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  • 1.
    Alfthan, Johan
    KTH, Superseded Departments, Solid Mechanics.
    A simplified network model for mechano-sorptive creep in paper2003In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 29, no 7, p. 228-234Article in journal (Refereed)
    Abstract [en]

    A simplified network model for mechanosorptive creep is presented. The model resembles Cox's model for fibrous materials, but creep and the influence of bonds are included in addition to the elastic behaviour of the fibres. Three different creep laws describing the creep of individual fibres are applied in the simulations of creep of the network. Results from simulations using the model are presented. The influence of the amplitude of moisture content changes is discussed. It is shown that the model may produce macroscopic strains that are linear in stress, even though the creep of the fibres is nonlinear This may explain why both regular creep and mechanosorptive creep at small loads appear to be linear in stress.

  • 2.
    Alfthan, Johan
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    A micromechanical model for mechanosorptive creep in paper2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 3, p. 98-104Article in journal (Refereed)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling, a phenomenon known as mechanosorptive creep or accelerated creep. In this paper stress created at bonds due to anisotropic swelling during absorption and desorption of moisture, in combination with nonlinear creep, are proposed to be the cause for mechanosorptive creep. Two simplifled models are first discussed in order to demonstrate the suggested mechanism. A three-dimensional fibre network model composed of elastic fibres and inelastic bonds is then studied by finite element calculations. The relative sliding in the bonds is described by a nonlinear creep model which, in combination with anisotropic hygroexpansion of the fibres results in accelerated creep of the network.

  • 3.
    Asplund, G
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Norman, Bo
    KTH, Superseded Departments, Pulp and Paper Technology.
    Fibre orientation anisotropy profile over the thickness of a headbox jet2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 8, p. 217-221Article in journal (Refereed)
    Abstract [en]

    The fibre orientation anisotropy at various levels of the jet from a model headbox has been investigated. Stiff nylon fibres, 3 mm long, were added at extremely low concentrations to make it possible to observe also the centre of the jet. This meant that fibre interactions, such as floc forming, could not take place. Transparent, parallel walls enclosed the jet where fibre orientation was measured. A thin laser sheet illuminated the jet from the side and a video camera captured the light reflected perpendicularly from the fibres. Using image analysis, the orientation of the fibres was evaluated. A central vane was mounted in the headbox nozzle so the effects of the vane wake could be studied. The results show that the effect a the boundary layers, at the walls of a headbox and at the surface of a vane, was to locally reduce fibre orientation anisotropy. Depending on the vane tip shape, fibre orientation anisotropy could be additionally decreased. Overall, the fibre orientation anisotropy was weakly affected by changes inflow rate and strongly dependent on the contraction ratio in the nozzle; low speed and large contractions produced more anisotropic orientations.

  • 4. Axelsson, P.
    et al.
    Berggren, R.
    Berthold, F.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Molecular mass distributions of lignin and lignin-carbohyd rate complexes in birch Kraft pulps: Changes caused by the conditions in the cook and their relation to unbleached pulp brightness and bleachability2005In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 31, no 1, p. 19-27Article in journal (Refereed)
    Abstract [en]

    Lignin-carbohydrate complexes and their relationship to pulp bleachability and unbleached pulp brightness were studied in four birch kraft pulps produced at high and low hydroxide ion and sodium ion concentrations, using size-exclusion chromatography (SEC). About 75-80%of the lignin was found to be associated with carbohydrates, a larger part with hemicelluloses and a smaller part with cellulose. Easily bleached pulps, produced under high [OH-] or low [Na+] conditions, had more lignin associated with cellulose than their counterparts. Furthermore, a high [OH-] gave a residual lignin that was significantly more accessible in the residual lignin isolation, and where the inaccessible lignin was bonded to carbohydrates. Colour differences of pulps caused by variations in the cooking conditions, as studied in the SEC system, were associated with all the lignin, irrespective of whether it was associated with hemicelluloses or cellulose.

