No / The effect of side stream channel height on flow stability in 30 degrees coextrusion geometries was investigated. The studies were conducted on a Dow LD150R low density polyethylene melt using a single extruder to feed a flow cell in which the delivered melt stream was split before, and rejoined after, a divider plate in a slit die. Wave type interfacial instability occurred at critical stream thickness ratios. Reducing the side stream channel height broadened the layer ratio operating range before the onset of interfacial instability, therefore improving process stability. Stress fields were quantified and used to validate principal stress differences of numerically modelled flow. Stress field features promoting interfacial instability in each of the die geometries were identified. Interfacial instability resulted when the stress gradient across the interface was asymmetric and accompanied by a non-monotonic decay in the stress along the interface from its inception.

No / This report covers experimental studies and numerical modelling of interfacial instability in the bi-layer coextrusion flow of two low-density polyethylene melts. Melt streams are converged at an angle of 30° to a common die land. Melt stream confluence was observed in two coextrusion die arrangements. In one die design, which we term ‘bifurcated’ the melt stream is split by a divider plate in the die after being delivered from a single extruder. In the other design melt streams are delivered to a die from two separate extruders. In each die design melt flow in the confluent region and die land to the die exit was observed through side windows of a visualization cell. Velocity ratios of the two melt streams were varied and layer thickness ratios producing wave type interfacial instability determined for each melt for a variety of flow conditions. Stress and velocity fields in the coextrusion arrangements were quantified using stress birefringence and particle image velocimetry techniques. Wave type interfacial instability occurred in the processing of the low-density polyethylene melts at specific, repeatable, stream layer ratios. The birefringent pattern in the confluence region and the beginning of the die land appeared stable even when the extrudate exhibited instability. However, disturbances were observed in the flow field near the exit of the die land. The study demonstrates conclusively it is possible for interfacial instability to occur in the coextrusion of the same melt. The study also shows that wave type interfacial instability in the coextrusion process is not caused by process perturbations of extruder screw rotation. Increased melt elasticity appears to promote this type of instability. A modified Leonov model and Flow 2000™ software was used to simulate the LDPE melt flows through these geometries. There was reasonable agreement between modelled at experimentally determined stress fields. Modelling however provided far more detailed stress gradient information than could be resolved from the optical techniques. A total normal stress difference (TNSD) sign criterion was used to predict the critical layer ratio for the onset of the interfacial instability in one die arrangement and good agreement between theory and experiment has been obtained.

Les nanostructures 1D d'AlN promettent des nouvelles applications dans la technologie des semi-conducteurs, des antennes optiques et des résonateurs nanomécaniques. Elles peuvent également aboutir à l'évolution de nouveaux composants d'instrumentation. Cette étude explore deux voies originales pour élaborer des nanofilaments d'AlN en procédant à la mise en forme par électrofilage couplée à un procédé d'élaboration de céramique. Deux stratégies d'élaboration peuvent être considérées selon que le système initial contient de l'oxygène ou non. La maîtrise des conditions de mise en forme (paramètres d'électrofilage) ainsi que l'optimisation des solutions utilisées (teneur en polymère et en précurseur) et des traitements thermiques, ont permis d'obtenir des filaments de taille submicronique (entre 100 nm et 400 nm), ainsi que des tubes d'une grande pureté chimique et stables sous air jusqu'à 550°C. Il est démontré que la qualité des nano-objets d'AlN dépend de leur méthode de fabrication. L'étude basée sur deux méthodes de fabrication, l'une sous air et l'autre sous atmosphère contrôlée, permet de présenter les avantages et les inconvénients de chacune de ces deux approches, la première étant dite « low-cost » par rapport à la seconde / One-dimensional (1D) AlN nanostructures promise the achievement of new applications in semiconductor technology, optical antennas and nanomechanical resonators. They can also lead to the development of new components for instrumentation. This study explores two original methods to elaborate AlN nanofilaments performing shaping by electrospinning, coupled to a process for producing ceramic. Two strategies can be developed depending on whether the initial system contains oxygen or not. The control of the conditions of shaping (electrospinning parameters) and the optimization of the used solutions (polymer content and precursor) and heat treatments, allowed the obtainment of submicron sized filaments (between 100 nm and 400 nm), as well as tubes with a high chemical purity, and stable in air up to 550 °C. It is demonstrated that the quality of the AlN nano-objects depends on their method of elaboration. The study of the two used methods, one in air and the other under controlled atmosphere, can show the advantages and disadvantages of each of these two approaches, the first being "low-cost" comparing to the second

