Matériaux à base de maïs : de la qualité finale à la sélection variétale via le procédé de mise en forme

Que les matériaux à base de maïs soient considérés comme des substituts des matériaux plastiques, ou qu'ils se présentent comme des produits alimentaires expansés (céréales petit-déjeuner, biscuits...), il est important de pouvoir évaluer leurs propriétés mécaniques, pour adapter les conditions de transformation, favoriser la sélection de la matière première et optimiser leur qualité. Par analogie avec le modèle des solides composites, l'analyse thermomécanique dynamique (DMA) montre que le comportement dépend fortement de l'adhésion entre amidon et particules protéiques. Les variations de viscosité élongationnelle avec la teneur en protéines et son lien avec le module élastique E', pour T>Tg+30°C, suggèrent que cette morphologie est fonction des mécanismes d'écoulement et d'expansion lors du procédé. En établissant les relations structure-procédé-propriétés, ces travaux ont favorisé la sélection variétale et la conception de produits céréaliers à la texture optimisée

Thermoplastic materials based on biopolymer for their 3D printing by material extrusion

La Fabrication Additive (FA) ouvre des perspectives nouvelles pour mettre en forme des matériaux à base de polymères naturels et ainsi tirer parti de leurs propriétés intrinsèques, telles que comestibilité et biorésorbabilité. Cette thèse se concentre sur le procédé d’impression 3D par dépôt de fil fondu (FA-DFF) appliqué à la zéine, une protéine de réserve du maïs pouvant être mise en œuvre à l’état fondu en présence de plastifiants. Après avoir établi un cahier des charges déclinant les critères « matière » pour ce procédé, une formulation plastifiée par 20% de glycérol a fait l’objet d’une caractérisation complète des propriétés concernées. Son comportement thermomécanique et rhéologique peut être compatible avec un procédé FA-DFF alimenté par des filaments préalablement extrudés : Suffisamment rigide à 20°C, le matériau peut être extrudé à des températures supérieures à 120 °C. Son comportement rhéofluidifiant et son aptitude à la fusion-adhésion sont alors similaires à ceux de polymères standards tels que l’ABS et le PLA. Cependant, une réticulation progressive due à l’agrégation de la protéine à l’état fondu, mise en évidence par des caractérisations structurales, vient limiter sa fenêtre de mise en oeuvre. Néanmoins, il est possible de pallier à ce phénomène soit en modifiant le système d’alimentation matière du procédé, soit en modulant la formulation. Outre la combinaison du glycérol avec des additifs réducteurs ou dénaturants, l’intérêt de sa substitution par des liquides ioniques est mis en évidence, ces composés pouvant apporter des fonctionnalités pharmaceutiques aux objets imprimés, ce qui ouvrirait un champ d’applications nouvelles pour la zéine.Additive Manufacturing (AM) opens new perspectives for the processing and shaping of materials based on natural polymers. Their intrinsic properties such as edibility and bioresorbability could thus be exploited. This thesis focuses on 3D printing by molten Material Extrusion (AM-ME). It is applied to zein, a corn storage protein which is melt processable in presence of plasticizers. After listing the relevant material specifications for the AM-ME process, all the properties concerned were characterized for a formulation plasticized by 20% of glycerol. Its thermomechanical and rheological behaviour can be compatible with an AM-ME process fed by previously extruded filaments : While rigid enough at 20°C, the material can be extruded above 120°C. Its shear thinning behaviour and fusionbonding ability are similar to those of standard polymers such as ABS and PLA. However, a progressive crosslinking due to protein aggregation in the melt was shown by structural characterizations. The processing window is thus limited, but this issue can be addressed either by modifying the feeding system of the process, or by adapting the formulation. Glycerol can be combined with reducing or denaturing agents, or substituted by ionic liquids. The interest of these plasticizers is to allow bringing pharmaceutical functionalities to printed parts. This would open the field of new applications for zein

Contour Fitting of Fused Filaments Cross-Section Images by Lemniscates of Booth: Application to Viscous Sintering Kinetics Modeling

