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  • 1. Ala-Kaila, K.
    et al.
    Li, Jiebing
    KTH, Superseded Departments, Pulp and Paper Technology.
    Sevastyanova, O.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Apparent and actual delignification response in industrial oxygen-alkali delignification of birch kraft pulp2003In: TAPPI Journal, ISSN 0734-1415, Vol. 2, no 10, p. 23-27Article in journal (Refereed)
    Abstract [en]

    The time-dependent behavior of material that affects the kappa number of birch kraft pulp was experimentally tested in an industrial, two-stage, oxygen-alkali delignification process. The pulps were leached, and the leached material was divided into four different fractions: the wash loss fraction and the easily leachable, slowly leachable, and stagnant fractions. These fractions were further characterized according to their chemical natures, representing residual lignin, extractives, hexenuronic acids, and other chemical structures contributing to the kappa number of the pulps. The apparent and actual delignification responses in the two reactors and the effects of the leaching operation were thoroughly evaluated based on the behaviors to these different pulp components.

  • 2. Axegard, Peter
    et al.
    Bergnor, Elisabeth
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ekholm, Ulrika
    Bleaching of softwood kraft pulps with H2O2, O3, and ClO21996In: TAPPI Journal, ISSN 0734-1415, Vol. 79, no 1, p. 113-119Article in journal (Refereed)
    Abstract [en]

    Ozone or chlorine dioxide bleaching prior to hydrogen peroxide bleaching greatly improves the performance of the hydrogen peroxide stage. The efficiency is further improved by a chelating treatment immediately after the ozone or chlorine dioxide stage. With an optimal metal ion profile, laboratory bleached (OAZQP) softwood kraft pulps can reach brightness levels above 90% ISO, with 5-10% lower pulp strength properties and bleaching costs comparable to ECF bleaching. It also is possible to obtain full brightness with only hydrogen peroxide provided the metal ion profile is optimal, e.g., by using multiple QP treatments. The chemical consumptions, expressed as oxidation equivalents per decreased kappa number are the same as for sequences including ozone or chlorine dioxide. Ozone and chlorine dioxide are comparable as far as delignification and brightness efficiency go.

  • 3.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The hemicellulose composition of pulp fibres and their ability to endure mechanical treatmentIn: TAPPI Journal, ISSN 0734-1415Article in journal (Refereed)
  • 4.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The hemicellulose composition of pulp fibers and their ability to endure mechanical treatment2007In: TAPPI Journal, ISSN 0734-1415, Vol. 6, no 10, p. 19-24Article in journal (Refereed)
    Abstract [en]

    Two pulps of different hemicellulose content were subjected to high-intensity shear forces in a laboratory mixer to damage the fibers. The, ability of the fibers to resist the mechanical treatment was evaluated by comparing their strength that of undamaged pulps. The study showed that pulp produced at high hydroxide ion concentration, which resulted in lower xylan and, higher glucomannan content, was sensitive to mechanical treatment. The pulp strength decreased, evaluated as tear versus tensile index and as rewetted zero-span tensile index. Pulp with a higher xylan and lower glucomannan content could be subjected to mechanical treatment without losing strength.

  • 5. Buchert, Johanna
    et al.
    Bergnor, Elisabeth
    Lindblad, Gunnar
    Viikari, Liisa
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Significance of xylan and glucomannan in the brightness reversion of kraft pulps1997In: TAPPI Journal, ISSN 0734-1415, Vol. 80, no 6, p. 165-171Article in journal (Refereed)
    Abstract [en]

    The brightness reversion of kraft pulps is caused by the presence of residual lignin, chlorinated extractives, or oxidized carbohydrates. The effect of hemicellulose content, i.e., xylan (I) and glucomannan (II), on the thermal stability of modern bleached kraft pulps was investigated. Different O-delignified hard- and softwood kraft pulps were bleached with different bleaching sequences contg. ClO2, H2O2, or O3. Hemicellulose-degrading enzymes, i.e., xylanase or mannanase, were used for selective removal of the resp. hemicellulose from the pulps, and the role of partially removed I and II on the brightness stability of these pulps was studied. Because of the structure of kraft I, enzymic removal of I also resulted in a decreased carboxyl group content in the pulps, whereas II removal did not affect the carboxyl group content. By decreasing the carboxyl groups in the pulps in conjunction with I removal, the thermal aging of the pulps was significantly decreased. The role of II was less significant. Thus, the uronic acids present in the pulp participate in the brightness reversion of kraft pulps.

