The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Paul Kosma - One of the best experts on this subject based on the ideXlab platform.
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 2: Isolation and identification of chromophores
Cellulose, 2005Co-Authors: Thomas Rosenau, Antje Potthast, Immanuel Adorjan, Andreas Hofinger, Walter Milacher, Paul KosmaAbstract:The Lyocell Process is a modern ‘green’ industrial fiber-making technology, which employs N -methylmorpholine- N -oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell Processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluoride – acetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 1: Studies on model compounds and pulps
Cellulose, 2005Co-Authors: Immanuel Adorjan, Thomas Rosenau, Antje Potthast, Herbert Sixta, Paul KosmaAbstract:N -Methylmorpholine- N -oxide monohydrate (NMMO) is used as solvent for cellulose in the Lyocell Process as a modern industrial fiber-making technology. Undesired chemical side reactions and byproduct formation in the system cellulose/NMMO/water are known to cause detrimental effects, such as chromophore formation and discoloration of the resulting fibers. A detailed kinetic study on the influence of carbonyl structures on chromophore formation in NMMO melts was carried out employing UV spectroscopy. Different sugar model compounds, such as reducing or non-reducing sugars, and sugars with additional oxidized functions, were applied. The chromophore formation rate differed widely for various reducing sugar model compounds, with pentoses generally reacting faster than hexoses, and carbohydrates with protected reducing end being largely inert. The effect of carbonyl groups on chromophore generation has been studied further using oligomers and oxidized pulps with different contents of carbonyl groups. As in the case of model compounds, also for the pulps a linear correlation between carbonyl content and chromophore formation rate was established. A distinct effect of hemicelluloses was observed.
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Kinetic and chemical studies on the isomerization of monosaccharides in N-methylmorpholine-N-oxide (NMMO) under Lyocell conditions.
Carbohydrate Research, 2004Co-Authors: Immanuel Adorjan, Thomas Rosenau, John Sjöberg, Andreas Hofinger, Paul KosmaAbstract:The Lyocell Process is a modern and environmentally fully compatible industrial fiber-making technology. Cellulosic pulp is dissolved without chemical derivatization in a melt of N-methylmorpholine-N-oxide monohydrate (NMMO). In the present work, the reactions of monosaccharides under Lyocell conditions were investigated in detail, using capillary zone electrophoresis as the analytical technique to clarify the composition of reaction mixtures and to follow the kinetics. Under Lyocell conditions, xylose and glucose undergo two competitive reactions: rapid conversion to nonreducing products, and complete isomerization involving the whole carbohydrate backbone, via ketose intermediates. Sugar acids are present in minor amounts only, as demonstrated by employing isotopically labeled material for NMR techniques.
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instabilities in the system nmmo water cellulose Lyocell Process caused by polonowski type reactions
Holzforschung, 2002Co-Authors: Thomas Rosenau, Antje Potthast, Herbert Sixta, Andreas Hofinger, Paul KosmaAbstract:Polonowski type degradation reactions arc a major reason for the frequently observed instability of solutions of cellulose in N-methylmorpholine-N-oxide monohydrate (NMMO. 1). The degradation is induced by degradation products of cellulose and NMMO generated in situ in the Lyocell system. The presence of both an amine component such as morpholine or N-methylmorpholine, and an acid component is required for the decomposition Process to proceed. The latter might be a low-molecular-weight compound, such as formic acid, acetic acid or gluconic acid, or also a high-molecular-weight acid, such as polyglucuronic acid or ion exchange resin.
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Instabilities in the System NMMO/Water/Cellulose (Lyocell Process) Caused by Polonowski Type Reactions
Holzforschung, 2002Co-Authors: Thomas Rosenau, Antje Potthast, Herbert Sixta, Andreas Hofinger, Paul KosmaAbstract:Polonowski type degradation reactions arc a major reason for the frequently observed instability of solutions of cellulose in N-methylmorpholine-N-oxide monohydrate (NMMO. 1). The degradation is induced by degradation products of cellulose and NMMO generated in situ in the Lyocell system. The presence of both an amine component such as morpholine or N-methylmorpholine, and an acid component is required for the decomposition Process to proceed. The latter might be a low-molecular-weight compound, such as formic acid, acetic acid or gluconic acid, or also a high-molecular-weight acid, such as polyglucuronic acid or ion exchange resin.
Herbert Sixta - One of the best experts on this subject based on the ideXlab platform.
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Novel concepts of dissolving pulp production
Cellulose, 2013Co-Authors: Herbert Sixta, Mikhail Iakovlev, Lidia Testova, Annariikka Roselli, Michael Hummel, Marc Borrega, Adriaan Heiningen, Carmen Froschauer, Herwig SchottenbergerAbstract:Herein, we report about existing and novel dissolving pulp Processes providing the basis for an advanced biorefinery. The SO_2–ethanol–water (SEW) Process has the potential to replace the acid sulphite Process for the production of rayon-grade pulps owing to a higher flexibility in the selection of the raw material source, substantially lower cooking times, and the near absence of sugar degradation products. Special attention is paid to developments that target toward the selective and quantitative fractionation of paper-grade pulps into hemicelluloses and cellulose of highest purity. This target has been accomplished by the IONCELL Process where the entire hemicellulose fraction is selectively dissolved in an ionic liquid in which the H-bond basicity and acidity are adequately adjusted by the addition of a co-solvent. At the same time, pure hemicellulose can be recovered by further addition of the co-solvent, which then acts as a non-solvent. The residual pure cellulose fraction may then enter a Lyocell Process for the production of regenerated cellulose products.
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sulfur free dissolving pulps and their application for viscose and Lyocell
Cellulose, 2011Co-Authors: Gabriele Schild, Herbert SixtaAbstract:In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E) both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification in a Process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all Process modifications sulfur was successfully replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive viscose and Lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular viscose Processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant to steeping in the standard viscose Process. Simultaneously, the supramolecular structure of the cellulose is partly converted from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the Lyocell Process due to the outstanding solubility of the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and Lyocell fibers. The high molecular weight xylan of the CCE-treated pulps even took part in fiber forming.
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 1: Studies on model compounds and pulps
Cellulose, 2005Co-Authors: Immanuel Adorjan, Thomas Rosenau, Antje Potthast, Herbert Sixta, Paul KosmaAbstract:N -Methylmorpholine- N -oxide monohydrate (NMMO) is used as solvent for cellulose in the Lyocell Process as a modern industrial fiber-making technology. Undesired chemical side reactions and byproduct formation in the system cellulose/NMMO/water are known to cause detrimental effects, such as chromophore formation and discoloration of the resulting fibers. A detailed kinetic study on the influence of carbonyl structures on chromophore formation in NMMO melts was carried out employing UV spectroscopy. Different sugar model compounds, such as reducing or non-reducing sugars, and sugars with additional oxidized functions, were applied. The chromophore formation rate differed widely for various reducing sugar model compounds, with pentoses generally reacting faster than hexoses, and carbohydrates with protected reducing end being largely inert. The effect of carbonyl groups on chromophore generation has been studied further using oligomers and oxidized pulps with different contents of carbonyl groups. As in the case of model compounds, also for the pulps a linear correlation between carbonyl content and chromophore formation rate was established. A distinct effect of hemicelluloses was observed.
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instabilities in the system nmmo water cellulose Lyocell Process caused by polonowski type reactions
Holzforschung, 2002Co-Authors: Thomas Rosenau, Antje Potthast, Herbert Sixta, Andreas Hofinger, Paul KosmaAbstract:Polonowski type degradation reactions arc a major reason for the frequently observed instability of solutions of cellulose in N-methylmorpholine-N-oxide monohydrate (NMMO. 1). The degradation is induced by degradation products of cellulose and NMMO generated in situ in the Lyocell system. The presence of both an amine component such as morpholine or N-methylmorpholine, and an acid component is required for the decomposition Process to proceed. The latter might be a low-molecular-weight compound, such as formic acid, acetic acid or gluconic acid, or also a high-molecular-weight acid, such as polyglucuronic acid or ion exchange resin.
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Instabilities in the System NMMO/Water/Cellulose (Lyocell Process) Caused by Polonowski Type Reactions
Holzforschung, 2002Co-Authors: Thomas Rosenau, Antje Potthast, Herbert Sixta, Andreas Hofinger, Paul KosmaAbstract:Polonowski type degradation reactions arc a major reason for the frequently observed instability of solutions of cellulose in N-methylmorpholine-N-oxide monohydrate (NMMO. 1). The degradation is induced by degradation products of cellulose and NMMO generated in situ in the Lyocell system. The presence of both an amine component such as morpholine or N-methylmorpholine, and an acid component is required for the decomposition Process to proceed. The latter might be a low-molecular-weight compound, such as formic acid, acetic acid or gluconic acid, or also a high-molecular-weight acid, such as polyglucuronic acid or ion exchange resin.
Thomas Rosenau - One of the best experts on this subject based on the ideXlab platform.
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Drying of a cellulose II gel: effect of physical modification and redispersibility in water
Cellulose, 2017Co-Authors: Marco Beaumont, Antje Potthast, Martina Opietnik, Jakob König, Thomas RosenauAbstract:The agglomeration of cellulosic materials upon drying, often called hornification, causes a reduction of water retention, among other undesired effects. It is one of the main issues in industrial cellulose Processing, especially with regard to nanocelluloses. As a consequence, high transportation and storage costs arise since nanocelluloses need to remain in aqueous suspensions unless trade-offs in reactivity, redispersibility and surface properties are accepted. In this study, different drying strategies for TENCEL^® gel, a nanostructured gel derived from the Lyocell Process consisting of spherical particles, are compared and evaluated. First, freeze-drying with consideration of the influence of freezing temperature and the use of tert -butanol as cryo-protectant, and second, simple oven-drying at 60 °C. Surprisingly, oven-dried xerogels showed higher water retention values and also better colloidal stability than the cryogels. This is in stark contrast to cellulose nanofibrils for which freeze-drying has been shown to be significantly superior to oven drying in terms of redispersibility. For the TENCEL^® gel, oven-drying was thus selected and the influence of additives on the redispersibility of the cellulose II gel was studied by means of the common water retention value, particle size, colloidal stability, appearance of the redispersed gel and viscosity. The addition of the polysaccharides carboxymethyl cellulose or xanthan showed the most promising results with regard to redispersibility. Also sucrose and ammonium bicarbonate provided higher colloidal stabilities than that of the untreated TENCEL^® gel. The redispersibility of the cellulose II xerogels could thus be significantly improved by simple and cost-efficient mixing with additives prior to drying.
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Nanostructured Cellulose II Gel Consisting of Spherical Particles
ACS Sustainable Chemistry & Engineering, 2016Co-Authors: Marco Beaumont, Antje Potthast, Harald Rennhofer, Martina Opietnik, Helga C. Lichtenegger, Thomas RosenauAbstract:Cellulose nanofibrils (CNF) are usually obtained by breaking down the lignocellulosic structure of pulp, i.e., as cellulose I allomorph and according to rather energy-intensive pathways. In contrast to those approaches, TENCEL gel is obtained from a nonfibrous cellulose II precursor directly out of the Lyocell Process in a deceptively energy-efficient way: After enzymatic treatment and only one cycle in a high-pressure homogenizer (comparing to up to 20 cycles for CNF manufacture) the final gel is obtained. The utilization of a starting material from an already existing industrial Process is another distinct advantage. This novel cellulose II gel possesses a particle-like, homogeneous morphology and is composed of individual particles with a size of less than one micron, featuring the rheological behavior of a soft solid. The course of the gel production Process was studied with respect to changes in crystallinity, appearance and molecular weight, whereas the morphology and size of the final gel particles...
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 2: Isolation and identification of chromophores
Cellulose, 2005Co-Authors: Thomas Rosenau, Antje Potthast, Immanuel Adorjan, Andreas Hofinger, Walter Milacher, Paul KosmaAbstract:The Lyocell Process is a modern ‘green’ industrial fiber-making technology, which employs N -methylmorpholine- N -oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell Processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluoride – acetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 1: Studies on model compounds and pulps
Cellulose, 2005Co-Authors: Immanuel Adorjan, Thomas Rosenau, Antje Potthast, Herbert Sixta, Paul KosmaAbstract:N -Methylmorpholine- N -oxide monohydrate (NMMO) is used as solvent for cellulose in the Lyocell Process as a modern industrial fiber-making technology. Undesired chemical side reactions and byproduct formation in the system cellulose/NMMO/water are known to cause detrimental effects, such as chromophore formation and discoloration of the resulting fibers. A detailed kinetic study on the influence of carbonyl structures on chromophore formation in NMMO melts was carried out employing UV spectroscopy. Different sugar model compounds, such as reducing or non-reducing sugars, and sugars with additional oxidized functions, were applied. The chromophore formation rate differed widely for various reducing sugar model compounds, with pentoses generally reacting faster than hexoses, and carbohydrates with protected reducing end being largely inert. The effect of carbonyl groups on chromophore generation has been studied further using oligomers and oxidized pulps with different contents of carbonyl groups. As in the case of model compounds, also for the pulps a linear correlation between carbonyl content and chromophore formation rate was established. A distinct effect of hemicelluloses was observed.
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Kinetic and chemical studies on the isomerization of monosaccharides in N-methylmorpholine-N-oxide (NMMO) under Lyocell conditions.
Carbohydrate Research, 2004Co-Authors: Immanuel Adorjan, Thomas Rosenau, John Sjöberg, Andreas Hofinger, Paul KosmaAbstract:The Lyocell Process is a modern and environmentally fully compatible industrial fiber-making technology. Cellulosic pulp is dissolved without chemical derivatization in a melt of N-methylmorpholine-N-oxide monohydrate (NMMO). In the present work, the reactions of monosaccharides under Lyocell conditions were investigated in detail, using capillary zone electrophoresis as the analytical technique to clarify the composition of reaction mixtures and to follow the kinetics. Under Lyocell conditions, xylose and glucose undergo two competitive reactions: rapid conversion to nonreducing products, and complete isomerization involving the whole carbohydrate backbone, via ketose intermediates. Sugar acids are present in minor amounts only, as demonstrated by employing isotopically labeled material for NMR techniques.
Antje Potthast - One of the best experts on this subject based on the ideXlab platform.
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Drying of a cellulose II gel: effect of physical modification and redispersibility in water
Cellulose, 2017Co-Authors: Marco Beaumont, Antje Potthast, Martina Opietnik, Jakob König, Thomas RosenauAbstract:The agglomeration of cellulosic materials upon drying, often called hornification, causes a reduction of water retention, among other undesired effects. It is one of the main issues in industrial cellulose Processing, especially with regard to nanocelluloses. As a consequence, high transportation and storage costs arise since nanocelluloses need to remain in aqueous suspensions unless trade-offs in reactivity, redispersibility and surface properties are accepted. In this study, different drying strategies for TENCEL^® gel, a nanostructured gel derived from the Lyocell Process consisting of spherical particles, are compared and evaluated. First, freeze-drying with consideration of the influence of freezing temperature and the use of tert -butanol as cryo-protectant, and second, simple oven-drying at 60 °C. Surprisingly, oven-dried xerogels showed higher water retention values and also better colloidal stability than the cryogels. This is in stark contrast to cellulose nanofibrils for which freeze-drying has been shown to be significantly superior to oven drying in terms of redispersibility. For the TENCEL^® gel, oven-drying was thus selected and the influence of additives on the redispersibility of the cellulose II gel was studied by means of the common water retention value, particle size, colloidal stability, appearance of the redispersed gel and viscosity. The addition of the polysaccharides carboxymethyl cellulose or xanthan showed the most promising results with regard to redispersibility. Also sucrose and ammonium bicarbonate provided higher colloidal stabilities than that of the untreated TENCEL^® gel. The redispersibility of the cellulose II xerogels could thus be significantly improved by simple and cost-efficient mixing with additives prior to drying.
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Nanostructured Cellulose II Gel Consisting of Spherical Particles
ACS Sustainable Chemistry & Engineering, 2016Co-Authors: Marco Beaumont, Antje Potthast, Harald Rennhofer, Martina Opietnik, Helga C. Lichtenegger, Thomas RosenauAbstract:Cellulose nanofibrils (CNF) are usually obtained by breaking down the lignocellulosic structure of pulp, i.e., as cellulose I allomorph and according to rather energy-intensive pathways. In contrast to those approaches, TENCEL gel is obtained from a nonfibrous cellulose II precursor directly out of the Lyocell Process in a deceptively energy-efficient way: After enzymatic treatment and only one cycle in a high-pressure homogenizer (comparing to up to 20 cycles for CNF manufacture) the final gel is obtained. The utilization of a starting material from an already existing industrial Process is another distinct advantage. This novel cellulose II gel possesses a particle-like, homogeneous morphology and is composed of individual particles with a size of less than one micron, featuring the rheological behavior of a soft solid. The course of the gel production Process was studied with respect to changes in crystallinity, appearance and molecular weight, whereas the morphology and size of the final gel particles...
