Role of the interphase in the interfacial flow stability of multilayer coextrusion of compatible polymers

International audienceThe role of interphase triggered from interdiffusion process at neighboring layers on controlling the interfacial flow instability of multilayer coextrusion have been highlighted in this study using a compatible bilayer system. The polymers used are based on poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). The interdiffusion kinetics and the rheological and geometrical properties of the generated interphase have been modelized in real experimental conditions of the coextrusion process. Polymer chain orientation in coextrusion process was demonstrated to decelerate the interdiffusion coefficient. Furthermore, the interfacial shear stress was able to promote mixing and homogenizing process at the vicinity of the interface, which favors the development of the interphase. The convective mixing was evidenced by performing a pre-shear mode on PMMA/PVDF multilayer structures. The rheological and morphological properties of the interphase are related to a lot of parameters like contact time, processing temperature, interfacial shear stress and compatibility of the polymers, etc. Some key classical decisive parameters concerning the interfacial instability phenomena such as viscosity ratio, thickness ratio and elasticity ratio, etc. were highlighted during the coextrusion process. These key factors which are significant for the interfacial stability of coextrusion of incompatible multilayered polymers seem not that important for the studied compatible systems. The coextrusion of PMMA/PVDF compatible bilayers appears to be more stable. This would be attributable to the presence of the interphase generated from interdiffusion and favored from convective mixing. The interfacial flow instability of coextrusion can be reduced (or even eliminated) despite of the very high viscosity ratio and elasticity ratio of PMMA versus PVDF, especially at low temperatures. Overall, apart from the classical mechanical parameters, we have demonstrated that the creation of diffuse interphase that favors the homogenization should be taken into consideration as an important factor to remove the interfacial instability properties

Identification of a major QTL and candidate genes analysis for branch angle in rapeseed (Brassica napus L.) using QTL-seq and RNA-seq

IntroductionBranching angle is an essential trait in determining the planting density of rapeseed (Brassica napus L.) and hence the yield per unit area. However, the mechanism of branching angle formation in rapeseed is not well understood.MethodsIn this study, two rapeseed germplasm with extreme branching angles were used to construct an F2 segregating population; then bulked segregant analysis sequencing (BSA-seq) and quantitative trait loci (QTL) mapping were utilized to localize branching anglerelated loci and combined with transcriptome sequencing (RNA-seq) and quantitative real-time PCR (qPCR) for candidate gene miningResults and discussionA branching angle-associated quantitative trait loci (QTL) was mapped on chromosome C3 (C3: 1.54-2.65 Mb) by combining BSA-seq as well as traditional QTL mapping. A total of 54 genes had SNP/Indel variants within the QTL interval were identified. Further, RNA-seq of the two parents revealed that 12 of the 54 genes were differentially expressed between the two parents. Finally, we further validated the differentially expressed genes using qPCR and found that six of them presented consistent differential expression in all small branching angle samples and large branching angles, and thus were considered as candidate genes related to branching angles in rapeseed. Our results introduce new candidate genes for the regulation of branching angle formation in rapeseed, and provide an important reference for the subsequent exploration of its formation mechanism

Rhéologie interfaciale de matériaux multicouches modèles : Etudes fondamentales et application au procédé de la coextrusion

