Simulation directe 2D et 3D de la dispersion d'agglomérats sous cisaillement dans une matrice polymère

http://hdl.handle.net/2042/16467International audienceNous avons développé une méthode de simulation directe de la dispersion de charges sphériques dans une matrice polymère soumise à un cisaillement. L'agglomérat est immergé dans un fluide newtonien et incompressible. Il est considéré comme un assemblage de sphères liées entre elles par une énergie de cohésion, modélisée par une viscosité de cohésion. Les paramètres de ce modèle sont la contrainte hydrodynamique et la longueur caractéristique de la zone d'influence des sphères. Ce modèle simple permet une première approche du phénomène de dispersion dans un écoulement de cisaillement. Les tendances observées lors des simulations menées en 2D et 3D montrent qu'une augmentation du taux de cisaillement entraîne une érosion plus rapide de la charge = In this study, we present a direct numerical simulation of shear induced dispersion of spherical filler in polymer matrix. The agglomerate, immersed in an incompressible Newtonian fluid, is modelled by spherical particles linked together by cohesive energy. The numerical models computed both in 2D and 3D allow obtaining qualitative results of the agglomerate behaviour. Those results are in agreement with the experimentals in the literature

Comportement rhéologique et conductivité électrique de polyamides chargés de noir de carbone

National audienceDepuis plus de vingt ans, des “Polymer Processing Aids” (PPA) fluorés sont utilisés industriellement pour éliminer les défauts de peau de requin en extrusion. L'objectif de ce travail est de comprendre les mécanismes d'action de ces PPA. L'influence des PPA sur la pression en filière et sur l'aspect des extrudats est d'abord étudiée, montrant simultanément une chute de pression et une élimination progressive du défaut. La formation d'un dépôt en filière est ensuite analysée par microscopie électronique à balayage (MEB). On constate l'existence d'un dépôt hétérogène de fluoropolymère, sous forme de lignes parallèles à l'écoulement, qui apparaît en deux temps. Enfin, l'évolution des profils de vitesse permet de corréler la chute de pression en filière à l'apparition de glissement à la paroi, ainsi que le glissement obtenu à la densité de dépôt

Isothermal crystallization kinetic modeling of poly(etherketoneketone) (PEKK) copolymer

Isothermal melt and cold crystallizations of a poly(etherketoneketone) (PEKK) copolymer prepared from diphenyl ether (DPE), terephthalic acid (T) and isophthalic acid (I) with a T/I ratio of 60/40 have been investigated by differential scanning calorimetry, wide-angle X-ray scattering and polarized optical microscopy. For the first time, the two-stage overall crystallization kinetics of PEKK taking into account effects of nucleation and crystal growth has been identified by using a modified Hillier type model. The primary crystallization stage is found to be an instantaneous two dimensional nucleation growth with an Avrami exponent of 2 whereas the secondary stage is found to be an instantaneous one dimensional nucleation growth with an Avrami exponent of 1. The evolution of the crystallization kinetic constants for two-stage crystallizations has been modeled according to the Hoffman and Lauritzen growth theory. Due to low crystallization kinetics, a crystallization induction time has been added to obtain a good fit with experimental data. Based on this modeling, Time-Temperature-Transformation (TTT) diagrams of the relative volume crystallinity have been established for the overall crystallization mechanism and also for the separated primary and secondary crystallization mechanisms providing an original crystallization mapping of the material

A more reliable DSC-based methodology to study crystallization kinetics: Application to poly(ether ketone ketone) (PEKK) copolymers

To quantify the isothermal crystallization kinetics of poly(ether ketone ketone) (PEKK), the integration of the crystallization peak measured using differential scanning calorimetry is rendered difficult due to the thermal transient effects at the start of enthalpy recording. The different attempts to extrapolate this peak beginning often lead to false values of the Avrami exponent. A new crystallization kinetic assessment method is established here based on the derivative of the Hillier crystallization kinetic model. This method consists of directly fitting the transformation rate to the heat flow of the experimental crystallization, thus avoiding the extrapolation of the crystallization peak beginning. This method is successfully applied to two different PEKK grades with different crystallization kinetics. The identified crystallization parameters are modelled as a function of the crystallization temperature, and based on these modeling results, time-temperature-transformation diagrams of crystallinity were built to provide a useful tool for PEKK processing

Influence of thermal history on the mechanical properties of poly(ether ketone ketone) copolymers

Since poly(ether ketone ketone) (PEKK) is a good candidate as a matrix for composite structural parts, the mechanical properties of PEKK copolymers prepared from diphenyl ether, terephthalic acid (T), and isophthalic acid (I) with different T/I ratios were assessed at room temperature and above their glass transition temperature depending on the thermal history during processing. The influence of cooling conditions and macromolecular modifications at high exposure temperatures was investigated. Results show that modulus and yield properties for a given testing temperature follow a master curve driven mainly by crystallinity regardless of the PEKK copolymers. By modifying PEKK during exposures at 400°C, which leads to branching mechanisms before crystallization, it is shown that modified PEKKs follow the master curve, thus confirming the predominant role of crystallinity in small deformation properties. However, for some morphologies, depending on the crystallization conditions such as cold or melt crystallization, a slight deviation is observed from the global master curve.The authors wish to thank the Arkema Company for providing the PEKK materials and the French National Research Agency (ANR IMPEKKABLE project

