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  • 1.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging. KTH Royal Institute of Technology, Sweden.
    Stevanic Srndovic, Jasna
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Larsson, Per Tomas
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Pulp delignification and refining: impact on the supramolecular structure of softwood fibers2023In: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 30, no 16, p. 10453-10468Article in journal (Refereed)
    Abstract [en]

    The effect on softwood fiber wall nanostructure of kraft cooking, oxygen delignification and refining was evaluated by X-ray scattering. A recently developed simulation method for modelling small angle X-ray scattering (SAXS) data was used to estimate the apparent average sizes of solids (AAPS) and interstitial spaces in the fiber wall (AACS). Fiber saturation point and wide angle X-ray scattering were also used to calculate the pore volume in the fiber wall and the crystallite size of the fibril, respectively. The experimental modelled SAXS data was able to give consistent values for each kraft-cooked and oxygen-delignified pulp. Kraft delignification seems to have the major influence on the fiber nanostructure modification, while oxygen delignification has little or no significant impact even for different kappa numbers. The particle sizes values were more stable than the cavities sizes and no significant differences were seen between different delignification processes, refining or delignification degree. Pulps evaluated after PFI-refining, showed an increase in the fiber wall porosity evaluated by FSP and an increase in the interstitial spaces in the fiber wall, while the crystallite size and the particle sizes were very little or not affected at all. 

  • 2.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    Evaluating the Potential to Modify Pulp and Paper Properties through Oxygen Delignification2020In: ACS Omega, E-ISSN 2470-1343, Vol. 5, no 23, p. 13703-13711Article in journal (Refereed)
    Abstract [en]

    The potential to modify pulp and paper properties by oxygen delignification was assessed by looking beyond the ordinary purpose of oxygen delignification. Pulps with the same kappa number were obtained by both pulping and the combination of pulping and oxygen delignification, and the mechanical and chemical properties were compared. The oxidation of pulp components leads to an increase in carboxylic acid groups in the fibers, resulting in a large influence on fiber swelling, seen as an increase in the water retention value and fiber saturation point. The introduction of charged groups appears to replace some of the morphological changes caused by refining and enhance the strength of fiber-fiber joints, generating pulps with better refinability and higher tensile strength. Oxygen delignification was able to improve the tensile index with 6% at the same sheet density and less refining energy, when the amount of total fiber charges was higher than 140 μekv/g.

  • 3.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    The effects of high alkali impregnation and oxygen delignification of softwood kraft pulps on the yield and mechanical properties2022In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 37, no 2, p. 223-231Article in journal (Refereed)
    Abstract [en]

    This study investigated whether the yield improvement after high alkali impregnation (HAI) is maintained after oxygen delignification and whether the potential of oxygen delignification to increase the mechanical properties is affected by high alkali impregnation. The yield improvement achieved by high alkali impregnation (1 %) was preserved after oxygen delignification, particularly of glucomannan. The total fiber charge and swelling increased after oxygen delignification regardless of the type of impregnation in the cooking step. The tensile index improvement obtained by oxygen delignification was retained if this was preceded by high alkali impregnation. The stiffness index was higher and elongation slightly lower after HAI impregnation than after a standard (REF) impregnation. Fibers obtained through high alkali impregnation seem to be slightly less deformed and slightly wider than fibers obtained after a standard impregnation. 

  • 4.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Differences and similarities between kraft and oxygen delignification of softwood fibers: effects on chemical and physical properties2021In: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 28, no 5, p. 3149-3167Article in journal (Refereed)
    Abstract [en]

    The fiber properties after oxygen delignification and kraft pulping were studied by looking into the chemical characteristics and morphology. The effect of the two processes on the fibers was evaluated and compared over a wider kappa number range (from 62 down to15). Wide-angle X-ray scattering, nuclear magnetic resonance and fiber saturation point were used to characterize the fiber network structure. Fiber morphology and fiber dislocations were evaluated by an optical image analysis. The total and surface fiber charges were studied by conductometric and polyelectrolyte titrations. The fiber wall supramolecular structure, such as crystallinity, size of fibril aggregates, pore size and pore volume, were similar for the two processes. The selectivity, in terms of carbohydrate yield, was equal for kraft cooking and oxygen delignification, but the selectivity in terms of viscosity loss per amount of delignification is poorer for oxygen delignification. Clearly more fiber deformations (2–6% units in curl index) in the fibers after oxygen delignification were seen. Introduction of curl depended on the physical state of the fibers, i.e. liberated or in wood matrix. In the pulping stage, the fiber continue to be supported by neighboring fibers, as the delignified chips maintain their form. However, in the subsequent oxygen stage the fibers enter in the form of pulp (liberated fibers), which makes them more susceptible to changes in fiber form. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

  • 5.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Differences and similarities between kraft and oxygen delignification of softwood fibers: effects on mechanical properties2021In: Cellulose, ISSN 0969-0239, E-ISSN 1572-882X, Vol. 28, p. 3775-3788Article in journal (Refereed)
    Abstract [en]

    Charged groups in pulp have been shown to enhance the tensile strength of the paper produced from the pulp. Oxygen delignification introduces charged groups and it is of interest to determine how the delignification should be distributed between the cooking and the oxygen stage with respect to mechanical properties. A number of unbleached kraft cooked and oxygen delignified pulps within a wide kappa number range were produced and refined, and the effects of the refining on the morphology and mechanical properties were studied. The WRV correlated with the fiber charge and at a given fiber charge, kraft cooked and oxygen delignified pulps had the same WRV development in refining, although they had significantly different kappa numbers. The tensile strength development during refining depends on the fiber rigidity which is affected by the lignin content, the fiber charge and the chemical and mechanical processes used. Refining increased the curl of the kraft cooked pulps and decreased the curl of oxygen delignified pulps, irrespective of kappa number. A greater increase in tensile strength was seen for the pulps with a higher fiber charge and WRV, probably because of the greater degree of fibrillation achieved in the beating process. Despite the greater fiber deformation in the oxygen delignified pulps, the strength can be increased by a larger amount of charged groups and a greater swelling of the fibers. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s).

  • 6.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden.
    The impact of bleaching on the yield of softwood kraft pulps obtained by high alkali impregnation: Bleaching and high alkali impregnation impact2022In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 37, no 4, p. 593-608Article in journal (Refereed)
    Abstract [en]

    High alkali impregnation (HAI) increases the total yield of softwood pulps following kraft cooking. This yield improvement is also maintained after oxygen delignification. This study evaluates how bleaching with either chlorine dioxide or hydrogen peroxide affects the final yield of samples obtained with standard and HAI. The chemical composition, viscosity, brightness, mechanical and morphological properties were studied. Compared to cooking after standard impregnation the yield improvement achieved by HAI was preserved in both types of bleaching sequences (2 % units for chlorine dioxide and 4 % units for hydrogen peroxide). The introduction of charged groups into the cellulose fibers was higher with hydrogen peroxide bleaching than with chlorine dioxide however, no significant impact was seen on the swelling or mechanical properties. The brightness was higher for the pulps bleached with chlorine dioxide compared with hydrogen peroxide. Hydrogen peroxide bleaching resulted in similar brightness development for both standard and HAI. Fibers bleached with chlorine dioxide had the highest curl index (16-17 %) compared to the fibers bleached with hydrogen peroxide (15 %). © 2022 the author(s)

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