Mise en forme et caractérisation des mélanges polylactide/copolymère éther-amide

Les polymères bio-sourcés ont fait l’objet de nombreuses études dans le but de remplacer les matériaux plastiques provenant du pétrole. Parmi les matériaux bio-sourcés, le polylactide (PLA) est maintenant commercialisé pour des applications de thermoformages et d’emballages par extrusion soufflage. Sa transparence, son haut module d’Young, sa contrainte de traction maximale élevée et son coût relativement faible ont fait de ce polymère une solution commerciale viable. Toutefois, sa faible résistance aux chocs et aux hautes températures a limité son utilisation dans de nombreuses applications industrielles. L’étude ici menée s’intéresse à l’amélioration de la résistance en impact d’un grade de polylactide et tout particulièrement au lien entre la cristallinité des mélanges à base de PLA et leurs propriétés mécaniques. La résistance aux chocs du PLA a été augmentée par l’ajout d’un modifiant choc : un copolymère linéaire aléatoire d’éther-amide (PEBAX 3533TM). Un copolymère linéaire aléatoire d’éthylène, d’acrylate de méthyle et de méthacrylate de glycidyle (LOTADER AX8900TM) a aussi été utilisé pour compatibiliser le modifiant choc avec la matrice de PLA. Les propriétés rhéologiques, mécaniques et thermiques des mélanges trempés et recuits ont été analysées ainsi que leurs morphologies. D’un point de vue rhéologique, les mélanges ont été testés en cisaillement oscillatoire pour déterminer si les additifs utilisés pouvaient augmenter les propriétés à l’état fondu du PLA et améliorer sa résistance thermique. Des tests par DMA ont été effectués sur le PLA et les mélanges pour estimer leur tenue mécanique vis-à-vis de la température. La résistance au test impact Izod et les propriétés de traction ont été mesurées selon les standards ASTM. Une dispersion micrométrique du modifiant choc a été obtenue en présence du compatibilisant. Une estimation de la taille des cristaux de PLA par microscopie optique polarisée a été réalisée. Une augmentation significative de la ténacité des mélanges a été mesurée avec seulement 10 % en poids d’additifs. Les échantillons recuits ont montré les meilleures propriétés en impact avec une résistance atteignant 68 kJ/m2, soit 20 fois celle du PLA. ---------- Biobased polymers have been widely studied as substitutes for petroleum-based materials. Among these polymers, polylactide (PLA) has gained commercial acceptance in thermoformed and blow molded packaging applications because of its transparency, high tensile modulus and strength, and its cost competitiveness. However, the low impact strength of PLA and its poor temperature resistance have prevented its widespread use in many industrial applications. The present study focuses on the improvement of impact properties and particularly on the interaction between crystallinity development and mechanical properties of PLA-based blends. The PLA was toughened by the addition of a random linear ether-amide copolymer (Pebax 3533TM) that acted as an impact modifier. A random copolymer of ethylene, methyl-methacrylate and glycidyl-methacrylate (Lotader AX8900TM) was also used to reactively compatibilize the ether-amide copolymer with the PLA matrix. The rheological, mechanical and thermal properties of quenched and annealed blends and their morphology were investigated. In terms of melt rheology, the blends were investigated in oscillatory shear to determine if the impact modifiers could increase the melt strength of the material and its thermal stability. The Izod impact resistance and tensile properties were measured using standard testing protocols. The thermal resistance of the annealed blends was examined using dynamic mechanical analysis. A micron-size dispersion of the impact modifier was achieved in the presence of the reactive compatibilizer. Besides, the morphology of the crystals was analyzed using a polarized optical microscope. Significantly improved impact strength was found with as low as 10 wt% additives. Annealed samples showed the highest impact strength with values attaining 68 kJ/m², 20 times the one of PLA

A Useful Biomass Component for Simple Fabrication of the Honeycomb Poly(L-lactide) Film