International audienceA method for image analysis was implemented to determine the edge pixels of two biopolymer-based thermoplastic filaments during their hot melt isothermal sintering at 120 ◦C. Successive inverted ellipses are adjusted to the contour of the sintered filaments and lead to the identification of the parameters of the corresponding lemniscates of Booth. The different steps of the morphological image analysis are detailed, from 8-bit coded acquired images (1 frame/s), to the final fitting of the optimized mathematical functions describing the evolution of the filaments envelope. The complete sequence is composed of an initial pure viscous sintering step during the first minute, followed by viscoelastic swelling combined with melt spreading for a longer time, and then the stabilization of the sintered filaments shape for over 2 min at high temperatures. Using a master curve obtained from Hopper’s abacus, the characteristic viscous sintering time is assessed at tvs = 78 s, confirming the one previously found based on the measurement of the bonding neck length alone. Then, the full description of the evolution of the thermoplastic filaments envelope is assessable by image analysis during sintering trials as a result of its digital modeling as successive lemniscates of Booth, reflecting geometry changes in the molten state

Détermination des propriétés de fusion-adhésion de filaments extrudés à base de protéines de maïs

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Plasticized protein for 3D printing by fused deposition modeling

International audienceThe developments of Additive Manufacturing (AM) by Fused Deposition Modeling (FDM) now target new 3D printable materials, leading to novel properties like those given by biopolymers such as proteins: degradability, biocompatibility and edibility. Plasticized materials from zein, a storage protein issued from corn, present interesting thermomechanical and rheological properties, possibly matching with AM-FDM specifications. Thus commercial zein plasticized with 20% glycerol has a glass transition temperature (T-g) at about 42 degrees C, after storage at intermediate relative humidity (RH=59%). Its principal mechanical relaxation at T-a approximate to 50 degrees C leads to a drop of the elastic modulus from about 1.1 GPa, at ambient temperature, to 0.6 MPa at T-alpha+100 degrees C. These values are in the same range as values obtained in the case of standard polymers for AM-FDM processing, as PLA and ABS, although relaxation mechanisms are likely different in these materials. Such results lead to the setting up of zein-based compositions printable by AM-FDM and allow processing bioresorbable printed parts, with designed 3D geometry and structure

Modélisation des propriétés viscoélastiques linéaire d’amidon de pomme de terre amorphe en fonction de la température et la teneur en eau

Afin d’améliorer la connaissance des propriétés thermo-rhéologiques de l’’amidon de pomme de terre amorphe, dans une perspective de modélisation de sa mise en forme, son comportement viscoélastique linéaire a été étudié par analyse thermomécanique dynamique (DMA) en fonction de la température et de la teneur en eau. Des échantillons d’amidon extrudé ont été équilibrés pendant 3 semaines sous différentes humidités relatives pour atteindre des teneurs en eau comprises entre 9,3 et 17,2%. L’analyse DMA a été réalisée en mode traction-compression, en double balayage simultané en fréquence et en température. La perte d’eau au cours de l’analyse a été évaluée par analyse thermogravimétrique et via Tg mesurée par DSC. Une cartographie des modules de conservation et de perte (E’(ω) et E’’(ω)) en fonction de la teneur en eau réelle a ainsi été construite dans l’intervalle de températures étudié. Les courbes isothermes de grandeurs viscoélastiques ont été obtenues pour plusieurs teneurs en eau, par ajustement et interpolation des résultats. L’application du principe d’équivalence temps-température, en utilisant le facteur de translation aT(T) nous a permis d’obtenir des courbes maîtresses de E’(ω) et de E’’(ω) pour chaque teneur en eau. Ces résultats ont été ajustés par un modèle de Maxwell généralisé pour calculer le module de relaxation E(t) à la température de référence de 50°C et des temps de relaxation τ pour des valeurs discrètes de teneur en eau. Le modèle de Maxwell généralisé (n=7) a été utilisé pour calculer E(t) dans l’intervalle 10E-2 et 10E5 s. Le facteur de translation aT(T) a permis de déduire E(t) à n’importe quelle température dans l’intervalle étudié et, par interpolation, ses variations en fonction de la teneur en eau

Drug delivery system obtained by hot-melt processing of zein plasticized by a pharmaceutically active ionic liquid

