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Patrick Navard - One of the best experts on this subject based on the ideXlab platform.
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Polysaccharide Blend Fibres Formed from NaOH, N-Methylmorpholine-N-Oxide and 1-Ethyl-3-methylimidazolium acetate
Fibres and Textiles in Eastern Europe, 2010Co-Authors: Frank Wendler, Franck Meister, Dariusz Wawro, Ewa Wesolowska, Danuta Ciechanska, Bodo Saake, Juergen Puls, Nicolas Le Moigne, Patrick NavardAbstract:The aim of the study was to find new structured biopolymer blends bearing adjustable properties able to produce innovative materials. Apart from cellulose and three solvents (NaOH, N-Methylmorpholine-N-Oxide [NMMO] and 1-ethyl-3-methylimidazolium acetate [EMIMac]), 15 different polysaccharides were chosen to study the interactions ofpolysaccharides or their mixtures in solutions, as well as the solid state after forming. Dissolution screenings yielded promising polysaccharides, which were used for the preparation of cellulose/ polysaccharide solutions and subsequently for the shaping of blends with cellulose. The solubility and miscibility were evaluated by microscopy, DSC, particle analysis and rheology. Polysaccharides with a structure similar to that of cellulose, e.g., xylan, carrageenan or cellulose carbamate were not miscible, showing globular morphologies, whereas high-molar and side chains containing polysaccharides such as xanthan or tragacanth gum form co-continuous morphologies. The forming of blend fibres was nevertheless possible for all three solvents. The textile-physical properties of the blend fibres were slightly decreased compared to those of the unmodified fibre, in which fibres from NMMO and EMIMac had the highest performance. The presence of blended polysaccharides in the fibres produced was verified by residue sugar analysis, in which the highest amounts occurred for EMIMac fibres.
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Morphology of cellulose objects regenerated from cellulose-N-Methylmorpholine N-Oxide-water solutions
Cellulose, 2009Co-Authors: Olga Biganska, Patrick NavardAbstract:The precipitation in aqueous media of cellulose from solutions in N-Methylmorpholine N-Oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed.
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Morphology of cellulose objects regenerated from cellulose–N-Methylmorpholine N-Oxide–water solutions
Cellulose, 2008Co-Authors: Olga Biganska, Patrick NavardAbstract:The precipitation in aqueous media of cellulose from solutions in N -methylmorpholine N -oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed.
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Phase diagram of a cellulose solvent: N-Methylmorpholine-N-Oxide-water mixtures
Polymer, 2003Co-Authors: Olga Biganska, Patrick NavardAbstract:The phase diagram of the N-Methylmorpholine-N-Oxide-H2O mixtures from 0 to 100% has been determined. Three crystalline hydrates have been identified, the already known monohydrate, a dihydrate and a hydrate composed of 8 water molecules per NMMO. The melting temperature of the 8H(2)O-NMMO hydrate is -47degreesC with a melting enthalpy of about 80 J/g. The region between 25 and 55% of water does not show any crystallisation, but a glass transition around - 60 to - 100degrees C.
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Phase diagram of a cellulose solvent: N-Methylmorpholine–N-Oxide–water mixtures
Polymer, 2003Co-Authors: Olga Biganska, Patrick NavardAbstract:Abstract The phase diagram of the N -methylmorpholine– N -oxide–H 2 O mixtures from 0 to 100% has been determined. Three crystalline hydrates have been identified, the already known monohydrate, a dihydrate and a hydrate composed of 8 water molecules per NMMO. The melting temperature of the 8H 2 O–NMMO hydrate is −47 °C with a melting enthalpy of about 80 J/g. The region between 25 and 55% of water does not show any crystallisation, but a glass transition around −60 to −100 °C.
Paul Kosma - One of the best experts on this subject based on the ideXlab platform.
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Stabilization of cellulose solutions in N-Methylmorpholine-N-Oxide (Lyocell dopes) by addition of an N-Oxide as sacrificial substrate
Holzforschung, 2005Co-Authors: Thomas Rosenau, Antje Potthast, Peter Schmid, Paul KosmaAbstract:N-Methylene(morpholinium) ions (carbenium-iminium ions) are responsible for uncontrollable reactions of Lyocell dopes - solutions of cellulose in N-Methylmorpholine-N-Oxide monohydrate at process temperatures of approximately 100°C - as they are able to induce autocatalytic decomposition of the solvent. The carbenium-iminium ions derived from N-benzylmorpholine-N-Oxide (NBnMO) are less reactive, affording innocent products instead of entering an uncontrollable decomposition pathway. The dangerous carbenium-iminium ions derived from NMMO are efficiently scavenged by NBnMO, which is in turn converted into these innocent NBnMO-derived carbenium-iminium ions. Color generation in NBnMO-stabilized NMMO is far less pronounced, than in the case of the traditionally used phenolic antioxidant stabilizers. This suggests that NBnMO could be used in a novel approach to stabilize Lyocell solutions.
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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, Immanuel Adorjan, Andreas Hofinger, Walter Milacher, Antje Potthast, 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, Herbert Sixta, Antje Potthast, 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, Andreas Hofinger, John Sjoberg, Thomas Rosenau, 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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Studies on the carbenium-iminium ions derived from N-Methylmorpholine-N-Oxide (NMMO)
Tetrahedron, 2004Co-Authors: Thomas Rosenau, Antje Potthast, Paul KosmaAbstract:Abstract Two carbenium-iminium ions, an exo -centered species 2 and a ring-centered form 3 , are derived from the widely used oxidant and cellulose solvent N -methylmorpholine- N -oxide ( 1 ) by heterolytic degradation. 3 rearranges into 2 in the presence of water, in an endothermic, bimolecular reaction involving a highly organized transition state, which is the first example of a carbenium-iminium ion interconversion. The reaction mechanism was investigated by a combined approach consisting of trapping reactions, isotopic labeling, kinetic studies, and computations on the DFT level.
Thomas Rosenau - One of the best experts on this subject based on the ideXlab platform.
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A cautionary note on thermal runaway reactions in mixtures of 1-alkyl-3-methylimidazolium ionic liquids and N-Methylmorpholine-N-Oxide
Cellulose, 2017Co-Authors: Stefan Böhmdorfer, Thomas Röder, Antje Potthast, Takashi Hosoya, Thomas RosenauAbstract:N -Methylmorpholine- N -oxide (NMMO) cannot be completely separated by extraction from mixtures with common 1,3-dialkylimidazolium ionic liquids (ILs) due to strong ionic interactions between the two components. At elevated temperatures, above approx. 90 °C, especially under dry conditions and in the presence of acid, alkylating or acylating agents, remaining NMMO in ILs tends to undergo autocatalytic degradation. This is a highly exothermic, unstoppable process that results in explosions, flames, and complete charring of the reaction mixtures. Thus, caution must be exercised when drying or heating ILs that were in previous contact with NMMO, and the absence of amine oxide must be confirmed to avoid potential danger.
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Stabilization of cellulose solutions in N-Methylmorpholine-N-Oxide (Lyocell dopes) by addition of an N-Oxide as sacrificial substrate
Holzforschung, 2005Co-Authors: Thomas Rosenau, Antje Potthast, Peter Schmid, Paul KosmaAbstract:N-Methylene(morpholinium) ions (carbenium-iminium ions) are responsible for uncontrollable reactions of Lyocell dopes - solutions of cellulose in N-Methylmorpholine-N-Oxide monohydrate at process temperatures of approximately 100°C - as they are able to induce autocatalytic decomposition of the solvent. The carbenium-iminium ions derived from N-benzylmorpholine-N-Oxide (NBnMO) are less reactive, affording innocent products instead of entering an uncontrollable decomposition pathway. The dangerous carbenium-iminium ions derived from NMMO are efficiently scavenged by NBnMO, which is in turn converted into these innocent NBnMO-derived carbenium-iminium ions. Color generation in NBnMO-stabilized NMMO is far less pronounced, than in the case of the traditionally used phenolic antioxidant stabilizers. This suggests that NBnMO could be used in a novel approach to stabilize Lyocell solutions.
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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, Immanuel Adorjan, Andreas Hofinger, Walter Milacher, Antje Potthast, 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, Herbert Sixta, Antje Potthast, 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, Andreas Hofinger, John Sjoberg, Thomas Rosenau, 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.
Olga Biganska - One of the best experts on this subject based on the ideXlab platform.
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Morphology of cellulose objects regenerated from cellulose-N-Methylmorpholine N-Oxide-water solutions
Cellulose, 2009Co-Authors: Olga Biganska, Patrick NavardAbstract:The precipitation in aqueous media of cellulose from solutions in N-Methylmorpholine N-Oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed.
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Morphology of cellulose objects regenerated from cellulose–N-Methylmorpholine N-Oxide–water solutions
Cellulose, 2008Co-Authors: Olga Biganska, Patrick NavardAbstract:The precipitation in aqueous media of cellulose from solutions in N -methylmorpholine N -oxide (NMMO) hydrates is an important stage in the process of manufacturing of fibres, films and other cellulose objects. It is responsible for the formation of the structure of the regenerated object and their morphological characteristics significantly influence the properties of the final products. Regeneration of rather large cellulose objects was observed in situ by optical microscopy. It was found that all regenerated objects present an asymmetric structure composed of a dense skin surrounding a sub-layer characterised by the presence of finger-like voids. The porous texture of the cellulose parts between these voids is typical of the one obtained by spinodal decomposition. The morphologies of regenerated cellulose samples are described as a function of various parameters, initial cellulose solutions and composition and temperature of the aqueous regeneration bath. A mechanism of the structure formation during regeneration is proposed.
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Phase diagram of a cellulose solvent: N-Methylmorpholine-N-Oxide-water mixtures
Polymer, 2003Co-Authors: Olga Biganska, Patrick NavardAbstract:The phase diagram of the N-Methylmorpholine-N-Oxide-H2O mixtures from 0 to 100% has been determined. Three crystalline hydrates have been identified, the already known monohydrate, a dihydrate and a hydrate composed of 8 water molecules per NMMO. The melting temperature of the 8H(2)O-NMMO hydrate is -47degreesC with a melting enthalpy of about 80 J/g. The region between 25 and 55% of water does not show any crystallisation, but a glass transition around - 60 to - 100degrees C.
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Phase diagram of a cellulose solvent: N-Methylmorpholine–N-Oxide–water mixtures
Polymer, 2003Co-Authors: Olga Biganska, Patrick NavardAbstract:Abstract The phase diagram of the N -methylmorpholine– N -oxide–H 2 O mixtures from 0 to 100% has been determined. Three crystalline hydrates have been identified, the already known monohydrate, a dihydrate and a hydrate composed of 8 water molecules per NMMO. The melting temperature of the 8H 2 O–NMMO hydrate is −47 °C with a melting enthalpy of about 80 J/g. The region between 25 and 55% of water does not show any crystallisation, but a glass transition around −60 to −100 °C.
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Crystallisation of cellulose/N-Methylmorpholine-N-Oxide hydrate solutions
Polymer, 2002Co-Authors: Olga Biganska, Patrick Navard, Olivier BéduéAbstract:N-Methylmorpholine-N-Oxide (NMMO) hydrates are direct solvents for cellulose used commercially in the preparation of cellulose spinning dopes for fibre and film manufacturing. The fact that the cellulose/NMMO/water solutions can crystallise under cooling is important in the process of preparing fibres and films and in their structure formation. It is shown here that the major difference with classical polymer solutions is that the crystallisation of cellulose/NMMO/water solutions is only due to the crystallisation of the solvent, not of the cellulose. The reason for the decrease in crystallisation velocity with the increase in the cellulose concentration is the reduction in the crystallisable part of the solution. The concentration of water in solutions with the same cellulose content is found to strongly influence the crystallisation velocity and the morphology of crystallised solutions. The variation of the crystallisation velocity values with the type of cellulose can be explained by different amounts of free water bound to NMMO, that depend on the cellulose origin.
Valery G. Kulichikhin - One of the best experts on this subject based on the ideXlab platform.
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Films of Bacterial Cellulose Prepared from Solutions in N-Methylmorpholine-N-Oxide: Structure and Properties
Processes, 2020Co-Authors: I. S. Makarov, M. I. Vinogradov, Tatiana I. Gromovykh, Natalya A. Arkharova, Gulbarshin K. Shambilova, Pavel V. Zatonskih, Sergey V. Lutsenko, Valery G. KulichikhinAbstract:In the present study, one of the possible methods of the bacterial cellulose processing is proposed via its dissolution in N-Methylmorpholine-N-Oxide using the stage of mechano-chemical activation of the solid polymer–solvent system. Preliminary solid-phase activation is apparently a decisive factor affecting the dissolution rate of bacterial cellulose in N-Methylmorpholine-N-Oxide. The effects of bacterial cellulose concentration, solvent nature, degree of polymerization and temperature on dissolution time were studied. The rheological behavior of the solutions does not change at 120 °C for at least half an hour that allowed us to process such solutions for films preparation. The films from these solutions by means of dry-wet jet spinning in aqueous coagulant were formed. The structure of the nascent cellulose and formed films was tested by the X-ray diffraction method and SEM. The thermal behavior of the films revealed an increase in the carbon yield for the formed films compared to the nascent bacterial cellulose. The process of film pyrolysis is accompanied by exothermic effects, which are not typical for wood cellulose. Some reasons of such thermal behavior are considered.
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the role of isobutanol as a precipitant of cellulose films formed from n methylmorpholine n oxide solutions phase state and structural and morphological features
Polymer Science Series A, 2019Co-Authors: I. S. Makarov, L. K. Golova, M. I. Vinogradov, Natalya A. Arkharova, I. S. Levin, M V Mironova, G N Bondarenko, G A Shandryuk, Valery G. KulichikhinAbstract:The process of film formation including the initial treatment of thin layers of cellulose solutions in N-Methylmorpholine N-Oxide with isobutanol followed by washing with water is investigated in detail, and the structural and morphological features of the obtained films are examined. The phase state of the N-Methylmorpholine N-Oxide–isobutyl alcohol system is studied by differential scanning calorimetry and optical interferometry, and a diagram describing the crystalline equilibrium and allowing determination of the temperature–concentration “window” of compatibility of components is constructed. The dependence of viscosity of N-Methylmorpholine N-Oxide solutions in isobutanol on temperature confirms the phase composition of the system. The process of film formation is modeled by analyzing the diffusion zone of the cellulose solution–isobutyl alcohol system. The IR study of the interaction of N-Methylmorpholine N-Oxide containing 13.3% water with isobutanol shows that the affinity of isobutanol for water is much higher than that for N-Methylmorpholine N-Oxide. For this reason, when the spinning solution is brought in contact with isobutanol, the redistribution of water between the interacting components occurs and the structure of the heterogeneous gel-like complex cellulose–N-Methylmorpholine N-Oxide–isobutanol “is frozen,” as proved by the X-ray diffraction study of the films. Complete removal of the solvent and isolation of cellulose from this film proceed only upon subsequent washing with water. The X-ray diffraction and optical interferometry study of the effect of temperature on the interaction of a hot cellulose solution with cold isobutanol suggests that at room temperature the film obtained from solution contains inclusions of the vitrified N-Methylmorpholine N-Oxide. Under isothermal conditions (at a temperature of 90°С), the rate of interdiffusion grows appreciably and the solution preserves the homogeneous structure. Thus, the precipitation of cellulose from the bicomponent solvent N-Methylmorpholine N-Oxide–water upon contact first with isobutanol and then with water proceeds via two stages: initially the system undergoes phase separation and a concentrated solution is formed in the isobutanol-N-Methylmorpholine N-Oxide blend, from which cellulose precipitates upon interaction with water. When the process of primary interaction of the solution with alcohol is conducted under the conditions of compatibility of isobutanol with N-Methylmorpholine N-Oxide, a more homogeneous morphology of the films can be obtained.
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Cellulose Fibers from Solutions of Bacterial Cellulose in N-Methylmorpholine N-Oxide
Fibre Chemistry, 2019Co-Authors: I. S. Makarov, L. K. Golova, M. I. Vinogradov, Tatiana I. Gromovykh, Natalya A. Arkharova, I. S. Levin, Valery G. KulichikhinAbstract:Fibers of bacterial cellulose were obtained for the first time from solutions in N-Methylmorpholine N-Oxide (NMMO) by using the concept of solid-phase dissolution of bacterial cellulose. The mechanism of solid-phase dissolution of bacterial cellulose in NMMO is examined with due regard to the structural and morphological characteristics of native bacterial cellulose. By investigating the structure of the fibers it was possible to reveal the different orientation of the main diffraction planes of the outer shell and inner part of the fiber reflecting the structural aspect of the shell–core morphology. The fibrillar morphology of the fiber was established by scanning electron microscopy. The thermal characteristics of the fibers of bacterial cellulose differ radically from the characteristics of fibers of plant origin in the preponderance of condensation processes that produce exo effects on the thermograms and lead to increase of the carbon residue. The mechanical characteristics of the obtained fibers were characterized.
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Morphological Features and Rheological Properties of Combined Cellulose and Polyacrylonitrile Solutions in N-Methylmorpholine-N-Oxide
Polymer Science Series A, 2018Co-Authors: L. K. Golova, I. S. Makarov, M. I. Vinogradov, L. K. Kuznetsova, Valery G. KulichikhinAbstract:The combined solutions of cellulose and PAN in N-Methylmorpholine-N-Oxide at total polymer contents of 18 and 25% are obtained by solid-phase dissolution. The investigation of phase composition and morphology of these systems via optical methods shows that the solutions of cellulose and PAN in N-Methylmorpholine-N-Oxide are incompatible and form emulsions. The action of deformation on the emulsions leads to the appearance of orientational effects. If PAN predominates in droplets of the dispersed phase of cellulose solutions, this leads to the formation of fibrillar structures under shear stress, while in the case of PAN dispersion medium double emulsions are formed, in which internal droplets of the cellulose solution are most easily extended under shear. The rheological behavior of the combined systems is the direct consequence of structural-morphological transformations proceeding during deformation of the system. An analysis of the morphological and rheological features of heterophase systems reveals the concentration interval for the moldability of composite fibers from spinning emulsions.
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Solutions of acrylonitrile copolymers in N-Methylmorpholine-N-Oxide: Structure, properties, fiber spinning
European Polymer Journal, 2017Co-Authors: Valery G. Kulichikhin, I. S. Makarov, L. K. Golova, V.v. Makarova, Galina N. Bondarenko, Sergey O. Ilyin, Ivan Y. Skvortsov, A. K. BerkovichAbstract:Abstract Highly concentrated solutions of acrylonitrile copolymers (PAN) in N-Methylmorpholine N-Oxide (NMMO) were obtained via the solid-phase activation method. Specific interactions in the system at different stages of the dissolution process starting from solid-state activation and finishing with a transition to a viscous state were studied by IR spectroscopy, polarizing microscopy, interferometry and rheology. It was shown that the crucial factor determining a possibility of dissolution is the complex formation between carboxyl groups in the copolymer and the electron-donor N → O group in the solvent. This complex arises during the process of solid-phase activation of PAN and crystalline NMMO, which thereafter melts and transforms into a homogeneous solution having viscoelastic behavior. In the temperature range of 130–135 °C, irreversible chemical transformations take place in the solutions due to the coherent interaction between nitrile groups; these reactions lead to the formation of cyclic structures and conjugated sequences in the PAN chains. Rheological properties follow this process via specific viscosity and viscoelasticity evolution in time.
