Reactive Functionalized Multilayer Polymers in a Coextrusion Process: Experimental and Theoretical Investigations of Interfacial Instabilities

International audienceCoextrusion technologies are commonly used to produce multilayered composite sheets or films for a large range of applications from food packaging to optics. The contrast of rheological properties between layers can lead to interfacial instabilities during flow. Important theoretical and experimental advances regarding the stability of compatible and incompatible polymers have, during the last decades, been made using a mechanical approach. However, few research efforts have been dedicated to the physicochemical affinity between the neighboring layers. The present study deals with the influence of this affinity on interfacial instabilities for functionalized incompatible polymers. Polyamide (PA6)/polyethylene grafted with glycidyl methacrylate (PE-GMA) was used as a reactive system and PE/PA6 as a non reactive one. Two grades of polyamide (PA6) were used in order to change the viscosity and elasticity ratios between PE (or PE-GMA) and PA6. It was experimentally confirmed, in this case, that weak disturbance can be predicted by considering an interphase of non-zero thickness (corresponding to an interdiffusion/reaction zone) instead of a purely geometrical interface between the two reactive layers. According to rheological investigations from previous work, an experimental strategy was here formulated to optimize the process by listing the parameters that controlled the stability of the reactive multilayer flows. Plastic films with two layers were coextruded in symmetrical and asymmetrical configurations in which PA6 was the middle layer. Indeed, for reactive multilayered systems, the interfacial flow instability could be reduced or eliminated, for instance, by (i) increasing the residence time or temperature in the coextrusion bloc (for T above the reaction temperature T = 240°C), and (ii) reducing the total extrusion flow rate. The reaction rate/compatibilization played a major role that must be taken into account. Furthermore, the role of the viscosity ratio, elasticity ratio, and layer ratio of the stability of the interface were also investigated coupling to the physicochemical affinity. The results show that it is necessary to obtain links between the classic factors that are introduced in the evaluation of the theoretical, given by linear stability analysis/longwave asymptotic investigations, and its corresponding experimental stability charts. Hence, based on this analysis, guide-lines for a stable coextrusion of reactive functionalized polymers can be provided

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

Compounding and processing of biodegradable materials based on PLA for packaging applications: In greening the 21st century materials world.

Poly(lactic acid) is a well known polymer for more than 20 years in the biomedical fieldsapplications. Today, according to rising prices of oil and massive consumption of fossil resource,this biodegradable aliphatic polyester is on the way to be a wide used commodity polymer.Moreover PLA is as a “green plastic” because it is synthesized from annually renewable resources.In many ways similar to poly(ethylene terephtalate) such as rigidity, transparency, crystallizationkinetics and food contact ability, it fulfills the packaging industry requirements for most of the rigidobjects. But for applications like hot food packages, soft films and stretch blow bottles for examplesome properties of PLA have to be improved like heat deflection temperature (HDT), impactstiffness and gas barrier properties. There are many ways reported in literature today to improvethese properties. In order to compare it with other well known polymers, figure 1 representsthermal properties of PLA and these polymers. The aim of the work deals to identify actualweaknesses of commercial grades of PLA. Secondly, to present pertinent ways to improve PLA‟sproperties have been identified according to chosen process and final properties wished. This studyis composed of three main items. In a first time, a bibliographical study is necessary to identify thedifferent ways to improve PLA‟s properties used by researchers and industrials in literature. Themost significant ways will be describe here. Then PLA compound (PLA with additives or PLAcopolymers for examples) will be synthesized in conditions closed to industrial conditions studyingcrystallisation kinetic and rheological properties. In this step thermal, physico-chemical andmechanical properties of products synthesized will be characterized. At the end of this study thebest ways of improving PLA‟s behavior will be presented and describe

Blends based on poly(lactic acid) (structure/rheology/processing relationship)