This concept is the development of useful material based on biomass such as a poly(L--lactide)[PLLA] with new added-value to extend applications. PLLA, which is an attractive raw material produced from renewable resources, has received much attention for applications in bioabsorbable and biodegradable materials. However, PLLA is not utilized well for practical use. This paper has explored an additive compound, which is a biocompatible, to facilitate a regular patterned porous film from PLLA to provide a valuable material. The method we adopted was to form a regular pattern on polymer film containing a surfactant in order to help the amphiphilic polymer to migrate at the interface between the organic solvent and the water droplets as the water-assisted formation method. To give the regular patterned porous film, some compounds from biomass were used for the water-assisted formation method. As surfactants in PLLA solutions, the experimental results showed the effectiveness of soy-bean oil. The pore size and surface morphology on the film can be controlled through the moisture condition, the PLLA concentration, and the molecular weight of PLLA

Do photosynthetic cells communicate with each other during cell death? From cyanobacteria to vascular plants

As in metazoans, life in oxygenic photosynthetic organisms relies on the accurate regulation of cell death. During development and in response to the environment, photosynthetic cells activate and execute cell death pathways that culminate in the death of a specific group of cells, a process known as regulated cell death (RCD). RCD control is instrumental, as its misregulation can lead to growth penalties and even the death of the entire organism. Intracellular molecules released during cell demise may act as ‘survival’ or ‘death’ signals and control the propagation of cell death to surrounding cells, even in unicellular organisms. This review explores different signals involved in cell-cell communication and systemic signalling in photosynthetic organisms, in particular Ca2+, reactive oxygen species, lipid derivates, nitric oxide, and eATP. We discuss their possible mode-of-action as either ‘survival’ or ‘death’ molecules and their potential role in determining cell fate in neighbouring cells. By comparing the knowledge available across the taxonomic spectrum of this coherent phylogenetic group, from cyanobacteria to vascular plants, we aim at contributing to the identification of conserved mechanisms that control cell death propagation in oxygenic photosynthetic organisms.Fil: Aguilera, Anabella. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Distefano, Ayelen Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; ArgentinaFil: Jauzein, Cécile. No especifíca;Fil: Correa Aragunde, Maria Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; ArgentinaFil: Martinez, Dana Ethel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Martin, María Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; ArgentinaFil: Sueldo, Daniela Jorgelina. Norwegian University of Science and Technology; Norueg

Changes in community assemblages during the development of a thin layer of phytoplankton (TLP)

ASLO 2021 Aquatic Sciences Meeting, 22–27 June, VirtualHigh resolution measurements of phytoplankton (from pico- to mesoplankton) and physicochemical parameters were made from 2 to 14 July, 2018 in a coastal embayment (Ría de Pontevedra, NW Spain). The main objective of this work was to study changes in phytoplankton community structure during the development of a phytoplankton thin layer. The observational approach highlighted the role of short term changes of abiotic and biotic habitat conditions in the dynamics of phytoplankton assemblages. During relaxation conditions in the beginning of the cruise, small rounded dinoWagellates Alexandrium minutum (PSP toxins) and Scrippsiella cf. dominated. Then, during the transition from downwelling to upwelling conditions, a thin layer was formed, composed of Pseudo-Nitzschia spp (ASP toxins) and Leptocylindrus danicus. Fine spatial (cm-m) and temporal (hours-days) scale measurements were carried out. A combination of traditional microscopy analysis (279 samples analyzed at species level when possible) and imaging-in-Wow technique for morphometric characterization (280 samples generating about 480000 raw images, containing plankton, detritus and mineral particles) allowed us to assess the effect of the environmental =ltering on phytoplankton morphological and functional traits. The dynamics of co-occurring populations of Pseudo-nitzschia spp and Alexandrium minutum was considered in the frame of changing habitat conditionsThis study was funded by project REMEDIOS (CTM2016-75451-C2-2-R).N

