Cellulose Solvent Research Articles

Dew points of pure DBN and DBU and vapor–liquid equilibria of water + DBN and water + DBU systems for cellulose solvent recycling

Dew points of pure 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were measured using low pressure distillation. The distillation experiments were conducted within a 0.5–12.1kPa pressure range. The measured dew point data were in good agreement with the vapor pressure data available in the open literature. The combined measured dew point and literature vapor pressure data were modeled using an Antoine type equation.Vapor–liquid equilibrium (VLE) of water+DBN and water+DBU systems were measured using two variations of a static total pressure method. The VLE measurements were conducted within a 313–353K temperature range. The results indicate a negative deviation from Raoult’s law for both systems. Legendre polynomial and NRTL activity coefficient models were used to describe the liquid phases of the systems.

Maintenance-Free Cellulose Solvents Based on Onium Hydroxides

Here, we report maintenance-free cellulose solvents that dissolve much cellulose within a few minutes under mild conditions even in the presence of water. We have examined a series of aqueous solutions of tetraalky-phosphonium and tetraalkyl-ammonium hydroxides to clarify the effect of cation species on cellulose dissolving. Aqueous solutions of the many hydroxides examined here were found to dissolve cellulose at room temperature, and electrostatic interaction and/or steric hindrance of component ions are suggested to affect the cellulose-dissolving ability. In spite of increasing water content after dissolution of wet cellulose, the water content automatically reduced to less than 60% just by keeping the filtrated solution in the air. The solvation state of cellulose in aqueous onium hydroxide solutions is discussed with 13C NMR chemical shift of cellobiose signals in these solutions. They dissolve cellulose only when the 13C NMR signal of the carbon atom at the 12 position of cellobiose is 64.8 ppm or ...

Ioncell-F: ionic liquid-based cellulosic textile fibers as an alternative to viscose and Lyocell

Ioncell-F, a recently developed process for the production of man-made cellulosic fibers from ionic liquid solutions by dry-jet wet spinning, is presented as an alternative to the viscose and N-methylmorpholine N-oxide (NMMO)-based Lyocell processes. The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-ene acetate was identified as excellent cellulose solvent allowing for a rapid dissolution at moderate temperatures and subsequent shaping into continuous filaments. The highly oriented cellulose fibers obtained upon coagulation in cold water exhibited superior tenacity, exceeding that of commercial viscose and NMMO-based Lyocell (Tencel®) fibers. The respective staple fibers, which have been converted into two-ply yarn by ring spinning technology, presented very high tenacity. Furthermore, the Ioncell yarn showed very good behavior during the knitting and weaving processes, reflecting the quality of the produced yarn. The successfully knitted and woven garments from the Ioncell yarn demonstrate the suitability of this particular ionic liquid for the production of man-made cellulosic fibers and thus give a promising outlook for the future of the Ioncell-F process.

Preparation and Reinforcement of Dual-Porous Biocompatible Cellulose Scaffolds for Tissue Engineering.

1Biocompatible cellulose‐based aerogels composed of nanoporous struts, which embed interconnected voids of controlled micron‐size, have been prepared employing temporary templates of fused porogens, reinforcement by interpenetrating PMMA networks and supercritical carbon dioxide drying. Different combinations of cellulose solvent (Ca(SCN)2/H2O/LiCl or [EMIm][OAc]/DMSO) and anti‐solvent (EtOH), porogen type (paraffin wax or PMMA spheres) and porogen size (various fractions in the range of 100–500 μm) as well as intensity of PMMA reinforcement have been investigated to tailor the materials for cell scaffolding applications. All aerogels exhibited an open and dual porosity (micronporosity >100 μm and nanoporosity extending to the low micrometer range). Mechanical properties of the dual‐porous aerogels under compressive stress were considerably improved by introduction of interpenetrating PMMA networks. The effect of the reinforcing polymer on attachment, spreading, and proliferation of NIH 3T3 fibroblast cells, cultivated on selected dual‐porous aerogels to pre‐evaluate their biocompatibility was similarly positive.

A Simple and Efficient Approach to Cellulose/Silica Composite Aerogel with High Silica Utilization Efficiency

Cellulose aerogel is a fascinating material with high porosity, low density and biocompatibility. However, cellulose aerogel lacks sufficient thermal stability. Recombination between cellulose aerogel with silica is efficacious for enhance the cellulose aerogel’s thermal stability. This work described a simple and efficient approach to the cellulose/silica composite aerogel via a dropwise manner, using tetraethoxysilane as silicon source and NaOH solution as cellulose solvent. The result showed that the thermal stability of cellulose aerogel was enhanced by introducing silica. And by this manner, the utilization efficiency of silica was up to 95%. The composite aerogel had a low density and a high porosity, which promised the material a good heat insulation performance, and the thermal conductivity of the composite aerogel was low to 0.0161W/(m·K). Moreover, by adjusting cellulose concentration and tetraethoxysilane amount, the density, porosity and thermal conductivity of the composite aerogel could be controlled. This work contributed to improving the utilization efficiency of silica for the composite aerogel with better performances.

One-step green synthesis of non-hazardous dicarboxyl cellulose flocculant and its flocculation activity evaluation

The waste management of used flocculants is a thorny issue in the field of wastewater treatment. To natural cellulose based flocculants, utilization of hazardous cellulose solvent and simplification of synthetic procedure are the two urgent problems needing to be further improved. In this work, a series of natural dicarboxyl cellulose flocculants (DCCs) were one-step synthesized via Schiff-base route. The cellulose solvent (NaOH/Urea solution) was utilized during the synthesis process. The full-biodegradable flocculants avoid causing secondary pollution to environment. The chemical structure and solution property of the DCC products were characterized by FT-IR, 1H NMR, 13C NMR, TGA, FESEM, charge density and ζ-potential. Kaolin suspension and effluent from paper mill were selected to evaluate the flocculation activity of the DCCs. Their flocculation performance was compared with that of commercial cationic polyacrylamide and poly aluminium chloride flocculants. The positive results showed that the NaOH/Urea solvent effectively promoted the dialdehyde cellulose (DAC) conversion to DCC in the one-step synthesis reaction. The DCCs with the carboxylate content more than 1mmol/g exhibited steady flocculation performance to kaolin suspension in the broad pH range from 4 to 10. Its flocculation capacity to the effluent from paper mill also showed excellent.

On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions

The development of strategies for dissolution and regeneration of cellulose constitutes an increasingly active research field due to the direct relevance for many production processes and applications. A wide variety of suitable solvents for cellulose are already available. However, cellulose solvents are of highly different nature reflecting the great challenges in the understanding of the subtle balance between the different interactions. Here, we report on the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences for the characteristics of the regenerated material. While an aqueous tetrabutylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, a sodium hydroxide solution does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. The dramatic difference between a small inorganic cation and an amphiphilic cation indicates a critical role of hydrophobic interactions between cellulose molecules and provides support for the picture that cellulose molecules have pronounced amphiphilic properties. (C) 2015 Elsevier B.V. All rights reserved. (Less)

An Eco-friendly One-Step Synthesis of Dicarboxyl Cellulose for Potential Application in Flocculation

A simple one-step and homogeneous synthesis method of dicarboxyl cellulose for the flocculant application is developed via Schiff base route using the cellulose from Phyllostachys heterocycla. The bamboo pulp cellulose is dissolved in NaOH–urea solution and oxidized as dialdehyde cellulose by NaIO4, which is continuously reacted with the residual urea and NaOH in the original reaction system to synthesize dicarboxyl cellulose. This one-step method greatly reduces the complexity and heterogeneity of the traditional two-step synthesis procedure, and avoids greatly the environmental pollution caused by the cellulose solvent. The dicarboxyl cellulose is characterized by Fourier transform infrared spectroscopy and X-ray diffraction spectroscopy, which exhibits an excellent coagulation–flocculation capability to kaolin suspension with a turbidity removal of 99.5%.

Facile cellulose dissolution without heating in [C4mim][CH3COO]/DMF solvent

Novel cellulose solvents, [C4mim][CH3COO]/DMF, were designed by adding an aprotic polar solvent N,N-dimethylformamide (DMF) in 1-butyl-3-methylimidazolium acetate ([C4mim][CH3COO]). The solubilities of cellulose in [C4mim][CH3COO]/DMF solvents were determined at 25°C. The effects of molar ratio of DMF to [C4mim][CH3COO] on cellulose solubility and the possible dissolution mechanism of cellulose in [C4mim][CH3COO]/DMF solvent have been studied. Moreover, the regenerated cellulose from [C4mim][CH3COO]/DMF solvent were characterized by scanning electron micrograph (SEM) Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), and the degree of polymerization (DP) of regenerated cellulose was determined. The findings reveal that the facile dissolution of cellulose in such solvents is mainly attributed to the increased “free” [CH3COO]− anions and [C4mim]+ cations which result from the dissociation of [C4mim][CH3COO] by DMF. Moreover, the macromolecular chain of the cellulose is hardly broken during the dissolution and precipitation processes.

Dissolution and Regeneration in Films of Natural Luffa in 1-butyl-3-methylimidazolium Chloride

Regenerated cellulose film was successfully prepared from natural luffa, a new cellulose raw material. A pretreatment of natural luffa was carried out by an alkali and hydrogen peroxide mixed solution. The dissolution process of the pretreated luffa in 1-butyl-3-methylimidazolium chloride ([BMIM]C1) was observed by polarized optical microscope. The structures and properties of the luffa films were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), and porosity measurements. The results showed that the luffa fibers were transformed to fibrils after the pretreatment. [BMIM]Cl was a good non-derivatizing solvent for the luffa cellulose. The solution conditions were 80°C and 10 h for a 15% solution. After being regenerated, as films, from the luffa/[BMIM]Cl solution, the crystalline structure of the luffa film was transformed completely from cellulose I to cellulose II. The film showed the strong characteristic functional groups of cellulose in FTIR results. The surface of the film was smooth with a compact structure. The porosity of the film was 66.2% and the average pore size was 17.8 nm. It was thermally stabile up to 280°C.

Dissolution of cellulose with a novel solvent and formation of regenerated cellulose fiber

A new cellulose solution was prepared by a new cellulose solvent, tetrabutylammonium acetate (TBAA)/dimethyl sulfoxide (DMSO). A new kind of regenerated cellulose fibers was spun successfully for the first time from the cellulose solution by a wet spinning system. The dissolving process of cellulose in TBAA/DMSO was observed by confocal laser scanning microscope. The rheological of the cellulose dopes was determined by rotated rheometer, and the results showed that the cellulose/TBAA/DMSO solution was a typical shear-thinning fluid. In addition, the morphology, chemical structure and mechanical properties of the prepared cellulose fibers were characterized by scanning electron microscope (SEM), 13C CP/MAS NMR, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and electronic tensile tester, respectively. The SEM patterns showed that the regenerated fibers possessed a smooth surface and circular cross section. The results from 13C NMR and XRD patterns indicated that the novel fibers mainly exhibited amorphous cellulose. Meanwhile, the novel fibers have good mechanical properties.

From cellulose fibrils to single chains: understanding cellulose dissolution in ionic liquids.

Cellulose is the most abundant and renewable organic compound on Earth, it is however not soluble in common organic solvents and aqueous solutions. Cellulose dissolution is a key aspect to promote its value-added applications. Ionic liquids (ILs) have been shown to solubilize cellulose under relatively mild conditions. The easy processability of cellulose with ILs and their environmental-friendly nature prompted research in various fields such as biomass pretreatment and conversion, cellulose fiber and composite production, and chemical conversion of cellulose in ILs. Progress has been made on understanding the mechanism of cellulose dissolution in ILs, including the structural characteristics of ILs that are cellulose solvents, however many details remain unknown. In light of rapid development and importance of cellulose dissolution in the field of IL-based cellulose and biomass processing, it is necessary to provide an overview of current understanding of cellulose dissolution in ILs and outline possible future research trends. Recent literature studies suggest that synergistic effects between the anions and the cations of ILs need to be revealed, which requires refining the structure of cellulose elementary fibrils, simulation of more realistic cellulose fibrils and detailed studies on the solution structure of cellulose in ILs. After analyzing literature studies, three interacting modules are identified, which are crucial to understand the process of cellulose dissolution in ILs: (1) the structure of elementary fibrils; (2) solvation of cellulose in ILs; and (3) solution structure of cellulose solubilized in ILs. A coherent analysis of these modules will aid in better design of more efficient ILs and processes.

Probing cellulose amphiphilicity

Cellulose dissolution and regeneration is an increasingly active research field due to the direct relevance for numerous production processes and applications. The problem is not trivial since cellulose solvents are of remarkably different nature and thus the understanding of the subtle balance between the different interactions involved becomes difficult but crucial. There is a current discussion in literature on the balance between hydrogen bonding and hydrophobic interactions in controlling the solution behavior of cellulose. This treatise attempts to review recent work highlighting the marked amphiphilic characteristics of cellulose and role of hydrophobic interactions in dissolution and regeneration. Additionally, a few examples of our own research are discussed focusing on the role of different additives in cellulose solubility. The data does support the amphiphilic behavior of cellulose, which clearly should not be neglected when developing new solvents and strategies for cellulose dissolution and regeneration.

Ionic liquids: not always innocent solvents for cellulose

A comprehensive investigation into the limitations, reactivity and chemical decomposition mechanisms of ionic liquid–carbohydrate mixtures.

Dissolution Behavior of Cellulose in IL + DMSO Solvent: Effect of Alkyl Length in Imidazolium Cation on Cellulose Dissolution

Four cellulose solvents including [C2mim][CH3COO] + DMSO, [C4mim][CH3COO] + DMSO, [C6mim][CH3COO] + DMSO, and [C8mim][CH3COO] + DMSO were prepared by adding dimethyl sulfoxide DMSO in 1-ethyl-3-methylimidazolium acetate [C2mim][CH3COO], 1-butyl-3-methylimidazolium acetate [C4mim][CH3COO], 1-hexyl-3-methylimidazolium acetate [C6mim][CH3COO], and 1-octyl-3-methylimidazolium acetate [C8mim][CH3COO], respectively. The solubilities of cellulose in these solvents were determined at 25°C. The effect of the alkyl chain length in imidazolium cation on cellulose solubility was investigated. With increasing alkyl chain length in imidazolium cation, the solubility of cellulose increases, but further increase in alkyl chain length results in decreases in cellulose.

Effect of silver on cellulose fibre colour

Silver nanoparticles were embedded into cellulose fibres using N‐methylmorpholine N‐oxide as a direct cellulose solvent that was also the system from which silver nanoparticles were generated. The process of generation of silver nanoparticles in the N‐methylmorpholine N‐oxide enables the properties of cellulose fibres to be modified without any additional reducing agent, which makes this process more environmentally friendly. By varying the reaction time of the precursor with the N‐methylmorpholine N‐oxide, a range of nanoparticle sizes was obtained. The fibres contain the same concentration of silver, but, on account of the varying morphology of the nanoparticles, they show a range of colour shades. The primary aim of this study was to show how temperature and reaction time affect the basic parameters of the obtained nanoparticles (shape, size, and distribution in the polymer matrix of fibres), which consequently influences the colour of the modified cellulose fibres. Nanoparticles were characterised by dynamic light scattering and transmission electron microscopy methods, while the fibre hues were estimated by colorimetric analysis. Trichromatic coordinates of colour x, y were delineated, and the colour was identified by positioning the x and y values in the CIE chromaticity diagram. It is noted that many parameters, especially the diameter and shape of the silver nanoparticles, influence the colour of the fibre obtained.

Raman microscopic analysis of wood after treatment with the ionic liquid, 1-ethyl-3-methylimidazolium chloride

Abstract Japanese cedar (Cryptomeria japonica) was treated with the ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which is a solvent for cellulose, and the changes in the chemical components and their distribution in wood cell walls have been investigated by Raman microscopy. Raman spectra, recorded from various areas of the cell walls, showed that lignin in the compound middle lamellae (CML) and cell corners (CC) was resistant to the reaction with [C2mim][Cl], but its molecular structure changed partially. The reactivity of cellulose and hemicelluloses with [C2mim][Cl] was higher than that of lignin in the cell wall, and the cell wall structure was maintained even in an advanced state of the reactions. The effects of [C2mim]-[Cl] on cellulose and hemicelluloses in the cell wall were homogeneous, whereas that of lignin was inhomogeneous.

Dissolution of cellulose in 1-allyl-3-methylimizodalium carboxylates at room temperature: A structure–property relationship study

The development of highly efficient cellulose solvents is imperative to the effective utilization of cellulose. In this work, ionic liquids (ILs) with the same 1-allyl-3-methylimidazolium cation ([Amim]+) but different carboxylate anions, such as formate ([HCOO]−), acetate ([CH3COO]−), propionate ([CH3CH2COO]−), butyrate ([CH3CH2CH2COO]−), glycollate ([HOCH2COO]−), lactate ([CH3CHOHCOO]−) and benzoate ([C6H5COO]−) were synthesized, and their thermal properties and viscosities were determined. Then these ILs were used to investigate the effect of anion structure on solubility of cellulose in the ILs. It was shown that the viscosity and cellulose solubility depended strongly on the anion structure of the ILs. For example, at 30°C solubility of cellulose in [Amim][CH3CH2COO] was as high as 19.0%, whereas cellulose was not soluble in [Amim][HOCH2COO], [Amim][CH3CHOHCOO] and [Amim][C6H5COO]. In addition, solvatochromic UV/vis probe and 13C NMR measurements were performed to demonstrate dissolution mechanism of cellulose in the ILs. The results suggested that although cations of the ILs have un-negligible contribution to the highly efficient dissolution of cellulose, hydrogen bonding interactions of anions of the ILs with cellulose is predominant.

Fabrication of cellulose-based scaffold with microarchitecture using a leaching technique for biomedical applications

Providing a conclusive microenvironment for cell growth, proliferation and differentiation is a major developmental strategy in the tissue engineering and regenerative medicine. This is usually achieved in the laboratory by culturing cells in three-dimensional polymer-based scaffolding materials. Here, we describe the fabrication of a cellulose scaffold for tissue engineering purposes from cellulose fiber using a salt leaching method. The 1-n-allyl-3-methylimidazolium chloride (AmimCl) IL was used as a solvent for cellulose. The leaching methodology used in this study offers the unique advantage of providing effective control of scaffold porosity by simply varying cellulose concentration. Morphologic testing of the scaffolds produced revealed pore sizes of 200–500 μm. In addition, the scaffolds had high water adsorption rates and slow degradation rates. To further investigate the suitability of these scaffolds for tissue engineering applications, biocompatibility was checked using an MTT assay and confirmed by Live/Dead® viability testing. In addition, scanning electron microscopy and DAPI studies and in vivo experiment demonstrated the ability of cells to attach to scaffold surfaces, and a biocompatibility of matrices with cells, respectively. The authors describe the environmentally friendly fabrication of a novel cellulose-based tissue engineering scaffold.

Laser Induced Natural Fiber Welding of Cellulosic Substrates

As excellent solvents for cellulose and silk, certain ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium acetate (EMIAc),1,2 can be used for biopolymer modification and manipulation. Full dissolution and regeneration using IL solvents often results in biomaterials with inferior properties compared to the native material. When natural substrates are only partially dissolved and regenerated through a process we call Natural Fiber Welding (NFW), much of the native biomaterial structure can be maintained while still allowing for significant material modification. NFW enables the structural modification of the surface and incorporation of functional materials through the binding capability of the portion of dissolved biopolymer3-5. In the present work we have employed a laser as the heat source to initiate partial dissolution of a cellulose substrate causing NFW in a spatially-specific manner. By using a non-solvent for cellulose (e.g., water) with the ionic liquid as a means of inhibiting the dissolution process, heat becomes the controlling factor necessary to obtain significant biopolymer dissolution and mobilization. A CO2 laser was used to raster a specific pattern onto a cellulosic paper substrate coated with IL solution. Raster power, concentration of the ionic liquid and the number of laser passes affect the amount of heat absorbed into the biopolymer and the level of NFW. Through tensile testing, confocal microscopy, ATR-IR, and SEM imaging, the resulting modification of the biopolymers was characterized. References Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am Chem Soc, 2002, 124, 4974.Phillips, D. M.; Drummy, L. F.; Conrady, D. G.; Fox, D. M.; Naik, R. R.; Stone, M. O.; Trulove, P. C.; De Long, H. C.; Mantz, R. A. J Am Chem Soc., 2004, 126, 14350.Haverhals, L. M.; Reichert, W. M.; De Long, H. C.; Trulove, P. C. Cellulose, 2010, 2985, 425.Haverhals, L. M.; Sulpizio, H. M.; Fayos, Z. A.; Trulove, M. A.; Reichert, W. M.; Foley, M. P.; De Long, H. C.; Trulove, P. C.Cellulose, 2012, 19, 13.Haverhals, L. M.; Nevin, L. M.; Foley, M. P.; Brown, E. K.; De Long, H. C.; Trulove, P. C. Chem.Commun., 2012, 48, 6417.