| 1. |
- Andersson Trojer, Markus, 1981, et al.
(author)
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Directed self-assembly of silica nanoparticles in ionic liquid-spun cellulose fibers
- 2019
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 553, s. 167-176
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Journal article (peer-reviewed)abstract
- The application range of man-made cellulosic fibers is limited by the absence of cost- and manufacturing-efficient strategies for anisotropic hierarchical functionalization. Overcoming these bottlenecks is therefore pivotal in the pursuit of a future bio-based economy. Here, we demonstrate that colloidal silica nanoparticles (NPs), which are cheap, biocompatible and easy to chemically modify, enable the control of the cross-sectional morphology and surface topography of ionic liquid-spun cellulose fibers. These properties are tailored by the silica NPs’ surface chemistry and their entry point during the wet-spinning process (dope solution DSiO2 or coagulation bath CSiO2). For CSiO2-modified fibers, the coagulation mitigator dimethylsulphoxide allows for controlling the surface topography and the amalgamation of the silica NPs into the fiber matrix. For dope-modified fibers, we hypothesize that cellulose chains act as seeds for directed silica NP self-assembly. This results for DSiO2 in discrete micron-sized rods, homogeneously distributed throughout the fiber and for glycidoxy-surface modified DSiO2@GLYEO in nano-sized surface aggregates and a cross-sectional core-shell fiber morphology. Furthermore, the dope-modified fibers display outstanding strength and toughness, which are both characteristic features of biological biocomposites.
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| 2. |
- Hedlund, Artur, 1984
(author)
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Coagulation of Cellulose: from Ionic-Liquid Solution to Cellulose Nanostructure
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Abstract A linear chain of glucose monomers, cellulose, provides the structural reinforcement of the cell walls of plants and constitutes almost half of their dry mass. Wood and other plant-based raw materials are processed on a large industrial scale to isolate the cellulose, which is then dissolved. The resulting solutions can be shaped into films or fibers and solidified as such by immersion in a nonsolvent. The properties of the solidified cellulose products can, however, vary and are frequently not quite satisfactory. In the solidification process, cellulose forms one phase and the nonsolvent and solvent form a second phase, which is later removed through washing and drying. However, these phase separations of ternary mixtures are more complicated than the sentence above indicates. In fact, the details left out decide the properties of those variable materials. This thesis reports on the interdependencies between several parameters and aspects that are critical to cellulose phase separations: compound properties, phase equilibria for the ternary mixtures, the diffusion processes, and the nanostructures formed. Several new experimental methods were developed to measure the critical amounts of nonsolvent that induce coagulation, the mass transport of solvent and nonsolvent, and the rates of coagulation. The cellulose solutions of an ionic liquid, 1ethyl-3methyl-imidazolium acetate, [C2mim][OAc], with varied amounts of a cosolvent, DMSO, were coagulated in water, ethanol (EtOH), or 2-propanol (2PrOH). It was found that 2PrOH is, expressed in molar ratio, the strongest nonsolvent (> EtOH > water). However, the diffusive rates, D, and coagulation rates were in the opposite order (water > EtOH > 2PrOH). The observed differences between nonsolvent compounds were much larger for D[C2mim][OAc] than for DNonSolvent , for the rates of coagulation or for DDMSO, particularly with high cellulose concentration. More differences between water and alcohol as the nonsolvent were observed in the cellulose structures formed. Coagulation in water produced relatively well-ordered crystalline structures, whereas coagulation in alcohol did not. The differences between water and alcohol as the nonsolvent can be explained by different modes of phase separation and differences in nonsolvent interactions with [C2mim][OAc] and cellulose. To show the reader how we arrived at those conclusions, which have not been found in previous literature in the cellulose field, a substantial background regarding the properties and interactions of the compounds is supplied. Networks of cellulose nanofibrils were formed in all the nonsolvents tested, which explained the generally high diffusivities observed and the minor effect of cellulose on diffusion. It appeared that diffusion through the cellulose nanofibril network is similar to diffusion in a mixture of [C2mim][OAc] and nonsolvent only, which was confirmed with a simplistic computer model.
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| 3. |
- Hedlund, Artur, 1984, et al.
(author)
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Coagulation of EmimAc-cellulose solutions: dissolution-precipitation disparity and effects of non-solvents and cosolvent
- 2015
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In: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:1, s. 32-42
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Journal article (peer-reviewed)abstract
- 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 a and beta 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 M-w on solubility during dissolution did not apply to precipitation.
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