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  • 1.
    Aldaeus, Fredrik
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy. RISE, Innventia.
    Olsson, Anne-Mari
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy. RISE, Innventia.
    Stevanic Srndovic, Jasna
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy. RISE, Innventia.
    Miniaturized determination of ash content in kraft lignin samples using oxidative thermogravimetric analysis2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 2, p. 280-282Article in journal (Refereed)
    Abstract [en]

    A study has been made of several aspects of determination of ash content in kraft lignin samples using thermogravimetric analysis (TGA). Three different methods were used; with the main differences between the methods being that two have a temperature hold at 250 deg C to remove volatiles and that the three methods use different maximum temperatures, namely 525, 550 and 575 deg C, respectively. The three kraft lignins used were produced using the LignoBoost lignin isolation process. It has been demonstrated that the results obtained by the different temperature programmes showed no significant difference. The results were comparable with those from using oven ignition. Moreover, the limit of quantification was several orders of magnitude lower than when using oven ignition. It has been recommended that if TGA is used for determination of ash content, a temperature programme from a standard method should be used, which should be mentioned together with the results. The temperature programme in method one (corresponding to ISO 1762) was the shortest and the preferable method. A well as requiring less labour due to fewer movements in the analytical protocol, the TGA methods enabled a high sample throughput due to autosampling possibilities.

  • 2.
    Alfthan, Johan
    RISE, Innventia.
    Experimental study of non-linear stress relaxation and creep of paper materials and the relation between the two types of experiments2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 3, p. 351-357Article in journal (Refereed)
    Abstract [en]

    The non-linear time-dependent mechanical behaviour of three different commercial paper grades was investigated. Stress relaxation and creep tests were carried out in MD and CD using different load levels. The strain in each test was split in a linear part and a non-linear part. From the stress and the linear part of the strain in the test, a stress relaxation modulus or a creep compliance was calculated. The stress relaxation moduli and creep compliances determined in this way were observed to be independent of the load level. The stress relaxation moduli and creep compliances for each paper were further independent of the loading direction (MD/CD) when scaled by the elastic modulus. It was also shown that the stress relaxation modulus was approximately equal to the inverse of the creep compliance, which is what would have been expected if linear viscoelastic theory had been applicable.

  • 3.
    Alm, H.K.
    et al.
    RISE, Innventia.
    Ström, Göran
    RISE, Innventia.
    Karlström, Katarina
    Schoelkopf, J.
    Gane, P.A.C.
    Effect of excess dispersant on surface properties and liquid interactions on calcium carbonate containing coatings2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 1, p. 82-92Article in journal (Refereed)
    Abstract [en]

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

  • 4.
    Andersson, Christian
    et al.
    RISE, Innventia.
    Fellers, Christer
    RISE, Innventia.
    Evaluation of the stress-strain properties in the thickness direction: Particularly for thin and strong papers2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 287-294Article in journal (Refereed)
    Abstract [en]

    The performance of the paper in a number of converting operations such as creasing, bending, printing, and plastic coating put great demands on the mechanical properties in the thickness direction of the material. The knowledge of strength, elastic- and plastic behavior in tension and compression in the thickness direction is needed for a comprehensive description of the performance of the material in these operations. In spite of its importance, very few publications deal with the evaluation of the entire tensile stress-strain curve of paper in the thickness direction. A likely reason for this is the intrinsic difficulty of testing a thin, uneven, porous, fibrous and compressible material such as paper with sufficient precision and testing time efficiency. The z-directional strength test is usually performed by fastening the paper by means of double-adhesive tape to metal platens. The platens are fastened in a testing machine and strained to break. The adhesion of the tape is the limiting factors for how strong papers that can be tested. The tape-based method also is expected to have a lower limit in grammage due to the penetration of the adhesive. The aim of the present publication was to show a procedure how to evaluate the entire stress-elongation curve in the z-direction of papers, using a lamination method for fastening the paper to the metal platens. From this curve the z-strength, z-modulus, z-strain at break, zenergy at break and z-fracture energy could be extracted. Such information is, so far, non-existing in the literature.