La coextrusion est un process industriel de fabrication de films minces composés de plusieurs couches de polymères (PP/PP-g-Anhydride Maléique (PP-g-AM)/EVOH/PP-g-AM/PP) associant de propriétés intéressantes au matériau final. Lors de ce procédé, les films obtenus ne sont pas transparents mais présentent des granités. En effet, le liant ajouté contient des chaînes de PP-g-AM s’interpénètrent dans une couche du matériau et les têtes anhydride maléique réagissent avec l’autre couche créant in-situ des copolymères PP-g-AM-g-EVOH à l’interface.Mon premier travail était de mettre en évidence le rôle primordial des instabilités interfaciales sur la diminution de la transparence des films. Ceci a été rendu possible grâce à une observation des coupes transversales des films. Nous avons vu que plus la variation de l’épaisseur interne est grande, plus la qualité optique du film est mauvaise. Cette amplitude de variation est exacerbée dans le sens de la coextrusion. La cristallisation du PP observable au microscope optique par des sphérolites n’intervient qu’au second ordre.Il est connu que l’interface est stabilisée par la tension interfaciale, c’est pourquoi, dans un second temps, l’étude de l’interface a été menée La tension interfaciale a été mesurée par la méthode de relaxation de la goutte déformée. À une température supérieure à la température de fusion des deux polymères, l’EVOH est dispersé dans une matrice de liant PP-g-AM. Les gouttelettes d’EVOH sont soumises à un faible cisaillement. À l’arrêt de celui-ci, les gouttelettes relaxent pour retrouver leur forme d’équilibre, la forme sphérique. Le temps de relaxation est proportionnel à la tension interfaciale et au rapport des viscosités des polymères. Une des conséquences majeures de ces instabilités est la présence de défauts optiques rendant le film opaque, gênant pour les applications.Enfin, pour comprendre les résultats de tension interfaciale, il a fallu construire un protocole de dosage de copolymères à l’interface. Ce dosage absent de la littérature, a été le plus gros travail de ma thèse. Un protocole de dosage de copolymère à l’interface basé sur l’infrarouge est aujourd’hui validé et utilisé en recherche industrielle (ARKEMA, Serquigny). / Coextrusion is an industrial process which creates thin films of polymers (in this study : PP/PP-g-Anhydride Maleic (PP-g-AM)/EVOH/PP-g-AM/PP). These polymers give interesting properties to the final film. But some of these films have bad optical qualities with granity inside the film. Indeed, as the polymers are incompatibles, other polymers (PP-g-AM) which have adhesion role have to be added. These chains go into the interface to react with EVOH and create in situ way, copolymers PP-g-AM-EVOH.My first work was to identify the role of interfacial instabilities in the optical properties of the film. It was realised thanks to observations by optical microscope. Indeed, we have proove that there is a link between the variation of the intern thickness amplitude and the optical quality and this amplitude of variation grows in coextrusion direction. Spherulites in the bulk of each film influence less than the amplitude variation of intern thickness.This amplitude should depend on the interfacial tension, that is way, in the second part, we have measured the interfacial tension of different materials by drop deformed relaxtation method. At a temperature higher than the melted temperature of the polymers, a drop of EVOH is deformed in PP-g-AM matrix. A shear stress is applied to deformed the drop. When the shear stress is stopped, the drop from regular ellisoidal shape relaxes into its equilibrium shape, a spherical shape. The relaxation time is proportional to interfacial tension and viscosity ratio.This interfacial tension depends on the density of copolymers at the interface. So my final part was to caracterize copolymers. To titrate and study their reactivity, I had to set up a experiment which was not present in literature. This method was done by infrared and is now used in our industrial collaborator (ARKEMA, Serquigny).