  • 5.
    Axelsson, Patrik
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Condensation reactions of lignin during birch Kraft pulping as studied by thioacidolysis2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 12, p. 317-322Article in journal (Refereed)
    Abstract [en]

    The influences of kappa number and ionic strength during birch kraft cooking on the extent of lignin condensation have been studied using thioacidolysis and size exclusion chromatography. Thioacidolysis degrades alkyl-aryl ether bonds in lignin while leaving carbon-carbon and diaryl-ether bonds relatively intact. Therefore, the lignin structures not cleaved during thioacidolysis can be considered as relatively stable and may account,, for example,for the slow residual phase delignification in the kraft cook and for differences in bleachability. It was shown that condensed lignin structures are formed in the residual lignin during birch kraft cooking. The relative amount of such structures increased with decreasing kappa number or with increasing sodium ion concentration in the cook. These structures were also found in a xylan-lignin complex isolated from a birch kraft pulp. The condensed structures were only partly reactive during oxygen delignification.

  • 6.
    Danielsson, Lars-Göran
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Chai, S
    Behm, Mårten
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Renberg, Lars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    UV characterization of sulphide-polysulphide solutions and its application for process monitoring in the electrochemical production of polysulphides1996In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 22, no 6, p. J187-J191Article in journal (Refereed)
    Abstract [en]

    The UV spectral characteristics of some sulphur species of relevance for the electrochemical production of polysulphides have been studies. It was found that an isosbestic point exists in the hydrogen sulphide ion-polysulphide solution. The absorption at this point (249 nm) is proportional to the total sulphur concentration in the solution. The investigation also shows that the spectrum of a polysulphide solution can be regarded simply as the sum of contributions from charges hydrogen sulphide ion and zero-valent sulphur in polysulphides although a complicated equilibrium distribution of different species exists in the polysulphide solution. The spectrum provides enough information for the measurement of these forms of sulphur. Based on spectrophotometric measurements, a simple monitoring for changed hydrogen sulphide ion and polysulphide excess sulphur in the process liquor can be realized.

  • 7. Endres, I.
    et al.
    Vomhoff, H.
    Ström, Göran
    Microscale compression uniformity measurements on coated paper surfaces2005In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 31, no 2, p. 84-89Article in journal (Refereed)
    Abstract [en]

    This paper introduces a new static sensor technique that characterizes local pressure distributions on paper surfaces tinder compression. Contact areas and local pressure variations are determined using a high-resolution pressure-sensitive film, which has been developed recently at STFI-Packforsk. Compared to other commercially available pressure-sensitive films, this new film brings the advantages of a higher spatial resolution (3 pm) and a wider pressure range (1-100 MPa), which are necessary for analyzing a microporous material such as paper. The technique provides clear images of fine details such as fibre walls, collapsed lumens and fibre crossings. In initial experiments, a measure for the load coverage ability of a coating was obtained. It gives insight into how well a coating layer covers the nonuniformity of the base paper under compression. In future, the applicability of the technique will be tested in the fields of coating, calendering and printing.

  • 8. Gartner, A.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Oxidation of residual lignin with alkaline hydrogen peroxide. Part 1: Changes in hydrophilic groups2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 12, p. 448-454Article in journal (Refereed)
    Abstract [en]

    Residual lignin was isolated from an oxygen-bleached softwood kraft pulp and subjected to oxidation with alkaline hydrogen peroxide in order to study how the degradation of the lignin is influenced by parameters such as time, temperature, addition of stabilizing agents and metal ions. The oxidized lignin samples were analyzed with respect to carboxyl and phenolic hydroxyl content. It was found that the peroxide treatment resulted in a rapid increase in the amount of carboxyl groups, presumably due to the elimination of chromophoric groups. Phenolic hydroxyl groups in the lignin required a higher temperature to be oxidized and this led to the formation of more carboxyl groups. The presence of DTPA and/or Mg (II) stabilized the hydrogen peroxide against decomposition and suppressed the degradation of phenolic groups, while the carboxyl groups remained the same. The addition of transition metal ions to the reaction system resulted in a rapid decomposition of hydrogen peroxide but also in a rapid formation of carboxyl groups and a degradation of the lignin.

