Change search
Refine search result
1234 1 - 50 of 193
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Al-Dajani, W. W.
    et al.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    On the isolation and structure of softwood residual lignins2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 2, p. 193-198Article in journal (Refereed)
    Abstract [en]

    Different softwood residual lignins were isolated by acid hydrolysis of kraft and soda Pulps. Complete isolation of lignin Could not be achieved in one hydrolysis step. The yield of lignin varied between 35 and 55%. A more acidic, second hydrolysis step was therefore necessary to isolate almost all the lignin remaining in the Pulp residue, giving a total lipin yield of 91%. Alkaline extraction of the pulp was almost as efficient as acid hydrolysis in isolating residual lignins. However, alkaline extraction gave less pure lignin fractions and there was a clear indication of the existence of lignin-carbohydrate bonds. Pine wood meal was acid-hydrolyzed in the same way as the pulps. After two-stage acid hydrolysis, the combined lignin yield was only 45% of the Klason lignin content, which means that native lignin is more difficult to isolate front wood than residual lignin front a chemical pulp. It is Concluded that the difficulty encountered in isolating residual lignin by acid hydrolysis is a problem of limited accessibility due to a complex carbohydrate network surrounding the lignin.

  • 2.
    Ali, Silvia
    et al.
    STFI-Packforsk, Stockholm, Sweden .
    Salmén, Lennart
    From wood shavings to mechanical pulp - a new raw material?2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, ISSN 0283-2631, Vol. 20, no 4, p. 418-422Article in journal (Refereed)
    Abstract [en]

    Wood chips used in the thermomechanical pulping (TMP) process were originally designed to suit the chemical pulping process. The production of small wood pieces more suitable for the TMP process could lead to an energy saving in this energy-intensive process. This paper discusses the potential benefits of using wood shavings instead of chips as the raw material for TMP production. In some exploratory trials, wood shavings with a thickness of about 2 mm and wood chips were refined in two steps under normal TMP process conditions in a pilot refiner. The first-stage refining was performed under pressurized conditions at 130°C. The second-stage refining was performed at atmospheric pressure at approximately 100°C at four different energy levels. The quality of the pulp produced from wood shavings was found to be better than that of the pulp produced from wood chips, with respect to both strength properties (except tear index) and optical properties at comparable energy levels. The potential for energy savings at a given tensile index using wood shavings instead of the traditional chips is estimated to be about 25%.

  • 3. Alm, Hajer Kamal
    et al.
    Ström, Göran
    Karlström, Katarina
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Schoelkopf, Joachim
    Gane, Patrick A. C.
    Effect of excess dispersant on surface properties and liquid interactions on calcium carbonate containing coatings2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 1, p. 82-92Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to identify what effects excess amount of sodium polyacrylate, a commonly used dispersant, has on the coating properties and the interaction between ink and the paper coating in offset printing. Since polyacrylate strongly interacts with calcium ions, soluble calcium salt was added to some coating colours to illustrate the impact of charge neutralization by calcium ions. It was found that the coating structure was only slightly affected by the extra addition of polyacrylate, showing some weak flocculation, whereas the surface chemistry was strongly influenced. The coatings became more polar and interacted more strongly with water. This resulted in slower ink setting and reduced ink-paper coating adhesion, especially in the presence of applied water/dampening solution, which are identified as contributory factors in ink piling and print mottle.

  • 4.
    Anderfors, Mikael
    et al.
    Innventia AB, Sweden.
    Llindström, Tom
    Innventia AB, Sweden.
    Söderberg, Daniel
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Innventia AB, Sweden.
    The use of microfibrillated cellulose in fine paper manufacturing: Results from a pilot scale papermaking trial2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 3, p. 476-483Article in journal (Refereed)
    Abstract [en]

    In this work the strength enhancing capabilities of microfibrillated cellulose (MFC) in highly filled papers was studied. Both the MFC production and the paper making were done in pilot scale under realistic industrial conditions. The results clearly show that MFC (2.5 - 5.0wt-%) could improve the mechanical properties of highly filled papers (20 - 35 wt-% filler contents). All studied dry mechanical properties were improved and the improvements were most pronounced for Z-strength and fracture toughness. By combining the MFC with a C-starch dosage further improvements in mechanical properties could be achieved. The improvements in mechanical properties enabled increased filler content with retained properties. The filler increase could be achieved at the same time as the sheet formation and the dry content after pressing were improved.

  • 5. Andersson, Kerstin I.
    et al.
    Pranovich, Andrey V.
    Norgren, Magnus
    Eriksson, Marie
    Holmbom, Bjarne
    Effects of biological treatment on the chemical structure of dissolved lignin-related substances in effluent from thermomechanical pulping2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 2, p. 164-171Article in journal (Refereed)
    Abstract [en]

    Effluent from a TMP-based pulp and paper mill was collected at the inlet and outlet of the mill's biological treatment plant and fractionated by sorption on XAD-8 resin and MTBE precipitation. Fractionation indicated that the refractory dissolved organic material in biologically treated effluent was mainly composed of lignin-related substances. Characterisation of the lignin-related substances by chromatographic and spectrometric methods confirmed the similarities of the isolated material and milled wood lignin. Fractionation and characterisation of alkali-extracted material from solids (biosludge) in biologically treated effluent found evidence of lignin-related material. Results indicated that biological treatment had altered the chemical structure and molar-mass distribution of dissolved lignin-related substances.

  • 6.
    Ankerfors, Caroline
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lingström, Rikard
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ödberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A comparison of polyelectrolyte complexes and multilayers: Their adsorption behaviour and use for enhancing tensile strength of paper2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 1, p. 77-86Article in journal (Refereed)
    Abstract [en]

    This paper compares the adsorption behaviour and paper-strength-enhancing properties of polyelectrolyte complexes (PECs) and polyelectrolyte multilayers (PEMs) of polyallylamine hydrochloride and polyacrylic acid. Model adsorption experiments using SPAR (stagnation point adsorption reflectometry) and QCM-D (quartz crystal microbalance with dissipation) showed that the amount of complexes adsorbed was lower than the amount adsorbed when forming a multilayer using the same polymer system. From these experiments, in combination with AFM and ESEM imaging, it was concluded that the PEC adsorption stopped before full surface coverage was reached. Tensile testing of handsheets treated with PECs and PEM showed a significant increase in both tensile index and strain-at-break using both systems. The largest strength improvement was achieved with the fibres treated with the largest number of PEMs, but the largest effect per adsorbed amount of polymer was achieved by PEC treatment.

