Surface tension of concentrated cellulose solutions in 1-ethyl-3-methylimidazolium acetate

Four sources of cellulose with different molecular weights were dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate at 100 °C over a 10 h period. The solution densities were determined and these results were subsequently utilised to access the influence of dissolved cellulose on surface tension properties of cellulose/ionic liquid solutions. Surface tension measurements revealed increasing molecular weight and concentration reduced surface tension while temperature increases showed the opposite effect. These results are consistent with that of repulsive polymer-wall interactions near the interface in good solvent conditions. The semi-flexible nature of this carbohydrate in solution can help explain deviations of these results when compared to ideal flexible chains.     

Light scattering in diluted solutions of cellulose and hydroxypropylcellulose in 1-ethyl-3-methylimidazolium acetate

Diluted solutions of cellulose and hydroxypropylcellulose in 1-ethyl-3-methylimidazolium acetate were studied by the method of static light scattering. Mean molecular masses and the size of the particles of the studied polymers in solution, as well as the values of the second virial coefficient are reported.     

Partial cellulose acetylation in 1-ethyl-3-methylimidazolium acetate induced by dichloromethane

Cellulose acetate (CA) is one on the most important cellulose derivatives. The use of ionic liquids in cellulose processing was recently discovered to not exclusively act as a solvent but also as a reagent. Recent studies showed that bulky chlorides as well as acetyl chloride mixed with ionic liquids can facilitate cellulose acetylation. This work focused on a simple chloro-organic cosolvent, dichloromethane (DCM), and showed the ability of this relatively small molecule, mixed with the ionic liquid, to facilitate homogenous acetylation by displacement of the acetate ion of the ionic liquid with a chloride ion. Maximal acetylation achieved by this method was a degree of substitution (DS) of 1.9, were only a small fraction of DCM was utilized for acetylation, well below even that expected for equimolar reaction. The degree of substitution was controlled by the dichloromethane content, thus controlling its solubility in water. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2458–2462     

The undesirable acetylation of cellulose by the acetate ion of 1-ethyl-3-methylimidazolium acetate

Abstract  

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) is considered to be an inert solvent of cellulose and lignocellulosic biomass. Acetylation (1.7% mol, or DS 0.017) of cellulose after dissolution in technical grade [C2mim]OAc (150 °C for 20 min), is demonstrated by compositional analysis, FTIR analysis and ¹³C NMR spectroscopy (in [C2mim]OAc with ¹³C enriched acetate). This acetylation, in the absence of added acylating agents, has not been reported before and may limit [C2mim]OAc utility in industrial scale biomass processing, even at this low extent. For example, cellulose acetylation may contribute to IL loss in processes where the IL is recovered and reused and inhibit enzyme saccharification of cellulose in lignocellulosic biofuel production processes based on saccharification and fermentation.     

Interactions of collagen and cellulose in their blends with 1-ethyl-3-methylimidazolium acetate as solvent

Collagen/cellulose blended solutions with collagen/cellulose mass ratio (Col/Cel) of 0, 1/40, 1/20, 1/10 and 1/5 were prepared using [Emim]Ac as solvent. The interactions between the two polymers before and after regeneration were investigated. In steady shear flow, all of the experimental viscosity values were greater than those of the estimated values calculated from the log-additivity rule for each sample, suggesting interactions between the two polymers in solutions. All solutions exhibited shear thinning behavior and the flow curves could be described by Cross model. Zero shear viscosity (η ₀) versus Col/Cel was examined and a linear increase (from 8.73 to 16.39 Pa·s) can be observed for η ₀ as Col/Cel ≤ 1/10, while there was only a slight increase (from 16.39 to 18.42 Pa·s) in η ₀ as Col/Cel increased to 1/5. Dynamic rheology results suggested the existence of aggregates in solution with Col/Cel = 1/10. Furthermore, the activation energy of solution was 84.5 kJ mol^?1 as Col/Cel = 1/10, higher than that of cellulose solution (44.2 kJ mol^?1). Regenerated films were prepared and characterized to trace back the interactions between the two polymers in [Emim]Ac. Fourier transform infrared spectroscopy indicated the hydrogen-bond interaction between collagen and cellulose in films. The denaturation temperature of collagen in films with Col/Cel ≤ 1/10 could be improved, but it was decreased with the increase of collagen content, and finally was reduced to be close to that of collagen as Col/Cel = 1/5. The features of dynamic mechanical analysis for films were indicative of the lack of homogeneity between collagen and cellulose as Col/Cel = 1/5. Atomic force microscopy images further confirmed the phase-separation when Col/Cel = 1/5.     

