Amorphous magnesium silicate ultrasound-assisted precipitation in a mixing system: Population balance modelling and crystallization rates identification

International audienceNatural talc is a very interesting filler for plastic and rubber materials and paints because it enables polymer matrix properties to be improved. Nano-sized particles are required to get a good dispersion of the solid in the polymer matrix. However, at the moment the main drawback in the use of natural talc is that, with a conventional milling process, nanometric particle sizes are difficult and expensive to obtain. A process of magnesium silicate synthesis made by ultrasound-assisted precipitation has been developed in two steps. The first step consists of the synthesis of amorphous magnesium silicate by precipitation from sodium metasilicate and acid magnesium chloride. In the second step, the amorphous solid is transformed in a crystalline solid under pressure. In this study an ultrasound-assisted synthesis of amorphous magnesium silicate is proposed. Some process parameters (ultrasound power, initial reactants molalities and reactants flow rate) have effects on the particle-size distribution. The population balance is modelled and solved by moments method in the steady state to identify nucleation and growth rates and agglomeration kernel as a function of operating conditions and to understand how these conditions affect the particle-size distribution

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Etude de la précipitation de silicate de magnésium amorphe en présence d'ultrasons

National audienceÉtude de la précipitation de silicate de magnésium amorphe en présence d'ultrasons Campus Jarlard, 81013 ALBI cedex 9 (b) Imerys Talc, 2 place E. Bouillères 31036 TOULOUSE Résumé Le silicate de magnésium est formé par précipitation à partir de métasilicate de sodium et de chlorure de magnésium. Le rapport molaire initial Mg/Si est constant et égal à 0,75. La précipitation est réalisée dans une cuve agitée, équipée de quatre chicanes. Cette étude présente l'addition parallèle des réactifs par l'intermédiaire d'un mélangeur muni d'une sonde ultrasonore. Dans ce travail, ne sont présentés que les résultats en sortie de prémélangeur afin d'étudier l'influence des ultrasons. La connaissance de la constante d'équilibre du silicate de magnésium amorphe déterminée à l'aide du logiciel PHREEQC a permis de calculer les rapports de sursaturation du silicate de magnésium amorphe et de la silice amorphe en sortie du mélangeur pour les différents essais. Ainsi, il semblerait que seul le silicate de magnésium précipite dans le mélangeur quels que soient les paramètres de l'opération de précipitation. Les vitesses de nucléation et de croissance, et le noyau d'agglomération, ont pu être calculés dans le mélangeur, en fonction des paramètres opératoires. Pour cela, le mélangeur, qui fonctionne en continu, a été supposé parfaitement agité. Des mesures de distribution de temps de séjour ont été réalisées et ont montré qu'à débit moyen sans ultrasons et à tous débits étudiés avec ultrasons, le pré-mélangeur peut être considéré comme parfaitement agité (résultats non présentés dans ce travail). La diminution de la taille des particules et agglomérats sous l'effet des ultrasons serait due à une augmentation de la vitesse de nucléation, ainsi qu'à une diminution de la vitesse de croissance et du noyau d'agglomération. L'augmentation de la puissance ultrasonore dissipée dans la suspension permettrait d'accroître ces effets. Cependant, l'augmentation de la vitesse de nucléation serait limitée : à partir d'une certaine puissance ultrasonore, cette vitesse n'augmente plus. De plus, le rapport de sursaturation est modifié par l'utilisation des ultrasons, mais pas par l'augmentation de la puissance ultrasonore. La taille des particules et agglomérats a également tendance à diminuer à faibles molalités initiales des réactifs. On a pu observer deux effets inverses des molalités initiales des réactifs sur le rapport de sursaturation du silicate de magnésium amorphe, selon que la précipitation est assistée ou non par ultrasons. Dans le cas du recours aux ultrasons, la puissance ultrasonore serait inhibée lorsque la concentration en solide augmente. À faible molalité initiale des réactifs, l'utilisation d'ultrasons provoque une augmentation de la vitesse de nucléation et une diminution de la vitesse de croissance et du noyau d'agglomération qui seraient à l'origine de la diminution de la taille des particules et agglomérats. Mots-clés : ultrasons, silicate de magnésium, précipitatio

Compatibilization of polypropylene/polyamide 6 blends using new synthetic nanosized talc fillers: Morphology, thermal, and mechanical properties

