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Kathirgamanathan, Kalyani. "Modifications of cellulose using ionic liquids." Thesis, University of Auckland, 2010. http://hdl.handle.net/2292/5949.
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This project was focused on the modications of cellulose using ionic liquids. Cellulose is the most highly abundant natural biopolymer on earth. However the utilisation of cellulose requires chemical modication or physical dissolution in a suitable solvent. Recently ionic liquids have become the solvent of choice for cellulose and other biopolymers. This is because of their unique solvency power and the desirable properties such as non-ammability, thermal stability, and recyclability. The use of cellulose/ionic liquid combinations not only supports the green chemistry concept but also helps in the development of sustainable resources which could be used as replacement for petroleum feed stocks. In this research ionic liquids were used to dissolve cellulose. The ionic liquids used in this study were 1-butyl-3-methylimidazolium chloride, 1-allyl-3- methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate. Rheology, heating FTIR and Raman studies were performed with ionic liquids and cellulose solutions to understand the properties of ionic liquids and cellulose solutions. The spectra from the heating studies were subjected to two dimensional correlation analyses. The rheology studies suggest that the ionic liquids themselves exist in two states, liquid state and a network state and the two dimensional analyses of the heating spectra reveals that the hydrogen bonding between C2H of the imidazolium ring, anion and moisture was responsible for this network formation. The cellulose was regenerated or fractionally precipitated from solutions using water, ethanol or acetonitrile as non-solvent. This investigation suggests that protic solvents like water and ethanol are good solvents for gel formation and acetonitrile is a desirable solvent for fractionation. The regenerated and fractionated cellulose samples were characterised by SEM, NMR, FTIR, XRD, DSC, TGA and SEC-MALLS analyses. Nano/sub-micron sized particles of cellulose were produced from the fractionation of cellulose from solutions in 1-ethyl-3-methylimidazolium acetate. SEC-MALLS data indicate that fractionation according to molecular weight is possible with dilute solutions in ionic liquids. It was also observed that samples regenerated from solutions in 1-ethyl-3-methylimidazolium acetate were more ordered than the samples regenerated from chloride containing ionic liquids. These preliminary results show that the use of ionic liquids in the processing of cellulose has the potential to have many possible applications.
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Mangiante, Gino. ""Green" and innovative chemical modifications of cellulose fibers." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0024.
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Ce projet de recherche mené en collaboration avec le CTP (Centre Technique du papier) a eu comme objectif de mettre en place une stratégie de greffage de polymères sur des fibres de cellulose via « Chimie Click » dans l’eau et dans des conditions douces et respectueuses de l’environnement afin de conférer de nouvelles propriétés mécaniques aux papiers résultants. La première étape a été d’élaborer une fonctionnalisation alcyne des fibres dans des conditions douces – dans l’eau ou dans un mélange eau/isopropanol – permettant à la fois une fonctionnalisation conséquente tout en préservant la cristallinité de la cellulose, la structure fibre et les propriétés mécaniques. Différentes méthodes de microscopie ont été utilisées pour mieux comprendre l’impact de la fonctionnalisation sur les propriétés mécaniques. Afin d’améliorer les propriétés mécaniques du papier, le greffage sur les fibres de polyéthers d’alkyle fonctionnalisés azoture a été réalisé dans l’eau par cycloaddition de Huisgen d’azoture-alcyne catalysée par le cuivre (II) (CuAAC). Plusieurs polymères de natures différentes (poly(éthylène glycol) et poly[(éthylène glycol)-stat-(propylène glycol)]), de différentes masses molaires et fonctionnalités (mono- ou difonctionnels) ont été liés aux fibres de cellulose. L’ajout de chaînes de poly(éthylène glycol) s’est avéré avoir un effet lubrifiant entraînant une légère diminution de l’indice de traction mais une augmentation importante de la flexibilité du papier. De plus, le greffage de polymères difonctionnels a démontré des propriétés originales de résistance à l’eau sans changer la nature hydrophile des fibres de cellulose. Enfin, le couplage Thiol-Yne a permis de fixer de petites molécules hydrosolubles fonctionnalisées thiol sur des fibres modifiées alcyne en s’affranchissant du cuivre nécessaire à la réalisation de la réaction de CuAAC<br>This research project, in collaboration with CTP (Centre Technique du Papier), aimed at developing chemical pathway in water to graft polymers on cellulose fibers via “Click Chemistry” in eco-friendly and non-degrading conditions conferring new mechanical properties upon the resulting paper sheets. A first step was to develop a “green” alkyne derivatization method in mild conditions – through pure water or water/isopropanol mixture – allowing for a substantial alkyne functionalization without jeopardizing the cellulose crystallinity, the fiber structure, and maintaining good mechanical properties of the cellulose fibers and resulting paper sheets. To better understand how the functionalization impacts the mechanical properties, several microscopy methods were employed. Then, aiming at improving mechanical properties of the resulting paper, grafting of azidefunctionalized polyoxyalkylenes on alkyne-modified fibers was achieved via Copper(II)-Catalyzed Alkyne-Azide Cycloaddition (CuAAC) in pure water. Water soluble polymers of different nature (poly(ethylene glycol) or poly[(ethylene glycol)-stat-(propylene glycol)]), with different molar mass and functionality (one or two azide groups per macromolecular chain) were successfully attached on cellulose fibers. Grafting of PEG chains involved a slight decrease of the tensile index but a drastic increase of the flexibility of the paper sheet. Interestingly, fibers grafted with difunctional polymers demonstrated an original water resistance maintaining the hydrophilic nature of fibers. Finally, Thiol-Yne reaction was successfully carried out to attach small water soluble thiol-bearing reagents on alkyne-functionalized fibers in water as a metal-free alternative to CuAAC reaction
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Singh, Gargi. "Effect of surface modifications on biodegradation of nanocellulose and microbial response." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/76655.
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History teaches us that novel materials, such as chlorofluorocarbon and asbestos, can have dire unintended consequences to human and environmental health. The exponential growth of the field of nanotechnology and the products developed along the way provide the opportunity for a new paradigm of design thinking, in which human and environmental impacts are considered early on in product development. In particular, nanocellulose is touted as a promising green nanomaterial, as it is sourced from an effectively inexhaustible feedstock of wood-based cellulose and is assumed to be harmless to the environment since it is derived from a natural material and assumed to be biodegradable. The various forms of nanocellulose possess an impressive diversity of properties, making it suitable for a wide variety of applications such as drug delivery, reinforcement, food additives, and iridescent make-up. However, as nanomaterials can have different properties relative to their bulk form, it is questionable whether they are truly environmentally friendly, particularly in terms of their biodegradability and potential impacts to receiving environments.
Given the projected mass-scale application of nanocellulose and the inevitability of its subsequent release into environment, the purpose of this study was to determine the biodegradability of nanocellulose and the response of environmentally-relevant microbial communities. Specifically, it was hypothesized that cellulose in the nano size range would display distinct biodegradation patterns and rates, relative to larger forms of cellulose. Further, it was hypothesized that modification of nanocellulose, in terms of morphology and surface properties (e.g., charge), would further influence its biodegradability. Wetlands and anaerobic digesters were selected as two environmentally-relevant receiving environments that also play critical roles in global carbon turnover.
To examine the biodegradability of nanocellulose, two distinct microbial consortia were enriched from wetland (W) and anaerobic digester (AD) inocula and applied in parallel experiments. The consortia were grown under anaerobic conditions with microcrystalline cellulose as the sole carbon substrate over a period of 246 days before being aliquoted to microcosms for subsequent biodegradation assays. Various forms of nanocellulose were spiked into the microcosms and compared with microcrystalline cellulose as a non nano reference. Microcosms were sacrificed in triplicate with time to monitor cellulose degradation as well as various measures of microbial community response. Microbial communities were characterized in terms of gene markers for total bacteria (16S rRNA genes) and anaerobic cellulose degraders (glycoside hydrolase family 48 genes, i.e., cel48) as well as high throughput amplicon sequencing of 16S rRNA genes (V4 region). A series of three studies examined: 1) the effect of nanocrystalline versus microcrystalline cellulose; 2) the effects of nanocellulose morphology (crystalline rod versus filament) and surface functionalization (cationic and anionic); and 3) metagenomic characterization of cellulose degrading communities using next-generation DNA sequencing.
It was found that the nano- size range did not hinder cellulose degradation, in fact, nanocrystalline cellulose degraded slightly faster than microcrystalline cellulose according to 1st order kinetics (1st order decay constants: 0.62±0.08 wk-1 for anionic nanocrystalline cellulose versus 0.39±0.05 wk-1 for microcrystalline cellulose exposed to AD culture; 0.69±0.04 wk-1 for anionic nanocrystalline cellulose versus 0.58±0.05 wk-1 for microcrystalline cellulose exposed to W). Experiments comparing the effects of surface functionalization indicated that anionic nanocellulose degraded faster than cationic cellulose (1st order decay constants for cationic nanocrystalline cellulose: 0.48±0.06 wk-1 and 0.58±0.07 wk-1 on exposure to AD and W cultures respectively). Measurements of 16S rRNA and cel48 genes were consistent with this trend of greater biological growth and cellulose-degrading potential in the anionic nanocellulose condition, suggesting that surface properties can influence biodegradation patterns. Taxonomic characterization of 16S rRNA gene amplicons suggested that taxa known to contain anaerobic cellulose degraders were enriched in both W and AD consortia, which shifted in a distinct manner in response to exposure to the different cellulosic materials. This suggests that distinct groups of microbes may drive the biodegradation of different forms of cellulose. Further, metagenomic investigation provided new insight into taxonomic and functional aspects of anaerobic cellulose degradation, including identification of enzymatic families associated with degradation of the various forms of cellulose. Overall, the findings of this study advance understanding of anaerobic cellulose degradation and indicate that nanocellulose is likely to readily degrade in receiving environments and not pose an environmental concern.<br>Ph. D.
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BAUDOIN, REMY. "Modifications chimiques de microfibrilles de cellulose en vue de rendre leur surface hydrophobe." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10052.
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La cellulose a depuis longtemps ete utilisee comme renfort dans les materiaux synthetiques ou naturels. Notre etude a porte sur la modification des microfibrilles, elements structuraux de base de la cellulose, afin de diminuer l'hydrophilie de surface. Ceci permet d'augmenter l'affinite entre les microfibrilles et des solvants organiques peu ou pas hydrophiles. La dispersion homogene des microfibrilles ainsi modifiees dans des solvants organiques permet d'envisager leur utilisation comme renfort dans des materiaux composites et nanocomposites. Pour atteindre cet objectif, nous avons modifie la cellulose par etherification en milieu basique aqueux. Trois types de reactions ont ete etudies : l'addition conjuguee (cyanoethylation) l'etherification de williamson (benzylation) et l'ouverture d'epoxydes. Apres reaction, une partie des hydroxyles de surface, responsables du caractere hydrophile de la cellulose, est substituee par des groupements fortement hydrophobes. En augmentant l'encombrement sterique a la surface des microfibrilles et limitant l'acces aux groupements alcools qui n'ont pas reagi, la floculation par formation des ponts hydrogene entre les microfibrilles peut etre evitee. On facilite ainsi la dispersion dans les solvants organiques. Les reactions d'etherification ont ete etudiees sur differentes celluloses : les microcristaux ( whiskers ) de tunicine et de coton, cellulose modele, mais surtout la cellulose de parenchyme de betterave issue des dechets de l'industrie sucriere. Differentes celluloses ont ete obtenues dont l'hydrophilie varie avec le type de substituant et le degre de substitution. Pour caracteriser le taux de greffage de la cellulose modifiee, plusieurs techniques ont ete utilisees : l'analyse elementaire, la spectroscopie infrarouge et la rmn haute resolution. La diffraction des rayons x, la microscopie electronique a transmission et la rmn du solide ont ete employees pour observer la structure et la morphologie des microfibrilles.
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Tastet, Damien. "Modulation des propriétés macroscopiques des fibres de pin maritime par polymérisation radicalaire contrôlée amorcée depuis la surface : élaboration de bio-hybrides fonctionnels." Thesis, Pau, 2011. http://www.theses.fr/2011PAUU3026/document.
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Ce travail s’inscrit au sein du projet régional de recherche BEMA (Bois Eco Matériaux Aquitaine) qui allie partenaires universitaires et industriels afin de valoriser, à travers la filière panneaux de particules, des ressources abondantes en Aquitaine : le maïs et le Pin Maritime. L’objectif de cette thèse est de greffer de manière covalente des chaînes de polymère à la surface de fibres de bois afin de modifier leur état de surface et de favoriser leur comptabilisation avec un liant naturel et/ou synthétique. Pour atteindre cet objectif, nous avons choisi d’utiliser une technique de polymérisation particulière, la polymérisation radicalaire contrôlée. Le contexte scientifique international du début de la thèse montre la faisabilité du projet de par la réalisation de plusieurs études sur de la cellulose modèle de type papier filtre. Le défi de cette thèse consiste à transposer ce mécanisme sur des fibres de bois brutes afin de leur conférer de nouvelles propriétés (résistance à l’eau, caractère fongicide, meilleure comptabilisation…). Afin d’atteindre l’objectif énoncé ci-dessus, nous avons développé plusieurs aspects de la chimie des polymères en mettant en oeuvre différentes techniques de synthèse (RAFT, NMP) mais aussi de caractérisation adaptées à la présence de fibres de bois brutes (Mesure d’angle de contact, TGA, XPS). Enfin, nous avons valorisé la présence de polymères fonctionnels en insérant à la surface des fibres de bois des nanoparticules d’oxyde de silice ou de métaux de manière contrôlée<br>This work is part of the regional research project BEMA (Bois Eco Matériaux Aquitaine) which combines academic and industrial partners to develop, through the wood pannel industry, abundant resources in Aquitaine: corn and Maritime Pine. The objective of this thesis is to covalently graft polymer chains on the surface of wood fibers in order to modify their surface properties and to facilitate their compatibilization with natural and/or synthetic binders. To achieve this goal, we chose to use a special polymerization technique, the controlled radical polymerization. The international scientific context of the beginning of the thesis shows the feasibility of the project through several studies carried out on model cellulose, such as filter paper. The challenge of this thesis is to implement this mechanism on raw wood fibers to give them new properties (water resistance, fungicidal character, best compatibilization ...). To achieve the objective stated above, we investigated several polymer synthetic pathways (RAFT, NMP) but also characterization techniques (Contact angle measurements, TGA, XPS) suitable with the presence of raw wood fibers. What’s more, we have valued the presence of functional polymers by inserting at the wood fibers surface oxide nanoparticles of silica or metal in a controlled manner
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Le, Gars Manon. "Surface modifications of cellulose nanocrystals for biobased food packaging applications Polymerization of glycidyl methacrylate from the surface of cellulose nanocrystals for the elaboration of PLA-based nanocomposites Role of solvent exchange in dispersion of cellulose nanocrystals and their esterification using fatty acids as solvents." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI021.
