Cellulose in New Metal-Complexing Solvents. 2. Semidilute Behavior in Cd-tren

Direct Conversion of Mono- and Polysaccharides into 5-Hydroxymethylfurfural Using Ionic-Liquid Mixtures

Platform chemicals are usually derived from petrochemical feedstocks. A sustainable alternative commences with lignocellulosic biomass, a renewable feedstock, but one that is highly challenging to process. Ionic liquids (ILs) are able to solubilize biomass and, in the presence of catalysts, convert the biomass into useful platform chemicals. Herein, we demonstrate that mixtures of ILs are powerful systems for the selective catalytic transformation of cellulose into 5-hydroxymethylfurfural (HMF). Combining ILs with continuous HMF extraction into methyl-isobutyl ketone or 1,2-dimethoxyethane, which form a biphase with the IL mixture, allows the online separation of HMF in high yield. This one-step process is operated under relatively mild conditions and represents a significant step forward towards sustainable HMF production.

Cellulose/polycaprolactone blends regenerated from ionic liquid 1-butyl-3-methylimidazolium chloride

Ionic liquid solvent, 1-butyl-3-methylimidazolium chloride (BMIM[Cl]) was used to prepare cellulose/polycaprolactone (PCL) blend films. This solvent was recycled with high yield and purity after blend precipitation. The inter- and intra-molecular hydrogen bonding interactions in these blends were investigated by Fourier transform infrared (FTIR) spectroscopy and it was found that a new peak in the carbonyl region, assigned to hydrogen bonding between carbonyl groups of PCL and hydroxyl groups of cellulose in blends with PCL composition less than 40 wt%. Differential scanning calorimetry (DSC) results implied a partial miscibility of the two components by melting point depression. Moreover, the tensile properties of the blends can be adjusted by incorporating various amounts of PCL into cellulose. The blends show significant enhancement of thermal stability compared to the regenerated cellulose when the content of PCL is higher than 40 wt%. This work demonstrates an effective approach for the processing biodegradable blends from natural and synthetic polymers.

A THEORETICAL INVESTIGATION OF THE INTERACTIONS BETWEEN CELLULOSE AND 1-BUTYL-3-METHYLIMIDAZOLIUM CHLORIDE

To better understand the interactions between cellulose and imidazolium-based ionic liquids (ILs), quantum chemistry calculations have been performed on the systems composed of one cellulose unit with the anion, cation, and the ion pair of 1-butyl-3-methylimidazolium chloride ( [bmim]Cl ) by the density functional method. The relevant geometries, energies, electronic properties and IR characteristics have been systematically discussed. It is found that H-bond interaction is essential for the systems under consideration. The hydroxyls in cellulose bind to chloride anions strongly through H -bonds, which could be predominant to cellulose dissolution in ILs. Chloride anion prefers to occur between two adjacent hydroxyls in cellulose to form bridging OH⋯Cl⋯HO hydrogen bonds. In contrast, weak hydrogen bonds exist between the hydrogen atoms on the imidazolium cation and hydroxyl oxygen atoms of cellulose, which are too much weaker than the hydrogen bonds between the cellulose hydroxyls and chloride anions to be detected by the experiments. The phenomena of cellulose dissolution in ILs should be a result of the joint interactions of chloride anions and [bmim]+ cations with hydroxyls in cellulose.

Viscoelastic Behavior of Cellulose Acetate in a Mixed Solvent System

The effect of increasing water composition on the rheological and microstructural behavior of a ternary cellulose acetate (CA)/N,N-dimethylacetamide (DMA)/water system is examined. Addition of water to the CA/DMA system results in enhanced steady shear viscosity and dynamic viscoelastic properties and ultimately to phase-separated gel formation. The changes in dynamic rheological behavior of the system during gelation correlate well with the combined solubility parameter (delta) and, in particular, the Hansen hydrogen-bonding solubility parameter index (delta(h)) of the solvent system, suggesting hydrogen-bonding interactions may be the major route initiating the sol-gel process. For all gels studied, the elastic modulus and the critical stress to yield shifts to higher values with increasing CA concentration and/or water content. In addition, the elastic modulus exhibits a power-law behavior with water content, with the same power-law exponent observed for gels containing different CA concentrations. Addition of water leads to formation of a denser gel network, as evidenced from direct visualization of the gel microstructure through confocal microscopy.