  • 5.
    Ankerfors, Mikael
    et al.
    BillerudKorsnäs AB, Sweden.
    Lindström, Tom
    RISE, Innventia.
    Glad Nordmark, Gunborg
    RISE, Innventia.
    Multilayer assembly onto pulp fibres using oppositely charged microfibrillated celluloses, starches, and wetstrength resins: Effect on mechanical properties of CTMP-sheets2016In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 31, no 1, p. 135-141Article in journal (Refereed)
    Abstract [en]

    The effects of multilayering of microfibrillar cellulose (MFC) onto a chemi-thermomechanical pulp (CTMP), from which the fines material had been removed, were investigated with regard to the mechanical properties of hand-sheets. In one series of experiments, the CTMP was multilayered with cationic MFC/anionic MFC (C-MFC/A-MFC) at various addition levels and sheets made in a conventional sheet former, pressed, and dried at room temperature. This experimental series was complemented with a second series, where sheets were made in a Rapid Köthen sheet former. In a third series of experiments, the CTMP was multilayered using a cationic polyamideamine epichlorohydrine resin (PAE) and an AMFC. Sheets were formed using the Rapid Köthen sheet former. Finally, in a fourth series of experiments, the MFC multilayering experiments were compared with multilayering experiments using cationic starch/anionic starch (C-starch/A-Starch). MFC-multilayering (C-MFC/A-MFC) gave inferior strength gain at a low addition level compared to starch multilayering, but (compared on a weight basis) the strength seemed to level off using starches at high addition levels, whereas there were a continuous increase in strength using MFC multilayering. Multilayering using PAE/A-MFC was found to give a higher strength gain than both C-MFC/A-MFC and C-starch/A-starch multilayering. Sheet density was slightly affected (<14%) by the multilayering techniques used in these experiments.

  • 6.
    Ankerfors, Mikael
    et al.
    ÅF Industry, Sweden.
    Lindström, Tom
    RISE - Research Institutes of Sweden, Bioeconomy.
    Glad Nordmark, Gunborg
    RISE - Research Institutes of Sweden, Bioeconomy.
    The effects of different types of wet-end added microfibrillated celluloses on the properties of paper made from bleached kraft pulp2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 3, p. 336-345Article in journal (Refereed)
    Abstract [en]

    Research has been undertaken to compare the effects of different types of microfibrillated cellulose (MFC) on the mechanical properties of paper. Three types of MFC were produced: Enzyme MFC (low anionic charge density), Carboxymethylated MFC (high anionic charge density) and cationic MFC (high cationic charge density). The different MFCs required different retention aid strategies. The simplest retention strategy was selected to secure a high retention of MFC. Some experiments also focused on dewatering and pressability of wet webs with carboxymethylated MFC. Conventional isotropic laboratory handsheets were made using a never-dried unrefined elemental chlorine free (ECF)-bleached softwood kraft pulp. It has been shown that the evolution of the mechanical properties and scattering coefficients when plotted versus MFC content was very similar for the three types. However, Enzyme MFC gave a significantly better reinforcement effect. All three types of MFC had a similar effect on the sheet consolidation, reflected in sheet density. Evaluation of the dewatering and pressability of the wet sheets showed that if the MFC was aggregated by an appropriate retention strategy, the dewatering and pressability were not detrimental to the practical applicability of MFC.

  • 7.
    Ankerfors, Mikael
    et al.
    BillerudKorsnäs AB, Sweden.
    Lindström, Tom
    RISE, Innventia.
    Söderberg, L. Daniel
    KTH Royal Institute of Technology, Sweden.
    The use of microfibrillated cellulose in fine paper manufacturing: Results from a pilot scale papermaking trial2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 3, p. 476-483Article in journal (Refereed)
    Abstract [en]

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

  • 8. Antonsson, S.
    et al.
    Mäkelä, Petri
    RISE, Innventia.
    Fellers, Christer
    RISE, Innventia.
    Lindström, M. E.
    Comparison of the physical properties of hardwood and softwood pulps2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, p. 409-414Article in journal (Refereed)
    Abstract [en]