The grapevine (Vitis vinifera) LysM receptor kinases VvLYK1-1 and VvLYK1-2 mediate chitooligosaccharide-triggered immunity

Chitin, a major component of fungal cell walls, is a well-known pathogen-associated molecular pattern (PAMP) that triggers defense responses in several mammal and plant species. Here, we show that two chitooligosaccharides, chitin and chitosan, act as PAMPs in grapevine (Vitis vinifera) as they elicit immune signalling events, defense gene expression and resistance against fungal diseases. To identify their cognate receptors, the grapevine family of LysM receptor kinases (LysM-RKs) was annotated and their gene expression profiles were characterized. Phylogenetic analysis clearly distinguished three V. vinifera LysM-RKs (VvLYKs) located in the same clade as the Arabidopsis CHITIN ELICITOR RECEPTOR KINASE1 (AtCERK1), which mediates chitin-induced immune responses. The Arabidopsis mutant Atcerk1, impaired in chitin perception, was transformed with these three putative orthologous genes encoding VvLYK1-1, -2, or -3 to determine if they would complement the loss of AtCERK1 function. Our results provide evidence that VvLYK1-1 and VvLYK1-2, but not VvLYK1-3, functionally complement the Atcerk1 mutant by restoring chitooligosaccharide-induced MAPK activation and immune gene expression. Moreover, expression of VvLYK1-1 in Atcerk1 restored penetration resistance to the non-adapted grapevine powdery mildew (Erysiphe necator). On the whole, our results indicate that the grapevine VvLYK1-1 and VvLYK1-2 participate in chitin- and chitosan-triggered immunity and that VvLYK1-1 plays an important role in basal resistance against E. necator

The xyloglucans : are they new elicitors of <em>Arabidopsis thaliana</em> immunity ?

National audienceDamaged-Associated Molecular Patterns (DAMPs) are endogenous molecules released from the plant cell wall after wounding by pathogens. DAMPs are recognized by Pattern- Recognition Receptors (PRRs) that play a key role in plant immunity by mediating defense responses. The plant cell wall-derived oligogalacturonides (OG) are well characterized DAMPs that elicit plant immune responses such as MAPK activation, [Ca2+]cyt variations, H2O2 production, defense-related gene expression and enhanced resistance against Botrytis cinerea. Our study focused on a new polysaccharide component of the plant cell wall called xyloglucans (Xh) and compared the immune events triggered by OG and Xh in Arabidopsis thaliana. Our results indicated that Xh can be considered as new elicitors as they induced MAPK activation, the expression of defense-related genes, callose deposition and triggered immunity against Botrytis cinerea. By using a genetic approach, our data indicated that the Xh-triggered immunity against B. cinerea requires the phytoalexin and jasmonic aciddependent pathways

Are the xyloglucans new elicitors of plant immunity ?

National audienc

Comportement des matrices PEKK en oxydation

International audienceThe IMPEKKABLE project deals with the use of organic matrix composite materials such as thermoplastic matrix reinforced with continuous carbon fibers for “high temperature” parts. More precisely, it refers to the utilization of a new generation of C/PEKK composite for structural applications around 180°C above the glass transition of the thermoplastic matrix. The innovative and ambitious aspect of this study remains in the development of models and simulation tools aiming at predicting the thermo-mechanical behavior of these composites for long-term solicitations under these temperatures levels. Considering such conditions, creep recovering and recrystallization phenomenon as well as chemical evolutions are expected.Le projet IMPEKKABLE s’inscrit dans la thématique « stimuler le renouveau industriel », dans l’axe « matériaux et procédés » et concerne l’élargissement des domaines d’utilisation de matériaux avancés, tels que les composites à fibres continues de carbone et à matrice thermoplastique. Il adhère à l’objectif des constructeurs aéronautiques d’augmenter le champ d’application des composites à matrice organique à des pièces dites « chaudes » et porte plus particulièrement sur l’utilisation d’une nouvelle génération de composites C/PEKK pour des applications entre 150°C et 200°C. Le caractère novateur de l’étude réside dans la sollicitation de telles structures composites thermoplastiques au-delà de sa température de transition vitreuse en jouant sur les propriétés cristallines de la matrice pour assurer un comportement mécanique adéquat sur de longues durées en condition de service (sous contrainte, en température, en ambiance oxydante)

The xyloglucans : are they new elicitors of Arabidopsis thaliana immunity ?

Damaged-Associated Molecular Patterns (DAMPs) are endogenous molecules released from the plant cell wall after wounding by pathogens. DAMPs are recognized by Pattern- Recognition Receptors (PRRs) that play a key role in plant immunity by mediating defense responses. The plant cell wall-derived oligogalacturonides (OG) are well characterized DAMPs that elicit plant immune responses such as MAPK activation, [Ca2+]cyt variations, H2O2 production, defense-related gene expression and enhanced resistance against Botrytis cinerea. Our study focused on a new polysaccharide component of the plant cell wall called xyloglucans (Xh) and compared the immune events triggered by OG and Xh in Arabidopsis thaliana. Our results indicated that Xh can be considered as new elicitors as they induced MAPK activation, the expression of defense-related genes, callose deposition and triggered immunity against Botrytis cinerea. By using a genetic approach, our data indicated that the Xh-triggered immunity against B. cinerea requires the phytoalexin and jasmonic aciddependent pathways