  • 9. Gartner, A.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Oxidation of residual lignin with alkaline hydrogen peroxide. Part II: Elimination of chromophoric groups2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 7, p. 244-248Article in journal (Refereed)
    Abstract [en]

    Isolated residual lignin from art oxygen-bleached kraft pulp was subjected to oxidation with alkaline hydrogen peroxide under different time and temperature conditions in both the absence and presence of stabilizing agents and transition metal ions. The resulting lignin samples were analyzed by UV/VIS and FTIR spectroscopy. The analyses demonstrate the occurrence at a temperature as low as 50 degreesC: of a rapid but limited elimination of chromophoric groups, resulting in the formation of carboxyl groups. The presence of DTPA and magnesium ions stabilizes the hydrogen peroxide towards decomposition and the chromophore elimination is improved. At a higher oxidation temperature, 80 degreesC, the effect of added stabilizer(s) is particularly pronounced. Addition of transition metal ions resulted in a rapid decomposition of hydrogen peroxide and the introduction of new chromophoric groups.

  • 10. Girlanda, O.
    et al.
    Hallbäck, N.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Tryding, J.
    Defect sensitivity and strength of paperboard in out-of-plane tension and shear2005In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 31, no 2, p. 100-104Article in journal (Refereed)
    Abstract [en]

    This paper considers the effects of defects in the form of cracks on the failure properties in the thickness direction of multilayered board. The objective was to study how the peak stress value changes with various crack lengths under various load conditions. Specimens with manufactured cracks cut parallel to the machine-direction-cross-machine-direction plane were glued in the Arcan device and tested under pure tensile stress and mixed shear-tensile stress. The lower peak out-of-plane tensile stress measured in damaged samples indicates a defect sensitivity in multilayered board. The results for one type of board show that the loss in tensile strength is independent of the crack length. On the other hand, mixed shear and tensile stress behaviour does not appear to be influenced by the presence of cracks.

  • 11. Granberg, H.
    et al.
    Rundlof, M.
    Mattsson, Lars
    KTH, Superseded Departments, Production Engineering.
    Influence of surface-induced nonuniform reflectance on the diffuse reflectance factor. Part I: Model predictions2003In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 29, no 8, p. 247-253Article in journal (Refereed)
    Abstract [en]

    The Kubelka Munk (KM) model is used frequently as a tool to design paper to reach a desired opacity and whiteness. The input data in this modelling, the scattering and absorption coefficients, are commonly derived from diffuse reflectance factor measurements. The quality of the coefficient values is dependent on the structure of the samples and the backings from which they were obtained. In this paper we focus on modelling the influence of nonflectance factors obtained using the d/0degrees standardized uniform reflectance induced by the surface structure, and how it affects the diffuse reflectants factors obtained using the d/0degrees standardized measurement geometry. From the analysis, we conclude that the structure of the surface facing the detector may have a significant effect on the instrument readings depending on whether the sample is glossy or reflects diffusely from the surface. Based on this surface reflectance, we analyze various situations of relevance for the papermaker and show that common-practice application of the KM model to reflectance factor measurements may lead to serious misinterpretations.

  • 12. Granberg, H.
    et al.
    Rundlof, M.
    Mattsson, Lars
    KTH, Superseded Departments, Production Engineering.
    Influence of surface-inducled nonuniform reflectance on the diffuse reflectance factor. Part II: Experimental verification on coated substrates2003In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 29, no 8, p. 254-259Article in journal (Refereed)
    Abstract [en]

    Many authors have found that the Kubelka-Munk (KM) scattering coefficient, s(c), of a coating applied to a substrate decreases with increasing coat weight. This decrease is usually explained by a structural/porosity change with coating thickness or a penetration of the coating into the paper In this paper we propose an alternative explanation to the observed decrease in sc, namely the misinterpreted diffuse reflectance factors for non-Lambertian reflecting substrates and coatings. This explanation was recently proposed by the authors; the second part presented here provides experimental support for the presence of a nonuniform reflectance distribution and its influence on KM fitted data. Three different coated systems are considered, using a transparent film, abase paper and a synteape film as substrate. The effect of the surface reflectance of the substrate and of the coated substrate can explain the apparent decrease in sc as an artifact when measuring a sample with an instrument having a d/0degrees geometry.

