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  • 1.
    Barbier, Christophe
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Larsson, PL
    KTH Stockholm.
    Östlund, S
    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-Article in journal (Refereed)
    Abstract [en]

    To achieve a better understanding of the folding properties of coated papers pertinent to the mechanical behaviour, a microscopic investigation was performed. The influence on the damage levels in the coating from such features as delamination, humidity and paper thickness have been studied

  • 2.
    Barros, Gustavo Gil
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Johansson, Per-Åke
    STFI-Packforsk AB, Stockholm, Sweden .
    Prediction of UnCovered Area occurrence in flexography based on topography: A feasibility study2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 172-179Article in journal (Refereed)
    Abstract [en]

    This investigation concerns the development and prediction of uncovered areas (UCA) in flexographic full-tone prints based purely on substrate topographic information. Four different predictive models based on topography thresholding were proposed and tested using two independent quality judgement criteria. 

  • 3.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Johansson, Caisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Flexographic Ink-Coating Interactions: Effects of Porous Structure Variations of Coated Paperboard2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 4Article in journal (Refereed)
    Abstract [en]

    Ink transfer and ink penetration into a coated surface, and variations thereof, influences the print density, mottling and dot gain, which affects the achievable print quality and visual appearance. The pressure in the printing nip and the porosity of the substrate are conditions and properties that will regulate the amount of ink that penetrates into a porous coating structure. The purpose of this study was to relate print quality aspects to ink penetration of water-based flexographic ink into calcium carbonate based coatings of differently engineered structures. Pilot-coated paper-boards with different coating porosities were printed in a laboratory flexographic printer. Results indicate that ink transfer distribution is strongly affected by the roughness and the porosity of the substrate. A coating layer of broad pigment particle size distribution resulted in a lower print density, compared to coatings of narrowly distributed particle sizes. A structure characterized by larger pore volume and greater dominating pore radius, showed a higher amount of z-directional ink penetration, which was supported by estimating the penetration using a physical model accounting for both capillary- and pressure driven penetration. A coating with narrow particle size distribution also showed a lower dot gain.

  • 4.
    Boudreau, Jonna
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Beghello, Luciano
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    A Method of Measuring the Thickness of the Coating on a Dryer Cylinder2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 3, p. 309-312Article in journal (Refereed)
  • 5.
    Boudreau, Jonna
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Hollmark, Holger
    Hollmark Imptec AB.
    Beghello, Luciano
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Chemical and Morphological Analyses of the Tissue Yankee Coating2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 1, p. 52-59Article in journal (Refereed)
  • 6.
    Carlsson, Gunilla
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Axrup, Lars
    Stora Enso, Karlstad Res Ctr, SE-65009 Karlstad, Sweden.
    Ljungqvist, Carl-Henrik
    Stora Enso, Karlstad Res Ctr, SE-65009 Karlstad, Sweden..
    Nyflott, Asa
    Stora Enso, Karlstad Res Ctr, SE-65009 Karlstad, Sweden.;Karlstad Univ, SE-65188 Karlstad, Sweden..
    The use of fluorescence microscopy and image analysis to characterize the porous structure in micro fibrillar cellulose gel - Part I: Brownian motion2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 2, p. 190-197Article in journal (Refereed)
    Abstract [en]

    The porous structure of a micro fibrilar cellulose, MFC, gel was studied by fluorescence microscopy and image analysis. The Brownian motion of fluorescent labelled carboxylated latex spheres, probes, was investigated at both high, 0.1-5 wt%, and low, 0-20 ppm, concentrations of MFC. The developed tracking program provides trajectories for probes. The trajectories can be studied according to either the individual approach or the ensemble approach to give complementary information regarding the fibrilar system. The Brownian motion can be used in the range 0 to 1.0 wt% MFC and the percentage of idle probes can be used when the concentrations exceeds 1.0 wt% MFC. The Brownian motion was found to be pH dependent both for the low and the high concentration regimes.

  • 7.
    Carlsson, Gunilla
    et al.
    Karlstad University, Division for Chemistry.
    van Stam, Jan
    Karlstad University, Division for Chemistry.
    Interactions between Charged Latex Colloids and Starch Polyelectrolytes Studied with Fluorescence  Microscopy with Image Analysis2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 192-199Article in journal (Refereed)
    Abstract [en]

    The interactions between carboxylated polystyrene latex probe particles and ionically substituted starches have been investi-gated by fluorescence microscopy with image analysis. The degree of substitution of the starches was varied, as was also thepolyelectrolyte molecular weight and the probe size. 

  • 8.
    Deshpande, Raghu
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Sundvall, Lars
    MoRe Research, Örnsköldsvik, Sweden.
    Grundberg, Hans
    Domsjö Fabriker AB, Örnsköldsvik, Sweden.
    The Initial Phase of Sodium Bisulfite Pulping of Pine, Part II2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 379-385Article in journal (Refereed)
    Abstract [en]

    Single stage sodium bisulfite cooking of pine was carried out to investigate the influence of time and temperature in the initial phase of the cook. The cooking experiments were carried out using either a lab or a mill prepared cooking acid and the initial stage of the cook was extended up to 5 h cooking time. The impact of temperature on wood components and side reactions was analyzed between 142°C and 165°C. Arrhenius equation was used to determine the influence of temperature on wood components during the initial phase of bisulfite cooking and the activation energy was calculated for delignification rate, cellulose degradation and hemicellulose dissolution with regard to glucomannan and xylan. The extent of extractives removal at different temperature and time was also analyzed.