  • 7. Antonsson, S.
    et al.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Hogskolan, K. T.
    Ragnar, M.
    A comparative study of the impact of the cooking process on oxygen delignification2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 4, p. 388-394Article in journal (Refereed)
    Abstract [en]

    The impact of oxygen delignification on chemical pulps of a given kappa number manufactured in different ways (using kraft, prehydrolysis kraft and magnesium sulphite cooking) has been investigated. The prehistory of the pulps proves to be a very important factor in determining the response to oxygen delignification, i.e. the degree of delignification. It is shown that this is not due to different amounts of hexenuronic acid (HexA) in the different pulps, although this is an important factor behind the high residual kappa number after oxygen delignification of birch kraft pulp. Oxygen delignification of sulphite pulps proves to be efficient even at kappa numbers significantly lower than 10. These pulps show the greatest yield loss over the oxygen delignification. It is likely that Lignin Carbohydrate Complexes (LCC) complexes play a very important role in limiting the speed of reaction of oxygen delignification. Due to the very different prehistories of the pulps investigated, it is probable that the LCC:s are native and not formed during cooking.

  • 8.
    Antonsson, Stefan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Henriksson, Gunnar
    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 lignin and xylan on some kraftliner pulp properties2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, p. 403-408Article in journal (Refereed)
    Abstract [en]

    This study investigates the influence of lignin and hemicellulose content on the mechanical and physical properties of softwood kraft liner pulp. Tensile properties, hygroexpansion, and mechano-sorptive creep properties were measured. The lignin and hemicellulose contents were modified by chlorite delignification and xylanase treatment.

    After treatment, the chemical composition of the pulps was 3-14% Klason lignin, 69-77% cellulose, 16-21% hemicellulose, and 4-7% xylan. In the tested pulps, low lignin content tended to decrease hygroexpansion as well as increase tensile stiffness and mechano-sorptive creep stiffness. Xylan contributed less to the pulp sheet properties, but at equal lignin contents, higher xylan content tended to give increased hygroexpansion and worse mechano-sorptive creep properties.

  • 9.
    Antonsson, Stefan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Karlström, Katarina
    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.
    Applying a novel cooking technique to produce high kappa number pulps: the effects on physical properties2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, p. 415-420Article in journal (Refereed)
    Abstract [en]

    A recently developed kraft cooking technique, with a longer impregnation time at lower temperatures to facilitate diffusion over consumption of active cooking chemicals, makes it possible to produce kraftliner pulp without inline refining. This technique was applied to prepare two pulps with different lignin contents, which were compared with two industrial pulps from conventional kraft cooks in order to evaluate the physical properties of the pulps.

    It was demonstrated that pulps with lower lignin content can increase tensile stiffness, decrease hygroexpansion, and decrease the mechano-sorptive creep of handsheets. However, no difference in SCT and tensile energy absorption values due to different lignin contents was observed. It was further demonstrated that pulps made with Extended Impregnation Cooking (EIC) results in straighter pulp fibres with higher cellulose content. These pulps tended to have lower mechano-sorptive creep than conventional pulps. A higher brightness of the pulp sheets can also be obtained by choosing a higher alkali profile.

  • 10.
    Antonsson, Stefan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Mäkelä, Petri
    Innventia AB.
    Fellers, Christer
    Innventia AB.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Comparison of the physical properties between hardwood and softwood pulps2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, p. 409-414Article in journal (Refereed)
    Abstract [en]

    High mechano-sorptive creep resistance, i.e., good creep resistance in environments with changing relative humidity, is one of the key requirements for linerboards. The aim of this study was to investigate the influence of pulp types and pulp properties on the mechano-sorptive creep of kraftliner. A high-yield softwood, kraftliner pulp, and four different hardwood pulps were investigated. The physical properties of laboratory sheets were evaluated, with emphasis on the mechano-sorptive creep properties.

    The results showed that the density increase due to increased beating significantly improved the tensile stiffness of all pulps, while its effect on the isocyclic creep stiffness was less pronounced. The hardwood pulps showed higher tensile stiffness, better mechano-sorptive creep properties, and lower hygroexpansion than the softwood pulp at a given density. However, the softwood pulp did exhibit better tensile strength and fracture toughness properties than the hardwood pulps.

    The results imply that hardwood pulps can be competitive with softwood pulps in kraftliners, provided that their tensile strength and fracture toughness properties can be improved by, for example, chemical means. Furthermore, the isocyclic creep stiffness correlates with the ratio of tensile stiffness to hygroexpansion, indicating that this ratio can be used for engineering estimates of the mechano-sorptive creep performance of paper materials.

  • 11.
    Areskogh, Dimitri
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Henriksson, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Fenton's reaction: a simple and versatile method to structurally modify commercial lignosulphonates2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 1, p. 90-98Article in journal (Refereed)
    Abstract [en]

    Treatment of lignosulphonates with hydrogen peroxide and Fe (II) acetate under mild conditions can be used to increase the molecular weight and content of carboxylic acids. Such Fenton's oxidation can produce, in some of the conditions of and lignosulphonate concentration, a two-fold increase in the molecular weight and a 6-7 fold increase in the carboxylic acid content. The structural modifications of lignosulphonate may increase the technical performance of the product in several applications. Possible reaction mechanisms of the Fenton system are proposed and discussed.

  • 12. Axelsson, P.
    et al.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, A.
    Influence of alkali profiling in birch kraft pulping on QPQP bleachability2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 1, p. 37-43Article in journal (Refereed)
    Abstract [en]

    The influence of different aspects of alkali profiling in the kraft cook on QPQP bleachability of oxygen-delignified birch pulp was investigated. The use of a levelled-out alkali profile was compared to a conventional, and different modifications to the levelled-out alkali profile, like alkali charge, degree of delignification and amount of dissolved organic substance and ionic strength in the cooking liquor were studied. The alkali profile itself was found to have a significant effect where a levelled-out alkali profile showed a superior bleachability compared to a conventional one. The bleachability improved with an increased alkali charge towards the end of the cook, a high kappa number after cooking or by a cooking liquor exchange in order to decrease the amount of dissolved organic substance and the ionic strength towards the end of the cook. When a levelled-out alkali profile was used, the bleachability correlated well with the light-absorption of the lignin in the unbleached pulp, where a pulp with a brighter lignin consumed less peroxide in the QPQP sequence, for the pulp to reach 89% brightness.

  • 13. Axelsson, P.
    et al.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, A.
    The influence of alkali charge and temperature in the kraft cook on the QPQP bleachability and the kappa number composition of birch pulp2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 3, p. 206-212Article in journal (Refereed)
    Abstract [en]

    The main objective of this investigation was to study how the alkali charge and the temperature in the kraft cook influence the QPQP bleachability of oxygen-delignified birch pulp. The bleachability was evaluated as the normalised consumption of bleaching chemicals required to reach a certain light absorption coefficient of the pulp. All the pulps had a kappa number of about 17 after the cook and a kappa number of about 10 after oxygen delignification. The alkali charge significantly affected the bleachability and the best bleachability was obtained for an intermediate level alkali charge ([HO-](initial)=1,35 mol/L, corresponding to an effective alkali charge of 21.6% on wood). An increase in cooking temperature gave only a slight increase in bleachability. The contributions to the kappa number of lignin, hexenuronic acids (HexA) and other non-lignin structures were also investigated. Lignin contributed to about 60% of the kappa number in pulps after the cook, to about 40% in pulps after the oxygen delignification, and to about 30% after QPQP bleaching. Hexenuronic acids contributed between 3.7 to 4.7 kappa number units in all pulps, which makes them the largest contributors to the kappa number in oxygen-delignified and QPQP bleached pulps. Other non-lignin structures, were contributing about 3 kappa number units in pulps after the cook, but decreased to less than I kappa number unit after QPQP bleaching. No great differences in the composition of the kappa number could be seen between pulps produced under different pulping conditions, except that there was a somewhat lower hexenuronic acid content in the pulps produced with the highest alkali charge or at the highest cooking temperature.

