Acétate de cellulose

Résumé

L'acétate de cellulose est une matière plastique inventée en 1865. C'est l'ester acétate de la cellulose. Sous forme de fibres (fil textile, autrefois appelée acétol), ce produit a été vendu sous le nom de rayonne, soie artificielle, viscose, etc. L'acétate de cellulose a connu de nombreux usages, comme base de films en photographie, vernis (dont pour l'aéronautique lors de la Première Guerre mondiale), comme faux-émail ou encore comme composant de certains adhésifs ou explosifs ; on l'utilise encore comme matière plastique, par exemple dans les montures de lunettes ou les poignées de tournevis. Plus récemment, il est utilisé pour la confection de cartes à jouer (notamment la marque Kem) ou même de filtres à cigarettes. Histoire Paul Schützenberger prépare, dès 1865, un acétate de cellulose, mais il est difficile à dissoudre et donc à utiliser. En 1894, et Edward John Bevan déposent un brevet pour la fabrication de l'acétate de cellulose qui deviendra le procédé indu

Source officielle

https://fr.wikipedia.org/wiki/Ac%C3%A9tate_de_cellulose

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Surfactant-mediated interaction of fragrances with cellulose model surfaces

Mahtab Varnous

Odor perception may be considered from different perspectives: the physicochemical properties of odorants and target surfaces of interest, the biological aspects of electing odorant molecules by odorant receptors and their related downstream cellular signaling, and finally the physiological dimension of the sensing individual. This work concentrates on physico-chemical investigations, with the objective of developing novel analytical approaches to study in real time how odorant molecules together with their surfactant matrix interact with target surfaces of interest. Specifically the work presented in this thesis, deals with perfume-surfactant adsorption on cellulose model layers which should mimic the cotton fibres of fabrics. Surface sensitive attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy has been used to monitor the perfume-surfactant adsorption process. The thesis is structured as follows: The first part concerns the preparation of cellulose model surfaces. Cellulose layers with thicknesses in the range of 50-500 nm have been achieved by first spin coating of trimethysilylcellulose (TMSC) on silicon wafers or ATR-Ge crystals followed by a simple regeneration procedure. Physicochemical characterisation of these layers was performed by different techniques. The second part focuses on surfactant-perfume system. Multilamellar, sonicated and extruded vesicles of cationic surfactant dimethyldioctadecyl-ammonium chloride (DODAC), as commercially used in formulations containing fragrances, were prepared and used to entrap the perfumes. Theses vesicles were characterized by spectroscopic and microscopic techniques. Finally in the last part of this work, the adsorption and desorption kinetics of vesicles and fragrances on cellulose model surfaces are presented. The experiments were performed using an ATR-FTIR flow cell with different DODAC-perfume dispersions. The results obtained for adsorption of perfumes and surfactants to the cellulose model surfaces were compared with experiments performed on real cotton fabric.

EPFL2006

Chargement

Foaming Biocomposites of Microfibrillated Cellulose and Polylactic Acid Paper

Carole Boissard, Pierre-Etienne Bourban, Mallory Genoud, Jan-Anders Månson, Razvan Cristian Neagu

2011

Chargement

With the unsustainable use of fossil fuels increasing strains on human institutions and ecosystems, the development of a renewable energy alternative is of paramount importance. Second generation biorefineries, based on the production of fuels and chemicals from lignocellulosic biomass, appear as attractive alternative to their non-renewable counterparts. Within the multiplicity of existing valorisation routes, enzymatic hydrolysis of lignocellulosic biomass into its constituent sugars has generated considerable interest, notably in the context of biofuels production. However, major hurdles stemming from the intricate structure of the lignocellulosic feedstocks still impede large-scale deployment of this process. The multiplicity of highly intertwined spatiotemporal factors impacting the enzymatic hydrolysis of lignocellulosic biomass represents a challenge to rationally design efficient hydrolysis process. Here, we propose a theory-based modelling framework relying on pore-diffusion and surface reaction to explore the effects of recognised bottlenecks on the enzymatic hydrolysis of lignocellulosic substrates. The model is based on a set of partial differential equations describing the evolution of the substrate morphology to investigate the interplay between experimental conditions and the physical characteristics of biomass particles as the reaction proceeds. The overall quantity of cellulase present in the hydrolysis mixture is carefully considered to investigate its interplay with the available accessible cellulose surface. Also, non-uniformity in terms of cellulose accessibility and cellulose digestibility are introduced in the model to weight their influence on observed hydrolysis rates. Finally, deactivation mechanisms are considered through unproductive adsorption of cellulases on both cellulose and lignin fractions, with the existence of such phenomena alleged to be critical in the efficiency of the hydrolysis process. Based on predictions of our model, we were able to confirm the critical role of cellulose accessibility, as defined by the combination of particle size, porosity and accessible cellulose surface, in dictating early reaction rates for a range of pretreated beech wood substrates. While high biomass loading should be favoured to improve enzyme penetration in the substrates, high enzyme loadings going beyond the initial number of cellulose adsorption appeared beneficial in notably two cases: (i) to promote internal diffusion in large particles and (ii) counteract undesired enzyme adsorption on lignin. For the latter, a relatively low increase in enzyme loading was sufficient to offset the resulting slowdown. We also showed that the existence of structural heterogeneities, and in particular non-uniform pore volume distribution within the lignocellulosic samples, contribute to the rate slowdown observed at later stage of the hydrolysis, while not explaining it in its entirety. Unproductive adsorption to cellulose, coupled to decrease in the cellulase efficiency at the cellulose surface, appeared as major contributor to the rate slowdown. Overall, we show how the use of a theory-based model can help decouple and evaluate the effects of key factors in the enzymatic hydrolysis of lignocellulosic biomass. As such, our model can help pave the way towards efficient integrated rational design strategies for enzyme process engineering for biomass conversion.

EPFL2021

Chargement

EPFL2021

Surfactant-mediated interaction of fragrances with cellulose model surfaces

Mahtab Varnous

EPFL2006