International audienceZein-based filaments containing 20 weight% [Lidocainium][Ibuprofenate] used as a doubly Active Pharmaceutical Ingredient-Ionic Liquid (API-IL) were obtained by extrusion at 130°C.The plasticizing effect of the active ingredient on the zein amorphous matrix was assessed by Differential Scanning Calorimetry, with the decrease of the glass transition temperature (Tg) from 77°C, for the raw zein, to 53°C. After storage under standard conditions (relative humidity 59%, 20°C) the extrudates were rigid, with a high storage modulus (E′) at ambient temperature of about 3 GPa. They had a main mechanical relaxation (Tα) beginning at 55°C and leading to their flowing at temperature above 130°C, as determined by Dynamic Mechanical Analysis, with E′ below 1 MPa and tanδ above 1. Their structure was evaluated by Wide Angle X-ray Scattering and NMR analyses were used to evaluate the API-IL stability that was shown after thermomechanical processing. Release experiments performed under simulated physiological conditions on filaments evidenced a release of 85% after 7 days immersion. These results demonstrate the interest of using an API-IL to act as plasticizer for a resorbable biopolymer. 2 The resulting material can be shaped by continuous thermomechanical process and used as drug delivery system

Flow and foam properties of extruded maize flour and its biopolymer blends expanded by microwave

International audienceMaize flour and blends from starch and zein biopolymers were processed as dense materials by extrusion (120 degrees C, 300 J.g(-1)) and press-molding (140 degrees C, 10 min) at a constant moisture content (26% wb), and then foamed by microwave heating. The mechanical properties of foams, determined by a 3-point bending test, were governed by density, in agreement with an open solid foam model. The density and 3D cellular structure of the foams were determined by X-ray tomography. In the same interval of density [0.15, 03 g.cm(-3)], foams from microwaved materials had a finer cellular structure than directly expanded materials at extruder outlet. The study of melt rheological behavior with Rheoplast (R) (100-160 degrees C, SME <= 200 J.g(-1)) showed that protein content (0-15%) did not affect shear viscosity but increased elongational viscosity. This trend, similar to the one reported for the storage modulus in a rubbery state, could be attributed to dissipative effects in a starch/protein interphase, explaining the difference of expansion between starch, blends and flour

The role of mechanical properties of brittle airy foods on the masticatory performance: experimental and modelling approches

International audienceThis work investigates the mastication of two samples of typical cereal food products previously characterised by different sensory, textural and mechanical properties, by two complementary approaches. Electromyographic records and image analysis of chewed food particles first confirm the importance of the brittle behaviour of the products on human mastication. For both products, the fragmentation is followed by a significant agglomeration after less than 10 chewing cycles, both phenomena being correlated to the force magnitude and its evolution. Then, artificial mastication is undertaken to shed more light on the capability of the chewing simulator to discriminate both products under dry mastication conditions. The results depict a qualitative agreement with human mastication and texture properties

Modeling of starchy melts expansion by extrusion

International audienceBackground: Expansion phenomenon is a key-point of the development of extruded starchy foods. Despite the huge number of studies, the complexity of the phenomenon still challenges its modeling. Current available models based on continuum mechanics are still too complex to be coupled with any 1D extrusion model available, in order to predict the density and the cellular structure of the starchy foams. Scope and approach: In this paper, the different modeling approaches for vapor expansion are reviewed. Then, a survey of the different mechanisms (bubbles nucleation, growth, coalescence, shrinkage and setting), using qualitative knowledge representation and reasoning, allows to improve the understanding of the effect of extrusion variables (temperature, moisture content, die geometry …) and material rheological properties on the expansion phenomenon. Based on experimental results reported in the literature, a phenomenological model of expansion can then be suggested. Key findings and conclusions: The knowledge representation and reasoning leads to a concept map of the causal influences between input, physical mechanisms and output variables. The phenomenological model would allow to predict output variables characterizing foam macrostructure (bulk expansion indices and anisotropy factor) and cellular fineness based on X-ray tomography measurements. A scale down from macrostructure to cellular structure could be achieved by establishing a link between anisotropy factor and cellular fineness. Once validated, this model could be coupled with any 1D extrusion model in order to build a global model for the design of cereal-based extruded foods