Les travaux de cette thèse concernent des études fondamentales liées à la rhéologie interfaciale des systèmes polymères multicouches. Les matériaux choisis sont à base de deux polymères compatibles,PVDF et PMMA de différentes masses molaires. Ces systèmes ont été étudiés sous sollicitations en cisaillement et en élongation suivant les deux régimes en viscoélasticité linéaire (VEL) et non-linéaire (VENL). Les études en VEL ont permis d’étudier la cinétique de développement de l’interphase. Quant aux études en VENL, elles ont permis d’étudier les propriétés intrinsèques de l’interphase simulant ainsi les conditions de mise en œuvre proches de celles des procédés usuels. On démontre ainsi que la rhéologie joue le rôle d’une sonde très fine pour explorer les propriétés aux interfaces des matériaux multicouches. Des modélisations ont été établies en se basant sur les mécanismes physiques mis en jeu. Dans un premier temps, le comportement rhéologique à l’état fondu des multicouches a été étudié par spectrométrie mécanique dynamique en VEL. Les cinétiques d'interdiffusion ainsi que le développement de l’interphase générée aux interfaces de bicouches symétriques et asymétriques ont été étudiés. Les résultats obtenus ont été analysés et modélisés en se basant sur les concepts de la dynamique moléculaire en l’occurrence le modèle de Doi et Edwards. De plus, un nouveau modèle rhéologique a été développé. Il a permis de quantifier les coefficients d'interdiffusion. Les coefficients de friction des chaines et les propriétés rhéologiques de l’interphase ont été modélisés à leur tour. Les résultats obtenus corroborent ceux de la littérature, obtenus par des méthodes spectroscopiques sophistiquées. Le modèle a permis de quantifier les grandeurs viscoélastiques et l’épaisseur de l’interphase. Dans un second temps, des expérimentations en VENL ont été réalisées. Un modèle original a été également proposé pour décrire le comportement relatif à la relaxation des multicouches et de l'interphase. De plus, la sensibilité de la densité d’enchevêtrement a été étudiée pendant et après sollicitations. On démontre que sa présence retarde l'écoulement interfacial surtout sous hautes déformations et vitesses de déformation. En outre, les études des structures multicouches sous sollicitation élongationnelle ont montrées que les propriétés dépendent du rapport de viscosité des couches et les propriétés de l’interphase diffuse. Les travaux de cette thèse mettent en lumière la compétition entre l’effet négatif de l'orientation des chaînes et l'effet favorable de l'écoulement sur les cinétiques de la diffusion. Ensuite, des cartes de stabilités des écoulements stratifiés ont été établies.. La présence de l'interphase diffuse a contribué à une élimination des instabilités. On montre ainsi qu’outre la cinématique de l’écoulement en cisaillement et en élongation, les propriétés de l’interphase ont un rôle important dans la stabilité des écoulements stratifiés en coextrusion.Fundamental studies have been devoted in this work to probe and modelize the interfacial phenomena at multilayered polymer systems based on two model compatible polymers of PVDF and PMMA with varying molar masses. Linear and nonlinear rheology have been demonstrated to be sensitive to the presence of diffuse interphase triggered from interdiffusion at polymer/polymer interface. Firstly, the interdiffusion kinetics as well as the development of the interphase decoupled to flow as generated at a symmetrical (self diffusion) and an asymmetrical (mutual diffusion) bilayer have been investigated using small-amplitude oscillatory shear measurements. Results were analyzed according to Doi-Edwards theory (tube model) and the effects of annealing factors as well as structural properties on the diffusion kinetics have been studied. The PMMA/PVDF mixtures have been examined to be a couple of weak thermorheological complexity, owning close monomeric friction coefficients of each species in the present experimental conditions. Based on this physics, a new rheological model was developed to quantify the interdiffusion coefficients by taking into account the component dynamics in mixed state and the concept of interfacial rheology. Rheological and geometrical properties of the interphase have been able to be quantified through this model, as validated by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX) and transmission electron microscopy (TEM). Secondly, experiments of step strain, startup in simple shear and in uni-axial extension have been carried out on the PMMA/PVDF multilayer structures. An original model was proposed to fit the stress relaxation behavior of multilayer structures and to estimate the relaxation behavior of the interphase. Lack of entanglement at the interface and weak entanglement intensity at the diffuse interphase make them to be subsequently readily to suffer from interfacial yielding even interfacial failure during and after continuous large deformations. Interphase delays the interfacial yielding to a larger external deformation or a higher deformation rate. Besides, elongational properties of the multilayer structures have been shown to be a function of composition as controlled by layer number(interfacial area) and interphase properties (rheology related to entanglement intensity). Finally, the diffuse interphase development coupled to flow in practical coextrusion process has been considered. The compromising result between negative effect of chain orientation and favorable effect of flow on diffusion kinetics gives rise to a broadening interphase after coextrusion. Presence of the diffuse interphase was demonstrated to significantly weaken (or even eliminate) the viscous and elastic instabilities despite of the high rheological contrast. Hence, this work gives guidelines on the key role of the interphase plays in structure-property-processing relationships

Understanding of Transient Rheology in Step Shear and Its Implication To Explore Nonlinear Relaxation Dynamics of Interphase in Compatible Polymer Multi-microlayered Systems

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Rhéologie interfaciale de matériaux multicouches modèles.

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A state of the art of interfacial rheology and coextrusion process.

International audienceA state of the art of interfacial rheology and coextrusion process

Role of the interphase in the interfacial flow stability of multilayer coextrusion of compatible polymers

International audienceThe role of interphase triggered from interdiffusion process at neighboring layers on controlling the interfacial flow instability of multilayer coextrusion have been highlighted in this study using a compatible bilayer system. The polymers used are based on poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). The interdiffusion kinetics and the rheological and geometrical properties of the generated interphase have been modelized in real experimental conditions of the coextrusion process. Polymer chain orientation in coextrusion process was demonstrated to decelerate the interdiffusion coefficient. Furthermore, the interfacial shear stress was able to promote mixing and homogenizing process at the vicinity of the interface, which favors the development of the interphase. The convective mixing was evidenced by performing a pre-shear mode on PMMA/PVDF multilayer structures. The rheological and morphological properties of the interphase are related to a lot of parameters like contact time, processing temperature, interfacial shear stress and compatibility of the polymers, etc. Some key classical decisive parameters concerning the interfacial instability phenomena such as viscosity ratio, thickness ratio and elasticity ratio, etc. were highlighted during the coextrusion process. These key factors which are significant for the interfacial stability of coextrusion of incompatible multilayered polymers seem not that important for the studied compatible systems. The coextrusion of PMMA/PVDF compatible bilayers appears to be more stable. This would be attributable to the presence of the interphase generated from interdiffusion and favored from convective mixing. The interfacial flow instability of coextrusion can be reduced (or even eliminated) despite of the very high viscosity ratio and elasticity ratio of PMMA versus PVDF, especially at low temperatures. Overall, apart from the classical mechanical parameters, we have demonstrated that the creation of diffuse interphase that favors the homogenization should be taken into consideration as an important factor to remove the interfacial instability properties

Fundamental Studies of Interfacial Rheology at Multilayered Model Polymers for Coextrusion Process

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Role of the interphase in the interfacial flow stability in coextrusion of compatible multilayered polymers

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