PLA-PHA blends: morphology, thermal and mechanical properties

International audienceBiotechnological polymers such as polylactides (PLA) and polyhydoxyalkanoates (PHA) are alternatives to petroleum-based polymers and represent an attractive growing market. These sustainable polymers are becoming more competitive due to the increase of the price of the oil barrel and overall concern about the limits of petrol feedstock. However, the polymers from renewable resources have often serious disadvantages as compared with conventional synthetic polymers. One is poor mechanical properties which limit their practical applications. Blending of polymers is a useful way of obtaining new materials with improved properties, which can overcome the drawbacks of the pure components. The physical and mechanical properties of blends can be tuned by choosing the proper polymers, varying the composition of the blend and preparation conditions. Most of the studies on PLA and PHA blends that have been reported in the literature concern the blends prepared by solvent casting. Only few studies have been conducted on the preparation and characterization of PLA/PHA blends by melt mixing [1] despite the fact that both polymers are thermoplastics and their processing is similar to the classical oil-based polymers. In the present research work, blends of a polylactide and a poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) prepared by melt-mixing have been studied

Preparation and characterization of Polyhydroxyalkanoates (PHA) and Polylactide (PLA) blends

International audiencePolylactide (PLA) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) blends were prepared in different compositions by melt mixing. The miscibility of the two components was first characterized by differential scanning calorimetry (DSC) experiments, which showed the immiscibility of the components for all blend compositions. The morphology was studied using scanning electron microscope (SEM) and optical microscopy in reflection. Nodular and co-continuous morphologies were observed depending on the composition. The rheology of the pure polymers and of the PLA/PHBV blends was investigated in the dynamic mode. The results showed a significant role of the interfaces with an increase of the complex viscosity at small frequencies

Tensile Properties of Pla And Phbv Blends: Anomalous Elongation and Aging

International audiencePolylactide (PLA) and polyhydroxyalkanoates (PHA) are polymers made from renewable resources. Despite their growing competitiveness with conventional petrol-based polymers, they still have some disadvantages such as poor (fragile) mechanical properties. Blending is a potentially prospective way of obtaining new materials with improved properties, which can overcome the drawbacks of the pure components. In this work, PLA and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) blends were prepared via melt mixing. Their morphology was observed by scanning electron microscopy and their tensile properties were studied

Rheological properties of molten flax- and Tencel®-polypropylene composites: Influence of fiber morphology and concentration

International audienceThe rheological properties of short fiber reinforced polypropylene were investigated. Flax and Tencel® are two cellulose based fibers used in this study. Flax fibers are extracted from the bast of plants. They are composed of thin elementary fibers and rigid thick bundles made of elementary fibers “glued” together. Tencel® is a man-made cellulosic fiber spun from cellulose solution, with a uniform diameter, thin, and flexible. First, fiber dimensions before and after compounding were analyzed. Both types of fibers were broken during compounding. Flax shows larger length and diameter than Tencel®, but aspect ratio of flax is smaller. The reason is that after compounding flax remained in bundles. Dynamic viscosity, elastic and viscousmoduli were studied as a function of fiber type, concentration (from 0 to 30 wt. %), and composite temperature (from 180 to 200 °C). All Tencel®-based composites showed higher apparent yield stress,viscosity, and moduli compared to flax-based composites at the same fiber concentrations. The results are analyzed in terms of the influence of fiber type, aspect ratio, and flexibility. The importance of considering fiber morphology is demonstrated as far as it controls fiber flexibility and fiber-fiber interactions

Influence of ZnO on the properties of dilute and semi-dilute cellulose-NaOH-water solutions

International audienceThe influence of ZnO as cellulose-8%NaOH-water solution stabilizer against gelation is studied. Cellulose intrinsic viscosity in 8%NaOH-water as a function of solution temperature is investigated in the presence and absence of ZnO. The addition of ZnO did not bring any improvement in terms of solvent thermodynamic quality. Non-dissolved ZnO particles were observed above 0.8-0.9% ZnO in 8%NaOH-water. Gelation of cellulose-8%NaOH solutions with and without ZnO are studied for various cellulose and ZnO concentrations (4-6% and 0-1.5%, respectively) in a wide range of temperatures (-5 °C to 50 °C). Gelation times were exponentially increasing with increasing ZnO concentration and with decreasing cellulose concentration and solution temperature. Gelation times of cellulose-NaOH-water-ZnO systems were found to follow a semi-empirical model correlating these three parameters. We suggest that ZnO is acting as water molecular "binder" stabilizing cellulose-NaOH-water solutions