Future HAB science: Directions and challenges in a changing climate

There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends

Biological flora of Central Europe: Cyperus esculentus L

This paper presents information on all aspects of the biology of Cyperus esculentus L. (yellow nutsedge) and deals with its taxonomy, morphology, genetic diversity, distribution, habitat requirements, ecology and life cycle, with special emphasis on uses and cultivation, history of introduction, impact and management in Europe. C. esculentus is a tuber geophyte and most likely originates from the Mediterranean and Southwest Asia. It is a variable plant and four wild-type varieties are presently recognized, in addition to a cultivated form. C. esculentus reproduces primarily by its underground tubers, although abundant seeds are produced. In temperate climates, tubers usually sprout in late spring and the plant withers at the beginning of the winter. C. esculentus is only cultivated in the València region in Spain. Invasion foci emerged across Europe at the beginning of the 1980s and at present, C. esculentus is most abundant on arable land and in ruderal habitats, followed by riverine vegetation. In heavily infested regions of Europe, C. esculentus causes substantial yield losses in field crops and although different management strategies are available, C. esculentus remains difficult to control.Follak, S.; Belz, R.; Bohren, C.; Castro, OD.; Guacchio, ED.; Pascual-Seva, N.; Schwarz, M.... (2016). Biological flora of Central Europe: Cyperus esculentus L. Perspectives in Plant Ecology, Evolution and Systematics. 23:33-51. doi:10.1016/j.ppees.2016.09.003S33512

Étude de la microstructure et du comportement mécanique de la fibre de soie

Natural polymers seem to be more and more a credible alternative for many applications such as technical or biomedical applications. They have evident qualities such as modularity, durability, and usually biocompatibility. Nevertheless a detailed understanding of the mechanisms governing the behaviour of these materials is difficult and usually incomplete. This study deals with the understanding of the relationship between the mechanical behaviour and microstructure of silk fibres. Precise mechanical characterization has been carried out, sometimes with original experiments such as the association of a mechanical testing machine and electronic microscopy. Hence, it has been shown that silk presents a composite behaviour and all its constituents are important explaining the mechanical behaviour of industrial silk yarns. This behaviour has been described under different atmospheric conditions of temperature and humidity. This characterization has been linked with a microstructural description using X-ray diffraction and Raman spectroscopy techniques. Notably, Raman spectrometry has been associated with an in situ mechanical tester machine. This has permitted a discussion about the link between microstructure and mechanical behaviour. In this way, it has been proved that it is possible to control microstructure and mechanical behaviour using biotechnologic methods at the genetic level. This opens new ways for promising improvements for such material. Finally, a model has been developed, which is simple but effective, based on a physical description of the material. This has validated the advances, made in this study, into the understanding of silk. These results are expected to encourage other numerical studies on assemblies, in order to bring a new point of view about industrial products.Les polymères naturels présentent de plus en plus une alternative crédible pour de nombreuses applications techniques et biomédicales. Ils possèdent des qualités de modularité, de durabilité, souvent de biocompatibilité, qui leurs sont propres. Mais la compréhension détaillée des mécanismes qui gouvernent le comportement de tels matériaux est difficile et reste souvent incomplète. Cette étude a cherché à mieux comprendre le lien qui existe entre le comportement mécanique et la microstructure pour la fibre de soie. Une caractérisation minutieuse du comportement mécanique a donc été effectuée par des moyens parfois originaux comme l'association entre une machine de traction et une observation en microscopie électronique. Il a ainsi été montré l'aspect composite du fil de soie industriel et l'importance des différents éléments constitutifs de la soie. Le comportement de la fibre a également été décrit dans différentes conditions atmosphériques d'humidité et de température. Cette caractérisation s'est accompagnée d'une description de la microstructure en utilisant des techniques telles que la diffraction aux rayons X et la spectrométrie Raman. Notamment, la spectrométrie Raman a pu être associée à une traction in situ. Ceci a permis d'établir des liens entre mécanique et microstructure. Il a ainsi été prouvé notre capacité à modifier la microstructure et le comportement mécanique de la soie par voie biotechnologique en modifiant le génome du Bombyx mori. Ce qui ouvre une nouvelle voie d'innovation prometteuse pour améliorer ce type de matériau. Enfin, une modélisation simple mais robuste basée sur une description physique du matériau a permis de valider les avancées faites quant à la compréhension de ce polymère. Le comportement en environnement contrôlé a été étudié. Ces résultats pourraient alimenter des études numériques sur des assemblages, plus proches du produit fini