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1
Ravachol, Julie. "Rôle des glycosides hydrolases de famille 9 dans la dégradation de la cellulose et exploration du catabolisme de xyloglucane chez Ruminiclostridium cellulolyticum". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4054.
Testo completoAbstract (sommario):
R. cellulolyticum est une bactérie mésophile, anaérobie stricte et cellulolytique, qui sécrète des macro-complexes multienzymatiques (cellulosomes) très performants dans la dégradation des polysaccharides de la paroi végétale. Les Glycoside Hydrolases de famille 9 (GH9) sont toujours surreprésentées chez les bactéries à cellulosomes. Le génome de R. cellulolyticum code 13 GH9 dont 12 participent aux cellulosomes. Mon travail de thèse a consisté à étudier l’ensemble des GH9 de R. cellulolyticum, en déterminant leurs activités à l’état libre et en complexes, afin d’élucider leurs rôles dans la dégradation de la cellulose. Les GH9 ont chacune des activités et des spécificités de substrats différentes. Deux GH9 présentent des activités atypiques, puisque l’une d’elles est inactive et l’autre est une xyloglucanase. Les caractérisations en complexes ont souligné l’importance de la diversité des GH9 et ont montré qu’elles agissent en synergie dans la dégradation de la cellulose. De plus, l’élargissement du panel des GH9 de R. cellulolyticum par l’introduction d’une cellulase exogène de Lachnoclostridium phytofermentans a permis d’améliorer les capacités cellulolytiques de la clostridie. L’activité xyloglucanase d’une des GH9 m’a poussé à étudier le catabolisme du xyloglucane chez R. cellulolyticum. Ce travail a mis en exergue la présence d’un équipement spécialisé dans l’utilisation de ce sucre. Ainsi, après une dégradation du xyloglucane par les enzymes cellulosomales en xyloglucane dextrines, ces dernières sont importées dans le cytoplasme par un transporteur ABC spécifique puis hydrolysées séquentiellement par les enzymes cytoplasmiques en mono et disaccharides assimilablesRuminiclostridium cellulolyticum is a mesophilic and strictly anaerobic bacterium. It produces multienzymatic complexes called cellulosomes which efficiently degrade the plant cell wall polysaccharides. Family-9 Glycoside Hydrolases (GH9) are plethoric in cellulosome-producing bacteria. The genome of R. cellulolyticum thus encodes for 13 GH9 enzymes, 12 of them participate to the cellulosomes.My Ph. D. aimed at characterizing all GH9 enzymes from R. cellulolyticum, by determining their activities in a free and complexed states, in order to elucidate their role in cellulose degradation. All GH9 enzymes exhibit various activities and substrate specificities. Two of them have atypical activities, since one is inactive and one is a xyloglucanase. Results obtained when all GH9 are in complex highlighted the importance of GH9 diversity and revealed they act synergistically in cellulose depolymerization. Moreover, expanding the panel of GH9 enzymes by introducing an exogenous cellulase from Lachnoclostridium phytofermentans improved the cellulolytic capacities of R. cellulolyticum. The xyloglucanase activity of one GH9 enzyme prompted me to investigate the xyloglucan catabolism in R. cellulolyticum. This work uncovered the presence of a specialized equipment for xyloglucan utilization. After extracellular digestion of xyloglucan by cellulosomal enzymes, xyloglucan dextrins are imported into the cytoplasm via a specific ABC-transporter and sequentially hydrolyzed by cytoplasmic enzymes into fermentable mono and disaccharides
2
Cervin, Nicholas. "Porous Cellulose Materials from Nano Fibrillated Cellulose". Licentiate thesis, KTH, Fiberteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-104196.
Testo completoAbstract (sommario):
In the first part of this work a novel type of low-density, sponge-like material for the separation of mixtures of oil and water has been prepared by vapour deposition of hydrophobic silanes on ultra-porous nanocellulose aerogels. To achieve this, a highly porous (> 99 %) nanocellulose aerogel with high structural flexibility and robustness is first formed by freeze-drying an aqueous dispersion of the nanocellulose. The density, pore size distribution and wetting properties of the aerogel can be tuned by selecting the concentration of the nanocellulose dispersion before freeze-drying. The hydrophobic light-weight aerogels are almost instantly filled with the oil phase when they selectively absorb oil from water, with a capacity to absorb up to 45 times their own weight. The oil can also be drained from the aerogel and the aerogel can then be subjected to a second absorption cycle.In the second part of the work a novel, lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified NanoFibrillated Cellulose (NFC). Confocal microscopy and high-speed video imaging show that the long-term stability of the wet foams can be attributed to the octylamine-coated, rod-shaped NFC nanoparticles residing at the air-liquid interface which prevent the air bubbles from collapsing or coalescing. Careful removal of the water yields a porous cellulose-based material with a porosity of 98 % and a density of 30 mg cm-3. These porous cellulose materials have a higher Young’s modulus than other cellulose materials made by freeze drying and a compressive energy absorption of 56 kJ m-3 at 80 % strain. Measurements with an autoporosimeter reveal that most pores are in the range of 300 to 500 μm.QC 20121107
3
Peri, Suma Lee Yoon Y. "Kinetic investigation and modeling of cellulase enzyme using non-crystalline cellulose and cello-oligosaccharides". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Summer/Theses/PERI_SUMA_47.pdf.
Testo completo
4
Mokatse, Khomotso. "Production, characterization and evaluation of fungal cellulases for effective digestion of cellulose". Thesis, University of Limpopo (Turfloop Campus), 2013. http://hdl.handle.net/10386/1129.
Testo completoAbstract (sommario):
Thesis (M.Sc. (Microbiology)) --University of Limpopo, 2013The production of cellulase is a key factor in the hydrolysis of cellulosic materials and it is essential to make the process economically viable. Cellulases are the most studied multi- enzyme complex and comprise of endo-glucanases (EG), cellobiohydrolases (CBH) and β- glucosidases (BGL). The complete cellulase system; comprising CBH, EG and BGL components thus acts synergistically to convert crystalline cellulose to glucose. Cellulases are currently the third largest industrial enzyme worldwide. This is due to their wide applications in cotton processing, paper recycling, juice extraction, as detergent enzymes and additives in animal feed. In this study, production of cellulase by five fungal isolates (BTU 251-BTU 255) isolated from mushrooms, was investigated and optimised. Internal transcribed spacer regions (ITS1 and ITS4) were applied to identify the five fungal microorganisms. Isolates were identified as follows: BTU 251 as Aspegillus niger,BTU 253 as Penicillium polonicum, and BTU 255 as Penicillium polonicum. Cellulase was produced in shake flask cultures using Mandel’s mineral solution medium and Avicel as a carbon source. Cellulase activity was tested using 3, 5-Dinitrosalicylic acid assay and zymography, A. niger BTU 251 showed five activity bands ranging from 25- 61 kDa had an average nkat of 7000. Cultures from BTU 252 were the least active with an average nkat/ml of 200 and one activity band of 25 kDa. P. polonicum BTU 253 showed three activity bands ranging between 45 and 60 kDa and had an average nkat/ml of 2200. BTU 254 showed five activity bands ranging from 22- 116 kDa and had average nkat of 350. P. polonicum BTU 255 produced the highest cellulase activity of 8000 nkat/ml and with three activity bands estimated at 45-60 kDa on zymography. The optimal temperature for activity of the cellulases was between 55-70°C and enzymes were most active within a pH range of 4-6. Optimal pH for production of cellulases by P. polonicum BTU 255, P. polonicum BTU 253 and A. niger BTU 251 was 4 while optimal temperature for production of the cellulases was between 50-55°C. Total cellulase activity was determined using Whatman No.1 filter paper as a substrate and β- glucosidase production was determined in polyacrylamide gels using esculin as a substrate. In the hydrolysis of crystalline cellulose (Avicel), a combination of A. niger BTU 251 and P. polonicum BTU 255 (1:1), (1:9), (1:3), and (1:2) produced maximum glucose as follows: 1:1 (0.83g/L), 1:9 (10.4g/L), 1:3 (0.77g/L) and 1:2 (0.73g/L). Cellulases from P. polonicum BTU 255 were partially purified using affinity precipitation and analysed using MALDI- TOF/TOF. Peptide sequences of P. polonicum obtained from MALDI-TOF/TOF analysis were aligned by multiple sequence alignment with C. pingtungium. Conserved regions were identified using BLAST anaylsis as sequences of cellobiohydrolases. More research is required in producing a variety of cellulases that are capable of hydrolysing crystalline cellulose, the current study contributes to possible provision of locally developed combinations of cellulases that can be used in the production of bioethanol.
5
Schult, Tove. "Properties of acid sulfite cellulose for cellulose derivatives". Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2000. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1508.
Testo completo
6
Linder, Markus. "Structure-function relationships in fungal cellulose-binding domains /". Espoo, Finland : VTT, Technical Research Centre of Finland, 1996. http://www.vtt.fi/inf/pdf/publications/1996/P294.pdf.
Testo completo
7
Gal, Laurent. "Etude du cellulosome de Clostridium cellulolyticum et de l'un de ses composants : la cellulase CelG". Aix-Marseille 1, 1997. http://www.theses.fr/1997AIX11071.