  • 14.
    Axelsson, Patrik
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Influence of the conditions during birch kraft cooking on unbleached brightness, and on ECF- and TCF-bleachability2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 3, p. 309-317Article in journal (Refereed)
    Abstract [en]

    The influences on ECF and TCF bleachability of the hydroxide ion, hydrogen sulphide ion and sodium ion concentrations as well as of the amount of dissolved wood components (DWC) in a birch kraft cook were investigated. The pulping was carried out using a so-called constant composition cooking technique, where a high liquor-to-wood ratio enables an almost constant concentration of the cooking chemicals during the entire cook. This cooking method also renders possible to vary each cooking variable separately. The pulps were oxygen-delignified and bleached in a D(EOP)DD and a Q(OP)Q(PO) sequence. The presence of DWC caused a significant rate increasing effect on the delignification. An increase in hydroxide ion concentration, an increase in hydrogen sulphide ion concentration or a decrease in sodium ion concentration improved both the ECF and the TCF bleachability, but the DWC had no significant effect on the bleachability. Further a correlation was found between the bleachability and the brightness of the oxygen-delignified pulp.

  • 15. Backa, Stefan
    et al.
    Ragnar, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Pulp bleaching with peracetic acid generated from acetylated polymeric carbohydrates and hydrogen peroxide - Proof of principle2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 4, p. 409-414Article in journal (Refereed)
    Abstract [en]

    The generation of peracetic acid in the pulp mill may open up new opportunities to use this bleaching chemical. The generation of peracetic acid from acetylated carbohydrates and hydrogen peroxide followed by bleaching of pulp in a T stage was therefore studied with special emphasis on the COD content in the bleaching effluent from this stage. This preliminary work demonstrates that peracetic acid can be generated from acetylated polymeric carbohydrates and hydrogen peroxide, and that this peracetic acid will bleach pulp fibres as effectively as distilled peracetic acid. It is also shown that most of the deacetylated polymeric carbohydrate (in this case cationic starch) adsorbs to the fibre and does not affect the COD content of the filtrate after the T stage. The peracetic acid has been generated with and without pulp present. The peracetic acid yield from polymeric activators and hydrogen peroxide was lower than that from acetylated glucose. The peracetic acid yield can be further be optimised with respect to the acetylated polymer structure, process parameters and added peracetic acid stabilisers. No effect on the tensile strength was observed when cationic starch was used as an acetyl carrier in a TCF sequence with a final (PO) stage. Most of the cationic starch was probably removed in the washing after the (PO) stage pulp. To avoid this, the (PO) stage should be exchanged for a neutral or acidic bleaching stage or the cationic starch should be exchanged to a carbohydrate that better adsorbs to the fibre under alkaline conditions.

  • 16.
    Barbier, Christophe
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Experimental investigation of damage at folding of coated papers2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 1, p. 34-38Article in journal (Refereed)
    Abstract [en]

    An experimental investigation of damage occuring at folding of coated paper has been performed. For this purpose an experimental device was constructed in such a way that close resemblance with an industrial situation was achieved. During the experiments the influence on the damage levels in the coating from such features as delamination, humidity and paper thickness have been studied using an optical microscope. The behaviour of two different paper materials has been investigated. A stress (or strain) based fracture criterion is relevant for the present problem but biaxiality of stresses as well as in-plane anisotropy must be taken into account. It was observed that cracking of the coating would not lead to subsequent cracking of the paper substrate and that delamination occurred during folding, in the base stock and not at the paper/coating interface, but its quantitative influence as regards cracking could not be determined. The influence from sheet grammage was investigated and it was found that the only case when (visible) cracks did not appear was at low values. High humidity did not affect the cracking.

  • 17.
    Bergström, Roger
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Åkesson, Krister
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norman, Bo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A twin-wire model gap former: design and evaluation methods2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, p. 54-58Article in journal (Refereed)
    Abstract [en]

    A one-sided model twin wire gap former, the KTH-former has been developed. The former consists of headbox with transparent gables, forming unit, including a forming roll with a transparent surface and outer forming wire and a reservoir system for water/fibre suspension handling. To allow the study of blade forming, a blade can be introduced against the outer wire to generate a pressure pulse.

    Two measurement techniques have been utilized to study the flow mechanisms of fibre suspension flow in the forming zone;

    A pressure sensor has been used to study the dewatering pressure along the forming zone.

    A high speed video system was used to visually study the suspension flow.

    The study was made with pulp fibres. Fibre floes were introduced in the center of the headbox at the beginning of the linear nozzle contraction, by an introduction tube with an inner diameter of 10 mm. The acceleration in the nozzle contraction was used to separate the fibre floes in the Suspension making them move individually, thus making the visualisations easier. To avoid the problem of floc break-down at nozzle exit when using a conventional linear nozzle with parrot's beak outlet, two Curved contraction blocs were inserted, giving a more constant acceleration profile, letting the floes keep their integrity in the emerging jet.

    The high speed video system had two main arrangements, for the Study of floc behaviour in the forming zone. A mirror installed on the machine structure visualised a certain area of the forming zone. Alternatively, a mirror fastened to the back plate of the forming roll followed a specific area of the wire (and roll), making it possible to follow the floes through the entire forming zone. It is then possible to detect any relative motion between floes and wire.

  • 18.
    Björkman, Ulf
    KTH, Superseded Departments, Pulp and Paper Technology.
    Break-up of suspended fibre networks2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 32-37Article in journal (Refereed)
    Abstract [en]

    Suspended fibre networks form when flowing fibre suspensions come to rest. When stresses on such a network increases, the network is broken down and the fibre suspension eventually returns to a flowing condition. Here a series of experiments are described showing that the initiation of this break-down process leads to network-free voids opening up in the direction parallel to the largest compression.

  • 19.
    Björkman, Ulf
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Paper Technology.
    Floc dynamics in flowing fibre suspensions2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 247-252Article in journal (Refereed)
    Abstract [en]

    Fibre suspensions are ubiquitous in nature and technology. They occur in flowing form and as extended networks. Flow of fibre suspensions takes place in smaller network portions, fibre floes. Fibre networks normally form when fibre flows stop and vice versa. Traditionally, fibre suspensions are treated as systems of fibres. Here they will be treated as crowded systems of compressible floes. With a large Couette device it is shown that these floes split and fuse, shrink and swell and behave much like a particulate system composed of compressible floes suspended in a liquid, which can move in and out of the floes. The investigated average shear rate range is from zero to about 600 s(-1).