  • 9.
    Deshpande, Raghu
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Sundvall, Lars
    MoRe Research.
    Grundberg, Hans
    Domsjö.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Some process aspects on single-stage bisulfite pulping of pine2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 379-385Article in journal (Refereed)
    Abstract [en]

    Sulfite pulping of pine is well-known to be a risky process because problematic lignin conden-sation reactions can occur resulting in poor pulp quality. However, sulfite pulping of pine is interesting of economic reasons as pine wood is cheaper than spruce. Therefore it has become interesting to investigate sulfite pulping again to determine if old data are still valid. Thus sodium bisulfite pulping of pine was carried out to investigate the influence of time, temperature and cooking acid quality. A small comparison of spruce pulping was also included. By using different cooking temperatures the activation energies for delignification and for degradation of cellulose and hemicelluloses could be determined. The results showed no lignin condensation reactions, thus it was not problematic to carry out these pine cooking experiments. It was found that glucomannan had higher activation energy than xylan and the activation energies of these hemicelluloses were lower than the corresponding value for the lignin degradation. It was found that the activation energy for bisulfite pulping of pine was slightly lower than the activation energy for bisulfite pulping of spruce.

  • 10.
    Ekbåge, Daniel
    et al.
    Store Enso Pulp & Paper Asia AB, Karlstad Res Ctr, POB 9090, SE-65009 Karlstad, Sweden..
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Potential energy improvements in a multiple-effect evaporation system: Case studies of heat recovery2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 4, p. 583-591Article in journal (Refereed)
    Abstract [en]

    The primary objective of this study was to quantify the amount of excess energy that is present in the evaporation system of an integrated pulp and paper-board mill and to analyze a number of energy recovery cases. These focus on improving the energy efficiency in the evaporation plant and are mainly based on the process data of performance tests from the full-scale production site. A computer script was developed in order to analyze the process streams and can be used to construct the Grand Composite Curve (GCC) of the evaporation system. In addition, the study identified seasonal variations in the potential excess of energy (higher in warmer weather and lower, or even non-existent, in colder) and suggestions are made as to how this energy may be used in a thermodynamically optimal way. In the case studies, the thermodynamically optimal method of recovering heat involved a combination of sensible heat and flash evaporation, indicating the maximum reduction in steam consumption. For the case of only utilizing sensible heat outside the evaporator system to pre-heat one of the liquor flows, the results indicated a lower reduction in steam but also a lower capital cost.

  • 11.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    The Arrhenius Equation is Still a Useful Tool in Chemical Engineering2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 1, p. 21-24Article in journal (Refereed)
    Abstract [en]

    The Arrhenius equation correlates the rate of a chemical reaction with the corresponding activation energy, reaction time and reaction temperature, where the latter is measured in Kelvin. Although the equation is rather simple it can be used to summarize the kinetics of most chemical reactions in a surprisingly good manner. The activation energy is an interesting parameter that can be seen as an energy barrier which the reacting chemicals have to pass before a chemical reaction is initiated. Thus, the higher the activation energy, the lower is the rate of the chemical reaction. Moreover, the equation can also be used, for example, to forecast the influence of a higher temperature on the composition of a product consisting of components with different activation energies. In such a case, a component with higher activation energy will increase its rate of reaction more than a component with lower activation energy. The composition of the original product will thus obtain a shrinking fraction of the fast reacting component. The report gives some guidelines of how to calculate the activation energy for a given case in a pulp mill.

  • 12.
    Girlanda, Orlando
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Fellers, Christer
    STFI-Packforsk AB, Stockholm.
    Evaluation of the tensile stress-strain properties in the thickness direction of paper materials2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 1, p. 49-56Article in journal (Refereed)
  • 13. Hallberg Hofstrand, Erik
    et al.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science.
    Rättö, Peter
    Dynamic measurements of nip force variations during post-printing of corrugated board2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 1, p. 111-114Article in journal (Refereed)
  • 14.
    Hellström, Pia
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). AkzoNobel Pulp & Performance Chem, SE-44580 Bohus, Sweden.
    Heijnesson-Hulten, Anette
    AkzoNobel Pulp & Performance Chem, SE-44580 Bohus, Sweden..
    Paulsson, Magnus
    AkzoNobel Pulp & Performance Chem, SE-44580 Bohus, Sweden.;Mid Sweden Univ, FSCN, SE-85170 Sundsvall, Sweden..
    Håkansson, Helena
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Fenton pre-treated microfibrillated cellulose evaluated as a strength enhancer in the middle ply of paperboard2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 4, p. 732-740Article in journal (Refereed)
    Abstract [en]

    Microfibrillated celluloses (MFCs), produced by various pre-treatments of a fully bleached birch kraft pulp, were evaluated as strength enhancers in test sheets representing the middle ply of paperboard. The furnish consisted of hydrogen peroxide bleached high temperature spruce chemithermomechanical pulp (HT-CTMP), MFC and a retention system containing cationic starch and an anionic silica sol. The MFC was prepared via a mechanical treatment in a colloid mill after pretreatment with Fenton's reagent, monocomponent endoglucanase or acidic hydrogen peroxide. Addition of 5% MFC, produced with Fenton pre-treatment, resulted in improved HT-CTMP properties with respect to increased tensile index (similar to 35%), z-directional strength (similar to 50%), tensile stiffness index (similar to 25%) compared to HT-CTMP test sheets prepared without MFC addition. The strength improvement was linearly correlated to the density of the tests sheet, to the surface area (BET) and to the surface charge of the enzymatic or chemically pre-treated MFCs.

  • 15.
    Henriksson, Gunnar
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    What are the biological functions of lignin and its complexation with carbohydrates?2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 4, p. 527-541Article in journal (Refereed)
    Abstract [en]

    This critical review discusses how lignin can fulfill its biological functions with a focus on the potential importance of covalent bonds between lignin and polysaccharides. Biological function and definition of lignin are discussed. There are several direct and indirect indications that covalent bonds between lignin and polysaccharides are common in wood, and there are mechanistic explanations for the formation of these bonds, with the exception of phenyl glycosides. Grasses might have a unique pathway for formation of links between lignin and hemicellulose. The monolignol structures might be evolutionary "designed" for forming covalent bond to polysaccharides during polymerization, and hemicelluloses might have the ability to some extent control the lignin structure and frequency of covalent bonds between lignin and polysaccharides. These bonds represent both technical problems and possibilities.