  • 6.
    Dogaris, Ioannis
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Lindström, Mikael
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Henriksson, Gunnar
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Critical parameters for tall oil separation I: The importance of the ratio of fatty acids to rosin acids2019In: TAPPI Journal, ISSN 0734-1415, Vol. 18, no 9, p. 547-555Article in journal (Refereed)
    Abstract [en]

    Tall oil is a valuable byproduct in chemical pulping of wood, and its fractions have a large spectrum of applications as chemical precursors, detergents, and fuel. High recovery of tall oil is important for the economic and environmental profile of chemical pulp mills. The purpose of this study was to investigate critical parameters of tall oil separation from black liquor. To investigate this in a controlled way, we developed a model test system using a "synthetic" black liquor (active cooking chemicals OH- and HS- ions), a complete process for soap skimming, and determination of recovered tall oil based on solvent extraction and colorimetric analysis, with good reproducibility. We used the developed system to study the effect of the ratio of fatty acids to rosin acids on tall oil separation. When high amounts of rosin acids were present, tall oil recovery was low, while high content of fatty acids above 60% significantly promoted tall oil separation. Therefore, manipulating the content of fatty acids in black liquor before the soap skimming step can significantly affect the tall oil solubility, and hence its separation. The findings open up chemical ways to improve the tall oil yield. Application: Controlling the ratio of fatty acids to rosin acids in kraft pulping can significantly affect the tall oil separation and improve its yield and quality.

  • 7. Elsander, A.
    et al.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Oxalic acid formation during ECF and TCF bleaching of kraft pulp2000In: TAPPI Journal, ISSN 0734-1415, Vol. 83, no 2, p. 73-77Article in journal (Refereed)
    Abstract [en]

    Formation of oxalic acid during bleaching of softwood kraft pulp was studied. The bleaching agents used were oxygen, hydrogen peroxide, chlorine dioxide, peracetic acid, and ozone. Formation of oxalic acid increased linearly with the reduction in kappa number. However, bleaching with peracetic acid produced less oxalic acid than the other bleaching agents. In ozone bleaching, about one-third of the oxalic acid formed is adsorbed on the pulp and not released until pulp pH is increased during a later stage, where it could combine with calcium ions to produce a calcium oxalate scale.

  • 8. Hoc, Miroslav
    Fiber rising in papers containg mechanical pulp1989In: TAPPI Journal, ISSN 0734-1415, Vol. 72, no 4, p. 165-169Article in journal (Refereed)
  • 9. Krochak, P.
    et al.
    Fasci, Giuseppe Carmine
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Norman, B.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Bridging chemical dosage, mixing quality, and variability in paper sheets2015In: TAPPI Journal, ISSN 0734-1415, Vol. 14, no 5, p. 311-320Article in journal (Refereed)
    Abstract [en]

    In the first part of this work, a series of paper production trials were performed on a forming experimental (FEX) pilot machine to investigate the distribution of additives in the final product. In these trials, a blue color was dosed into the stock before the headbox instead of a retention aid. Fine paper sheets were produced using twin-wire forming. Visual inspection of the sheets revealed surprisingly high levels of variability of the blue color. In the second part, the effect of different dosage nozzle configurations on downstream mixing quality of a single-component, polyacrylamide retention aid was studied using two-phase computational fluid dynamics. A non-Newtonian model for this phase was implemented using rheological parameters obtained through a combination of numerical and experimental analysis. Dosage was made into a turbulent pipe flow under typical industrial approach flow conditions. The effect of the number of dosage points, impingement angle, dosage location, and dosage speed on mixing uniformity was investigated qualitatively and quantitatively. Results from these studies indicate the existence of optimal dosage configurations and point toward strong coupling between chemical addition strategy, mixing quality, and chemical variability in final products. Application: Mills can gain valuable information, including dosage nozzle configuration and dosage conditions, for optimizing mixing of retention aids in the approach flow during paper production.

