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  • 101.
    Neuman, Magnus
    et al.
    Mid Sweden University, Sweden.
    Coppel, Ludovic Gustafsson
    RISE, Innventia.
    Edström, Per
    Mid Sweden University, Sweden.
    A partial explanation of the dependence between light scattering and light absorption in the Kubelka-Munk model2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 426-430Article in journal (Refereed)
    Abstract [en]

    The Kubelka-Munk scattering and absorption coefficients of a set of paper samples are assessed using reflectance measurements in d/0 geometry. The coefficients display the widely studied dependence between light scattering and light absorption, since the light scattering coefficient decreases in regions of high absorption. It is shown using general radiative transfer theory that part of this dependence can be explained and eliminated by taking into account the geometry of the d/0 instrument and the single scattering anisotropy, thus capturing the angular variations of the light reflected from the samples. These findings allow the papermaker to better predict the reflectance from mixtures of pulps, fillers, dye, and FWA, and to better evaluate bleaching efforts.

  • 102. Neuman, RD
    et al.
    Berg, JM
    Claesson, PM
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Direct measurement of surface forces in papermaking and paper coating systems1993In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 8, p. 96-104Article in journal (Refereed)
    Abstract [en]

    The interaction forces between surfaces of cellulose, hemicellulose and mineral filler were directly measured for the first time using the surface force technique of Israelachvili and co-workers (Israelachvili, Adams 1978). A spin-coating technique was developed to prepare thin films (30-40 nm) of cellulose on the mica substrates employed in the surface force apparatus. The cellulose layers have a molecular scale roughness and, when immersed in water, swell considerably. The measured force vs. distance profile is characterized by three distinct regimes and is interpreted in terms of a simple model for the cellulose-water interface, namely, the water-swollen cellulose layer has long (and weakly) charged cellulose chains or "molecular fibrils" extending about 100 nm from its surface. Conventional DLVO theory cannot explain the forces observed between cellulose surfaces. Steric forces rather than electrostatic forces dominate the interactions due to the dangling tails of cellulose chains and the compressibility of the cellulose layer. Surface force measurements were also performed on adsorbed xylan layers. Nonequilibrium layers, whose structure and surface forces are dominated by the dangling tails of polysaccharide chains, adsorb via a "polymer reshuffling" mechanism consistent with the size (and charge) distribution for xylan molecules. In addition, the mechanism of calcium ion-induced aggregation of kaolin suspensions was investigated by studying the forces between model (mica) surfaces immersed in an aqueous sodium polyacrylate solution. An adhesive primary minimum, attributed to calcium ion-mediated electrostatic bridges, offers an explanation for the aggregates of face-to-face associated kaolin particles. The surface force technique clearly represents a novel approach for both applied and fundamental studies of the surface and colloid chemistry of papermaking and paper coating systems.

  • 103.
    Nordström, Bengt
    et al.
    SCA R&D Centre, Sweden.
    Hermansson, Lennart
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy.
    Effect of fiber length on formation and strength efficiency in twin-wire roll forming2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 1, p. 119-125Article in journal (Refereed)
    Abstract [en]

    A change in fiber length is known to change fiber flocculation and formation of machine-made paper, but it has been unclear how a change in formation through fiber length affects strength efficiency. (The strength efficiency reflects how well the furnish strength, as indicated by the handsheet strength, is utilized in the machine-made paper.) The effect of fiber length on strength efficiency in twin-wire roll forming was presently investigated by examining two furnishes with different average fiber length, prepared from the same batch of softwood kraft pulp, over a wide range of headbox consistencies on a pilot machine. An increase in fiber length resulted not only in worse Ambertec formation over the whole range of headbox consistencies but also in faster relative deterioration of the formation with increasing consistency. Tensile strength efficiency and Z-strength efficiency were both reduced when the formation was impaired through increased fiber length, and the effect was similar to the effect of a corresponding change in formation through headbox consistency. A given change in formation, through fiber length or headbox consistency, had a larger relative effect on Z-strength efficiency than on tensile strength efficiency.

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  • 104.
    Nordström, Bengt
    et al.
    SCA, Sweden.
    Hermansson, Lennart
    RISE - Research Institutes of Sweden, Bioeconomy, Papermaking and Packaging.
    Effect of machine speed on formation and strength efficiency in twin-wire roll forming of never-dried unbleached softwood kraft pulp2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 2, p. 271-278Article in journal (Refereed)
    Abstract [en]

    There is a constant drive to increase machine speed in the production of kraftliner and most other major paper grades, but the separate effect of the machine speed on the paper properties has been unclear. The effect of machine speed in twin-wire roll forming of never-dried unbleached softwood kraft pulp was evaluated here in a pilot machine investigation by examining three machine speed levels (500, 750, and 1000 m/min) over a series of jet-to-wire speed differences. Similar headbox consistency and draw from wire section to winding were employed at the different machine speed levels. An increase in the machine speed had a favorable effect on formation and Z-strength efficiency over a wide range of jet-to-wire speed differences, whereas the machine speed had an insignificant effect on tensile strength efficiency and tensile stiffness efficiency. For all properties, the overall shape of the jet-to-wire speed difference curve remained similar when changing the machine speed.

  • 105.
    Nordström, Bengt
    et al.
    SCA R&D Centre, Sweden.
    Hermansson, Lennart
    RISE, Innventia.
    Effect of refining on strength efficiency in twin-wire roll forming of never-dried unbleached softwood kraft pulp2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 4, p. 624-633Article in journal (Refereed)
    Abstract [en]

    Whereas refining is required for the strength development of chemical pulps, it has been unclear how refining affects the utilization of the furnish strength, as reflected by the handsheet strength, in the machine-made paper (strength efficiency). This work examined effects of refining on formation and strength efficiency in twin-wire roll forming of never-dried unbleached softwood kraft pulp in a pilot machine investigation comprising three separate sections. The first section showed that a change in refining energy has no significant effect on formation, tensile strength efficiency, tensile stiffness efficiency, or compression strength efficiency at a given consistency when the fiber length remains similar. The second section demonstrated that a change in kappa number has no significant effect on formation or tensile strength efficiency at a given consistency when the fiber length of the refined pulp remains similar. Here, an increase in kappa number involved an increase in refining energy. The third section showed that a reduction in headbox consistency results in an improvement in formation and tensile strength efficiency that is similar in magnitude over the whole refining curve.

  • 106.
    Nordström, Bengt
    et al.
    SCA R&D, Sweden.
    Hermansson, Lennart
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Papermaking and Packaging.
    Effect of softwood kraft fiber coarseness on formation and strength efficiency in twin-wire roll forming2018In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 33, no 2, p. 237-245Article in journal (Refereed)
    Abstract [en]

    It has been unclear how fiber coarseness affect formation and the utilization of furnish strength in the machine-made paper (strength efficiency). In this work, the effect of softwood kraft fiber coarseness on formation and strength efficiency in twin-wire roll forming was examined in a pilot machine investigation. A reduction in softwood kraft fiber coarseness from 0.21 to 0.17 mg/m, associated with a reduction in fiber grammage from 6.2 to 5.2 g/m2, was found to have no significant effect on formation at the point of minimum shear during dewatering. The insignificant effect of reduced coarseness can be interpreted as the net result of two effects, namely, an increase in the number of fiber layers at a given grammage (favorable) and an increase in the flocculation tendency (unfavorable). While the effect of coarseness was negligible at the point of minimum shear, coarser fibers enabled larger improvement in formation through the jet-to-wire speed difference. In correspondence to the insignificant effect on formation, fiber coarseness had a negligible effect on tensile strength efficiency and Z-strength at the point of minimum shear. The larger improvement in formation through the jet-to-wire speed difference for the coarser fibers was reflected in a favorable effect on Z-strength efficiency.