    High mechano-sorptive creep resistance, i.e., good creep resistance in environments with changing relative humidity, is one of the key requirements for linerboards. The aim of this study was to investigate the influence of pulp types and pulp properties on the mechano-sorptive creep of kraftliner. A high-yield softwood, kraftliner pulp, and four different hardwood pulps were investigated. The physical properties of laboratory sheets were evaluated, with emphasis on the mechanosorptive creep properties. The results showed that the density increase due to increased beating significantly improved the tensile stiffness of all pulps, while its effect on the isocyclic creep stiffness was less pronounced. The hardwood pulps showed higher tensile stiffness, better mechano-sorptive creep properties, and lower hygroexpansion than the softwood pulp at a given density. However, the softwood pulp did exhibit better tensile strength and fracture toughness properties than the hardwood pulps. The results imply that hardwood pulps can be competitive with softwood pulps in kraftliners, provided that their tensile strength and fracture toughness properties can be improved by, for example, chemical means. Furthermore, the isocyclic creep stiffness correlates with the ratio of tensile stiffness to hygroexpansion, indicating that this ratio can be used for engineering estimates of the mechano-sorptive creep performance of paper materials.

  • 9.
    Athley, Karin
    et al.
    RISE, Innventia.
    Granlöf, Lars
    RISE, Innventia.
    Söderberg, L. Daniel
    RISE, Innventia.
    Ankerfors, Mikael
    RISE, Innventia.
    Ström, Göran R.
    RISE, Innventia.
    Mechanical retention - Influence of filler floc size and grammage of the fibre web2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 202-207Article in journal (Refereed)
    Abstract [en]

    An investigation of the impact of particle size on the mechanical retention of particles in a fibre network has been conducted. The particles used were five sets of quartz particle fractions having fairly narrow particle size distributions with average particle size ranging from a few μm to around 100 μm. The particles were used to model flocculated filler aggregates as part of a larger study of the effect of pre-flocculation on mechanical retention. Pre-flocculation of the filler is a possible strategy to increase the filler content of paper without deterioration of strength properties. A modified laboratory hand sheet former, known as the Rapid Drainage Device (RDD) was used. The major modification consisted of a long pipe that acted as a suction leg, which provides a dewatering vacuum at the same level as on a paper machine. The experimental results showed that mechanical filler retention increased linearly with particle size and grammage of the fibre layer above a critical grammage which depended on particle size. The linear relation was also seen in a pilot scale trial on the FEX pilot-paper machine at Innventia. During this trial fine paper was produced using pre-flocculated filler where the mean particle size of the flocs and fibres was measured in the flow to the headbox. The results from this pilot trial show that mechanical retention is an important part of the total filler retention. Drainage time and therefore drainage resistance increased with the grammage of the fibre layer and amount of quartz particle added. Drainage time, compared at total grammage (i.e. the sum of fibre and quartz particle grammage) was lowest for a fraction of medium-sized particles, with a median size of 35 μm. There was no obvious effect on retention or drainage resistance of a change in the dewatering pressure from 27.5 to 41.5 kPa.

  • 10.
    Aulin, Christian
    et al.
    RISE Research Institutes of Sweden.
    Flodberg, Göran
    RISE Research Institutes of Sweden.
    Ström, Göran
    RISE Research Institutes of Sweden.
    Lindström, Tom S. C.
    RISE Research Institutes of Sweden.
    Enhanced mechanical and gas barrier performance of plasticized cellulose nanofibril films2022In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 37, no 1, p. 138-148Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils (CNF) are mixed with plasticizers; sorbitol and glycerol, through high-pressure homogenization to prepare multifunctional biohybrid films. The resulting plasticized films obtained after solvent evaporation are strong, flexible and demonstrate superior toughness and optical transparency. The oxygen barrier properties of the biohybrid films outperform commercial packaging materials. The sorbitol-plasticized CNF films possess excellent oxygen barrier properties, 0.34 cm3·μm/m2·day·kPa at 50 % relative humidity, while significantly enhancing the toughness and fracture strength of the films. CNF films plasticized by 20 wt.% of sorbitol and glycerol could before rupture, be strained to about 9 % and 12 %, respectively. The toughness of the plasticized films increased by ca. 300 % compared to the pristine CNF film. Furthermore, the water vapor barrier properties of the biohybrid films were also preserved by the addition of sorbitol. CNF films plasticized with sorbitol was demonstrated to simultaneously enhance fracture toughness, work of fracture, softening behavior while preserving gas barrier properties. Highly favorable thermomechanical characteristics were found with CNF/sorbitol combinations and motivate further work on this material system, for instance as a thermoformable matrix in biocomposite materials. The unique combination of excellent oxygen barrier behavior, formability and optical transparency suggest the potential of these CNF-based films as an alternative in flexible packaging of oxygen sensitive devices like thin-film transistors or organic light-emitting diode displays, gas storage applications and as barrier coatings/laminations in packaging applications, including free-standing films as aluminium-replacement in liquid board and primary packaging, as replacement for polyethylene (PE) in wrapping paper, e. g. sweats and confectionary.

