Starch-cellulose crosslinking - Towards a new material

International audienceThis work describes a simple method for direct cross-linking of modified polysaccharides. Azide cellulose and alkyne starch were synthesized using classical methods. The two components were cross-linked in the presence of Cu(I) catalyst, a type of Huisgen's 1,3-dipolar azide-alkyne cycloaddition which is also defined as a "click chemistry" reaction, leading to the formation of starch crosslinked to cellulose. The modified polysaccharides were characterized by NMR, FTIR and X-ray photoelectron spectroscopies and the resulting material was analyzed using scanning electron microscopy (SEM)

Réticulation de fibres lignocellulosiques et d amidon (Vers de nouveaux matériaux pour l industrie papetière)

Au travers de ce manuscrit, nous présentons la mise au point d'une réaction de réticulation entre l'amidon et les fibres lignocellulosiques de la pâte à papier. Ce travail a pour but d'explorer de nouveaux champs d'applications, et de nouvelles voies de valorisations des pâtes papetières. La réticulation permet à la fois d'intégrer l'amidon à la pâte, et de former un réseau tridimensionnel renforcé, pouvant conduire à de nouveaux matériaux plus résistants. Nous avons choisi, pour ce couplage, la cycloaddition 1,3-dipolaire de Huisgen catalysée par le cuivre. Deux approches de synthèse ont été envisagées. D'une part, l'amidon propargylées. Dans le but de nous affranchir des solvants organiques, nous avons étudié les réactions de propargylation et de tosylation des fibres lignocellulosiques dans l'eau, en utilisant la cellulose microcristalline comme modèle pour la mise au point. L'étude a tout d'abord été réalisée dans le système NaOH/H2O, puis la soude a été remplacée par du chlorure de sodium. La réaction de couplage a été réalisée dans l'eau. L'analyse des précurseurs et des produits de réticulation a été effectuée par XPS, DRX, MEB, et par une série de tests physiques. L'évaluation des propriétés physiques des différentes feuilles intégrant des fibres lignocellulosiques modifiées, et d'amidon modifié, nous a permis de confirmer le couplage. Les valeurs de résistance des feuilles, contenant l'amidon azidé et les fibres propargylées, se sont montrées nettement supérieures aux feuilles de pâte Kraft de références.Through this work, we present the development of a crosslinking reaction between starch and lignocellulosic fibers of the pulp. This work aims to explore new applications and new ways of valuation of paper pulp. This crosslink incorporates both starch and pulp to create a strengthened three-dimensional network, which could lead to more resistant material. The 1-3 dipolar cycloaddition reaction of Huisgen catalised by copper was chosen for this crosslink. Two synthetic routes have been tested. First, propargyled starch was coupled with azitated pulp fibers, and secondly, azitated starch was coupled with propargyled pulp fibers. In order to avoid organic solvents, the propargylation and tosylation of lignocellulosic fibers were studied in water, using microcrystalline cellulose as a model for development. The first approach was conducted thanks to the system NaOH/H2O, then soda was replaced by sodium chloride. The crosslinking reaction was carried out in water. The analysis of precursors and products of crosslinking was performed by XPS, XRD, SEM and by a serie of physical tests. The evaluation of physical properties of various sheets, incorporating modified lignocellulosic fibers and modified starch, confirmed the chemical crosslinking. The resistance values of the sheets containing azidated starch and propargyles fibers, are superior to those of the reference sheets with Kraft pulp.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Pyrimidine-purine and pyrimidine heterodinucleosides synthesis containing a triazole linkage.