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  • 107.
    Nordström, Bengt
    et al.
    SCA R&D, Sweden.
    Hermansson, Lennart
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy.
    Effect of the ratio of softwood kraft pulp to recycled pulp on formation and strength efficiency in twin-wire roll forming2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 2, p. 229-236Article in journal (Refereed)
    Abstract [en]

    Research has been undertaken to investigate how the tensile strength efficiency and Z-strength efficiency in twin-wire roll forming is affected when changing formation through the softwood kraft content in a mixture with recycled pulp. The effect of a change in formation through the softwood kraft content and the effect of a change in formation through headbox consistency were also compared. Five kraft contents (0, 25, 50, 75 and 100%) were investigated at volumetric headbox flow rates of 111 and 1,77l/sm. Three additional flow rates were used at a kraft content of 50%. Impaired formation through the softwood kraft content reduced tensile strength efficiency and Z-strength efficiency. Both these properties were similarly affected whether the formation was changed by the softwood kraft content or the headbox consistency. The relative impact of formation was larger for Z-strength efficiency compared with tensile strength efficiency. The reduction in tensile strength efficiency was replicated in a smaller relative increase in tensile strength for machine-made paper than for handsheets made of the furnish. Considering the effect on strength efficiency when evaluating furnishes has been demonstrated as an important concern.

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  • 108.
    Nordström, Bengt
    et al.
    SCA R&D, Sweden.
    Hermansson, Lennart
    RISE - Research Institutes of Sweden, Bioeconomy.
    One-sided versus two-sided roll forming of never-dried softwood kraft pulp: effects on formation and strength efficiency2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 3, p. 407-414Article in journal (Refereed)
    Abstract [en]

    Research has been undertaken to demonstrate the effect on z-strength of headbox consistency in one-sided versus two-sided roll forming of unbleached softwood kraft pulp over a wide range of jet to wire speed differences. In addition, formation and tensile strength were evaluated. Using a pilot machine, each forming method was examined at two headbox consistency levels (0.4 and 0.6%). The wire speed was varied from 550 to 660m/min while maintaining the headbox conditions, resulting in a change in grammage from approximately 71gsm to 61gsm. A significantly higher Z-strength was noted for one-sided roll forming at a headbox consistency of 0.4% compared with two-sided roll forming. However, an increase in consistency resulted in a ore similar Z-strength through a larger reduction in Z-strength efficiency for one-sided than two-sided roll forming. In addition, Z-strength was promoted by formation improvement through the jet to wire speed difference in both one-sided and two-sided roll forming of the furnish. The effects of the jet to wire speed difference on formation and tensile strength efficiency in one-sided roll forming of the present furnish were relatively more favourable and more similar to the effects in two-sided roll forming.

  • 109.
    Nordström, Bengt
    et al.
    SCA, Sweden.
    Hermansson, Lennart
    RISE - Research Institutes of Sweden, Bioeconomy, Papermaking and Packaging.
    Successive twin-wire roll forming of two-ply paper with softwood kraft pulp and recycled pulp - Effect of kraftply formation on Z-strength2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 4, p. 639-645Article in journal (Refereed)
    Abstract [en]

    Kraftliner and kraft-top liner typically consists of two or more plies that are formed separately and combined by couching. The Z-strength tends to be limited by the ply adhesion, and the softwood kraft pulp used is commonly refined beyond the optimum for tensile strength to ensure sufficient Z-strength. In this work, two-ply forming by successive twin-wire roll forming, was evaluated with moderately refined never-dried unbleached softwood kraft pulp and recycled pulp in different plies. Successive twin-wire roll forming involved two-sided roll forming of the first ply and onesided roll forming of the second ply directly onto the first ply. Two-sided roll forming of the recycled pulp and onesided roll forming of the kraft pulp was evaluated in parallel to the reversed combination. The Z-strength was found to be limited by the strength of the kraft ply rather than by the ply adhesion. The effect on Z-strength when changing headbox consistency or when going from one-sided to two-sided roll forming for the kraft ply was in agreement with results for single-ply forming. Besides the favorable findings for Z-strength, the results suggest that successive roll forming enables an efficient utilization of the tensile strength potential of the softwood kraft pulp. 

  • 110.
    Nygårds, Mikael
    RISE, STFI-Packforsk.
    Experimental techniques for characterization of elasticplastic material properties in paperboard2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 4, p. 432-437Article in journal (Refereed)
    Abstract [en]

    Four experimental techniques to characterize elastic-plastic material properties for paperboard are presented. To evaluate properties as a function of paperboard thickness the bottom, middle and top plies were separated by grinding. The different plies have been characterized with respect to in-plane tension, cyclic ZD tension, out-of-plane shear and cyclic ZD compression. These tests were chosen since they are easily interpreted in term of stresses and strains, and give a good set of elastic-plastic material properties that are needed to describe the mechanical properties of the materials. For the ZD tension and compression tests several loading/unloading cycles were used in order to evaluate how the elastic modulus evolves as a function of deformation. For the ZD tension it was observed that the elastic modulus degrade faster than the strength. For all tests functions that describe the stress-strain curves are proposed and hence material parameters with a physical interpretation were introduced.

  • 111.
    Nygårds, Mikael
    RISE, STFI-Packforsk.
    Modelling the out-of-plane behaviour of paperboard2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 1, p. 72-76Article in journal (Refereed)
    Abstract [en]

    A material model consisting of a continuum and an interface model was proposed. When the models are used together the mechanical properties of paperboard can be accounted for. The continuum model was elastic-plastic in shear and compression, while only elastic in tension. In the continuum model two different yield surfaces were used to initiate plastic deformation; one for compression and one for combined shear and normal stresses. The elastic-plastic interface model accounts for separation in the normal and tangential directions. The models have been numerically implemented into the finite element software Abaqus (2007). The implementations were used to show that the response of a cyclic tension and cyclic compression test can be predicted. Moreover, simulations with combined compression and shear stresses were presented.