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 2: Isolation and identification of chromophores
Cellulose, 2005Co-Authors: Thomas Rosenau, Antje Potthast, Immanuel Adorjan, Andreas Hofinger, Walter Milacher, Paul KosmaAbstract:The Lyocell Process is a modern ‘green’ industrial fiber-making technology, which employs N -methylmorpholine- N -oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell Processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluoride – acetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.
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Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 1: Studies on model compounds and pulps
Cellulose, 2005Co-Authors: Immanuel Adorjan, Thomas Rosenau, Antje Potthast, Herbert Sixta, Paul KosmaAbstract:N -Methylmorpholine- N -oxide monohydrate (NMMO) is used as solvent for cellulose in the Lyocell Process as a modern industrial fiber-making technology. Undesired chemical side reactions and byproduct formation in the system cellulose/NMMO/water are known to cause detrimental effects, such as chromophore formation and discoloration of the resulting fibers. A detailed kinetic study on the influence of carbonyl structures on chromophore formation in NMMO melts was carried out employing UV spectroscopy. Different sugar model compounds, such as reducing or non-reducing sugars, and sugars with additional oxidized functions, were applied. The chromophore formation rate differed widely for various reducing sugar model compounds, with pentoses generally reacting faster than hexoses, and carbohydrates with protected reducing end being largely inert. The effect of carbonyl groups on chromophore generation has been studied further using oligomers and oxidized pulps with different contents of carbonyl groups. As in the case of model compounds, also for the pulps a linear correlation between carbonyl content and chromophore formation rate was established. A distinct effect of hemicelluloses was observed.
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instabilities in the system nmmo water cellulose Lyocell Process caused by polonowski type reactions
Holzforschung, 2002Co-Authors: Thomas Rosenau, Antje Potthast, Herbert Sixta, Andreas Hofinger, Paul KosmaAbstract:Polonowski type degradation reactions arc a major reason for the frequently observed instability of solutions of cellulose in N-methylmorpholine-N-oxide monohydrate (NMMO. 1). The degradation is induced by degradation products of cellulose and NMMO generated in situ in the Lyocell system. The presence of both an amine component such as morpholine or N-methylmorpholine, and an acid component is required for the decomposition Process to proceed. The latter might be a low-molecular-weight compound, such as formic acid, acetic acid or gluconic acid, or also a high-molecular-weight acid, such as polyglucuronic acid or ion exchange resin.
Xuechao Hu - One of the best experts on this subject based on the ideXlab platform.
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properties and structure of mwnts cellulose composite fibers prepared by Lyocell Process
Journal of Applied Polymer Science, 2012Co-Authors: Huihui Zhang, Jiang Lu, Yihui Jian, Huili Shao, Xuechao HuAbstract:Lyocell fiber is a new kind of regenerated cellulose fiber and expected to replace the Rayon fiber to be not only used in the textile field but also used in the fields of industry and aerospace after being modified. In this work, the multi-walled carbon nanotubes (MWNTs)/Lyocell composite fibers were prepared under different draw ratios by dry-wet spinning and their electrical properties, mechanical properties, and structure were investigated. It was found that an appropriate amount of MWNTs could be dispersed homogeneously in the Lyocell matrix and could improve the mechanical and thermal properties of composite fiber. The results of wide angle X-ray diffraction (WAXD) showed that the MWNTs in the composite fiber almost aligned along the axis of the fibers and the orientation of MWNTs increased with the increasing draw ratio. Furthermore, it was found that more MWNTs content and lower draw ratio could improve the electrical conductance of the composite fiber. The composite fiber containing 5 wt % MWNTs has a volume conductivity of 8.8 × 10−4 S/cm, which is five orders higher than that of pure Lyocell fiber. These results indicate that the MWNTs/Lyocell composite fiber has potential applications in the areas of precursor of carbon fiber and conductive fiber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
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Properties and structure of MWNTs/cellulose composite fibers prepared by Lyocell Process
Journal of Applied Polymer Science, 2011Co-Authors: Jiang Lu, Huihui Zhang, Yihui Jian, Huili Shao, Xuechao HuAbstract:Lyocell fiber is a new kind of regenerated cellulose fiber and expected to replace the Rayon fiber to be not only used in the textile field but also used in the fields of industry and aerospace after being modified. In this work, the multi-walled carbon nanotubes (MWNTs)/Lyocell composite fibers were prepared under different draw ratios by dry-wet spinning and their electrical properties, mechanical properties, and structure were investigated. It was found that an appropriate amount of MWNTs could be dispersed homogeneously in the Lyocell matrix and could improve the mechanical and thermal properties of composite fiber. The results of wide angle X-ray diffraction (WAXD) showed that the MWNTs in the composite fiber almost aligned along the axis of the fibers and the orientation of MWNTs increased with the increasing draw ratio. Furthermore, it was found that more MWNTs content and lower draw ratio could improve the electrical conductance of the composite fiber. The composite fiber containing 5 wt % MWNTs has a volume conductivity of 8.8 × 10−4 S/cm, which is five orders higher than that of pure Lyocell fiber. These results indicate that the MWNTs/Lyocell composite fiber has potential applications in the areas of precursor of carbon fiber and conductive fiber. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
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A comparative study of bamboo Lyocell fiber and other regenerated cellulose fibers 2nd ICC 2007, Tokyo, Japan, October 25–29, 2007
Holzforschung, 2009Co-Authors: Gesheng Yang, Huili Shao, Yaopeng Zhang, Xuechao HuAbstract:Abstract A new type of regenerated cellulose fiber can be made from bamboo cellulose by the Lyocell Process. In this paper, the morphology and crystal structure of the bamboo Lyocell fiber was investigated by optical microscopy, scanning electron microscopy, and wide angle X-ray diffractometry. Moreover, the mechanical properties, fibrillation behavior, moisture adsorption property, negative ion effect, and antibacterial capability of the bamboo Lyocell fiber were studied. The results showed that the bamboo Lyocell fiber proved to be similar to the structure and properties of wood Lyocell fiber, such as smooth surface, circular cross-section, high crystallinity, high tensile strength, low elongation at break, good moisture adsorption property, and easy fibrillation. Furthermore, the bamboo Lyocell fiber surpassed wood Lyocell fiber concerning negative ion effect and antibacterial property.
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precipitation kinetics of cellulose in the Lyocell spinning Process
Industrial & Engineering Chemistry Research, 2006Co-Authors: Xuechao HuAbstract:The average concentration of N-methylmorpholine-N-oxide (NMMO) in the running Lyocell filament was measured in the coagulation Process by which the precipitation kinetics of cellulose in the Lyocell Process was studied. It was found that there are two diffusion regimes in the coagulation Process of cellulose in the Lyocell Process. The fast regime is completed within 1 s, causing formation of hydrogen bonds between the molecules of NMMO and water. The apparent diffusion coefficients of NMMO in both the fast and slow regimes of the coagulation Process of the Lyocell Process were estimated by Fick's second law. It was found that apparent diffusion coefficients in both the fast and slow regimes decrease with increasing filament diameter and NMMO concentration in the coagulation bath. The apparent diffusion coefficient of NMMO in the fast regime is about one-tenth of that in the slow regime, which is in the range of 4−8 × 10-7 cm2/s.
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an analysis of Lyocell fiber formation as a melt spinning Process
2001Co-Authors: Yiyi Shen, Huili Shao, Chengxun Wu, Xuechao HuAbstract:In order to gain an understanding of the Process of Lyocell fiber formation, the melting and solidification behaviors, heat capacity and density of cellulose N-methylmorpholine-N-oxide monohydrate (NMMO-MH) solutions were studied by differential scanning calorimetry (DSC) and dilatometry, and the diameter development of Lyocell fibers in the air gap was measured online. It was found that the Lyocell Process can be considered as both a melt–spinning Process in the air gap and a wet-spinning Process in the coagulation bath. Cellulose chains in the solutions hindered the crystallization of NMMO-MH, and the melting point of the solutions decreased with increasing cellulose concentration. The density of cellulose NMMO-MH solutions decreased linearly with increasing temperature in the solid or the liquid state, and it increased with increasing cellulose concentration. The heat capacity of the solutions increased slightly with increasing temperature and concentration. The development of fiber diameter, the velocity gradient, and the gradient of the filaments in the air gap were limited to a short distance from the spinneret orifice. The position at which the velocity and the tensile stress gradient reached their maximum values moved closer to the spinneret orifice with increasing take-up speed.