Linear viscoelasticity of poly(acrylonitrile-co-itaconic acid)/1-butyl-3-methylimidazolium chloride extended from dilute to concentrated solutions

The solution rheology of poly(acrylonitrile-co-itaconic acid) (poly(AN-co-IA)) in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) spanning dilute, semidilute unentangled and entangled regimes were investigated. The exponents in the specific viscosity η_sp ～ overlap parameter c[η] power law were 1, 2 and 4.7 for dilute, semidilute unentangled and entangled regimes, respectively, which were found to be consistent with the scaling prediction for neutral linear polymers in θ-solvent. For dilute solutions (lower than 0.9 wt.%), the linear viscoelastic responses were observed to be in good agreement with the Zimm model (Flory exponent ν = 0.5). While for semidilute unentangled solutions (between 0.9 and 8 wt.%), results obtained had been found to be consistent with Rouse model. Considering Flory exponent ν = 0.5 and the concentration dependences of the specific viscosity and relaxation time, it had been evaluated that poly(AN-co-IA) in [BMIM]Cl behaves as a neutral polymer in θ-solvent. It had also been suggested that according to the unusual deviation of Cox-Merz rule, poly(AN-co-IA)/[BMIM]Cl solutions are typical neutral polymeric liquids for the concentrated solutions but have shown a more complicated behavior at high deformation rates.     

The effect of subcritical carbon dioxide on the dissolution of cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) readily dissolves high concentrations of cellulose. However, the high viscosity of [emim][OAc] (162 cP at 20 °C) could limit its use as a solvent for cellulose. Dissolved CO₂ has been shown to decrease the viscosity of ILs. In this study, a 50 psi CO₂ environment was applied for the dissolution of cellulose in [emim][OAc] to determine if the cellulose dissolution could be enhanced. Dissolution profiles of 4 wt% cellulose dissolved in [emim][OAc] were obtained over a 24 h period. A 75% increase in the amount of dissolved cellulose was observed with the application of a 50 psi CO₂ environment.     

Enzymatic saccharification of cellulose in aqueous-ionic liquid 1-ethyl-3-methylimidazolium dimethylphosphate-DMSO media

Ionic liquid (IL) 1-ethyl-3-methylimidazolium dimethylphosphate ([Emim]DMP) was chosen as an environment-friendly solvent to enzymatically hydrolyze cellulose in situ. Under optimal reaction condition, 80.2 % of cellulose (10 mg mL⁻¹) were converted to glucose in aqueous-IL-DMSO (φ _r = 74: 25: 1) media at 55°C in 18 h. Finally, fermentability of the recovered hydrolyzates was evaluated using Saccharomyces cerevisiae which is able to ferment hydrolyzates efficiently, the ethanol production was 0.44 g g⁻¹ of glucose within 24 h of the process. Such information is vital for the saccharification of more complex cellulose materials and for the fermentation of hydrolyzates into biofuel.     

Regenerated cellulose film with enhanced tensile strength prepared with ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc)

In this study, environmentally friendly regenerated cellulose films with enhanced tensile strength were successfully prepared by incorporation of plasticizer agents using 1-ethyl-3-methylimidazolium acetate as solvent. The results of morphology from scanning electron microscopy and atomic force microscopy showed that cellulose films possessed homogeneously, and exhibited smooth structure. ¹³C CP/MAS NMR spectra showed that the regenerated cellulose films were transferred from cellulose I to cellulose II. Moreover, the incorporation of plasticizer agents, especially in the presence of glycerol, significantly improved the tensile strength of cellulose film (143 MPa) as compared to the controlled sample. The notable properties of the regenerated cellulose films are promising for applications in transparent packaging.     

Thermophysical properties of 1-methyl-3-methylimidazolium dimethylphosphate and 1-ethyl-3-methylimidazolium diethylphosphate

The density and surface tension of 1-methyl-3-methylimidazolium dimethylphosphate, [C₁mim](CH₃O)₂PO₂ and 1-ethyl-3-methylimidazolium diethylphosphate, [C₂mim](CH₃CH₂O)₂PO₂ ionic liquids have been measured over the temperature range from (283.15 to 338.15) K. The coefficients of thermal expansion were calculated from the experimental density results using an empirical correlation for T = (283.15 to 338.15) K. Molecular volume and standard entropies of these ILs were calculated from the experimental density values. The surface properties of ILs were investigated. The critical temperature and enthalpy of vapourization were also discussed.     