  • 112.
    Nygårds, Mikael
    et al.
    RISE, Innventia. KTH Royal Institute of Technology, Sweden.
    Bhattacharya, Abhijit
    ITC Limited, India.
    Krishnan, S. V. R.
    ITC Limited, India.
    Optimizing shear strength profiles in paperboard for better crease formation2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 3, p. 510-520Article in journal (Refereed)
    Abstract [en]

    The tensile properties and shear strength profiles have been evaluated for three paperboards having different through thickness profiles. Paperboard with a 1) strong middle ply and a weak bottom interface, 2) weak middle ply and top interface and 3) weak top and bottom interfaces. The creasing and folding performances at different crease depths were evaluated, and it was concluded that it is preferable to have a weak bottom interface to form a well-defined crease that bulged out and formed a well-shaped crease. Package formation of a cigarette package was evaluated as the ability to use multiple creases to form round corners. In addition, the in-plane crack tendency on the outside of the crease, and the forming of a smooth crease line on the inside of the crease were studied. The ability to form rounded corners coincided well with the formation of well-shaped crease lines. Creases with a weak bottom interface did also generate good looking rounded corners. If also the top interface was weak, in-plane cracks on the outside of the crease could be prevented. A well-shaped crease also resulted in a straight and well defined crease line on the inside of a folded corner. Finally, the evaluation of shear strength profiles was a good tool to confirm process changes that were made to make paperboards with different through thickness profiles.

  • 113.
    Nygårds, Mikael
    et al.
    RISE, Innventia.
    Sundström, Jonas
    RISE, Innventia.
    Comparison and analysis of in-plane compression and bending failure in paperboard2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 432-440Article in journal (Refereed)
    Abstract [en]

    In-plane compression of paperboard, using long (LCT) and short compression test (SCT), and bend-ing, using the L&W creasability tester, have been ana-lyzed using three paperboards with similar strength prop-erties but different ZD profiles. The failure loads from the methods have been compared and the failure mechanisms analyzed. It was shown that at maximum bending moment from bending of samples using L=10 mm and L=50 mm, the SCT value and the maximum bending force from LCT all varied linearly with each other, indicating that same dam-age mechanism is activated. It was suggested that delamination cracks were initiated during SCT and LCT as well as during bending when plastic deformation had been initiated in an outer ply subjected to compressive stress. The plastic deformation would be initiated when the yield stress in the ply was reached, determined by an in-plane tensile test. When plastic deformation takes place, it will generate shear induced delamination cracks in locations with low shear strengths, e.g. in the interfaces or within the middle ply. The location depends on the material design strategy used in manufacturing the paper quality. To control the in-plane compression properties in pa-perboard one should control the yield stress (or possibly the failure stress) of the outer plies. Increased stress gives higher in-plane compression strength. Moreover, the interfaces strength is important, since increased interface strength (or lack of interfaces) prevents delamination.

  • 114.
    Oko, Asaf
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Medicinteknik.
    Claesson, Per M.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik. KTH Royal Institute of Technology, Sweden.
    Niga, Petru
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Life Science.
    Swerin, Agne
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Measurements and dimensional scaling of spontaneous imbibition of inkjet droplets on paper2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 1, p. 156-169Article in journal (Refereed)
    Abstract [en]

    We investigate theoretically and experimentally the spontaneous imbibition of water based inkjet formulations utilizing paper capillary rise and imbibition of inkjet drops. We approximate the paper structure to a two dimensional anisotropic porous material, and using Darcy's law as a base, we derive dimensionless groups that scale drop imbibition. This derivation is based on a previous dimensional scaling of drop imbibition on thick isotropic porous material. We apply this scaling to a paper substrate by measuring the average drop imbibition rate, and perform paper capillary rise experiments to obtain the average system parameters required for the scaling. The results suggest that this approach is a valuable tool to predict drop imbibition rates on paper. We then continue and perform the same sets of experiments on a different paper with similar structure that is surface treated (surface sized) with CaCl2 salt, an additive that is known to improve print quality. We find that due to rapid aggregation of the colorant ink by the CaCl2, the imbibition rate is slowed down in the capillary rise experiments, i.e., on much larger scales compared to a single inkjet drop. However, the presence of CaCl2 has only minor effect over the average imbibition rates of single drops. Imbibition rates on the CaCl2 surface sized paper did not give adequate scaling as a result of the fact that the aggregation was not included the theoretical assumptions behind the scaling.

  • 115.
    Olm, Leelo
    et al.
    RISE, Innventia.
    Tormund, Disa
    RISE, Innventia.
    Lundqvist, Fredrik
    RISE, Innventia.
    High sulphidity kraft pulping2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, p. 433-439Article in journal (Refereed)
    Abstract [en]

    The object of this project was to evaluate the effect of high sulphidity on the performance of the kraft cooking process. Softwood (SW) mix (50/50 of spruce, Picea abies, and pine, Pinus sylvestris) and a hardwood (HW: birch, Betula pendula) have been explored as wood raw material. The reference kraft cook was carried out at 35% sulphidity. The laboratory kraft cooking trials showed that the rate of delignification in kraft cooking increases with increasing sulphidity for both these raw materials. An increase in sulphidity from 35% to 80% increases the apparent delignification rate by a factor of almost two. The faster delignification rate could be exploited as an increase in production and/or as a reduction in EA charge (2%-units for both raw materials) and/or as a decrease in cooking temperature (5°C for SW) at the same production. The yield of softwood kraft pulp at a given kappa number was not affected by the increase in sulphidity. For hardwood, the combination of high sulphidity and reduced effective alkali charge gave an increase in pulp yield of one %-unit. The pulp viscosity at a given kappa number was increased. The high sulphidity in SW kraft cooking (at a given EAcharge) led to a slightly better bleachability in an OD(E+P)DD bleaching sequence. The fully bleached SW kraft pulp at 80% sulphidity had a slightly higher tear index and higher fibre strength than the corresponding reference kraft pulp at 35% sulphidity. The other strength properties were virtually unchanged. The fully bleached HW kraft pulp at 80% sulphidity showed better optical properties, light scattering and opacity, which are, in fact, the critical properties for fully bleached hardwood pulps.

  • 116. Opedal, Mihaela Tanase
    et al.
    Stenius, P.
    Johansson, L.
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Colloidal stability and removal of extractives from process water in thermomechanical pulping2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, p. 248-257Article in journal (Refereed)
  • 117. Opedal, Mihaela Tanase
    et al.
    Stenius, Per
    Gregersen, Øjvind
    Johansson, Lars
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Hill, J.
    Flocculation of colloidal wood extractives in process water from precompression of chips in thermo-mechanical pulping2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, p. 64-71Article in journal (Refereed)
  • 118. Opedal, Mihaela Tanase
    et al.
    Stenius, Per
    Gregersen, Øjvind
    Johansson, Lars
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Hill, J.
    Removal of dissolved and colloidal substances in water from compressive pre-treatment of chips using dissolved air flotation: Laboratory Tests.2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, p. 72-80Article in journal (Refereed)
  • 119. Opedal, Mihaela Tanase
    et al.
    Stenius, Per
    Johansson, Lars
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Hill, J
    Sandberg, C.
    Removal of dissolved and colloidal substances in water from compressive pre-treatment of chips using dissolved air flotation: Pilot Trial2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, p. 364-371Article in journal (Refereed)
  • 120.
    Osong, Sinke Henshaw
    et al.
    Mid Sweden University, Sweden.
    Norgren, Sven
    Mid Sweden University, Sweden.
    Engstrand, Per O.
    Mid Sweden University, Sweden.
    Lundberg, Mathias
    Mid Sweden University, Sweden.
    Hansen, Peter
    RISE, Innventia.
    Crill: A novel technique to characterize nano-ligno-cellulose2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 2, p. 190-194Article in journal (Refereed)
    Abstract [en]

