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  • 1.
    Berg, Jan-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Gradin, Per A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Effect of Temperature on Fracture of Spruce in Compression, Investigated by Use of Acoustic Emission Monitoring2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 8, p. 294-299Article in journal (Refereed)
    Abstract [en]

    Acoustic Emission (AE) monitoring during compression of wood has been used to investigate the fracture history with specific emphasis on its dependence on temperature, moisture content, strain and loading direction. The wood was compressed in both the lateral and longitudinal directions in order to select preferred modes of deformation to achieve desired irreversible changes in the wood structure. The elastic modulus, the compressive strength and the cumulated number of AE events decreased with increasing temperature. It was concluded that the most efficient loading direction is longitudinal in order to introduce flaws in wood under compression and that a longitudinal compression of 24%, corresponding to a specific energy input of 3 kWh/ton, is needed in order to achieve substantial changes in the wood structure. The compression should be carried out at temperatures well below 120°C in order to introduce many failure sites.

  • 2. Granberg, H
    et al.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Quantification of the intrinsic error of the kubelka–munk model caused by strong light absorption2003In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 29, no 11, p. 386-390Article in journal (Refereed)
    Abstract [en]

    The Kubelka-Munk (KM) model is widely used within the paper industry to interpret diffuse reflectance factor measurements of paper and its components. It has been found in the literature that the addition of a dye colorant to a paper sheet not only increases its KM light absorption coefficient, but for strong absorption also decreases its KM light scattering coefficient. This effect has previously been attributed to the intrinsic error of the KM model induced by light absorption that tends to orient of the light fluxes perpendicular to the sheet. In the present work we have mapped the intrinsic error of the KM model by comparing light scattering calculations from the KM model with the more accurate Discrete Ordinate Radiative Transfer model DORT2002. We found that the models agree within 2.3% in reflectance, and that the intrinsic error in the KM model explains about 1/5 of the previously observed interdependence of the KM coefficients for heavily dyed sheets.

  • 3. Gurnagul, Norayr
    et al.
    Howard, R.C.
    Zou, Xuejun
    Uesaka, Tetsu
    Page, Derek
    THE MECHANICAL PERMANENCE OF PAPER - A LITERATURE-REVIEW1993In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 19, no 4, p. J160-J166Article in journal (Refereed)
  • 4.
    Klinga, Niklas
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Sandberg, C
    Energy efficient high quality CTMP for paperboard2008In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 34, no 2, p. 98-106Article in journal (Refereed)
    Abstract [en]

    This paper discusses the relationship between bulk and internal bond strength in paper sheets and their dependency on fibre length, fibre flexibility and fibre surface properties. It also discusses an interesting process concept for manufacturing of energy efficient high quality CTMP for paperboard. Post-refining pilot trials of spruce HTCTMP with an initial freeness of 740 ml were carried out at Metso Paper R&D in Sundsvall, Sweden. Both gentle high consistency and severe low consistency post-refining were performed. High consistency post-refining, at high energy input, gave freeness levels below 70 ml and still preserved the fibre length. These fibres were characterised by a very high flexibility giving sheets with a tensile index as high as 64 kNm/kg. Long fibres can however cause formation problems on a board machine which in turn can lead to poor surface properties, hence shorter fibres are from that perspective desirable. The low consistency post-refining resulted in a rapid drop in freeness due to fibre cutting. This was achieved at an extremely low specific energy input, which probably preserved most of the original fibre stiffness. In spite of this low energy input it was possible to reach the same Z-strength at a given bulk, as for the high consistency post-refined pulp. This implied that high bulk at certain internal bond strength could be achieved with stiff fibres even though the content of long fibres was low. Energy efficient low consistency post-refining of spruce HTCTMP yields high quality pulp at a total energy input of ~800 kWh/admt and is an interesting process concept for production of pulps intended for paperboard.

  • 5.
    Norgren, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Nilvebrant, Nils-Olof
    Physiochemical differences between dissolved and precipitated Kraft lignin fragments as determined by PFG NMR, CZE and quantitative UV spectrophotometry2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 11, p. 359-363Article in journal (Refereed)
    Abstract [en]

    A combination of analytical techniques, specifically capillary zone electrophoresis, H-1 pulsed-field gradient nuclear magnetic resonance se (diffusion measurements and quantitative UV spectrophotometric measurements, was used to investigate physicochemical differences between dissolved and precipitated kraft lignin (KL)fragments, obtained from the same sample. Precipitation was induced by heating alkaline (pOH4)Indulin AT solutions, containing various concentrations of NaCl (0.20-1.0 mol/L), at 75 degreesC. Depending on the salt concentration in the samples, different amounts of KL were precipitated. The KL precipitated at the lowest NaCl concentrations was found to consist of the largest lignin fragments whereas, at high NaCl concentrations, the KL fragments in the supernatants were found to be of comparably lower mean molecular weights. From the outcome of the investigation, it was found that the combination of analytical techniques used provides the possibility of collecting important information about physicochemical characteristics related to the solution behaviour of industrial lignins.

  • 6.
    Norgren, Sven
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Moisture-induced surface roughness in TMP sheets2008In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 34, no 3, p. 139-146Article in journal (Refereed)
    Abstract [en]

    The present study evaluates effects of moisture on sheet properties made different Bauer-McNett fractions from TMP, both individually and in combinations. It is well known that the coarse, stiff, long fibre fractions cause surface roughness in dry sheets. However, this study indicates that these fibres remain relatively unchanged when moisture diffuses into the sheet structure, i.e., the degree of decollapse is low. The fibres from the middle fraction rise easily, causing the greatest change in surface roughness when moisture is added to the sheet. Sheets including both coarse fibres and fibres from the middle fractions display the highest surface roughness values at a high moisture content. The trials also indicate that fines contribute to increased surface roughness: when the degree of bonding in the sheet structure is increased, there is a risk that the whole structure or the flocks, instead of the individual fibres, may swell.

  • 7. Provatas, N.
    et al.
    Uesaka, Tetsu
    Modelling paper structure and paper-press interactions2003In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 29, no 10, p. 332-340Article in journal (Refereed)
  • 8. Rundlöf, Mats
    et al.
    Htun, Myat
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mechanical pulp fines of poor quality - Characteristics and influence of white water2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 9, p. 308-316Article in journal (Refereed)
    Abstract [en]

    Fines from white water were compared with fresh TMP fines from the same mill. The white-water fines gave a low er tensile strength of handsheets and a stronger light absorption. The surface composition (ESCA) and contact angle indicated more extractives on the surface of these fines. The total extractives content was much higher; no other large differences in chemical composition or morphology were found. Addition of unbleached white water to fresh fines had no effect on the tensile strength, whereas addition of white water subjected to hydrogen peroxide bleaching gave an immediate decrease.

  • 9. Rundlöf, Mats
    et al.
    Htun, Myat
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    The importance of the experimental method when evaluating the quality of fines of mechanical pulps2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 9, p. 301-307Article in journal (Refereed)
    Abstract [en]

    Changes in properties of TMP fines brought about by the method of fractionation were investigated. Fines fractionated from white water by Baller McNett showed a higher tensile index and a lower light absorption compared with fines obtained using a Britt dynamic drainage jar (BDDJ). This was attributed to the large volume of tap water and thus more extensive washing of the fines in the Bauer McNett. This was strongly supported by the fact that acetone extraction improved the strength properties of these fines drastically. Fines fractionated from a fresh TMP by the Bauer McNett had a stronger light absorption and lower light scattering than those obtained by the BDDJ. This was attributed to the use of tap water and the loss of small particles in the Bauer McNett. Since the washing of mechanical pulp influences the properties significantly, the BDDJ method is recommended because it uses less water and of a more defined quality than does the Bauer McNett.

  • 10.
    Svensson, Birgitta
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, M.
    Höglund, Hans
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Sliding Friction Between Wood and Steel in a Saturated Steam Environment2006In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 32, no 1, p. 38-43Article in journal (Refereed)
    Abstract [en]

    To understand friction under refining conditions, measurements of sliding friction between wood and steel were made in a steam environment. To achieve various testing temperatures (100-170°C), the steam pressure was set to various levels. Two wood species, Norway spruce and Radiata pine, were examined in this study. The friction coefficients of native wood increased with temperature up to a critical point where fibres started to wear from the surface. This point was observed at a lower temperature for Radiata pine than for Norway spruce. After extracting the samples with acetone and dichloromethane, friction-augmenting effects were observed and local friction maxima appeared for both spruce and pine at ∼125°C. It is suggested that these local maxima are due to energy-dissipative processes and related to the softening temperature of lignin. Experiments with sulphonated samples of Norway spruce supported this suggestion.

  • 11. Uesaka, Tetsu
    DIMENSIONAL STABILITY OF PAPER - UPGRADING PAPER PERFORMANCE IN END USE1991In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 17, no 2, p. J39-J46Article in journal (Refereed)
  • 12.
    Walter, Karin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Paulsson, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Wackerberg, Eva
    Energy efficient refining of Black spruce TMP by using acid hydrogen peroxide: Part 3. Chemical and morphological characterisation2010In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 36, no 1-2, p. 2-9Article in journal (Refereed)
  • 13. Wågberg, Lars
    et al.
    Forsberg, Sven
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Johansson, A
    Juntti, P
    Engineering of fibre surface properties by application of the polyelectrolyte multilayer concept: Part I: Modification of paper strength2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 7, p. 222-228Article in journal (Refereed)
    Abstract [en]

    Consecutive layers of cationic polyallylamine and anionic polyacrylic acid have been deposited on both unbeaten and beaten fully bleached cellulosic fibres. By preparing sheets of these fibres and by forming 5-10 layers of these polyelectrolytes on the unbeaten fibres, it was possible to develop the same strength as can be achieved by conventional beating. Experiments show that considerable strength improvement can be achieved with this type of treatment also on beaten fibres. Atomic force microscopy investigations of multilayers of the polylectrolytes formed on silicon oxide surfaces showed that the thickness of 10 layers of polyelectrolytes was 52 nm. Since the strength improvement was significant with 5 layers, it is suggested that a 26 nm thick multilayer of polyelectrolytes is sufficient to create a strong joint between fibres. The structure of the polyelectrolyte multilayers formed on the fibres was not determined.

  • 14.
    Zhang, Jin
    et al.
    McMaster Ctr. for Pulp/Paper Res., Department of Chemical Engineering, McMaster University, Hamilton, Ont. L8S 4L7, Canada.
    Pelton, Robert
    McMaster Ctr. for Pulp/Paper Res., Department of Chemical Engineering, McMaster University, Hamilton, Ont. L8S 4L7, Canada.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Rundlöf, M.
    SCA Research AB, SE-850 03 Sundsvall.
    The effect of molecular weight on the performance of paper strength-enhancing polymers2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 5, p. 145-151Article in journal (Refereed)
    Abstract [en]

    The influence of dextran molecular weight (77 000 to 2 000 000) on the strength of fibre-fibre bonds was investigated. A series of cationic dextrans with different molecular weights, from 77 000 to 2 000 000, was prepared and the adsorption behaviour on fibre was characterized. The maximum amount of adsorbed dextran increased with decreasing molecular weight, while the adsorbed layer thickness on colloidal silica increased with increasing molecular weight. At saturation coverage, the molecular weight of dextran did nor affect the tensile strength of handsheets made from unbeaten bleached kraft pulp. The strength improvement with polymer addition did not correspond to increased optical bonded area (opacity). The external surface of fibre accessible to dextran of molecular weight 2 000 000 was estimated as 35 m(2)/g.

  • 15. Zou, Xuejun
    et al.
    Gurnagul, Norayr
    Uesaka, Tetsu
    THE ROLE OF LIGNIN IN THE MECHANICAL PERMANENCE OF PAPER .1. EFFECT OF LIGNIN CONTENT1993In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 19, no 6, p. J235-J239Article in journal (Refereed)
1 - 15 of 15
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