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  • 1.
    Bengtsson, Jenny
    et al.
    RISE - Research Institutes of Sweden, Bioeconomy, Biobased Materials. Chalmers University of Technology, Sweden.
    Jedvert, Kerstin
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Hedlund, Artur
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Mass transport and yield during spinning oflignin-cellulose carbon fiber precursors2019In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 5, p. 509-516Article in journal (Refereed)
    Abstract [en]

    Lignin, a substance considered as a residue in biomass and ethanol production, has been identified as a renewable resource suitable for making inexpensive carbon fibers (CFs), which would widen the range of possible applications for light-weight CFs reinforced composites. Wet spinning of lignin-cellulose ionic liquid solutions is a promising method for producing lignin-based CFs precursors. However, wet-spinning solutions containing lignin pose technical challenges that have to be solved to enable industrialization. One of these issues is that a part of the lignin leaches into the coagulation liquid, which reduces yield and might complicate solvent recovery. In this work, the mass transport during coagulation is studied in depth using a model system and trends are confirmed with spinning trials. It was discovered that during coagulation, efflux of ionic liquid is not hindered by lignin concentration in solution and the formed cellulose network will enclose soluble lignin. Consequently, a high total concentration of lignin and cellulose in solution is advantageous to maximize yield. This work provides a fundamental understanding on mass transport during coagulation of lignin-cellulose solutions, crucial information when designing new solution-based fiber forming processes.

  • 2.
    Bengtsson, Jenny
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Olsson, Carina
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Hedlund, Artur
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Bialik, Erik
    Molecules in Motion, Sweden.
    Understanding the Inhibiting Effect of Small-Molecule Hydrogen Bond Donors on the Solubility of Cellulose in Tetrabutylammonium Acetate/DMSO2017In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, no 50, p. 11241-11248Article in journal (Refereed)
    Abstract [en]

    Certain ionic liquids are powerful cellulose solvents, but tend to be less effective when small-molecule hydrogen bond donors are present. This is generally attributed to competition with cellulose for hydrogen bonding opportunities to the anion of the ionic liquid. We show that the solubility of cellulose in dimethyl sulfoxide solutions of tetrabutylammonium acetate is less strongly affected by water than by ethanol on a molar basis, contrary to what can be expected based on hydrogen bond stoichiometry. Molecular dynamics simulations indicate that the higher tolerance to water is due to water-cellulose interactions that improves solvation of cellulose and, thereby, marginally favors dissolution. Through Kirkwood-Buff theory we show that water, but not ethanol, improves the solvent quality of DMSO and partly compensates for the loss of acetate-cellulose hydrogen bonds.

  • 3.
    Hedlund, Artur
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Structure of cellulose coagulated from different EmimAc-DMSO solutions2016Conference paper (Other academic)
  • 4.
    Hedlund, Artur
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Hagman, Joel
    RISE, Swerea.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Theliander, Hans
    RISE, Swerea. Chalmers University of Technology, Sweden.
    Hagström, Bengt
    RISE, Swerea.
    Cosolvent and non-solvent effects on EmimAc-cellulose solutions’ rheology investigated inoscillatory shear and elongation2016In: 6th Avancell conference, 2016Conference paper (Other academic)
  • 5.
    Hedlund, Artur
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, IVF. Chalmers University of Technology, Sweden.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Hagman, Joel
    Lund University, Sweden.
    Olsson, Ulf
    Lund University, Sweden.
    Theliander, Hans
    Chalmers University of Technology, Sweden; KTH Royal Institute of Technology, Sweden.
    Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate: contrasting coagulation mechanisms2019In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 26, no 3, p. 1545-1563Article in journal (Refereed)
    Abstract [en]

    Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].

  • 6.
    Hedlund, Artur
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, IVF. Chalmers University of Technology, Sweden.
    Köhnke, Tobias
    RISE, Swerea, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Coagulation of cellulose-EmimAc-DMSO solutions studied in order to control properties of wet-spun cellulose fibers2016In: The 7th Workshop on cellulose, regenerated cellulose and cellulose derivatives, 2016, p. 49-52, article id 15Conference paper (Other academic)
  • 7.
    Hedlund, Artur
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Coagulation of EmimAc-cellulose solutions: Dissolution-precipitation disparity and effects of non-solvents and cosolvent2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 1, p. 32-42Article in journal (Refereed)
    Abstract [en]

    Coagulation values (CVs) of cellulose/1-ethyl-3-methylimidazolium acetate (EmimAc)/dimethyl-sulfoxide (DMSO) solutions for water, ethanol (EtOH) and 2-propanol (2-PrOH) were measured by using a light-scattering technique. Expressed in moles per mole, CVs of H2O were roughly twice as high as the CVs of EtOH and 2-PrOH at equal cellulose concentration for EmimAc solutions without the addition of a cosolvent. We explain this observation mainly in terms of alcohol alkyl chains efficiently obstructing EmimAc anions, preventing anions from simultaneously interacting with cellulose hydroxyls. DMSO was found to mitigate the coagulating effect of water and, to a lesser extent, the effect of alcohols. The explanation may be the different enthalpies of mixing for water and alcohols, with DMSO. An explanation on a more practical level, is based on how the solvatochromic α and β parameters change due to small amounts of the different non-solvents. Small additions of methanol induce disproportionately large changes from basic towards acidic properties for DMSO, meanwhile, the same stoichiometric addition of water induces only minor changes. Precipitation occurred at concentrations of non-solvent much higher than the concentrations that limit dissolution. The most likely explanation for this is a metastable region in the phase diagram. It was also seen that the typically observed inhibitive effect of high Mw on solubility during dissolution did not apply to precipitation.

  • 8.
    Hedlund, Artur
    et al.
    RISE - Research Institutes of Sweden, Materials and Production, IVF. Chalmers University of Technology, Sweden.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden, Materials and Production, IVF.
    Mass transport during coagulation of cellulose-ionic liquid solutions in different non-solvents2019In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882XArticle in journal (Refereed)
    Abstract [en]

    Abstract: Cellulose can be regenerated from cellulose-ionic liquid (IL) solutions by immersion in water or alcohols. These compounds are potent non-solvents due to their proton-donating ability in hydrogen bonds to IL anions. Although they share this fundamental way of reducing IL solvent quality, coagulation in water is distinctly different from coagulation in alcohols with regard to the microstructures formed and the mechanisms that generate the microstructures. In this study, the possibility of mass-transport effects on microstructures was investigated. The mass-transport of all components: non-solvent (EtOH, 2PrOH), IL ([C2mim][OAc]), and a co-solvent (DMSO), during coagulation was studied. The data was compared to previous data with water as the non-solvent. Results showed that diffusion is essentially limited to a continuous non-solvent-rich phase that is formed during phase separation in all non-solvents. There were also significant differences between non-solvents. For instance, [C2mim][OAc] diffusion coefficients were 6–9 times smaller in 2PrOH than in water, and there were apparent effects from cellulose concentration in 2PrOH that were not observed in water. The differences stem from the interactions between solvent, non-solvents, and cellulose, which can be both mutual and competitive. Weaker [C2mim][OAc]-non-solvent interactions with alcohols give more persistent [C2mim][OAc]-cellulose interactions than with water as the non-solvent, which has consequences for mass-transport. Graphic abstract: [Figure not available: see fulltext.]. © 2019, The Author(s).

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