  • 13.
    Gustafsson, Roland
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Polysulphide pretreatment of softwood for increased delignification and higher pulp viscosity2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 5, p. 129-135Article in journal (Refereed)
    Abstract [en]

    The effect of polysulphide pretreatment under various conditions prior to a kraft cook was investigated for spruce (Picea abies) chips using a technique with a liquor:wood ratio of 67:1 to keep the liquor composition as constant as possible during the pretreatment and cooking phases. If the polysulphidepretreatment is carried out at a very high hydroxide concentration, 1.5 mol OH-/L, three independent positive effects (compared with a corresponding sulphide pretreatment without polysulphide) can be observed: more extensive delignification; higher pulp, viscosity; and higher carbohydrate yield. When the alkali change was changed in the subsequent kraft cook (in the range 0.15-0.60 mol/L), the increase in delignification extent as a result of polysulphide pretreatment was not affected but the relative carbohydrate yield increase was favoured by a higher alkali charge during cooking. On the other hand, the absolute carbohydrate yield is favoured by a intermediate alkali charge.

  • 14. Johansson, E. E.
    et al.
    Lind, Johan
    KTH, Superseded Departments, Chemistry.
    Ljunggren, S.
    Aspects of the chemistry of cellulose degradation and the effect of ethylene glycol during ozone delignification of kraft pulps2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 7, p. 239-244Article in journal (Refereed)
    Abstract [en]

    The viscosities of oxygen-predelignified kraft pulps were measured as they were ozonated at high consistency. The degree of degradation of thc cellulose was calculated from the viscosities as direct (ds) and indirect, alkali-induced, scissions (als) in the polymer: Als was derived using the decrease in the observed degradation when a borohydride reduction preceded the alkaline extraction of the ozonated pulps. The mechanism of these Scissions is discussed in terms of free-radical reactions and their relative significance. A given charge of ozone to a lignin-containing or lignin-free pulp produced similar degrees of carbohydrate degradation, indicating that the degradation does not depend greatly on the presence of the lignin in the pulp. Ethylene glycol (EG) increases the selectivity during ozone delignification much more than methanol. This effect is optimal at pH3 and 25 wt% EG in the reaction system. The increased selectivity may have several possible reasons. one is the limited extent of free-radical reactions (e.g. hydroxyl radicals) occurring in the carbohydrate chain.

  • 15.
    Johansson, Erik
    et al.
    KTH, Superseded Departments, Chemistry.
    Lind, Johan
    Ljunggren, Sten
    Aspects on the chemistry of cellulose degradation and the effect of ethylene glucol duringozone delignification of kraft pulps2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220Article in journal (Other academic)
  • 16.
    Ko, Jordan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Zahrai, Said
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Simulating single-phase swirling flows in hydrocyclones2007In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 3, p. 133-137Article in journal (Refereed)
    Abstract [en]

    This study aims to develop a numerical methodology for modelling single-phase hydrocyclone flows without employing empirical model modifications. Its final application to the design of novel hydrocyclones requires it to be accurate for diverse geometries and operating conditions. Different solution methods offering increasing degrees of solution accuracy and requiring different lengths of simulation time were developed. When used together appropriately, these methods provide timely and valuable information suitable for various stages qf the hydrocyclone design cycle.

  • 17.
    Li, Jiebing
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Rapid and direct pulp kappa number determination using spectrophotometry - Comments2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 4, p. 111-111Article in journal (Refereed)
  • 18.
    Li, Jiebing
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Sevastyanova, Olena
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Fibre and Polymer Technology.
    The relationship between kappa number and oxidizable structures in bleached kraft pulps2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 8, p. 262-266Article in journal (Refereed)
    Abstract [en]

    The relationship between residual oxidized lignin structures in spruce and birch kraft pulps and their kappa number contribution after each stage in an ODEQP (spruce) and an OQ(OP)Q(PO) (birch) sequence, respectively, has been investigated. Analysis by a modified kappa number method (OxDem kappa number) as well as by determination of permanganate oxidation equivalents on various isolated residual lignin samples revealed that the relationship between the lignin content and kappa number gradually changes as the bleaching sequence proceeds, giving values that differ substantially from that found in unbleached kraft pulp. These effects can be attributed to the successive oxidative fragmentation of aromatic rings and the formation of carboxyl and non-aromatic unsaturated structures in the residual lignin structure. Therefore, a kappa number determination on pulp which has been subjected to an oxidative stage will result in an underestimation of the lignin content.