  • 10. Lucisano, M. F. C.
    et al.
    Martin, Andrew R.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Visualization of liquid-vapor phase change phenomena in impulse technology2006In: TAPPI Journal, ISSN 0734-1415, Vol. 5, no 6, p. 15-21Article in journal (Refereed)
    Abstract [en]

    This paper addresses two unresolved aspects in the physics of impulse technology. In our initial study, we used a modified laboratory platen press to investigate contact phenomena at the interface between the wet web and the hot press. We replaced the heated press platen with a preheated glass plate and used high-speed photography to visualize the interfacial interactions. The results confirm that little or no steam is formed before the point of maximum applied load for contact times typical of industrial pressing operations (25 ms). Steam generation during the nip compression phase could be observed only for pulse lengths well beyond-those encountered in industrially relevant impulse press nips (250 ms). In a complementary study, flashing phenomena were investigated in STFI's FlashLab, an experimental facility for the study of phase-change phenomena in water-saturated porous media. Model experiments under well-defined conditions showed that delamination can be prevented by an appropriate unloading strategy. Moreover, we observed that flashing-assisted displacement dewatering occurred when the hydraulic pressure was released. We discuss its significance for impulse pressing efficiency in this report. Application: Insights from this study will help in the further development and possible commercialization of impulse drying systems.

  • 11. Lucisano, M. F. C.
    et al.
    Petrini, J. B.
    Martin, Andrew R.
    KTH, Superseded Departments, Energy Technology.
    The role of evaporative dewatering in impulse pressing2003In: TAPPI Journal, ISSN 0734-1415, Vol. 2, no 3, p. 26-32Article in journal (Refereed)
    Abstract [en]

    The objective was to link heat transfer to water removal mechanisms, specifically evaporative dewatering, in impulse pressing experiments. Two independent laboratory devices-a platen press and a shoe press-were used to impulse press fiber webs made from softwood bleached kraft (SBK) over a range of basis weights (20 200 g/m(2)). In the platen press experiments, evaporative dewatering was evaluated by comparing the measured heat input to the amount of heat theoretically required to vaporize the water in excess of unheated wet pressing. Evaporative dewatering was found to be most pronounced for lightweight sheets, and enhanced dewatering can be attributed to this mechanism and other high-temperature mechanisms for basis weights above 60 g/m(2). In the shoe press experiments, a composite sheet of five 30-g/m(2) webs was used to evaluate profiles for resulting dryness, density, and water retention value (WRV) in the thickness direction. Evaporative effects were confined principally to the layer directly in contact with the heated surface.

  • 12.
    Martin, Andrew R.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Lucisano, M. F. C.
    Characterizing liquid-vapor phase change phenomena in impulse technology with resistivity probes2006In: TAPPI Journal, ISSN 0734-1415, Vol. 5, no 5, p. 22-26Article in journal (Refereed)
    Abstract [en]

    This study used resistivity probes for the dynamic detection of liquid-vapor phase change inside wet paper webs undergoing impulse pressing. The probes were made from thin copper wires insulated with a high-temperature polymeric material (overall diameter-of 50 mu m). The gap between the exposed ends served as the probe tip. The validity of this technique in impulse pressing experiments was demonstrated in two ways: (1) tests with both dry and wet sheets showed that the probe response was unaffected by the fiber network itself; and (2) heated trials with low applied pressure and long residence times (> 1 s) clearly showed the propagation of a vapor front through the sheet, as predicted by theory. Impulse pressing, experiments were subsequently conducted with a platen press under realistic operating conditions (i.e. surface tempera tures up to 300 degrees C, nip residence times of approximately 25 ms, and maximum applied pressure around 4 MPa). Results show that steam was detected inside the sheet only upon unloading of the hot nip for the layers closest to the heated surface.

  • 13. Nordström, Anders Lars
    et al.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Carlsson, Leif A.
    Influence of gravity on curl of horizontal paper sheets2001In: TAPPI Journal, ISSN 0734-1415, Vol. 84, no 5, p. 73-73Article in journal (Refereed)
    Abstract [en]

    The influence of gravity on the out-of-plane hygroinstability (curl) of horizontal paper sheets was studied analytically and experimentally. Nondimensional parameters describing the relative importance of moisture and gravity on paper deflections are defined. An approximative analysis based on cylindrical bending allows prediction of contact length, taking into account moisture and gravity. Linear and geometrically nonlinear finite-element analyses were performed on sheets resting on a flat horizontal surface. The contact problem was solved using an algorithm incorporated in the finite-element code. Gravity reduced the deflections and flattened the sheet over a contact region that decreases with increasing basis weight. The results indicate that the influence of gravity should be considered when evaluating the curl for horizontal papers of basis weight below 120 g/m2(superscript) and size equal to or larger than A4 (210 mm × 297 mm). Two-ply laboratory sheets of 60- and 100-g/m2(superscript) basis weight were manufactured from bleached chemical pulp. Vertical deflections were measured on horizontal sheets measuring 17 cm × 23 cm. It was found that gravity substantially reduced the deflections and that the sheets flattened in a central contact region. The predicted and experimentally observed deflections agreed within (Plus over Minus)1 mm.

  • 14. Ragauskas, Arthur J.
    et al.
    Lindström, Tom
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Nanocellulose and the future2014In: TAPPI Journal, ISSN 0734-1415, Vol. 13, no 5, p. 5-6Article in journal (Refereed)
  • 15.
    Sevastyanova, Olena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Forsström, A.
    Wackerberg, E.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Bleaching of eucalyptus kraft pulps with chlorine dioxide: Factors affecting the efficiency of the final D stage2012In: TAPPI Journal, ISSN 0734-1415, Vol. 11, no 3, p. 43-53Article in journal (Refereed)
    Abstract [en]

    We investigated the bleaching efficiency of the final chlorine dioxide (D 2) stage in the D 0(EP)D 1D 2 bleaching sequence, focusing on the effect of pH in relation to the bleaching history of pulp samples. The samples used were unbleached kraft Eucalyptus grandis pulps with kappa no. 14.8 and the same pulp oxygen-delignified to kappa nos. 12 and 9.8. The samples were bleached according to the D 0(EP)D 1 sequence to a brightness of about 86% ISO and then submitted to the final D 2 stage under identical conditions (e.g., chlorine dioxide charge, time, temperature, and final pH). The target final brightness was 90.5% ISO. Changes in the kappa number, brightness, viscosity, and contents of hexenuronic acid, 4-O-methylglucuronic acid, and the total amount of carboxylic acid (COOH) groups in pulps were monitored during the bleaching sequence. The final brightness of eucalyptus kraft pulps increased when the terminal pH of the D 2 stage was raised from 3.0 to 6.5. The 90.5% ISO target brightness in the D 2 stage was achieved for all pulps within a pH range of 4.5-6.5, but this required adjusting final pH for individual samples. The optimal pH value with respect to pulp viscosity was between 3 and 5. Despite dissimilar conditions applied in previous bleaching stages, the samples after the D 1 stage revealed similar residual lignin contents as shown by kappa number analysis. The content of hexenuronic acid in the samples, however, varied broadly, from 2 to 26 mmol/kg. Conductometric titration showed different amounts of carboxylic acid groups in pulps after the D 1 stage, of which hexenuronic acid accounted for only a minor part. The variations in the fiber charge resulted from the different bleaching conditions applied before the D 2 stage. The fiber charge affected the alkali demand in the final D 2 stage, whereas variations in the alkali demand affected the initial pH and associated process kinetics. Lower total fiber charge was found to be beneficial for improved final brightening and viscosity when bleached at higher final pH. Application: This study will help pulp mill engineers to better understand how a pulp's oxidative history may affect the process kinetics in the final D bleaching stage. Fiber charge is important when selecting optimal pH for the final brightening of eucalyptus kraft pulps.

  • 16. Taube, Fabian
    et al.
    Shchukarev, Andrei
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Gellerstedt, Göran
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Agnemo, Roland
    Peroxomolybdate catalysts in pulp hydrogen peroxide bleaching: Improvement in hexeneuronic acid removal and delignification2008In: TAPPI Journal, ISSN 0734-1415, Vol. 7, no 3, p. 8-14Article in journal (Refereed)
    Abstract [en]

    We have studied the catalytic effects of peroxomolybdates, i.e., [MoO(O-2)(2)(OH)(H2O)], on hydrogen peroxide bleaching on hardwood and softwood pulps in terms of kappa number reduction, hexeneuronic acid (HexA) removal, and delignification. We found that, in the case of hardwood pulp, the decrease of HexA in the peroxomolybdate bleaching stage corresponds to more than 60% of the kappa number reduction obtained in that stage. In the case of pine pulp, inclusion of molybdate in the peroxide stage lowered the kappa number by 4.1. This work also shows that hydrogen peroxide, in the absence of molybdate, did not react to any noticeable extent with neither the lignin model compounds or HexA, under otherwise similar conditions. In order to investigate the oxidation mechanism, lignin model compounds with different side chain structures were reacted with peroxomolybdate. H-1-NMR revealed that lignin model compounds with double bond structure in conjugation with the aromatic ring has an extreme fast speed to react with the peroxomolybdate catalysts, systems, presumably through hydroxylation reactions. This mechanism was supported by XPS analysis of the pulp samples, in which the activated hydrogen peroxide was found to act in a similar fashion on surface lignin as well. In conclusion, molybdate activated hydrogen peroxide can be considered a very efficient and selective bleaching agent.

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