  • 11. Back, EL
    et al.
    Laudi, B
    Elftonson, J
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Effect of modifiers on wax properties and on dispersibility under hot alkaline conditions1995In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 10, p. 122-128Article in journal (Refereed)
    Abstract [en]

    This paper is one in a series of papers presenting a process for the removal of modified waxes from old corrugated containers by washing after alkaline hot dispersion of the recycled pulp. It presents experiments for selection of the most useful dispersants to be incorporated as wax modifiers already before the wax application. Criteria for selection were their effect on wax properties such as water and moisture resistance and their efficiency for dispersion to minimum size under hot alkaline conditions. The dispersants must also permit simple coagulation of the wax dispersion for its removal from a closed white water system. The dispersion experiments were carried out on a laboratory scale in the absence of fibers at 90°C and pH 9 to 11. Evaluated was the turbidity both at that temperature and after cooling to 20°C. For the final selection, the particle size distribution at 20°C was also measured. A few per cent of a commercial stearic acid with a minor addition of a nonionic fatty alcohol ethoxylate formula R-O-(CH2)2-O-]nH, was found to be a most suitable and economic wax additive.

  • 12.
    Bialik, Marta
    et al.
    RISE, Innventia.
    Moosavifar, A.
    Sedin, M.
    Theliander, H.
    Using the pitzer method to estimate the boiling point rise in black liquor solutions2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 2, p. 172-182Article in journal (Refereed)
    Abstract [en]

    The boiling point rise (elevation) of aqueous industrial solutions is often of significant importance for the design of process conditions, equipment, heat balances, etc. However, few rigorous methods exist for predicting boiling point elevation in complex, multicomponent, electrolyte solutions. An example of such a solution is the black liquor obtained in kraft pulp production: a complex mixture of organic and inorganic ions including Na +, K + OH -, HS - C0 3 2- S0 4 2- S 20 3 2- CH 3COO - various phenolates and many more. This work shows one application of the semi-empirical Pitzer method to the theoretical prediction of the boiling point rise in industrial black liquor solutions. The values of the boiling point elevation were measured in two series of black liquors from representative Swedish mills, including both the original and lignin-lean black liquor at different solid contents. The results show a good agreement between experimental and predicted values at low to moderate solid content, and good qualitative prediction at high solid content.

  • 13.
    Björk, Elisabeth
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging. Mid Sweden University, Sweden.
    Vomhoff, Hannes
    Holmen, Sweden.
    Engstrand, Per
    Mid Sweden University, Sweden.
    Production of fines from refined kraft pulp by fractionation with micro-perforated screens2021In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 36, no 3, p. 456-Article in journal (Refereed)
    Abstract [en]

    The objective in this work was to obtain a fine fraction of kraft pulp, with as high concentration as possible, in a pilot-scale fractionation with micro-perforated screen baskets. The influence of screen basket surface, hole size, feed concentration, pulp type and refining segment design was investigated. The results showed that a smooth screen basket surface improved the fractionation efficiency of the unrefined pulp compared to a profiled screen basket, despite a larger hole size. A significantly higher fine fraction concentration was obtained when using refined hardwood pulp compared to when using softwood pulp, which was explained with its lower average fibre length and narrower and thus more flexible fibre fragments. The pilot trials also showed that the screening process could be operated at feed concentrations similar to those directly after a refiner, 30-40 g/l. This was demonstrated in a process layout with partial recirculation where a refiner and a micro-perforated screen basket were operated in series in pilot scale. 

  • 14.
    Brodin, Fredrik Wernersson
    et al.
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Eriksen, Øyvind
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Preparation of individualised lignocellulose microfibrils based on thermomechanical pulp and their effect on paper properties2015In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, no 3, p. 443-451Article in journal (Refereed)
    Abstract [en]

    Although mechanical pulp can be considered as a potential raw material for preparation of microfibrils, suitable pre-treatment methods have been missing. Consequently, the objectives of this study were firstly to find a suitable procedure to prepare lignocellulose microfibrils (LCMF) from fractionated thermo-mechanical pulp (TMP) and secondly to evaluate if these TMP-based materials could be used as paper additives to increase paper strength. Carboxymethylation was found to be a suitable pretreatment for both TMP fines and TMP fibres to enable preparation of individualised LCMF after subsequent homogenisation treatment. After air drying, this material formed dense continuous films in conformity with films prepared from cellulose microfibrils (CMF) originating from chemical pulp. Homogenisation only or sulphonation followed by homogenisation did not fibrillate the TMP samples into individualised LCMF. Analysis of paper properties showed that addition of 20% LCMF to a standard TMP furnish improved tensile strength index by 15%. The LCMF-containing papers were also more brittle (less elongation) than the other paper sheets in this study. Similar tensile strength index was also obtained for TMP fines treated by sulphonation followed by homogenisation.

  • 15.
    Brodin, Fredrik Wernersson
    et al.
    Chalmers University of Technology, Sweden.
    Sonavane, Yogesh
    Aalto University, Finland.
    Sedin, Maria
    RISE, Innventia.
    Displacement washing of TEMPO-oxidized softwood kraft pulp: Effects of change in fiber properties2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, no 3, p. 366-376Article in journal (Refereed)
    Abstract [en]

    Bleached softwood kraft pulp fibers were treated using TEMPO oxidation at two different dosages of NaClO. A batch of non-oxidized reference pulp was also prepared with a concentration of the tracer (Na) similar to the oxidized batches. A total of 15 washing experiments were conducted and the dispersion model was used to characterize washing behavior. TEMPO oxidation resulted in a major increase in the amount of carboxylate groups in the pulps and a considerable decrease in fiber/particle size in relation to the reference pulp fibers. Oxidized fibers also had less fiber curl than reference fibers. Water retention values were greater in the oxidized pulps and the oxidized fibers exhibited major swelling during the washing operation, while reference fibers had only minorswelling. The amount of sodium in the filter cakes after washing corresponded to the amount of carboxylate groups in the pulps. Swelling of oxidized pulp fibers needs to be considered in order to describe filtration and washing. The average specific filtration resistance for all pulps in this study was in the order of 1010-1011 m/kg, i.e. moderately easy to filter. The most oxidized pulp had the highest average specific filtration resistance and the lowest value for the estimated effective longitudinal dispersion coefficient, in agreement with theory.

  • 16.
    Brännvall, Elisabet
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Biorefinery and Energy.
    Kulander, Ida
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Biorefinery and Energy.
    Consequences in a softwood kraft pulp mill of initial high alkali concentration in the impregnation stage2019In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 34, no 1, p. 28-35Article in journal (Refereed)
    Abstract [en]

    Impregnation with high initial concentration is fast and efficient, leading to a homogeneous delignification in the subsequent cook, resulting in improved screened pulp yield. To obtain high initial alkali concentration, the white liquor flow needs to be significantly increased. The moisture content of the wood chips and the alkali concentration of the white liquor limit the initial alkali concentration of the impregnation liquor that can be reached. It is therefore of interest to evaluate the possibility to implement high alkali impregnation (HAI) industrially and the consequences this would have on the mill system. The effect of HAI on mass and energy balances in a kraft pulp mill has been studied using mill model simulations. The sensitivity to disturbances in important parameters for process control has been compared to impregnation scenarios used industrially. It was shown that high initial alkali concentration can be achieved on industrial scale by increased white liquor flow. HAI has a positive effect on recovery flows and reduces the need for make-up chemicals. The HAI concept is less sensitive to variations in process parameters, such as chip moisture and white liquor concentration, thus diminishing the risk of alkali depletion in chip cores. © 2019 Brännvall and Kulander.