Thermophysical properties of aqueous solutions of the 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid

Thermophysical behavior of the binary system [water + 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid (IL)] was thoroughly characterized through systematic measurements of (vapor + liquid) equilibria (water activity a_w), mixing enthalpy, density, viscosity, and refractive index. The measurements were performed in the entire composition range and/or specifically in the highly dilute IL region, at T = 298.15 K or as a function of temperature in the range from (288.15 to 318.15) K. Effective experimental methods minimizing IL sample consumption, using flow arrangements, instrument couplings and high degree of automation were preferably employed. In particular, the a_w determination based on the chilled-mirror dew point technique and implemented by an AquaLab 4TE instrument was identified as a generally superior approach to study VLE of (water + IL) systems. Excess thermodynamic properties (Gibbs free energy, enthalpy, heat capacity, and volume) and property deviations from the linear mixing rule (viscosity, refractive index) were evaluated, Padé approximants being used to correlate adequately their complex composition dependences. The extensive a_w data were processed by a two-step procedure fitting first the temperature dependence at each isopleth and subsequently the composition dependence at each isotherm. Good estimates could be thus obtained for derivative thermal properties (enthalpy, heat capacity). Alternatively, the water activity and excess enthalpy data were correlated simultaneously by a NRTL-type model, providing their compact, thermodynamically consistent and adequate representation. Despite small absolute values of excess Gibbs free energy (G^E), the system is revealed to be highly nonideal, the small G^E resulting from close compensation of its large enthalpy and entropy contributions. Large endothermic effects and an enhanced increase of entropy upon mixing found for this system indicate relative weakness of interactions between unlike molecules and a massive structure breakage in the solution. Positive values of excess volume and negative values of viscosity and refractive index deviations found in the major part of the composition range corroborate this general energetic and structural pattern, although the situation appears to be more complicated in the highly dilute IL region, where these properties congruently exhibit a sign inversion.     

Impact of 1-butyl-3-methylimidazolium chloride on the electrospinning of cellulose acetate nanofibers

Additives like ionic liquids (ILs) have proven to be excellent materials useful in improving the electrospinnability and conductivity of both synthetic and biopolymers. The aim of this study is to investigate the effect of 1-buthyl-3-methylimidazolium chloride [BMIM]Cl on the electrospinnability of cellulose acetate (CA). The results showed that [BMIM]Cl has the greater effect on viscosity and conductivity of the spinning solution while the morphology of the nanofibers significantly improved as the concentration of the IL increases from 0% to 12% (v/v) of [BMIM]Cl. To understand the interaction between CA and [BMIM]Cl, Fourier-transform infrared spectroscopy (FTIR) has been used. Observations by scanning electron microscopy (SEM) suggested that [BMIM]Cl significantly altered the morphology of the CA nanofibers and 12% (v/v) of [BMIM]Cl would be an ideal concentration producing uniform fibers with a mean diameter of 180nm. In addition, the membranes showed a significant increase in conductivity (from 0 to 2.21 × 10^?7S/cm) as the concentration of ionic liquid increases up to 12% (v/v) that indicates a successful loading of IL inside the nanofibers.     

Carbon dioxide solubility in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate

In this work, we present new solubility results for carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate for temperatures ranging from (303.2 to 343.2) K and pressures up to 5.9 MPa using a thermogravimetric microbalance. Carbon dioxide solubilities were determined from absorption saturation (equilibrium) results at each fixed temperature and pressure. The buoyancy effect was accounted for in the evaluation of the carbon dioxide solubility. A highly accurate equation of state and a group contribution predictive method for carbon dioxide and for ionic liquids, respectively, were employed to determine the effect of buoyancy on carbon dioxide solubility. The solubility measurements are presented as a function of temperature and pressure. An extended Henry’s law equation was used to correlate the present experimental solubility values and the result was satisfactory.     

Influence of temperature on sage seed gum (Salvia macrosiphon) rheology in dilute and concentrated regimes

Herein, the influence of temperature (10°C, 30°C, 50°C, 70°C, and 90°C) on the dynamic (using amplitude sweep, frequency sweep, and temperature sweep tests), steady-shear, thixotropy (using hysteresis loop, single shear decay, and in-shear structural recovery tests), yield stress (static and dynamic yield stresses), and dilute solution (intrinsic viscosity ([η]), voluminosity (v_s), shape factor (v), Berry number (C[η]), and chain flexibility) properties of sage seed gum (SSG) have been studied. In this way, the effect of type of thermal procedure (iso-thermal and non-isothermal), temperature program (temperature gradient and temperature profile sweeps), and the rate of thermal program (1, 5, and 10°C/min) on the structural changes during heating and cooling stages were also investigated. Furthermore, the time–temperature superposition and Cox–Merz rules were tested on dynamic and steady shear rheological data.     

Chemical potentials in aqueous solutions of some ionic liquids with the 1-ethyl-3-methylimidazolium cation

We determined the vapor pressures of aqueous solutions of 1-ethyl-3-methylimidazolium ([C 2mim])-based ionic liquids (IL) with counteranions, tetrafluoroborate (BF 4 (-)), trifluoromethanesulfonate (OTF (-)), and iodide (I (-)). Because in literature the evidence is accumulating and pointing to the fact that ionic liquid ions do not dissociate in aqueous media for the most of the concentration range, we analyzed the vapor pressure data on the basis of binary mixture, and the excess chemical potentials of each component were calculated. From these, the intermolecular interactions in terms of excess chemical potential and hence the concentration fluctuations were evaluated. Though any further discussion into the mixing schemes of the mixture awaits the excess partial molar enthalpy and hence the excess partial molar entropy data, the net interaction in terms of excess chemical potential indicates that the affinity of each IL is ranked in the descending order [C 2mim]I > [C 2mim]OTF > [C 2mim]BF 4. This is consistent with our earlier findings that [C 2mim] (+) is modestly amphiphilic with almost equal hydrophobicity and hydrophilicity, I (-) is a hydrophile, and OTF (-) is amphiphilic, and BF 4 (-) is believed to be strongly hydrophobic.     

Ionic liquid 1-ethyl-3-methylimidazolium acetate: an attractive solvent for native chemical ligation of peptides

The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C₂mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C₂mim][OAc]. In addition to improving the solubility of the peptides in [C₂mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced.     

Thiophene separation from aliphatic hydrocarbons using the 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid

The ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate has been tested as solvent for the separation of thiophene from aliphatic hydrocarbons. Liquid–liquid equilibrium data have been determined for ternary systems containing the ionic liquid, thiophene and C₆, C₇, C₁₂ or C₁₆ alkanes at T = 298.15 K. The performance of the ionic liquid as solvent in such systems has been evaluated. The experimental data were correlated using the NRTL and UNIQUAC equations, and the binary interaction parameters have been reported. The phase diagrams for the ternary mixtures including both the experimental and calculated tie-lines have been presented.     

Thermodynamic investigations of 1-ethyl-3-methylimidazolium tetrafluoroborate and cycloalkanone mixtures

The densities, ρ, speeds of sound, u, and heat capacities, (C _P)_mix, for binary 1-ethyl-3-methylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures within temperature range (293.15–308.15 K) and excess molar enthalpies, H ^E, at 298.15 K have been measured over the entire composition range. The excess molar volumes, V ^E, excess isentropic compressibilities, \( \kappa_{\text{S}}^{\text{E}}, \) and excess heat capacities, \( C_{\text{P}}^{\text{E}}, \) have been computed from the experimental results. The V ^E, \( \kappa_{\text{S}}^{\text{E}} \) , H ^E, and \( C_{\text{P}}^{\text{E}} \) values have been calculated and compared with calculated values from Graph theory. It has been observed that V ^E, \( \kappa_{\text{S}}^{\text{E}} \) , H ^E, and \( C_{\text{P}}^{\text{E}} \) values were predicted by Graph theory compare well with their experimental values. The V ^E, \( \kappa_{\text{S}}^{\text{E}}, \) and H ^E thermodynamic properties have also been analyzed in terms of Prigogine–Flory–Patterson theory.     

Cation-anion interactions in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-based ionic liquid electrolytes

An important step in developing ionic-liquid-based electrolytes for lithium rechargeable batteries is obtaining a molecular-level understanding of the ionic interactions that occur in these systems. In this study, 1-ethyl-3-methylimidazolium trifluoromethansulfonate ([C2mim]CF3SO3) is complexed with LiCF3SO3, and the local structures of the CF3SO3- and [C2mim]+ ions are investigated with infrared and Raman spectroscopy. The isolation and subsequent refinement of a Li[C2mim](CF3SO3)2 crystal provides further insight into the structure of the [C2mim]CF3SO3-LiCF3SO3 solutions. Minor changes are observed in the infrared and Raman spectra of dilute [C2mim]CF3SO3-LiCF3SO3 solutions compared to pure [C2mim]CF3SO3. However, a suspension of very small Li[C2mim](CF3SO3)2 crystallites forms at a solution composition of [C2mim]CF3SO3:LiCF3SO3 = 10:1 (mole ratio), placing an upper limit on the solubility of LiCF3SO3. Essentially no changes are observed in the vibrational modes of the [C2mim]+ cations over the entire range of LiCF3SO3 compositions studied, suggesting that the addition of these compounds does not significantly perturb the local structure of the [C2mim]+ cations. The salt used in this study has a common anion with the ionic liquid; thus, the ion cloud surrounding the [C2mim]+ ions, which must be primarily composed of CF3SO3- anions, is not significantly altered with the addition of LiCF3SO3.