  • 19.
    Lindgren, C. T.
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael E.
    KTH, Superseded Departments, Pulp and Paper Technology.
    The kinetics of residual delignification and factors affecting the amount of residual lignin during kraft pulping1996In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 22, no 8, p. J290-J295Article in journal (Refereed)
    Abstract [en]

    Kraft pulping of softwood can be divided into three phases: the initial, the bulk and the residual delignification phases. The rate of delignification in the residual phase and the amount of lignin to be removed in this slow phase have been studied as a function of the conditions in the kraft cooking of Norwegian spruce chips, Picea abies. The variables studied were concentration of OH-, concentration of HS-, ionic strength and temperature. The amount of lignin remaining undissolved in the wood residue at the transition from bulk to residual delignification is decreased by increasing the concentration of OH- and by increasing the concentration of HS- in the bulk phase. The amount of residual lignin is also decreased by a lower ionic strength in the bulk phase. The temperature in the range of 150 to 180 degrees C affected the lignin content at the transition from bulk to residual delignification but not the amount of residual lignin extrapolated to the beginning of the cook. Only the hydroxide ion concentration and the temperature seem to have an influence on the rate of delignification in the residual phase. The rate of delignification in the residual phase is well described by the following equation: dL(r)/dt = (0.0032 + 0.0020 . [OH-]) (. e) -146 000/8.314 . (1/T - 1/443.15)(Lr).

  • 20.
    Nordström, A.
    et al.
    Mo Och Domsjö AB, Research and Development.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Carlsson, L. A.
    Dept. Mech. Engin., Florida Atlantic Univ..
    Influence of sheet dimensions on curl of paper1998In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 24, no 1, p. 18-25Article in journal (Refereed)
    Abstract [en]

    Out-of-plane hygroinstability (curl) of cross-plied square paper sheets made from bleached chemical pulp has been studied analytically and experimentally. Theoretically, it is shown that nonlinear kinematics and bifurcation response must be accounted for in the analysis of curl in paper. Furthermore, a dimensionless formulation of the governing plate equations for the curl curvatures revealed that a single dimensionless loading parameter controls the curl characteristics. Cross-ply sheets of various dimensions were manufactured from bleached chemical pulp to experimentally examine the curvatures and verify analytical results. Measured changes in curvatures were compared with predictions from linear and nonlinear laminate theory and nonlinear finite element analysis. Good overall agreement was observed between analytical and numerical results and between measured and calculated curvature changes.

  • 21. Norgren, Magnus
    et al.
    Edlund, H.
    Nilvebrant, N. O.
    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.

  • 22. Nygards, Mikael
    et al.
    Fellers, C.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Measuring out-of-plane shear properties of paperboard2007In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 2, p. 105-109Article in journal (Refereed)
    Abstract [en]

    Two experimental procedures were used to test the shear properties of three paperboards. First, a douhle-notch shear specimen was used. In this test, an in-plane tensile test specimen was utilized. To generate a shear test from the specimen, two notches were cut through the specimen, one from each side of the specimen. This test procedure is simple and easily can be used for production control. Second, a rigid-block shear test was used. In this test, the paper boards were glued with photo-mounting tissue between two steel blocks. The specimen was tested with displacement control in an MTS system. From both shear tests, maximum shear stresses were calculated and compared. It was shown that reproducible results were achieved by both methods.

  • 23. Rundlof, M.
    et al.
    Htun, M.
    Hoglund, H.
    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.

  • 24. Rundlof, M.
    et al.
    Htun, M.
    Hoglund, H.
    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.