Cellulose Ester / Polyolefin Binary Blends : Rheology, Morphology and Impact Properties

International audienceDue to depletion of fossil resources and global environmental respect awareness, interest in biobased plastic materials is tremendously growing. Direct extraction of vegetal polymers like cellulose followed by a chemical modification to bring new properties is one of the paths to produce a bioplastic. Progressively replaced by oil-based polymers in the sixties, thermoplastic cellulose esters are now reconsidered for various materials applications. To improve mechanical weaknesses of cellulose esters based materials, the technique of blending has been widely used. Various blending candidates of cellulose esters have been studied, but mostly with the goal to make the material biodegradable. For this purpose Polyestercarbonates, Polylactides and Polyhydroxyalcanoates were used. To our knowledge, small interest has been paid on durable cellulose ester based blends. More particularly, only few studies have considered the good mechanical properties of cost-effective and easy-available polyolefins as blending partners of cellulose esters

Polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends: Morphology and mechanical properties

International audienceThe morphology and the mechanical properties of polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends of various compositions were studied. The statistical analysis of the scanning electron microscopy images allowed finding two statistical ensembles of the minor-phase particles. The first ensemble involves the dispersed particles, whereas the second one contains the coalesced particles. The mean diameters of both dispersed and coalesced minor-phase particles were calculated and plotted against the blend composition. Young's modulus, tensile strength, elongation at break, and Charpy impact strength of the blends were determined and examined as a function of the blend composition. The Young's modulus values were shown to be in accordance with theoretical predictions

Modélisation du revêtement de matière liquide lors d'un processus de trempage - approche thermomécanique et validation expérimentale

http://hdl.handle.net/2042/15853International audienceCe papier a pour objectif de présenter les premiers essais de modélisation du procédé de trempage d'un moule cylindrique dans un bain de polymère. L'objectif est de pouvoir prédire numériquement l'épaisseur de couche liquide extraite autour du moule après sa sortie du bain. Une rhéologie anisotherme newtonienne a été utilisée dans un premier temps. Les premiers résultats obtenus ont montré que l'épaisseur extraite n'était pas constante le long du moule ; elle est maximale à l'extrémité inférieure et minimale à l'extrémité supérieure. Des problèmes d'instabilités à l'interface matière/air et de pertes de matière apparaissent, une approche d'introduction de la tension de surface sera présentée = This paper describes the modelling of the dip-coating process over a cylindrical mould which is dipped into a liquid polymer bath at a constant speed. The goal of this work is to numerically predict the thickness of the layer extracted on the mould. An anisotropic newtonian rheology is used as a first approximation. The results show that the thickness is heterogeneous along the mould: maximal at the bottom and minimal at the top. The approach of encounting of the interfacial tension liquid/air in order to avoid surface instabilities and mass loss will be also presente

Solvent release from highly swollen gels under compression: an important phenomenon that has to be taken into account

National audienceThe behavior of a strongly charged polyelectrolyte gel under a uniaxial compression was studied, demonstrating the evidence of gel deformation and volume loss at the same time. A theoretical approach shows that solvent release takes place for both weakly charged and neutral gels, being more pronounced for polyelectrolyte hydrogels = Nous avons étudié le comportement de gels fortement polyélectrolytiques sous compression uniaxiale. Il est observé que le gel se déforme et expulse de son solvant en même temps. Une analyse théorique prédit cette perte de solvant pour des gels faiblement chargés comme pour des gels neutres. Le phénomène est plus prononcé pour le cas du gel polyélectrolytique

3D numerical simulation of the behaviour of a spherical particle suspended in a Newtonian fluid and submitted to a simple shear

International audienceThe 3D flow around a rigid spherical particle suspended in a Newtonian fluid and submitted to simple shear is numerically studied using Rem3D® finite element code. The sphere motion is imposed by a sticking contact between the sphere and the fluid. The effect of the particle size as compared with the finite dimension of the shear cell was investigated. The direct calculations show that 3D modelling is necessary to correctly predict the sphere behaviour. The proximity of the particle and the cell walls strongly affects the flow velocities, the sphere motion (increase of the rotation period of the sphere) and the stress field (change of orientation angle and increase of maximal local stresses)