Testo completoAbstract (sommario):
Le cellulosome de la bacterie cellulolytique clostridium cellulolyticum atcc 35319 a ete etudie. C'est un complexe de 600 kda, en moyenne, qui degrade efficacement la cellulose cristalline. Il est constitue de plusieurs proteines de masse moleculaire relative variant entre 170 et 30 kda. L'utilisation du minicipc1 biotinyle a permis de montrer qu'au moins treize d'entre elles possedaient une dockerine. Parmi celles-ci, les proteines cela, celc, cele, celf et celg, dont les genes sont clones et sequences, ont ete identifiees. Afin de rechercher de nouveaux genes cel codant pour des proteines possedant une dockerine, une marche sur le chromosome en aval de cele a ete entreprise. Elle a revele l'existence de trois nouveaux genes impliques dans la cellulolyse : cipx, celh et celj. - cipx est une proteine tres originale constituee d'un domaine de type linker et d'une cohesine. - celh et celj, tout comme celg, possedent un domaine catalytique de la famille 9 de la classification des glycosyl-hydrolases, suivi d'un domaine de type cbd de la famille iii et enfin d'une dockerine c-terminale. Pour tenter de comprendre le role joue par ce dernier type de proteines dans la cellulolyse, la caracterisation biochimique de celg a ete entreprise. Le gene celg a ete surexprime chez escherichia coli et la proteine recombinante correspondante a ete purifiee. Celg est une endoglucanase qui degrade efficacement la cmc et le glucane d'orge. Elle est egalement active sur la cellulose amorphe et degrade les cellodextrines ayant un degre de polymerisation superieur ou egal a trois. Contrairement aux autres endoglucanases caracterisees jusqu'a present chez c. Cellulolyticum, celg degrade les celluloses cristallines, et en particulier la bmcc de maniere tres efficace. Pour etudier l'influence relative de chacun des domaines de celg dans ce mecanisme, differentes constructions genetiques, permettant la synthese du domaine catalytique seul ou du domaine de type cbd fusionne derriere la glutathion-s-transferase, ont ete realisees. Dans tous les cas, les proteines recombinantes ne presentent ni activite catalytique ni proprietes d'adhesion a la cellulose. L'ensemble de ces resultats suggere qu'a la difference de la plupart des cellulases, les differents domaines constitutifs de celg ne sont pas independants. La presence d'au moins deux autres proteines homologues a celg (celh et celj) au sein du systeme cellulolytique de c. Cellulolyticum suggere que ces proteines jouent un role fondamental dans les mecanismes de degradation de la cellulose chez cet organisme.
8
Lane, J. M. "Solid state NMR studies of cellulose and cellulose acetate". Thesis, University of East Anglia, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374690.
Testo completo
9
Hu, Gang. "Adsorpton and Activity of Cellulase Enzymes on Various of Cellulose Substrates". NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-04222009-234535/.
Testo completoAbstract (sommario):
The objective of this research is to understand the interfacial behavior of cellulase enzymes and its effect on cellulose hydrolysis. This research began with an in-situ monitoring of cellulose hydrolysis using a piezoelectric based quartz crystal microbalance. The time-course kinetics was modeled using a dose response model. The adsorption indicated by the frequency drop followed a Langmuir model as cellulase enzyme increased. Another important part of this research is the development of a new cellulase activity assay based on the piezoelectric technique. This assay provides an easier and more user friendly method for cellulase enzyme activity measurement. It also helps to clarify an element of the interpretation of frequency drops after the injection of cellulase solutions in the hydrolysis of cellulose film, which has been neglected in previous research. Interfacial adsorption of cellulase protein was also investigated using the depletion method. The effects of substrate properties, primarily the crystallinity, which was characterized using X-ray diffraction, were investigated. The effect of surface area, which was measured using both laser light scattering and BET adsorption, on cellulase adsorption were also investigated. It was found that crystallinity played a more important role in cellulase adsorption than surface areas of cellulosic substrate. In characterization of cellulosic substrates, the water retention value (WRV) was also investigated. The results indicated that lower crystallintiy substrates have higher water retention ability. The cellulase adsorption, as well as desorption, was also studied by using sodium dodecyle sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The adsorption results followed the same trend as indicated by the depletion methods. The various isozymes demonstrated a uniform adsorption in proportion to their concentrations. Desorption appeared uniform. Higher pH was found to create higher desorption for a particular cellulase from a particular substrates. It was also found that cellulase from Trichoderma reesei had higher affinity to cellulosic substrates used in this work than the one from Aspergillus niger.
10
Qian, Chen. "Adsorption of Xyloglucan onto Cellulose and Cellulase onto Self-assembled Monolayers". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/42496.
Testo completoAbstract (sommario):
Adsorption of xyloglucan (XG) onto thin desulfated nanocrystalline cellulose (DNC) films was studied by surface plasmon resonance spectroscopy (SPR), quartz crystal microbalance with dissipation monitoring (QCM-D), and atomic force microscopy (AFM) measurements. These studies were compared to adsorption studies of XG onto thin sulfated nanocrystalline cellulose (SNC) films and regenerated cellulose (RC) films performed by others. Collectively, these studies show the accessible surface area is the key factor for the differences in surface concentrations observed for XG adsorbed onto the three cellulose surfaces. XG penetrated into the porous nanocrystalline cellulose films. In contrast, XG was confined to the surfaces of the smooth, non-porous RC films. Surprisingly surface charge and cellulose morphology played a limited role on XG adsorption.
The effect of the non-ionic surfactant Tween 80 on the adsorption of cellulase onto alkane thiol self-assembled monolayers (SAMs) on gold was also studied. Methyl (-CH3), hydroxyl
(-OH) and carboxyl (-COOH) terminated SAMs were prepared. Adsorption of cellulase onto untreated and Tween 80-treated SAMs were monitored by SPR, QCM-D and AFM. The results indicated cellulase adsorption onto SAM-CH3 and SAM-COOH were driven by strong hydrophobic and electrostatic interactions, however, hydrogen bonding between cellulase and SAM-OH was weak. Tween 80 effectively hindered the adsorption of cellulase onto hydrophobic SAM-CH3 substrates. In contrast, it had almost no effect on the adsorption of cellulase onto SAM-OH and SAM-COOH substrates because of its reversible adsorption on these substrates.Master of Science
11
Du, Plessis Lisa. "Co-expression of cellulase genes in Saccharomyces cerevisiae for cellulose degradation". Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/1818.
Testo completo
12
Tahara, Naoki. "STUDIES ON CELLULASES IN A CELLULOSE-PRODUCING BACTERIUM, ACETOBACTER XYLINUM". Kyoto University, 1998. http://hdl.handle.net/2433/182416.
Testo completo
13
Tchunden, Jeannette. "Cellulolyse Anaérobie Mésophile : étude de l'amélioration de la production de cellulases par Cl. cellulolyticum ATCC 35319". Nancy 1, 1990. http://docnum.univ-lorraine.fr/public/SCD_T_1990_0044_TCHUNDEN.pdf.
Testo completoAbstract (sommario):
Cl. Cellulolyticum est une bactérie cellulolytique mésophile isolée au laboratoire à partir d'herbes en décomposition. Cette bactérie est capable de dégrader la cellulose en une seule étape en acides organiques et en éthanol. Mais l'activité cellulolytique de la souche reste faible. Pour arriver à une possibilité d'utilisation industrielle de la bactérie, les performances cellulolytiques de la souche doivent être améliorées. L'amélioration de la production de cellulases par cl. Cellulolyticum passe à la fois par l'amélioration de ses conditions de culture et l'amélioration de la souche. Ainsi nous avons montré qu'une culture en fermenteur avec régulation de ph à 7,2 par une solution d'ammoniac 4n conduit à une plus forte production de cellulases. Par l'emploi du rayonnement ultraviolet comme agent mutagène et de cellobiose comme crible de sélection, nous avons isolé le mutant 42 qui produit deux fois plus de cellulases que la souche parent. Nous avons également montré que la cellulose avicel est meilleure inductrice de l'endo et de l'exoglucanase aussi bien chez cl. Cellulolyticum que chez le mutant. L'étude de l'association de cl. Cellulolyticum et du mutant 42 a permis de produire 4,7 fois plus d'activité xylanasique.
14
Meng, Xianzhi. "Assessing the effect of pretreatment on cellulose accessibility for cellulosic biofuels production". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54347.
Testo completoAbstract (sommario):
Biomass recalcitrance has been recognized as one of the major barriers that hided the cost-effective conversion of lignocellulosic biomass to bioethanol, therefore the current bioconversion process require an essential step known as pretreatment to increase the cellulose accessibility. This thesis provides information about changes in cellulose accessibility upon different pretreatments, along with how these pretreatments alter the chemical and physical structures of biomass, will be extremely helpful to further optimize the current pretreatment process. Multiple promising analytical techniques including Simons’ stain, NMR cryoporometry, relaxometry, mercury porosimetry was introduced and successfully applied on pretreated biomass samples to characterize the cellulose accessible surface area and biomass porosity. Different pretreatments increase cellulose accessibility through different mechanisms to different extent. Dilute acid pretreatment is more effective than steam explosion in terms of increasing accessible surface area of cellulose as reflected by Simons’ stain and NMR cryoporometry, while NMR relaxometry suggested steam explosion is more effective at pore expansion for the cell wall water pools detected by changes in NMR relaxation time. Alkaline pretreatment decreased cellulose degree of polymerization, cellulose crystallinity, lignin content and subsequently increased cellulose accessibility, with sodium hydroxide pretreatment proved to be much more effective compared lime or soaking in ammonia pretreatment. Delignification through alkaline-based pretreatment is found less effective than removal of hemicellulose using acid in terms of cellulose accessibility increase. Lignin didn’t directly dictate cellulose accessibility but rather restricted xylan accessibility which in turn controls the access of cellulase to cellulose. Pore size distribution analysis based on mercury porosimetry also indicated that the most fundamental barrier in terms of biomass porosity scale for efficient enzymatic hydrolysis is the nano-pore space formed between coated microfibrils, despite some of the porous architecture such as cell lumen and pit could be severely destroyed after pretreatment. The action of cellulase on the characteristics of cellulosic fractions obtained from pretreated biomass was also investigated. Cellulose accessibility was found to increase at the beginning of hydrolysis, and after reaching a maximum value then starting to decrease. Enzymatic hydrolysis resulted in a rapid decrease in the cellulose degree of polymerization then gradually leveled off, suggesting the existence of a synergistic action of endo- and exo-glucanases that contribute to the occurrence of a peeling off type mechanism.