  • 25.
    Seppänen, Rauni
    et al.
    KTH, Superseded Departments, Chemistry.
    von Bahr, Maria
    KTH, Superseded Departments, Chemistry.
    Tiberg, F.
    KTH, Superseded Departments, Chemistry.
    Zhmud, B.
    KTH, Superseded Departments, Chemistry.
    Surface energy characterization of AKD-sized papers2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 3, p. 70-73Article in journal (Refereed)
    Abstract [en]

    Experimental papers with varying alkylketene dimer load were prepared and characterized with respect to size retention, reaction and hydrolysis. The characterization was done by using extraction studies, in combination with X-ray photoelectron spectroscopy and gas chromatography. The surface energy of the produced papers was evaluated using the Good-Oss method. It was shown that by stepping up size additions, both the polar and van der Waals components of the surface energy are reduced.

  • 26.
    Sjödahl, Ragnar
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    The influence of industrial black liquor on the delignification rate in the kraft cooking2007In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 4, p. 240-245Article in journal (Refereed)
    Abstract [en]

    The effect of dissolved wood components in industrial black liquor on the rate of delignification in softwood kraft cooking has been studied The results show that, when industrial black liquor was added, the delignification rate increased significantly during the bulk phase and decreased during the residual phase. A softwood black liquor was fractionated with ceramic membranes with various cut-offs, to see the way the addition of various molecular weight fractions of the black-liquor lignin affected the delignification rate. The results show that the delignification rate is dependent more on the content of phenolic groups than on the size of the lignin fragments. However, a low molecular-weight lignin fraction has a higher content of phenolic groups than a high molecular-weight fraction does. These results may explain one reason for the positive effect of adding industrial black liquor to the bulk phase of a softwood kraft cook.

  • 27.
    Sjöstrom, Karin
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Changes within the modified kraft process aiming to improve TCF bleachability1999In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 25, no 5, p. 176-182Article in journal (Refereed)
    Abstract [en]

    the investigated process modifications were: presulphonation, postsulphonation, polysulphide pretreatment and polysulphide pretreatment combined with a postsulphonation. The influence of the degree of delignification in the cook, on the selectivity and bleachability, was also investigated. The pulps were produced from softwood chips and were oxygen delignified before bleaching according to an AZQP sequence. All the investigated process variants had better process selectivity (pulp viscosity at a given brightness) and the pulps produced with a postsulphonation showed better bleachability, than the reference pulp. The bleachability and the process selectivity was improved by interrupting the cook at a higher kappa number and instead extending the delignification in the oxygen stage.

  • 28. Solberg, D.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    On the mechanism of GCC filler retention during dewatering - New techniques and initial findings2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 6, p. 183-188Article in journal (Refereed)
    Abstract [en]

    The main objective of this present investigation was to clarify the mechanism of ground calcium carbonate (GCC) retention during dewatering through a thick pad of pulp fibres. The effect of filtration was studied by examining the filler particle size distribution before and after filtration of a filler suspension through a thick pad of pulp fibres. Changes in the wet-web pore size distribution in beds with and without filler were measured by liquid porosimetry. The filler distribution through the bed was obtained in SEM micrographs. The results indicate that deposition on fibres is the dominant process. for the retention of commercial GCC particles with a mean particle size of 0.6 and 0.8 pm. Effects of filtration (sieving) were marginal even though experimental conditions (laminar flow and a very high grammage) were chosen to favour such a process.

  • 29. Stenberg, N.
    et al.
    Fellers, C.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Measuring the stress-strain properties of paperboard in the thickness direction2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 6, p. 213-221Article in journal (Refereed)
    Abstract [en]

    In this paper, a device for measuring stress-strain properties in the thickness direction of paperboard is presented. The device is used for out-of-plane tensile, compression and shear loading. In order to measure stress and strain accurately: the deformation of the test piece is restricted to two directions in the desired plane of deformation by means of an attached fixture. The paperboard is first glued io metal blocks with a high-viscosity adhesive and these blocks are then attached ro the device using a fast-curing epoxy adhesive. To find the true strain in the material, knowledge of the penetration nf the adhesive into the surface of the paper structure is important. A method for determining the penetration of the adhesive, based on a comparison of stress-deformation curves for glued and non-glued rest pieces, is presented, Finally: true stress-strain curves in tension, compression, and shear are presented together with an analysis of the accuracy of the method.

  • 30.
    Stevanic Srndovic, Jasna
    et al.
    STFI-Packforsk, Swedish Pulp and Paper Research Institute.
    Salmén, Lennart
    STFI-Packforsk, Swedish Pulp and Paper Research Institute.
    Interactions among Components in the Primary Cell Wall of Norway Spruce (Picea Abies (L.) Karst.): Effect of a Low Sulphonation Pretreatment2008In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 34, no 2, p. 107-112Article in journal (Refereed)
    Abstract [en]

    Dynamic Fourier Transform Infra-Red (FT-IR) spectroscopy was used to examine the effect of a low sulphonation treatment on the ultrastructure of the primary cell wall of spruce wood. Sheets made from enriched primary cell wall material coming from a low sulphonated thermomechanical pulp were used for studying the viscoelastic response of the polymers using dynamic FT-IR spectroscopy. The overall ultrastructure of the primary cell wall remained largely unaltered, due to the exceptionally low degree of sulphonation used. However, an increased softening of the material as well as a weakening of the lignin,pectin, lignin, protein and pectin, protein interactions were observed. The suggestion is that, together with a structural modification of the lignin, it is the increased viscoelasticity of the material, resulting from the breaking down of the interactions among the polymers, that is the cause for the lower energy demand, when refining correspondingly low sulphonated chips.

  • 31.
    Söderberg, L. Daniel
    et al.
    KTH, Superseded Departments, Mechanics.
    Alfredsson, P. Henrik
    KTH, Superseded Departments, Mechanics.
    Experiments concerning the origin of streaky structures inside a plane water jet2000In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 26, no 11, p. 395-400Article in journal (Refereed)
    Abstract [en]

    It is believed that the characteristics of a headbox jet are of vital importance for the formation in the final paper sheet. To better understand the physics of free, plane liquid jets, experiments have been made with wafer emanating from two different nozzles: a plane channel flow nozzle where viscous effects are of importance; and a slid nozzle, which closely approximates art inviscid jet. Both types of flow have been visualized and the visualization of the jet emanating from a channel showed that a strong streamwise streaky structure was created inside the jet a distance downstream the nozzle. These streaks do not originate from the nozzle but instead from the break-lip of two-dimensional waves on the jet travelling in the streamwise direction. This streaky structure could not be found at any velocity (<15 m/s) in the jet from the slit nozzle.

  • 32.
    Teder, Ants
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Sjöstrom, Karin
    KTH, Superseded Departments, Pulp and Paper Technology.
    A comparison of bleachability in TCF sequences for alkaline sulphite and kraft pulps1996In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 22, no 8, p. J296-J300Article in journal (Refereed)
    Abstract [en]

    The bleachability in different totally chlorine-free (TCF) bleaching sequences was investigated for two types of alkaline sulphite pulps, ASAM and MSSAQ, and compared with that of pulps produced by different new and industrially applied modified kraft pulping processes. The TCF sequences included oxygen, ozone, peroxide and complexing agent stages. The alkaline sulphite pulps were found to be easier to bleach in terms of the consumption of oxidative agents required to reach a given brightness than the pulps produced by the different modified kraft pulping processes. The relationship between pulp brightness and pulp viscosity was also much better for the sulphite pulps, although the new types of kraft pulps are gradually approaching the level of the alkaline sulphite pulps in this respect. There was no significant difference between the ASAM (alkaline sulphite anthraquinone methanol) and the two-stage MSSAQ (minisulphide sulphite anthraquinone) processes.

  • 33. Toven, K.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Kleppe, R.
    Moe, S.
    Use of chlorine dioxide and ozone in combination in prebleaching2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 9, p. 305-310Article in journal (Refereed)
    Abstract [en]

    (DZ)Eo prebleaching of oxygen-delignified softwood kraft pulp gave a synergistic delignification effect compared to the effect of chlorine dioxide and ozone Separately, and the (DZ)Eo process was somewhat better than (ZD)Eo prebleaching in terms of delignification. The solubilization of the lignin in chlorine dioxide and ozone bleaching seems to be governed by the large number of carboxyl groups introduced into the lignin structure. The efficient delignification obtained in (DZ)Eo prebleaching may be explained by the ability of chlorine dioxide and ozone to degrade different Apes of lignin structures. Whereas chlorine dioxide mainly degrades phenolic lignin structures, ozone is capable of degrading both phenolic and non-phenolic lignin structures. The (DZ) treatment initially allows chlorine dioxide to degrade the phenolic lignin structures, and leaves the non-phenolic and less reactive lignin structures for the ozone treatment.

  • 34. Viforr, Silvia
    et al.
    Salmén, Lennart
    Optimal shear/compression forces: a way of collapsing coarse TMP fibres2007In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 1, p. 22-28Article in journal (Refereed)
    Abstract [en]

    Fundamental studies of wood have indicated that, with a proper combination of shear and compression forces, it might he possible to collapse wood fibres effectively. To study the applicability of such a combination of shear and compression forces for fibre deformation, a laboratory device for carrying out tests continuously on coarse fibre mats was constructed. Coarse mechanical pulp fibres in the form of sheets were fed through the device, applying differential speeds on two rolls for providing various combinations of shear and compression forces. With the application of a limited shear force, as compared to the compression forces, fibre collapse and bonding could he improved with only a limited amount of work. This indicates a potential for improved paper strength properties in mechanical pulp fibres. Reducing the speeds of the rolls and increasing the temperature proved to he favourable for improving fibre collapse.

  • 35.
    Wärja, Mathias
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Björkqvist, O.
    Evaluation of a Condition Based Index Supporting System Reliability and Maintenance Decisions2005In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220Article in journal (Other academic)
  • 36.
    Wågberg, Lars
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Forsberg, S.
    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.

  • 37. Zhang, J.
    et al.
    Pelton, R.
    Wågberg, Lars
    Rundlof, M.
    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.

  • 38.
    Östlund, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Carlsson, Leif
    Fellers, Christer
    Residual stresses in paperboard through the manufacturing process2005In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 31, no 4, p. 197-201Article in journal (Refereed)
    Abstract [en]

    The residual stresses in a machine-made multi-ply board with chemical pulp in all plies were monitored as the board progressed after the initial drying through calendering, moisture treatments and coating. After drying, the stresses were compressive near the surfaces. In the coated board at the end of the machine, the stress state was reversed to a large extent with tensile stresses in the outermost layers. The various moisture applications on the board in the post-processing steps are regarded to have caused the change in the residual stress state. In another machine-made board, with mechanical pulp in the middle plies, the stresses after drying were limited to the surface plies made from chemical pulp, but were again compressive at the surfaces. This stress state was largely unaffected by post-processing. The possibility for stress reversal and the implications on in-plane and out-of-plane dimensional stability of the boards are discussed.

  • 39.
    Östlund, Magnus
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Carlsson, Leif
    Fellers, Christer
    The influence of drying conditions on residual stress build-up in paperboard2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 11, p. 312-316Article in journal (Refereed)
    Abstract [en]

    The through-thickness distributions of in-plane residual stress have been determined for some laboratory-made paperboards. The effects of drying variables such as temperature, moisture flow resistance at the surfaces and thickness of the boards on residual stresses were studied. The drying rate was shown to influence residual stresses only for relatively slow drying. Residual stresses correlate well with the moisture gradient during drying for various drying methods. Some effects of the drying conditions on paper tensile stiffness are discussed. One-sided heating for curl control is also discussed.

  • 40.
    Östlund, Magnus
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Carlsson, Leif
    Fellers, Christer
    The influence of drying restraints and beating degree on residual stress build-up in paperboard2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 11, p. 289-293Article in journal (Refereed)
    Abstract [en]

    The through-thickness distribution of in-plane residual stress has been determined for laboratory-made paperboards, to study the causes of these stresses. The degree of restraint during drying is shown not to influence the residual stresses in a significant way. However, a higher level of beating of the pulp leads to higher residual stresses. The drying gradient through the sheet combined with the shrinkage of paper as moisture content decreases is suggested as the main reason for residual stress build-up. No effect an free shrinkage was seen when attempting to limit the drying gradients by decreasing the grammage.

  • 41.
    Östlund, Sören
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Niskanen, Kaarlo
    KCL.
    Kärenlampi, Petri
    University of Helsinki.
    On the prediction of the strength of paper structures with a flaw1999In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 25, no 10, p. 356-360Article in journal (Refereed)
1 - 41 of 41
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