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  • 1.
    Berg, Jan-Erik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Gulliksson, Mårten E.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Gradin, Per A.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    On the energy consumption for crack development in fibre wall in disc refining - A micromechanical approach2009Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 63, nr 2, s. 204-210Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analytical model has been applied to calculate the acquired strain energy density in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load. The energy density was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy is needed to create cracks at higher microfibril angles. The energy density was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy density was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data.

  • 2. Bäckström, Marie
    et al.
    Kolar, Marie-Claude
    Htun, Myat
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Characterisation of fines from unbleached kraft pulps and their impact on sheet properties2008Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 62, nr 5, s. 546-552Artikkel i tidsskrift (Fagfellevurdert)
  • 3.
    Carlsson, Peter
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för teknik, fysik och matematik.
    Distributed optimization with a two-dimensional drying model of a board, built up by sapwood and heartwood2001Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 55, nr 4, s. 426-432Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Optimization with distributed computing is performed on a two-dimensional orthotropic drying model which allows boards with arbitrary outtake of the log and sapwood/heartwood distribution in the cross section. Drying schedules with an optimized variation of temperature and humidity which yields minimized drying time are created at the same time as moisture, stress and deformation levels are considered. A numerical example with distributed computing of a board with a mixture of sapwood and heartwood is presented. Drying starts from the fibre saturation point.

  • 4.
    Fernando, D.
    et al.
    Department of Forest Products/Wood Science, Wood Ultrastructure Research Centre (WURC), Swedish University of Agricultural Sciences, P.O. Box 7008, SE-750 07 Uppsala, Sweden.
    Muhic, D
    Holmen Paper AB, Braviken Mill, Norrköping, Sweden.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Daniel, G
    Department of Forest Products/Wood Science, Wood Ultrastructure Research Centre (WURC), Swedish University of Agricultural Sciences, P.O. Box 7008, SE-750 07 Uppsala, Sweden.
    Surface and internal micro/ultrastructure of TMP fibres produced during high-intensity refining elucidate the development of pulp and paper properties2012Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, nr 4, s. 467-475Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Refining during mechanical pulping causes delamination and internal fibrillation (D/IF) of the fibre wall and changes the surface ultrastructure. Fundamental knowledge about these phenomena at the fibre cell wall level helps our understanding of the development of pulp and paper properties, which in turn facilitates the optimization of processes, helping to save energy and improve the characteristics of final products. In the present study, pulps were produced by double-disc (DD) refined thermomechanical processes (DD-TMP) and have been characterized at the fibre cell wall micro/ultrastructural level based on Fernando and Daniel’s method (2010) of Simons ’ staining and scanning electron microscopy (SEM). The pulps studied were never-dried Norway spruce DD-TMP from a full-scale mill trial running under different process conditions; a) varying refining intensity, achieved by using a high-intensity turbine segment (HTS) and a standard (Ref) segment from Metso, and b) varying specific energy consumption (SEC). Improved energy efficiency was obtained with HTS segments, giving adequate or better pulp properties with respect to elongation, light scattering, Canadian Standard Freeness (CSF) at a similar tensile index level and lower energy consumption. Energy efficiency was gained through an elevated degree of D/IF and S2 fibrillation with low energy input. Both the SEC and segment designs had a significant impact on elevating the degree of D/IF. Statistical evaluation of fibre development with respect to D/IF gave evidence for improved energy efficiency in HTS refining. Ultrastructural studies on fibre surfaces showed that HTS refining produced better external fibrillation and leads to exposing the secondary S2 wall as fibre outer layer with different ribbon-type S2 fibrillation. Information obtained at the fibre wall level concerning D/IF and surface ultrastructure contribute to the fundamental knowledge about the pulp and handsheet properties and the energy efficiency of TMP processing. Copyright © by Walter de Gruyter·Berlin·Boston.

  • 5.
    Fernando, Dinesh
    et al.
    Wood Ultrastructure Research Centre (WURC), Department of Forest Products/Wood Science, Swedish University of Agricultural Sciences, Uppsala.
    Muhic, Dino
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Daniel, Geoffrey
    Wood Ultrastructure Research Centre (WURC), Department of Forest Products/Wood Science, Swedish University of Agricultural Sciences, Uppsala.
    Fundamental understanding of pulp property development under different thermomechanical pulp refining conditions as observed by a new Simons' staining method and SEM observation of the ultrastructure of fibre surfaces2011Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, nr 6, s. 777-786Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons' staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under differentprocess conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP. © 2011 by Walter de Gruyter Berlin Boston.