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Ce projet vise à développer de nouvelles modifications chimiques de surface des nanocristaux de cellulose (NCC), afin d'améliorer leur compatibilité avec le polymère biosourcé qu'est l'acide polylactique (PLA), afin de combiner leurs propriétés intrinsèques respectives. Ainsi, des matériaux multiphasiques ont été produits à partir de PLA en y incluant des nanomatériaux cellulosiques. L'application visée est celle de l'emballage alimentaire, et l'amélioration des propriétés barrières du PLA, notamment vis-à-vis de l'oxygène et de la vapeur d'eau, est alors un point clé dans la caractérisation des produits finis. Plus précisément, dans ce projet, différentes voies sont proposées pour le greffage de divers composés - polymères ou molécules - à la surface des nanocristaux de cellulose. Le succès de ces greffages a été confirmé et quantifié via diverses techniques de caractérisation. Les NCC ainsi modifiés sont ensuite introduits dans un matériau PLA à travers deux stratégies différentes : soit en tant que nanocharges dans une matrice PLA, avec des taux d'inclusion compris entre 2 et 10% massique, soit en tant que couches internes dans des matériaux multicouches de PLA. Dans les deux cas, les matériaux finaux, préparés à partir de PLA et de nanomatériaux cellulosiques modifiés, présentent des propriétés intéressantes et encourageantes en termes d'homogénéité, de transparence, et de barrière à l'oxygène et à la vapeur d'eau, conformément aux propriétés requises pour les matériaux de conditionnement alimentaire<br>The purpose of this project is to develop new surface chemical modifications of cellulose nanocrystals (CNCs), in order to enhance their compatibility with biobased poly(lactic acid) (PLA) polymer, and to combine their respective outstanding intrinsic properties. Biobased PLA-based multi-phase materials, including the designed nanostructures, are produced. Furthermore, the final materials are expected to be used in food packaging sector, and the improvement of the barrier properties of the PLA, especially towards oxygen and water vapour, is a key point in the characterization of the materials. In this project, different routes are proposed for the grafting of various compounds - polymers or singles molecules - on the surface of the CNCs. Their grafting efficiency has been confirmed and carefully characterized. The modified CNCs are then introduced in PLA-based materials via two different strategies. Indeed, they are either used as nanofillers in a PLA matrix with inclusion rates comprised between 2 and 10 wt%, or as an inner layer of PLA-based multi-layered materials. In both cases, final PLA-based materials including various designed cellulosic nanomaterials exhibit enhanced and highly encouraging properties in terms of homogeneity, transparency, and barrier towards oxygen and water vapour, in accordance with required properties for food packaging materials
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Pegg, Timothy Joseph. "Cell Wall Carbohydrate Modifications during Flooding-Induced Aerenchyma Formation in Fabaceae Roots." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1626443795433208.
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Josefsson, Peter. "Biochemical modification of wood components." Licentiate thesis, Stockholm : Fibre and Polymer Technology, KTH, the Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4171.
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Xu, Hui. "Genetic Modification of Thermotoga to Degrade Cellulose." Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1430913637.
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Persson, Per. "Strategies for cellulose fiber modification." Doctoral thesis, KTH, Fibre and Polymer Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3730.
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<p>This thesis describes strategies for and examples ofcellulose fiber modification.The ability of an engineered biocatalyst, acellulose-binding module fused to the<i>Candida antarctica</i>lipase B, to catalyze ring-openingpolymerization of e-caprolactone in close proximity tocellulose fiber surfaces was explored. The water content in thesystem was found to regulate the polymer molecular weight,whereas the temperature primarily influenced the reaction rate.The hydrophobicity of the cellulose sample increased as aresult of the presence of surface-deposited polyester.</p><p>A two-step enzymatic method was also investigated. Here,Candida antarctica lipase B catalyzed the acylation ofxyloglucan oligosaccharides.The modified carbohydrates werethen incorporated into longer xyloglucan molecules through theaction of a xyloglucan endotransglycosylase. The modifiedxyloglucan chains were finally deposited on a cellulosesubstrate.</p><p>The action of<i>Candida antarctica</i>lipase B was further investigated inthe copolymerization of e-caprolactone and D,L-lactide.Copolymerizations with different e-caprolactone-to-D,L-lactideratios were carried out. Initially, the polymerization wasslowed by the presence of D,L-lactide. During this stage,D,L-lactide was consumed more rapidly than ε-caprolactoneand the incorporation occurred dimer-wise with regard to thelactic acid units.</p><p>Morphological studies on wood fibers were conducted using asol-gel mineralization method. The replicas produced werestudied, without additional sample preparation, by electronmicroscopy and nitrogen adsorption. Information concerning thestructure and accessibility of the porous fiber wall wasobtained. Studies of never-dried kraft pulp casts revealedmicro-cavities and cellulose fibrils with mean widths of 4.7(±2) and 3.6 (±1) nm, respectively.</p><p>Finally, cationic catalysis by simple carboxylic acids wasstudied. L-Lactic acid was shown to catalyze the ring-openingpolymerization of ε-caprolactone in bulk at 120 °C.The reaction was initiated with methylß-D-glucopyranoside, sucrose or raffinose, which resultedin carbohydrate-functionalized polyesters. The regioselectivityof the acylation was well in agreement with the correspondinglipase-catalyzed reaction. The polymerization was alsoinitiated with a hexahydroxy-functional compound, whichresulted in a dendrimer-like star polymer. The L-lactic acidwas readily recycled, which made consecutive reactions usingthe same catalyst possible.</p><p><b>Keywords:</b><i>Candida antarctica</i>lipase B, cationic catalysis,cellulose-binding module, dendrimer, enzymatic polymerization,fiber modification, silica-cast replica, sol-gelmineralization, organocatalysis, xyloglucanendotransglycosylase</p>
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Eyley, Samuel. "Surface modification of cellulose nanocrystals." Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594860.
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Cellulose nanocrystal surface modification is an expanding area in cellulose research and this thesis aims to add knowledge to this growing field. Two esterification techniques new to cellulose nanocrystal research were applied successfully to the formation of esters of (methylthio)acetic add, two pyridinum substituted benzoic acids and rnethacrylic acid. The efficacy of the two methods was compared with each other and with those used in the literature. Two click chemistry reactions were also applied to cellulose nanocrystals. Azidation of chlorinated cellulose nanocrystals allowed application of copper(I) catalysed azidealkyne cydoaddition to the grafting of two irnidazoliurn salts and ferrocene to cellulose nanocrystals. Attachment of a disulfide to cellulose nanocrystais lead to a one-pot disulfide reduction and thiol Michael addition to graft cellulose nanocrystals with pentabromobenzyl acrylate. These different surface modification strategies were used to prepare a variety of surface active nanopartides for further application. Cationic cellulose nanocrystals were produced with higher surface charge density than previously reported in the literature. The cationic nature of the nanocrystals was probed using an anionic dye adsorption methodology. The variation in anion affinity for imidazolium grafted cellulose nanocrystals was determined using a batch mixing methodology with ion chromatography. Cellulose (methylthio)acetate nanocrystals were tested as a potential supported sulfur ylid in the rhodiurn(II) acetate and sulfide co-catalysed conversion of aldehydes to epoxides. This proved unsuccessful with by-products suggesting fa ilure to form supported ylids. Finally, cellulose nanocrystals were modified with a multidentate amine ligand using a diisocyanate and the resulting nanocrystals used to bind palladiurn(II) acetate. These nanocrystals were tested in Sonogashlra reactions for recydability of the palladium catalyst. Significant leaching of the palladium catalyst occurred without the use of a copper co-catalyst and the exact nature of the palladium species present on the surface of the nanocrystals remains unknown
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Bell, Thomas James. "Cellulose modification using ionic liquids." Thesis, University of Leicester, 2006. http://hdl.handle.net/2381/29976.
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The aim of this project was to investigate ways of chemically modifying cellulose using ionic liquids. Cellulose is a readily available, naturally occurring, polymeric carbohydrate which is ideal for chemical modification owing to the high density of its functional groups. However, it is insoluble in all common organic solvents. Therefore, interest has recently turned to the use of a novel class of solvents, ionic liquids, which have been found to dissolve cellulose. Initially, studies were undertaken into the acylation of simple carbohydrates using a Lewis acidic choline based ionic liquid, (ZnCl 2)2ChCl. It was found that the yields obtained were comparable to those achieved when traditional solvents and catalysts have been used. It was also found that when only one equivalent of acylating agent was used, all of the carbohydrate hydroxyl groups were acylated. This was thought to be unique to this ionic liquid system. The acetylation of cellulose was also studied in (ZnCl2)2ChCl. Here, it was discovered that the ionic liquid alters the morphology of cellulose by wetting or dissolution thus enabling a range of acetylated products to be produced. Research into the cationic modification of cellulose in an ionic liquid based on chlorcholine chloride (ClChCl) and urea was also undertaken. In this case, it was found that the ionic liquid could act as both the reagent and solvent. It was shown using this system, that all the available (surface) hydroxyl groups on cellulose were modified and that the material produced was significantly more hydrophilic than unmodified cellulose. Finally, preliminary investigations were untaken into other potential surface modifications of cellulose in ionic liquids.
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Sandberg, Birgersson Paulina. "Transparent paper: Evaluation of chemical modification routes to achieve self-fibrillating fibres." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-281347.
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Transparenta papper tillverkade av cellulosa nanofibriller (CNF), visar stor potential att kunna ersätta petroleumbaserade plaster inom många användningsområden, till exempel för mat- och varuförpackningar. CNF, även känt som nanocellulosa, kombinerar viktiga cellulosaegenskaper, med unika egenskaper hos nanomaterial. Denna kombination av egenskaper möjliggör tillverkning av ett pappers-liknande material som uppvisar både utmärkta mekaniska egenskaper och hög transparens. Användningen av nanocellulosa är dock förknippad med diverse utmaningar, för att materialet ska kunna bli kommersiellt slagkraftigt. En av de främsta utmaningarna är nanocellulosas höga affinitet för vatten och dess höga specifika yta som försvårar hanteringen av materialet. Avvattningen av nanocellulosadispersioner, för att tillverka transparenta papper, kan ta upp till flera timmar. För att övervinna detta hinder, har avdelningen för Fiberteknologi vid KTH tillsammans med BillerudKorsnäs AB, nyligen utvecklat en metodik för att skapa så kallade själv-fibrillerande fibrer (SFFer). Dessa fibrer möjliggör en snabbavvattnad papperstillverkningsprocess med makroskopiska vedbaserade fibrer, som efter tillverkning av pappret omvandlas till ett nanocellulosapapper, det vill säga ett nanopapper. För att erhålla SFFer krävs det att höga koncentrationer av karboxyl- och aldehydgrupper introduceras i cellulosafibrerna. Införandet av dessa funktionella grupper, möjliggör självfibrilleringen då SFFerna utsätts för moderata alkali-koncentrationer. I den ursprungliga studien som utfördes av Gorur m.fl., introducerades de funktionella grupperna med hjälp av sekventiell TEMPO- och periodatoxidation. I detta examensarbete, har alternativa kemiska metoder för att introducera samma kemiska funktionalitet som TEMPO-periodatsystemet undersökts. Huvudsyftet med arbetet är att besvara frågan: Hur påverkar olika kemiska behandlingar vid SFF tillverkningen, de kemiska och fysikaliska egenskaperna hos de modifierade fibrerna, samt de slutgiltiga pappersegenskaperna? För att besvara frågan, preparerades fibrer med liknande karboxyl- och aldehydinnehåll med hjälp av följande tre kemiska metoder: 1) TEMPO- följd av periodatoxidation (detta kommer att användas som referenssystem); 2) periodat- följd av kloritoxidation; 3) karboxymetylering följd av periodatoxidation. Egenskaperna hos fibrerna undersöktes med avseende på aldehyd- och karboxylinnehåll, avvattningspotential och förmåga att självfibrillera. Papper tillverkades med hjälp av en vakuumfiltreringsuppställning och följande egenskaper undersöktes hos pappret: mekaniska egenskaper (dragstyrka, brottsyrka och Young’s modul); optiska (transparens och ytreflektion); samt syrgaspermeabilitet. De erhållna fibrerna från samtliga tre kemiska modifieringar visade på självfibrillerande egenskaper i alkaliska lösningar. Detta beteende styrker hypotesen att ett strategiskt införande av ett högt karboxyl- och aldehydinnehåll leder till självfibrillerande fibrer. Transparenta papper tillverkade av fibrer som utsatts för TEMPO-periodatoxidation samt klorit-periodatoxidation, visade på utmärkta mekaniska egenskaper, hög transparens och bra barriäregenskaper - jämförbara med vad som vanligen kan noteras hos papper tillverkat av nanocellulosa. Samtliga egenskaper förbättrades ytterligare efter fibrillering av fibrerna i papperen. De karboxymetylerade-periodatoxiderade materialet, å andra sidan, uppvisade andra egenskaper jämfört med de två, tidigare nämnda, metoderna. TEMPO-periodat- och periodat-klorit-pappersmassan var halvgenomskinlig och geléliknande, medan den karboxymetylerade-periodatoxiderade massan var mer lik det omodifierade materialet. Detsamma gällde det tillverkade pappret som liknade ett konventionellt papper. Det var inte heller möjligt att åstadkomma en fibrillering av det karboxymetylerade-periodatoxiderade-pappret som utsattes för behandling med alkaliska lösningar. Avvattningstiden vid papperstillverkningen varierad mellan 4 och 60 sekunder, och karboxymetylering-periodat oxidation visade på snabbast avvattningstid. Den förlängda avvattningstiden i jämförelse med studien utförd av Gorur m.fl., tros främst bero på att ett filtreringsmembran med mindre porer användes på vakuumfiltreringsuppställningen, istället för en avvattningsvira som tidigare använts. Sammanfattningsvis så har det visat sig möjligt att tillverka självfibrillerande fibrer med hjälp av samtliga tre undersökta kemiska modifieringar. SFFer möjliggör tillverkning av snabbavvattnade transparenta nanocellulosapapper och visar på så vis på hög potential att kunna ersätta olje-baserade plaster till många förpackningsapplikationer.<br>Transparent papers made from cellulose nanofibrils (CNF), derived from e.g. wood, show great potential to replace petroleum-based plastics in many application areas, such as packaging for foods and goods. CNF, also known as nanocellulose, combine important cellulose properties with the unique features of nanoscale materials, gaining paper-like materials with outstanding mechanical properties and high transparency. However, nanocellulose faces various challenges in order to make the products commercially competitive. One of the main challenges is accompanied with nanocelluloses’ high affinity for water, which makes processing difficult. Dewatering of a nanocellulose dispersion in order to produce transparent paper may take up to several hours. To overcome this obstacle, the Fibre technology division at KTH Royal Institute of technology and BillerudKorsnäs AB have recently developed a new concept of self-fibrillating fibres (SFFs). This material enables fast-dewatering papermaking using fibres of native dimensions and conversion into nanocellulose after the paper has been prepared. In order to obtain SFFs, proper amounts of charged groups and aldehyde groups need to be introduced into the cellulose backbone. When SFFs are exposed to high alkali concentration, i.e. > pH=10, the fibres self-fibrillates into CNFs. In the original study, the functional groups were introduced through sequential TEMPO oxidation and periodate oxidation. In this work, alternative chemical routes have been examined to prepare SFFs with the same functional groups as introduced with the TEMPO-periodate system. The aim of the thesis has been to answer: how does different chemical routes to prepare transparent nanopaper made from SFFs affect the chemical and physical properties of the modified fibres, as well as the final physical properties of the transparent papers? To answer the question, fibres with similar carboxyl and aldehyde contents were prepared using three chemical routes: 1) TEMPO oxidation followed by periodate oxidation (which was used as reference system); 2) periodate oxidation followed by chlorite oxidation; 3) carboxymethylation followed by periodate oxidation. The properties of the fibres were examined regarding aldehyde and carboxyl content, dewatering potential and self-fibrillating ability. Papers were produced using a vacuum filtration set-up and the properties investigated were the mechanical; tensile strength, strain at failure and Young’s modulus, the optical properties; transparency and haze, as well as the oxygen permeability. In order to investigate the impact of the fibrillation of the papers, the properties were measured for both unfibrillated and fibrillated samples. Furthermore, the gravimetric yield after each chemical modification procedure was examined, as well as the dewatering time during sheet making. Fibres obtained from all three chemistries demonstrated self-fibrillating properties in alkaline solutions. This strengthens the hypothesis that the strategical introduction of aldehydes and carboxyl groups is the main feature responsible for the self-fibrillating ability of the fibres. Transparent papers made from fibres treated through TEMPO-periodate oxidation and periodate-chlorite oxidation showed excellent mechanical, optical and barrier properties, comparable to those seen in nanocellulose papers. The properties were further increased after fibrillation. The carboxymethylated-periodate oxidized fibres, on the other hand, behaved differently from the others. While the TEMPO-periodate and periodate-chlorite pulp was semi-translucent and gel-like, the carboxymethylated-periodate oxidized fibres resembled more the unmodified material. Likewise, the properties of those papers resembled conventional paper and no fibrillationwas experienced after immersing the papers in alkaline solution, according to the same protocol developed for the other two chemistries. The dewatering time during sheet making ranged from 4–60 seconds (carboxymethylation-periodate oxidation showing the fastest dewatering rates). The increased dewatering time compared to earlier studies is believed to mainly be due to the use of a filtration membrane on the vacuum filtration set-up, instead of a metallic wire with larger pores. Overall, SFFs was successfully produced using three different chemical routes. SFFs enables production of fast-dewatering transparent nanocellulose papers that shows the potential to replace oil-based plastics in many packaging applications.
