Cellulose dissolution in mixtures of ionic liquids and molecular solvents: The fruitful synergism of experiment and theory (original) (raw)
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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...
Holzforschung, 2019
Dissolution of microcrystalline cellulose (MCC) in pure ionic liquids (ILs) and IL/dimethyl sulfoxide (DMSO) mixtures (mole fraction χDMSO = 0.2–0.9) was quantified using a specially constructed mechanical stirring system that allows reproducible agitation speed; temperature control, and minimum solution-air contact. The electrolytes employed were: 1-(n-butyl)-3-methylimidazolium acetate (C4MeIm AcO), 1-(methoxyethyl)-3-methylimidazolium acetate (C3OMeIm AcO), 1,8-diazabicyclo[5.4.0]undec-7-enium acetate (DBU AcO), tetramethylguanidinium acetate (TMG AcO), and tetra(n-butyl)ammonium fluoride hydrate (TBAF·xH2O). The effects on MCC dissolution of IL/DMSO composition, and temperature (50, 70°C) were studied. C4MeIm AcO and C4MeIm AcO/DMSO were more efficient solvents than their C3OMeIm AcO counterparts, due to “deactivation” of the ether oxygen of C3OMeIm AcO. MCC dissolution by C4MeIm AcO/DMSO was compared with DBU AcO/DMSO, TMG AcO/DMSO at χDMSO = 0.6, and TBAF·xH2O/DMSO at χDMSO = ...
On the dissolution state of cellulose in cold alkali solutions
Cellulose, 2017
We have characterized the dissolved state of microcrystalline cellulose (MCC) in cold alkali [2.0 M NaOH(aq)] solutions using a combination of small angle X-ray (SAXS) and static light scattering (SLS), 1 H NMR, NMR self-diffusion, and rheology experiments. NMR and SAXS data demonstrate that the cellulose is fully molecularly dissolved. SLS, however, shows the presence of large concentration fluctuations in the solution, consistent with significant attractive cellulose-cellulose interactions. The scattering data are consistent with fractal cellulose aggregates of micrometre size having a mass fractal dimension D $ 1:5. At 25 C the solution structure remains unchanged on the time scale of weeks. However, upon heating the solutions above 35 C additional aggregation occurs on the time scale of minutes. Decreasing or increasing the NaOH concentration away from the ''optimum'' 2 M also leads to additional aggregation. This is seen as an increase of the SAXS intensity at lower q values. Addition of urea (1.8 and 3.6 M, respectively) does not significantly influence the solution structure. With these examples, we will discuss how scattering methods can be used to assess the quality of solvents for cellulose. Keywords Microcrystalline cellulose (MCC) Á Cold alkali (NaOH) Á Small angle X-ray scattering (SAXS) Á Static light scattering (SLS) Á NMR Á Rheology Á Urea Á Co-solvent Á Temperature dependence Á Aggregation
Competing forces during cellulose dissolution: From solvents to mechanisms
Current Opinion in Colloid and Interface Science, 2014
Cellulose is a polymer so widely abundant and versatile that we can find it almost everywhere in many different forms and applications. Cellulose dissolution is a key aspect of many processes; the present treatise reviews the main achievements in the dissolution area. In particular, the main solvents used and underlying mechanisms are discussed. As is described, cellulose solvents are of highly different nature giving great challenges in the understanding and analyzing the subtle balance between different interactions. Recent work has much emphasized the role of cellulose charge and the concomitant ion entropy effects, as well as hydrophobic interactions.
Dissolution Behavior of Different Celluloses
Biomacromolecules, 2011
Celluloses from different origins were dissolved stepwise in N,N-dimethylacetamide/lithium chloride (9% v/w; DMAc/LiCl) with the aim to study the time course of the dissolution process, completeness of dissolution in the dissolved fractions, possible discrimination effects, and differences between the celluloses. Cellulosic pulps from both annual plants and different wood species were analyzed. The obtained fractions were subject to gel permeation chromatography (GPC) with multiple detection to monitor the development of molecular mass distribution (MMD), molecular mass, and recovered mass. The dissolution behavior of accompanying xylans was followed by quantitative analysis of the uronic acids by fluorescence labeling -GPC. The morphological changes at the remaining fibers in the stepwise dissolution were addressed by SEM. The time needed to dissolve completely the cellulosic pulp differed from species to species, mainly between pulps from annual plants and pulps from wood. Annual plants generally needed much longer to dissolve completely. In the beginning of the dissolution, the dissolved fractions of annual plants showed a distinct discrimination effect because they were enriched in hemicellulose. By contrast, wood pulps dissolve fast and without distinct changes in the MMD of the dissolved fractions over time. Bagasse pulp is an exception to the observation for annual plants and rather resembled the behavior of wood celluloses. Prolonged dissolution times, as often practiced in cellulose GPC, do not lead to any improvements regarding the determination of molecular mass, MMD, and recovered mass of injected sample, so that the dissolution times required for reliable GPC analysis can be significantly shortened, which will be important for biorefinery analytics with high numbers of samples.
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.
Cellulose Solubility in Ionic Liquid Mixtures: Temperature, Cosolvent, and Antisolvent Effects
The journal of physical chemistry. B, 2016
Select ionic liquids (ILs) dissolve significant quantities of cellulose through disruption and solvation of inter- and intramolecular hydrogen bonds. In this study, thermodynamic solid-liquid equilibrium was measured with microcrystalline cellulose in a model IL, 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIm][DEP]) and mixtures with protic antisolvents and aprotic cosolvents between 40 and 120 °C. The solubility of cellulose in pure [EMIm][DEP] exhibits an asymptotic maximum of approximately 20 mass % above 100 °C. Solubility studies conducted on antisolvent mixtures with [EMIm][DEP] and [BMIm][Cl] indicate that protic solvents, ethanol, methanol, and water, significantly reduce the cellulose capacity of IL mixtures by 38-100% even at small antisolvent loadings (<5 mass %). Alternatively, IL-aprotic cosolvent (dimethyl sulfoxide, dimethylformamide, and 1,3-dimethyl-2-imidazolidinone) mixtures at mass ratios up to 1:1 enhance cellulose dissolution by 20-60% compared to pure...
Dissolution of cellulose in aqueous NaOH solutions
Cellulose, 1998
Dissolution of a number of cellulose samples in aqueous NaOH was investigated with respect to the influence of molecular weight, crystalline form and the degree of crystallinity of the source samples. A procedure for dissolving microcrystalline cellulose was developed and ...
Dissolution state of cellulose in aqueous systems. 1. Alkaline solvents
Cellulose, 2015
PT ssNMR allows the study of dissolved and solid fractions in a single step. Acidic solvents lead to degradation of cellulose in solution. Is possible identify cellulose degradation products in solution by PT ssNMR. C 6 carbon is preferentially protonated/deprotonated when extreme pHs are used.
Dissolution kinetics of cellulose in ionic solvents by polarized light microscopy
Cellulose
Aiming to increase the scarce information available on the kinetics of cellulose dissolution, we have applied an image-assisted technique based on the luminance evolution as cellulose dissolves to study this process under different experimental conditions. This protocol was validated via direct determination of the cellulose dissolved. In all cases datapoints were linearly fitted assuming a pseudo-zero order reaction which facilitates the comparison between datasets. To study the solvent effect we have used three ionic liquids with large basicity and found significantly different rates of dissolution, from faster to slower: [C$$_2$$ 2 C$$_1$$ 1 Im][OAc]>[C$$_1$$ 1 C$$_1$$ 1 Im][DMP]>[C$$_2$$ 2 C$$_1$$ 1 Im][DEP]. Solvatochromic parameters and viscosity of the solvent media were determined and the latter was identified as a key factor slowing the process as it reduces ionic mobility. The weight of viscosity was estimated by removing the viscosity effect with a tuned solvent med...