New synthetic nanotalc and a commercially available natural fine talc (Luzenac© A3) were chosen in order to establish a comparative study in terms of their contributions on the improvement of the morphology as well as the final properties of PP/PA6 blends prepared by melt processing. At first, the TEM and SEM micrographs showed that both talc particles have a preferential affinity for the more hydrophilic polyamide 6 phase compared with the continuous PP matrix. Moreover, in both cases, the addition of talc fillers induces a significant decrease of the size of the PA6 domains but the better compatibilization efficiency was obtained in the presence of synthetic nanotalc particles. In this work, the positive change induced by the talc nanofillers on the crystallization kinetics and final morphology was highlighted. In addition, compared with natural talc, a highly level of dispersion of talc layers has been obtained with the synthetic nanotalc which is more hydrophilic. Thus, this better dispersion greatly improves the thermal stability of PP/PA6 blends and leads to better mechanical properties (+ 40% in Young's modulus).Fil: Mohamed, Yousfi. Université de Lyon. Lyon; Francia. INSA Lyon. Villeurbanne; Francia. Centre National de la Recherche Scientifique; FranciaFil: Sebastien, Livi. Centre National de la Recherche Scientifique; Francia. Université de Lyon. Lyon; Francia. INSA Lyon. Villeurbanne; FranciaFil: Dumas, Angela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Université de Toulouse. Toulouse; Francia. Centre National de la Recherche Scientifique; FranciaFil: Crépin Leblond, Jérome. Imerys Talc. Toulouse; FranciaFil: Greenhill Hooper, Mike. Imerys Talc. Toulouse; FranciaFil: Duchet Rumeau, Jannick. Université de Lyon. Lyon; Francia. INSA Lyon. Villeurbanne; Francia. Centre National de la Recherche Scientifique; Franci

Ionic compatibilization of polypropylene/polyamide 6 blends using an ionic liquids/nanotalc filler combination: morphology, thermal and mechanical properties

International audienceIn this study, room temperature ionic liquids (RTILs) based on phosphonium cations have been used as effective compatibilizers of polyolefin/polyamide 6/synthetic talc blends using a melt extrusion process. Thus, different ionic liquids functionalized by various counteranions (phosphinate versus bistriflimide) were introduced at various concentrations (1, 5 and 10 wt%) in the polymer mixtures. Then, the crystallization behaviour, the thermal and mechanical properties of blends as well as the morphologies were investigated. The transmission electronic microscopy (TEM) micrographs demonstrated that the use of a very low amount of ILs (1 wt%) led to a significant reduction of the size of the dispersed PA 6 phase. Moreover, the thermal properties of PP/PA6/talc were dramatically enhanced (+80 degrees C) and the mechanical performance was improved without reducing the strain at break suggesting a synergistic effect between nanotalc and ionic liquids

Use of new synthetic talc as reinforcing nanofillers for polypropylene and polyamide 6 systems: thermal and mechanical properties.

International audienceNew layered synthetic nanotalc prepared at a lab-scale by a conventional hydrothermal process and commercial natural fine talc were used in order to establish a comparative study in terms of their contributions on the improvement of the final properties of two different polymers: a nonpolar polyolefin matrix and a polyamide. All samples were prepared by melt extrusion in a co-rotating micro compounder. The surface properties of talc -surface energy and isoelectric point- were probed. The particles crystalline structure and the distribution/dispersion within the polymer matrix were performed using transmission electron microscopy and X-ray diffraction. The effect of talc particles on the cristallinity, the thermal and mechanical properties was highlighted as a function of the surface properties of talc. In the case of talc filled PP systems, it seems that the incorporation of both natural and synthetic talc greatly improves the thermal stability of polypropylene matrix. The highest elastic modulus was obtained in presence of highly nucleating natural talc. Oppositely the best ductility was observed for the synthetic talc filled PP systems. For PA6/talc nanocomposites, a remarkable improvement in the dispersion of talc layers was shown and a significant increase in Young's modulus was determined due to the closer affinity between the hydrophilic nanotalc lamellae and the polar PA6 matrix

CARACTERISATION PAR CHROMATOGRAPHIE GAZEUSE INVERSE DE DIFFERENTS SILICATES DE MAGNESIUM SYNTHETIQUES.

International audiencePour permettre une meilleure dispersion des particules de talc dans des matrices polymères, celles-ci doivent présenter une taille nanométrique non accessible par broyage. Apparaît alors comme une alternative au broyage la synthèse de silicate de magnésium comprenant deux étapes : une précipitation à pression atmosphérique conduisant à un produit amorphe, suivie d'une étape sous pression permettant de transformer le produit amorphe en produit cristallin. Les propriétés de surface des différents produits synthétisés lors de la première étape, essentielles lors des interactions silicate de magnésium-matrice polymère, ont été caractérisées par chromatographie gazeuse inverse. La composante dispersive de l'énergie de surface γ s d a été déterminée pour des silicates de magnésium synthétisés, comparée avec celle du talc naturel et corrélée avec d'autres caractéristiques comme le volume des micro et méso-pores et la dispersibilité des solides dans l'eau

Myartspace: Design and evaluation of support for learning with multimedia phones between classrooms and museums

This paper presents a description and evaluation of Myartspace, a service on mobile phones for inquiry-led learning that allows students to gather information during a school field trip which is automatically sent to a website where they can view, share and present it, back in the classroom or at home. The evaluation focused on three levels: a micro level, concerned with issues of usability; a meso level, which examined educational effectiveness in terms of learning breakthroughs and breakdowns; and a macro level, which looked at the impact of the new technology on school museum visits practice. Issues of implementing mobile learning across school and museum settings are identified and cross-level influences are discussed. The study showed that the service was effective in enabling students to gather information in a museum and this provided resources for effective construction and reflection in the classroom. Minor usability problems did not detract from the learning, however there are significant issues concerning how to structure the visit and on the viability of Myartspace as a regular service