Les travaux de cette thèse concernent des études fondamentales liées à la rhéologie et dynamique des chaines aux interfaces/interphases dans des structures polymères multi- micro et nano-couches obtenues par le procédé de coextrusion. Des couples de matériaux modèles présentant une compatibilisation physique et/ou chimique aux interfaces ont été étudiés. L’objectif ultime consiste en la compréhension des phénomènes multi-physiques et multi-échelles mis en jeu lors de l’élaboration du confinement de ces matériaux. Dans un premier temps, l'influence de «l'interphase diffuse» sur le comportement rhéologique aux échelles micro- et nanométriques a été étudiée. Malgré le caractère compatible du système PVDF/PMMA, ce travail met en évidence que les chaines macromolécules des deux polymères présentent une certaine hétérogénéité locale dans la dynamique spatiale, allant de l’échelle des segments jusqu’à la conformation globale des chaînes. L’étude par spectroscopie diélectrique, montre que cette hétérogénéité est dépendante de la composition de l'interphase. Cette dernière est gouvernée à son tour par la diffusion mutuelle des chaines aux interfaces. Les résultats obtenus ont été analysés et modélisés en se basant sur les concepts de la dynamique moléculaire. La deuxième partie de cette étude porte en l’étude de l’effet d’une interphase diffuse (et ou réactive) sur les propriétés microstructurales, rhéologique et en particulier sur la dynamique moléculaire dans les multi- micro et nano-couches confinés. Les systèmes élaborés ont été analysés à différentes échelles par différents moyens spectroscopiques. L’effet du confinement sur la structure cristalline est mis en exergue. Ces systèmes ont été étudiés sous sollicitations en cisaillement et en élongation en viscoélasticité linéaire (VEL) et non-linéaire (VENL). Des modélisations ont été alors possible et elles étaient établies en se basant sur les mécanismes physiques et physico-chimiques mis en jeu. En concomitance avec cette seconde partie, nous avons démontré que la formation du copolymère greffé au niveau de cette interphase réactive présente une influence sur la dynamique moléculaire aux échelles micro- et nanométriques. Par conséquent, un nouveau processus de relaxation interfaciale diélectrique est démontré. Sa signature est dépendante du temps ouvert à la réaction ainsi que du nombre de couches. Le dernier volet de la thèse a porté sur l'effet du l’ultra-confinement sur les propriétés microstructurales, la dynamique et les propriétés diélectriques à l’état fondu et solide. En outre, des moyens type 2D-WAXS/SAXS, spectroscopie diélectrique multifréquences ont été déployés pour mener à bien ces travaux. Enfin, les résultats de cette thèse présentent une première approche pour le contrôle des propriétés d’interphases dans les structures multinanocouches. Les applications visées sont principalement la plastronique, l’énergie ou l’emballage alimentaire à propriétés Ultra-barrière. / Interphase developed at the polymer–polymer interface crucially determines the overall macroscopic properties of multilayered polymers from coextrusion. A better understanding of the interfacial properties involving rheology and dynamics is essential for establishing the processing-structure-property relationship. Therefore, this thesis is focused on a fundamental study of the role of interphase in rheology and dynamics of multicomponent polymers, towards tailoring the interface/interphase in multilayered structures from coexrusion process. The work proceeded from the diffuse interphase in compatible multilayered systems to the reactive interphase in reactive counterparts. Starting with a preliminary study on a model compatible system of PVDF/PMMA blends, we firstly revealed their blending phenomena and physics, involving dynamic heterogeneity in segmental and terminal scales, and locally structural heterogeneity due to the nanoscale interphase. Particularly, the local heterogeneity significantly altered the thermorheological and dynamic behaviours. Based on the findings with blends, we were able to further clarify the effects of interdiffusion and diffuse interphase formation on the structure, rheology and dynamics in compatible multilayered PVDF/PMMA systems fabricated by forced-assembly multilayer coextrusion. The remarkable changes in the rheological and dynamic behaviors of these compatible multilayers were explained in terms of the physical picture for interdiffusion mechanism and physics of diffuse interphase occurring in coextrusion process. Secondly, we incorporated in situ interfacial chemical reaction to multilayered systems based on PVDF-g-MAH/PA6 in comparison to PVDF/PA6 pair, thereby allowing us to probe the generated reactive interphase with graft copolymers from bilayer to multi nanolayers. Influence of interfacial reaction and formed interphase on the resulting macroscopic rheological behaviors and microscopic dynamics were preliminarily elaborated using a stacked model bilayer of PVDF-g-MAH/PA6, by taking into account the factors involving interfacial morphology development, copolymer architecture and reaction extent/time, etc. Based on this preliminary investigation, we further probed the role of interfacial reaction and reactive intephase formation in the coextruded multilayered structures alternating of PVDF-g-MAH/PA6 with the layer thickness varying from micro- to nanoscale. Therein, we investigated systematically the layer architecture/structure, morphology, dielectric properties, charge transport dynamics, and especially the uniaxial extensional rheology of the reactive multilayered polymers in the presence of reactive interphase. Findings obtained in this thesis are aimed at a better understanding of the interfacial properties including rheology, dynamics and dielectric properties, towards controlling the interface/interphase and confinement in multilayered polymers from coextrusion and for their advanced applications.

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This work demonstrates the effectiveness of coextrusion as a method to manufacture negative stiffness inclusions for use in vibrational damping applications. The theory and mechanics of negative stiffness and coextrusion are introduced and the process of creating and extruding a feed rod with negative stiffness architecture explained. Coextrusion is shown to be a viable method to create negative stiffness inclusions / text

The flow and stability of co-extruded layers of different polymers in a forced assembly process is studied computationally to determine the extent of the stable process window and the types of instabilities that occur. Recent advances in layer-multiplying co-extrusion of incompatible polymers have made possible the fabrication of multilayered nanostructures with improved barrier, thermal and mechanical behavior. However, existing layering techniques are very sensitive to mismatches in viscosity and elasticity of the co-extruded polymers which often give rise to layer non-uniformity and flow instabilities, such as encapsulation. Simulations of the flows inside the feedblock and the successive multiplier dies of the multi-layering system are used to track the interface and predict instabilities and degrees of encapsulation as a function of process parameters, primarily the flow rates and rheology of the polymers. Encapsulation is found to be negligible in practice in the feedblock even for large viscosity contrasts and differences in elasticity between the two co-extruded polymers. Encapsulation or pinch-off of interfaces is more severe in the multiplier dies when there the rheologies of the polymers differ. A secondary flow due to the second normal stress differences for non-Newtonian fluids is primarily responsible for the encapsulation. A new multiplier design is proposed and simulated. The pressure drop in the proposed design is half that of the current design, which is useful for extruding highly elastic materials. Further, the degree of encapsulation is also reduced. The results of the simulations are validated with experimental measurements of pressure drop and flow visualization provided by research collaborators. / text

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