  • 20.
    Björkman, Ulf
    KTH, Superseded Departments, Pulp and Paper Technology.
    Stress generation and transmission in suspended fibre networks2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 38-43Article in journal (Refereed)
    Abstract [en]

    Suspended fibre networks are viewed as particulate systems of closely packed non-adherent compressible flocs suspended in an incompressible penetrating matrix. Experiments show that stress chains form upon compression because the flocs stand in the way of each other. If tensile stresses are applied, the. flocs separate without significant resistance. Network voids open up between and parallel to the stress chains. The reason is that the fibres create compressible flocs with a Poisson ratio less than 0.5.

  • 21.
    Borodulina, Svetlana
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Extracting fiber and network connectivity data using microtomography images of paper2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 469-478, article id 07315Article in journal (Refereed)
    Abstract [en]

    We apply image analysis methods based on micro-computed tomography (μCT) to extract the parameters that characterize the structure and bonding parameters in the fiber network of paper. The scaling and variational properties of μCT images are examined by analyzing paper structural properties of two 1 × 1 mm2 test pieces, which have been cut out from a low-grammage handsheet. We demonstrate the applicability of the methods for extracting the free fiber length, fiber cross-sectional data, the distances between the fibers, and the number of fiber-to-fiber bonds, which are the key properties required for the adequate representation of the network in numerical models. We compare the extracted connectivity data with the early reported analytical estimations and conclude that the number of contacts in three-dimensional networks is controlled by the fiber aspect ratio. In addition, we compare the cross-sectional data with those measured by the fiber morphology characterization tools and estimate the fiber shrinkage from completely wet to dry state to be nearly 20%.

  • 22.
    Borodulina, Svetlana
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Kulachenko, Artem
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Galland, Sylvain
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Nygårds, Mikael
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center BiMaC Innovation.
    Stress-strain curve of paper revisited2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 318-328Article in journal (Refereed)
    Abstract [en]

    We have investigated a relation between micromechanical processes and the stress-strain curve of a dry fiber network during tensile loading. By using a detailed particle-level simulation tool we investigate, among other things, the impact of "non-traditional" bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds. This is probably the first three-dimensional model which is capable of simulating the fracture process of paper accounting for nonlinearities at the fiber level and bond failures. The failure behavior of the network considered in the study could be changed significantly by relatively small changes in bond strength, as compared to the scatter in bonding data found in the literature. We have identified that compliance of the bonding regions has a significant impact on network strength. By comparing networks with weak and strong bonds, we concluded that large local strains are the precursors of bond failures and not the other way around.

  • 23.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Eriksson, Malin
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Fibre surface modifications of market pulp by consecutive treatments with cationic and anionic starch2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 2, p. 244-248Article in journal (Refereed)
    Abstract [en]

    Bleached softwood kraft pulps were coated with one to three layers of starch, which lead to tensile strength improvement. The strength increase was larger when a never-dried pulp was treated compared to treatment of a once-dried pulp, although equal amounts of starch were adsorbed in both cases. When the never-dried, starch-treated pulp was dried and subsequently reslushed, its tensile strength was higher than that of the never-dried reference pulp. It also required less PFI beating to reach a certain tensile index. Starch-treatment can thereby be a way of improving the tensile strength and beatability of market pulp.

  • 24.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Gustafsson, R.
    Teder, A.
    Properties of hyperalkaline polysulphide pulps2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 4, p. 436-440Article in journal (Refereed)
    Abstract [en]

    The term hyperalkaline polysulphide pulping is used to denote a process utilising a polysulphide pretreatment step at high alkalinity. The stabilising effect of polysulphide on carbohydrates is enhanced by higher alkali concentrations. The high alkali concentration in the stabilisation stage also increases the delignification rate in the subsequent cooking stage. In order to keep the alkali at a high level, hyperalkaline polysulphide pulping employs two pretreatment stages. In the first stage, the alkali charge is aimed to neutralise the acids formed of the wood components. The succeeding stage is the actual hyperalkaline polysulphide stage. It has a noticeably higher alkali concentration, thus promoting an efficient carbohydrate stabilisation by the polysulphide. The hyperalkaline polysulphide pretreatment makes it possible to obtain a pulp with high viscosity and yields good bleachability and good strength properties. The pulps however, need more beating energy to reach a high tensile strength than kraft and normal polysulphide pulps.

  • 25.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Characterisation of dissolved spruce xylan in kraft cooking2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 380-385Article in journal (Refereed)
    Abstract [en]

    Xylan dissolved during kraft cooking and later redeposited on fibre surfaces has been demonstrated to affect paper strength properties. Earlier studies have demonstrated that it is the xylan characteristics, rather than simply the amount of xylan, that influence the strength-enhancing effect of xylan. To use xylan optimally, it is useful to understand xylan’s beneficial characteristics and how cooking conditions affect them.

    In this study, spruce chips were kraft cooked under various cooking conditions and the xylan in the black liquor was characterized. We found that dissolved spruce xylan had a much higher amount of bound lignin than found in previous studies of xylan dissolved from hardwoods. The ionic strength of the cooking liquor affected the amount of dissolved xylan as well as the uronic acid content of the xylan.

  • 26.
    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.
    A study on the difference industrially and in tensile strength between laboratory-cooked pulp2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 222-226Article in journal (Refereed)
    Abstract [en]

    The tensile strength levels of industrially produced pulp and corresponding laboratory-cooked pulps were investigated. The industrial pulp had a lower tensile strength, which could not be explained by fibre form or fibre strength. It was concluded that bonding strength was the limiting factor for the tensile strength of the industrial pulp. The industrial pulp, despite of its higher hemicellulose content, had a lower surface charge. The xylan precipitated onto the fibres during the industrial cook was probably more degraded and consequently with lower degree of polymerisation and fewer charged groups.

  • 27. Bäckström, M
    et al.
    Brännvall, Elisabet
    KTH, Superseded Departments, Pulp and Paper Technology.
    Effect of primary fines on cooking and TCF-bleaching1999In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 14, no 3, p. 209-213Article in journal (Refereed)
    Abstract [en]

    When pulp is separated into fibre fractions on the basis of size, the smallest fraction obtained is called fines. Primary fines are found in cooked pulp not subjected to beating and secondary fines are created in the cause of beating. Fines have higher lignin and metal ion contents than the fibre fractions of the pulp. In this study, the effect of the primary fines on cooking and bleaching has been investigated. The results showed that removal of the primary fines during cooking had no positive effect on the delignification. The pulp viscosity at a certain kappa number and the H-factor to reach this kappa number were the same, regardless of whether or not the primary fines were present. However, the primary fines had a profound effect on bleaching when a QP sequence was used. An increase of approximately 2 ISO-brightness units was obtained by removing the primary fines prior to bleaching. Pulps with and without primary fines showed no significant difference in metal ion content or light scattering coefficient. The light absorption coefficient was, however, higher in the pulp with fines. The improved bleachability of the pulps without fines was therefore probably caused by differences in lignin content and in the lignin structure rather than by differences in metal ion content.

  • 28. Bäckström, Marie
    et al.
    Melander, Erik
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Study of the influence of charges on refinability of bleached softwood kraft pulp2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 4, p. 588-595Article in journal (Refereed)
    Abstract [en]

    To investigate how the number of charged groups affects the refinability of pulp, different levels of fibre charge were introduced to fully bleached softwood kraft pulp by bulk carboxymethylation. The chemical compositions of the fibres thus remained similar and the effect of the charge could be evaluated. The pulps were refined in a PFI-mill. The introduction of additional charges clearly resulted in a higher refinability in terms of a higher WRV for a given energy input. However, the increase in swellability was not accompanied by a corresponding increase in tensile index. The highly charged pulps suffered severe damage to the fibre wall during refining, showing that the combination of high charge levels and mechanical forces cause destruction of the fibre wall, which inhibits paper strength development.

  • 29. Bäckström, Marie
    et al.
    Tubek-Lindblom, Anna
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Studies of the influence of deflocculants and flocculants on the refining efficiency on a pilot scale2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 3, p. 319-326Article in journal (Refereed)
    Abstract [en]

    The objective of the present investigation was to study the influence of flocculants and deflocculants on refining efficiency. The refining was performed with the aid of a conical refiner at EuroFEX, and the refining response was evaluated as the change in fibre properties and in the mechanical properties of handsheets. Using the same furnish, an unbleached never-dried softwood pulp, the effect of fibre dimensions on floe strength was excluded as much as possible. The degree of flocculation was changed by addition of APAM, CPAM, guar gum and CMC. The floe strength was characterized using a parallel plate rheometer. The added chemicals, except for APAM, affected the relation between power input and gap clearance. To reach a certain power the fibres treated with guar gum, CMC or CPAM required a narrower gap clearance than the reference pulp or when APAM was added to the fibres. Refining at a narrower gap clearance increased the refining efficiency in terms of WRV and paper property development, as long as fibre length reduction could be avoided.

  • 30.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. D.
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Fibre orientation measurements near a headbox wall2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 2, p. 204-212Article in journal (Refereed)
    Abstract [en]

    Experimental results on the fibre orientation in a laboratory scale headbox are reported. Images containing fibres in approximately 1 mm thick slices parallel to the wall were captured at different wall distances. A steerable filter was used to determine the orientation of bleached and unbeaten birch fibres, suspended in water, at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only dilute suspensions were studied. It is shown that the fibre orientation distribution varies with the distance from the wall. Sufficiently far upstream in the headbox a more anisotropic distribution is found closer to the wall.

  • 31.
    Carlsson, Allan
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Söderberg, L. Daniel
    Lundell, Fredrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Fibre orientation near a wall of a headbox.2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, p. 204-212Article in journal (Refereed)
    Abstract [en]

    Experimental results on the fibre orientation in a laboratory scale headbox are reported. A steerable filter was used to determine the orientation of bleached unbeaten birch fibres at different distances from one of the inclined walls of the headbox contraction. Due to optical limitations only dilute suspensions were studied. It is shown that the fibre orientation distribution varies with the distance from the wall. Sufficiently far upstream in the headbox a more anisotropic distribution is found closer to the wall as compared to farther away from the wall.

  • 32. Christiernin, M.
    et al.
    Henriksson, Gunnar
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Brumer, Harry
    KTH, Superseded Departments, Biotechnology.
    Teeri, Tuula T.
    KTH, Superseded Departments, Biotechnology.
    Lindström, T.
    Laine, J.
    The effects of xyloglucan on the properties of paper made from bleached kraft pulp2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 2, p. 182-187Article in journal (Refereed)
    Abstract [en]

    Xyloglucan was adsorbed onto bleached soft-wood kraft pulp followed by preparation and analysis of handsheets with respect to sheet formation as well as sheet mechanical and optical properties. Adsorption of xyloglucan was found to be slow. After more than 20 hrs adsorption, equilibrium had not been reached. The amount of xyloglucan adsorbed increased with beating, but neither the rate of adsorption nor the quantity adsorbed was significantly affected by temperature. Xyloglucan was found to be practically irreversibly adsorbed onto the fibres and the effects of xyloglucan on paper sheet properties were investigated after thorough washing of the pulp. The adsorption characteristics of xyloglucan confirm observations by other authors on other cellulose substrates. Tensile index values for handsheets formed with the xyloglucan-containing pulps were higher than those measured for control pulps with a comparable beating degree. The light scattering coefficient was, however, not affected by xyloglucan adsorption. Hence, the increase in tensile strength is attributed to an increased relative bond strength between the fibres. Tensile strength versus tear strength relationship was similar for pulps with and without xyloglucan, but water retention value and dewatering resistance were lower for the xyloglucan treated pulps than for the reference pulps at the same tensile strength. In addition, formation was improved for pulps with adsorbed xyloglucan. The conclusion is that xyloglucan is a promising wet end additive that decreases the necessity for beating of the pulp and improves the formation of paper.

  • 33.
    Danielsson, Sverker
    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.
    Influence of birch xylan adsorption during kraft cooking on softwood pulp strength2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 4, p. 436-441Article in journal (Refereed)
    Abstract [en]

    The dissolution, degradation and redeposition of xylan in the kraft cooking of birch pulp were investigated. The molecular weight of the dissolved xylan was determined through gel permeation chromatography, and the loss in molecular weight could be correlated with the amount of degraded xylan in the initial stages of the kraft cook. This indicates that peeling is the only significant xylan degradation reaction taking place early in the cook. Two different birch black liquors containing xylan with molecular weights of 12.20 g/mol and 5.95 g/mol, respectively, were added to softwood kraft cooks in order to determine the effect of birch xylan on pulp strength properties. The results show an increase in both tensile strength and tensile stiffness. The magnitude of the strength increase was greatly affected by the molecular weight of the xylan added. Adding high-molecular-weight xylan increased the tensile strength by more than 10%, as measured at a beating degree of 1000 PFI revolutions. Tensile stiffness was also increased by xylan addition, though more so when the xylan was of high rather than low molecular weight.

  • 34.
    De Magistris, Federica
    et al.
    Karstad University.
    Salmén, Lennart
    STFI-Packforsk AB.
    Finite Element Modelling of wood cell deformation transverse to the fibre axis2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 2, p. 240-246Article in journal (Refereed)
    Abstract [en]

    Modelling of wet wood under compression and combined shear and compression load was performed to simulate the mechanical pulping of wood chips in refiners. Experiments have shown that the wet fibre network exhibit two different deformation modes; an S-shape mode associated with compression and a brick-shape mode associated with combined shear and compression. To study the factors governing the mechanical behaviour of the fibre network a material model with the characteristics originating from the properties of the wood polymers was developed and was used in a three-dimensional finite element analysis. The effects of material properties were investigated by comparing models with anisotropic one-layer cell walls and orthotropic multi-layer cell walls. The deformation achieved both under compression and under combined shear and compression was found to be similar independent of the material constants used or the number of layers of the cells walls. This implies that the most important factor governing the deformation pattern of the fibre network is the cell structure itself.