  • 16.
    Hämäläinen, Pyry
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Hallbäck, Nils
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Barbier, Christophe
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Development and evaluation of a high-speed creping simulator for tissue2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 448-458Article in journal (Refereed)
    Abstract [en]

    An innovative creping simulator for tissue has been developed to meet the requirements set by both industrial needs, such as speed and process step duration, and research ambitions, such as flexibility for modifications and efficient operation. Some of these factors can be difficult to achieve with the previously introduced simulators. Lower speeds and much longer process step times can jeopardize results when, for instance, the drying time of chemicals is longer and the speed of creping is slower than in a tissue mill. The newly developed simulator has been used to investigate the effects of paper grammage, creping angle, temperature of dryer, speed and the horizontal force experienced during tissue creping. Results show good agreement with results of industrial-scale tissue production, with the exception of shrinkage which was greater. It was observed that the grammage influences the final thickness and the shrinkage of creped sheets, and that creping speed affects the creping frequency, thickness and shrinkage. The temperature of the surface of a sled mimicking the Yankee cylinder was shown to influence creping frequency and thickness. The horizontal friction force during creping appears to increase if drying temperature is lowered.

  • 17.
    Javed, Asif
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Rättö, Peter
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Järnström, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Ullsten, Henrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Crack analysis of barrier coatings based on starch and starch-PVOH with and without plasticizer2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 2, p. 336-347Article in journal (Refereed)
  • 18.
    Javed, Asif
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Rättö, Peter
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Järnström, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Ullsten, Henrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Lignin-containing coatings for packaging materials2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 548-556Article in journal (Refereed)
  • 19.
    Javed, Asif
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Ullsten, Henrik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Ernstsson, Marie
    SP Technical Research Institute of Sweden, SP Chemistry, Materials and Surfaces.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science.
    Study of starch and starch-PVOH blends and effects of plasticizers on mechanical and barrier properties of coated paperboard2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 499-510Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of self-supporting films based on starch-plasticizer and starch-PVOH-plasticizer and the barrier properties of paperboard coated with solutions of these polymers have been studied. The plasticizers used were glycerol, polyethylene glycol and citric acid. It was shown that the addition of a plasticizer and PVOH to starch substantially increases the flexibility of starch films. It was seen that curing the self-supporting films led to a decrease in flexibility. After heat-treatment, a substantial increase in storage modulus was observed only in the starch-PVOH-citric-acid blend films. Tensile tests on the films indicate that citric acid did not cause any noticeable phase separation. Citric acid acted as a compatibilizer for starch-PVOH blends even though a similar enrichment of PVOH at the air-solid interface was observed with both citric acid and polyethylene glycol as plasticizer. The properties of barrier coatings greatly reflected the compatibility of starch-PVOH blends containing citric acid. The only plasticizer that resulted in a lower water vapour transmission rate through the starch and starch-PVOH coatings was citric acid, which suggests that cross-linking took place. With four layers, coatings based of starch-PVOH possessed the same oxygen-transmission rate with citric acid as without citric acid.

  • 20.
    Johansson, Dan
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Carbohydrate degradation during softwood Kraft cooking: influence on cellulose viscosity, carbohydrate composition and hexenuronic acid content2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 3, p. 292-298Article in journal (Refereed)
    Abstract [en]

    A kinetic model, including the variables temperature as well as hydroxide ion, sulphide ion and sodium ion concentrations, was fitted to laboratory data from kraft cooking of industrial Norway spruce chips. The model described well the data for carbohydrates, for hexenuronic acids and for the intrinsic viscosity. 

  • 21.
    Johansson, Johan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    The influence of magnesium oxide charge on kappa number after oxygen delignification of softwood acid sulfite pulp2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 4, p. 599-603Article in journal (Refereed)
    Abstract [en]

    A laboratory study has been carried out on the utilization of magnesium oxide (MgO) as alkali in an oxygen delignification stage after acid sulfite pulping of softwood. The first objective was to reconfirm results from previous researchers to better understand the process mechanism concerning optimum MgO charge with respect to kappa number reduction. The second objective was to determine if for example the ionic strength could be an important variable in such a stage. It was found that the MgO charge should not be too high as this resulted in reduced degree of delignification which was unexpected. The results also suggested that the ionic strength in the liquor could be an important parameter in the oxygen delignification stage and that it should not be too high. Thus, ionic strength effects seemed to be present already at 0.02 mol/l which is below the normal ion concentration in a pulp mill. The results indicated that there are at least two chemical activities that are competing in an MgO based oxygen delignification stage. The alkalinity is one and a higher alkalinity improves the degree of delignification. The other seemed to be the ionic strength and if this is too high the degree of delignification will go down.

  • 22.
    Johansson, Kristin
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre.
    Jönsson, Leif J.
    Department of Chemistry, Umeå University.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre.
    Oxygen scavenging enzymes in coatings: Effect of coating procedures on enzyme activity2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 2, p. 197-204Article in journal (Refereed)
    Abstract [en]

    The oxygen content in food packaging may be reduced by attaching oxygen scavengers to the packaging material. The critical parameters that determine the oxygen-scavenging ability of an enzyme-based coating i.e. pH, heat and coating color formulation were evaluated. Glucose oxidase, catalase and glucose were added to latex dispersions in the preparation of the coating colors. The enzymes were entrapped in the coating layers after coating and drying. The clay concentration and drying conditions were varied and the enzymatic activity of the coated layer was evaluated. The need for a pH-buffered system was also studied and the results indicated that, when using a carboxylated latex of a standard coating grade, a buffered system was not needed. A rapid drying at a high temperature was preferred over a slow drying at a low temperature in order to prevent pre-oxidation of the substrate in the wet coating color. The scavenging capacity of the coating was dependent on the amount of substrate for the enzyme reaction left after complete drying. The concentration of clay in the coating formulation was shown to have a marked impact on the oxygen-scavenging ability of the coated layer. The enzyme activity was increased by the addition of clay up to a pigment volume concentration (PVC) of ca. 10%. At higher concentrations of clay, the enzyme activity decreased until the critical pigment volume concentration (CPVC) was reached, probably due to the prevention of diffusion of oxygen and consumption of glucose in the coating process before the layer was completely dried. Further additions of clay above the CPVC resulted in an increased enzyme activity, probably due to the creation of a porous structure.

  • 23.
    Johnson, Johanna
    et al.
    Karlstad University, Faculty of Technology and Science.
    Rättö, Peter
    Karlstad University, Faculty of Technology and Science.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science.
    Blohm, Erik
    STFI, Swedish Pulp and Paper Research Institute, Stockholm, Sweden.
    Measuring the dynamic pressure in a flexographic central impression printing press2004In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 1, p. 84-88Article in journal (Refereed)
  • 24.
    Kihlman, Jonas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    The Sequential Liquid-Lignin Recovery and Purification process: Analysis of integration aspects for a kraft pulp mill2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 4, p. 573-582Article in journal (Refereed)
  • 25.
    Kjellgren, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science.
    Engström, Gunnar
    Karlstad University, Faculty of Technology and Science.
    Influence of base paper on the barrier properties of chitosan-coated papers2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 5, p. 685-689Article in journal (Refereed)
  • 26.
    Kjellgren, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Engström, Gunnar
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Influence of paper structure on barrier properties of starch-coated greaseproof paper2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 87-90Article in journal (Refereed)
  • 27.
    Kjellgren, Henrik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Engström, Gunnar
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Oxygen permeability of polyethylene-extrusion-coated greaseproof paper2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 3, p. 272-276Article in journal (Refereed)
    Abstract [en]

    Polyethylene-extrusion-coated greaseproof paper exhibited significantly lower oxygen permeability than predicted from the oxygen permeability of polyethylene and greaseproof paper itself. Two mechanisms proposed for the superior oxygen permeability of polyethylene-extrusion-coated greaseproof paper were compared. 

  • 28.
    Kullander, Johan
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences.
    Barbier, Christophe
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Evaluation of furnishes for tissue manufacturing; suction box dewatering and paper testing2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 1, p. 143-150Article in journal (Refereed)
    Abstract [en]

    Water removal on a tissue machine becomes progressively more difficult and expensive in each successive zone. A good way to reduce cost can therefore be to improve the dewatering prior to evaporative drying. This can be done by selecting proper raw materials and optimizing the treatment of the fibres in the furnish.

    In this work, four pulps beaten to different levels were studied in vacuum dewatering trials. Mixing of the pulps, common in tissue manufacturing, was also performed. To simulate the suction boxes on a tissue machine, bench-scale laboratory equipment was used. Conditions typically used on a tissue machine regarding dwell times and vacuum levels were chosen. Paper properties relevant for tissue, like wet strength and absorption were measured on non-creped papers. To obtain information about the fibre properties, fibre characterization and microscope studies were also conducted.

    Vacuum dewatering in tissue manufacturing is shown to be affected by the choice of pulp which can be explained by structural differences in the networks caused by variations in fibre properties. Beating has a strong negative impact on the solids contents reached, which is believed to be an effect of both internal and external fibrillation. These results, together with additional data from mixing and paper testing, give a better understanding of how the furnish should be prepared to reduce energy use in the process and still fulfil consumer requirements on properties.

  • 29.
    Kullander, Johan
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Barbier, Christophe
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Evaluation of furnishes for tissue manufacturing: wet pressing2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 5, p. 947-951Article in journal (Refereed)
    Abstract [en]

    Wet pressing is the last operation on the tissue machine in which water can be removed prior to the expensive evaporative drying of the web. An increase in dryness at this stage can lead to major savings during the manufacturing process. A higher solids content can be achieved by suitable selection of raw materials and by optimizing the treatment of the fibres in the furnish. In this work, wet pressing was evaluated with four pulps beaten to different levels in a PFI mill. Wet pressing was done in a dynamic press simulator and conditions representative of tissue machines with regard to nip pressures and dwell times were chosen. Water retention and thermoporometry were used to determine the pore structure of the fibres. Thickness measurements were made to determine the permanent deformation of the sheets after the pressure pulse.

    Wet pressing in tissue manufacturing is shown to be affected by the choice of pulp, which can be explained by differences in pore structure of the fibres and consequently differences in ability to retain water. More water available before pressing leads to more water that can be removed. Beating has a negative impact on the solids contents reached after pressing, which is believed to be an effect of both internal and external fibrillation. These effects of beating seem mainly to affect the dryness after vacuum dewatering, which is also reflected after pressing. Beating delaminates macropores in the fibre wall but has a minor effect on micropores. Both water between the fibres and water in macropores are removed during pressing. These results give knowledge of how the furnish should be prepared in order to reduce energy consumption in the process.

  • 30.
    Land, Cecilia
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Effect of web tension on load- and moisture-induced waviness2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 237-241Article in journal (Refereed)
    Abstract [en]

    Research has been carried out to explore the moisture-induced waviness in paper dried under tension between rolls. The role of the web tension in out-of-plane buckling was investigated. A paper web was preconditioned at 40% RH and tensions of 480-1400N/m applied to the web while the humidity was increased to 80%RH. The topography of the paper was measured at intervals of 180s. A 70gsm paper made on a hybrid former and coated and calendered and the tensile stiffness measured after conditioning at humidities of 50%RH, 70%RH and 85%RH. When the web tension was increased from 480N/m to 1,400N/m, the wavelength decreased from 34mm to 16mm. No significant web tension effect was observed after drying. Under all tensions, the average roughness was approximately 50 micron. When moisture was involved, even when the tension was maintained in the elastic range, the waviness was permanent

  • 31.
    Land, Cecilia
    Karlstad University, Faculty of Technology and Science.
    Effect of web tension on load- and moisture-induced waviness2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 2, p. 237-241Article in journal (Refereed)
    Abstract [en]

    Paper is affected by both tension and moisture. When paper is tensed between rollers, shrinkage and expansion are restricted. Waves can then appear on the paper web. These conditions are assumed to be partly responsible for the waviness problem in heatset web offset printing. The printed papers then exhibits a wavy shape, with corrugations aligned in the printing direction. The waves caused by mechanical loading and moisture were evaluated. The change in topography of a paper web under tension was studied during moistening and drying. A 70 g/m2 paper was tested at tension levels between 480 N/m and 1400 N/m. The moisture uptake was 3 – 5 g/m2. The wavelength of the topography decreased with increasing web tension. The tension had no significant effect on the height of the waviness. Four weeks storage of the samples did not yield any significant relaxation of the waviness amplitude.

  • 32.
    Land, Cecilia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Stolpe, Lennart
    Karlstad University, Faculty of Technology and Science.
    Wahlström, Torbjörn
    Stora Enso, Karlstad, Sweden.
    Beghello, Luciano
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    MD strain and bagginess due to calendering2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 1, p. 106-117Article in journal (Refereed)
  • 33.
    Land, Cecilia
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Wahlström, Torbjörn
    Stora Enso, Karlstad, Sweden.
    Stolpe, Lennart
    Beghello, Luciano
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Plastic strain of moisture streaks at different moisture contents2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 4, p. 481-487Article in journal (Refereed)
    Abstract [en]

    An uneven moisture profile in the paper web during drying can cause runnability problems due to slack areas in the paper web. This study aims at indentifying the moisture level at which it is most important to keep the moisture even. This was evaluated with a laboratory study of plastic strain after loading wet paper samples to strains between 0.3-4% and unloading. The papers tested were made from softwood bleached kraft pulp and the moisture content varied between 9 and 50%. The plastic strain was highest at a moisture content of 20-30%, but the sensitivity to moisture variations was highest at a moisture content of 10-20%. The paper was also sensitive to moisture variations above a moisture content of 30%.

    According to calculations based on the laboratory results, moist streaks appearing at a high moisture content would turn into short streaks, and moist streaks appearing at a low moisture content would turn into long streaks. A machine trial with moist streaks applied at high moisture resulted in short streaks in the paper, confirming the qualitative results of the laboratory study.

  • 34.
    Mesic, Behudin Beko
    et al.
    Scion, Rotorua, New Zealand..
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science.
    Johnston, James
    Victoria Univ Wellington, Wellington, New Zealand..
    Latex-based barrier dispersion coating on linerboard: Flexographic multilayering versus single step conventional coating technology2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 2, p. 349-359Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate the possibility of using the flexographic printing process for the deposition of multilayered latex-based barrier dispersion coatings on linerboard to improve its moisture barrier properties. A coating formulation developed for a conventional coater has been tested using a flexographic printing web press. The performance of multi-layering of up to six layers was compared with a single step conventional coating process in terms of runnability and barrier performance. A commercial linerboard was used as substrate for both processes. The coated linerboard samples were examined using scanning electron microscopy and surface profiling, and were characterized with respect to their coating grammage, WVTR and water absorption (Cobb(120)) properties. The impact of waxes on water absorption was also investigated for the two coating strategies. The results show that for a similar total coating grammage ( about 6 g m(-2)), samples coated using the flexographic press showed better barrier performance and less cracks on the coated surfaces than samples coated using a conventional coating process.

  • 35.
    Montibon, Elson
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Jarnstrom, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Love, Karen T.
    Scion, Rotorua 3010, New Zealand..
    Electroconductive paper - a study of polymer deposition and conductivity influenced by sheet forming and fibre beating2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 4, p. 473-480Article in journal (Refereed)
    Abstract [en]

    A conducting polymer modified paper was produced by depositing poly(3,4-ethylenedioxy thiophene)/poly(4-styrene sulfonate) (PEDOT:PSS) and N-methylpyrrolidone blend onto dynamically-formed and handsheet-formed paper substrates. The effect of fibre beating on the conducting polymer deposition and the bulk conductivity of the coated papers was investigated. A bulk electrical conductivity of the order 10(-1) S/cm was, established for unbeaten samples coated with PEDOT:PSS dispersion. It was observed that the bulk conductivity of the coated papers depended on the quantity of PEDOT:PSS deposited; although at a lower polymer application, degree of fibre beating was of higher consequence. This was due to the increased surface contact of the highly refined and well-packed fibres which decreased the distance between PEDOT molecules. To understand the nature of the conductance, the location of the conducting polymer within the paper substrate was investigated by mercury porosimetry, nitrogen adsorption analysis and scanning electron microscopy. Results showed a preferential deposition of PEDOT:PSS at fibre crossings as a remnant of the wetting front. In addition, traces of PEDOT:PSS could be seen throughout the fibre network. Still, the detailed conductance process remains unknown as the presence and contribution of ions to conductance cannot be excluded. The influence of the deposited polymer on the physical behaviour of the substrate was examined by tensile index data and contact angle measurement. No detrimental effect of the water from the PEDOT:PSS solution was observed.

  • 36.
    Montibon, Elson
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Love, Karen T.
    Scion, New Zealand.
    Electroconductive paper: a study of polymer deposition and conductivity influenced by sheet forming and fibre beating2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 4, p. 473-480Article in journal (Refereed)
  • 37.
    Nilsson, Lars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Stenström, Stig
    Lunds universitet.
    Predicting water removal during vacuum dewatering from fundamental fibre property data2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 2, p. 265-271Article in journal (Refereed)
    Abstract [en]

    Control of the solids content after vacuum dewatering is vital for efficient control and energy use of the paper machine. Dewatering is a complex function of many parameters such as fibre and pulp properties as well as settings on the paper machine and a predictive model for dewatering will require extensive and detailed studies of the occurring physical phenomena. The hypothesis investigated in the present study is that fibre width and fibre length density measured for fibres suspended in water can be used for estimating the achievable dryness in vacuum dewatering. The hypothesis was tested by comparing model predictions to experimental data for 11 different pulps. The results show that the dryness after vacuum dewatering can be estimated from the fibre length density and the fibre width for the fresh pulps using an elliptical fibre cross-section model with a ratio of 0.48 between the short and long axes. For the dried pulps a lower value was needed to reach a good agreement.

  • 38.
    Nilsson, Lars
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Tysén, Aron
    Innventia AB.
    Vomhoff, Hannes
    Innventia AB.
    The influence of grammage and pulp type on through air drying2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 4, p. 651-659Article in journal (Refereed)
    Abstract [en]

    The influence of grammage and pulp type on through air drying was studied. The temperature of a sample was measured during the drying process and the observed temperature changes were used to evaluate the drying process. Laboratory sheets with grammages 15- 60 g/m², from two softwood and two hardwood bleached chemical pulps were used. All samples were analysed with respect to formation, flow resistance, modified permeability, mean drying time, non-uniformity of drying time, and area- and mass-specific drying rate. The pulps had different modified permeabilities but showed similar behaviour when analysed as a function of grammage. A constant value was found for higher grammages, while an increase in modified permeability was found at decreasingly low grammages. Almost all pulp and grammage combinations had similar area-specific drying rates, but the mass-specific drying rates decreased with grammage. However, the samples with lower grammages had mass specific drying rates independent of modified permeability, where samples with increasing grammage showed an increasing dependency. This implies that the drying efficiency at low grammages was not controlled by the volume flow of the drying air. A good correlation was found between energy needed to evaporate water and energy supplied by the drying air as estimated from the surface temperature and air flow measurement. The surface temperature can therefore be used to quantify the drying process.

  • 39.
    Nyflött, Åsa
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Axrup, Lars
    Stora Enso.
    Carlsson, Gunilla
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013), Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Wahlström, Torbjörn
    Stora Enso.
    Influence of kaolin addition on the dynamics of oxygen mass transport in polyvinyl alcohol dispersion coatings2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 3, p. 385-392Article in journal (Refereed)
    Abstract [en]

    The permeability of dispersion barriers produced from polyvinyl alcohol (PVOH) and kaolin clay blends coated onto polymeric supports has been studied by employing two different measurement methods: the oxygen transmission rate (OTR) and the ambient oxygen ingress rate (AOIR). Coatings with different thicknesses and kaolin contents were studied. Structural information of the dispersion-barrier coatings was obtained by Fourier transform infrared spectroscopy (FTIR) spectroscopy and scanning electron microscopy (SEM). These results showed that the kaolin content influences both the orientation of the kaolin and the degree of crystallinity of the PVOH coating. Increased kaolin content increased the alignment of the kaolin platelets to the basal plane of the coating. Higher kaolin content was accompanied by higher degree of crystallinity of the PVOH. The barrier thickness proved to be less important in the early stages of the mass transport process, whereas it had a significant influence on the steady-state permeability. The results from this study demonstrate the need for better understanding of how permeability is influenced by (chemical and physical) structure.

  • 40.
    Olsson, Robert
    et al.
    Karlstad University, Faculty of Technology and Science.
    Yang, Li
    Karlstad University, Faculty of Technology and Science.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science.
    Water retention of flexographic inks and its influence on final print gloss2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 287-292Article in journal (Refereed)
  • 41.
    Olsson, Robert
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Yang, Li
    van Stam, Jan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre. Karlstad University, Faculty of Technology and Science, Materials Science.
    Effects on ink setting in flexographic printing: coating polarity and dot gain2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 5, p. 569-574Article in journal (Refereed)
    Abstract [en]

    Research has been carried out to study the factors that affect ink setting, with particular focus on the effects of coating polarity and the printing pressure in flexographic printing. Different coating layers were prepared on non-porous polyester films. The coating colours were based on calcium carbonates of different particle sizes, lattices of different polarities and a carboxymethyl cellulose (CMC) thickener. Two latex films were prepared to characterise the surface tension properties through contact angle measurements, which were repeated several times for each latex film and testing fluid. The coating layers were printed in a laboratory printing press under different printing pressures using a water-based flexographic ink. Results showed different print densities for a given amount of ink transferred on the different substrates, with the latex character rather than the pore size of the substrates affecting the print density. Compared with the less polar substrate, the more polar substrate resulted in a higher print density. A non-linear relationship between physical dot enlargement and printing pressure was visualised, resulting from increasing printing form deformation. A mathematical model for printing plate deformation has been proposed that takes into account elastic deformations. It was found that the diameter of the printed halftone dot was larger in the print direction than in the cross print direction. (7 fig, 6 tab, 17 ref)

  • 42.
    Osterberg, Monika
    et al.
    Aalto University, Finland.
    Sipponen, Mika Henrikki
    Aalto University, Finland.
    Henriksson, Gunnar
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Editorial: From understanding the biological function of lignin in plants to production of colloidal lignin particles2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 4, p. 483-484Article in journal (Refereed)
    Abstract [en]

    There is a paradigm shift going on in lignin utilization. High-volume materials and chemicals, as well as more engineered materials, like carbon fibers or active carriers, are currently being developed. However, in order to enhance lignin utilization in these and other value-added products, there is a need for better understanding of lignin function in woody tissues plus control over isolation, fractionation and other processing technology. Therefore, part of this issue is dedicated to articles about lignin. These range from lignin extraction to scale-up of the colloidal lignin particle production process. Focus is on fundamental understanding of interactions, a necessity for successful applications of this complex biopolymer.

  • 43.
    Ragnarsson, Micael
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Bousfield, Douglas
    University of Maine, Forest Bioproducts Research Institute.
    Engström, Gunnar
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre.
    The effect of Moisture on Deformation of Starch Containing Coating Layers during Calendering, studied using Confocal Laser Scanning MicroscopyIn: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Article in journal (Other academic)
    Abstract [en]

    The effect of moisture level on the deformation of coating layers during calendering was studied using Confocal Laser Scanning Microscopy (CLSM) and porosimetry. Model draw down coatings with starch/latex and carboxymethyl cellulose (CMC)/latex on polyester and on paper were dried at different relative humidities. The samples were calendered and despite their higher moisture content, the starch/latex coatings did not deform much more than the CMC/latex coatings.  For coatings dried between 20 and 50% ambient relative humidity (RH), no significant changes in deformation behavior or in moisture content were observed. When the RH was increased to 90%, the moisture content and the deformation during calendering was much higher with both systems indicating that the interaction between latex and water plays an important role for the compression during calendering. An inverse relationship between fluorescence intensity and porosity was observed on coated polyester sheets when measured by the CLSM technique, but the cause of the relationship is unclear and there may have been more than one mechanism. Studies of coated paper showed that Starch/latex coatings have a higher standard deviation in the fluorescence intensity than CMC/latex coatings, indicating a less uniform surface in the case of the starch/latex coatings. The cause of this non-uniformity remains unclear, but it has the potential to impact print properties.

  • 44.
    Ragnarsson, Micael
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Engström, Gunnar
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Porosity Variations in Coating Layers - Impact on Back-trap Mottle2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 2, p. 257-263Article in journal (Other academic)
    Abstract [en]

    A pilot coating trial was performed to study 1) whether the drying strategy introduces porosity variations in the coating layer and 2) whether porosity variations caused by the subsequent supercalendering are linked to back-trap mottle in offset prints. The porosity variations and the mean porosity were indirectly measured using a burn-out test. Coating colours were compared with three different binder systems 1) carboxy methyl cellulose (CMC)/SB-latex, 2) dextrin/SB-latex and 3) oxidized starch/SB-latex. The results showed that neither the mean porosity nor the porosity variations were affected by the drying strategies studied. During calendering the coating with the CMC/SB-latex binder system was compressed the most, but the porosity variations were nevertheless small. Both the compression and the porosity variations were influenced by the drying strategy, which shows that the strategy had an impact on the mechanical properties of the dry coating layer. With CMC/SB-latex and dextrin/SB-latex, the mottle increased when the porosity variations introduced by the calendering increased. In the case of the oxidized starch/SB-latex, the opposite was true. It was concluded that with CMC/SB-latex and dextrin/SB-latex, print mottle is caused by calendering and with oxidized starch/SB-latex by non-uniformities introduced during dewatering and drying, possibly binder migration.

  • 45.
    Ragnarsson, Micael
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Järnström, Lars
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Engström, Gunnar
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Shrinkage of Coating LayersIn: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Article in journal (Refereed)
    Abstract [en]

    The shrinkage of coating layers during the process of consolidation between the first critical concentration (FCC) and the second critical concentration (SCC) has been studied. Ground calcium carbonate (GCC) grades with different particle size distributions together with binder systems based on CMC/latex, dextrin and oxidized starch were used in the formulations of the coating colors. The aim was to investigate differences in shrinkage behavior between these systems. The porosity and the pore radius of the coatings at FCC (filter cake) and SCC (final dry coating) were measured. The coating colors were rheologically characterized. It was shown that the shrinkage was governed by the capillary forces developed in the filter cake during the consolidation process. These forces were greater for dextrin than for CMC/latex and oxidized starch. This was attributed to a weaker chemical interaction between this binder and the pigment. At a given capillary pressure, the dextrin-containing coating was found to shrink more than the other two coatings. This is suggested to be due to a softer or more plastic deformable filter cake.

  • 46.
    Rahman, H.
    et al.
    Mittuniversitetet.
    Engstrand, P.
    Mittuniversitetet.
    Sandström, P.
    SCA R&D.
    Sjöstrand, Björn
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Dewatering properties of low grammage handsheets of softwood kraft pulps modified to minimize the need for refining2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 3, p. 397-403Article in journal (Refereed)
    Abstract [en]

    Previous paper (Rahman et al. 2017) showed that the yield of softwood kraft pulp increased by the addition of either polysulfide or sodium borohydride because of higher hemicellulose retention. An increase in hemicellulose content can make dewatering more difficult as WRV of the pulp increases, but instead, an overall increase in pulp yield could improve dewatering as a sheet of a certain weight will contain fewer fibres, giving a more open sheet structure. It was therefore of interest to measure the dewatering properties of low grammage handsheets (20 g/m2) under conditions mimicking the tissue paper machine dewatering processes, and sheet strength properties, WRV, °SR and fibre dimensions were also studied. The results showed that the positive influence of overall yield increase dominated over the negative influence of an increase in hemicellulose content on the dewatering properties, particularly at lower refining energy levels. Moreover, higher yield and higher hemicellulose content pulps had a higher tensile index at the same dryness. A given tensile index was achieved with less refining energy. The results indicate that increased yield and hemicellulose content by modification of the kraft pulping process will result in a pulp with a potential to improve tissue paper quality.

  • 47. Rättö, Peter
    et al.
    Hornatowska, Joanna
    Barbier, Christophe
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Influence of the distribution of the shape and size distribution of pigment particles on cracking in coating layers during creasing2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 4, p. 714-720Article in journal (Refereed)
    Abstract [en]

    The crack area on a coated board was measured after creasing and folding and the crack area on a coated copy paper was measured after folding. A clay pigment and two Ground Calcium Carbonate (GCC) pigments were used. The GCC pigments differed in their particle size distribution. The binder was either an S/B latex or an S/B latex combined with starch. The type of pigment seemed to have the greatest influence on the crack area in creased and folded board. Clay showed a larger crack area than the GCC with a broad particle size distribution. The GCC with a narrow particle size distribution showed a considerably larger crack area than both the clay pigment and the GCC with a broad particle size distribution. The coatings containing starch generally showed a larger crack area than the coatings that only contained the S/B latex. After the folding of the copy paper, the crack area showed a slightly different pattern. Here, it seemed that the binder was of greater importance than the type of pigment, with the coatings containing only latex showing a considerably lower crack area than the coatings containing starch. The coatings that were based on the clay pigment showed similar values as the coatings based on the GCC pigment with the broad particle size distribution. The coatings based on the GCC with the narrow particle size distribution showed displayed considerably higher crack areas than the coatings based on the other two pigments. The cracking tendency of the coatings, based on the GCC with the narrow particle size distributions was probably due to a greater demand for latex, i.e. smaller particles in the GCC with broad particle size distribution would probably fill in the voids and the GCC with the broad particle size distribution will therefore demand less binder. It was further suggested that the different loadings on the coating layer during the creasing and folding of the board, compared to the folding of copy paper, explain the different results obtained with the two base-substrates. 

  • 48.
    Sjöstrand, Björn
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Barbier, Christophe
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Nilsson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Rewetting after high vacuum suction boxes in a pilot paper machine2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 4, p. 667-672Article in journal (Refereed)
    Abstract [en]

    Increased energy efficiency is a major concern for all companies today. Not only does the cost efficiency follow energy efficiency but also environmental and sustainability aspects motivate more energy efficient production lines. A study has been made on a pilot paper machine with the purpose to show the magnitude and time of rewetting after high vacuum suction box dewatering. The grammages used in this study were 20 and 100 g/m2 to cover both tissue and printing paper grades. Machine speed was varied from 400 to 1600 m/min and the maximum pressure drop in the suction box was 32 kPa. The pulp used was unbeaten, chemical, fully bleached softwood from Sweden. Rewetting is observed when the dewatering in the suction box is sufficiently high. No rewetting takes place when the dewatering in the suction box is limited due to insufficient pressure drop and dwell time. The time for the rewetting is in the range of 10-50 ms and in this study the maximum rewetting observed is 180 g/m2, or 6.1% decrease in dryness. The mechanisms behind the phenomenon are believed to be capillary forces caused by sufficiently low sheet moisture and expansion of the network. This study shows that rewetting is so fast that it would be difficult to prevent it without changing major machine parameters.

  • 49.
    Thorman, Sofia
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). RISE Bioeconomy.
    Ström, Göran
    RISE Bioeconomy.
    Gane, Patrick. A. C.
    OmyaInternationalAG, Switzerland; Aalto University, Finland.
    Impact of non-uniform water absorption on water-interference print mottle in offset printing2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 1, p. 150-163Article in journal (Refereed)
    Abstract [en]

    Print mottle is a serious and yet common print defect in offset printing. An imbalance between the feed of fountain solution and the ability of the paper substrate to absorb and transport this water away from the surface can cause moisture/water interference problems. In the study presented here, we have investigated the uniformity of aqueous absorption and coating structure of pilot-coated papers with different types and dosages of dispersants and linked this to print mottle and uncovered areas (UCA). In earlier studies, the print quality of these papers indicated that a moderate addition of excess dispersant caused ink refusal, ink-lift-off (ink-surface adhesion failure) and water-interference mottle when printing at elevated fountain feed. In the present study, we have shown that a majority of the samples with uneven water/moisture absorption and an uneven burn-out reflectance tended to have more severe printing problems related to surface-moisture/water.An aqueous staining technique was used to characterise the absorption non-uniformities. This method has been developed previously with focus on absorption of flexographic water-based inks but can clearly give relevant information also for offset printing, when it comes to moisture/water interference mottle.

  • 50.
    Thorman, Sofia
    et al.
    Innventia AB, Stockholm.
    Ström, Göran
    Innventia AB, Stockholm.
    Hagberg, Anni
    Innventia AB, Stockholm.
    Johansson, Per-Åke
    Innventia AB, Stockholm.
    Uniformity of liquid absorption by coatings: Technique and impact of coating composition2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 456-465Article in journal (Refereed)
    Abstract [en]

    The interaction between a liquid and a paper surface is important for a number of paper treatment processes, where absorption is of special significance during printing. Many absorption measurement techniques use a large available volume of liquid to characterise absorption, when compared to the volume of the coating. The uniformity of the absorption is also seldom characterised. We have developed a new technique, which is presented in this article, to study the uniformity of absorption of a small amount of liquid. This technique is based on the short-time absorption (tenth of a second) of a coloured liquid, the blotting of excess liquid and a characterisation of the pattern of the stain. This method made it possible to detect differences among coating layers with different compositions. In many cases, the absorption non-uniformity could be linked to variations in the coating thickness and/or wettability. The thinner and thicker areas of the coating layers were interpreted as having different pore structures. Neither the coating thickness nor the wettability could provide a full explanation, which showed the need to develop a method to characterise absorption uniformity instead of only relying on measuring the total absorption potential.

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