15
Yang, Han. "Investigation and characterization of oxidized cellulose and cellulose nanofiber films". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106551.
Testo completoAbstract (sommario):
Over the last two decades, a large amount of research has focused on natural cellulose fibers, since they are "green" and renewable raw materials. Recently, nanomaterials science has attracted wide attention due to the large surface area and unique properties of nanoparticles. Cellulose certainly is becoming an important material in nanomaterials science, with the increasing demand of environmentally friendly materials.In this work, a novel method of preparing cellulose nanofibers (CNF) is being presented. This method contains up to three oxidation steps: periodate, chlorite and TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) oxidation. The first two oxidation steps are investigated in the first part of this work. Cellulose pulp was oxidized to various extents by a two step-oxidation with sodium periodate, followed by sodium chlorite. The oxidized products can be separated into three different fractions. The mass ratio and charge content of each fraction were determined. The morphology, size distribution and crystallinity index of each fraction were measured by AFM, DLS and XRD, respectively. In the second part of this work, CNF were prepared and modified under various conditions, including (1) the introduction of various amounts of aldehyde groups onto CNF by periodate oxidation; (2) the carboxyl groups in sodium form on CNF were converted to acid form by treated with an acid type ion-exchange resin; (3) CNF were cross-linked in two different ways by employing adipic dihydrazide (ADH) as cross-linker and water-soluble 1-ethyl-3-[3-(dimethylaminopropyl)] carbodiimide (EDC) as carboxyl-activating agent. Films were fabricated with these modified CNF suspensions by vacuum filtration. The optical, mechanical and thermo-stability properties of these films were investigated by UV-visible spectrometry, tensile test and thermogravimetric analysis (TGA). Water vapor transmission rates (WVTR) and water contact angle (WCA) of these films were also studied.Au cours des deux dernières décennies, une grande quantité de recherches ont portées sur les fibres de cellulose naturels, car ils sont «verts» et de matières premières renouvelables. Récemment, la science des nanomatériaux a attiré l'attention en raison de la gamme grande surface et les propriétés uniques des nanoparticules. La cellulose est en train de devenir un matériau important dans la science des nanomatériaux, à la demande croissante de matériaux écologiques. Dans ce travail, un nouveau procédé de préparation de cellulose nanofibres (CNF) est présenté. Cette méthode contient un maximum de trois étapes d'oxydation: oxydations au periodate, au chlorite et au TEMPO (2,2,6,6-tétraméthylpipéridinyle-1-oxyle). Les deux premières étapes d'oxydation sont étudiées dans la première partie de ce travail. La pâte de cellulose a été oxydée à des degrés divers par un à deux étapes d'oxydation au periodate de sodium, suivi par le chlorite de sodium. Les produits oxydés peuvent être séparés en trois fractions différentes. Le ratio de la masse et le contenu de charge de chaque fraction ont été déterminés. La morphologie, la distribution de la taille et l'indice de cristallinité de chaque fraction ont été mesurés par l'AFM, DLS et XRD, respectivement. Dans la seconde partie de ce travail, des CNF ont été préparés et modifiés dans diverses conditions, y compris (1) l'introduction de diverses quantités de groupes aldéhyde sur les CNF par oxydation au periodate, (2) les groupes carboxyle sous forme de sodium sur les CNF ont été convertis à leur forme acide par traitement avec un type d'acide résine échangeuse d'ions; (3) ces CNF ont été réticulés de deux manières différentes en employant dihydrazide adipique (ADH) en tant que cross-linker et soluble dans l'eau 1-éthyl-3-[3- (diméthylaminopropyl)] carbodiimide (EDC) comme agent activateur de carboxyle. Les films ont été fabriqués avec ces suspensions de CNF modifiés par filtration sous vide. Les propriétés optiques, mécaniques et la thermo-stabilité de ces films ont été étudiées par spectrométrie UV-visible, essai de traction et de l'analyse thermogravimétrique (TGA). Les taux de transmission de vapeur d'eau (WVTR) et l'angle de contact de l'eau (WCA) de ces films ont également été étudiés.
16
Mayende, Lungisa. "Isolation of a Clostridium Beijerinckii sLM01 cellulosome and the effect of sulphide on anaerobic digestion". Thesis, Rhodes University, 2007. http://hdl.handle.net/10962/d1004032.
Testo completoAbstract (sommario):
Cellulose is the most abundant and the most resistant and stable natural organic compound on earth. Enzyme hydrolysis is difficult because of its insolubility and heterogeneity. Some (anaerobic) microorganisms have overcome this by having a multienzyme system called the cellulosome. The aims of the study were to isolate a mesophilic Clostridium sp. from a biosulphidogenic bioreactor, to purify the cellulosome from this culture, to determine the cellulase and endoglucanase activities using Avicel and carboxymethylcellulose (CMC) as substrates and the dinitrosalicyclic (DNS) method. The organism was identified using 16S rDNA sequence analysis. The sequence obtained indicated that a strain of Clostridium beijerinckii was isolated. The cellulosome was purified from the putative C. beijerinckii sLM01 host culture using affinity chromatography purification and affinity digestion purification procedures. The cellulosomal and non-cellulosomal fractions of C. beijerinckii sLM01 were separated successfully, but the majority of the endoglucanase activity was lost during the Sepharose 4B chromatography step. These cellulosomal and non-cellulosomal fractions were characterised with regards to their pH and temperature optima and effector sensitivity. Increased additions of sulphide activated the cellulase activity of the cellulosomal and non-cellulosomal fractions up to 700 %, while increased additions of sulphate either increased the activity slightly or inhibited it dramatically, depending on the cellulosomal and non-cellulosomal fractions. Increased additions of cellobiose, glucose and acetate inhibited the cellulase and endoglucanase activities. pH optima of 5.0 and 7.5 were observed for cellulases and 5.0 for endoglucanases of the cellulosomal fraction. The noncellulosomal fraction exhibited a pH optimum of 7.5 for both cellulase and endoglucanase activities. Both fractions and enzymes exhibited a temperature optimum of 30 °C. The fundamental knowledge gained from the characterisation was applied to anaerobic digestion, where the effect of sulphide on the rate-limiting step was determined. Sulphide activated cellulase and endoglucanase activities and increased the % chemical oxygen demand (COD) removal rate. Levels of volatile fatty acids (VFAs) were higher in the bioreactor containing sulphide, substrate and C. beijerinckii. Sulphide therefore accelerated the rate-limiting step of anaerobic digestion.
17
Roussos, Sevastianos. "Croissance de Trichoderma harzianum par fermentation en milieu solide : physiologie, sporulation et production de cellulases /". Paris : Ed. de l'ORSTOM, 1987. http://catalogue.bnf.fr/ark:/12148/cb349545941.
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18
El-Turabi, Mohammed El Hassan. "The reactions of cellulose and modified cellulose with amide/formaldehyde resins". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329190.
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Arca, Hale Cigdem. "Cellulose Esters and Cellulose Ether Esters for Oral Drug Delivery Systems". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82920.
Testo completoAbstract (sommario):
Amorphous solid dispersion (ASD) is a popular method to increase drug solubility and consequently poor drug bioavailability. Cellulose ω-carboxyesters were designed and synthesized specifically for ASD preparations in Edgar lab that can meet the ASD expectations such as high Tg, recrystallization prevention and pH-triggered release due to the free -COOH groups. Rifampicin (Rif), Ritonavir (Rit), Efavirenz (Efa), Etravirine (Etra) and Quercetin (Que) cellulose ester ASDs were investigated in order to increase drug solubility, prevent release at low pH and controlled release of the drug at small intestine pH that can improve drug bioavailability, decrease needed drug content and medication price to make it affordable in third world countries, and extent pill efficiency period to improve patient quality of life and adherence to the treatment schedule. The studies were compared with cellulose based commercial polymers to prove the impact of the investigation and potential for the application. Furthermore, the in vitro results obtained were further supported by in vivo studies to prove the significant increase in bioavailability and show the extended release.
The need of new cellulose derivatives for ASD applications extended the research area, the design and synthesis of a new class of polymers, alkyl cellulose ω-carboxyesters for ASD formulations investigated and the efficiency of the polymers were summarized to show that they have the anticipated properties. The polymers were synthesized by the reaction of commercial cellulose alkyl ethers with benzyl ester protected, monofunctional hydrocarbon chain acid chlorides, followed by removal of protecting group using palladium hydroxide catalyzed hydrogenolysis to form the alkyl cellulose wcarboxyalkanoate. Having been tested for ASD preparation, it was proven that the polymers were efficient in maintaining the drug in amorphous solid state, release the drug at neutral pH and prevent the recrystallization for hours, as predicted.Ph. D.
20
Liang, Jiarong. "Cellulose oxalates in biocomposites". Thesis, KTH, Fiber- och polymerteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297506.
