bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactions of Ionic Liquids with Polysaccharides – 2: Cellulose
Authors: Heinze Thomas , Dorn Susann , Schöbitz Michael , Liebert Tim , Köhler Sarah , Meister Frank 
Published: February 2008

AbstractSome general comments about ionic liquids (ILs) and carbohydrates are given. The main scope of the review is to discuss the present state of the art of chemical modification of cellulose applying IL as reaction media considering own research results. ILs, namely 1‐butyl‐3‐methylimidazolium chloride (BMIMCl), 1‐ethyl‐ 3‐methylimidazolium chloride (EMIMCl), 1‐butyl‐2,3‐dimethylimidazolium chloride (BDMIMCl), 1‐allyl‐2,3‐dimethylimidazolium bromide (ADMIMBr) and 1‐ethyl‐3‐ methylimidazolium acetate (EMIMAc) are solvents for cellulose (even for high molecular bacterial synthesized cellulose) and can easily be applied as reaction media for cellulose modification. We investigated the homogeneous acylation, carbanilation and silylation of the biopolymer cellulose. Under mild conditions and within short reaction time at low temperature (65 °C to 80 °C) and low excess of reagent, various cellulose esters and carbanilates, dendronized cellulose and trimethylsilyl cellulose were obtained. The DS of the cellulose derivatives can be controlled by varying the reaction time, reaction temperature and the IL used as reaction medium.
New Developments in Dissolving and Processing of Cellulose in Ionic Liquids
Authors: Hermanutz Frank , Gähr Frank , Uerdingen Eric , Meister Frank , Kosan Birgit 
Published: February 2008

AbstractIonic liquids (IL) are new direct dissolving systems for cellulose characterized by unique dissolving properties and simple technical handling. Selected IL‐systems are non toxic and chemically as well as physically neutral which represents an advantage as compared to the commonly used direct solvent N‐methyl‐ morpholine‐N‐oxide (NMMO). Fibres can easily be prepared by coagulation in water. The BASF company as a leading producer of ionic liquids investigates the technical conversion of the preparation of cellulosic fibres using ionic liquids in cooperation with the Institut für Textilchemie und Chemiefasern (ITCF), Denkendorf and the Thüringisches Institut für Textil‐ und Kunststoff‐Forschung (TITK), Rudolstadt. The major targets of this project are the selection of appropriate IL‐systems, the IL recycling, rheology of spinning dopes and the charcterization of resulting fibre profiles. Essential results of this work and the potential for establishing a technical‐ scale process are summarized.
Innovative Concepts for the Shaping and Modification of Cellulose
Authors: Liebert Tim 
Published: February 2008

AbstractThe conception and first results for a newly established project at the Center of Excellence for Polysaccharide Research in Jena are described. The work is focused on the investigation of new cellulose solvents and activating agents. Besides the use of a variety of Ionic Liquids it is the interaction of carbohydrates with boric acid and boronic acid, which will be exploited for the regeneration and chemical modification of the biomacromolecule. Two new ILs bearing cellulose activating anions were discovered which can dissolve the polysaccharide. Studies on the dissolution and chemical conversion of cellulose in ILs show the potential for homogeneous reactions but also reveal a number of side reactions especially for acetate containing ILs. In case of boronic acids a covalent binding on the secondary OH functions of glucose and glucose based polymers can be evidenced for the first time at intact molecules.
Treatment in Swelling Solutions Modifying Cellulose Fiber Reactivity – Part 1: Accessibility and Sorption
Authors: Jaturapiree Adisak , Ehrhardt Anelise , Groner Sibylle , Öztürk Hale Bahar , Siroka Barbora , Bechtold Thomas 
Published: February 2008

AbstractOf prime importance in reactions involving insoluble cellulosic fibers is the sorption of reagents, which is governed by their degrees of accessibility in substrates. Swelling treatments of cellulosics in alkali solutions alter substrate accessibility leading to changes in their reactivity. In this paper, the first of a two‐part series, we collate and examine the results from various studies involving different techniques to characterize modifications in cellulosic fibers after swelling treatments in alkali solutions. Results from measurements of structure and accessibility in fibers with techniques such as water retention, inverse size exclusion chromatography (ISEC), iodine sorption, fiber diameters, and fiber‐splitting propensities indicate that the influence of swelling treatments on fiber structure/accessibility is differs with alkali type. The results show that a non‐uniform rather than uniform distribution of reagents within structures is a more accurate representation of reactions involving swollen cellulosic fibers. Hence, the observed changes in cellulose‐fiber reactivity are governed by the degrees of fiber swelling, and reagent sorption and accessibility during swelling treatments.
Treatment in Swelling Solutions Modifying Cellulose Fiber Reactivity – Part 2: Accessibility and Reactivity
Authors: Bui Huong M. , Lenninger Margit , Manian Avinash P. , Abu‐Rous Mohammad , Schimper Christian B. , Schuster K. Christian , Bechtold Thomas 
Published: February 2008

AbstractThe reorganization of cellulose fibers by swelling treatments in alkali solutions results in numerous changes to fiber structure, causing changes of chemical reactivity in the fiber‐solution heterogeneous system. An important part of the change in chemical reactivity is the change of fiber accessibility because it results in exclusion of chemicals such as reagents or catalysts from the fiber. In the second of a two‐part series of papers, we examine the influence of changes in fiber accessibility and/or reactivity due to treatment in swelling solutions on the performance or behavior of substrates during and after chemical finishing treatments. Changes in fiber accessibility due to alkali treatments are visualized with fluorescence microscopy. The effect of alkali treatments on enzymatic hydrolysis and pad‐dry‐cure crosslinking treatments of cellulose substrates are discussed as representative examples to demonstrate the effects of swelling processes on fiber reactivity and accessibility. Model calculations indicate that a considerable redistribution of chemicals in substrates occurs during dry‐cure operations resulting from molecule‐specific exclusion effects. Pilling tests on lyocell knit‐fabrics show the impact of preceding alkali processes on the final physical performance of textile fabric highlighting the importance of correct selection of alkali processes to achieve desired behavior.
Studies on the Stabilization of Modified Lyocell Solutions
Authors: Wendler Frank , Konkin Alexander , Heinze Thomas 
Published: February 2008

AbstractAdditives with functional properties makes the Lyocell process a versatile tool for the creation of new innovative materials beyond the textile sector. Occupying functional groups or active surfaces the additives emphasize the suitability of Lyocell fibers, but simultaneously enhance the complexity of chemical reactions in cellulose/N‐methylmorpholine‐N‐oxide (NMMO) solutions, respectively. Concerning to the concentration acidic ion exchange resins, activated charcoals, carbon black etc. shift the start of decomposition to lower temperatures, decrease the viscosity, enhance the formation of amines as the main degradation products or cause autocatalytic reactions.New routes in stabilization of modified Lyocell solutions applying a polymeric stabilizer system are described. Using calorimetric, UV/VIS, ESR and HPLC analysis the degradation processes and thermal stability of modified Lyocell solutions compared to the unstabilized were studied. Moreover, as kinetic investigations show a distinguished behavior for modified solutions autocatalytic reactions can be suppressed by the stabilizing system. ESR kinetic study of radicals reveals that formation and recombination rates of radical reactions depend on cellulose concentration in Lyocell solutions and additional ingredients.
Hemicellulose in Dissolving Pulp and its Behaviour during its Processing to Viscose
Authors: Fischer Klaus , Schmidt Ingeborg 
Published: February 2008

AbstractThe amount of “hemicellulose” in pulps varies according to wood species, and the pulping processes including their bleaching agents.Making viscose cellulosic and non‐cellulosic material is removed during mercerisation which is the first processing step. Low molecular weight material is also formed during the reduction of the degree of polymerisation in order to fit the alkali cellulose for xanthation and dissolving, respectively.In this work commercially available dissolving pulps with respect to their behaviour during the preparation of viscose fibres shall be discussed. For these investigations a Eucalyptus sulphite and a Eucalyptus pre‐ hydrolysed sulphate pulps were selected.
Properties and Applications of Cellulose Acetate
Authors: Fischer Steffen , Thümmler Katrin , Volkert Bert , Hettrich Kay , Schmidt Ingeborg , Fischer Klaus 
Published: February 2008

AbstractCellulose acetate is one of the most important esters of cellulose. Depending on the way it has been processed cellulose acetate can be used for great varies of applications (e.g. for films, membranes or fibers). The properties of the applied cellulose acetates are very important for these applications. A special field for using cellulose acetate is the synthesis of porous, spherical particles, so called cellulose beads. Different types of technical cellulose acetates were used and their ability to form such cellulose beads was characterized. First the different types of cellulose acetates were characterized by means of solubility; turbidity and degree of substitution. In addition the molar mass and the distribution of substituents along the polymeric chain were analyzed. Next, the cellulose beads were synthesized within an emulsion process using these different cellulose acetates. Then the properties (particle size, porosity, morphology) of the cellulose beads were determined. Finally, the relationship between the characteristic of cellulose acetates and properties of cellulose beads was investigated.
Substitution Patterns of Cellulose Ethers ‐ Influence of the Synthetic Pathway
Authors: Bert Volkert , Wagenknecht Wolfgang 
Published: February 2008

AbstractCommercial cellulose ethers are usually prepared under heterogeneous reaction conditions. In contrast, this contribution also describes the derivatization under homogeneous conditions in N‐methylmorpholine‐N‐oxide monohydrate (NMMNO*H2O) and under heterogeneous conditions after converting native cellulose to amorphous cellulose. Amorphous cellulose is prepared by dissolving cellulose in NMMNO*H2O followed by precipitation in different media. The degree of order and the porosity of the regenerated cellulose is significantly influenced by the content of water in the precipitating agent. The differences are described by measurements using wide angle X‐ray scattering, solid‐state 13C‐NMR, mercury porosimetry, and water/liquid retention values. Three synthetic pathways (heterogeneous, heterogeneous with amorphous cellulose and homogeneous) are compared regarding the structure‐property relationship of the cellulose ethers formed. Carboxymethylation, hydroxyethylation, hydroxypropylation and sulfoethylation are considered in detail. The choice of synthetic pathway has a significant influence on the degree of substitution (DS), the distribution of substituents on the level of the anhydroglucose unit (AGU), solubility behavior, and the viscosity of aqueous solutions. In general an increasing solubility and an increasing viscosity are observed from heterogeneous to heterogeneous with amorphous cellulose to homogeneous reaction conditions. There is a remarkable difference between the heterogeneously produced cellulose ethers with a DS distribution C2 ≥ C6 > C3 and the strictly homogeneous etherification in NMMNO*H2O/organic solvent systems with a DS distribution of C3 > C2 ≫ C6. This high regioselectivity at the secondary OH‐groups of the AGU may be caused by the strong solvation behavior of NMMNO*H2O and thereby a protecting function at the C6‐OH‐group.
Novel Bulky Esters of Biopolymers: Dendritic Cellulose
Authors: Pohl Matthias , Schaller Jens , Meister Frank , Heinze Thomas 
Published: February 2008

AbstractDendronized cellulose derivatives are discussed. Regarding our own studies, novel bulky esters of cellulose were synthesized homogeneously in N,N‐ dimethyl acetamide/LiCl or dimethyl sulfoxide in combination with fluoride ions by conversion of the biopolymer with 3,5‐dihydroxybenzoic acid based aryl polyester dendrons. The carboxylic acid moieties were efficiently activated in situ with N,N′‐carbonyldiimidazole or the acid chloride was applied. Cellulose esters with values of the degree of substitution of up to 0.7 were obtained. The functionalization analyzed by NMR spectroscopy occurs not only at position 6 (primary hydroxyl group) but also the secondary one at position 2.
Characterization of Highly Porous Materials from Cellulose Carbamate
Authors: Pinnow Manfred , Fink Hans‐Peter , Fanter Carola , Kunze Jürgen 
Published: February 2008

AbstractHighly porous cellulose was formed by gelation of cellulose carbamate solutions in caustic soda. Two methods for gel preparation were optimized for the formation of beads and bulky materials – the chemical precipitation from dilute sulfuric acid and the thermal gelation by annealing at elevated temperatures. Various methods were used for characterizing of the pores of low density materials: scanning electron microscopy, small angle X‐ray scattering, mercury intrusion and nitrogen sorption. These methods were optimized and used for characterizing the complete pore system from micro to macro pores. The effects of different preparation (cellulose carbamate concentration in caustic soda) and processing (precipitation, drying and pyrolysis) on the pore structure were studied by the set of complementary methods. Aerocell samples with a minimum density of 0.06 g/cm3 were prepared from cellulose carbamate. They are characterized by a broad pore size distribution ranging from 0.5 nm to 1 mm, specific internal surfaces of up to 660 m2/g and total pore volumes of up to 18 cm3/g.
Efficient Method for the Preparation of Pure, Water‐Soluble Cellodextrines
Authors: Liebert Tim , Seifert Marit , Heinze Thomas 
Published: February 2008

AbstractAn efficient method towards water soluble cellodextrine mixtures is described and detailed information on structure analysis is given. For cellulose degradation in good yield, treatment of cellulose with 85% phosphoric acid for 30 minutes at room temperature and a hydrolysis of 20 hours at 55 °C are suitable. With a work up in tetrahydrofuran (THF), a yield of almost 70% raw product is achievable. After separation of a water insoluble fraction, a yield of 53% of cellodextrines with a degree of polymerization (mean weight average, $\overline {DP} _{\rm w} $) of 7.5 and a polydispersity index of 1.7 is obtained. These cellodextrines are soluble in water, dimethyl sulfoxide (DMSO) and dimethyl acetamide (DMA)/LiCl. Detailed structure analysis by one and two‐dimensional NMR, FTIR and mass spectroscopy revealed that the substance consists only of β‐1 → 4 linked glucoses. A partial functionalization was excluded by 13C NMR‐ and 31P decoupled 1H NMR spectroscopy.
Studies into the Early Degradation Stages of Cellulose by Different Iron Gall Ink Components
Authors: Henniges Ute , Banik Gerhard , Reibke Rebecca , Potthast Antje 
Published: February 2008

AbstractSelective fluorescence labelling of oxidized cellulose functionalities followed by GPC‐MALLS was used to get a deeper insight into ink‐induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied.Five different ink modifications were applied on model papers and underwent mild accelerated aging at 55 °C and cycling humidity (7 days) followed by a short period of static humid aging at 80 °C (2 days). Pure ink constituents like tannic acid or iron sulphate do not result in the same degree of oxidation or chain scission as complete inks. Balanced ink degrades paper more than single compounds, but less than unbalanced inks. Interestingly, some degradation occurs already during or shortly after the application process of unbalanced inks on paper. It could be demonstrated that this oxidation proceeded in a rather high Mw area, while the subsequent aging steps affected predominantly regions of shorter cellulose chains.
New Possibilities of the Acetosulfation of Cellulose
Authors: Hettrich Kay , Wagenknecht Wolfgang , Volkert Bert , Fischer Steffen 
Published: February 2008

AbstractRegioselectively substituted cellulose sulfates in C2/3‐, C2/6‐, or C6‐position of the anhydroglucose unit are accessible by certain synthesis routes. Thereby, products with different properties and various application areas are resulted. Important characteristics of cellulose sulfates regarding their applications are solubility (e.g. in water), rheological behavior, different interaction with low or high molecular cations, thermo reversible gel formation, enzymatic degradability, anticoagulant and antiviral activity. In C6‐position substituted cellulose sulfates can be synthesized in principle by acetosulfation. The acetosulfation is a quasi‐homogeneous synthesis proceeding under gradually dissolution of the cellulose by using different reactivity of the primary and secondary OH‐groups as soon as converting cellulose acetate sulfates. After precipitation of the polymer the acetyl groups are cleaved in alkaline solution. The focus of our study was firstly the investigation of the acetosulfation in different polar aprotic solvents by various sulfating and acetylating agents. In general it should be investigated if C6 substituted cellulose sulfates can be obtained by acetosulfation with different solvents and agents. The products were characterized by 13C‐NMR and Raman spectroscopy.
Improvement of Fibre‐Matrix‐Adhesion of Natural Fibres by Chemical Treatment
Authors: Reich Stefan , ElSabbagh Ahmed , Steuernagel Leif 
Published: February 2008

AbstractPlastics, also called synthetic polymers, are playing an important role in daily living. To raise more applications it is necessary to modify known polymeric systems to reach improved materials/material systems.A possibility to create new optimised materials out of neat polymers is offered by compounding them with different filling material. Besides chemical modification of polymers, mixing, combining or use of different fillers, one possibility is given by the composite technique, whereas the combination of the polymeric matrix and the embedded reinforcement (e.g. fibre) are yielding in optimised materials adjusted to the required properties. Concerning the polymeric matrix, either thermoplastic or thermoset material can be used. In case of the reinforcement, either synthetic (carbon‐, glass‐ or polymeric fibres) or natural fibres are introduced to composites.To obtain an appropriate adhesion of the matrix to the reinforcement system, synthetic fibres are equipped with an avivage. For natural fibres, there are no such materials available and the hydrophilic property of this system surface prevents an adhesion to hydrophobic polymers, as well as to sizings.In this paper, ways are shown to modify the natural fibres via chemical treatment to yield higher physical properties at better adhesion. Also we will explain activities on the use of natural fibres as reaction systems and processing tools as well as the attempt to isolate the different compounds of the neat fibre via selective work‐up.
Comparative Synthesis Studies Towards Methyl and Phenyl 4‐Deoxy‐β‐L‐threo‐hex‐4‐enopyranosiduronic Acid as Model Compounds of Hexenuronic Acid Moieties in Hardwood Pulps
Authors: Tot Ivana , Krainz Karin , Potthast Antje , Suess Ulrich , Rosenau Thomas 
Published: February 2008

AbstractThe present study describes two approaches to synthesize hexenuronic acid model compounds in which the xylan backbone is replaced by a simple substituent, either methyl or phenyl. To general pathways towards the two products are offered: the first one, starting from glucuronic acid and involving formation and reopening of the 1,6‐lactone, was especially suitable to afford the phenyl derivative 8. The second one, by contrast, is more appropriate for the methyl compound 12; it starts from galactose and involves TEMPO oxidation and conversions of the intermediate 1,3‐lactone. Both pathways were optimized on a mg scale and subsequently upscaled to afford the targets in gram amounts. The “detour” via the methyl glucopyranosiduronate – instead of using the free acid – proved to be crucial in boosting the yield in the elimination step.
One‐dimensional analysis of a poroelastic medium during freezing
Authors: Boukpeti Nathalie 
Published: February 2008

AbstractA solution to the problem of freezing of a poroelastic material is derived and analysed in the case of one‐dimensional deformation. The solution is sought within the framework of thermo‐poroelasticity, with specific account of the behaviour of freezing materials. The governing equations of the problem can be combined into a pair of coupled partial differential equations for the temperature and the fluid pressure, with particular forms in the freezing and the unfrozen regions. In the freezing region, the equations are highly non‐linear, partly due to the dependence of thermal and hydraulic properties on water saturation, which varies with temperature. Consequently, the solution is obtained through numerical methods, with special attention to the propagation of the freezing front boundary. The response to one‐dimensional freezing is illustrated for the case of cement paste. Finally, the influence on the solution of varying selected parameters is analysed, such as the temperature boundary conditions, the parameters characterizing the geometry of the porous system, the ratio of fluid and thermal diffusivities, and the rate of cooling applied at the freezing end. Copyright © 2008 John Wiley & Sons, Ltd.
Simplified coupled chemo‐mechanical modeling of cement pastes behavior subjected to combined leaching and external sulfate attack
Authors: Bary B. 
Published: February 2008

AbstractIn the context of radioactive waste storage, underground concrete structures may be subjected to external sulfate attack due to penetration of sulfate combined with leaching. This paper proposes a coupled chemo‐mechanical modeling relying on a simplified chemical description of the solid phase composing the cement paste to address this issue. The sulfate and calcium species diffusing through the pore solution are supposed to completely control the chemical system, in particular the precipitation of gypsum and ettringite, which may lead to significant macroscopic expansions and cracking. The crystallization pressure generated by the growing crystals is introduced in the modeling through a poroelasticity analogy. Based on a representation of the cement paste of the matrix‐inclusion type, the application of the Mori–Tanaka (MT) scheme provides estimates of the mechanical and diffusive properties and of the interaction coefficient as a function of the degradation state. The obtained coupled system is applied to two‐dimensional numerical simulations of laboratory tests; the confrontation between experimental and computational results shows a good agreement in terms of both hydrated product evolutions as a function of time and macroscopic cracking appearance. Copyright © 2008 John Wiley & Sons, Ltd.