    The CrillEye is a technique for qualitatively assessing loose slender and fibrillar particles created during pulping. It has also been demonstrated that the crill measurement technique can easily be used to measure the degree of fibrillation of mechanical pulp based nano-ligno-cellulose (NLC). The measurement technique is based on an optical response of a suspension at two wavelengths of light; UV and IR. The UV light contains information on both fibres and crill, while IR only contains information on fibres. The resolution on the CrillEye module is based on optical response of the pulp and on an analogue signal analysis making it concentration independent. Characterization of particle-size distribution of nano-ligno-cellulose is both important and challenging. The objective of the work presented in this paper was to study the crill values of TMP and CTMP based nano-ligno-celluloses as a function of homogenization time. Results showed that the crill value of both TMP-NLC and CTMP-NLC correlated fairly well with the homogenization time.

  • 121.
    Ottesen, Vegar
    et al.
    NTNU Norwegian University of Science and Technology, Norway.
    Kumar, Vinay Santhosh
    Åbo Akademi University, Finland.
    Toivakka, Martti
    RISE - Research Institutes of Sweden, Bioeconomy, PFI.
    Chinga-Carrasco, Gary
    Syverud, Kristin
    RISE - Research Institutes of Sweden, Bioeconomy, PFI. NTNU Norwegian University of Science and Technology, Norway.
    Weiby Gregersen, Öyvind
    NTNU Norwegian University of Science and Technology, Norway.
    Viability and properties of roll-to-roll coating of cellulose nanofibrils on recycled paperboard2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 2, p. 179-188Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils (CNF) are, due in large part to excellent gas barrier properties, a potential environmentally friendly alternative to inorganic and petrochemical coatings of e.g. paperboard in packaging applications. In the current paper successful roll-to-roll coating of three qualities of CNF is demonstrated on a recycled quality, porous paperboard using a custom-built pilot machine. Single layers of three different thicknesses were applied for each coating. The three CNF qualities used were carboxymethylated CNF (CNF-C), TEMPOoxidized CNF (CNF-T) and mechanically produced CNF without chemical pre-treatment (CNF-M). All three qualities, which have a range of surface charge, fibril size and fibril size distribution, are shown to produce films that adhere well to the base board. It is revealed that the coating is suspended across surface pores in the base board, as opposed to penetrate into the base board pore structure. Samples were investigated for air and water permeability, gloss, surface roughness and hole density in the coating. Chemically pretreated qualities outperform CNF-M. Addition of 5 wt% carboxy-methyl cellulose (CMC) was shown to reduce hole formation, improve gloss and reduce surface roughness. For thick applications of pre-treated CNF, in particular CNF-C, mechanical strength of the board in and out of the plane increase beyond the un-treated or water treated base board. Possibly a consequence of matter migrating through the base board from the CNF suspension.

  • 122.
    Ottesen, Vegar
    et al.
    NTNU Norwegian University of Science and Technology, Norway.
    Syverud, Kristin
    RISE, Innventia, PFI – Paper and Fiber Research Institute. NTNU Norwegian University of Science and Technology, Norway.
    Gregersen, Øyvind W.
    NTNU Norwegian University of Science and Technology, Norway.
    Mixing of cellulose nanofibrils and individual furnish components: Effects on paper properties and structure2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 3, p. 441-447Article in journal (Refereed)
    Abstract [en]

    Thermo-mechanical pulp (TMP) handsheets with different fractions of cellulose nano fibrils (CNF) and ground calcium carbonate (GCC) were made. CNF and retention chemicals were added in three different ways; to GCC, to long fibre fraction (LFF) or to complete furnish. The different addition strategies affected dewatering time, tensile strength and permeability, however opacity was not affected. Depending on filler and CNF levels, adding CNF to GCC produced the most beneficial effects on paper properties; CNF had a lower impact on dewatering times and permeability and GCC reduced strength less than for competing strategies. Adding CNF to LFF produced the least beneficial results using the same metrics. Scanning electron microscopy (SEM) analysis of the sheets reveal that sheets produced using the different strategies are structurally different; adding CNF and retention chemicals to GCC appears to have increased GCC clustering, whereas adding CNF and retention chemicals to LFF appears to have increased the fraction of GCC adsorbed on the fiber walls. CNF and retention chemical addition to complete furnish showed GCC clustering and adhering to the fiber walls, of which clustering appeared the most common.

  • 123.
    Ovaskainen, Louise
    et al.
    KTH Royal Institute of Technology, Sweden.
    Olin, Pontus
    KTH Royal Institute of Technology, Sweden.
    Tuominen, Mikko
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Pettersson, Torbjörn
    KTH Royal Institute of Technology, Sweden.
    Wågberg, Lars Göran
    KTH Royal Institute of Technology, Sweden.
    The effect of different wear on superhydrophobic wax coatings2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 2, p. 195-203Article in journal (Refereed)
    Abstract [en]

    Wear resistance of superhydrophobic coatings made by spraying a crystallizing wax from supercritical carbon dioxide solutions was evaluated using several methods. Scratch tests were performed using a tip in contact with the surface using atomic force microscope (AFM). Compression tests were performed by applying different loads on a rubber stamp placed on the surface. Frictional wear was evaluated by stroking an index finger over the surfaces while measuring applied load and friction. The wetting properties of the coatings were subsequently evaluated as advancing and receding water contact angles, superhydrophobic sliding resistance according to a recently developed method and surface roughness, coating morphology was studied using scanning electron microscopy and optical profilometry. Scratching with tip of an AFM cantilever with a force of 12 nN removed major fraction of the wax coating from underlying silica substrate whereas subjecting the surfaces to a compressive load up to 59 kPa did not significantly influence the superhydrophobicity of the coatings. Frictional wear measurements indicate that superhydrophobic properties were immediately lost after pressing and moving a finger over the coating, as movement of the finger destroyed the fine surface structure. Nevertheless, the surfaces could withstand up to 200000 falling water drops without losing their superhydrophobicity. © 2017 De Gruyter Open Ltd. All rights reserved.

  • 124.
    Persson, Johanna
    et al.
    RISE, Innventia.
    Dahlman, Olof B.
    RISE, Innventia.
    Albertsson, Ann Christine
    KTH Royal Institute of Technology, Sweden.
    Edlund, Ulrica
    KTH Royal Institute of Technology, Sweden.
    Modification of birch xylan by lactide-grafting2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 3, p. 518-524Article in journal (Refereed)
    Abstract [en]

    4-O-methylglucuronoxylan, isolated by ultrafiltration from a birch kraft cooking liquor, was delignified and subsequently modified by grafting lactide-chains onto the hydroxyl groups via ring opening polymerization with L-lactide. The structures and average molar masses of the lactide-grafted xylan polymers were characterised by NMR and SEC respectively. By varying the lactide-to-xylan feed ratio, graft polymers with different graft levels were synthesized. The degree of substitution of the hydroxyls in the xylan back-bone ranged from 0.7 to 1.7 with lactide side-chains having an average length of 1.2 to 2.5 lactide units. The side-chain length and degree of substitution influenced the hydrophobicity, thermal properties and tensile strength properties. A glass transition could be detected for lactide-grafted xylan polymers with lactide chains longer than 1.8 lactide units. Solution-cast thin films prepared from lactide-grafted xylans exhibited strong tensile strength and high modulus with decreasing strength and increasing elongation at break as the lactide chain length was increased.

  • 125.
    Prahl Wittberg, Lisa
    et al.
    KTH Royal Institute of Technology, Sweden.
    Björkman, Magnus
    RISE, Innventia.
    Khokhar, Gohar T.
    KTH Royal Institute of Technology, Sweden.
    Mohlin, Ulla Britt
    RISE, Innventia.
    Dahlkild, Anders A.
    KTH Royal Institute of Technology, Sweden.
    Flow conditions in the grooves of a Low-Consistency refiner2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 173-183Article in journal (Refereed)
    Abstract [en]

    The flow pattern in the grooves plays a major role for the homogeneity of refining as well as for the transfer and loading of fiber flocs in refining position on the bar edges. However, it is an area where very little information is available. In the present study, flow conditions in the grooves in a Low-Consistency (LC) - disc refiner were studied both experimentally and numerically. The experimental study involved high-speed imaging through a 3 cm peephole into a commercial refiner. The Computational Fluid Dynamics (CFD) simulation focused on the flow condition in a radial groove, considering both Newtonian and non-Newtonian flows. Flow conditions for stator and rotor grooves were modeled along the groove at different angular speeds and pressure differences over the refiner. Both the experimental and the modeling results show a dual flow pattern in the grooves; a rotational/spiral movement at the top of the groove and a flow in the direction of the groove at the bottom, which to the authors knowledge has not been reported in literature. The strong vortical motion at the top of the grooves observed both for the rotor and the stator are believed to be important for placing the fibers onto the bar edges and to induce shear forces in such a way that the fibers get treated. Moreover, a large sensitivity to suspension properties in terms of the development of flow pattern was detected.

  • 126.
    Rahman, Hafizur
    et al.
    SCA R&D Centre, Sweden.
    Lindström, Mikael E.
    KTH Royal Institute of Technology, Sweden.
    Sandström, Peter
    SCA R&D Centre, Sweden.
    Salmen, Lennart
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy.
    Engstrand, Per
    Mid Sweden University, Sweden.
    The effect of increased pulp yield using additives in the softwood kraft cook on the physical properties of low-grammage handsheets2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 2, p. 317-323Article in journal (Refereed)
    Abstract [en]

    The effect of increasing the pulp yield by the addition of sodium borohydride (NaBH4) or polysulfide (PS) in softwood kraft cooking, i.e. enhancing the retention of glucomannan, on the physical properties of low-grammage handsheets was studied. In addition to the yield improvement, an increase in tensile index was observed, especially at lower degrees of beating. These higher yield pulps showed an increase in pore volume, indicating an increased degree of swelling of the fibres. Presumably, the increased flexibility of the fibres affects the bonding strength and leads to the higher tensile index observed.

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  • 127.
    Rentzhog, M
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Fogden, A
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Correlations between properties of water-based flexographic inks and their print uniformity on PE-coated board2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, p. 403-410Article in journal (Refereed)
    Abstract [en]

    Uniformity of fulltone flexographic prints on PEcoated board was investigated for a large matrix of aqueous inks with varying acrylic-based vehicles and pigment concentrations, and with their applied amounts varied using a wide range of anilox volumes. Print mottle was characterised by coefficient of variation of reflectance, and partitioned into different feature-size classes. For all prints the mottle was caused by the residual pattern of white (poorly-covered) stripes originating from the anilox ruling, and subsequently distorted and redistributed to both finer and coarser length scales during transfer to, and flow on, the print substrate. Accordingly, mottle was largest on the sub-millimetre scales encompassing these stripe features, and generally increased with anilox volume, approximately proportionally so on above-millimetre scales. While greater pigmentation naturally increased both print density and mottle, the vehicle also exerted a strong influence, with mottle decreasing with increased content of soluble (versus emulsion) polymers. The latter was principally due to the associated increase in lowshear viscosity and decreased surface tension, both serving to reduce substrate dewetting. Empirical relations accurately correlating mottle to these two ink properties, and anilox volume and print density, were established.

  • 128.
    Rentzhog, M
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Fogden, A
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Effect of corona treatment of PE-coated board on water-based flexographic print resistance2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 202-210Article in journal (Refereed)
    Abstract [en]

    The effect of corona treatment of polyethylene-(PE-) coated liquid packaging board on its surface chemistry was quantified using surface energy determination by drop spreading and dyne-liquids, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The increase in total surface energy, due to its polar component, with increasing corona dosage, and its decrease on aging and washing, was strongly correlated to surface oxidation fraction from XPS. A fine structure of nano-mounds formed by oxidised material was revealed by AFM, with size and substrate coverage increasing with corona dosage, but no longer visible after washing. Resistance properties of water-based flexographic prints on these treated PE substrates were tested, with only wet rub resistance exhibiting a significant dependence on corona dosage. This property first increased at lower dosages before decreasing at higher levels, presumably due to worsened water resistance from soluble oxidised material dissolved in the ink film.

  • 129.
    Rentzhog, M
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Fogden, A
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Influence of formulation and properties of water-based flexographic inks on printing performance for PE-coated board2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, p. 410-417Article in journal (Refereed)
    Abstract [en]

    In this study the flexographic printing of low-density polyethylene- (LDPE-) coated liquid packaging board is analysed for a range of water-based inks, varying in type of pigment and acrylate-polymer vehicle and pigment/vehicle mixing proportions. One vehicle is solely based on emulsion polymer, another contains solution polymer, and the third is a 50/50 blend of these two. Vehicle type and relative amount are shown to have a strong and systematic bearing on the absolute amount of ink transferred and its corresponding print density, gloss, and uniformity. For both ink colours (cyan and black), transferred amount increases with pigment content and is highest for the 50/50 intermediate vehicle. Print density and homogeneity are generally highest for the vehicle containing highest content of solution polymer, at least with the lower anilox volumes, and this vehicle also gives highest print gloss. The wet amount of ink transferred is shown to be well correlated to its surface tension and viscosity

  • 130.
    Rentzhog, M
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Fogden, F
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Rheology and surface tension of water-based flexographic inks and implications for wetting of PE-coated board2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, p. 399-409Article in journal (Refereed)
    Abstract [en]

    This study systematically characterises a matrix of water-based flexographic inks with respect to their rheology, surface tension and wetting of liquid packaging board, to provide a basis for interpretation and prediction of their printing performance. For all pigment and acrylate polymer vehicles and mixing proportions the inks were shown to be shear thinning and thixotropic, with plastic viscosity, yield stress and storage and loss moduli increasing strongly with content of solution polymer (at comparable solids contents). The solution polymer decreases the static surface tension of the inks, but generally leads to an increase in their equilibrium drop contact angle on the polyethylene- (PE-) coated board due to increase in the ink-board interfacial energy. The solution polymer also decreases the drop spreading rate, and a simple model is tested to express the spreading dynamics in terms of equilibrium contact angle and a rate parameter given by the effective ratio of surface tension to viscosity.