Ce travail de thèse porte sur l étude des relations structure/procédés de mise en forme/propriétés finales de matériaux polymères à base de PLA/PBAT. Ces derniers sont destinés à l emballage alimentaire en vue de remplacer le polyéthylène téréphtalate (PET). Cependant le PLA a certaines limites de processabilité par les technologies de la plasturgie. Le renforcement de ses propriétés à l état fondu a été obtenu grâce à l introduction d un époxyde multifonctionnel capable de réagir avec les bouts de chaînes des polyesters. Aussi, des mélanges à base de PLA/PBAT ont été mis en œuvre en vue de conférer la ductilité au matériau final. La première étape consiste en la compréhension des mécanismes de dégradation thermique et hydrolytique des deux polymères PLA et PBAT au cours des processus de mise en œuvre. En effet, la réaction d extension des chaînes couplée au branchement induits par l époxyde multifonctionnel palie cette dégradation. Les mécanismes d extension de chaînes et de branchements sous-jacents ont été mis en évidence par l analyse des énergies d activation, des spectres de relaxation à l état fondu ainsi que celle des grandeurs physico-chimiques en solution. En outre, les représentations de Van-Gurp-Palmen confirment la co-existence de chaînes macromoléculaires linéaires et aléatoirement branchées. La seconde étape de ce travail a été dédiée à la compatibilisation des mélanges PLA/PBAT par ce même époxyde multifonctionnel. Des études expérimentales modèles basées sur la détermination de la tension interfaciale et la modélisation rhéologique ont montré le rôle majeur de compatibilisant induit par cet agent réactif. Ainsi, la diminution de la tension interfaciale confère à ces matériaux une meilleure cohésion interfaciale et une morphologie fine et homogène de la phase dispersée, accompagnée par l amélioration des propriétés mécaniques. L étude des propriétés rhéologiques en cisaillement et en élongation des matériaux modifiés a permis de montrer une meilleure tenue mécanique à l état fondu. Ainsi, une meilleure aptitude à l extrusion gonflage a été démontrée en élargissant leurs cartes de stabilité. Parallèlement à ces travaux, des études de bi-étirage des polymères seuls, de leurs homologues modifiés et de leurs mélanges montrent un durcissement structural, dû à la cristallisation induite sous déformation. Les morphologies cristallines ont été analysées finement par des méthodes calorimétriques et spectroscopiques. Enfin, ces études ont été transposées à l élaboration et à la compréhension des comportements d une formulation industrielle complexe à base de PLA, PBAT et de farine céréalière plastifiée.The ultimate aim of the present thesis focuses on the structure/processing/properties relationship of the PLA/PBAT materials. The latters are intended for food packaging in order to replace poly (ethylene terephthalate (PET). However, PLA has a limited processability in conventional technologies of plastics industry. The strengthening of its melt properties has been achieved through the incorporation of a multifunctional epoxide, able to react with the end chains of polyesters. Furthermore, PLA/PBAT blends were prepared to make the final material more ductile. The first part of the study consists on the understanding of thermal and hydrolytic degradation mechanisms of neat PLA and PBAT polymers upon processing. Indeed, the degradation was overcome through the chain extension reaction coupled to branching, induced by the multifunctional epoxide. The chain extension and branching mechanisms were highlighted by the analysis of the activation energy and the relaxation spectra in the molten state as well as the physico-chemical properties in solution. Moreover, the Van-Gurp-Palmen plots confirm the co-existence of linear and randomly branched macromolecular chains. The second part has been dedicated to the compatibilization of PLA/PBAT blends by the multifunctional epoxide. Experimental models studies, based on the assessment of the interfacial tension, and the rheological modeling showed the major role of the reactive epoxide agent as a compatibilizer. Thus, the decrease of the interfacial tension gives a better cohesive interface with finer and homogenous morphology of the dispersed phase, accompanied with an improvement of the mechanical properties. The study of the shear and elongation rheological properties of modified materials showed an enhancement of their melt strength. Therefore, a better ability to be blown has been demonstrated, by expanding their stability maps. Besides, biaxial stretching studies of neat polymers, their modified counterparts as well as their blends show a structural strain hardening, due to a strain-induced crystallization. The crystalline phases were analyzed thanks to calorimetric and spectroscopic methods. Finally, the present studies have been used to elaborate and understand the behavior of a complex industrial formulation based on PLA, PBAT and thermoplastic cereal flour.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

La renaissance des matériaux - un film de Laurence Scarbonchi

Participation à un reportage sur les biomatériau

Optimisation et modélisation du procédé de rotomoulage

Le rotomoulage est un procédé de transformation des matières plastiques qui permet principalement la réalisation de pièces creuses de grandes dimensions, sans reprise, ni lignes de soudure. Ce procédé est connu depuis une cinquantaine d années, mais utilise un savoir-faire empirique. Les inconvénients majeurs du rotomoulage sont aujourd hui le temps de cycle et la non maîtrise du procédé. Les objectifs de ce projet sont d une part de mieux comprendre les relations qui existent entre le matériau, le procédé et les propriétés des pièces finales et d autre part, d avoir un meilleur contrôle du procédé en analysant et modélisant les échanges thermiques. C est dans ce cadre que s est déroulée cette thèse CIFRE au Laboratoire de Recherche Pluridisciplinaire en Plasturgie et au Pôle Européen de Plasturgie, en partenariat avec MECAPLAST GROUP et la Région Rhône-Alpes. Durant le processus de mise en œuvre par rotomoulage, le matériau polymère subit différentes transformations physiques : la fusion, la coalescence des particules, la densification du volume à l état fondu et la solidification. La compréhension de ces mécanismes a permis d expliquer les défauts qui apparaissent dans les pièces finales. Afin d étudier les phénomènes d échanges thermiques, un dispositif expérimental instrumenté simulant de manière locale la paroi du moule a été mis en place. Il a permis de valider une modélisation des échanges thermiques qui tient compte de l évacuation de l air dans le polymère. D autre part, une analyse expérimentale des transferts thermiques a été réalisée en utilisant une métrologie thermique fine, notamment par fluxmètrie, in situ, directement sur la machine de rotomoulage.Rotational Molding is the best method for producing large hollow plastic articles without weld lines. But it is a quite complex and empirical process. Constant quality in technical parts requires the mastery of the process by controlling on line the main physical phenomena. One of these of first importance is heat transfers. During the processing time, polymer powder melts, then the phenomena of particle coalescence and melt densification occur. After cooling, the molded part is obtained. The understanding of sintering phenomenon, linked to polymer structure, may explain surface defects and bubbles in rotationally molded parts. That s why this project has been carried out. It is divided into two parts: the first part deals with the relationship between the material structure, the process and the final properties; the second part deals with the modelling of heat transfers during the process. Firstly, material properties such as polymer structure, rheological parameters and surface tension were studied and linked to sintering kinetics. Secondly, samples were molded with a pilot-scale rotational molding machine. This work enabled us to model the sintering phenomenon and to bind its kinetics with polymer structure, rheological properties and final parts properties. An experimental analysis of heat transfer in rotational molding process was also lead by using an instrumented mold associated with an original radio transmission data acquisition system. Moreover, a thermal model was developped by using a static heated plate in order to validate the numerical results. This modelling took into account the sintering phenomenon.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF