Simple, expedient methods for the determination of water and electrolyte contents of cellulose solvent systems (original) (raw)
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Cellulose, 2002
The water content in the binary system N,N-dimethylacetamide/lithium chloride (DMAc/LiCl), a common cellulose solvent, has been proven to be a crucial parameter. A quick determination of water content in DMAc based on the solvatochromism of a UV-active betain probe dye has been developed and validated. An analogous method, based on the solvatochromic fluorescence shift of Zelinskij's dye, which strongly depends on the solvent polarity, was established for water determination in DMAc containing LiCl. Precise physicochemical data of the system DMAc/LiCl, such as density, viscosity, and conductivity, have been obtained. The limiting solubility for LiCl in absolute DMAc is 8.46 wt%. As shown by light scattering experiments, water in DMAc/LiCl induces aggregation upon standing for longer periods of time, which is even more prominent for diluted solutions and those having a poor state of dissolution.
Biomacromolecules, 2005
The present work deals with the effects of structural variables of celluloses on their dissolution in the solvent system LiCl/N,N-dimethylacetamide, LiCl/DMAc. Celluloses from fast growing sources (sisal and linters), as well as microcrystalline cellulose (avicel PH-101) were studied. The following structural variables were investigated: index of crystallinity, I c ; crystallite size; polymer porosity; and degree of polymerization determined by viscosity, DPv. Mercerization of fibrous celluloses was found to decrease DPv, I c , the specific surface area, and the ratio pore volume/radius. The relevance of the structural properties of cellulose to its dissolution is discussed. Rate constants and activation parameters of cellulose decrystallization, prior to its solubilization, have been determined under nonisothermal conditions. The kinetic parameters calculated showed that dissolution is accompanied with small, negative enthalpy and a large, negative entropy of activation.
Characterization of the Bacterial Cellulose Dissolved on Dimethylacetamide/Lithium Chloride
Palavras-chave: Celulose bacteriana, Acetobacter xylinum, Dimetilacetamida, cloreto de lítio, Ressonância Magnética Nuclear,difração de raio-X. Characterization of the bacterial cellulose dissolved on dimethylacetamide/lithium chloride The main barrier to the use of cellulose is his insolubility on water or organic solvents, but derivates can be obtained with the use of ionic solvents. Bacterial cellulose, is mainly produced by the bacterium Acetobacter xylinum, and is identical to the plant, but free of lignin and hemicellulose, and with several unique physical-chemical properties. Cellulose produced in a 4 % glucose medium with static condition was dissoluted on heated DMAc/LiCl (120 °C, 150 °C or 170 °C). The product of dissolved cellulose was observed with 13 C-nmr and the effect on crystalline state was seen with x-ray crystallography. The crystalline structure was lost in the dissolution, becoming an amorphous structure, as well as Avicel ® . The process of dissolution of the ...
Current Chromatography, 2014
This review describes several methods for activating cellulose so that it dissolves in N,Ndimethylacetamide/lithium chloride and can then be analyzed by size exclusion chromatography (SEC) and light scattering for the determination of molar mass and molar mass distribution (MMD). This contribution lists the effects of these methods and approaches on the molar mass distribution of cellulose. Cellulose I and cellulose II behave differently and are considered separately. The activation procedures are grouped according to mechanical, chemical, and biological mechanisms. The mechanical processes include milling, freeze drying, steam explosion, and ultrasonic treatment, while chemical mechanisms are heating, irradiation, alkaline pretreatment, and derivatization strategies are discussed. Treatments with ethylene diamine and ionic liquids are also summarized from chemical aspects. Enzymes represent the biological strategy for treating solubility problems involving cellulose. These activation mechanisms are reviewed with regard to their efficiency, effect on MMD, and possible side reactions.
Overview of Methods for the Direct Molar Mass Determination of Cellulose
Molecules, 2015
The purpose of this article is to provide the reader with an overview of the methods used to determine the molecular weights of cellulose. Methods that employ direct dissolution of the cellulose polymer are described; hence methods for investigating the molecular weight of cellulose in derivatized states, such as ethers or esters, only form a minor part of this review. Many of the methods described are primarily of historical interest since they have no use in modern cellulose chemistry. However, older methods, such as osmometry or ultracentrifuge experiments, were the first analytical methods used in polymer chemistry and continue to serve as sources of fundamental information (such as the cellulose structure in solution). The first part of the paper reviews methods, either absolute or relative, for the estimation of average molecular weights. Regardless of an absolute or relative approach, the outcome is a molecular weight average (MWA). In the final section, coupling methods are described. The primary benefit of performing a pre-separation step on the molecules is the discovery of the molecular weight distribution (MWD). Here, size exclusion chromatography (SEC) is unquestionably the most powerful and most commonly-applied method in modern laboratories and industrial settings.
Molecules, 2020
We studied the dissolution of microcrystalline cellulose (MCC) in binary mixtures of dimethyl sulfoxide (DMSO) and the ionic liquids: allylbenzyldimethylammonium acetate; 1-(2-methoxyethyl)-3-methylimidazolium acetate; 1,8-diazabicyclo [5.4.0]undec-7-ene-8-ium acetate; tetramethylguanidinium acetate. Using chemometrics, we determined the dependence of the mass fraction (in %) of dissolved cellulose (MCC-m%) on the temperature, T = 40, 60, and 80 °C, and the mole fraction of DMSO, χDMSO = 0.4, 0.6, and 0.8. We derived equations that quantified the dependence of MCC-m% on T and χDMSO. Cellulose dissolution increased as a function of increasing both variables; the contribution of χDMSO was larger than that of T in some cases. Solvent empirical polarity was qualitatively employed to rationalize the cellulose dissolution efficiency of the solvent. Using the solvatochromic probe 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (WB), we calculated the empirical polarity ET(WB) of c...
Cellulose Dissolution in an Alkali Based Solvent: Influence of Additives and Pretreatments
Journal of the Brazilian Chemical Society, 2013
A distinção entre termodinâmica e cinética de dissolução da celulose raramente tem sido considerada na literatura. Neste trabalho, discutimos este tema e fundamentamos as nossas hipóteses recorrendo a experiências simples. É do conhecimento geral que a celulose pode ser dissolvida no solvente aquoso de hidróxido de sódio (NaOH/H 2 O) a baixa temperatura. Neste trabalho, demonstramos que este solvente alcalino pode ser consideravelmente melhorado em relação à sua estabilidade, solubilidade e propriedades reológicas se forem usados diferentes aditivos (sais e moléculas anfifílicas) na fase de dissolução. Este trabalho indica novos caminhos relativamente à dissolução da celulose em solventes aquosos, de uma forma mais econômica e ambientalmente amigável, aumentando o seu potencial comercial. The distinction between thermodynamic and kinetics in cellulose dissolution is seldom considered in the literature. Therefore, herein an attempt to discuss this topic and illustrate our hypotheses on the basis of simple experiments was made. It is well-known that cellulose can be dissolved in a aqueous sodium hydroxide (NaOH/H 2 O) solvent at low temperature but it is here shown that such an alkaline solvent can be considerably improved regarding solubility, stability and rheological properties as a whole if different additives (salts and amphiphilic molecules) are used in the dissolution stage. This work probes new aqueous routes to dissolve cellulose, thereby improving the potential to commercially dissolve cellulose in an inexpensive and environmentally friendly manner.
Molecules (Basel, Switzerland), 2018
There is a sustained interest in developing solvents for physically dissolving cellulose, i.e., without covalent bond formation. The use of ionic liquids, ILs, has generated much interest because of their structural versatility that results in efficiency as cellulose solvents. Despite some limitations, imidazole-based ILs have received most of the scientific community's attention. The objective of the present review is to show the advantages of using quaternary ammonium electrolytes, QAEs, including salts of super bases, as solvents for cellulose dissolution, shaping, and derivatization, and as a result, increase the interest in further investigation of these important solvents. QAEs share with ILs structural versatility; many are liquids at room temperature or are soluble in water and molecular solvents (MSs), in particular dimethyl sulfoxide. In this review we first give a historical background on the use of QAEs in cellulose chemistry, and then discuss the common, relatively ...
Journal of Molecular Liquids, 2023
We studied the dissolution of microcrystalline cellulose (MCC) in binary mixtures of dimethyl sulfoxide (DMSO) and the ionic liquids: allylbenzyldimethylammonium acetate; 1-(2-methoxyethyl)-3-methylimidazolium acetate; 1,8-diazabicyclo [5.4.0]undec-7-ene-8-ium acetate; tetramethylguanidinium acetate. Using chemometrics, we determined the dependence of the mass fraction (in %) of dissolved cellulose (MCC-m%) on the temperature, T = 40, 60, and 80 • C, and the mole fraction of DMSO, χ DMSO = 0.4, 0.6, and 0.8. We derived equations that quantified the dependence of MCC-m% on T and χ DMSO. Cellulose dissolution increased as a function of increasing both variables; the contribution of χ DMSO was larger than that of T in some cases. Solvent empirical polarity was qualitatively employed to rationalize the cellulose dissolution efficiency of the solvent. Using the solvatochromic probe 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (WB), we calculated the empirical polarity E T (WB) of cellobiose (a model for MCC) in ionic liquid (IL)-DMSO mixtures. The E T (WB) correlated perfectly with T (fixed χ DMSO) and with χ DMSO (fixed T). These results show that there is ground for using medium empirical polarity to assess cellulose dissolution efficiency. We calculated values of MCC-m% under conditions other than those employed to generate the statistical model and determined the corresponding MCC-m% experimentally. The excellent agreement between both values shows the robustness of the statistical model and the usefulness of our approach to predict cellulose dissolution, thus saving time, labor, and material.