| 1. |
- Testova, Lidia, et al.
(author)
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Dissolving-grade birch pulps produced under various prehydrolysis intensities : Quality, structure and applications
- 2014
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In: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 21:3, s. 2007-2021
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Journal article (peer-reviewed)abstract
- Aqueous-phase prehydrolysis followed by alkaline pulping is a viable process to produce wood-based dissolving pulps. However, detailed characterisation of the achievable pulp quality, performance and cellulose structure is yet lacking. In this study, the production of hemicellulose-lean birch soda-anthraquinone pulps after prehydrolysis under various intensities was investigated. Increasing prehydrolysis intensity resulted in pulps of higher purity but lower cellulose yield and degree of polymerisation. Higher cellulose yield by using sodium borohydride during pulping was achieved at the expense of reducing pulp purity. Cellulose crystallinity was similar in all pulps indicating simultaneous degradation of both crystalline and amorphous cellulose regions. Reinforced prehydrolysis seemingly increased the cellulose crystal size and the interfibrillar distances. Moderate intensity prehydrolysis (170 °C) resulted in a pulp well suited for viscose application, whereas reinforced prehydrolysis favoured the production of acceptable cellulose triacetate dope. The performance of the pulps in viscose and acetate applications was strongly related to the chemical and structural properties.
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| 2. |
- Tolonen, Lasse K., et al.
(author)
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Solubility of Cellulose in Supercritical Water Studied by Molecular Dynamics Simulations
- 2015
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:13, s. 4739-4748
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Journal article (peer-reviewed)abstract
- The insolubility of cellulose in ambient water and most aqueous systems presents a major scientific and practical challenge. Intriguingly though, the dissolution of cellulose has been reported to occur in supercritical water. In this study, cellulose solubility in ambient and supercritical water of varying density (0.2, 0.7, and 1.0 g cm(-3)) was studied by atomistic molecular dynamics simulations using the CHARMM36 force field and TIP3P water. The Gibbs energy of dissolution was determined between a nanocrystal (4 x 4 x 20 anhydroglucose residues) and a fully dissociated state using the two-phase thermodynamics model. The analysis of Gibbs energy suggested that cellulose is soluble in supercritical water at each of the studied densities and that cellulose dissolution is typically driven by the entropy gain upon the chain dissociation while simultaneously hindered by the loss of solvent entropy. Chain dissociation caused density augmentation around the cellulose chains, which improved water-water bonding in low density supercritical water whereas the opposite occurred in ambient and high density supercritical water.
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| 3. |
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| 4. |
- Wohlert, Jakob, et al.
(author)
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A simple model for cellulose solubility in supercritical water
- 2015
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In: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 30:1, s. 14-19
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Journal article (peer-reviewed)abstract
- A simple model for the hydration of a polar molecule is developed in order to provide a description of cellulose solubility in water under ambient and supercritical conditions. The change in free energy upon hydration is regarded as the sum of the energy cost of forming a cavity and a polar contribution. The model is able to predict the existence of an optimal density for dissolution of polar solutes in supercritical water. Those results are in line with earlier experiments and simulations showing that water at high temperature and pressure dissolves cellulose, and that an optimal density for dissolution exists. The present study shows that the density dependence comes from the fact that both the cavity formation energy and the polar energy are highly density dependent but with opposing behaviour. The cavity formation energy increases with density, whereas the polar energy decreases. Based on the present model, it is possible to rationalize a few basic strategies regarding cellulose dissolution in aqueous media. To increase solubility, one can either increase the polar/electrostatic contribution, or more importantly, one can decrease the cost of cavity formation, e.g. by introducing co-solvents, changing temperature and/or pressure.
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