méthodes isoconversionnelles sont appliquées pour mieux comprendre le mécanisme mis en jeu. Elles permettent de mettre en évidence une dépendance de l'énergie d'activation avec le taux d'avancement. Trois réactions distinctes ont lieu et ne peuvent être prises en compte par un modèle global. Il est donc nécessaire d'utiliser un modèle multi - réactions. L'évolution de la viscosité en condition isotherme est reliée au taux d'avancement de la réaction à l'aide d'un modèle phénoménologique. Le temps de gel est déterminé par le croisement de la tangente de l'angle de perte en fonction du temps à différentes fréquences = The crosslinking kinetics and rheological behavior of a polyurethane system during curing were investigated for mold filling modeling. The important parameters required in modeling with reactive systems are the viscosity and its evolution with time. Hence, cure kinetics study is necessary to quantify the extent of chemical reaction and to predict the temperature distribution inside the mold. In this study, isoconversional method is applied to understand the reaction complexity. The activation energy depends on the extent of conversion. It can be shown that three parallel reactions occur during the evolution of global reaction in nonisothermal conditions. A simple multi-step model can therefore involve the three parallel independent reactions. Viscosity was measured as a function of time and was found independent of shear rate. Isothermal viscosity rise was related to extent of reaction by a phenomenological model. The gelation time is determinated by the δtan crossover at different frequencies

Blockade of IL-33R/ST2 Signaling Attenuates Toxoplasma gondii Ileitis Depending on IL-22 Expression

Oral T. gondii infection (30 cysts of 76K strain) induces acute lethal ileitis in sensitive C57BL/6 (B6) mice with increased expression of IL-33 and its receptor ST2 in the ileum. Here we show that IL-33 is involved in ileitis, since absence of IL-33R/ST2 attenuated neutrophilic inflammation and Th1 cytokines upon T. gondii infection with enhanced survival. Blockade of ST2 by neutralizing ST2 antibody in B6 mice conferred partial protection, while rmIL-33 aggravated ileitis. Since IL-22 expression further increased in absence of ST2, we blocked IL-22 by neutralizing antibody, which abrogated protection from acute ileitis in ST2 deficient mice. In conclusion, severe lethal ileitis induced by oral T. gondii infection is attenuated by blockade of ST2 signaling and may be mediated in part by endogenous IL-22

Injection de systèmes réactifs : détermination de lois cinétiques et rhéologiques et modélisation

The behaviour of two reactive systems, a natural rubber's formulation and a thermoset polyurethane (PU), is studied in the aim of modelisation. Some new methodologies of characterization are suggested to perform the quality of the measures. Various techniques are used in order to characterise the reaction kinetic of PU as the differential scanning calorimetry (DSC) or the titration. Isoconversionnal analysis shows three kinetic reactions which give a 3D network. Kinetic model used here is the addition of three Piloyan models. Techniques used to study natural rubber kinetic are rheometry, DSC and swelling. The simple model called Isayev model gives good results even if it doesn't take into account the reversion. Coran Ding and Leonov model has a lot of parameters but gives very good results. Then rheology is studied. For PU, kinetic and rheology are coupled. Hence the study is called rheokinetic study. We used Castro and Macosko model. Natural rubber is unreactive during the mold filling. Therefore kinetic is decoupled from rheology which is modelised by a Carreau Yasuda model. Wall slip is characterised by the Mooney method and modelised by using a Norton Hoff law (wall slip) and a Cross model (shearing). Thermomecanical sensibility is treated by using an energetic slip factor which depends on specific energy and matter temperature. Third part gives a confrontation between injection trials and calculated results obtained from a filling simulation software REM3D. PU injection used a transparent mold. Various techniques as visual techniques, titration or temperature measure, are used to characterize the process. The kinetic results are in agreement with the simulation. We use a spiral mold for natural rubber. Mold pressures are in agreement with simulation but some differences are noted for the nozzle pressure which is attributed to the elongational effects not taken into account in the viscous model.Le comportement de deux matériaux réactifs, une formulation élastomère de caoutchouc naturel et un système thermodurcissable polyuréthane (PU), est étudié pour être modélisé. De nombreuses méthodologies sont mises au point dans ce travail pour améliorer les mesures. La cinétique réactionnelle du PU est suivie par calorimétrie différentielle (DSC) et par titrage chimique. L'analyse isoconversionnelle met en évidence trois réactions chimiques formant un réseau tridimensionnel. Le modèle cinétique met en série trois modèles de Piloyan. La cinétique du caoutchouc naturel est suivie par rhéomètrie, par DSC et par gonflement. Le modèle d'Isayev, très simple, donne des résultats satisfaisants mais ignore la réversion. Le modèle de Coran Ding et Leonov, ayant de nombreux paramètres, donne de très bons résultats. La rhéologie est ensuite étudiée. Pour le PU, le couplage cinétique-rhéologie est nécessaire et conduit à une étude rhéocinétique. Le modèle de Castro et Macosko est utilisé. Le caoutchouc naturel, non réactif durant le remplissage, permet de découpler cinétique et rhéologie. Le modèle de Carreau Yasuda est alors utilisé. Le glissement à la paroi est étudié avec la méthode de Mooney et modélisé par un couplage entre une loi de Norton Hoff (glissement) et le modèle de Cross (cisaillement). La sensibilité au traitement thermomécanique est prise en compte par un facteur de glissement énergétique fonction de l'énergie spécifique et de la température matière. La troisième partie valide les modèles et leur implémentation dans un logiciel de simulation de remplissage REM3D. L'injection du PU est réalisée dans un moule transparent. Basés sur la visualisation, le titrage et le suivi de température, les résultats sont en accord avec la simulation au niveau cinétique. Pour le caoutchouc, un moule spirale est utilisé. Dans le moule, les pressions mesurées et calculées sont proches. Un écart apparaît dans la buse et est attribué aux effets élongationnels non pris en compte dans le modèle visqueux utilisé

Relationships between mastication conditions and rheological behavior of a natural rubber

International audienceThe mastication of natural rubber results in the shortening of the long molecular chains, which affects the viscosity of the material. Mechanical and thermo-oxidative breakdowns are the two major factors that interfere during mastication and processing of natural rubber. In an attempt to characterize the viscous behavior of a such product during processing, rheological properties of unvulcanized rubber are studied with a capillary rheometer and a parallel plate rheometer, in small amplitude oscillatory shear. An investigation is carried out with an internal mixer to determine the effect of mastication and temperature on the rheological properties. The influence of thermomechanical effect is quantified as a function of the specific energy and mastication temperature. Depending on mastication conditions, the variation of viscosity may be important and its decrease is quantified by integrating the specific energy and the mastication temperature in a Carreau-Yasuda model

Curing kinetics and chemorheological analysis of polyurethane formation

International audienceThe cross-linking kinetics and the rheological behavior of a polyurethane system during curing are investigated by DSC and small amplitude oscillatory shear rheometry. In this study, isoconversional methods are applied to understand the reaction complexity. The activation energy depends on the extent of conversion. It can be shown that three parallel reactions occur during the evolution of the global reaction in non-isothermal conditions. An original multi-step model can involve these three parallel independent reactions. Dynamic viscosity is measured as a function of time and is found independent of shear rate. Isothermal viscosity rise is related to reaction extent by a phenomenological model. The gelation time is deter-mined by the tanδ crossover at different frequencie

Protein delivery by porous cationic maltodextrin-based nanoparticles into nasal mucosal cells: Comparison with cationic or anionic nanoparticles

International audienceDifferent types of biodegradable nanoparticles (NPs) have been studied as delivery systems for proteins into nasal mucosal cells, especially for vaccine applications. Such a nanocarrier must have the ability to be loaded with proteins and to transport this payload into mucosal cells. However, comparative data on nanoparticles' capacity for protein loading, efficiency of subsequent endocytosis and the quantity of nanocarriers used are either lacking or contradictory, making comparisons and the choice of a best candidate difficult. Here we compared 5 types of nanoparticles with different surface charge (anionic or cationic) and various inner compositions as potential vectors: the NPL (cationic maltodextrin NP with an anionic lipid core), cationic and anionic PLGA (Poly Lactic co-Glycolic Acid) NP, and cationic and anionic liposomes. We first quantified the protein association efficiency and NPL associated the largest amount of ovalbumin, used as a model protein. In vitro, the delivery of fluorescently-labeled ovalbumin into mucosal cells (airway epithelial cells, dendritic cells and macrophages) was assessed by flow cytometry and revealed that the NPL delivered protein to the greatest extent in all 3 different cell lines. Taken together, these data underlined the potential of the porous and cationic maltodextrin-based NPL as efficient protein delivery systems to mucosal cells

New ethical diagnostic tool for immunological monitoring of toxoplasmosis in sheep

National audienceToxoplasmosis is a cosmopolitan infectious disease caused Toxoplasma gondii. Congenital toxoplasmosis is a major public and veterinary health problem. Approximately 3000 pregnant women become infected each year in France with, in 10% of cases, transplacental transmission of the parasite to the foetus. At the same time, it is one of the major causes of abortions in small ruminants in French farms and has also been responsible for the mortality of many animal species in zoos for decades. From a veterinary point of view, the seroprevalence of toxoplasmosis is important and often underestimated in France, as in Europe, in ruminant farms. In order to propose a non-invasive screening test for toxoplasmosis, we have developed a swab and established the proof of concept in ewes, the natural host of toxoplasma. The sampling consisted of a direct collection of saliva from 51 experimentally infected Prealpes ewes by simple mechanical chewing of an absorbent cotton for one minute to measure the salivary IgG response and to correlate it with the serum IgG response. The swab with saliva is placed in a collector inside a centrifuge tube. The tubes are centrifuged and then collect of saliva in the bottom of the conical tube. Seroconversion of the ewes was monitored at seven days and two months post-infection. A significant correlation was observed between serum and salivary IgG kinetics (R = 0.8). Moreover, the salivary response showed a very high specificity. We have developed a simple non-invasive sampling tool that reduces the stress of the ewe during sampling. Salivary monitoring is as specific and sensitive as serological monitoring in the context of toxoplasmosis, while preserving animal welfare. This refinement tool will allow farmers to have a better sanitary follow-up for toxoplasmosis in their sheep flock. This toxoplasmosis sanitary follow-up will have an impact on the evaluation of the transmission risks for the human species and thus an improvement of the effective prevention of the disease in pregnant women

Direct antiviral properties of TLR ligands against HBV replication in immune-competent hepatocytes

Abstract Current therapies for chronic hepatitis B virus (HBV) infections are effective at decreasing the viral load in serum, but do not lead to viral eradication. Recent studies highlighted the therapeutic or “adjuvant” potential of immune-modulators. Our aim was to explore the direct anti-HBV effect of Toll-Like-Receptors (TLR) agonists in hepatocytes. HBV-infected primary human hepatocytes (PHH) or differentiated HepaRG cells (dHepaRG) were treated with various TLR agonists. Amongst all TLR ligands tested, Pam3CSK4 (TLR1/2-ligand) and poly(I:C)-(HMW) (TLR3/MDA5-ligand) were the best at reducing all HBV parameters. No or little viral rebound was observed after treatment arrest, implying a long-lasting effect on cccDNA. We also tested Riboxxol that features improved TLR3 specificity compared to poly(I:C)-(HMW). This agonist demonstrated a potent antiviral effect in HBV-infected PHH. Whereas, poly(I:C)-(HMW) and Pam3CSK4 mainly induced the expression of classical genes from the interferon or NF-κB pathway respectively, Riboxxol had a mixed phenotype. Moreover, TLR2 and TLR3 ligands can activate hepatocytes and immune cells, as demonstrated by antiviral cytokines produced by stimulated hepatocytes and peripheral blood mononuclear cells. In conclusion, our data highlight the potential of innate immunity activation in the direct control of HBV replication in hepatocytes, and support the development of TLR-based antiviral strategies