  • 35.
    De Magistris, Federica
    et al.
    STFI-Packforsk AB.
    Salmén, Lennart
    STFI-Packforsk AB.
    Mechanical behaviour of wet wood in sequences of compression and combined compression and shear2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 231-236Article in journal (Refereed)
    Abstract [en]

    During the refining of mechanical pulp, a process occurring at high speed at temperatures of 140-160°C, the flexibility and bonding ability of the wood fibres increase. To understand the mechanical behaviour of the fibres in this operation, the deformation at low speed of wet wood specimens at 50°C and 90°C were studied under different combinations of shear and compression loading using a modification of the Arcan device. The deformation in earlywood was studied using an image analysis procedure together with measurements of the work done under different loading conditions. The deformation under combined shear and compression load was different from that in pure compression. In the first cycle under compression, the fibre cell walls were bent in a characteristic "S" shape, whereas under the combined load the cells deformed according to a "brick" shape. After a first cycle under combined load, the cells deformed according to the "brick" shape even when subjected to a second load under pure compression. The first deformation cycle required the largest amount of work. Since less energy was needed for the first cycle under a combined load than under a compression load, the application of a combined load as a first cycle may be a way to permanently deform fibres using less work.

  • 36.
    Duker, Elisabeth
    et al.
    STFI-Packforsk AB.
    Ankerfors, Mikael
    STFI-Packforsk AB.
    Lindström, Tom
    STFI-Packforsk AB.
    Glad Nordmark, Gunborg
    STFI-Packforsk AB.
    The use of CMC as a dry strength agent - the interplay between CMC attachment and drying.2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 65-71Article in journal (Refereed)
    Abstract [en]

    This paper deals with the ability to use high molecular weight CMC as a dry strength agent in paper and how the drying of the pulp, either before or after the CMC attachment, affects the mechanical properties of the paper. The effect of the counter-ion form used during drying and reslushing was also investigated. In the case of the calcium and hydrogen counter-ion forms, drying after CMC attachment had no impact on the attached amount. The sodium form did, however, result in some detachment of CMC. When the pulp was dried prior to CMC treatment, the counter-ion form had no effect on the attached amount. It was also shown that drying of a CMC-treated pulp reduced the positive effect of CMC on the mechanical properties. Nevertheless, the mechanical properties were still better than those of paper made from the never-dried reference pulp. The relative effect of CMC on the mechanical properties was independent of the drying strategy used and the counter-ion form did not affect the mechanical properties. However, surface carboxymethylation prior to drying resulted in sheets with better final mechanical properties than sheets made from pulp that had first been dried and then surface carboxymethylated.

  • 37.
    Duker, Elisabeth
    et al.
    STFI-Packforsk AB.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Tom
    STFI-Packforsk AB.
    The effects of CMC attachment onto industrial and laboratory-cooked pulps2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 356-363Article in journal (Refereed)
    Abstract [en]

    The effect of surface carboxymethylation of industrial and laboratory-cooked pulp was studied regarding attached amount, fibre properties and paper sheet strength. The strength development was compared with the effects of PFI beating. Attachment of CMC was shown to be equally effective with industrial pulp as with laboratory-produced pulp. The attachment level was 100% for both pulp types and no difference in paper strength enhancement could be detected. CMC attachment had a small impact on sheet density, especially compared to PFI beating. Moreover, surface carboxymethylation was shown to increase the shape factor, reduce the number of kinks per fibre and to increase the rewetted zero-span index. This straightening effect of CMC was interpreted in terms of an increase in carboxyl group repulsion on the fibre surface and is probably a factor contributing to the increase in paper strength. Differences in fibre curl between industrial and laboratory-cooked pulp decreased when CMC was attached to the fibre surface. This may explain why no differences in CMC efficiency could be detected.

  • 38.
    Duker, Elisabeth
    et al.
    STFI-Packforsk AB.
    Lindström, Tom
    STFI-Packforsk AB.
    On the mechanisms behind the ability of CMC to enhance paper strength.2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 57-64Article in journal (Refereed)
    Abstract [en]

    The attachment of CMC to pulp is known to have a strong impact on the tensile strength properties. The mechanisms behind the strength-enhancing ability of the CMC have been investigated by studying the effect of surface carboxymethylation on some basic fibre and sheet properties. Standard methods were used for the strength evaluation, and the relative bonded area was determined from both light-scattering measurements and BET-analysis. The effect of CMC on the shear bond strength was calculated using Page's equation. The attachment of CMC was shown to increase the shape factor and reduce the number of kinks per fibre, which is beneficial for the tensile strength. Surface carboxymethylation also increased the relative bonded area, but on a small-scale structural level detectable only using BET-analysis and not by the scattering coefficient. The sheet density was not affected by the treatment. CMC attachment also increased the shear bond strength. In order to use Page's equation for this evaluation, the relative bonded area had to be determined by BET-analysis. The positive effect of CMC on sheet formation also contributed to an increase in tensile strength.

  • 39. Durruty, Julie
    et al.
    Sewring, Tor
    Schneider, Helen
    Schneider, Lynn
    Mattsson, Tuve
    Theliander, Hans
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Filtration properties of kraft lignin: The influence of xylan and precipitation conditions2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 4, p. 508-526Article in journal (Refereed)
    Abstract [en]

    LignoBoost lignin powder was dissolved together with xylan and re-precipitated. The influence of the (i) precipitation temperature, (ii) rate of acidification and (iii) final pH of the slurries on the resulting material and its filtration properties was investigated. In the case of slow acidification, larger agglomerates were obtained for slurries with higher precipitation temperatures as well as with higher ionic strengths. Fast acidification led to a more heterogeneous formation of particles, having a broader particle size distribution, compared to slow acidification. Chemical analysis of different layers of the filter cakes formed revealed that xylan was distributed evenly on the solid lignin, reinforcing the hypothesis that xylan is sorbed onto the lignin agglomerates when precipitated together with lignin. Furthermore, the resulting lignin-xylan mixtures were found to be more difficult to filter in the case of a higher final pH of the slurry (pH 4), close to the pKa values of the carboxylic acid groups of xylan, compared to lower pH values (pH 1-3). This is likely the result of an increase in electrostatic repulsive interactions between the particles/agglomerates at higher pH: a locally more porous solid structure is formed, leading to a larger solid/liquid surface area during filtration.

  • 40. Edstrom, Per
    et al.
    Neuman, Magnus
    Avramidis, Stefanos
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis, NA.
    Andersson, Mattias
    Geometry Related Inter-Instrument Differences in Spectrophotometric Measurements2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 2, p. 221-232Article in journal (Refereed)
    Abstract [en]

    The L&W Elrepho d/0 and the Spectrolino 45/0 instruments are examined using paper samples with different properties. External factors that influence the measurements such as the sample background, the instrument calibration and the sample inhomogeneity are studied, and a methodology for their minimization is presented. Experimental measurements show that such external factors, if not minimized by proper routines, affect the inter-instrument differences far more (up to 4-5 Delta E-ab(star)) than the instrument geometry (the effect of which is small and of order 0.1 Delta E-ab(star)). The DORT2002 radiative transfer model is used to simulate differences caused by instrument geometry. The simulated and measured differences are found to agree in magnitude, and the differences are mapped against sample properties. It is observed that the 45/0 instrument detects higher reflectance from paper samples with negligible absorption and transmittance. When there is considerable absorption (dyed samples) or transmittance (thin samples), the d/0 instrument detects higher reflectance. The physical mechanism behind this behavior is studied and explained using DORT2002, and the instrument differences are shown to depend on the anisotropy of the reflected light. The model/measurement agreement is satisfactory as the characteristic behavior is captured in almost all cases studied. This new understanding is important for facilitating accurate data exchange between the paper and graphic arts industries, but also for interpretation of reflectance measurements in general.