International audienceThis article describes a synthetic route to generate two purine-pyrimidine and pyrimidine heterodinucleosides. Both microwave activated regioselective alkylation using hydride and copper-catalyzed-azide-alkyne-cycloaddition (CuAAC) were used in order to perform the synthesis

Advances in cellulose chemistry - Microwave-assisted synthesis of propargylcellulose in aqueous medium

International audienceA fast and simple reaction activated by microwave irradiation permits the "green synthesis" of propargylcellulose in an aqueous alkaline medium. The influence of several reaction parameters such as amount of propargyl bromide, reaction time or microwave activation on the reaction efficiency are reported herein. The propargylcellulose samples obtained, with degrees of substitution (DS) from 0.35 to 1.88, were characterised by means of FTIR and NMR spectroscopy

Tosylcellulose synthesis in aqueous medium

International audiencep-Toluenesulfonyl cellulose was prepared by reacting cellulose in aqueous medium, instead of via traditional routes, which involve the use of DMAc/LiCl, or more recently, ionic liquids. The influence of several parameters on the reaction efficiency has been studied; amount of tosylchloride, presence of triethylamine, reaction time and use of sodium hydroxide or sodium chloride. The resulting p-toluenesulfonyl cellulose samples were characterized by means of FTIR and NMR spectroscopy. The effects of solvent on the crystalline change during tosylation were investigated by X-ray diffraction (XRD). The degree of substitution (DS) was determined by 1H NMR and confirmed by X-ray photoelectron spectroscopy (XPS). Tosylcelluloses with DS from 0.1 to 1.7 have been prepared

Synthesis of meso-substituted dipyrromethanes using iodine-catalysis

International audienceThis Letter presents a non-conventional synthesis of meso-substituted dipyrromethanes, using molecular iodine as the catalyst. Various aromatic dipyrromethanes were obtained in good yields after a preliminary study using nitrobenzaldehyde. The reactants and reagents were used as such, without prior distillatio

Chitosan as an adhesive

International audienceChitosan is a well-known polysaccharide abundantly published during the last decades. This heteropolymer, composed of 2-acetamido-2-deoxy-d-glucopyranose and 2-amino-2-deoxy-d-glucopyranose, is obtained after alkaline deacetylation of chitin from crustaceans, fungi and other non-vegetable organisms. Soluble only at acidic pH, it is the unique polycationic polysaccharide extracted from bioresources. This characteristic gives to it original and specific properties finding some applications in several industrial fields but especially in the biomedical one because of its biocompatibility and its non-toxicity. Besides these traditional applications other ones begin actually to appear in the literature. They focus on the development of chitosan-based adhesives, binders or films. This review synthetizes the state of the art on this domain, but also deals with the assessment of chitosan environmental impact

Chemical Modification of Kraft Cellulose Fibres: Influence of Pretreatment on Paper Properties

Chemical modifications of cellulose fibres (kraft pulp) in NaOH/H2O and NaCl/H2O systems were investigated. Handsheets were prepared that contained 25% of the modified fibres. Changes in the modified samples were examined by measuring their mechanical and optical properties and comparing them to those made with unmodified fibres. The observed differences were explained and supported by structural analyses, by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the NaOH/H2O pretreatment led to a significant deterioration of optical and strength properties of the handsheets. These modifications affected both the inner part of the crystalline cellulose (change from cellulose I to cellulose II) and the morphology of the fibers. Conversely, these properties slightly improved after propargylation, due to the propargyl functional groups. For the NaCl/H2O system, a significant enhancement of the mechanical properties of the handsheets was noted, such as an increase of up to 108% of the tear index. The propargylation further increased the tear index (by 157%). These enhancements were not accompanied by significant changes at both the micrometric and nanometric scales, except for the increase of the crystallinity index after propargylation

Polysaccharides: The "click" chemistry impact

International audiencePolysaccharides are complex but essential compounds utilized in many areas such as biomaterials, drug delivery, cosmetics, food chemistry or renewable energy. Modifications and functionalizations of such polymers are often necessary to achieve molecular structures of interest. In this area, the emergence of the "click" chemistry concept, and particularly the copper-catalyzed version of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides, had an impact on the polysaccharides chemistry. The present review summarizes the contribution of "click" chemistry in the world of polysaccharides