  • 131.
    Rättö, Peter
    et al.
    RISE, Innventia.
    Hornatowska, Joanna
    RISE, Innventia.
    Barbier, Christophe
    Karlstad University, Sweden.
    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, 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.

  • 132.
    Rättö, Peter
    et al.
    RISE, Innventia.
    Hornatowska, Joanna
    RISE, Innventia.
    Changhong, X.
    Stockholm University, Sweden.
    Terasaki, O.
    Korea Advanced Institute of Science and Technology, South Korea.
    Cracking mechanisms of clay-based and GCC-based coatings2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 485-492Article in journal (Refereed)
    Abstract [en]

    A new method to produce SEM cross sections was used to analyze coated and creased samples. It was found that the binder surrounded the smaller particles leaving the large pores around the larger pigment particles. Consequently, cracks would propagate next to the large particles, and at least one crack area also showed a clear pigment surface, indicating an adhesive failure between the binder and the pigment particles. GCC and clay showed different cracking directions. GCC-based coatings showed cracks that had been initiated at the surface of the coating layer and then went through the thickness direction of the coating layer. The clay-based coatings on the other hand showed cracks that could be initiated anywhere in the thickness direction in the coating layer and then continued at an angle in the thickness direction. The cracking behaviour of the clay based coatings was probably due to anisotropic mechanical properties combined with shear stresses or out-of-plane tensile stresses during creasing.

  • 133.
    Rönnols, Jerk
    et al.
    RISE, Innventia.
    Schweinebarth, Hannah
    RISE, Innventia.
    Jacobs, Anna
    RISE, Innventia.
    Stevanic Srndovic, Jasna
    RISE, Innventia.
    Olsson, Anne-Mari
    RISE, Innventia.
    Reimann, Anders
    RISE, Innventia.
    Aldaeus, Fredrik
    RISE, Innventia.
    Structural changes in softwood kraft lignin during nonoxidative thermal treatment2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 4, p. 550-561Article in journal (Refereed)
    Abstract [en]

    Heat treatment is a promising pre-processing method in the conversion of kraft lignins to carbon fibers. In this study, a kraft lignin was subjected to heat treatment at different lengths of time and at different temperatures. The molecular structure of the untreated and four heat treated lignins were investigated mainly by a variety of nuclear magnetic resonance spectroscopy (NMR) methods. The results were compared to structural information obtained by pyrolysis-gas chromatography-/mass spectrometry (py-GC/MS) and Fourier transform infrared spectroscopy (FTIR). It was observed that during the thermal treatment, the amount of β-O-4 ether moieties decreased, and an intramolecular conversion of secoisolariciresinol residues to cyclic ethers occurred. The effects on shape and size of the lignins were investigated by size exclusion chromatography (SEC) and NMR-diffusion measurements, by which the hydrodynamic radii were found to increase as a result of thermal treatment. It is discussed whether this depends on reduced flexibility and/or increased molar mass. In addition, the trends from the SEC and NMR analyses were compared to changes in glass transition temperature as determined by differential scanning calorimetry (DSC).

  • 134.
    Salmen, Lennart
    et al.
    RISE, Innventia.
    Hornatowska, Joanna
    RISE, Innventia.
    A comparison of fibre deformations from mill like and laboratory kraft cooking of softwood2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 2, p. 211-217Article in journal (Refereed)
    Abstract [en]

    The fact that industrial pulps have a lower strength than their corresponding laboratory pulps is an unsolved problem affecting in various ways the potential fibre utilisation in different mills. The loss of pulp strength has to a great extent been attributed to changes at the fibre level. In order to clarify in what way changes in fibre properties contribute to the strength losses, cooking experiments were conducted using a laboratory batch digester in which mechanical forces may be introduced. Fibre properties, i.e. fibre structure and fibre strength, of laboratory-made pulps were compared with those of an industrial pulp. It was concluded that two essentially different mechanisms may be identified; one related to the transverse fibre shape, the other to fibre damage. The latter is manifested as lower rewetted zero-span strength which reduces tear resistance and tensile strength of the pulp. The former is a collapse of the fibre, reducing the lumen area and resulting in a pulp with lower water-retaining capacity, given sheets of lower density and a pulp that has to be beaten to a higher degree to reach the desired bonding and the desired tensile strength.

  • 135.
    Salmen, Lennart
    et al.
    RISE, Innventia.
    Lindström, Mikael
    RISE, Innventia. KTH Royal Institute of Technology, Sweden.
    Improved pulp yield and strength by retained glucomannans in kraft pulping of softwood2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 4, p. 584-590Article in journal (Refereed)
    Abstract [en]

    The possibilities of improving yield and strength properties of softwood bleached kraft pulps by retaining a higher content of glucomannan during kraft cooking using additives that decrease the rate of carbohydrate degradation were looked upon. In addition the effect of an increased alkaline concentration, favouring stopping reactions over peeling reactions was explored. Yield increases in the range of 2 to 4%-units were achieved using additives. In the case of the higher alkali charge instead a small yield decrease was noticed. Higher alkali charge in general resulted in a larger loss of xylan in the pulp. When examining the effects of the application of shearing forces at the end of the cook, mimicking industrial pulps, all cooks using high alkali conditions were affected by a large decrease in strength properties, both in tensile index and tear index as well as in fibre strength measured as re-wet Zero-span. For pulps cooked with polysulphide and H2S additions, stabilising the glucomannan degradation, the strength reductions were smaller than for the reference pulps. This resulted in pulps with both a higher yield and similar or better strength properties than those for the reference pulp. These pulps also had better beatability, i.e. the tensile strength increased faster during PFI-beating than for the reference pulp.

  • 136. Saltberg, A.
    et al.
    Brelid, H.
    Lundqvist, Fredrik
    RISE, Innventia.
    The effect of calcium on kraft delignification: Study of aspen, birch and eucalyptus2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, p. 440-447Article in journal (Refereed)
    Abstract [en]

    Metal ions can be removed from wood chips by acidic leaching. The rate of kraft delignification may be enhanced by such a chip pre-treatment, but whether this effect is present or not, is dependent on wood species and cooking liquor composition. Acidic chip leaching of birch (Betula pendula) and aspen (Populus tremula) was shown to give a large increase in the rate of delignification when carbonate-free white liquor, prepared in the laboratory, was used. Removal of calcium ions from the wood chips during the acidic leaching was shown to be the principal reason for the increase in the delignification rate. In trials where the cook was not preceded by acidic leaching, the addition of carbonate to the white liquor eliminated the retarding effect of calcium. The addition of the chelating agent DTPA (diethylenetriaminepentaacetic acid) also counteracted the calcium-effect. Since carbonate forms solid calcium carbonate precipitates and DTPA forms Ca-DTPA complexes, it can be concluded that non-chelated calcium ions in the cooking liquor decrease the rate of lignin solubilisation. The delignification rate of eucalyptus (Eucalyptus globulus) was not significantly affected by calcium-removal or by the addition of carbonate or DTPA to the white liquor. A tentative explanation for this could be that substances released from eucalyptus during cooking form complexes with calcium ions and may thereby prevent the calcium-effect on delignification. This explanation is supported by results from trials where birch and eucalyptus chips were cooked together.

  • 137.
    Seppänen, R
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Tiberg, F
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Valignat, M-P
    Mechanism of internal sizing by alkyl ketene dimers (AKD). The role of spreading monolayer2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, p. 452-458Article in journal (Refereed)
  • 138.
    Sjöberg, M
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Järnström, L
    Lazarus, E
    Influence of latex surface properties on interactions with starch and carboxymethyl cellulose in coating colours2000In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, p. 431-439Article in journal (Refereed)
    Abstract [en]

    Coating colour structure and properties are to a large extent dependant on the behaviour of the latex binder and its interaction with other coating components. Added water-soluble polymers such as starch and carboxymethyl cellulose (CMC) in general have a marked effect on the stability of the dispersed latex particles. This paper presents a systematic study of how the distribution of latex in coating colours containing oxidised starch, amphoteric (both anionic and cationic groups) starch or CMC depends on latex parameters such as polymer particle size, charge and surfactant composition. A series of seven model styrene-butadiene latexes was investigated. Complex formation between surfactant and starch occurred when the hydrophobic part of the surfactant was an alkyl chain. None of the surfactants containing an aryl group showed any tendency to formation of starch-surfactant complexes at low ionic strengths. In that respect, both starch grades behaved similarly to each other. No interactions between surfactant and CMC were detected. For calcium carbonate based coating colours containing the amphoteric type of starch, low shear rate viscosity was substantially higher when a model latex containing the alkyl type of surfactant was used compared to any other investigated model latex of the same particle size and degree of carboxylation. Similar effects were observed for colours containing the oxidized starch. Coated papers were produced by means of a Helicoater. Gloss and ink requirement were affected by the starch-latex interactions. It was also found that CMC flocculated all model latexes, even though CMC was not adsorbed on the latex particles. The flocculation concentration was dependent on the particle size of the latex and the ionic strength of the suspension. Calcium carbonate based coating colours containing CMC were formulated with the model latexes. Measurements of coated layer properties (when drawn down on synthetic paper) indicated that the density was slightly lower when the non-ionic surfactant latex was used. However, since CMC destabilised all model latex grades, print properties did not alter systematically after a change of latex type, CMC level or CMC grade. An important conclusion was, even though clear colloid interaction effects were observed in model systems, that the impact of these effects are probably small for real coating colours, full scale coating runnability and print properties. This can be explained by the complexity of coating colours and the coating process.

  • 139.
    Sjöström, Lars
    et al.
    RISE, STFI-Packforsk.
    Jacobs, Anna
    RISE, STFI-Packforsk.
    Rådeström, Rune
    RISE, STFI-Packforsk.
    Nordlund, Maria
    RISE, STFI-Packforsk.
    Effects of released organic substances on sizing efficiency: Influence of origin, composition and molecular properties of the organic material2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 5, p. 575-585Article in journal (Refereed)
  • 140.
    Ström, G
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Carlsson, G
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Schulz, A
    Chemical composition of coated paper surfaces determined by means of ESCA1993In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 8, p. 105-112Article in journal (Refereed)
    Abstract [en]

    Laboratory coated papers with different pigment compositions (clay and calcium carbonate) and pilot coated papers with different types of latex binders have been characterized by electron spectroscopy for chemical analysis (ESCA). The surfaces were very rich in carbon and approximately 90% of the carbon signal originated from the latex binder. The variable angle technique showed that the outermost surface layer of the coated papers was free from thin overlayers. This made it possible to calculate the paper surface area fractions of clay, calcium carbonate and latex binder. The area fraction of latex in the paper surface decreases with increasing specific surface area of the coating pigments and the area fraction of clay is proportional to the content of clay in the coating colour when this is expressed in area-% instead of weight-%.

  • 141.
    Ström, G
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Härdin, A-M
    Salminen, P
    A novel formulation approach for improving fibre coverage during blade coating1995In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 10, p. 227-233Article in journal (Refereed)
    Abstract [en]

    It is generally understood that increased pigment aggregation and structuring of wet coating colour improves fibre coverage, but reduces runnability on the blade coater. This paper presents a formulation approach which results in formation of a significant coating structure only after the blade. The approach is based on the laboratory observation that the structuring effect of small amounts of a salt is inversely dependent on coating colour pH. The combination of calcium chloride addition and the use of ammonia for pH control is therefore proposed. The evaporation of ammonia after the blade results in pH reduction and allows the formation of pigment structure during coating consolidation. Results from laboratory studies and pilot coater trials are presented. The latter suggest that the proposed approach provides significant improvements in fibre coverage, surface smoothness and opacity, but that surface strength is reduced. Laboratory results and the observed good blade runnability indicate that the coating structuring is obtained only after the blade, as the ammonia evaporates.

  • 142.
    Ström, G
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Kunnas, A
    The effect of cationic polymers on the water retention value of various pulps1991In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 6, p. 12-19Article in journal (Refereed)
    Abstract [en]

    The effect of cationic polymers (cationic corn and potato starches, polyacrylamide and fractionated modified polyethylene imine) on the water retention value (WRV) of different pulps (bleached chemithermomechanical pulp (CTMP), bleached kraft pulp and unbleached sulfide pulp) was investigated. The pulps were in hydrogen ion state. It was found that for for well refined CTMP and processed pulps the WRV decreases upon polymer addition. Decreases of up to 10-20% were observed. The reduction in the WRV is explained in terms of the penetration of cationic polymers into the surface region of the fiber wall where the polymer neutralizes ionized surface groups, and of an aggregation of fibrils located on the external fiber surface. The penetration mechanism is supported by the fact that increases in electrophoretic mobility caused by polymer adsorption decrease with time for those pulps which show a decrease in WRV upon polymer addition. Such a mobility decraease is not found for the low refined CTMP and in this pulp the WRV does not decrease.

  • 143. Ström, G
    et al.
    Stenius, P
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Lindström, M
    Ödberg, L
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Surface chemical aspects of the behavior of soaps in pulp washing1990In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 5, p. 44-51Article in journal (Refereed)
    Abstract [en]

    In a kraft pulp washing line the wood resin consists of fatty acid and rosin acid soaps and a variety of neutral components. The removal of this material in the washing line is highly dependent on soap solubility, micelle formation, solubilization and the colloidal stability of precipitated resin particles. This papers summarizes several studies of the colloidal behavior of resin in model systems consisting of sodium abietate, sodium oleate and a model mixture of neutral components, and presents new data on micellization and solubilization. The highest solubility of the soaps and maximum solubilization of neutral compounds occurs at moderate ionic strength in mixed oleate/abietate solutions (1:2-2:1 by weight). Micelle formation is promoted by low temperature and moderate ionic strength; the solubilizing capacity of the micelles increases with temperature. Colloidal particles formed by precipitated resin are stabilized by kraft lignin. The model results are compared with an analysis of the distribution of resin in a pulp washing line. This distribution can be clearly understood from the results of the model study.

  • 144.
    Ström, Göran
    et al.
    RISE, STFI-Packforsk.
    Karathanasis, Michael
    RISE, STFI-Packforsk.
    Relationship between ink film topography and print gloss in offset prints on coated surfaces2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 2, p. 156-163Article in journal (Refereed)
    Abstract [en]

    Model coatings with different micro roughness but similar and low macro roughness were prepared and laboratory printed. The coating micro roughness strongly affected the print gloss at low inking levels, corresponding to one or two full tone layers. The effect of coating micro roughness decreased with ink amount and was insignificant at inking levels of 3-4 g/m2, which corresponds roughly to three to four full tone layers. A strong correlation between ink film micro roughness and print gloss was established. Remaining ink filament patterns that had survived the ink levelling process were observed with a fast-setting coating but not with a slow-setting coating. The amplitude of the filaments was a few tenths of a urn only and was strongly dependent on ink amount. The filaments were observed in wavelength bands between 15 and 125 ÎŒm, which can be regarded as a sub-macro roughness region. Their impact on print gloss was estimated on some 6 gloss units.

  • 145.
    Svedberg, Anna
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Processum.
    Lindström, Tomas
    A pilot web former designed to study retentionformation relationships2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 2, p. 185-194Article in journal (Refereed)
    Abstract [en]

    A pilot-scale fourdrinier former has been developed for the purpose of investigating the relationship between retention and paper formation (features, retention aids, dosage points, etc.). The main objective of this publication was to present the R-F (Retention and formation)-machine and demonstrate some of its fields of applications. For a fine paper stock (90% hardwood and 10% softwood) with addition of 25% filler (based on total solids content), the relationship between retention and formation was investigated for a microparticulate retention aid (cationic Polyacrylamide together with anionic montmorillonite clay). The retention-formation relationship of the retention aid system was investigated after choosing standardized machine operating conditions (e.g. the jet-to-wire speed ratio). As expected, the formation was impaired when the retention was increased. Since good reproducibility was attained, the R-F (Retention and formation)-machine was found to be a useful tool for studying the relationship between retention and paper formation.

  • 146.
    Svedberg, Anna
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Processum.
    Lindström, Tomas
    The effect of various retention aids on retention and formation2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 2, p. 195-203Article in journal (Refereed)
    Abstract [en]

    The interdependency between retention and paper formation was studied using a previously designed R-F (Retention and formation)-machine. The objective of the work was to investigate the retentionformation relationship for different types of retention aid systems. Both single-component cationic Polyacrylamides with varying molecular weights and polyacrylamide-based microparticulate retention aids were investigated on the R-F-machine, for-a fine paper stock with addition of 25% filler (based on total solids content). Results showed that the retention-formation relationship was not dependent on the retention aid systems used, since all systems provided similar relationships. In terms of the retention performance, significant differences were observed, depending on the choice of microparticle system and molecular weight of the used cationic Polyacrylamide.

  • 147.
    Thorman, Sofia
    et al.
    RISE - Research Institutes of Sweden, Bioeconomy, Papermaking and Packaging. Karlstad University, Sweden.
    Ström, Göran
    RISE - Research Institutes of Sweden, Bioeconomy, Papermaking and Packaging.
    Gane, Patrick A. C.
    Omya Internatioanl AG, 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. .

  • 148.
    Thorman, Sofia
    et al.
    RISE, Innventia.
    Ström, Göran R.
    RISE, Innventia.
    Hagberg, Anni
    RISE, Innventia.
    Johansson, Per Åke
    RISE, Innventia.
    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. 459-465Article 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.

  • 149.
    Tuominen, Mikko
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Material och ytteknik.
    Teisala, Hannu
    Tampere University of Technology, Finland.
    Haapanen, Janne
    Tampere University of Technology, Finland.
    Aromaa, Mikko
    Tampere University of Technology, Finland.
    Mäkelä, Jyrki M.
    Tampere University of Technology, Finland.
    Stepien, Milena
    Tampere University of Technology, Finland.
    Saarinen, Jarkko J.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. Åbo Akademi University, Finland .
    Toivakka, Martti
    Åbo Akademi University, Finland .
    Kuusipalo, Jurkka
    Tampere University of Technology, Finland.
    Adjustable wetting of liquid flame spray (LFS) TiO2-nanoparticle coated board: Batch-type versus roll-to-roll stimulation methods2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 2, p. 271-279Article in journal (Refereed)
    Abstract [en]

    Superhydrophobic nanoparticle coating was created on the surface of board using liquid flame spray (LFS). The LFS coating was carried out continuously in ambient conditions without any additional hydrophobization steps. The contact angle of water (CAW) of ZrO2, Al2O3 and TiO2 coating was adjusted reversibly from >150° down to ~10-20° using different stimulation methods. From industrial point of view, the controlled surface wetting has been in focus for a long time because it defines the liquid-solid contact area, and furthermore can enhance the mechanical and chemical bonding on the interface between the liquid and the solid. The used stimulation methods included batch-type methods: artificial daylight illumination and heat treatment and roll-to-roll methods: corona, argon plasma, IR (infra red)- and UV (ultra violet)-treatments. On the contrary to batch-type methods, the adjustment and switching of wetting was done only in seconds or fraction of seconds using roll-to-roll stimulation methods. This is significant in the converting processes of board since they are usually continuous, high volume operations. In addition, the creation of microfluidic patterns on the surface of TiO2 coated board using simple photomasking and surface stimulation was demonstrated. This provides new advantages and possibilities, especially in the field of intelligent printing. Limited durability and poor repellency against low surface tension liquids are presently the main limitations of LFS coatings.

  • 150.
    Tysen, Aron
    et al.
    RISE, Innventia.
    Vomhoff, Hannes
    RISE, Innventia.
    Method for the quantification of in-plane drying nonuniformity2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 2, p. 286-295Article in journal (Refereed)
    Abstract [en]

    A method has been developed in order to determine the in-plane non-uniformity of drying of wet paper samples dried by an air flow. The surface temperature of the samples, recorded by an infrared camera, is used to determine a mean drying time and the local drying time of each pixel. Based on the initial dryness and the mean drying time, a mean drying rate can be obtained, and furthermore, the drying time of each pixel can be presented as a 2-dimensional map. Apart from conventional statistical information on the variation in drying time, the map also gives information regarding the size and shape of the drying non-uniformity. The pressure drop over the sample and the air flow rate through the sample were used to calculate a flow resistance as a function of grammage. Laboratory sheets with grammages between 15 and 45 g/m2, made from an unrefined bleached chemical hardwood pulp, were analysed. A considerable variation in local drying time was observed, despite their anticipated uniform formation. The mean drying time increased linearly with increasing grammages, thus the mean drying rate was not dependent on grammage. The flow resistance of the sheets increased with increasing grammage. The air flow rate through the sheet appeared not to be critical for the drying rate at the given experimental conditions.

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