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Lin, Ning. "Cellulose nanocrystals : surface modification and advanced materials." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI034/document.
Full textAbstract:
Ce travail porte sur les propriétés des nanocristaux de cellulose, leur modification de surface et le développement de matériaux avancés. Diverses approches sont utilisées sur ces substrats nanométriques visant à modifier leurs propriétés de surface et étendre leur utilisation dans des applications très sophistiquées, telles que la postsulfation et la désulfatation, le greffage et l'adsorption de polymères, l’oxydation sélective, le greffage moléculaire et l'inclusion "hôte-invité". Sur la base de modifications de surface, l'analyse des propriétés (pour différents taux de groupements sulfates) et divers nanomatériaux dérivés des nanocristaux de cellulose sont étudiés et préparés, notamment des nanocristaux sulfatés à différents taux, des nanocomposites extrudés, des éponges biocomposites et des hydrogels supramoléculaires. L'effet d’un gradient de groupements sulfates sur la chimie de surface, la morphologie et les propriétés physiques des nanocristaux de cellulose est discuté et notamment quatre modèles de section transversale sont comparés pour la détermination de la mesure du degré de substitution surfacique des nanocristaux de cellulose. Une stratégie nouvelle de protection impliquant une double couche polymère et la compatibilisation physique et/ou chimique des nanocristaux de cellulose est proposée afin de promouvoir à la fois la stabilité thermique des nanoparticules et la compatibilité des nanocristaux avec des matrices polymères non polaires au cours de la mise en forme par extrusion. En participant àla réticulation pour la construction de matériaux avancés, des nanocristaux de cellulose sélectivement oxydés (et de la cellulose microfibrillée oxydée pour comparaison) sont introduits dans de l'alginate pour développer des éponges biocomposites présentant une meilleure stabilité mécanique et une meilleure stabilité structurelle. Grâce à la conception intelligente par inclusion 'hôte-invité' in situ entre des nanocristaux de cellulose chimiquement modifiés et la cyclodextrine,deux polysaccharides hydrophiles sont combinés dans des hydrogels supramoléculaires pour l'administration de médicaments. En un mot, cette thèse contribue à l’avancée des nanocristaux de cellulose dans les domaines de l'analyse des propriétés et le développement des applications<br>The present work focuses on the properties of cellulose nanocrystals, their surface modification and development of advanced materials. Diverse approaches are employed on these nanoscaled substrates aiming to modify their surface properties and extend their use in highly sophisticated applications, such as postsulfation and desulfation, polymer grafting and adsorption, selective oxidation, molecular grafting, and ‘host-guest' inclusion. On the basis of surface modifications, properties analysis (for different sulfate group contents) and various nanomaterials derived from cellulose nanocrystals are investigated and prepared, including gradient sulfated nanocrystals, extruded nanocomposites, biocomposite sponges, and supramolecular hydrogels. The effect of gradient degrees of sulfate groups on cellulose nanocrystals to surface chemistry, morphology and physical properties are discussed, particularly four cross-section models are compared for the determination of the surface degree of substitution on cellulose nanocrystals. A novel strategy involving a double-polymer-layer shield and physical and/or chemical compatibilization of cellulose nanocrystals is proposed, in order to realize both improvement of thermal stability and promotion of compatibility for nanocrystals with non-polar polymeric matrices during processing by melt-extrusion. With the idea of participating as crosslinking aid for the construction of advanced materials, selectively oxidized cellulose nanocrystals (with oxidized microfibrillated cellulose as comparison) are introduced in alginate for the development of biocomposite sponges with improved mechanical stability or structural stability. Through the smart design of in situ ‘host−guest' inclusion between chemically modified cellulose nanocrystals and cyclodextrin, two hydrophilic polysaccharides are combined in supramolecular hydrogels for use as drug delivery. In a word, this dissertation contributes to the advances of cellulose nanocrystals in the topics of property analysis and application development
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Hansson, Susanne. "ARGET ATRP as a Tool for Cellulose Modification." Doctoral thesis, KTH, Ytbehandlingsteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105762.
Full textAbstract:
The importance of finding new applications for cellulose‐based products has increased, especially to meet the demand for new environmentally friendly materials, but also since the digitalization of our society will eventually decrease the need for paper. To expand the application area of cellulose, modification to improve and/or introduce new properties can be a requisite. Thus, the focus of this study has been to achieve fundamental knowledge about polymer grafting of cellulose via well‐controlled radical polymerization. Cellulose, in the form of filter paper, has successfully been grafted via activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of the monomers: methyl methacrylate, styrene, and glycidyl methacrylate. The advantages of ARGET ATRP are that only a small amount of a copper catalyst is required and the reaction can be performed in limited amount of air; yet, providing for relatively well‐controlled reactions. These benefits can render ARGET ATRP an attractive method for industrial utilization. The contact‐angle measurements of the grafted filter papers confirmed that the hydrophobicity of cellulose was significantly increased, even for shorter graft lengths. FT‐IR spectroscopy established that the amount of polymer successively increased with monomer conversion. High‐resolution FT‐IR microscopy (FT‐IRM) was proven to be a very useful technique for the analysis of cellulose substrates, displaying the spatial distribution of polymer content on cellulose fibers. The polymer was shown to be fairly homogenously distributed on the fiber. An initiator with a reducible disulfide bond rendered cleavage of the polymer grafts possible, employing mild reaction conditions. The cleaved grafts and the free polymers – formed from a sacrificial initiator in parallel to the grafting – were shown to have similar molar masses and dispersities, confirming that the grafts can be tailored by utilizing a sacrificial initiator. Moreover, the initiator content on filter paper and microcrystalline cellulose was assessed. A comparison between the two grafting techniques, grafting‐from cellulose via ARGET ATRP and grafting‐to cellulose via copper(I)‐catalyzed alkyne‐azide cycloaddition, was performed. To achieve a trustworthy comparison, the free polymer formed in parallel to the grafting‐from reaction was employed as the prepolymer in the grafting‐to approach, resulting in nearly identical graft length on the substrates for the two grafting methods. FT‐IRM analyses verified that under the selected conditions, the grafting‐from technique is superior to the grafting‐to approach with respect to controlling the distribution of the polymer content on the surface. The results were corroborated with X‐ray photoelectron spectroscopy.<br><p>QC 20121126</p>
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Moses, Alvira. "Synthesis of surface active alkanes for cellulose modification." Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/4874.
Full textAbstract:
119 leaves single sided printed, preliminary pages and numbered pages 1-101. Includes bibliography and a list of tables, figures, schemes and abbreviations. Digitized at 300 dpi (OCR), used Bizhub 250.<br>Thesis (MSc (Polymer Science))--University of Stellenbosch, 2006.<br>ENGLISH ABSTRACT: The properties and interactions of cellulose surfaces are of a great technical interest
during papermaking and recycling. Sizing, the modification of fiber surfaces, e.g. with
the purpose to reduce water penetration into the paper structure, plays an important role
in obtaining paper with good printability and water resistance. Water resistance is the key
end-property of paper being investigated in this study.
Firstly a comparison was made between the degree of surface modification of cellulose
by means of anionic, nonionic and reactive surfactants. The amount of surfactant
adsorbed by the paperboard was determined and the paper surface evaluated via scanning
electron microscopy (SEM). The sizing efficiency of the three industrial surfactants was
evaluated in order to establish the surfactant structure best suited for sizing recycled
paperboard. This was done via the Cobb test, an industrial method to measure water
uptake by paper, and contact angle measurements. The reactive surfactant was found to
have the best sizing efficiency and focus shifted to synthesizing selected copolymer
surfactants via free radical copolymerization.
Two copolymers were synthesized, with maleic anhydride as the polar part in both. Butyl
methacrylate and lauryl methacrylate were selected as the hydrophobic parts in the
respective copolymer systems. The unavailability of reactivity ratios for the respective
copolymer systems led to the use of in situ proton nuclear magnetic resonance
spectroscopy CH NMR) for the determination of the co-monomer incorporation in both
copolymer systems. Quantitative 13C NMR spectroscopy was also employed in order to
establish the co-monomer content of the isolated copolymers obtained during bench-scale
(laboratory) experiments.
Lastly, a comparison of the degree of surface modification of cellulose was made
between that which was achieved with the industrial reactive surfactant and that with the
two synthesized polymeric reactive surfactants. The two synthesized polymeric
surfactants were found to have a better sizing efficiency than the industrial reactive
surfactant, and the maleic anhydride-lauryl methacrylate copolymer system gave the best
results.<br>AFRIKAANSE OPSOMMING: Die eienskappe en interaksies van sellulose-oppervlaktes is van groot tegniese belang
gedurende die vervaardiging en hergebruik van papier. Oppervlakte behandeling, die
modifikasie van vesel-oppervlaktes bv. met die doel om water indringing in die
papierstruktuur te verminder, speel 'n belangrike rol in die daarstel van papier met goeie
drukkwaliteit en waterweerstand. Waterweerstand is die sleuteleienskap van papier wat in
hierdie werkstuk ondersoek word.
Eerstens is daar 'n vergelyking getref tussen die verandering van sellulose-oppervlaktes
deur middel van anioniese, nie-ioniese en reaktiewe sepe. Die hoeveelheid seep
geabsorbeer deur die papierbord is bepaal en die papier-oppervlak ondersoek deur middel
van skandeer-elektronmikroskopie (SEM). Die behandelingsdoeltreffendheid van die drie
industriele sepe is ondersoek om vas te stel watter seep die beste struktuur het om
hergebruikte papierbord effektief te behandel. Dit is gedoen deur middel van die Cobbtoets,
'n industriele metode om wateropname van papier te meet, asook
kontakhoekmetings. Daar is gevind dat die reaktiewe seep die beste
behandelingsdoeltreffendheid het en daar is vervolgens gekonsentreer op die bereiding
van geselekteerde reaktiewe kopolimeersepe deur middel van vryeradikaalkopolimerisasie.
Twee kopolimere is berei, met maleienanhidried as die polere gedeeite van albei.
Butielmetakrilaat en laurielmetakrilaat is gekies vir die nie-polere gedeeltes van die
onderskeie kopolimeersisteme. Die onbeskikbaarheid van reaktiwiteitsverhoudings vir
die onderskeie kopolimeersisteme het gelei tot die gebruik van in situ proton kern
magnetiese resonansie spektroskopie eH KMR) vir die bepaling van die ko-monomeer
insluiting in beide kopolimeersisteme. Kwantitatiewe koolstofdertienkemmagnetieseresonansie
spektroskopie (13C KMR) is ook gebruik om die ko-monomeerinhoud van die
geisoleerde kopolimere, verkry tydens laboratoriumeksperimente, te bepaal.
Laastens is 'n vergelyking getref tussen die graad van modifikasie van selluloseoppervlaktes
deur middel van die industriele reaktiewe seep in vergelyking met die twee
bereide polimeriese reaktiewe sepe. Daar is gevind dat die twee gesintetiseerde
polimeriese sepe beter behandelingsdoeltreffendheid as die industriele reaktiewe seep het,
met die maleienanhidried-laurielmetakrilaat-kopolimeersisteem wat die beste resultaat
lewer.
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Cobo, Sanchez Carmen. "Modification of nanofibrillated cellulose with stimuli-responsive polymers." Thesis, KTH, Skolan för kemivetenskap (CHE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156201.
Full textAbstract:
Research of new sustainable and low cost materials, such as cellulose, is of high interest. Modifications of the cellulose can be performed in order to create a “smart” material which responds to external stimuli, such as variations in pH and temperature, by changing its properties. This “smart” behavior is observed in some polymers, however, for certain applications they exhibit poor mechanical properties. These polymers can be bound by physical adsorption to cellulose, both in macro and nano scale, creating an improved “smart” composite material. In this project, thermoresponsive block-copolymers with different lengths of poly (diethylene glycol) methacrylate (PDEGMA) and poly N-(2-dimethylamino ethyl) methacrylate (PDMAEMA) in only one length, PDMAEMA-b-PDEGMA, were synthesized employing atom transfer radical polymerization (ATRP). 1H-NMR, SEC and DLS were used to characterize the block-copolymers. UV-Vis spectroscopy was employed to confirm the thermo-responsive behavior of the charged and uncharged block-copolymers, being lower for the higher molecular weight ones due to the higher polymer-polymer interactions. In a second step, PDMAEMA was charged positively by quaternization of its amine group with ICH3. Polyelectrolyte titration was used to determine the total number of charges in the quaternized block-copolymers. In addition, TEMPO-oxidized nanofibrillated cellulose (NFC) was produced by procedures found in literature. Finally, adsorption of the cationic block-copolymers onto the anionic NFC in tris base at pH 8.3 was performed and purified by consecutive filtrations, creating a novel smart composite material with different PDEGMA lengths in the block-copolymer. FT-IR confirmed that the block-copolymers were successfully adsorbed to the NFC. TGA results showed a higher thermal stability for the composite than for the TEMPO-NFC and quaternized block-copolymers. The block-copolymer modified NFC exhibited thermoresponsive behavior with LCST’s ranging from 30 to 44 °C, from higher to lower molecular weights, respectively. Adsorption of polyelectrolytes in modified cellulose could be a promising way to create smart improved materials in further research.
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GHANDCHI, PEYMAN. "Modification chimique de la cellulose par greffage d'hydrogels." Paris 6, 1999. http://www.theses.fr/1999PA066211.
Full textAbstract:
La modification chimique de la cellulose par greffage d'hydrogels de poly(n-hydroxymethylacrylamide) ou de poly(chlorure d'acryloyloxyethyltrimethylammonium) et de ses copolymeres a ete etudiee. Ces hydrogels n'ayant pas fait l'objet d'etudes anterieures, leur synthese a ete decrite et leur caracterisation structurale et physico-chimique ont ete effectuees. Les hydrogels de poly(n-hydroxymethylacrylamide) sont obtenus en absence de tout reticulant. Le chauffage de la solution de polymerisation induit des reactions d'autocondensation des groupes n-methylol, responsables de la reticulation observee. Le gonflement a l'equilibre de ces hydrogels depend de la concentration initiale en monomere et varie entre 6 et 34. Ces hydrogels ne presentent aucune interaction avec les solutions de sels et de tensio-actifs. Les hydrogels de poly(chlorure d'acryloyloxyethyltrimethylammonium) presentent des gonflements a l'equilibre de 100 a 700, ce qui leur confere un caractere de polymere superabsorbant. Ils sont cependant tres sensibles a la force ionique du milieu et a la presence de tensio-actifs. La retention de ces hydrogels sur la cellulose depend fortement de la nature de l'hydrogel et de ses groupements fonctionnels. Ainsi, du fait de leur reactivite importante, les groupements n-methylol du poly(n-hydroxymethylacrylamide) permettent une retention forte de cet hydrogel, alors que les hydrogels de poly(chlorure d'acryloyloxyethyltrimethylammonium) et de ses derives sont faiblement retenus. L'incorporation de l'hydrogel de poly(n-hydroxymethylacrylamide) accentue l'hydrophilie de la cellulose de facon importante.
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BOISSET, CLAIRE. "Modification de materiaux cellulosiques par des enzymes cellulolytiques." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10225.
Full textAbstract:
La cellulose est le biopolymere le plus abondant sur terre, et l'etude de sa degradation presente une importance ecologique et industrielle croissante. Trois aspects fonctionnels et structuraux des cellulases ont ete abordes au cours de ce travail: l'adsorption, les interactions avec la cellulose cristalline et l'organisation des differents domaines constitutifs des cellulases. Les observations faites en microscopie electronique sur la morphologie de la degradation de fibres de coton, ont permis de mieux cerner le mode d'action d'une endoglucanase, eg v de humicola insolens, sur un substrat cellulosique industriel. Grace a un immunomarquage a l'or colloidal, nous avons pu visualiser les sites de fixation de eg v a la surface des fibres de coton. L'etude de la degradation enzymatique de microcristaux de cellulose de valonia natifs et modifies par trois cellulases de humicola insolens, met en evidence que l'ultrastructure du substrat est le facteur determinant de la reactivite enzymatique. Nos travaux demontrent qu'une diminution du degre de cristallinite et une augmentation de la surface accessible entraine un accroissement important de la reactivite du substrat. Les etudes en diffusion de la lumiere ont fourni des donnees precises sur les coefficients de diffusion de trois cellulases de humicola insolens ainsi qu'une estimation de la taille hydrodynamique de ces enzymes. De plus, cette technique represente un outil interessant pour analyser les differents variants produits lors d'une approche d'ingenierie des proteines. Elle permet, en effet, de suivre le comportement en solution d'un type de proteine en fonction de differents parametres tels que la temperature, le ph et la concentration en proteines
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Missoum, Karim. "Modification chimique de surface de NanoFibrilles de Cellulose (NFC)." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-01072240.
Full textAbstract:
Les nanocelluloses connaissent un fort développement depuis ces dernières décennies et font l'objet de nombreuses études menées par les industriels et/ou consortiums académiques. Cette étude s'insère dans le cadre d'un projet européen (SUNPAP) visant à l'industrialisation des nanofibrilles de cellulose (NFC). La présente thèse fait l'état de nouveaux procédés de modification chimique de surface des NFC dans une optique de chimie verte. Plusieurs stratégies ont été développées telle que l'emploi de liquides ioniques comme solvant de réaction (décrit comme solvants verts) ou l'utilisation d'une nanoemulsion en phase aqueuse permettant le greffage de surface des NFC. Dans le but d'étudier l'impact de ces modifications chimiques, les substrats ainsi traités ont été par la suite utilisés dans diverses applications. Ainsi, des bionanocomposites ont pu être produits, l'impact sur l'introduction de NFC (modifiées ou non) dans du papier a également été étudié. Une étude sur les propriétés antibactériennes et la biodégradabilité des NFC modifiées est également proposée. Une caractérisation approfondie des NFC vierges et modifiées a été réalisée. Des techniques puissantes et innovantes ont été utilisées pour caractériser ces substrats tels que l'XPS (X-ray Photoelectron Spectroscopy) ou encore la SIMS (Secondary Ion Mass Spectrometry). Toutes ces modifications, applications et caractérisations proposées constituent une avancée et des perspectives prometteuses dans le monde des nanocelluloses.
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Meng, Xiangtao. "Chemical Modification of Cellulose Esters for Oral Drug Delivery." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71383.
Full textAbstract:
Polymer functional groups have critical impacts upon physical, chemical and mechanical properties, and thus affect the specific applications of the polymer. Functionalization of cellulose esters and ethers has been under extensive investigation for applications including drug delivery, cosmetics, food ingredients, and automobile coating.
In oral delivery of poorly water-soluble drugs, amorphous solid dispersion (ASD) formulations have been used, prepared by forming miscible blends of polymers and drugs to inhibit crystallization and enhance bioavailability of the drug. The Edgar and Taylor groups have revealed that some cellulose omega-carboxyalkanoates were highly effective as ASD polymers, with the pendant carboxylic acid groups providing both specific polymer-drug interactions and pH-triggered release through swelling of the ionized polymer matrix. While a variety of functional groups such as hydroxyl and amide groups are also of interest, cellulose functionalization has relied heavily on classical methods such as esterification and etherification for appending functional groups. These methods, although they have been very useful, are limited in two respects. First, they typically employ harsh reaction conditions. Secondly, each synthetic pathway is only applicable for one or a narrow group of functionalities due to restrictions imposed by the required reaction conditions.
To this end, there is a great impetus to identify novel reactions in cellulose modification that are mild, efficient and ideally modular. In the initial effort to design and synthesize cellulose esters for oral drug delivery, we developed several new methods in cellulose functionalization, which can overcome drawbacks of conventional synthetic pathways, provide novel cellulose derivatives that are otherwise inaccessible, and present a platform for structure-property relationship study.
Cellulose omega-hydroxyalkanoates were previously difficult to access as the hydroxyl groups, if not protected, react with carboxylic acid/carbonyl during a typical esterification reaction or ring opening of lactones, producing cellulose-g-polyester and homopolyester. We demonstrated the viability of chemoselective olefin hydroboration-oxidation in the synthesis of cellulose omega]-hydroxyesters in the presence of ester groups. Cellulose esters with terminally olefinic side chains were transformed to the target products by two-step, one-pot hydroboration-oxidation reactions, using 9-borabicyclo[3.3.1]nonane (9-BBN) as hydroboration agent, followed by oxidizing the organoborane intermediate to a primary alcohol using mildly alkaline H2O2. The use of 9-BBN as hydroboration agent and sodium acetate as base catalyst in oxidation successfully avoided cleavage of ester linkages by borane reduction and base catalyzed hydrolysis.
With the impetus of modular and efficient synthesis, we introduced olefin cross-metathesis (CM) in polysaccharide functionalization. Using Grubbs type catalyst, cellulose esters with terminally olefinic side chains were reacted with various CM partners including acrylic acid, acrylates and acrylamides to afford families of functionalized cellulose esters. Molar excesses of CM partners were used in order to suppress potential crosslinking caused by self-metathesis between terminally olefinic side chains. Amide CM partners can chelate with the ruthenium catalyst and cause low conversions in conventional solvents such as THF. While the inherent reactivity toward CM and tendency of acrylamides to chelate Ru is influenced by the acrylamide N-substituents, employing acetic acid as a solvent significantly improved the conversion of certain acrylamides. We observed that the CM products are prone to crosslinking during storage, and found that the crosslinking is likely caused by free radical abstraction of gamma-hydrogen of the alpha, beta-unsaturation and subsequent recombination. We further demonstrated successful hydrogenation of these alpha, beta-unsaturated acids, esters, and amides, thereby eliminating the potential for radical-induced crosslinking during storage.
The alpha, beta-unsaturation on CM products can cause crosslinking due to gamma-H abstraction and recombination if not reduced immediately after reaction. Instead of eliminating the double bond by hydrogenation, we described a method to make use of these reactive conjugated olefins by post-CM thiol-Michael addition. Under amine catalysis, different CM products and thiols were combined and reacted. Using proper thiols and catalyst, complete conversion can be achieved under mild reaction conditions. The combination of the two modular reactions creates versatile access to multi-functionalized cellulose derivatives.
Compared with conventional reactions, these reactions enable click or click-like conjugation of functional groups onto cellulose backbone. The modular profile of the reactions enables clean and informative structure-property relationship studies for ASD. These approaches also provide opportunities for the synthesis of chemically and architecturally diverse cellulosic polymers that are otherwise difficult to access, opening doors for many other applications such as antimicrobial, antifouling, in vivo drug delivery, and bioconjugation. We believe that the cellulose functionalization approaches we pioneered can be expanded to the modification of other polysaccharides and polymers, and that these reactions will become useful tools in the toolbox of polymer/polysaccharide chemists.<br>Ph. D.
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Erdas, Yonca. "Novel chemical modification of cellulosic substrates." Thesis, University of Manchester, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488431.
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Constrained by lack of availability of suitable land the consumption of cotton has leveled off while that of polyester has increased rapidly, the demand for clothes, which are made from cotton is increasing in the highly sophisticated countries. Cotton production is criticised as it is a polluting process and the land could be used for food production in the poor countries. Therefore much attention has been directed towards re-engineering of synthetic fibres aimed at mimicking cotton properties such as breathability, comfort, antistatic and dyeability. Even so world cotton production is still growing slowly; it is expected to increase to 20.1 m tonnes for 2003/04, according to the International Cotton Advisory Committee. It is likely that there will always be a demand for cotton, and more research will be directed to environmentally friendly cotton production, coloration and finishing. Coloration of cotton is carried out by using vat, sulphur, azoic, direct and reactive dyes. Reactive dyes are a very important group of dyestuffs for colouring cotton because of their desirable properties which include unrestricted shade range, ease of application, low cost and good fastness to light, washing and rubbing. When they are applied to cellulose by an exhaustion process, they require relatively high levels of electrolyte (salt) to increase the substantivity of the anionic dyestuff for cellulose and thereby achieve high visual colour yields. Discharge of highly saline effluent is becoming environmentally less acceptable, as increased salinity in rivers upsets the delicate balance of aquatic flora and fauna. Hence some recent developments in cotton dyeing with reactive dyes have focused on reduced salt usage. This thesis evaluates one of the options for low salt cotton reactive dyeing; chemical modification (pre-treatment) of cellulose with cationic agents. This has the effect of eliminating the inherent electrostatic repulsion between the anionic (negative) dye and the fibre, so that the use of electrolyte can either be reduced or eliminated. The (negative) surface charge of cotton was modified to a positive charge by using initially a commercial polymeric cationic fixing agent. The amount of cationic agent applied by an exhaustion technique to a cotton fabric, was quantitatively determined using Congo Red, the method being based on the titration of a known concentration of Congo Red with a solution of the treatment agent. The application of this procedure to determine the exhaustion properties of potential cationic pre-treatment agents for cotton was then studied. The pre-treated cotton was dyed to evaluate the effect of the treatment on both dye exhaustion and fixation under three different sets of dyeing conditions and a comparison was made with untreated cotton dyed conventionally. Lower colour yield, inferior wash and light fastness, shade change, ring dyeing and poor migration (levelness) were obtained on the pre-treated fabric. Therefore, pre-treatment of cotton with polymeric cationic agents was adjudged to be of no further interest. To avoid the technical problems associated with the use of polymeric pre-treatment agents, further modification of cotton was carried out with low molecular weight (monomeric) species. A systematic study of the introduction of different amino groups into cotton, via reaction with a commercially available reactive, water soluble dichlorotriazine agent followed by amination with different amines, was undertaken. Where possible, the characterization of the reaction products was made by using a variety of analytical methods. Once the resulting adducts had been characterised, the dyeing behaviour of reactive dyes on the derived substrate was evaluated. The present study also involved the synthesis and application of other pre-treatment agents, e.g. 2,4-bis(4-sulphophenylamino-)-6-chlorotriazine and dyes with a view to obtaining a better understanding of the causes of the shade changes arising from the use of cationic agents to cotton.
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Song, Delong. "Starch crosslinking for cellulose fiber modification and starch nanoparticle formation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39524.
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As a low cost natural polymer, starch is widely used in paper, food, adhesive, and many other industries. In order to improve the performance of starch, crosslinking is often conducted either in the processes of starch modification or during the application processes. Many crosslinkers have been developed in the past for crosslinking starch. Ammonium zirconium carbonate (AZC) is one of the common crosslinkers for crosslinking starch in aqueous solutions, having been widely used as a starch crosslinking agent in paper surface coating for more than 20 years. However, the mechanisms of starch crosslinking with AZC have not been well studied. In order to optimize the crosslinking chemistry of starch and find new paths for the utilization of starch in papermaking, a better understanding of the starch crosslinking mechanism is necessary.
This thesis focuses on the fundamental study of starch crosslinking in an aqueous solution and its applications in fiber surface grafting, filler modification, and starch nanoparticle formation. Particularly, the thesis contains three major parts:
(1) Mechanism study of starch crosslinking induced by AZC:
In this thesis, the crosslinking (or gelation) kinetics of starch/AZC blends were investigated by using rheological measurements. The evolution of viscoelastic properties of AZC solutions and the AZC-starch blends was characterized. It was found that for both AZC self-crosslinking and AZC-starch co-crosslinking, the initial bond formation rate and the gel strength had a strong power law relationship with the concentrations of both AZC and starch. It is suggested that the development of the crosslinking network is highly dependent on the AZC concentration, while the starch concentration effect is less significant. It was determined that the activation energy of AZC self-crosslinking was approximately 145-151 kJ/mol, while the activation energy of AZC-starch co-crosslinking was 139 kJ/mol.
(2) Fiber and filler modifications with starch and crosslinkers:
Besides reacting with starch, AZC can react with cellulose which also contains hydroxyl groups. Theoretically, it is possible to use AZC as a crosslinker / coupling agent to graft starch onto cellulose fibers. It is believed that the grafted starch on fiber surfaces can improve the fiber bonding capability. In this thesis, a facile method to graft starch onto cellulose fiber surfaces through the hydrogen bond formation among cellulose, starch and AZC was developed. Compared with the paper sheets made of fibers with an industry refining level (420 ml CSF), the paper sheets made of fibers with a much lower refining degree but with grafted starch showed higher paper strengths, including the tensile strength, stiffness and z direction tensile; meanwhile, a faster drainage rate during web formation could also be achieved.
Not only can the fiber-fiber bonding be improved by grafting starch onto fiber surfaces, but the filler-fiber bonding can also be improved if starch can be effectively coated on the filler surface. This concept has been supported by the early studies. In this thesis, the effects of the crosslinking of starch in the filler modification for the papermaking application were also studied.
(3) Mechanism of starch nanoparticle formation during extrusion with crosslinkers:
It was reported that starch crosslinking could facilitate the reduction of starch particle size during reactive extrusion. However, the mechanism of the particle size reduction by starch crosslinking was not illustrated. The reason that the crosslinking can cause the particle size reduction of starch during extrusion is fundamentally interesting. In this thesis, the mechanism of starch particle size reduction during extrusion with and without crosslinkers was investigated by identifying the contributions of thermal and mechanical effects. The effects of extrusion conditions, including temperature, screw speed, torque, starch water content and crosslinker addition, on the particle size were studied. It was found that the addition of crosslinkers could significantly increase the shear force (torque), and consequently facilitate the reduction of the particle size. The results indicate that for extrusion without a crosslinker, the starch particle size decreased with the increase of temperature. At 100 degree Celsius, the starch particles with a size of 300 nm could be obtained. With the addition of appropriate crosslinkers (glyoxal), the starch particle size could be reduced to around 160 nm, even at a lower extrusion temperature of 75 degree Celsius .
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Paquet, Olivier. "Modification de la surface de la cellulose par les organosilanes." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-01017164.
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Ce manuscrit de thèse traite de la modification de fibres de cellulose, en solutions purement aqueuses, par les organosilanes. Les réactions en phase aqueuse de silanes portants différents groupements chimiques réactifs ont été évaluées in-situ par spectrométrie par résonance magnétique nucléaire et l'influence de divers paramètres (pH, concentration, température) a été étudiée. Les aminosilanes se sont montrés particulièrement adaptés à l'utilisation en conditions correspondant à celles couramment utilisées dans le procédé papetier. En outre, l'adsorption des agents chimiques les plus prometteurs sur des surfaces modèles de cellulose a été testée par la technique microbalance à quartz, en fonction des mêmes paramètres. Cette étude a montré qu'une bonne couverture de la surface est atteinte avec des cinétiques de quelques minutes, et a été suivie d'une légère adsorption continue dans le temps. La nature des interactions entre divers silanes et la cellulose a été testée, et a révélé que le greffage, réalisé avec succès dans ce travail, relève d'interactions fortes. Enfin, deux types de fibres (résineux et feuillus) ont été utilisés afin de mesurer le potentiel d'utilisation des organosilanes pour répondre à une problématique industrielle impliquant les propriétés mécaniques du papier et sa douceur. Des résultats mitigés ont été obtenus, bien que le succès du procédé de greffage ait été avéré pour les différentes fibres.
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Aoki, Dan. "Functional Developments of Cellulose Derivatives by Heteroatomic Modification and Multicomposition." Kyoto University, 2011. http://hdl.handle.net/2433/152019.
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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(農学)<br>甲第16412号<br>農博第1897号<br>新制||農||994(附属図書館)<br>学位論文||H23||N4637(農学部図書室)<br>29043<br>京都大学大学院農学研究科森林科学専攻<br>(主査)教授 西尾 嘉之, 教授 木村 恒久, 教授 髙野 俊幸<br>学位規則第４条第１項該当
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Lin, Fangbo. "Modification régiosélective de nanocristaux de cellulose : synthèse, assemblages et propriétés fonctionnelles." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALV029.
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Les nanocristaux de cellulose (NCC) ont été identifiés comme des briques de base particulièrement attractives pour la conception de matériaux biosourcés innovants. Ces nanoparticules sont en effet issues d'une source abondante et renouvelable, les fibres de cellulose, et possèdent des propriétés exceptionnelles : très grande surface spécifique, faible densité, non-toxicité, biocompatibilité et propriétés mécaniques comparables à celles du Kevlar. Une caractéristique encore peu exploitée de ces nano-objets est leur polarité chimique. En effet, la biosynthèse conduit à des extrémités différentes des bâtonnets d'un point de vue chimique, ce qui permet de générer des NCC fonctionnalisés de manière asymétrique. En plus de l’utilisation de la cellulose native, il est possible de produire des NCC constitués de l'allomorphe II de la cellulose (NCC-II). Les NCC-II présentent une géométrie assez similaire à celle des NCC, mais les deux extrémités des bâtonnets peuvent être modifiées chimiquement. Ce projet de thèse s'est donc concentré sur de nouvelles stratégies pour modifier efficacement de manière régiosélective les NCC et les NCC-II afin de générer des assemblages innovants et fonctionnels.Tout d'abord, une stratégie de croissance in situ a été développée pour optimiser de manière drastique le marquage régiosélectif des NCC et NCC-II avec des nanoparticules d'or par rapport aux données de la littérature (le rendement du marquage est passé d'environ 15 à 80%). Ce développement nous a permis d’approfondir les connaissances fondamentales sur les nanocristaux en confirmant l’arrangement antiparallèle des chaînes de cellulose dans les NCC-II et en montrant que les NCC dérivés du coton sont constitués d'un assemblage parallèle de cristallites élémentaires chimiquement polaires.Deuxièmement, les deux types de particules ont été fonctionnalisées de manière régiosélective avec des chaînes de polymères thermosensibles en utilisant une stratégie en deux étapes d'oxydation suivie d’un couplage peptidique. Dans le cas des NCC, les particules hybrides résultantes s’assemblent sous l’effet d’une augmentation de la température en agrégats sous forme d'étoile composés de 3 à 6 nanocristaux fixés par leurs extrémités. En utilisant les NCC-II, une association réversible déclenchée par la température en réseaux supra-microniques est obtenue par chaînage des NCC-II modifiés. Les caractéristiques structurales de ces nouveaux objets et de leurs assemblages ont été étudiées par microscopie électronique à transmission, diffusion dynamique de la lumière et la diffusion des rayons X ou des neutrons aux petits angles. Des mesures de rhéologie ont démontré que dans les deux cas, au-dessus de la LCST des chaînes de polymères greffés, on obtient un comportement de type gel mais que la structure du réseau conduit à des effets plus importants que les complexes en forme d'étoile.Enfin, l'optimisation du processus de greffage a été étudiée et l'utilisation de DCC/DMAP ou de 4-PPY comme catalyseurs et du DMF comme solvant s’est avérée la plus efficace. L'utilisation du N-oxyde de N-Méthylmorpholine (NMMO) dans le but d’induire un gonflement des extrémités des NCC et de favoriser la réaction a également été étudiée. Cependant, aucun gonflement n'a pu être détecté mais le traitement avec NMMO a eu un effet notable sur la séparation des cristallites élémentaires formant les NCC.Comme les modifications entreprises concernent une fraction très réduite des unités anhydroglucose disponibles, une caractérisation quantitative directe de la modification régiosélective des NCC reste difficile, même si l'utilisation de techniques avancées telles que les méthodes de diffusion donnent des informations fructueuses. Toutefois, les travaux menés montrent qu'une telle fonctionnalisation localisée, associée à l'utilisation de particules biosourcées, permet un contrôle fin de l'assemblage en structures innovantes qui donnent naissance à de nouvelles propriétés macroscopiques<br>Cellulose nanocrystals (CNCs) have been identified as highly attractive building blocks for the design of innovative biosourced materials. These nanoparticles are indeed derived from an abundant and renewable source, cellulose fibers, and possess exceptional properties such as a very large surface area, a low density, non-toxicity, biocompatibility and mechanical properties comparable to those of Kevlar. An interesting feature of these nano-objects, which has not been widely exploited yet, is their chemical polarity. Indeed, the biosynthesis leads to different extremities of the rods from a chemical point of view, which makes it possible to generate asymmetrically functionalized CNCs. Alternatively, CNCs made of the allomorph II of cellulose (CNC-II) can also be produced. CNC-II particles exhibit a rather similar geometry as CNCs but both rod ends are amenable to chemical modification. This thesis project has thus focused on new strategies to efficiently modify in a regioselective manner CNCs and CNC-II particles in order to generate innovative and functional assemblies.First, an in situ growth strategy was developed to drastically optimize the regioselective labelling of CNCs and CNC-II with gold nanoparticles when compared to literature data (labelling yield increased from about 15 to 80%). This development allowed us to get insight into fundamental morphological features by confirming the antiparallel packing of cellulose chains in CNC-II and by showing that CNCs derived from cotton are made of a parallel assembling of chemically polar elementary crystallites.Secondly, both types of nanocellulose particles were successfully regioselectively functionalized with thermosensitive polymer chains using a two-step oxidation and peptide coupling strategy. In the case of CNCs, the resulting hybrid particles underwent a thermally induced-aggregation into star-shaped aggregates composed of 3 to 6 nanocrystals attached by their ends. Using CNC-II particles, a reversible temperature-triggered association into supra-micronic networks could be obtained through end-to-end attachment of the cellulose rods. The structural features of these new objects and their assemblies were characterized by transmission electron microscopy, dynamic light scattering and small angle X-ray or neutron scattering. Rheology measurements were used to show that in both cases, above the LCST of the grafted polymer chains, a gel-like behavior is obtained but the network structure led to stronger effects than the star-shaped complexes.Finally, the optimization of the grafting process was investigated and the use of DCC/DMAP or 4-PPY as catalysts of the peptide coupling and DMF as the solvent turned out to be the best conditions.The use of N-Methylmorpholine N-oxide (NMMO) to induce a swelling of the CNC ends and favor the reaction was also studied. However, no swelling could be detected but the treatment with NMMO had a noticeable effect of separating the elementary crystallites forming the CNCs.Since the undertaken modifications concern a very reduced fraction of the available anhydroglucose units, a quantitative direct characterization of the regioselective derivatization of CNCs remains challenging, even if the use of advanced techniques such as scattering methods give fruitful information. However, the present work shows that such a site-selective functionalization coupled with the use of biosourced particles allows a fine tuning of stimuli-sensitive assembling into innovative structures that give rise to new macroscopic properties
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Utsel, Simon. "Surface Modification of Cellulose-based Materials for Tailoring of Interfacial Interactions." Doctoral thesis, KTH, Fiberteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102368.
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The awareness of our need for a sustainable society has encouraged the search for renewable, high quality materials that can replace oil-based products. This, in combination with increased competition in the forest industry, has stimulated a lot of research into different types of wood-based materials where cellulose-rich fibers are combined with different types of polymers. There is hence a great need to develop efficient fiber modification techniques by which the fibers can be tailored to obtain specific properties. A significant change in properties can be achieved by modifying only the surface of fibers although only a relatively small amount of the total fiber material is modified. In this thesis, several surface modification techniques are presented as new tools to design the properties of different cellulose-based materials. In paper I, thermoresponsive nanocomposites have been assembled from specially designed thermoresponsive block copolymers and nanofibrillated cellulose. The block copolymers have one thermoresponsive block and one cationically charged block which can thus attach the polymer to an oppositely charged fiber/fibril surface. Multilayers were assembled with these block copolymers and nanofibrillated cellulose (NFC) utilizing the Layer-by-Layer (LbL) technique, resulting in thin films with a thermoresponsive behavior. In papers II and III, amphiphilic block copolymers with one less polar high molecular weight block and one cationic block were synthesized for use as a compatibilizer between fibers/fibrils and less polar polymer matrices in composites. The less polar block consisted of polystyrene (PS) in paper II and poly(ɛ-caprolactone) (PCL) in paper III. These polymers self-assemble into cationic micelles in water which can adsorb to oppositely charged surfaces, such as cellulose-based fibers/fibrils, in water under mild conditions and decrease the surface energy of the surface. Atomic force microscopy (AFM) was used to evaluate the adhesive properties of surfaces treated with these compatibilizers which clearly showed the formation of physical entanglements across the interfaces, which are essential for improved interfacial adhesion in the final composites. This modification technique could probably be utilized to make fiber-based composites with better mechanical properties. To be able to better compare this physical modification technique with a more traditional covalent grafting-from approach a method to measure attached amounts of grafted PCL onto cellulose model surfaces was developed in paper IV using a quartz crystal microbalance (QCM). In paper V, multilayers of poly(allylamine hydrochloride) (PAH) and hyaluronic acid (HA) were assembled using the LbL technique and surface structure, build-up and adhesive behavior of the multilayers were evaluated. AFM force measurements showed that a significant adhesion even at long separation distances between two surfaces treated with PAH/HA multilayers could be achieved due to extensive interdiffusion across the interface during contact, leading to significant disentanglement during separation. Fundamental parameters contributing to improved adhesion for this type of system have been evaluated and this knowledge could be used to improve cellulose-based fiber networks and possibly also other types of cellulose-based materials. In paper VI, click chemistry was used to covalently attach dendrons to cellulose surfaces and further modify them with mannose groups to obtain specific interactions with Concanavalin A. The protein interactions were studied at different protein concentrations with a QCM. The multivalent dendronized surface showed a 10-fold increase in sensitivity to the protein compared to a monovalent reference surface demonstrating greatly improved interfacial interactions. This approach could be used to improve interactions at different types of interfaces.<br><p>QC 20120918</p>
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Utsel, Simon. "Surface modification of cellulose-based fibres for use in advanced materials." Licentiate thesis, KTH, Fiber- och polymerteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25245.
Full textAbstract:
The awareness of our need for a sustainable society has encouraged the search for renewable, high quality materials that can replace oil-based products. This, in combination with increased competition in the forest industry, has stimulated a lot of research into different types of wood-based materials where cellulose-rich fibres are combined with different types of polymers. There is hence a large need to develop efficient fibre modification techniques by which the fibres can be tailored to obtain specific properties. Furthermore, by modifying only the surface of fibers a significant change in properties can be achieved although only a relatively small amount of the total fibre material is modified. The potential impact of a surface modification increases tremendously when nano-sized fibres are used due to the larger interfacial area between the fibres and their surroundings. Interest in smaller building blocks in the nanometer range has continued to grow rapidly in recent years due to both the availability and preparation/synthesis of smaller building blocks and to the discovery of the high performance of these types of nanocomposites. In this thesis, three different types of surface modifications are presented as new tools to design the properties of new novel cellulose-based materials. In the first work, thermoresponsive nanocomposites have been assembled from specially designed thermoresponsive polymers and nanofibrillated cellulose. The polymers have one thermoresponsive block and one cationically charged block which can thus attach the polymer to an oppositely charged fibre/fibril surface. Multilayers were assembled with these polymers and the nanofibrillated cellulose utilizing the layer-by-layer technique, resulting in thin films with thermoresponsive behavior which for example could be used for controlled drug-release applications. In the second work, an amphiphilic block copolymer with one high molecular weight hydrophobic polystyrene block and one cationic block was synthesized for use as a compatibilizer between fibres and hydrophobic polymer matrices in composites. These polymers self-assemble into micelles in water with the hydrophobic part in the core of the micelle and the cationic part in the shell. Due to the cationic charges, these micelles adsorb to oppositely charged surfaces where the hydrophobic parts can be liberated on the surface by a heat treatment, leading to a new, less hydrophilic, surface with a contact angle close to that of pure polystyrene. Atomic force microscopy was used to measure the adhesive properties of a polymer-treated surface using a polystyrene probe at different temperatures and contact times. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglement between the polystyrene blocks at the treated surface and the probe. The relative increase in adhesion with contact time was higher at the lower temperature whereas the absolute value of the adhesion was higher at the higher temperature, most probably due to a larger molecular contact area. This odification technique could be utilized to make fibrebased composite materials with better mechanical properties. In the third work, click chemistry was used to covalently attach dendrons to cellulose surfaces and further to modify them with mannose groups to obtain specific interactions with Concanavalin A. The protein interactions were studied at different protein concentrations with a quartz crystal microbalance. The multivalent dendronized surface showed a 10-fold increase in sensitivity to the protein compared to a monovalent reference surface. This could be used to design more sensitive cellulose-based biosensors in the future.<br>Det finns idag en stor insikt av att vi behöver nya miljövänliga processer och produkter för att kunna skapa ett långsiktigt hållbart samhälle. Denna medvetenhet har stimulerat sökandet efter förnyelsebara, högkvalitativa material som kan ersätta oljebaserade produkter. I kombination med den ökande konkurrensen inom skogsindustrin, har detta stimulerat forskning inom olika typer av träbaserade material där cellulosarika fibrer kombineras med olika typer av polymerer så att vi använder vår förnyelsebara skogsråvara i så kallade högvärdesprodukter. Det finns därför ett stort behov av utveckling av effektiva tekniker för fibermodifiering där fibrer kan skräddarsys för att erhålla specifika egenskaper. Genom att endast modifiera fibrernas yta kan dessutom en markant förändring i egenskaper erhållas genom att endast modifiera en relativt liten del av det totala fibermaterialet. Den potentiella effekten av ytmodifiering ökar dessutom avsevärt när cellulosananofibriller används, eftersom gränsytan mellan fibrillerna och dess omgivning ökar dramatiskt när storleken minskar med flera tiopotenser. Intresset för mindre byggstenar i nanometerområdet har fortsatt att öka snabbt under de senaste åren, både tack vare tillgängligheten och ny teknik för tillverkning/syntes av mindre byggstenar, och insikter av de mycket goda egenskaper som den här typen av nanokompositer besitter. I föreliggande avhandling presenteras tre olika typer av fibermodifiering som kan användas som nya redskap för att skräddarsy egenskaper hos nya cellulosabaserade material. I det första arbetet har termoresponsiva nanokompositer byggts upp från specialtillverkade termoresponsiva polymerer och nanofibrillerad cellulosa. Polymererna har ett block som är termoresponsivt samt ett andra block som är katjoniskt laddat och därmed kan fästa polymeren till en motsatt laddad fiber/fibrillyta. Multiskikt byggdes upp med dessa polymer och den nanofibrillerade cellulosan genom att använda lager-på-lager tekniken, vilket resulterar i tunna filmer med termoresponsivt beteende som exempelvis skulle kunna användas för kontrollerad frisättning av läkemedel. I det andra arbetet har en amfifil block copolymer med ett högmolekulärt hydrofobt polystyrenblock och ett katjoniskt block syntetiserats för användning som kompatibilisator mellan fibrer och hydrofoba polymer matriser i fiber/fibrill förstärkta kompositer. Dessa polymerer självorganiseras i form av miceller i vatten med den hydrofoba delen i kärnan av micellen och den katjoniska delen i skalet. Eftersom micellerna har katjoniska laddningar adsorberar de till motsatt laddade ytor där de hydrofoba delarna kan frigöras på ytan efter en värmebehandling vilket leder till en ny, mindre vattenvätbar, yta. Ett atomkraftsmikroskop användes för att mäta de adhesiva egenskaperna mellan en polymerbehandlad yta och en polystyrenprob vid olika temperaturer och kontakttider. Adhesionen ökade med kontakttiden för de behandlade ytorna, troligtvis beroende på molekylär intrassling mellan polystyrenblock på den behandlade ytan och polystyrenproben. Den relativa adhesionsökningen, med ökad kontakttid, var högre vid den lägre temperaturen medan den absoluta adhesionskraften var högre vid den högre temperaturen, vilket troligen beror på en högre molekylär konataktyta vid den högre temperaturen. I det tredje arbetet användes klick-kemi för att kovalent fästa dendroner till cellulosaytor och vidare modifiera dem med mannosgrupper för att erhålla specifik växelverkan med Concanavalin A. Proteininteraktionerna studerades vid olika proteinkoncentrationer med hjälp av en kvartskristallmikrovåg. Den flervärda dendroniserade ytan visade en 10-faldig ökning i känslighet gentemot proteinet jämfört med den envärda referensytan. Detta skulle kunna användas för att skräddarsy känsligare cellulosabaserade biosensorer i framtiden.<br>QC 20101014
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Claisse, Nathalie. "Préparation et modification d'oligosaccharides de cellulose par chimie douce bio-inspirée." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00849149.
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La valorisation de la biomasse saccharidique pour la production de dérivés biosourcés d'intérêt est un enjeu important. La cellulose est le polysaccharide le plus abondant sur Terre et représente une source de matière première considérable. Dans ce travail, de nouveaux procédés de dépolymérisation de la cellulose pour l'obtention contrôlée de cellodextrines sont décrits. Ils proposent une approche alternative plus douce aux procédés de production actuels en privilégiant l'utilisation d'enzymes, et de liquides ioniques comme solvants alternatifs. Ce travail rapporte l'élaboration de deux méthodes d'obtention contrôlée d'oligosaccharides à partir de cellulose et de cellulose acétate par combinaisons successives d'hydrolyses acide et enzymatique. Ces procédés ont permis l'obtention de cellodextrines de tailles ciblées avec de bons rendements, et constituent une voie prometteuse pour la valorisation de la cellulose en dérivés biosourcés. La deuxième partie de ce travail consiste en la modification chimio-enzymatique des oligosaccharides de cellulose produits pour leur valorisation en biomolécules d'intérêt, plus particulièrement dans le domaine de l'agrochimie. Les cellodextrines sont utilisées en tant que base saccharidique pour la synthèse d'analogues de lipo-chitooligosaccharides comme potentiels fertilisants verts. Deux méthodes de préparation ont été élaborées à l'aide des glycoside-hydrolases comme outils de synthèse. Les stratégies développées permettent un accès efficace à la synthèse d'analogues et peuvent être adaptées pour la production d'autres molécules.
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Hua, Kai. "Nanocellulose for Biomedical Applications : Modification, Characterisation and Biocompatibility Studies." Doctoral thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267301.
Full textAbstract:
In the past decade there has been increasing interest in exploring the use of nanocellulose in medicine. However, the influence of the physicochemical properties of nanocellulose on the material´s biocompatibility has not been fully investigated. In this thesis, thin films of nanocellulose from wood (NFC) and from Cladophora algae (CC) were modified by the addition of charged groups on their surfaces and the influence of these modifications on the material´s physicochemical properties and on cell responses in vitro was studied. The results indicate that the introduction of charged groups on the surface of NFC and CC results in films with decreased surface area, smaller average pore size and a more compact structure compared with the films of unmodified nanocelluloses. Furthermore, the fibres in the carboxyl-modified CC films were uniquely aggregated and aligned, a state which tended to become more prevalent with increased surface-group density. The biocompatibility studies showed that NFC films containing hydroxypropyltrime-thylammonium (HPTMA) groups presented a more cytocompatible surface than unmodified NFC and carboxymethylated NFC regarding human dermal fibroblasts. Carboxymethyl groups resulted in NFC films that promoted inflammation, while HPTMA groups had a passivating effect in terms of inflammatory response. On the other hand, both modified CC films behaved as inert materials in terms of the inflammatory response of monocytes/macrophages and, under pro-inflammatory stimuli, they suppressed secretion of the pro-inflammatory cytokine TNF-α, with the effects of the carboxylated CC film more pronounced than those of the HPTMA CC material. Carboxyl CC films showed good cytocompatibility with fibroblasts and osteoblastic cells. However, it was necessary to reach a threshold value in carboxyl-group density to obtain CC films with cytocompatibility comparable to that of commercial tissue culture material. The studies presented here highlight the ability of the nanocellulose films to modulate cell behaviour and provide a foundation for the design of nanocellulose-based materials that trigger specific cell responses. The bioactivity of nanocellulose may be optimized by careful tuning of the surface properties. The outcomes of this thesis are foreseen to contribute to our fundamental understanding of the biointerface phenomena between cells and nanocellulose as well as to enable engineering of bioinert, bioactive, and bioadaptive materials.
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CHAUVELON, GAELLE. "Modifications chimiques de celluloses modeles et issues de sons de cereales." Nantes, 1998. http://www.theses.fr/1998NANT2127.
Full textAbstract:
Les sons de ble et de mais sont riches en polysaccharides ( 700 mg/g), notamment en heteroxylanes et en cellulose. Des echantillons enrichis en cellulose ( 400 a 700 mg/g) ont ete obtenus. Ces echantillons presentent une cellulose peu cristalline mais avec des differences notables de degre de polymerisation ($$d$$p$$v de 270 a 1250). Deux types de modification chimique de ces residus cellulosiques ont ete effectues et les proprietes des derives obtenus ont ete etudiees. L'esterification de la cellulose par le chlorure d'acide laurique a ete realisee. Un pretraitement d'activation par l'acide sulfurique qui conduit a la formation d'un sulfate de cellulose instable et a une diminution du $$d$$p$$v des chaines cellulosiques est necessaire. Cette activation ameliore la reactivite de la cellulose et des laurates de cellulose ont ete obtenus (ds entre 1,9 et 2,8). La teneur en cellulose de l'echantillon est un parametre determinant pour l'obtention de rendement eleve ( 2 g/g) mais un residu d'esterification constitue de lignine et de cellulose residuelle est toujours obtenu ( 1 g/g). Les esters sont filmogenes et les proprietes mecaniques interessantes (contrainte maximale 2 mpa et elongation 130%) comparables a celles observees pour d'autres biopolymeres. L'acide laurique joue le role de plastifiant interne. L'obtention d'un derive acetyle hydrosoluble a ete mise au point a partir des residus cellulosiques. La presence simultanee d'anhydride acetique et d'acide sulfurique dans le milieu reactionnel conduit a la formation directe d'un sulfo-acetate de cellulose de degre d'acetylation compris entre 1,8 et 2,4 et de degre de sulfatation egal a 0,3. La presence des sulfates, repartis de facon homogene et esterifiant uniquement les fonctions hydroxyles primaires, confere a ce derive une solubilite dans l'eau. Les sulfo-acetates de cellulose possede des proprietes de polymeres associatifs avec une viscosite intrinseque elevee ( 1000 ml/g) et forme des gels pour des concentrations superieures a 15 mg/ml.
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Vitiello, Sergio. "Modifications fonctionnelles des cellules immunitaires liées à l'asymétrie cérébrale." Bordeaux 2, 1993. http://www.theses.fr/1993BOR28224.
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Fillat, Latorre Amanda. "Flax fibre modification using enzyme systems to obtain high-value cellulose products." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/38251.
Full textAbstract:
The aim of this thesis is to modify flax pulp fibres (Linum usitatissimum) by more
friendly environmental processes. Pulp and paper research is focussing through
enzyme systems investigation for developing green chemistry technologies due to
existing environmental concerns and to legal restrictions. Moreover, it exists also an
increasing strategic interest in using flax fibres to obtain high-quality specialty papers.
That is why we study the application of biotechnology as an efficient alternative to
traditional industrial processes based on the use of chemical agents.
This work is framed by two of the main research topics of the Paper and Graphic
Specialty Laboratory in the Textile and Paper Engineering Department of the
Universitat Politècnica de Catalunya. One research line is based on pulp bleaching and
is focused basically on the study of enzymatic systems as biobleaching agents; the
other research topic that has been recently introduced in our investigation group is the
use of enzymes as functionalisation agents by promoting the grafting of several
compounds. Laccase is the main enzyme used in this thesis; it is an oxidoreductase that
can assist reactions in an eco-friendly way since laccase uses air and produces water as
the only by-product. Moreover, laccase can work under mill conditions and has wide
application potential.
The first part of this thesis involved the use of enzymes to bleach flax pulp. The aim
was to explore the potential of various natural mediators (lignin-derived compounds)
for delignifying flax fibres in order to identify the most efficient and ecofriendly choice
among them. Afterwards, we assessed the use of various enzyme delignification stages
in an industrial bleaching sequence. The ensuing totally chlorine free (TCF) sequence
comprised various laccase-mediator system treatments (L stage) followed by a by a
chelating stage (Q stage) and a subsequent bleaching step with hydrogen peroxide (Po
stage). A xylanase pretreatment was additionally carried out. Laccases used came from
the fungi Pycnoporus cinnabarinus and Myceliophthora thermophila; the performance
of several natural mediators was compared with the obtained with the application of
various synthetic mediators. In addition, the lack of studies on the properties of
effluents from the treatment of non-wood pulp with laccase and natural mediators led
A-1
A-2
us to examine effluent properties upon biotreatments and after different bleaching
stages. The results obtained warrant upscaling any of the biobleaching sequences for
flax pulp as they provide sustainable flax fibre with a high cellulose content and
brightness above 80% ISO. The use of xylanase pretreatment was found to efficiently
remove HexA and enhance delignification by laccase.
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Ahrenstedt, Lage. "Surface modification of cellulose materials : from wood pulps to artificial blood vessels." Licentiate thesis, KTH, School of Biotechnology (BIO), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4437.
Full textAbstract:
<p>This thesis describes the improvement of two radically different cellulose materials, paper and artificial blood vessels, constructed from two diverse cellulose sources, wood pulp and <em>Acetobacter xylinum</em>. The improvement of both materials was possible due to the natural affinity of the hemicellulose xyloglucan for cellulose.</p><p>Chemical and mechanical pulps were treated with xyloglucan in the wet-end prior to hand sheet formation or by spray application of dry hand sheets, loading a comparable amount of xyloglucan. The tensile strength increases for the wet-end treatment and spray application were 28% and 71% respectively for bleached soft wood, compared to untreated sheets (20.7 Nm/g). The corresponding strength increases for hand sheets made of thermo-mechanical pulp were 6% and 13% respectively compared to untreated sheets (42.4 Nm/g). The tendency for chemical pulp to be superior to mechanical pulp with respect to strength increase was valid even for tear strength and Scott-Bond. These results suggest, in agreement with other studies, that adhesion of xyloglucan to wood fibres is dependent on their degree of surface lignification.</p><p>Also, a method was developed to increase the blood compatibility of artificial blood vessels constructed of bacterial cellulose. Xyloglucan was covalently linked to the endothelial cell adhesion motif (Arg-Gly-Asp). To obtain this, new solid-phase coupling chemistry was developed. Xyloglucan oligosaccharides (XGO) were transformed into XGO-succinamic acid via the corresponding XGO--NH<sub>2 </sub>derivative prior to coupling with the N-terminus of the solid-phase synthesised Gly-Arg-Gly-Asp-Ser peptide. The resin-bound glyco-peptide was then cleaved and enzymatically re-incorporated into high molecular weight xyloglucan. The glyco-peptide was further adsorbed onto bacterial cellulose scaffolds, increasing the adhesion and proliferation of endothelial cells and therefore blood compatibility.</p>
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Yang, Liangyu. "Chemical modification of cellulose substrates with carboxylic acids and phosphorus containing acids." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581972.
Full textAbstract:
The principle objectives of this research were to chemically modify cellulose using either carboxylic acids or phosphorus containing acids. Carboxylic acids were reacted with isocyanic acid derived from sodium cyanate, in order to synthesise reactive anhydrides, amides and polyamide compounds. The application of these intermediate compounds to cellulose was in tempted. The phosphonation of cellulose using phosphorous acid resulted in a substrate which exhibited flame retardant properties. Firstly, the stability and the nature of the reagents were investigated by Fourier transform infrared spectroscopy (FTIR), Fourier transform Raman (FT-Raman) and Capillary electrophoresis (CE). Secondly, the process of phosphonation was investigated to determine the optimum reagents / concentrations / pH and other application conditions on various cellulose substrates. The treated cotton fabrics were found to give excellent flame retardancy; such fabrics were analysed by different technique, including FTIR, FT -Raman, Nuclear magnetic resonance (NMR), Thermogravimetric analysis (TGA), Scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX), fluorescence microscopy and cationic dye staining. All the analysis results clearly showed that these phosphonation treatments introduced flame retardant properties to cotton fabrics which were durable to repeated alkaline launderings. The results of this research have been used to help launch a commercially viable flame retardant product. Compared to other products currently occupying the market huge advantages in terms of avoidance of formaldehyde are evident.
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Mazza, Mathieu. "Modification chimique de la cellulose en milieu liquide ionique et CO2 supercritique." Phd thesis, Toulouse, INPT, 2009. http://oatao.univ-toulouse.fr/7832/1/mazza.pdf.
Full textAbstract:
L'estérification de la cellulose a été réalisée dans deux milieux non-conventionnels. D'un coté, Le CO2 supercritique a permis l'obtention d'esters de cellulose à très faible degré de substitution (DS) en milieu hétérogène. D'un autre coté, les liquides ioniques utilisés ont permis de réaliser l'estérification de la cellulose en milieu homogène et d'obtenir des composés avec un large choix de DS. Parmi ces liquides ioniques, le BMIMCl a conduit à la formation d'ester gras de cellulose à faible DS et avec un caractère thermoplastique innovant. Le deuxième liquide ionique utilisé, découvert grâce à une étude turbidimétrique mise au point lors de ce travail de thèse, a permis d'obtenir des esters gras de cellulose à fort DS dans des conditions opératoires douces.
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Marchal, Ingrid. "Modification des capacités de glycosylation des cellules d'insectes." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2001. http://tel.archives-ouvertes.fr/tel-00258437.
Full textAbstract:
L'utilisation thérapeutique de glycoprotéines recombinantes produites dans le système baculovirus-cellules d'insectes reste limitée par le potentiel de glycosylation de ces cellules, qui produisent essentiellement des structures O- et N-glycanniques courtes. Notre travail s'inscrit donc dans un effort global d'"humanisation" de la glycosylation des protéines produites dans les cellules de Lépidoptères.<br />Nous nous sommes d'abord attachés à comprendre la voie de maturation des N-glycannes dans des cellules Sf9. L'utilisation d'inhibiteurs de la maturation ou du trafic intracellulaire nous a permis d'identifier des intermédiaires clés et de confirmer l'hypothèse que la maturation des N-glycannes dans les cellules d'insectes et de mammifères suivent un chemin métabolique parallèle jusqu'à la formation de l'espèce GlcNAcMan3[Fuc]GlcNAc2. Chez les insectes, cette structure est ensuite substrat d'une β-N-acétylglucosaminidase qui produit l'espèce finale Man3[Fuc]GlcNAc2.<br />Cette voie de maturation peut néanmoins être déviée vers la synthèse de N-glycannes de type complexe par l'addition de glycosyltransférases absentes : ainsi, l'expression d'une β1,4-galactosyltransférase permet la synthèse de l'espèce GalGlcNAcMan3[Fuc]GlcNAc2.<br />Notre intérêt s'est ensuite porté sur l'ingénierie de la sialylation dans les cellules d'insectes, compliquée par l'absence du donneur d'acides sialiques, le CMP-Neu5Ac. Notre stratégie a été d'exprimer la trans-sialidase de Trypanosoma cruzi sur la membrane plasmique des cellules, afin qu'elle puisse sialyler les glycoprotéines sécrétées en utilisant des donneurs du milieu. La construction exprimée grâce à un vecteur baculovirus code une enzyme active, dont une partie est retrouvée sur la membrane plasmique et sur l'enveloppe des particules virales, tandis qu'une partie, croissante avec l'infection, est soluble. Néanmoins, le système permet une sialylation quantitative d'accepteurs exogènes.<br />Notre étude contribue à montrer que l'ingénierie de la glycosylation dans le système baculovirus-cellules d'insectes est envisageable. Pour résoudre le problème de la sialylation, la trans-sialidase est une alternative possible aux sialyltransférases.
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Bruce, Carl. "Surface Modification of Cellulose by Covalent Grafting and Physical Adsorption for Biocomposite Applications." Doctoral thesis, KTH, Ytbehandlingsteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155920.
Full textAbstract:
There is an increasing interest to replace fossil-based materials with renewable alternatives. Cellulose fibers/nanofibrils (CNF) are sustainable options since they are biobased and biodegradable. In addition, they combine low weight with high strength; making them suitable to, for example, reinforce composites. However, to be able to use them as such, modifications are often necessary. This study therefore aimed at modifying cellulose fibers, model surfaces of cellulose and CNF. Cellulose fibers and CNF were thereafter incorporated into composite materials and evaluated. Surface-initiated ring-opening polymerization (SI-ROP) was performed to graft ε-caprolactone (ε-CL) from cellulose fibers. From these fibers, paper-sheet biocomposites were produced that could form laminate structures without the need for any addition of matrix polymer. By combining ROP and atom transfer radical polymerization (ATRP), diblock copolymers of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and PCL were prepared. Quaternized (cationic) PDMAEMA, allowed physical adsorption of block copolymers onto anionic surfaces, and, thereby, alteration of surface energy and adhesion to a potential matrix. Furthermore, the architecture of block copolymers of PCL and PDMAEMA was varied to investigate effects on morphology/crystallinity and adsorption behavior. In addition, poly(butadiene) was also evaluated as the hydrophobic block in the form of cationic and anionic triblock copolymers. Polystyrene (PS) was covalently grafted from CNF and used as reinforcement in PS-based composites. In an attempt to determine stress transfer from matrix to CNF, a method based on Raman spectroscopy was utilized. Covalent grafting and physical adsorption of PCL from/onto CNF were compared by incorporating modified CNF in PCL matrices. Both approaches resulted in improved mechanical properties compared to unmodified CNF, but even at low amounts of modified CNF, covalent grafting gave tougher materials and indicated higher interfacial adhesion.<br><p>QC 20141117</p>
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Credou, Julie. "Simple, biocompatible and robust modification of cellulose membranes for the eco²-friendly preparation of immunoassay devices." Palaiseau, Ecole polytechnique, 2014. https://tel.archives-ouvertes.fr/tel-01071399/document.
Full textAbstract:
Depuis le papyrus, la cellulose a tenu un rôle important dans notre culture, en particulier comme papier. Aujourd’hui, ce produit ancien trouve de nouvelles applications dans le secteur des papiers bioactifs. Des dispositifs de détection faits de papier tels que les bandelettes sont peu coûteux, rapides, faciles à utiliser, et donc très prometteurs pour le diagnostic de terrain dans les zones reculées. Récemment, les biocapteurs papier ont évolué vers des dispositifs microfluidiques 3D et des plateformes multiplexées. Or, le développement de ces biocapteurs papier multiplexés fait souvent appel à des méthodes incompatibles avec le matériau classique des bandelettes : la nitrocellulose. Celle-ci tend donc à être remplacée par la cellulose. Ce changement de matériau implique la mise en oeuvre d’une immobilisation covalente des biomolécules qui préserve leur activité biologique. Par ailleurs, les enjeux mondiaux actuels incitent à se tourner vers des matériaux et procédés à la fois respectueux de l’environnement et rentables économiquement. La cellulose est un polymère naturel abondant et donc un matériau idéal pour le développement de dispositifs de diagnostic. Toutefois, le matériau support n’est pas le seul aspect à considérer. L’ensemble de la conception du dispositif, l’immobilisation des agents de capture, le traitement des membranes, tout doit répondre aux défis écologiques et économiques. La modification localisée des surfaces de cellulose semble alors cruciale puisqu’elle permet d’économiser des composés coûteux et de moduler localement les propriétés de surface. Dans ce contexte, trois procédés de modification facile et durable de feuilles de cellulose ont été développés. Tous sont respectueux de l’environnement, simples, polyvalents et économes aussi bien en temps qu’en argent. Le premier est une procédure de fonctionnalisation de membranes de cellulose pour l’immobilisation covalente d’anticorps. Tandis que la modification chimique de la cellulose se fait habituellement dans des conditions rudes et dans des solvants organiques, la méthode développée ici a été réalisée dans l’eau, à température ambiante, en une seule étape. Des feuilles de papier ont ainsi été modifiées, portant alors différentes fonctions chimiques permettant de greffer des biomolécules par des techniques de bioconjugaison classiques. Elles ont ensuite été testées comme bandelettes. Le second est une procédure de photoimmobilisation sans produit chimique qui permet d’immobiliser des anticorps sur la cellulose sans aucun intermédiaire de couplage ni aucun prétraitement des biomolécules ou du substrat. Cette technique a été combinée à l’impression jet d’encre pour localiser les anticorps selon tout motif désiré. Des anticorps natifs ont ainsi été imprimés et immobilisés sur des feuilles de papier qui ont ensuite servi de bandelettes. Leurs performances ont été évaluées en termes de limite de détection et se sont montrées comparables à celles de la nitrocellulose. Le troisième est une méthode de greffage de polymères sur membranes de cellulose. Contrairement aux précédents, ce procédé vise à augmenter la fonctionnalité des portions non-détectrices des dispositifs papier. Mais il peut aussi être utilisé comme une autre méthode de fonctionnalisation pour l’immobilisation covalente d’anticorps. Alors que le greffage de polymères sur cellulose se fait d’ordinaire par des procédures complexes et coûteuses, l’approche employée ici a été réalisée dans l’eau, à température ambiante, en une seule et courte étape. Des feuilles de cellulose ont ainsi été greffées de divers polyacryliques, d’abord globalement par trempage puis localement par impression. Toutes ces stratégies peuvent aider à immobiliser de manière localisée des protéines sensibles sur des feuilles de cellulose. Plus généralement, ce sont de puissants outils pour facilement moduler les propriétés des surfaces de celluloses selon des motifs complexes, dans des conditions douces et biocompatibles<br>Since the papyri, cellulose has played a significant role in human culture, especially as paper. Nowadays, this ancient product has found new applications in the expanding sector of bioactive paper. Simple paper-based detection devices such as lateral flow immunoassays (LFIAs) are inexpensive, rapid, userfriendly and therefore highly promising for providing resource-limited settings with point-of-care diagnostics. Recently, paper-based biosensing technology has trended towards three-dimensional microfluidic devices and multiplexed assay platforms. Yet, many multiplexed paper-based biosensors implement methods incompatible with the conventional LFIA carrier material: nitrocellulose. It thus tends to be replaced by pure cellulose. This major material change implies to undertake a covalent immobilization of biomolecules on cellulose which preserves their biological activity. Furthermore, the current global issues have stimulated the search for both ecologically and economically friendly (eco²-friendly) materials and processes. As a sustainable and affordable biopolymer, cellulose is an ideal material for developing diagnostic devices. However, the frame material is not the only aspect to consider. The whole device design and production, as well as the biosensing material immobilization or the non-sensing membranes treatment, should be as eco²-friendly as possible. Hence, the spatially controlled modification of cellulose surface seems crucial in the development of such devices since it enables to save expensive matter and to pattern surface properties. In any case, modification procedures should abide by the economic and ecological objectives aforementioned. In this perspective, three processes allowing easy, robust and sustainable modification of cellulose sheets were developed. All are environmentally friendly, simple, time and cost-saving, and versatile. The first procedure is a functionalization of cellulose membranes for covalent antibody immobilization. While cellulose chemical modification is usually operated under harsh conditions in organic solvents, the diazonium-based procedure developed was performed in water, at room temperature, in a single step. Paper sheets have thus been modified and bear different chemical functions which enable to graft biomolecules by common bioconjugate techniques and to perform LFIAs. The second is a chemical-free photoimmobilization procedure which allowed antibodies to be immobilized on cellulose without any photocoupling intermediate nor any biomolecule or substrate pretreatment. This immobilization technique was further combined to inkjet printing to localize the antibodies according to any pattern desired. Native antibodies have thus been printed and immobilized on paper sheets which therefore enable to perform LFIAs. Membranes’ performances were evaluated in terms of visual detection limit and challenged nitrocellulose performances. The third is a modification of cellulose membranes by polymer grafting. Unlike the two previous processes, this technique was developed in order to increase the functionality of the non-sensing cellulose parts of paper-based devices. Yet, it may be employed as another functionalization method for covalent antibody immobilization on cellulose. While cellulose graft copolymerization is usually performed through complex and expensive procedures, the diazonium-based approach employed was performed in water, at room temperature, in a short single step. Cellulose sheets have thus been grafted with several acrylic polymers, first globally through a dipping procedure and then locally by inkjet printing. All the strategies developed herein would be helpful to immobilize sensitive proteins on selected specific areas of cellulose sheets. More generally, these are powerful tools for easy and rapid modulation of cellulose surface properties according to complex designs, under soft and biocompatible conditions
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Gradwell, Sheila Elizabeth. "Self-Assembly of Pullulan Abietate on Cellulose Surfaces." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/10095.
Full textAbstract:
Wood is a complex biocomposite that exhibits a high work of fracture, making it an ideal model for multiphase man-made materials. Typically, man-made composites demonstrate interfacial fracture at failure due to abrupt transitions between neighboring phases. This phenomenon does not occur in wood because gradual phase transitions exist between regions of cellulose, hemicellulose, and lignin and therefore adhesion between adjacent phases is increased. The formation of interphases occurs as a consequence of the self-assembly process which governs the formation of wood. If this process was understood more thoroughly, perhaps tougher man-made, biobased composites could be prepared. To study self-assembly phenomena in wood, a system composed of a model copolymer (pullulan abietate, DS=0.027) representing the lignin-carbohydrate complex (LCC) and a model surface for cellulose fibers was used. The self-assembly of the polysaccharide pullulan abietate (DS=0.027) onto a regenerated cellulose surface prepared using the Langmuir-Blodgett (LB) technique was studied via surface plasmon resonance (SPR). Rapid, spontaneous, and desorption-resistant cellulose surface modification resulted when exposed to the model LCC. Adsorption was quantified using the de Feijter equation revealing that between 9-10 anhydroglucose units (AGUs) adsorb per nm&178; of cellulose surface area when cellulose is exposed to pullulan abietate (DS=0.027) compared to the adsorption of 6.6 AGUs per nm&178; of cellulose surface area when cellulose is exposed to unsubstituted pullulan.<br>Master of Science
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Zhu, Qin. "Étude des modifications de la sialylation des cellules malignes et metastatiques." Lille 1, 1989. http://www.theses.fr/1989LIL10174.
Full textAbstract:
La transformation maligne des cellules conduit à des modifications importantes de la glycosylation. L'étude comparée de 7 lignées cellulaires uroepithéliales présentant des degrés différents de transformation nous a permis de montrer que les cellules tumorigènes et invasives sont enrichies en glycannes de type n-acetyl lactosaminique tri- et tétra-antennes, par rapport aux glycannes présents dans les lignées non tumorigènes et non invasives. Parallèlement, l'apparition d'une potentialité métastasique semble être associée à une augmentation de la sialylation des cellules tumorales. L'analyse comparée des cellules du carcinome pulmonaire de Lewis à haut et à faible pouvoir métastasique par des lectines marquées et par l'analyse quantitative des acides sialiques cellulaires nous a permis de confirmer cette hypothèse. La mise au point d'une méthode simple nous a permis d'étudier la modification de l'acide sialique de fibroblastes murins transformés par l'oncogène c-Ha-ras. Cette étude a montré l'apparition d'acide n-glycolylneuraminique dans les cellules transformées. Pris dans leur ensemble, ces différents résultats dénotent du rôle essentiel que semblent jouer les acides sialiques dans les phénomènes de métastases
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Argüeso, Lleida Andrea. "Développement d’approches de modifications ciblées du méthylome dans les cellules mammifères." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAJ068.
Full textAbstract:
La méthylation de l’ADN est une modification épigénétique sur les cytosines des dinucléotides CpG catalysée par les enzymes DNMT. Les cellules cancéreuses présentent des hyperméthylations aberrantes sur les promoteurs de gènes dits suppresseurs de tumeurs, ce qui contribue à leur répression transcriptionnelle et favorise la progression tumorale. De par sa nature réversible, la méthylation de l’ADN est une cible de choix pour des thérapies épigénétiques ; cependant, les inhibiteurs de DNMT ont une action de déméthylation globale du génome qui conduit à une forte toxicité. Mon travail a consisté à développer des stratégies de déméthylation ciblée sur des régions spécifiques du génome. Premièrement, j’ai validé une stratégie induisant une reprogrammation épigénétique spécifique et durable du gène suppresseur de tumeurs SERPINB5 dans des cellules de cancer du sein. Deuxièmement, j’ai optimisé des stratégies d'édition de l’épigénome comme outil en recherche fondamentale<br>DNA methylation takes place on cytosines of CpG dinucleotides in mammals and is catalysed by DNMT enzymes. Cancer cells are characterised by frequent promoter hypermethylation leading to transcriptional repression of tumor suppressor genes and favouring tumor progression. Because of its reversible nature, DNA methylation is a target of choice in epigenetic therapies. However, current DNMT inhibitors act in a global and non-specific manner, leading to side effects and toxicity in normal cells. During my thesis I have developed strategies to perform targeted demethylation in specific regions of the genome without affecting global methylation. First, I have validated a strategy inducing the specific and durable epigenetic reprogramming of the tumor suppressor gene SERPINB5 in a breast cancer cell line, which can pave the way to further biomedical research. Second, I have optimised epigenome editing strategies as a regular tool in basic research
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Butchosa, Robles Núria. "Tailoring Cellulose Nanofibrils for Advanced Materials." Doctoral thesis, KTH, Biokompositer, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155056.
Full textAbstract:
Cellulose nanofibrils (CNFs) are nanoscale fibers of high aspect ratio that can be isolated from a wide variety of cellulosic sources, including wood and bacterial cellulose. With high strength despite of their low density, CNFs are a promising renewable building block for the preparation of nanostructured materials and composites. To fabricate CNF-based materials with improved inherent rheological and mechanical properties and additional new functionalities, it is essential to tailor the surface properties of individual CNFs. The surface structures control the interactions between CNFs and ultimately dictate the structure and macroscale properties of the bulk material. In this thesis we have demonstrated different approaches, ranging from non-covalent adsorption and covalent chemical modification to modification of cellulose biosynthesis, to tailor the structure and surface functionalities of CNFs for the fabrication of advanced materials. These materials possess enhanced properties such as water-redispersibility, water absorbency, dye adsorption capacity, antibacterial activity, and mechanical properties. In Paper I, CNFs were modified via the irreversible adsorption of carboxymethyl cellulose (CMC). The adsorption of small amounts of CMC onto the surface of CNFs prevented agglomeration and co-crystallization of the nanofibrils upon drying, and allowed the recovery of rheological and mechanical properties after redispersion of dried CNF samples. In Paper II, CNFs bearing permanent cationic charges were prepared through quaternization of wood pulp fibers followed by mechanical disintegration. The activation of the hydroxyl groups on pulp fibers by alkaline treatment was optimized prior to quaternization. This optimization resulted in individual CNFs with uniform width and tunable cationic charge densities. These cationic CNFs demonstrated ultrahigh water absorbency and high adsorption capacity for anionic dyes. In Paper III, via a similar approach as in Paper II, CNFs bearing polyethylene glycol (PEG) were prepared by covalently grafting PEG to carboxylated pulp fibers prior to mechanical disintegration. CNFs with a high surface chain density of PEG and a uniform width were oriented to produce macroscopic ribbons simply by mechanical stretching of the CNF hydrogel network before drying. The uniform grafted thin monolayer of PEG on the surface of individual CNFs prevented the agglomeration of CNFs and facilitated their alignment upon mechanical stretching, thus resulted in ribbons with ultrahigh tensile strength and modulus. These optically transparent ribbons also demonstrated interesting biaxial light scattering behavior. In Paper IV, bacterial cellulose (BC) was modified by the addition of chitin nanocrystals (ChNCs) into the growing culture medium of the bacteria Acetobacter aceti which secretes cellulose in the form of entangled nanofibers. This led to the in situ incorporation of ChNCs into the BC nanofibers network and resulted in BC/ChNC nanocomposites exhibiting bactericidal activity. Further, blending of BC nanofibers with ChNCs produced nanocomposite films with relatively lower tensile strength and modulus compared to the in situ cultivated ones. The bactericidal activity increased significantly with increasing amount of ChNCs for nanocomposites prepared by direct mixing of BC nanofibers and ChNCs. In Paper V, CNFs were isolated from suspension-cultured wild-type (WT) and cellulose-binding module (CBM) transformed tobacco BY-2 (Nicotiana tabacum L. cv bright yellow) cells. Results from strong sulfuric acid hydrolysis indicated that CNFs from transgenic cells overexpressing CBM consisted of longer cellulose nanocrystals compared to CNFs from WT cells. Nanopapers prepared from CNFs of transgenic cells demonstrated significantly enhanced toughness compared to CNFs of WT cells.<br><p>QC 20141103</p><br>CARBOMAT
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Chartrand, Ariane. "La modification chimique en surface de la cellulose microcristalline et son application dans les composites de polyéthylène." Mémoire, Université de Sherbrooke, 2016. http://hdl.handle.net/11143/9446.
Full textAbstract:
Dans le contexte de la production d’éthanol cellulosique, la cellulose doit être hydrolysée par voie chimique ou enzymatique. Dans ce procédé d’hydrolyse, la partie cristalline de la cellulose est plus difficilement fragmentable, ce qui entraîne des coûts supplémentaires dues au temps de traitement plus élevé ou à la quantité supplémentaire de produits chimiques nécessaires. Dans l’optique de réduire les coûts de l’hydrolyse tout en recherchant une voie pour valoriser la cellulose cristalline, l’idée de fabriquer des composites polymères/cellulose est attrayante. L’objectif du présent travail a donc été de valider si la cellulose microcristalline tirée d’un processus d’hydrolyse acide pourrait mener à de nouveaux matériaux composites à valeur ajoutée. Un obstacle anticipé dans le projet a été la faible adhésion de la cellulose, hydrophile et polaire, aux polymères généralement beaucoup moins polaires. Le développement de composites performants et l’atteinte de teneurs élevés en cellulose microcristalline a donc inclus, sur le plan chimique, l’objectif de comparer divers traitements de surface de la cellulose qui permettrait de pallier aux défis anticipés. La méthodologie utilisée dans ce projet a consisté à développer et optimiser un protocole de modification chimique sur de la cellulose microcristalline commerciale à l’échelle laboratoire. Les celluloses modifiées ont été soumises à une caractérisation par analyse de l’angle de contact pour caractériser l’hydrophobicité des fibres, par spectrométrie photoélectronique X pour l’analyse de la composition chimique des fibres, par granulométrie laser pour mesurer la longueur des différentes fibres et microscopie optique pour l’observation de la longueur des fibres. Toutes les techniques ont été utilisées afin de comparer les propriétés des celluloses modifiées à celles de la cellulose de référence. La cellulose de référence et les celluloses modifiées chimiquement ont ensuite été mélangées à des concentrations de 0 à 50% avec du polyéthylène de basse densité à l’état fondu en utilisant un mélangeur interne de type Brabender®. Les composites ont été caractérisés par microscopie électronique à balayage pour analyser la morphologie de mélange sur les surfaces de rupture et l’homogénéité du mélange, par des analyses rhéologiques afin d’obtenir la viscosité en fonction du cisaillement et par des essais de traction afin de déterminer leur Module de Young, leur résistance à la traction et leur élongation à la rupture. Ces caractéristiques permettent de prévoir la performance des composites dans des applications structurales.
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Pettersson, Jesper. "Chemical Modification of NFC: Development of Renewable Barriers for Packaging Applications." Thesis, KTH, Skolan för kemivetenskap (CHE), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146309.
Full textAbstract:
Globalization and centralization have resulted in prolonged transportation time between producer and consumer, and thus put more demand on the perseveration of a product for longer duration and protect it from oxidation. The presence of oxygen in packages severely foreshortens the storage life as it yield losses of nutrients and allow microbial growth, which can cause changes in smell, taste as well as discoloration. Earlier food and beverage containers were made in inorganic materials e.g. metal and glass, however lately more and more focus have been on synthetic organic materials as these show several advantages, e.g. weight. However, still today most of the commercial packaging materials, organic or inorganic, are not considered to be environmental friendly. Thus, efforts have to be made today in order to invent alternative materials that can make the society of tomorrow more sustainable. Cellulose is the most abundant biopolymer in the world, hence making it desirable to use in “green” packaging applications. Furthermore, cellulose has proven being able to form films with great gas barrier potential under specific conditions. However, cellulose based materials are sensitive to moisture with severely increased oxygen transmission with increased relative humidity as a result; hence it is desired to make cellulose less hygroscopic by chemical modification. First, nanofibrillated cellulose (NFC) with 720 mmol carboxylic groups/g fiber was produced by oxidation of dissolving pulp before homogenization. Thereafter a polymer was synthesized utilizing Initiator A as an initiator at T1 and T2. The polymer synthesized at T1 yielded a polymer with a viscosity average molecular weight of 5770 g/mol. The polymer was then grafted on the oxidized NFC through a coupling reaction performed in Buffer C using Coupling agent A. The grafting procedure was performed in Buffer C at ambient conditions giving rise to a material composed of 33 wt% synthetic polymer and 67 wt% NFC. The coupling was conducted several times in order to investigate how the final product can be affected by varying reactant feed and dispersion method. Finally, films of NFC and NFC-g-Polymer were manufactured by vacuum filtration from a 0.05 wt% Solvent A dispersion and were evaluated with field emission scanning electron microscopy.
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Pouzet, Martial. "Modification de l’énergie de surface du bois par fluoration." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC086/document.
Full textAbstract:
La disponibilité, les aspects écologiques et économiques du bois sont autant d’avantages qui expliquent le large champ d’applications de ce matériau dans plusieurs domaines tels que la papeterie, l’ameublement, la menuiserie ou la construction. Cependant, le bois est un matériau hygroscopique très sensible aux variations d’humidité et de température ambiante. Le gonflement et le retrait causés par l’adsorption et la désorption de l’eau engendrent des fissures et des déformations dans le bois, le rendant incompatible avec certaines applications.Dans cette étude, une méthode originale a été appliquée sur des échantillons de bois (douglas et sapin) pour diminuer leur caractère hydrophile : la fluoration directe par du fluor moléculaire F2. Le greffage covalent des atomes de fluor sur la surface du bois, grâce à une substitution des groupements C-OH par des liaisons C-F, a été validé par spectroscopie infrarouge et par Résonance Magnétique Nucléaire du 19F.Le bois, qui est intrinsèquement hydrophile, acquiert un caractère hydrophobe comparable à celui du Téflon grâce à la fluoration. Des études de vieillissements sous atmosphère ambiante et irradiation UV ont permis de déterminer une bonne durabilité du traitement. De plus, ce traitement permet d’obtenir un caractère hydrophobe sans changements structuraux (morphologie, densité et couleur) ou mécaniques majeurs. Grâce au caractère surfacique de la fluoration, la conservation de ces propriétés après la fluoration s’avère être un remarquable avantage par rapport aux autres traitements physiques et chimiques classiquement utilisés dans l’industrie du bois<br>The availability, the ecological and economic characteristics of wood are advantages which explain the very wide scope of applications of this material in several domains such as the paper industry, furniture, carpentry and construction. However, wood is a hygroscopic material, highly sensitive to ambient humidity and temperature. The swelling and the shrinking caused by water adsorption and desorption cycles lead to cracking and deformation in the wood volume, making it incompatible for some applications.In this study an original surface treatment was applied to wood samples (douglas and silver fir species) to decrease their hydrophilic character: direct fluorination using F2 gas. The covalent grafting of fluorine atoms onto extreme wood surfaces through a conversion of C-OH groups into C-F was evidenced by Fourier-Transform infrared spectroscopy and 19F solid state Nuclear Magnetic Resonance.The wood which is initially hydrophilic acquires a hydrophobic character comparable to that of Teflon, thanks to fluorination. Good durability of this treatment under ambient atmosphere and UV irradiation was also highlighted. Moreover, because it affects only the extreme surface, this treatment allowed us to obtain a hydrophobic character without major structural (morphology, density and colour) or mechanical changes. The maintaining of these properties after fluorination appears to be a remarkable advantage over other traditional physical and chemical wood treatments
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Thibault, Catherine. "Modifications fonctionnelles de la cellule b pancreatique chez le rat hyperglycemique." Paris 7, 1993. http://www.theses.fr/1993PA077212.
Full textAbstract:
Il est actuellement etabli que l'hyperglycemie des sujets atteints du diabete non-insulinodependant est en grande partie liee a une alteration de la secretion d'insuline qui correspond a une diminution de la reactivite des cellules b productrices d'insuline au glucose. Le but de cette these est d'etudier les relations entre l'hyperglycemie prolongee et la fonction insulinosecretoire. Chez le rat non diabetique, l'hyperglycemie provoque un etat d'hypersensibilite pancreatique au glucose sans que la reponse secretoire maximale soit modifiee. L'etude de l'effet de certains facteurs nerveux sur la secretion d'insuline montre que cette augmentation de la sensibilite pancreatique est liee, d'une part, a une diminution de l'activite sympathique inhibitrice et une augmentation de l'activite stimulante et d'autre part, a une elevation de la reponse insulinique a l'acetylcholine. Chez les rats presentant au prealable des degres varies d'intolerance au glucose, l'hyperglycemie induit des effets differents suivant la severite de l'atteinte pancreatique. Chez les rats legerement intolerants au glucose, l'hyperglycemie entraine une augmentation marquee de la secretion d'insuline. Chez les rats tres intolerants au glucose et diabetiques dont la masse des cellules b est fortement diminuee, cet effet potentialisateur sur la secretion d'insuline est respectivement tres faible ou totalement aboli. Chez les rats legerement intolerants, l'amplification de la reponse insulinique va de pair avec une augmentation importante du metabolisme des phosphoinositides. Au contraire, chez les rats diabetiques, l'hyperglycemie est sans influence sur ce metabolisme. En conclusion, la potentialisation par le glucose de la secretion d'insuline est un element important de la capacite fonctionnelle de la cellule b pancreatique et son alteration pourrait etre un des phenomenes initiaux qui conduirait de la simple intolerance au glucose au diabete non-insulinodependant
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Coleman, Heather Dawn. "Modification of cellulose biosynthesis through varied expression of sucrose metabolism genes in tobacco and hybrid poplar." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2891.
Full textAbstract:
UDP-glucose, the precursor for cellulose biosynthesis, can be produced via the
catalysis of sucrose by sucrose synthase (SuSy) or through the phosphorylation of
glucose-I-phosphate by UDP-glucose pyrophosphorylase (UGPase). As such, these
genes, together with sucrose phosphate synthase (SPS) which recycles fructose (an
inhibitor of SuSy), are interesting targets for altering carbon allocation in plants.
In an attempt to alter cell wall biosynthesis in plants, targeted overexpression of
SuSy, UGPase and SPS independently and in a pyramiding strategy was assessed in
tobacco. All lines displayed enhanced growth and biomass production, and in the case
of double and triple transgenics, there was an additive effect. Despite the increased
growth rates, there was no consistent change in soluble carbohydrate pools.
Furthermore, only the triple transgenics had constant changes in structural
carbohydrates: with increased hemicellulose content and slight increases in cellulose.
Collectively, these results support the role of SPS, SuSy and UGPase in maintaining
sink strength, but suggest that the reallocation of carbon to cellulose production in
tobacco may not be possible by overexpressing these genes.
In contrast, transgenic poplar overexpressing UGPase produced significantly
more cellulose than wild-type trees. However, this was accompanied by a severe
reduction in growth and the production of a salicylic acid glucoside (SAG) in significant
quantities. The UDP-glucose generated by UGPase overexpression appeared to
participate in both the synthesis of cellulose and SAG, suggesting that cellulose
biosynthesis may be limited by the cellulose synthase complex.
Poplar transformed with SuSy and with SuSy x UGPase also had increased
cellulose production. The trees were phenotypically normal, with only minor reductions
in height growth in some lines. It appears that UDP-glucose may be channelled directly
to the cellulose synthase complex by SuSy. The increased cellulose content was
associated with an increase in cell wall crystallinity, but there was no change in
microfibril angle, confirming the re-allocation to cellulose synthesis was not the result of
tension wood formation, again supporting the hypothesis that the cellulose synthase
complex is the limiting factor.
Clearly, it is possible to alter cellulose deposition in trees by augmenting sucrose
metabolism to produce UDP-glucose, the precursor to cellulose biosynthesis.
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Grooby, Paul. "Chemical modification of cellulosic fibres to enhance dyeability with reactive dyes." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275699.
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Oka, Mihir Anil. "PLA and cellulose based degradable polymer composites." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33829.
Full textAbstract:
We studied PLA-microcrystalline cellulose composites, focusing on the effects of processing, particle size and surface modification. The thermal and mechanical properties of these PLA based composites were studied and the effect of cellulose addition on PLA degradation was analyzed. For our system, the degradation rate was found to depend on initial sample crystallinity, pH of the degradation media and cellulose content of the composite. Composites were prepared using solution processing and melt mixing methods. The processing methods influenced the polymer's ability to crystallize affecting the mechanical properties. Isothermal crystallization studies carried out to study the kinetics of crystallization showed melt processed samples to have lower half time for crystallization and higher value for the Avrami exponent. The crystallization rate of PLA was also found to depend on surface chemical composition of cellulose particles and the particle size. Influence of filler surface modification on the composite properties was studied via grafting of lactic acid and polylactic acid to cellulose particles and the effect of filler size was studied using hydrolyzed microcrystalline cellulose particles. A simple esterification reaction that required no external catalyst was used for surface modification of cellulose particles. Surface modification of cellulose particles enhanced the static and dynamic mechanical properties of the composite samples due to improvement in the PLA-cellulose compatibility that resulted in better interfacial interactions. The utility of cellulose, available from a renewable resource, as an effective reinforcement for PLA is demonstrated.