  • 41.
    Ek, Monica
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Lennholm, Helena
    Iversen, Tommy
    A comment on the effect of carbonyl groups on the light-induced reversion of groundwood pulp1990In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 5, no 4, p. 159-160Article in journal (Refereed)
    Abstract [en]

    Sodium borohydride redn. of stone groundwood pulp from spruce (Picea abies) had no dramatic effect on the light-induced brightness reversion.  This indicates that the direct scission of phenacyl aryl ether linkages is not an important step in the initial chromophore formation.

  • 42.
    Ekevåg, Per
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Lindström, Tom
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Addition of carboxymethylcellulose to the kraft cook2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 2, p. 200-207Article in journal (Refereed)
    Abstract [en]

    The physical attachment of carboxymethylcellulose (CMC) onto kraft pulps during cooking and the effects of subsequent bleaching in an OD(EOP)DD sequence were investigated. Two CMC grades with different molecular weights and different degrees of substitution (D.S.) were used, CMC Finnfix WRH and CMC Cekol DVG. The effect of the CMC was studied by measuring the increase in the total charge density as well as in the surface charge density. In this way, both the total amount of attached CMC and the amount of the CMC attached onto the surface of the fibres Could be determined. Hand-sheets were made to study the effects of CMC addition on the physical properties of the paper. Different amounts of CMC were added to find the optimum, which was determined to be 1% CMC on wood. The proportion of CMC attached at a level addition of 1% (on wood) was about 40%. It was, however, found that a large part of the CMC was degraded during the cook. Whereas high molecular weight CMC is attached onto the surface of fibres, the degraded CMC is attached to the interior of the cell wall, decreasing the efficiency of the CIVIC to enhance the joint strength between fibres. The tensile index increased significantly, approximately 10% after beating to 2000 PFI revolutions, when 1% CMC Finnfix WRH on wood was added. The CMC Cekol DVG grade showed the greatest increase in tensile index, approximately 12% at 2000 PFI revolutions. The results of the bleaching of a sample treated with CMC Finnfix WRH showed that a part of the effect of CMC remains after bleaching. Most of the reduction in the positive effect was due to a loss of CMC molecules from the fibre surface.

  • 43.
    Enarsson, Lars-Erik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kinetics of sequential adsorption of polyelectrolyte multilayers on pulp fibres and their effect on paper strength2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 2, p. 258-266Article in journal (Refereed)
    Abstract [en]

    Conditions for sequential adsorption of polyelectrolyte multilayers (PEM) onto pulp fibres were investigated in terms of appropriate addition levels and adsorption times. The objective was a technical application for improved tensile strength of paper. Two common polyelectrolytes (PE) in papermaking, polyamideamine epichlorolrydrin (PAE) and carboxymethyl cellulose (CMC), were consecutively adsorbed onto long fibres from a bleached softwood kraft pulp, adding up to four PE layers on the fibre surfaces. Adsorption isotherms and adsorption kinetics were studied layer by layer, giving recommended addition levels and adsorption times for each layer. PAE adsorbed in larger amounts than CMC, 4 and 1 mg/g, respectively on fractionated pulp free of fines. For the kinetics, longer times were required to reach saturation adsorption for PAE compared to CMC, corresponding to three and two minutes, respectively. Tensile testing of handsheets based on both fractionated and beaten pulp showed that four PE layers increased the tensile index by about 50%, reaching levels of 34 (unbeaten) and 88 Nm/g (beaten), respectively. The effect of PEM on strain at break depended on the beating level as the fractionated pulp showed an improvement from 2.5 to 4.1% while beaten pulp showed a reduction from 6.1 to 4.5%.

  • 44.
    Eriksson, Malin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Pettersson, Gunilla
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Application of polymeric multilayers of starch onto wood fibres to enhance strength properties of paper2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 3, p. 270-276Article in journal (Refereed)
    Abstract [en]

    Polyelectrolyte multilayers of cationic and anionic starch have been used to enhance the strength properties of paper. All starches used in this investigation had a degree of substitution around 0.065. Optical reflectometry showed that a combination of cationic and anionic starch could form polyelectrolyte multilayers onto silicon oxide surfaces. The same combination of starches was then applied to unbeaten, bleached softwood kraft fibres to form three layers, i.e. a cationic/anionic/cationic starch combination. The results showed a significant increase in the paper strength properties in terms of tensile index, strain at break, and Scott Bond. The adsorbed amount of starch in the sheets, determined using an enzymatic method, was found to increase with each successive starch treatment. The increased paper strength was not only due to the increase in adsorbed amount of starch; rather, the chemical composition of the starch was also important. Cationic starch with high amylose content had a more positive effect on the paper strength properties. Furthermore, it was observed that anionic starch, despite being adsorbed in large amounts, did not contribute to the increase in tensile strength or strain at break to the same extent as did cationic starch. However, the out-of-plane properties, measured as Scott Bond properties, increased with the adsorbed amount, regardless of the chemical composition of the starch used in the outermost layer.

  • 45.
    Fall, Andreas B.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Burman, Ann
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Cellulosic nanofibrils from eucalyptus, acacia and pine fibers2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 1, p. 176-184Article in journal (Refereed)
    Abstract [en]

    The strong, environment-friendly and abundantly available cellulose nanofibril (CNF) is a very interesting building block for various types of material. To facilitate the industrial use of the fibrils, their liberation from the wood fiber wall needs to be improved particularly since the process requires a substantial amount of mechanical energy. In this work, the influence of wood species on fiber wall disintegration has been studied. Fibers from eucalyptus, acacia and pine were enzymatically treated and then mechanically fibrillated by an earlier reported process. The nanofibril yield, evaluated by centrifugation, was then compared to the charge density, wood polymer composition and cellulose DP of the original fibers. The results indicate that the CNF yield of the process increases with the increase of charge density of the fibers. It was also found that the charge density of the CNFs was higher than that of the original fibers. In the case of films produced from uncentrifuged dispersions, the results indicated improved mechanical properties with increasing CNF yield. Eucalyptus, with the highest yield, showed the highest Young's modulus and the highest stress at break of the investigated pulps, whereas the acacia showed the greatest strain at break. However, in the case of the films produced from fibrils after centrifugation, the same trend could not be observed. In this case, the pine showed the highest Young's modulus. The transparency of the films was however, as expected, greater as a result of the centrifugation procedure for all the investigated pulps.