Testo completoAbstract (sommario):
Under de senaste åren, på grund av överanvändningen av icke förnybara resurser har den ekologiska miljön på jorden påverkats allvarligt. I takt med detta ökade oron bland människor om att resurserna skulle ta slut. Därför är det nödvändigt att utveckla och använda mer miljövänliga förnybara resurser. Ett av dessa alternativ är cellulosabaserat material, vilket är ett utmärkt val. Vanligtvis består cellulosabaserat material av ett förstärkande material (cellulosafiber) och en matris (polymer eller metall). Dock bör kompatibiliteten mellan cellulosamaterialet och polymermatrisen ses över, eftersom generellt är kompatibiliteten mellan de låg. I detta projekt studerades olika metoder för att förbättra kompatibiliteten mellan cellulosamaterialet och polymermatrisen. Två cellulosamaterial (mikrokristallin cellulosa (MCC) och cellulosaoxalat (COX)) behandlades med olika modifieringsmetoder för att förbättra kompatibiliteten och gränssnittsinteraktionen mellan materialen. För att modifiera MCC och COX användes bland annat kulmalning, vatten som dispergeringsmedel, förestring av cellulosafibrerna med oljesyra under olika reaktionstider (6, 18, respektive 48 timmar), samt att tillsätta ett kompatibiliseringsmedel, maleinsyraanhydrid-ympad polypropylen (MAPP), i olika halter (1% respektive 2%). För att framställa kompositproverna användes extrudering och formsprutning. Dragprovning genomfördes för att testa de mekaniska egenskaperna hos proverna. Ytterligare karakteriseringsanalyser som utfördes på de olika cellulosapulvren var kontaktvinkeln (CA), svepelektronmikroskopi (SEM), infrarödspektroskopi (FTIR), och röntgendiffraktion (XRD). Resultatet från dragprovningen visade att COX-proverna med 1% MAPP som kompatibilisator gav den högsta draghållfastheten och Youngs modul av alla kompositproverna som producerades i detta exjobb. Användningen av MAPP som kompatibiliseringsmedel visade ett bättre resultat än de andra undersökta metoderna för att förbättra kompatibiliteten mellan den hydrofila ytan på MCC/COX och den hydrofoba ytan på polymermatrisen. Att använda MAPP som kompatibilisator bör prioriteras vid tillverkningen av kompositmaterial.In recent years, with the excessive use of non-renewable resources on the earth, the ecological environment has been seriously affected. At the same time, humans began to worry about running out of resources. Therefore, it is necessary to develop environmentally friendly renewable resources. Cellulose-based material is an excellent choice. Commonly, cellulose-based material consists of reinforcement (cellulose fiber) and matrix (polymer or metal). However, the compatibility between cellulosic material and polymer matrix should be considered. In general, the compatibility between them is poor. In this project, several methods to improve the compatibility between the cellulose material and polymer matrix were studied. Two cellulosic materials (microcrystalline cellulose (MCC) and cellulose oxalate (COX)) were treated with different modification methods to improve the compatibility and interfacial interaction between the cellulosic material and polymer matrix. Ball milling, using water as a dispersing agent, using oleic acid to esterify cellulose fiber for different reaction times (6 h, 18 h, and 48 h), and using different concentrations (1% and 2%) of maleic anhydride grafted polypropylene (MAPP) as compatibilizers were applied to improve the compatibility between cellulose fiber and polymer matrix. To produce the composite specimens, extrusion and injection molding were utilized. Tensile testing was done to test the mechanical properties of the specimens. Contact angle (CA), scanning electron microscope (SEM), Fourier Infrared Spectrometer (FTIR), X-ray diffraction (XRD) were also performed on the various cellulose powders as characterization methods. According to the result of tensile testing, COX samples with 1% MAPP as compatibilizer, showed the highest tensile strength and Young’s modulus of all the composite samples produced in this master thesis. Using MAPP as a compatibilizer shows a better result than using other methods to improve the compatibility between hydrophilic MCC/COX surface and hydrophobic PP matrix. The use of MAPP as a compatibilizer should be prioritized when producing composite materials.
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Nutt, Anu. "Hydrolytic and Oxidative Mechanisms Involved in Cellulose Degradation". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Universitetsbiblioteket [distributör], 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6888.
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Ubhayasekera, Wimal. "Structural studies of cellulose and chitin active enzymes /". Uppsala : Dept. of Molecular Biology, Swedish University of Agricultural Sciences, 2005. http://epsilon.slu.se/200518.pdf.
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Astorsdotter, Jennifer. "Dewatering Cellulose Nanofibril Suspensions through Centrifugation". Thesis, KTH, Skolan för kemivetenskap (CHE), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215079.
Testo completoAbstract (sommario):
Cellulose nanofibrils (CNF) is a renewable material with unique strength properties. A difficulty in CNF production is that CNF suspensions contain large amounts of water. If CNF suspension volume can be decreased by dewatering facilitated by centrifugation, then transportation costs and storage costs can be reduced. The aim of this thesis is to investigate the impact various parameters have on CNF centrifugation dewatering and identify optimal conditions for maximal water removal. A laboratory study was conducted using four materials; 2.0 w% enzymatically treated CNF (CNF1), 1.9 w% carboxymethylated CNF (CNF2) and two commercial samples (1.9 w% CNFA and 1.8 w% CNFB). The main method was analytical centrifugation up to 2330 g. Parameters tested were initial concentration before centrifugation, temperature, NaCl addition, pH, and applied solid compressive pressure (g-force and surface weight). In addition to centrifugation experiments the four materials were characterized with laser diffraction, UV-vis absorption, Dynamic light scattering, and dry weight measurements. Analysis of the experimental data collected show that increase in initial concentration give a higher final concentration, but less water is removed. Furthermore, temperature changes have no effect on separation of CNF and water. At an applied solid compressive pressure of 3 kPa and initial concentration at 1.5 w% the concentrations 5.5 w%, 1.5 w%, 4.0 w%, and 4.3 w% can be reach for CNF1, CNF2, CNFA, and CNFB respectively. After extrapolation of polynomial functions fitted to experimental data an applied solid compressive pressure of 22 kPa and initial concentration at 1:5 w%, the concentrations 9.1 w%, 1.5 w%, 6.9 w%, and 7.9 w% are predicted for CNF1, CNF2, CNFA, and CNFB respectively. The thickening of CNF suspensions achieved and predicted in this thesis implies possibilities for large amounts of water removal, e.g. the water content in a CNF1 suspension is reduced from 65.7 litres/kg CNF to 10.0 litres/kg CNF at the solid compressive pressure 22 kPa. The concentrations at 22 kPa are determined by extrapolation from experimental data <3 kPa solid compressive pressure. The carboxymethylated CNF2 can not be dewatered unless it is diluted or if salt or pH is adjusted. This is directly correlated to the electrostatic forces in the suspension and the Debye length. Addition of salt or lowered pH also eliminate any concentration gradients in diluted and centrifuged CNF2 suspensions.Cellulosa nanofibriller (CNF) är ett förnybart material med unika styrkeegenskaper. En svårighet med produktion av CNF är att CNF suspensioner innehåller stora mängder vatten. Om volymerna av CNF suspensioner kan minskas med avvattning genom centrifugering, då kan transport- och lagerkostnader sänkas. Målet med det här examensarbetet är att undersöka vilken inverkan olika parametrar har på CNF-avvattning genom centrifugering och identifiera optimala förhållanden för maximalt avlägsnande av vatten. En laboratoriestudie utfördes på fyra olika material. De fyra materialen är 2 w% enzymatiskt behandlad CNF (CNF1), 1.9 w% karboxymetylerad CNF (CNF2) och två kommersiella prover (1.9 w% CNFA och 1.8 w% CNFB). Den huvudsakliga metoden var analytisk centrifugering upp till maximalt 2330 g. De testade parametrarna var initial koncentration innan centrifugering, temperatur, NaCl tillsats, pH, och applicerat fast kompressionstryck (g-kraft och ytvikt). Förutom centrifugeringsexperimenten så karaktäriserades the fyra mmaterialen med laser diffraktion, UV-vis absorption, dynamisk ljusspridning och vägningar av torrhalt. Analys av den experimentella data som insamlats visar att en ökad initial koncentration ger en högre slutkoncnentration, men mindre vatten kan bortföras. Temperaturförändringar har ingen effekt på separation av CNF och vatten. Vid ett applicerat fast kompressibelt tryck på 3 kPa och en initial koncentration 1.5 w% kan koncentrationerna 5.5 w%, 1.5 w%, 4.0 w%, och 4.3 w% nås för CNF1, CNF2, CNFA, och CNFB. Efter extrapolering av polynoma funktioner passad till experimentell data förutspås att koncentrationerna 9.1 w%, 1.5 w%, 6.9 w%, och 7.9 w% kan nås för CNF1, CNF2, CNFA, and CNFB vid 22 kPa och en initial koncentration på 1.5 w%. Förtjockningen av CNF suspensioner som kan, eller förutspås kunna nås genom centrifugering i det här examensarbetet innebär att det är möjligt att avlägsna stora mängder vatten, till exempel kan vatteninnehållet i CNF1 minskas från 65.7 liter/kg CNF till 10.0 liter/kg CNF vid 22 kPa fast kompressionstryck. Koncentrationerna vid 22 kPa fast kompressionstryck är extrapolerade från exprimentell data <3 kPa fast kompressionstryck. Den karboy- metylerade CNF2 kan inte avvattnas om den inte späds ut eller om salt eller pH justeras. Detta är direkt kopplat till de elektrostatiska krafterna i suspensionen och Debye längden. Tillsats av salt eller sänkt pH eliminerar också de koncentrationsgradienter som kan förekomma i utspädda centrifugerade CNF2 suspensioner.
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Bansal, Prabuddha. "Computational and experimental investigation of the enzymatic hydrolysis of cellulose". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42773.
Testo completoAbstract (sommario):
The enzymatic hydrolysis of cellulose to glucose by cellulases is one of the major steps in the conversion of lignocellulosic biomass to biofuel. This hydrolysis by cellulases, a heterogeneous reaction, currently suffers from some major limitations, most importantly a dramatic rate slowdown at high degrees of conversion in the case of crystalline cellulose. Various rate-limiting factors were investigated employing experimental as well as computational studies. Cellulose accessibility and the hydrolysable fraction of accessible substrate (a previously undefined and unreported quantity) were shown to decrease steadily with conversion, while cellulose reactivity, defined in terms of hydrolytic activity per amount of actively adsorbed cellulase, remained constant. Faster restart rates were observed on partially converted cellulose as compared to uninterrupted hydrolysis rates, supporting the presence of an enzyme clogging phenomenon.
Cellulose crystallinity is a major substrate property affecting the rates, but its quantification has suffered from lack of consistency and accuracy. Using multivariate statistical analysis of X-ray data from cellulose, a new method to determine the degree of crystallinity was developed. Cel7A CBD is a promising target for protein engineering as cellulose pretreated with Cel7A CBDs exhibits enhanced hydrolysis rates resulting from a reduction in crystallinity. However, for Cel7A CBD, a high throughput assay is unlikely to be developed. In the absence of a high throughput assay (required for directed evolution) and extensive knowledge of the role of specific protein residues (required for rational protein design), the mutations need to be picked wisely, to avoid the generation of inactive variants. To tackle this issue, a method utilizing the underlying patterns in the sequences of a protein family has been developed.
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Lever, Mitchell. "Cellulose to ethanol conversion with on-site cellulase production using solid-state fermentation". Thesis, Lever, Mitchell (2009) Cellulose to ethanol conversion with on-site cellulase production using solid-state fermentation. PhD thesis, Murdoch University, 2009. https://researchrepository.murdoch.edu.au/id/eprint/32795/.
Testo completoAbstract (sommario):
The economics and environmental sustainability of enzymatic lignocellulose-to-ethanol conversion processes are adversely affected by the use of purchased cellulase preparations. Commercial cellulase preparations lack the microorganisms that produce them and thus cannot be cultured on-site, resulting in a significant ongoing expense. Commercial cellulase production is energy intensive and a significant contributor to the overall environmental impact of the cellulose to ethanol conversion process...
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D'Amour, Roger. "Modèle réactionnel de la dépolymérisation hydrolytique de la cellulose en cellulose microcristalline". Mémoire, Université de Sherbrooke, 2001. http://savoirs.usherbrooke.ca/handle/11143/1152.
Testo completoAbstract (sommario):
Cette étude s'inscrit dans une vision globale de valorisation de la biomasse. Concrètement, le Groupe de Recherche sur les Technologies et Procédés de Conversion du département de génie chimique de l'Université de Sherbrooke mise sur la conversion d'hydrates de carbone en sucres fermentescibles aux fins de production de bio éthanol. Ce mémoire est axé sur la conversion de la cellulose en ses unités constitutives, soient les micro cristallites et puis le monomère de glucose. Les mécanismes moyennant lesquels la cellulose se transforme progressivement englobent des transformations structurelles suivant des cinétiques complexes caractéristiques de systèmes non-homogènes. Lors de l'hydrolyse, la cellulose subit une dépolymérisation progressive entraînant l'élimination des zones amorphes et l'obtention des cristallites (ou micro cristallites) constitutifs. Ces derniers sont très compacts et extrêmement résistants à la solvatation et la pénétration d'eau, étape incontournable pour effectuer l'hydrolyse. Des essais de gonflement de la cellulose par des solvants (acétone, éthylène glycol), ainsi que par cisaillement, n'ont pas réussi, dans les conditions de travail utilisées, à déstructurer les cristallites. Ce mémoire présente une modélisation de type phénoménologique pour la dépolymérisation. Développée à partir de considérations structurelles, la modélisation est basée sur un paramètre de sévérité qui introduit la température, le temps et l'action catalytique. La concordance entre les résultats expérimentaux obtenus dans différents réacteurs permet de conclure que la dépolymérisation de la cellulose pourra désormais être couplée avec une nouvelle approche issue de ces travaux.
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D'Amour, Roger. "Modèle réactionnel de la dépolymérisation hydrolytique de la cellulose en cellulose microcristalline". Sherbrooke : Université de Sherbrooke, 2001.
Cerca il testo completo
28
Fischer, Martin. "Polymeranaloge Carbanilierung von Cellulose". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1106412216968-39405.
Testo completoAbstract (sommario):
Characterization of cellulose by its molecular weight distribution is afforded after polymeranalogeous dissolution. Additionally, a molecular dispersion of the polymer is a prerequisite. Common processes are dissolution of cellulose in dimethylacetamide-lithiumchloride, nitration and carbanilation. Degradation of the polysaccharide chains can occur in each of the mentioned processes. It is shown that degradation in pyridine occurs via beta-elimination at carbonyl groups along the cellulose chains. Carbanilierung in DMSO is much more pronounced. It comprises oxidation along the Pfitzner-Moffatt-mechanism and subsequent beta-elimination at the thus formed carbonyl-groups. This was elucidated with model systems and by investigation of the carbanilation in different media. Carbonyl groups of cellulose are masked through reaction with phenylisocyanate. This was shown with model. Therefore, the determination of carbonyl groups in cellulose-tricarbanilates is not possible. The separation of low-molecular weight byproducts was optimised. The influence of pretreatment and preactivation of cellulose-samples on the completeness of the conversion was studied. A standard protocol for the carbanilation of cellulose is providedCellulose wird u.a. durch ihre Molmassenverteilung charakterisiert, deren Ermittlung ein polymeranaloges Verfahren zur molekulardispersen Auflösung des Polymers erfordert. Hierfür sind die Direktlösung, die Nitrierung und die Carbanilierung in Gebrauch. Bei allen Prozessen kann es zum Abbau der Polysaccharidketten kommen, wobei diesen Prozessen wenig Beachtung geschenkt wurde. In der Arbeit wird gezeigt, daß der Abbau bei der Carbanilierung in Pyridin durch Beta-Eliminierung an vorhandenen Carbonylgruppen erfolgt. Die Carbanilierung in DMSO fällt stets stärker aus als bei Einsatz von Pyridin und umfasst die Prozesse Oxidation nach dem Pfitzner-Moffatt-Mechanismus und anschließende Beta-Eliminierung an den neu gebildeten Carbonylgruppen. Dies wird durch Untersuchungen an Modellsystemen und am Polymer herausgearbeitet. Carbonylgruppen an Cellulose werden durch die Umsetzung mit Phenylisocyanat maskiert, was an Modellverbindungen gezeigt wurde (Bildung von Endioldicarbanilaten und carbanilierten Halbacetalen). Ihre Bestimmung in Cellulosecarbanilaten ist daher nicht möglich. Die Abtrennung von niedermolekularen Nebenprodukten der Umsetzung wurde optimiert. Der Einfluss der Vorbehandlung und Voraktivierung von Celluloseproben auf die Vollständigkeit der Umsetzung wurde eingehend untersucht. Es wird ein Standardverfahren zur Carbanilierung von Cellulose angegeben
29
Helle, Steve. "Biosurfactants & cellulose hydrolysis". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61308.
Testo completoAbstract (sommario):
The action of many antimicrobial agents is dependent on their ability to interact with biological membranes. A group of polypeptide antibiotics was found to have surface activite properties. One of them, gramicidinS, produced a minimum in the surface tension curve, which was attributed to instabilities in the intra-molecular hydrogen bonds. Biosurfactants were found to have a great effect on the two phase hydrolysis of cellulose by cellulase. Seven times as much sugar was produced by the hydrolysis of Sigmacell 100 when the biosurfactant sophorolipid was present. The surfactant affects the adsorption of cellulase onto cellulose, and prevents the cellulase from binding irreversibly to the cellulose and becoming inactive.
30
Symington, Mark C. "Cellulose based composite materials". Thesis, University of Strathclyde, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501684.
Testo completoAbstract (sommario):
Natural fibre composites are a fast growing research area, with many observable research branches. In this thesis, studies into natural fibre composites are undertaken. This includes work into the base fibre mechanical properties, pre-processing techniques and the influence of alkalisation and silanation, both common fibre processing methods used to improve interfacial properties. The effects of these pre-processing techniques were also evaluated using Fourier transform infrared spectroscopy (FT-IR). It was observed that the processing had shown definite signs of altering the surface functional groups. For the studies into the base fibre strengths, it was found that natural fibres are highly variable. with the testing complicated by difficulties in measuring cross sectional areas. It was also found that natural fibres are sensitive to moisture, which affects their mechanical properties somewhat, although no conclusive trends were derived.
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Gandhi, U. P. "Diffusion in cellulose derivatives". Thesis, Cardiff University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376555.
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32
Mao, Rui. "Mechanics of cellulose nanopapers". Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/24706.
Testo completoAbstract (sommario):
Cellulose nanopaper is a fibrous network composed of cellulose nanofibres connected by hydrogen bonds, which shows pronounced mechanical and physical properties. This thesis investigates the mechanics of cellulose nanopaper from various aspects. First, the fracture properties of cellulose nanopaper were investigated using experimental and modelling approaches. It was found that the fracture strength of notched nanopaper is insensitive to notch length. Cohesive zone models were used to describe the fracture behaviour of notched cellulose nanopaper. Fracture energy was extracted from the cohesive zone models and divided into an energy component consumed by damage in materials and a component related to pull-out and bridging of nanofibres between cracked surfaces which is not facilitated by short nanofibres in nanopaper. Strain mapping revealed a small region of highly localized strain ahead of the notch tip with multiple stress concentration sites which are indicative of a stress delocalization mechanism. Secondly the inelastic deformation mechanisms of cellulose nanopaper were investigated. Results indicate that the inelastic deformation of cellulose nanopaper does not originate from fibre slippage and shearing as often suggested in literature but originates from inelastic deformation in amorphous regions in the cellulose nanofibres itself. It is proposed that this mechanism is associated with segmental motion of cellulose molecules facilitated by the breakage of hydrogen bonds within these amorphous regions. Thirdly, the effect of preparation methods on the mechanical properties of cellulose nanopaper was investigated. The influence of processing parameters such as compaction pressure and temperature was investigated and the mechanical properties of these nanopapers were compared with nanopaper prepared by a suspension casting method. Finally, a micromechanical fibrous network model was used to investigate the parameters that determine the elastic modulus of cellulose nanopaper. The effect of fibre size, waviness and modulus, inter-fibre bond density as well as network density on elastic modulus was investigated.
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Joubert, Fanny. "Chemically modified hydroxyethyl cellulose". Thesis, Durham University, 2014. http://etheses.dur.ac.uk/11122/.
Testo completoAbstract (sommario):
Synthetic, man-made polymers are produced from petroleum, however this activity may well decrease as a function of time because of the non-renewability of the oil. This will result in the decreased production of synthetic polymers with consequent problems to our everyday life because of their ubiquity (food, furniture, containers, electronics…). An alternative could be the use of biopolymers such as cellulose, starch, proteins, amylose and chitin which are extracted from renewable sources. Cellulose is the most abundant biopolymer on earth and is principally found in the cell walls of plants. Cellulose presents interesting properties such as a high thermal stability and high strength, however the principal drawback is its insolubility in both organic and aqueous solvents limiting considerably its use in industry. Chemical modification of the hydroxyl groups of cellulose overcomes some of this problem. In fact, hydroxyethyl cellulose (HEC), where the hydroxyl groups have been modified with ethylene oxide, shows good solubility in aqueous solvents (dimethyl sulfoxide, water) due to the interruption of the cellulose H-bonding networks. Although the chemical modification of cellulose has improved considerably the physical properties of cellulose, the derivatives are usually not competitive against synthetic polymers. Due to its solubility and the presence of the three hydroxyl groups, HEC was chosen as a substrate for chemical modification, with the aim of mimicking the properties of synthetic polymers. The synthetic polymer of reference in our work was poly(N-vinylpyrrolidone) (PVP) because of its solubility in organic and aqueous solvents and sorption properties. The introduction of lactam groups onto HEC could produce a material with properties similar to PVP and this was the goal of our work. Three methods for modifying HEC with lactam groups are reported. The first was the functionalization of HEC with 1-(hydroxymethyl)-2-pyrrolidone (HMP) with degrees of functionalization up to ~0.9 on the primary alcohol functionality of HEC. The functionalized HECs showed markedly different properties to unfunctionalized HEC, such as increased the thermal stability and reduced viscosity. The two others methods led to the preparation of well-defined HEC-g-PVPs using a “grafting from” strategy combined with Atom Transfer Radical Polymerisation (ATRP) and “grafting to” combined with Reversible Addition-Fragmentation Chain-Transfer (RAFT) polymerisation. The ATRP of N-vinylpyrrolidone (NVP) from a prior-synthesised macro-initiator, Br-HEC, did not work efficiently; however, RAFT polymerisation of NVP using an alkyne-terminated xanthate as transfer agent produced an 80% monomer conversion with a 1.4 ƉM. The alkyne-terminated PVP was coupled successfully to partially 15N-labelled N3-HEC and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) was confirmed by 15N NMR spectroscopy. The versatility of the method was demonstrated using poly(N-isopropyl acrylamide) (PNIPAAM) which was synthesised using an alkyne-terminated trithiocarbonate as transfer agent with a 90% monomer conversion and a 1.2 ƉM. Subsequently, this straightforward method was used to prepare anti-microbial graft-copolymers of HEC from an ionic liquid (IL) monomer, 1-(11-acryloyloxyundecyl)-3-methylimidazolium bromide which was polymerised in high monomer conversion (70-80%) with some evidence of control over molecular weight distribution (ƉM =1.5). The influence of the chain length of the grafts on the antibacterial effects was minor with a 20 and 39 µg/mL minimum inhibition concentration (MIC) for E. coli and for S. aureus respectively. The MICs were comparable to those measured for ampicillin, which is known as an antibiotic, indicating the strong effect of our HEC-g-P(IL) on bacteria.
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Wilsby, Astrid. "Insight in cellulose degradation". Thesis, KTH, Fiber- och polymerteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302670.
Testo completoAbstract (sommario):
I strävan efter att minska textilindustrins omfattande miljöpåverkan utvecklas nya metoder för textilåtervinning. Idag återvinns bomullstyg av Renewcell på deras anläggning i Kristinehamn. Den återvunna produkten, Circulose®, är en dissolvingmassa som kan användas för att spinna nya viskosfibrer som man i sin tur kan använda för att göra nya kläder. Föreliggande arbete är en förstudie om möjligheten att optimera Renewcellls återvinningsprocess. Arbetet inkluderar en optimering av massaprocessen vilket resulterar i en mer effektiv process som minskar förbrukningen av processkemikalier.To reduce the extensive environmental impact of the textile industry, new methods for textile recycling are being developed. Today, cotton-based fabric is recycled by Renewcell at their facility in Kristinehamn. The recycled product, Circulose®, is a dissolving pulp that can be used to spin new viscose fibers, which in turn can be used to make new clothes. The present work is a feasibility study on the possibility of optimizing Renewcell's recycling process. The work includes an optimization of the pulp process, which results in a more efficient process with a reduced consumption of process chemicals.
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de, Mourgues Marius. "Composite Cellulose Nanofibrils Filaments". Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277919.
Testo completoAbstract (sommario):
Biodegradable polymers are emerging as a new solution to satisfy the increasing demand of greenenvironmentally friendly material. At the same time, the interest for lighter and stronger structures never stops growing. In this paper, we report the production steps to achieve cellulose nanofibrils (CNF) composite filaments via a new green synthesis route known as wet spinning. This new technique avoids the traditional harmful viscose process and produces biodegradable CNF filaments with interesting mechanical properties. This approach is then applied to produce never seen before composite CNF filaments using a three-layered head extruder. In order to obtain conductive filaments, PEDOT/PPS is successfully mixed with CNF to produce in-situ composite filaments. Scanning electron microscopy (SEM), atomic force measurements and tensile tests are employed to characterize the properties of the filaments.Biologiskt nedbrytbara polymerer börjar framträda som en lösning för det ökade behovet avmiljövänliga material. Samtidigt så växer intresset för lättare och starkare strukturer. I denna rapport tar vi upp produktionsstegen för att uppnå nanofibril komposit cellulosa fibrer (CNF), med hjälp av en ny grön polymerisation mest känd som ”wet spinning”. Med denna nya teknik så behövs inte dem traditionella miljöfarliga viskosprocesserna och man producerar biologiskt nedbrytbara CNF filaments med intressanta mekaniska egenskaper. Denna metod appliceras sen för att producera en komposit som aldrig setts innan. CNF fibrer som består av tre lager ”head-extruder”. För att få fibrer med ledningsförmåga så mixas PEDOT/PPS med CNF för att producera ”in-situ komposit fibrer”. Svepelektronmikroskop (SEM), atomkraftsmikroskopi och töjningstester används för att karaktärisera egenskaperna av fibrerna.
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Pillai, Karthik. "Bio-inspired Cellulose Nanocomposites". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/28575.
Testo completoAbstract (sommario):
Natural composites like wood are scale-integrated structures that range from molecular to the macroscopic scale. Inspired by this design, layer-by-layer (LbL) deposition technique was used to create lignocellulosic composites from isolated wood polymers namely cellulose and lignin, with a lamellar architecture. In the first phase of the study, adsorption of alkali lignin onto cationic surfaces was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Complete coverage of the cationic surface with alkali lignin occured at low solution concentration; large affinity coefficients were calculated for this system at differing pH levels. Adsorption studies with organosolv lignin in an organic solvent, and spectroscopic analysis of mixtures of cationic polymer with alkali lignin revealed a non-covalent interaction. The work demonstrated how noncovalent interactions could be exploited to molecular organize thin polyphenolic biopolymers on cationic surfaces. The second phase of the study examined the adsorption steps during the LbL assembly process to create novel lignocellulosic composites. LbL assembly was carried out using oxidized nanocellulose (NC) and lignin, along with a cationic polymer poly(diallyldimethylammonium chloride) (PDDA). QCM-D was used to follow the sequential adsorption process of the three different polymers. Two viscoelastic models, namely Johannsmann and Voigt, were respectively used to calculate the areal mass and thickness of the adsorbed layers. Atomic force microscopy studies showed a complete coverage of the surface with lignin in all the disposition cycles, however, surface coverage with NC was seen to increase with the number of layers. Free-standing composite films were obtained when the LbL process was carried out for 250 deposition cycles (500 bilayers) on a cellulose acetate substrate, following the dissolution of the substrate in acetone. Scanning electron microscopy of the cryo-fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle was estimated to be 17 nm. The third phase of the study investigated the effect of LbL ordering of the polymers versus a cast film composed of a blended mixture of the polymers, using dynamic mechanical analysis. A tan ï ¤ peak was observed in the 30 â 40 ºC region for both films, which was observed in the neat NC film. Heating of the samples under a compressive force produced opposite effects in the films, as the LbL films exhibited swelling, whereas the cast films showed densification. The apparent activation energy of this transition (65 â 80 kJ mol-1) in cast films, calculated based on the Arrhenius equation was found to be coincident to those reported for the ï ¢ transition of amorphous cellulose. The peak was seen to disappear in case of LbL films in the second heat, whereas it was recurring in case of cast films of the blended mixture, and neat NC films. Altogether, the together the work details a novel path to integrate an organized lignin and cellulose molecular structure, albeit modified from their native form, into a three-dimensional composite material.Ph. D.
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Inman, Sharon. "Cellulose bilayer tablet interfaces". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/11775.
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Fugelstad, Johanna. "Cellulose Biosynthesis in Oomycetes". Licentiate thesis, Stockholm : KTH Biotechnology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9282.
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Feng, Xianhua Pelton Robert H. "Polyvinylamine carboxymethyl cellulose complexes". *McMaster only, 2006.
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Steele, David Fraser. "Amine/microcrystalline cellulose interactions". Thesis, University of Bath, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275882.
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Blell, Rebecca. "Microfibrillated cellulose based nanomaterials". Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE023.
Testo completoAbstract (sommario):
La cellulose étant l'un des biopolymères les plus abondants, elle est employée dans ce travail de thèse sous sa forme nano-fibrille (2 à 5nm de diamètre et plusieurs microns de long) pour préparer des nanomatériaux durables. Les microfibrilles de cellulose (MFC) chargées positivement ou négativement sont assemblées en couches minces dans ces nanomatériaux par la méthode « Layer by Layer » (LbL) par trempage, pulvérisation ou spin assisté. Les différences entre ces films LbL à base de MFC et les films LbL à base de polymères standards sont discutées brièvement et sont reliées à la forme nanofibrillaire de la cellulose. Les MFC réagissent comme des nano-objets anisotropes et rigides. Les films LbL de MFC sont ensuite intégrés à des membranes de séparation, entre la couche polymérique de séparation et le support poreux, pour améliorer le débit à travers ces membranes. Ces films minces sont également déposés sur des aérogels de cellulose pour améliorer la stabilité de ces aérogels en milieu aqueux. Dans les deux applications, les résultats était encouragent et montre une validation de principeCellulose, one of the most abundant biopolymers, is used in this PhD work in its nanofibrillated form, 2-5 nm in diameter and microns long, to prepare sustainable nanomaterials. Both positively and negatively charged microfibrillated celluloses (MFC) are assembled in these nanomaterials using the versatile Layer by Layer (LbL) assembly methods: dipping, spray assisted-deposition and spin-assisted deposition. A brief comparison between the MFC based LbL assembled films and the standard polymeric LbL films is carried out. Thedifferences between the two species are related to the fibrillar form of cellulose. MFC behaves like rigid anisotropic nano-objects. MFC LbL assembled films are then integrated in separation membranes between active polymeric separation layers and a mechanically stable porous support to improve the flux through these membranes. MFC LbL assembled films are also coated on cellulosic aerogels to improve the wet stability of these aerogels. In both cases, results were encouraging and showed a proof of concept
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Seeta, R. "Enzymatic hydrolysis of cellulose". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1987. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3280.
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Chakrabarti, Ajoy Chuni Carleton University Dissertation Biology. "One-step conversion of cellulose to fructose using co-immobilized cellulase, B-glucosidase and glucose isomerase". Ottawa, 1988.
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Cerclier, Carole. "Films multicouches à base de polymères végétauxβ : élaboration et application à la détection d'activités enzymatiques". Nantes, 2010. http://archive.bu.univ-nantes.fr/pollux/show.action?id=19992f55-8948-4aa3-b33f-69e1bae3bb65.
Testo completoAbstract (sommario):
La cellulose et le xyloglucane constituent un réseau majeur de la paroi des cellules végétales. Ces molécules sont liées par des interactions de Van der Waals et des liaisons hydrogène que nous avons mis à profit pour l’élaboration de films multicouches nanométriques. En fonction de leur épaisseur et de leur indice de réfraction, les films nanométriques peuvent présenter des couleurs qui sont dues à des phénomènes d’interférences. De tels films composés de nanocristaux de cellulose et de xyloglucane peuvent être valoriser comme détecteurs d’activité enzymatique de cellulases. En effet, l’action d’une enzyme hydrolytique peut être détectée par une diminution de l’épaisseur du film qui résulte en un changement de couleur. Les modes de croissance de deux types de films ont été étudiés afin de déterminer les conditions opératoires les plus appropriées pour l’obtention de films colorés. La structure interne de ces films a été déterminée par réflectivité de neutrons à l’état sec et en solution pour évaluer les différences de structures. Les cinétiques de dégradation des films par les cellulases ont également été comparées par QCM-D. Il s’avère que la détection de l’activité de cellulases avec les films nanométriques est plus rapide et plus sensible qu’une méthode colorimétrique utilisée usuellement. L’utilisation des films nanométriques pour la détection d’activité est également applicable à d’autres systèmes enzyme/substratCellulose and xyloglucan represent a major network from plant cell wall. Theses molecules are linked by Van der Waals interactions and hydrogen bonds and we have used these interactions in order to elaborate nanometric multilayered films. According to their thickness and refractive index, nanometric films can present bright colours due to interference phenomena. Such films composed of cellulose nanocrystals and xyloglucan can be used as cellulases enzymatic activities detector. Hydrolytic enzyme action can actually be detected by film thickness decrease and results in a colour change. Growth mode has been studied for two kinds of film and the better conditions were chosen to obtain coloured films. Films internal structure has been investigated by neutron reflectometry on dry films and films in solution in order to evaluate the structures differences. Films hydrolysis kinetics has also been compared by QCM-D. Cellulases activities detection using nanometric films is faster and more sensitive than a colorimetric method usually used. We have also proved that this technique can be used for other enzyme/substrate systems
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Oliveira, Marcelo Miranda de. "Nanostructure variability of cellulose from plants and the impact on cellulose nanocrystals production". Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-07112018-101553/.
Testo completoAbstract (sommario):
This work investigates the compositional and nanostructural variability of celluloses isolated from plants and the impact of the variability in the production of cellulose nanocrystals. A variable set of cellulose isolated from plants were generated starting with a range of feedstocks (coconut fiber, sisal fiber, eucalyptus sawdust, pine sawdust, sugarcane rind and sugarcane pith), applying a range of cellulose isolation processes (acetossolv, liquid hot water, alkaline, and liquid hot water + alkaline) and adding commercial cellulose (eucalyptus kraft pulp, dissolving pulp, and microcrystalline cellulose) as reference materials. The nanostructural characteristics were evaluated by calorimetric thermoporometry, X-ray diffraction, and moisture sorption isotherms. Composition was evaluated by standard wet chemical analysis and insights on functional groups were obtained by infrared spectroscopy. The cellulose nanocrystals were produced by acid hydrolysis with sulfuric acid and characterized by atomic force microscopy and X-ray diffraction. The measured parameters of the isolated celluloses were spread, showing we could achieve a highly diverse set of substrates. Significant correlations between measured variables across the sample set, indicating possible unforeseen multivariate relations among cellulose features. For example, we could show that cellulose monolayer hydration is determined by both hemicelluloses content (compositional parameter) as well as cellulose crystal width (structural parameter). Cellulose nanocrystals were successfully produced, although in some cases such as for the acetossolv pulps the acid conditions were too aggressive and oxidized the substrates. Finally, some quantitative correlations were seen between the parameters of cellulose substrates and the resulting cellulose nanocrystals. These results supply the first hints about how the nanostructural variability of isolated cellulose can influence the cellulose nanocrystals produced from them.Este trabalho investiga a variabilidade composicional e nanoestrutural de celuloses isoladas de plantas e o seu impacto na variabilidade na produção de nanocristais de celulose. Um conjunto variável de celuloses isoladas de plantas foi gerado a partir de uma série de matérias-primas (fibra de coco, sisal, serragem de eucalipto, serragem de pinheiro, casca de cana e miolo de cana), aplicando uma série de processos de isolamento de celulose (hidrotérmico, alcalino, hidrotérmico + alcalino e acetosolve) e adicionando celuloses comerciais (polpa kraft de eucalipto, polpa para dissolução e celulose microcristalina) como materiais de referência. As características nanoestruturais foram avaliadas por termoporometria calorimétrica, difração de raios X e isotermas de sorção de umidade. A composição foi avaliada por análise química húmida padrão e os conhecimentos sobre grupos funcionais foram obtidos por espectroscopia de infravermelhos. Os nanocristais de celulose foram produzidos por hidrólise ácida com ácido sulfúrico e caracterizados por microscopia de força atômica e difração de raios-X. Os parâmetros medidos das celuloses isoladas foram distribuídos, demonstrando que poderíamos alcançar um conjunto altamente diversificado de substratos. Correlações significativas entre as variáveis medidas foram observadas em todo o conjunto amostral, indicando possíveis relações multivariadas imprevistas entre as características da celulose. Por exemplo, poderíamos demonstrar que a monocamada de hidratação de celulose é determinada tanto pelo conteúdo de hemiceluloses (parâmetro de composição) quanto pela largura do cristal de celulose (parâmetro estrutural). Os nanocristais de celulose foram produzidos com sucesso, embora em alguns casos, como nas polpas acetosolve, as condições ácidas fossem muito agressivas e oxidassem os substratos. Finalmente, algumas correlações quantitativas foram observadas entre os parâmetros dos substratos de celulose e os nanocristais de celulose resultantes. Estes resultados fornecem as primeiras dicas sobre como a variabilidade nanoestrutural da celulose isolada pode influenciar os nanocristais de celulose produzidos a partir deles.
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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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Ulfstad, Louise. "Rheological study of cellulose dissolved in aqueous ZnCl2 : Regenerated cellulosic fibres for textile applications". Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-28781.
Testo completoAbstract (sommario):
The most known regenerated cellulosic fiber is viscose, produced in a wet spinning process, but due to cost and environmental issues other processes have been developed. Lyocell fibers, produced in air-gap spinning, have superior dry and wet strenght and a lower environmental impact compared to viscose. Research in different cellulose solvent has increased significantly tha last decadess, due to an increased cotton price and a decreased paper production, providing more wood pulp to production of regenerated cellulosic fibers. Inorganic molten salt hydrates have the ability of dissolving cellulose for production of textile fibers. Aqueous zinc chloride was investigated at Swerea IVF from dissolution of cellulose to fiber spinning. Aqueous zinc chloride has a dissolving capacity of up to at least 13.5 % cellulose, possibly much higher. Dissolving concentration ZnCl2/water range from 65-76 % amd lowest possible ZnCl2 concentration increases as the cellulose concentration increases. Above around 68 % ZnCl2 results in a significantly increased viscosity due to a polymeric structure formed by zinc chloride, creating a network of cellulose-zinc complexes and causing a gel behaviour of the dope difficult to use in spinning processes. The dissolving capacity of 68 % ZnCl2 is only about 8 % cellulose, which is very low compared to other solvents used today e.g. Lyocell and ILs. Additions of 0.3 % CaCl2 or 0.05-0.1 % NaOH is used to decrease degradation of cellulose. The addition causes ans increased viscosity, which is either a result of less degradation of the interaction of the added molecules to zinc-cellulose complexes. Addition of NaOH results in a temperature dependent geleation at increased temperatures (75˚C and 80˚C), which also might be an effect of the interaction. Highest tensile strenght was reached for wet spun fibers coagulated in ethanol of 9.5 % cellulose with 0.1 % NaOH addition, with a tenacity of 13-15 cN/tex, elongation of 10-12 % and wet strenght 30 % of dry strenght. Beacuse of many disadvantages of zinc chloride as a solvent, e.g. degradation of cellulose, corrosivity and the viscosity and gel behaviour at cellulose concentrations of 9.5 % and 13.5 % cellulose, a future possibility of a conventional production of textile fibers appears to be quite limited.
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Hogan, Charlene M. "Enzymatic and structural factors limiting hydrolysis of cellulose by Trichoderma harzianum E58 cellulases". Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/5574.
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Mba, Medie Felix. "Le rôle des cellulases dans les interactions entre les mycobactéries du complexe Mycobacterium tuberculosis et les amibes libres". Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX20695/document.
Testo completoAbstract (sommario):
Le génome de Mycobacterium tuberculosis, l’agent causal de la tuberculose, code pour une protéine ayant la capacité de se fixer sur la cellulose (Rv1987), une cellulase potentielle (Rv1090), et une cellulase pleinement active (Rv0062). Cette observation est surprenante, car la cellulose est un composant majeur des parois des cellules végétales, tandis que M. tuberculosis est un pathogène humain sans contact connu avec des plantes. Nous avons émis l’hypothèse que ces protéines pourraient jouer un rôle dans les interactions entre les mycobactéries du complexe M. tuberculosis avec les kystes d’amibes libres, dont la paroi contient également de la cellulose. Dans notre travail de thèse, nous avons cherché par une analyse in silico la présence de ces trois gènes chez toutes les bactéries ayant un génome complètement séquencé présentes dans la base de données CAZy (accessible en ligne à l’adresse www.cazy.org). Cette étude a montré que seulement 2,5% des bactéries codent pour les trois gènes simultanément. Parmi ces bacteries, nous avons ensuite confirmé expérimentalement par PCR et séquençage la présence des gènes Rv0062, Rv1090 et Rv1987 chez les mycobactéries du complexe M. tuberculosis. Nous avons ensuite vérifié la transcription de ces trois gènes chez la souche de référence M. tuberculosis H37Rv, puis produit dans Escherichia coli des protéines de fusion Rv1090 et Rv1987 et montré qu'elles étaient capables d'hydrolyser la cellulose (Rv1090) et de s’y fixer (Rv1987). De plus, nous avons mis en place un model expérimental d’interaction entre les mycobactéries du complexe M. tuberculosis et les amibes libres dans le but de comprendre le rôle des gènes Rv0062, Rv1090 et Rv1987. Dans un premier temps nous avons montré que M. tuberculosis, Mycobacterium bovis, Mycobacterium canettii ainsi que Mycobacterium avium utilisé ici comme un controle positif étaient capables de survivre dans le cytoplasme des amibes libres telles que Acanthamoeba polyphaga. Ensuite, nous avons montré que M. tuberculosis et M. bovis mais pas M. canettii étaient capables de survivre à l’intérieur des kystes d’amibes. Enfin nous avons montré que M. tuberculosis, M. bovis et M. canettii étaient capables de survivre dans le sol pendant au moins 6 mois. Les données établies dans cette thèse soutiennent le rôle des cellulases dans la survie environnementale des mycobactéries du complexe M. tuberculosis, et ouvrent la voie à l’étude de cette phase méconnue dans le cycle de ces organismesThe genome of Mycobacterium tuberculosis, the causative agent of tuberculosis, encodes a protein with the ability to bind to cellulose (Rv1987), one potential cellulase (Rv1090), and one fully active cellulase (Rv0062). This observation is puzzling, because cellulose is a major component of plant cell walls, whereas M. tuberculosis is a human pathogen without known contact with plants. We hypothesized that these genes could play a role in the interactions between M. tuberculosis complex organisms and amoebal cysts, whose wall contains cellulose.In our thesis work, we have searched by in silico analysis for the presence of these three genes in all bacteria with complete sequenced genomes present in the CAZy database (available online at www.cazy. org). This study showed that only 2.5% of bacteria encode the three genes simultaneously. Among these bacteria we have confirmed experimentally by PCR and sequencing the presence of Rv0062, Rv1090 and Rv1987 in the M. tuberculosis complex organisms. We have checked the transcript of the three genes in the reference strain M. tuberculosis H37Rv and we subsequently produced Rv1090 and Rv1987 fusion proteins in Escherichia coli and demonstrated that they were indeed able to hydrolyze (Rv1090) and to bind (Rv1987) cellulose. In addition, we have developed an experimental model of interaction between M. tuberculosis organisms and the free-living amoebae in order to understand the role of Rv0062, Rv1090 and Rv1987 genes. Initially we have shown that M. tuberculosis, Mycobacterium bovis, Mycobacterium canettii and Mycobacterium avium used here as a positive control were able to survive in the cytoplasm of the free-living amoeba such as Acanthamoeba polyphaga. We have further shown that M. tuberculosis and M. bovis but not M. canettii were able to survive within the amoebal cysts. Finally we have shown that M. tuberculosis, M. bovis and M. canettii were able to survive in soil for at least 6 months. The data obtained in this thesis support the role of cellulase in the survival of M. tuberculosis complex organisms in the environment and pave the way for the study of this unknown phase in the cycle of these organisms
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Falcoz-Vigne, Léa. "Caractérisation et modélisation des interactions cellulose - hémicelluloses au sein des microfibrilles de cellulose (MFC)". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAV091/document.
Testo completoAbstract (sommario):
Le cadre de cette étude est le coût énergétique lié à la production des Microfibrilles de Cellulose (MFC) qui est aujourd’hui un facteur limitant à son développement à l’échelle industrielle. Le but de cette étude est de caractériser les interactions cellulose/hémicellulose au sein de ces systèmes.Des MFC provenant de différentes pâtes à papier chimiques ont été caractérisées par RMN du solide afin d’obtenir des informations à l’échelle moléculaire. Suite à l’optimisation d’un protocole expérimental, les hémicelluloses contenues dans les MFC issues de pâte kraft de bouleau ont ensuite été extraites avec un rendement de 60% et sont composés uniquement d’un homopolymère de xylan de DP 75.La turbidimétrie a été utilisée pour qualifier la qualité des suspensions, dont il a été montré qu’elle dépend fortement du procédé de mise en pâte et du séchage. Des corrélations positives ont été établies entre l’état de dispersion et les propriétés mécaniques de feuilles de papier additionnées de microfibrilles. L’analyse RMN de modèles biomimétiques reconstitués a confirmé le changement de conformation du xylan lorsqu’il est adsorbé sur la cellulose et les mesures de surface spécifique ont montré que seule la couche de xylan en contact avec la cellulose était concernée par ce changement.Les interactions cellulose/xylane ont été étudiées par RMN du solide et par dynamique moléculaire atomistique (MD). Les simulations MD ont montré que le xylan s’adsorbe parallèlement aux chaines de cellulose. Des mesures d'interaction sur ce système ont conduit à une mesure d'énergie de 9kJ/résidu de xylose.Des tests de mesure d’adhésion ont également été réalisés à partir d’un modèle trois couches constitué de xylan entre deux films de cellulose et une forte adhésion a pu être observée.L’utilisation de xylanase comme prétraitement est proposé pour améliorer la production des MFCThe study was motivated by the necessity to reduce the high energy costs of Micro-Fibrillated Cellulose (MFC) production, which is a limiting factor for its industrial development and aimed at understanding the cellulose/hemicelluloses interaction within this system. MFC resulting from different chemical pulps were characterized by solid-state NMR spectroscopy to get information on the hemicelluloses content and molecular conformation. By optimizing an extraction protocol, more than 60% of the residual hemicelluloses were extracted from birch kraft MFC and characterized as a high purity homopolymer of β-1,4 linked xylan of DP 75.Turbidimetry was used to qualify the quality of the suspensions, which strongly depended on the pulping and drying history. Positive correlations between the state of dispersion, specific surface and mechanical properties of MFC-reinforced handsheets were evidenced.Cellulose/xylan interactions were investigated using solid-state NMR and atomistic molecular dynamics (MD) simulation. NMR spectra confirmed that xylan in contact with cellulose altered its conformation, from the three-fold helix to a presumable cellulose-like two-fold one. In combination with specific surface area measurements, the conformational change was shown to happen only for the first layer of xylan adsorbed in direct interaction with the cellulose surface. MD simulations showed that adsorbed xylan tends to align parallel to the cellulose chain direction fully extended. Interaction energy between xylan chain and cellulose surface estimated with MD was 9kJ/xylose. Then a three-layers system made of xylan between two cellulose films were built to perform adhesion tests that showed strong adhesion between xylan and cellulose surfaces. Xylanase was proposed as a pulp pretreatment for MFC production