Characterization of Aggregate Structure in Mercerized Cellulose/LiCl·DMAc Solution Using Light Scattering and Rheological Measurements

The structure of a semidilute solution of mercerized cellulose (CC1m) in 8% (w/w) LiCl.DMAc, which contained some aggregates, was investigated using static and dynamic light scattering measurements. The static scattering function of the polymer solution containing a small amount of aggregates can be separated into fast- and slow-mode components by combining static and dynamic light scattering measurements. The osmotic modulus was identical for the fast-mode component of the CC1m solutions and the native cellulose (CC1) solutions, in which cellulose is dispersed molecularly. This indicates that the molecularly dispersed component of the CC1m solutions has an identical conformation with the cellulose molecules in the CC1 solutions. The correlation length was also identical for the fast-mode components of CC1m solutions and the CC1 solutions, indicating that these solutions have the same mesh size of the polymer entanglement. These observations for the fast-mode components are consistent with the concentration dependence of the zero shear rate viscosity and the plateau modulus estimated in the rheological measurements. The slow-mode component, on the other hand, gave information on the aggregate structure in the CC1m solution. The radius of gyration of the aggregate structure estimated from the slow-mode component was about 70 nm, which is independent of the concentration of the solution. The plots for particle scattering factor of the slow-mode component lay between the theoretical curve of a sphere and a Gaussian chain, implying that the structure of the aggregate in the CC1m solution is like a multiarm polymer. A characteristic time of the slow-mode component calculated with the translational diffusion coefficient and the radius of gyration were almost identical with the relaxation time of the long-time relaxation observed in the rheological measurements. This indicates that the long-time relaxation of CC1m solutions originates in the translational diffusion of the aggregate structure in the solution.

SEC−MALS−QELS Study on the Molecular Conformation of Cellulose in LiCl/Amide Solutions

The SEC-MALS-QELS (size-exclusion chromatography equipped with multiangle light scattering and quasi-elastic light scattering detectors) method using lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) and LiCl/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) as mobile phases was applied to cellulose and cellulose tricarbanilate (CTC) samples with various average degree of polymerization (DP) values. Molecular conformations of cellulose and CTC in the solvents were then discussed and compared on the basis of the relationships between the radii of gyration (R(g,z) or S(2)(z)(1/2)), the hydrodynamic radii (R(h,z)), and weight-average DP (DP(w)) or the contour lengths (L(w)). The Benoit-Doty theory for wormlike polymer chains was applied to the R(g) vs L(w) data obtained, and the theoretical curves with Kuhn segment lengths l(K) of around 18 nm were found to fit the data of both cellulose and CTC molecules in the solvents. It was concluded from the obtained results that both cellulose and CTC molecules have conformations essentially identical to each other in the solvents; they behave as typical semiflexible chains in good solvents.

Rheological Properties and Molecular Structure of Tunicate Cellulose in LiCl/1,3-Dimethyl-2-imidazolidinone

Solution properties and molecular structure of tunicate cellulose (TC), an animal cellulose from Halocynthia roretzi, were investigated in terms of rheological and dilute solution properties. The solvent used is 8 wt % LiCl/1,3-dimethyl-2-imidazolidinone (DMI). A solution of dissolving pulp (DP), derived from plant, was also used for comparison. The weight-average molecular weight, Mw, and the limiting viscosity number, [eta], of the TC were evaluated to be 413 x 10(6) and 2645 mL/g, respectively. The TC solution showed the same concentration dependence of GN (GN=5.49 x 10(6)phiw(2.1)4 Pa; phiw: weight fraction of cellulose in solution; GN: plateau modulus) as the DP solution and, moreover, also as the solution of cotton linter (CC) in 8 wt % LiCl/N,N-dimethylacetamide (DMAc). This exponent of 2.1(4) indicates that network structure by entanglements was formed in these solutions. According to the theory of Fetters et al., moreover, such identity means that all of these celluloses have the identical chain structure though their biological origins are far different. On the other hand, the phiw-dependence of eta0-etas (eta0=zero shear rate viscosity of solution; etas=solvent viscosity) was different between the TC and the DP solution in the semidilute regime: the TC solution exhibited eta0-etas proportional, variant phiw(7.5) and the DP solution eta0-etas proportional, variant phiw4. According to the theory of Doi-Edwards, this exponent of 4 (the DP solution) indicates that the DP behaves as flexible polymers in the solution. In contrast, the dependence for the TC solution seems unexplainable on the basis of molecular theories. This difference probably signifies the difference in the relaxation process or mechanism in entanglement systems.