  • 46. Falt, S.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Influence of electrolytes on the swelling and strength of kraft-liner pulps2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 1, p. 69-73Article in journal (Refereed)
    Abstract [en]

    In the present paper, the effect of common process electrolytes NaCl, Na2SO4 and CaCl2 on fibre swelling and paper strength has been investigated. Results show that there is an initial increase in the water retention value (WRV) of the fibres when the salt concentration is increased at a pH of 5 in the solution surrounding the fibres. At higher salt concentrations, the WRV decreases. This behaviour is most pronounced for Na2SO4 and smaller for NaCl and CaCl2. The increase in swelling is explained as being due to an increase in pH in the fibre wall and a subsequent increased dissociation of the carboxyl groups during the initial increase in ionic strength. When the electrolyte concentration is further increased, the difference in osmotic pressure between the interior of the fibre wall and the surrounding solution decreases and eventually the pressure difference drops to zero. It is also found that there is no unique relationship between the WRV and the strength of paper formed from the fibres treated with different electrolyte concentrations.

  • 47. Fellers, C.
    et al.
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Mäkelä, P.
    Evaluation of the Scott bond test method2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 231-236Article in journal (Refereed)
    Abstract [en]

    The Scott bond test is the most commonly used test method for quantifying the delamination resistance of paper and board. The objective of this investigation was to validate the hypothesis that the Scott bond value would be dominated by the total energy under the force elongation curve in a z-directional tensile test. The investigation comprised three types of hand sheets with comparatively low strength values. Three test methods were used to obtain the energy for delamination: 1) Z-test, a z-directional tensile test, 2) Scott bond test, and 3) Simulated Scott bond test, a Scott bond type of test performed in a hydraulic tensile tester. The test data were expressed as a correlation between the failure energy obtained from the Z-test and the other two tests. The results showed that the Scott bond test gave slightly higher values than the Z-test for the weakest paper, but that the value tended to be much higher for the stronger papers. On the other hand the Simulated Scott bond test tended to give lower values than the Z-test. High speed photography was used to reveal several energy consuming mechanisms in the Scott bond test that can explain why this test gave higher values than the Ztest. The lower values from the Simulated Scott bond values are more difficult to explain. At this stage we can suggest that the failure mechanism is different if the paper is delaminated by pure tension or by a gradual delamination as in the Scott bond test.

  • 48. Forsstrom, J.
    et al.
    Andreasson, B.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Influence of pore structure and water retaining ability of fibres on the strength of papers from unbleached kraft fibres2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 176-185Article in journal (Refereed)
    Abstract [en]

    The influence of pore structure and the water retaining ability of fibres on different strength properties of papers from unbleached kraft fibres was investigated and the effects of pulp yield, counter-ion types, pH and homification were determined. NMR relaxation measurements of water were used to determine the pore structure of the fibres and WRV and FSP measurements were used to determine their water retaining ability. The average pore radius, as determined by NMR, was almost unaffected by changes in pulp yield whereas changes in counter-ion and pH had a significant effect on the average pore radius. The detected changes in NMR were suggested to be due to changes in the swelling forces both within the fibre wall and at the fibre surface. The WRV value decreased with decreasing yield and it was significantly affected by pH and counter-ion. Changes in WRV were explained to be largely associated with changes in the amount of water associated with the fibre surface. The FSP values decreased with decreasing yield just as the WRV's. Homification upon drying and reslushing significantly lowered the average pore radius, whereas the FSP only showed a minor decrease, suggesting that the surface area available to water was changed without drastically changing the overall fibre wall volume. The differences between FSP NMR and WRV can hence be traced back to what the methods are actually measuring. It was concluded that the different measuring methods contain unique information and that a combination of the methods is necessary to give as complete a picture as possible over the changes that occur in the fibre wall upon varying the condition for the fibres. The influence of pore size on sheet tensile properties was also investigated. It was found that fibres with larger pores produced an increased tensile index and tensile stiffness of the paper made from these fibres. It was suggested that fibres with larger pores allow for a larger molecular contact area between fibres, stronger fibre/fibre joints and consequently a higher strength of the formed sheets.

  • 49. Forsstrom, J.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Influence of different storage conditions on deinking efficiency of waterbased flexographic ink from model cellulose surfaces and sheets2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 2, p. 250-256Article in journal (Refereed)
    Abstract [en]

    The influence of UV-Iight, temperature, atmospheric environment and storage time on the ink detachment of water-based flexographic ink printed on model cellulose surfaces was investigated using an impinging jet cell equipment. The printed surfaces were deinked using a NaOH solution (pH = 10) and the deinking process was monitored using a microscope equipped with a CCD camera. Images were collected at different time intervals during the detachment process and image analysis was used to quantify the ink detachment from the surface. Hand sheets, (the same pulp as used for model surface preparation) were also printed and stored under the same conditions, after which they were reslushed and deinked. The deinking efficiency of the recycled sheets was evaluated using brightness and ERIC (Effective Residual Ink Concentration) values. It was shown that UV-Iight had a negative effect on ink detachment both from the model cellulose surfaces and from the hand sheets. At storage temperatures of 55degreesC, (dark conditions were used) a large negative effect was observed for the cellulose surfaces while only a small effect on the ink detachment could be seen for the hand sheets. Ink detachment from the hand sheets became more difficult when increasing the storage temperature above 55degreesC, as detected as a decrease in brightness of the recycled and deinked sheets. A farther increase in the storage temperature to 105degreesC gave poorer ink detachment efficiency than storage under UV-Iight for the hand sheets. Air had a more negative effect on ink detachment than nitrogen.

  • 50. Forsström, Jennie
    et al.
    Torgnysdotter, Annsofie
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Influence of fibre/fibre joint strength and fibre flexibility on the strength of papers from unbleached kraft fibres2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 186-191Article in journal (Refereed)
    Abstract [en]

    The joint strength between single fibres and its influence on strength properties of papers was evaluated, taking into account the effect of pulp yield, ionic form of the carboxyl groups and drying. Fibre/fibre joint strength stayed almost constant for pulps with yield between 45 % and 50 %. Further increasing the pulp yield increased the joint strength until a maximum value was reached at a pulp yield of around 57 %, after which the joint strength decreased. Joint strength correlated well to paper tensile strength for never dried fibres, i.e. a lower joint strength resulted in lower sheet tensile index. The decrease in sheet tensile index was not as pronounced as the decrease in joint strength. Changing counter-ion from Na+ to Ca2(+) or H+ did not affect fibre flexibility, although it reduced the joint strength as the molecular contact area decreased due to a reduced swelling upon changing the counter-ions. Drying the high yield pulp lowered both the joint strength and the sheet tensile index to the same extent. The sheet tensile index, for the low yield pulp, decreased much more than the fibre/fibre joint strength after drying the fibres. In conclusion, a combination of a lower fibre flexibility, resulting in fewer contact points between fibres in the sheet, and a lower joint strength after drying was responsible for the reduction in sheet tensile index.

1234 1 - 50 of 193
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf