The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Akira Isogai - One of the best experts on this subject based on the ideXlab platform.
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Different Conformations of Surface Cellulose Molecules in Native Cellulose Microfibrils Revealed by Layer-by-Layer Peeling.
Biomacromolecules, 2017Co-Authors: Ryunosuke Funahashi, Tsuguyuki Saito, Yusuke Okita, Hiromasa Hondo, Mengchen Zhao, Akira IsogaiAbstract:Layer-by-layer peeling of surface molecules of Native Cellulose microfibrils was performed using a repeated sequential process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical-mediated oxidation followed by hot alkali extraction. Both highly crystalline algal and tunicate Celluloses and low-crystalline cotton and wood Celluloses were investigated. Initially, the C6-hydroxy groups of the outermost surface molecules of each algal Cellulose microfibril facing the exterior had the gauche–gauche (gg) conformation, whereas those facing the interior had the gauche–trans (gt) conformation. All the other C6-hydroxy groups of the Cellulose molecules inside the microfibrils contributing to crystalline Cellulose I had the trans–gauche (tg) conformation. After surface peeling, the originally second-layer molecules from the microfibril surface became the outermost surface molecules, and the original tg conformation changed to gg and gt conformations. The plant Cellulose microfibrils likely had disordered structures for ...
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introduction of aldehyde groups on surfaces of Native Cellulose fibers by tempo mediated oxidation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006Co-Authors: Tsuguyuki Saito, Akira IsogaiAbstract:Abstract Native Cellulose fibers were suspended in water and oxidized to various degrees with sodium hypochlorite and catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and sodium bromide at pH 10.5. The oxidation was accomplished within 30 min at room temperature. The TEMPO-oxidized Cellulose fibers were then converted to sheets like paper. Tensile strength of the sheets soaked in water, i.e. wet strength, showed a maximum value, when 0.3 mmol NaClO per gram Cellulose was used in the TEMPO-mediated oxidation. Aldehyde groups up to 0.225 mmol/g were introduced in Native Cellulose fibers by the TEMPO-mediated oxidation, and were stably present in there. However, only surface aldehyde groups in the TEMPO-oxidized Cellulose fibers contributed to the wet strength development of the sheets. Carboxylate groups were also formed not only surfaces but also insides of Cellulose fibers by the TEMPO-mediated oxidation, although they had nearly no contribution to wet strength development of the sheets. These surface aldehyde groups forms hemiacetal linkages with Cellulose hydroxyl groups at the inter-fiber bonds, resulting in the clear wet strength development of the sheets prepared thereof. The TEMPO-mediated oxidation is, therefore, applicable to introduction of not only carboxylate groups but also aldehyde groups to Native Cellulose surfaces as an efficient chemical modification under aqueous conditions.
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introduction of aldehyde groups on surfaces of Native Cellulose fibers by tempo mediated oxidation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006Co-Authors: Tsuguyuki Saito, Akira IsogaiAbstract:Abstract Native Cellulose fibers were suspended in water and oxidized to various degrees with sodium hypochlorite and catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and sodium bromide at pH 10.5. The oxidation was accomplished within 30 min at room temperature. The TEMPO-oxidized Cellulose fibers were then converted to sheets like paper. Tensile strength of the sheets soaked in water, i.e. wet strength, showed a maximum value, when 0.3 mmol NaClO per gram Cellulose was used in the TEMPO-mediated oxidation. Aldehyde groups up to 0.225 mmol/g were introduced in Native Cellulose fibers by the TEMPO-mediated oxidation, and were stably present in there. However, only surface aldehyde groups in the TEMPO-oxidized Cellulose fibers contributed to the wet strength development of the sheets. Carboxylate groups were also formed not only surfaces but also insides of Cellulose fibers by the TEMPO-mediated oxidation, although they had nearly no contribution to wet strength development of the sheets. These surface aldehyde groups forms hemiacetal linkages with Cellulose hydroxyl groups at the inter-fiber bonds, resulting in the clear wet strength development of the sheets prepared thereof. The TEMPO-mediated oxidation is, therefore, applicable to introduction of not only carboxylate groups but also aldehyde groups to Native Cellulose surfaces as an efficient chemical modification under aqueous conditions.
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TEMPO-mediated Oxidation of Native Cellulose
2005Co-Authors: Tsuguyuki Saito, Akira IsogaiAbstract:Linter Cellulose was oxidized with sodium hypochlorite with catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) under various conditions. After this TEMPO-mediated oxidation, fibrous water-insoluble fractions were collected, and characterized in terms of carboxyl and aldehyde contents, distribution of carboxylate and aldehyde groups, crystallinities and crystal sizes, morphology, etc. Carboxyl and aldehyde groups were introduced into the fibrous fractions up to about 0.7 and 0.3 mmol/g, respectively, by the oxidation, where recovery of the fibrous fractions were generally higher than 80%. The fibrous form of linter Cellulose can be maintained to some extent by selecting the oxidation conditions, where significant amounts of carboxyl and aldehyde groups are introduced into the fibrous fractions. The patterns of solid-state 13C-NMR spectra revealed that the oxidation occurred at the C6 primary hydroxyl groups of Cellulose. X-ray diffraction and electron microscopic analyses showed that such C6 oxidation took place homogeneously at the surfaces of Cellulose I crystallites or those of Cellulose microfibrils, without any oxidation at the C6 of inside Cellulose I crystallites. Thus, carboxylate and aldehyde groups introduced into the TEMPO-oxidized Celluloses are densely present on the surfaces of Cellulose I crystallites or those of Cellulose microfibrils.
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Intracrystalline deuteration of Native Cellulose
Macromolecules, 1999Co-Authors: Yoshiharu Nishiyama, Akira Isogai, Martin Müller, Takeshi Okano, Henri ChanzyAbstract:The easeof the hydrogen-deuterium exchange in the accessiblehydroxyl groups of Cellulose has also been used forneutron scattering studies. In a classical experimentwith Cellulose II fortisan fibers, a meaningful fiberperiodicity of 150-200 A was revealed by small-angleneutron scattering after exposing the fibers to D
Tsuguyuki Saito - One of the best experts on this subject based on the ideXlab platform.
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Different Conformations of Surface Cellulose Molecules in Native Cellulose Microfibrils Revealed by Layer-by-Layer Peeling.
Biomacromolecules, 2017Co-Authors: Ryunosuke Funahashi, Tsuguyuki Saito, Yusuke Okita, Hiromasa Hondo, Mengchen Zhao, Akira IsogaiAbstract:Layer-by-layer peeling of surface molecules of Native Cellulose microfibrils was performed using a repeated sequential process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical-mediated oxidation followed by hot alkali extraction. Both highly crystalline algal and tunicate Celluloses and low-crystalline cotton and wood Celluloses were investigated. Initially, the C6-hydroxy groups of the outermost surface molecules of each algal Cellulose microfibril facing the exterior had the gauche–gauche (gg) conformation, whereas those facing the interior had the gauche–trans (gt) conformation. All the other C6-hydroxy groups of the Cellulose molecules inside the microfibrils contributing to crystalline Cellulose I had the trans–gauche (tg) conformation. After surface peeling, the originally second-layer molecules from the microfibril surface became the outermost surface molecules, and the original tg conformation changed to gg and gt conformations. The plant Cellulose microfibrils likely had disordered structures for ...
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introduction of aldehyde groups on surfaces of Native Cellulose fibers by tempo mediated oxidation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006Co-Authors: Tsuguyuki Saito, Akira IsogaiAbstract:Abstract Native Cellulose fibers were suspended in water and oxidized to various degrees with sodium hypochlorite and catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and sodium bromide at pH 10.5. The oxidation was accomplished within 30 min at room temperature. The TEMPO-oxidized Cellulose fibers were then converted to sheets like paper. Tensile strength of the sheets soaked in water, i.e. wet strength, showed a maximum value, when 0.3 mmol NaClO per gram Cellulose was used in the TEMPO-mediated oxidation. Aldehyde groups up to 0.225 mmol/g were introduced in Native Cellulose fibers by the TEMPO-mediated oxidation, and were stably present in there. However, only surface aldehyde groups in the TEMPO-oxidized Cellulose fibers contributed to the wet strength development of the sheets. Carboxylate groups were also formed not only surfaces but also insides of Cellulose fibers by the TEMPO-mediated oxidation, although they had nearly no contribution to wet strength development of the sheets. These surface aldehyde groups forms hemiacetal linkages with Cellulose hydroxyl groups at the inter-fiber bonds, resulting in the clear wet strength development of the sheets prepared thereof. The TEMPO-mediated oxidation is, therefore, applicable to introduction of not only carboxylate groups but also aldehyde groups to Native Cellulose surfaces as an efficient chemical modification under aqueous conditions.
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introduction of aldehyde groups on surfaces of Native Cellulose fibers by tempo mediated oxidation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006Co-Authors: Tsuguyuki Saito, Akira IsogaiAbstract:Abstract Native Cellulose fibers were suspended in water and oxidized to various degrees with sodium hypochlorite and catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and sodium bromide at pH 10.5. The oxidation was accomplished within 30 min at room temperature. The TEMPO-oxidized Cellulose fibers were then converted to sheets like paper. Tensile strength of the sheets soaked in water, i.e. wet strength, showed a maximum value, when 0.3 mmol NaClO per gram Cellulose was used in the TEMPO-mediated oxidation. Aldehyde groups up to 0.225 mmol/g were introduced in Native Cellulose fibers by the TEMPO-mediated oxidation, and were stably present in there. However, only surface aldehyde groups in the TEMPO-oxidized Cellulose fibers contributed to the wet strength development of the sheets. Carboxylate groups were also formed not only surfaces but also insides of Cellulose fibers by the TEMPO-mediated oxidation, although they had nearly no contribution to wet strength development of the sheets. These surface aldehyde groups forms hemiacetal linkages with Cellulose hydroxyl groups at the inter-fiber bonds, resulting in the clear wet strength development of the sheets prepared thereof. The TEMPO-mediated oxidation is, therefore, applicable to introduction of not only carboxylate groups but also aldehyde groups to Native Cellulose surfaces as an efficient chemical modification under aqueous conditions.
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TEMPO-mediated Oxidation of Native Cellulose
2005Co-Authors: Tsuguyuki Saito, Akira IsogaiAbstract:Linter Cellulose was oxidized with sodium hypochlorite with catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) under various conditions. After this TEMPO-mediated oxidation, fibrous water-insoluble fractions were collected, and characterized in terms of carboxyl and aldehyde contents, distribution of carboxylate and aldehyde groups, crystallinities and crystal sizes, morphology, etc. Carboxyl and aldehyde groups were introduced into the fibrous fractions up to about 0.7 and 0.3 mmol/g, respectively, by the oxidation, where recovery of the fibrous fractions were generally higher than 80%. The fibrous form of linter Cellulose can be maintained to some extent by selecting the oxidation conditions, where significant amounts of carboxyl and aldehyde groups are introduced into the fibrous fractions. The patterns of solid-state 13C-NMR spectra revealed that the oxidation occurred at the C6 primary hydroxyl groups of Cellulose. X-ray diffraction and electron microscopic analyses showed that such C6 oxidation took place homogeneously at the surfaces of Cellulose I crystallites or those of Cellulose microfibrils, without any oxidation at the C6 of inside Cellulose I crystallites. Thus, carboxylate and aldehyde groups introduced into the TEMPO-oxidized Celluloses are densely present on the surfaces of Cellulose I crystallites or those of Cellulose microfibrils.
Eero Kontturi - One of the best experts on this subject based on the ideXlab platform.
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Surface-induced Frustration in Solid State Polymorphic Transition of Native Cellulose Nanocrystals
Biomacromolecules, 2017Co-Authors: Reeta Salminen, Niki Baccile, Mehedi Reza, Eero KontturiAbstract:The presence of an interface generally influences crystallization of polymers from melt or from solution. Here, by contrast, we explore the effect of surface immobilization in a direct solid state polymorphic transition on individual Cellulose nanocrystals (CNCs), extracted from a plant-based origin. The conversion from Native Cellulose I to Cellulose III crystal occurred via a host–guest inclusion of ethylene diamine inside the crystal. A 60% reduction in CNC width (height) in atomic force microscopy images suggested that when immobilized on a flat modified silica surface, the stresses caused by the inclusion or the subsequent regeneration resulted in exfoliation, hypothetically, between the van der Waals bonded sheets within the crystal. Virtually no changes in dimensions were visible when the polymorphic transition was performed to nonimmobilized CNCs in bulk dispersion. With reservations and by acknowledging the obvious dissimilarities, the exfoliation of Cellulose crystal sheets can be viewed as anal...
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Surface-induced Frustration in Solid State Polymorphic Transition of Native Cellulose Nanocrystals
Biomacromolecules, 2017Co-Authors: Reeta Salminen, Niki Baccile, Mehedi Reza, Eero KontturiAbstract:The presence of an interface generally influences crystallization of polymers from melt or from solution. Here, by contrast, we explore the effect of surface immobilization in a direct solid state polymorphic transition on individual Cellulose nanocrystals (CNCs), extracted from a plant-based origin. The conversion from Native Cellulose I to Cellulose III crystal occurred via a host-guest inclusion of ethylene diamine inside the crystal. 60% reduction in CNC width (height) in atomic force microscopy images suggested that when immobilized on a flat modified silica surface, the stresses caused by the inclusion or the subsequent regeneration resulted in exfoliation, hypothetically between the van der Waals bonded sheets within the crystal. Virtually no changes in dimensions were visible when the polymorphic transition was performed to non-immobilized CNCs in bulk dispersion. With reservations and by acknowledging the obvious dissimilarities, the exfoliation of Cellulose crystal sheets can be viewed as analogous to exfoliation of 2D structures like graphene from a van der Waals stacked solid. Here, the detachment is triggered by an inclusion of a guest molecule inside a host Cellulose crystal and the stresses caused by the firm attachment of the CNC on a solid substrate, leading to detachment of molecular sheets or stacks of sheets.
Monika Österberg - One of the best experts on this subject based on the ideXlab platform.
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Colloidal inonic self-assembly between anionic Native Cellulose nanofibrils and cationic block copolymer micelles into biomimetic nanocomposites
2013Co-Authors: Miao Wang, Mikael Ankerfors, Lars Berglund, Andreas Walther, Anna Olszewska, Jani-markus Malho, Felix H. Schacher, Janne Ruokolainen, Janne Laine, Monika ÖsterbergAbstract:Colloidal inonic self-assembly between anionic Native Cellulose nanofibrils and cationic block copolymer micelles into biomimetic nanocomposites
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Colloidal ionic assembly between anionic Native Cellulose nanofibrils and cationic block copolymer micelles into biomimetic nanocomposites.
Biomacromolecules, 2011Co-Authors: Miao Wang, Mikael Ankerfors, Lars Berglund, Andreas Walther, Anna Olszewska, Jani-markus Malho, Felix H. Schacher, Janne Ruokolainen, Janne Laine, Monika ÖsterbergAbstract:We present a facile ionic assembly between fibrillar and spherical colloidal objects toward biomimetic nanocomposites with majority hard and minority soft domains based on anionic reinforcing Native Cellulose nanofibrils and cationic amphiphilic block copolymer micelles with rubbery core. The concept is based on ionic complexation of carboxymethylated nanofibrillated Cellulose (NFC, or also denoted as microfibrillated Cellulose, MFC) and micelles formed by aqueous self-assembly of quaternized poly(1,2-butadiene)-block-poly(dimethylaminoethyl methacrylate) with high fraction of the NFC reinforcement. The adsorption of block copolymer micelles onto nanoCellulose is shown by quartz crystal microbalance measurements, atomic force microscopy imaging, and fluorescent optical microscopy. The physical properties are elucidated using electron microscopy, thermal analysis, and mechanical testing. The cationic part of the block copolymer serves as a binder to NFC, whereas the hydrophobic rubbery micellar cores are d...
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enzymatic hydrolysis of Native Cellulose nanofibrils and other Cellulose model films effect of surface structure
Langmuir, 2008Co-Authors: Susanna Ahola, Janne Laine, Monika Österberg, Xavier Turon, Orlando J RojasAbstract:Model films of Native Cellulose nanofibrils, which contain both crystalline Cellulose I and amorphous domains, were used to investigate the dynamics and activities of cellulase enzymes. The enzyme binding and degradation of nanofibril films were compared with those for other films of Cellulose, namely, Langmuir−Schaefer and spin-coated regenerated Cellulose, as well as Cellulose nanocrystal cast films. Quartz crystal microbalance with dissipation (QCM-D) was used to monitor the changes in frequency and energy dissipation during incubation at varying enzyme concentrations and experimental temperatures. Structural and morphological changes of the Cellulose films upon incubation with enzymes were evaluated by using atomic force microscopy. The QCM-D results revealed that the rate of enzymatic degradation of the nanofibril films was much faster compared to the other types of cellulosic films. Higher enzyme loads did not dramatically increase the already fast degradation rate. Real-time measurements of the cou...
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model films from Native Cellulose nanofibrils preparation swelling and surface interactions
Biomacromolecules, 2008Co-Authors: Susanna Ahola, Janne Laine, Jani Salmi, Leenasisko Johansson, Monika ÖsterbergAbstract:Native Cellulose model films containing both amorphous and crystalline Cellulose I regions were prepared by spin-coating aqueous Cellulose nanofibril dispersions onto silica substrates. Nanofibrils from wood pulp with low and high charge density were used to prepare the model films. Because the low charged nanofibrils did not fully cover the silica substrates, an anchoring substance was selected to improve the coverage. The model surfaces were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The effect of nanofibril charge density, electrolyte concentration, and pH on swelling and surface interactions of the model film was studied by quartz crystal microbalance with dissipation (QCM-D) and AFM force measurements. The results showed that the best coverage for the low charged fibrils was achieved by using 3-aminopropyltrimethoxysilane (APTS) as an anchoring substance and hence it was chosen as the anchor. The AFM and XPS measurements showed that the fibrils are c...
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Model Films from Native Cellulose Nanofibrils. Preparation, Swelling, and Surface Interactions
Biomacromolecules, 2008Co-Authors: Susanna Ahola, Janne Laine, Jani Salmi, Leenasisko Johansson, Monika ÖsterbergAbstract:Native Cellulose model films containing both amorphous and crystalline Cellulose I regions were prepared by spin-coating aqueous Cellulose nanofibril dispersions onto silica substrates. Nanofibrils from wood pulp with low and high charge density were used to prepare the model films. Because the low charged nanofibrils did not fully cover the silica substrates, an anchoring substance was selected to improve the coverage. The model surfaces were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The effect of nanofibril charge density, electrolyte concentration, and pH on swelling and surface interactions of the model film was studied by quartz crystal microbalance with dissipation (QCM-D) and AFM force measurements. The results showed that the best coverage for the low charged fibrils was achieved by using 3-aminopropyltrimethoxysilane (APTS) as an anchoring substance and hence it was chosen as the anchor. The AFM and XPS measurements showed that the fibrils are covering the substrates. Charge density of the fibrils affected the morphology of the model surfaces. The low charged fibrils formed a network structure while the highly charged fibrils formed denser film structure. The average thickness of the films corresponded to a monolayer of fibrils, and the average rms roughness of the films was 4 and 2 nm for the low and high charged nanofibril films, respectively. The model surfaces were stable in QCM-D swelling experiments, and the behavior of the nanofibril surfaces at different electrolyte concentrations and pHs correlated with other studies and the theories of Donnan. The AFM force measurements with the model surfaces showed well reproducible results, and the swelling results correlated with the swelling observed by QCM-D. Both steric and electrostatic forces were observed and the influence of steric forces increased as the films were swelling due to changes in pH and electrolyte concentration. These films differ from previous model Cellulose films due to their chemical composition (crystalline Cellulose I and amorphous regions) and fibrillar structure and hence serve as excellent models for the pulp fiber surface.
Reeta Salminen - One of the best experts on this subject based on the ideXlab platform.
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Surface-induced Frustration in Solid State Polymorphic Transition of Native Cellulose Nanocrystals
Biomacromolecules, 2017Co-Authors: Reeta Salminen, Niki Baccile, Mehedi Reza, Eero KontturiAbstract:The presence of an interface generally influences crystallization of polymers from melt or from solution. Here, by contrast, we explore the effect of surface immobilization in a direct solid state polymorphic transition on individual Cellulose nanocrystals (CNCs), extracted from a plant-based origin. The conversion from Native Cellulose I to Cellulose III crystal occurred via a host–guest inclusion of ethylene diamine inside the crystal. A 60% reduction in CNC width (height) in atomic force microscopy images suggested that when immobilized on a flat modified silica surface, the stresses caused by the inclusion or the subsequent regeneration resulted in exfoliation, hypothetically, between the van der Waals bonded sheets within the crystal. Virtually no changes in dimensions were visible when the polymorphic transition was performed to nonimmobilized CNCs in bulk dispersion. With reservations and by acknowledging the obvious dissimilarities, the exfoliation of Cellulose crystal sheets can be viewed as anal...
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Surface-induced Frustration in Solid State Polymorphic Transition of Native Cellulose Nanocrystals
Biomacromolecules, 2017Co-Authors: Reeta Salminen, Niki Baccile, Mehedi Reza, Eero KontturiAbstract:The presence of an interface generally influences crystallization of polymers from melt or from solution. Here, by contrast, we explore the effect of surface immobilization in a direct solid state polymorphic transition on individual Cellulose nanocrystals (CNCs), extracted from a plant-based origin. The conversion from Native Cellulose I to Cellulose III crystal occurred via a host-guest inclusion of ethylene diamine inside the crystal. 60% reduction in CNC width (height) in atomic force microscopy images suggested that when immobilized on a flat modified silica surface, the stresses caused by the inclusion or the subsequent regeneration resulted in exfoliation, hypothetically between the van der Waals bonded sheets within the crystal. Virtually no changes in dimensions were visible when the polymorphic transition was performed to non-immobilized CNCs in bulk dispersion. With reservations and by acknowledging the obvious dissimilarities, the exfoliation of Cellulose crystal sheets can be viewed as analogous to exfoliation of 2D structures like graphene from a van der Waals stacked solid. Here, the detachment is triggered by an inclusion of a guest molecule inside a host Cellulose crystal and the stresses caused by the firm attachment of the CNC on a solid substrate, leading to detachment of molecular sheets or stacks of sheets.