  • 6.
    Gorski, Dmitri
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Johansson, L
    Paper and Fibre Research Institute (PFI), Trondheim, Norway.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Refiner bleaching in a peroxide-based ATMP process compared with conventional bleaching2012Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, nr 3, s. 275-281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study was to compare refiner bleaching with conventional laboratory bleaching by means of hydrogen peroxide and magnesium hydroxide. Refiner bleaching in this study was a part of the ATMP (advanced thermo mechanical pulping) process, in which bleaching chemicals are added to the first stage refiner. Unbleached reference pulp which underwent similar mechanical treatment as refiner bleached pulp was used for laboratory bleaching. Bleaching efficiency was found to be almost equal for pilot scale refiner bleaching and conventional laboratory bleaching. A brightness increase of 10 ISO was reached with addition of 26 kg t -1 hydrogen peroxide leading to a final brightness of 66 ISO using both methods. Slightly more COD (52kg t -1 compared with 46 kg t -1) was generated in refiner bleaching compared with conventional laboratory bleaching to equal brightness with the same chemicals added. © 2012 by Walter de Gruyter Berlin Boston 2012.

  • 7.
    Hafrén, Jonas
    et al.
    Sveriges lantbruksuniversitet (SLU).
    Nelsson, Erik
    Gerritsen, Hans C.
    Utrecht university, The Nederlands.
    Bader, Arjen N.
    Utrecht university, The Nederlands.
    Optical properties of thermomechanical pulp (TMP) obtained from sulfite-pretreated Norway spruce with focus on two-photon spectral imaging (TPSI)2012Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, ISSN 0018-3830, Vol. 66, nr 7, s. 817-824Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chips of Norway spruce have been impregnated with Na2SO3 and refined at two specific energy consumptions levels at full mill scale. The optical properties of thermomechanical pulps (TMPs) obtained were analyzed in terms of brightness, light scattering, opacity, and autofluorescence by spectral imaging. Even at low sulfite dosage (0.24% sulfite by dry weight) light absorption was reduced, and the brightness was elevated, and a clear dose-response effect was observed. Two-photon spectral imaging (TPSI) showed that sulfonation, impregnation, and refining affect the fluorescence properties differently. Compared to native wood, both processed wood chips and pulp fibers revealed blue-shifted fluorescence maxima, a characteristic of shortened conjugated systems. Two subpopulations of fibers with different optical properties were observed, and the fluorescence of one fiber population was red shifted.

  • 8.
    Hellström, Lisbeth
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Gradin, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Engstrand, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Gregersen, Øyvind
    Department for Chemical Engineering, NTNU, Trondheim, Norway.
    Properties of wood chips for thermomechanical pulp (TMP) production as a function of spout angle2011Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, nr 6, s. 805-809Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spruce woodchipswere produced under well-controlled conditions in a laboratory woodchipper at spout angles of 30°, 40°, and 50° at a cutting rate of 20 m s-1 and with a nominalchip length of 25 mm. Thechips were then refined under thermomechanical pulp (TMP) conditions in a pilot refiner plant. The pulpproperties such as freeness, average fiber length, and shives content were determined and evaluated as a function of specific energy consumption. For a first stage refining and for a freeness value of 350 ml, a decrease in specific electrical energy consumption could be achieved by performing thewood chipping at a spout angle of 50° as compared to 30° which is the spout angle commonly used. A patent application regarding this method has been filed and is pending. It is realized that a freeness value is not directly indicative of any quality measure, such as, for example tensile index and light scattering coefficient but the obtained results can be interpreted to be promising. Further studies are needed regarding the impact of the modified chipping process.

  • 9.
    Hellström, Lisbeth M.
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Biller, Sven-Olov
    Andritz Iggesund Tools AB, Iggesund, Sweden.
    Edvardsson, Sverker
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Gradin, Per A.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    A theoretical and experimental study of the circular sawing process2014Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, nr 3, s. 307-312Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To gain further insight into the energy dissipation during the wood sawing process, a theoretical model has been developed. The model is based on the assumption that there are two basic causes for energy dissipation during sawing: the creation of a new surface and the compression of material below a saw tooth. It is assumed that both contributions can be dependent on the cutting angle (the angle between the fiber direction and the tangent to the path followed by a saw tooth) because a saw tooth changes its angle of attack during its way through a log. To determine this dependence of the dissipation on the cutting angle, a series of experiments with pine plank sawing were performed by means of different feeding rates and cutting angles while the electrical power supplied to the saw was measured. The parameters in the theoretical model were derived from the experimental findings. Finally, two tests were carried out under different conditions with respect to thickness and cutting angles and the validity of the model was confirmed concerning the prediction of the electrical power consumption.

  • 10.
    Isaksson, Per
    et al.
    Uppsala Univ, Angstrom Lab, SE-75121 Uppsala, Sweden.
    Gradin, Per A.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hellström, Lisbeth M.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    A numerical and experimental study regarding the influence of some process parameters on the damage state in wood chips2013Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, nr 6, s. 691-696Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The specific energy consumption during mechanical refining operation can be reduced by choosing the optimal process parameters in the wood chipping process such that a beneficial pretreatment is obtained. In the case of the utilization of a larger knife-edge angle, which is one such process parameter, the energy reduction is presumably due to the increased compressive loading parallel to the wood fibers. In the present article, a chip damage parameter D of spruce is in focus, which is relevant for cracking parallel to the fibers. D is defined and its dependence on the chip length and edge angle of the chipping knife is analyzed numerically by means of finite element analyses (FEA). The cutting force was measured in a pilot wood chipper for a number of knife-edge angles. There is a good correlation between the experimental results and those of FEA.

  • 11.
    Moilanen, Carolina
    et al.
    Tampere Univ Technol, Finland.
    Björkqvist, Tomas
    Tampere Univ Technol, Finland.
    Ovaska, Markus
    Aalto Univ, Finland.
    Koivisto, Juha
    Aalto Univ, Finland.
    Miksic, Amandine
    Aalto Univ, Finland.
    Engberg, Birgitta A.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Salminen, Lauri I.
    VTT, Finland.
    Saarenrinne, Pentti
    Tampere Univ Technol, Finland.
    Alava, Mikko
    Aalto Univ, Finland.
    Influence of strain rate, temperature and fatigue on the radial compression behaviour of Norway spruce2017Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, nr 6, s. 505-514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dynamic elastoplastic compression model of Norway spruce for virtual computer optimization of mechanical pulping processes was developed. The empirical wood behaviour was fitted to a Voigt-Kelvin material model, which is based on quasi static compression and high strain rate compression tests (QSCT and HSRT, respectively) of wood at room temperature and at high temperature (80-100 degrees C). The effect of wood fatigue was also included in the model. Wood compression stress-strain curves have an initial linear elastic region, a plateau region and a densification region. The latter was not reached in the HSRT. Earlywood (EW) and latewood (LW) contributions were considered separately. In the radial direction, the wood structure is layered and can well be modelled by serially loaded layers. The EW model was a two part linear model and the LW was modelled by a linear model, both with a strain rate dependent term. The model corresponds well to the measured values and this is the first compression model for EW and LW that is based on experiments under conditions close to those used in mechanical pulping.

  • 12.
    Norgren, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Lindström, Birger
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Dissociation of Phenolic Groups in Kraft Lignin at Elevated Temperatures.2000Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, nr 5, s. 519-527Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dissociation of the phenolic groups in a polydisperse, low molecular weight kraft lignin (Indulin AT) was studied in alkaline aqueous solutions in the temperature interval 21-70°C, using a UV-spectrophotometric method. It was found that at a constant concentration of hydroxide ions, the degree of dissociation was decreasing when the temperature was elevated. Dissociation curves and apparent pK0 values were also calculated for the polydisperse sample at the same conditions, using the van't Hoff and the Poisson-Boltzmann equations. At degrees of dissociation exceeding α ≈ 0.4, the outcome of the theoretical approach showed to be in good agreement with the experimentally obtained results. Furthermore, calculations were performed for different molecular weights of kraft lignin and from this it was found that the apparent pK0 is shifted to higher values by increasing molecular weight, due to an increased electrostatic attraction of the hydrogen ions, which is arising from a less curved surface. Predictions of the dissociation behavior at temperatures reached in the kraft process were performed and under these conditions, higher molecular weight lignin fragments seem never to reach the point of complete dissociation. It was also found that an increase in temperature results in phase separation in kraft lignin solutions with high ionic strengths and pH values close to the pKa of the phenolic groups.

  • 13.
    Norgren, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Lindström, Birger
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Physico-Chemical Characterization of a Fractionated Kraft Lignin2000Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, nr 5, s. 528-534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A kraft lignin was leached from a softwood pulp and fractionated by ultrafiltration. The fractions were characterized in respect to phenolic group content, molecular weight distributions and self-diffusion coefficients. The 1H-Pulsed Field Gradient (PFG) NMR self-diffusion measurements and the High-Pressure Size Exclusion Chromatography (HPSEC) analysis of the fractions, were seen to correlate fairly well. From the self-diffusion measurements, the mass-weighted median hydrodynamic radii of the diffusants in the fractions, were calculated assuming spherical fragments. Furthermore, the content of phenolic groups in the fractions, was found to decrease by increasing hydrodynamic radius and molecular weight, but the calculated median surface charge densities of the macromolecules, were determined to be constant in the range of oligomers up to at least 65 structural units.

  • 14.
    Norgren, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Notley, Shannon M
    Department of Applied Mathematics, ANU, Australia.
    Study of thin films of kraft lignin and two DHPs by means of single-molecule force spectroscopy (SMFS)2012Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, nr 5, s. 615-622Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adhesion of single and associated lignin chains to a substrate has been studied by means of single-molecule force spectroscopy (SMFS). Softwood kraft lignin (KL) and two lignin polymer models (dehydrogenation polymers, DHPs) based on coniferyl alcohol (DHPc.alc.)and coniferaldehyde (DHPc.ald.) were in focus. The desorption force from the "silicon nitride SMFS tip" for the KL was significantly greater than that of the DHPs. The higher desorption force was interpreted as being due to the interaction of carboxyl groups through hydrogen bonding with the tip as well as to the less compact polymeric layer at the interface. The distribution of the extended chain lengths was determined, and self-association of lignin chains was observed. For both KL and the DHPc.ald., chains were extended significantly beyond the limit that would be expected for polymers with the corresponding degree of polymerization. The alpha-carbon on the DHPc.alc. has a strong intramolecular hydrogen bonding interaction with the adjacent aryl ether, which inhibits the possibility of the ether to participate in intermolecular hydrogen bonding with nearby lignin chains. Thus, the self-association for KL and DHPc.ald. was found to be dominated by intermolecular hydrogen bonding with carboxylic groups and aryl ether functionalities.

  • 15.
    Zasadowski, Darius
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Strand, Anders
    Laboratory of Wood and Paper Chemistry, Åbo Academy University, Porthansgatan 3, 20500 Turku, Finland .
    Sundberg, Anna
    Laboratory of Wood and Paper Chemistry, Åbo Academy University, Porthansgatan 3, 20500 Turku, Finland .
    Edlund, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Norgren, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Selective purification of bleached spruce TMP process water by induced air flotation (IAF)2014Inngår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, nr 2, s. 157-165Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The environmentally benign closure of water systems in paper mills leads to the problem of accumulation of dissolved and colloidal wood substances (DCS) in process water. Notably, pitch affects the pulp and paper production negatively and increases the demand for additional treatment of the process water. In the present article, the purification of thermomechanical pulping process water from the alkaline peroxide bleaching stage has been investigated, with the induced air flotation (IAF) in focus. The following parameters were considered concerning the IAF efficiency to remove detrimental substances: concentration of cationic foaming agent, pH value, calcium concentration, and temperature. The amounts and characteristics of residual DCS were determined by gas chromatography and turbidity measurements. Residual concentrations of the foaming agent dodecyltrimetylammonium chloride were determined by electrospray ionization mass spectrometry. Up to 90% of pitch was removed, whereas hemicelluloses, which are important in preventing pitch problems, remained in the waters. Up to 70% of the pectic acids accounted for the high cationic demand of the process waters were removed by optimization of the IAF parameters. The presented separation process gives new opportunities to a selective purification of the process waters.

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