Cellulose consolidation under high-pressure and high-temperature uniaxial compression

Materials based on cellulose cannot be obtained from thermoplastic processes. Our aim is to prepare all-cellulose materials by uniaxial high pressure thermocompression of cellulose. The effect of moisture content (0–8 w/w%) and temperature (175–250 °C) was characterized through the mechanical properties (bending and tensile), morphology (scanning electron microscopy, X-ray tomography) and microstructure (viscometric degree of polymerization, Raman spectroscopy, X-ray diffraction, solid-state NMR) of the specimens. The specimens were mechanically stronger in bending than in tension. They exhibited a more porous heart, a dense but very thin skin on the faces (orthogonal to the compression axis) and thick and extremely dense sides. During thermocompression severe friction between fibers caused a decrease in molecular weight while heating above the glass transition temperature was responsible for water migration towards the specimen heart. Most of the cohesion came from the small sides of the test samples (parallel to the compression axis) and seemed mainly related to the entanglement of amorphized cellulose at the interface between particles. Around 200 °C water accumulated and provoked delamination upon pressure release, but at higher temperatures water, in a subcritical state, may have been consumed during the hydrolysis of amorphous cellulose regions. The all-cellulose material with the best mechanical properties was obtained at 2% moisture and 250 °C. This work shows that thermocompression at high temperature with limited moisture may be viable to produce renewable, sustainable all-cellulose materials for application in biobased plastic substitutes including binderless boards

Automatisation du comptage et de la reconnaissance des espèces dans les passes à poissons par l'analyse de séquences d'images

Window panes are used to observe and count by species the fish which cross fish passes. Our goal is to automate this work by using a vision system. / Ce mémoire décrit les différentes étapes de l'étude menée pour automatiser le comptage et la reconnaissance des espèces par l'analyse de séquences d'images. Le chapitre I présente le contexte de l'étude. Le chapitre II développe les principes théoriques utilisés : reconnaissance de formes, reconnaissance d'espèces, processus de suivi des poissons développé pour le comptage. Le chapitre III présente la mise en oeuvre matérielle et logicielle des principes décrits.Dans le chapitre IV, les résultats obtenus sont exposés et commentés

Williams, S. Kim R.; Caldwell, Karin D. (Eds.) : Field-flow fractionation in biopolymer analysis

Book’s topic This book covers the application of field-flow fractionation (FFF) to different biopolymers, for (bio)medical applications (medical research, pharmaceutical industry, diagnostic), but also food, membrane technology, etc. FFF is a relatively old method which has encountered new youth and strong development in recent years. The book focuses mainly on asymmetric flow field-flow fractionation (AF4), which dominates the literature and the market, but other methods are also described and assessed

Using apparent molecular weight from SEC in controlled /living polymerization and kinetics of polymerization

Apparent molecular weights from size exclusion chromatography, that is molecular weights relative to standards of a nature different to that of the polymer sample being studied, are frequently used. We use calculations corresponding to realistic cases to provide guidelines for situations when, and to what extent, apparent molecular weights (MWs) can be meaningful. In controlled polymerization, we show how, without due care, use of apparent MW, could lead to the incorrect conclusion that the reaction was not controlled, whereas the true MWs would be close to theoretical values. We show here that the quality of the eluent as a solvent for the standard and the polymer sample is a good indication of the accuracy and the significance of the apparent polydispersity index. Accurate Mark–Houwink–Sakurada parameters are of limited availability, but the data about solvent quality available in handbooks or available from static light scattering measurements. Apparent Mn is of no use in controlled polymerization if simple simulations as performed in this work do not validate their use. The determination of transfer constants by the Mayo plot can be performed using apparent Mn without introducing any significant error, contrary to apparent weight-average molecular weight Mw or apparent ln number distribution

Etudes de la synthèse et de la structure par microscopie et spectroscopie électroniques de nanotubes de carbone purs et dopés à l'azote

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Cinétique de la polymérisation radicalaire des acrylates par polymérisation par LASER pulsé et chromatographie d'exclusion stérique multi-détection (PLP-SEC) (analyse critique)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Système de vision pour la surveillance des passes à Poissons

Le but de cet article est de présenter un système automatique pour la surveillance des passes à poissons basé sur l'analyse d'images (comptage et identification des espèces). Le système proposé fonctionne en deux phases : la première est une phase d'enregistrement sur le site d'images comprimées, la deuxième consiste en un dépouillement automatique des enregistrements. Ce dernier met en oeuvre un processus de suivi pour accomplir le comptage et un processus de reconnaissance d'espèces qui utilise, après extraction de caractéristiques pertinentes, une règle bayésienne de classement avec rejets

Image sequence processing to supervise fish passes

This paper presents an automatic system of fish identification and counting using image sequences taken in fish passes. At first, real time is not considered and, so, images have to be stored. We present the electronic system designed to code and store them in real time, on optical disks in files of sequences. Then, we describe the tracking process implemented to count the fish when they cross the pass from down-river to up-river, the recognition process and the overlap problem. A result file can be edited by a human operator. Obtained results are satisfactory with regard to static recognition and are improved by the temporal redundancy generated by the tracking process. The processing time is, on average, lower than the storage time and thus there is no data accumulation

Size-exclusion chromatography (SEC) of branched polymers and polysaccharides

Branched polymers are among the most important polymers, ranging from polyolefins to polysaccharides. Branching plays a key role in the chain dynamics. It is thus very important for application properties such as mechanical and adhesive properties and digestibility. It also plays a key role in viscous properties, and thus in the mechanism of the separation of these polymers in size-exclusion chromatography (SEC). Critically reviewing the literature, particularly on SEC of polyolefins, polyacrylates and starch, we discuss common pitfalls but also highlight some unexplored possibilities to characterize branched polymers. The presence of a few long-chain branches has been shown to lead to a poor separation in SEC, as evidenced by multiple-detection SEC or multidimensional liquid chromatography. The local dispersity can be large in that case, and the accuracy of molecular weight determination achieved by current methods is poor, although hydrodynamic volume distributions offer alternatives. In contrast, highly branched polymers do not suffer from this extensive incomplete separation in terms of molecular weight