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  • 17.
    Brännvall, Elisabet
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Walter, Karin
    Nouryon, Sweden.
    Process modifications to obtain a prehydrolysis kraft dissolving pulp with low limiting pulp viscosity2020In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 35, no 3, p. 332-341Article in journal (Refereed)
    Abstract [en]

    Cellulose can be directly dissolved in cold alkali without derivatization. However, this requires low cellulose molecular weight, i. e. low pulp viscosity, preferably below 300 mL g−1. This can be achieved by for example acid or enzymatic hydrolysis of the dissolving pulp. However, it would be beneficial to manufacture pulp with sufficiently low viscosity without an additional treatment stage prior to dissolution. Unit processes in pulping can be operated in such a way as to reduce the molecular weight of cellulose. The approach of the study was to modify the conditions in unit pulping processes in order to obtain a low pulp viscosity of fully bleached prehydrolysis kraft pulp. A high charge of alkali in the oxygen delignification reduced the cellulose molecular weight significantly. Increased temperature, 120 °C compared to 98 °C, had also a significant effect on viscosity. By performing peroxide bleaching at acidic pH, the viscosity could be sufficiently reduced even when oxygen delignification was performed at lower temperature. However, for high brightness, a chlorine dioxide stage is needed.

  • 18.
    Bäckström, Marie
    et al.
    RISE, STFI-Packforsk.
    Hammar, Lars-Åke
    RISE, STFI-Packforsk.
    Htun, Myat
    RISE, STFI-Packforsk.
    Beatability and runnability studies of ion-exchanged unbleached kraft pulps on a pilot scale2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 1, p. 94-100Article in journal (Refereed)
    Abstract [en]

    It has earlier been shown that the counter-ion to the charged groups in the fibre has a significant effect on the beatability of fibres, but large-scale investigations of this effect are scarce in the literature. The objectives of the present study were therefore to develop a technique to ion-exchange large quantities of industrial pulp into the Na +-form using complexing agents and to study the effect of industrial-scale refining on pulp fibres in the Na +-form and how the fibres respond to industrial-like papermaking. The results show that ion-exchange can indeed be conducted on a pilot-scale using complexing agents such as DTPA. The study further indicates that an energy reduction of 50% at a given WRV or tensile index may be achieved if the fibres are converted to Na +-form prior to pilot-scale refining. By applying these techniques in full-scale production, it should thus be possible to save significant amount of energy, especially in the case of papers made from unbleached pulp that usually demands a higher degree of beating to achieve sufficient strength.

  • 19.
    Bäckström, Marie
    et al.
    RISE, Innventia.
    Melander, Erik
    KTH Royal Institute of Technology, Sweden.
    Brännvall, Elisabet
    KTH Royal Institute of Technology, Sweden.
    Study of the influence of charges on refinability of bleached softwood kraft pulp2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 4, p. 588-595Article in journal (Refereed)
    Abstract [en]

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

  • 20.
    Bäckström, Marie
    et al.
    RISE, Innventia.
    Tubek-Lindblom, Anna
    RISE, Innventia.
    Wågberg, Lars
    RISE, Innventia.
    Studies of the influence of deflocculants and flocculants on the refining efficiency on a pilot scale2009In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 3, p. 319-326Article in journal (Refereed)
    Abstract [en]

    The objective of the present investigation was to study the influence of flocculants and deflocculants on refining efficiency. The refining was performed with the aid of a conical refiner at EuroFEX, and the refining response was evaluated as the change in fibre properties and in the mechanical properties of handsheets. Using the same furnish, an unbleached neverdried softwood pulp, the effect of fibre dimensions on floc strength was excluded as much as possible. The degree of flocculation was changed by addition of APAM, CPAM, guar gum and CMC. The floc strength was characterized using a parallel plate rheometer. The added chemicals, except for APAM, affected the relation between power input and gap clearance. To reach a certain power the fibres treated with guar gum, CMC or CPAM required a narrower gap clearance than the reference pulp or when APAM was added to the fibres. Refining at a narrower gap clearance increased the refining efficiency in terms of WRV and paper property development, as long as fibre length reduction could be avoided.

  • 21. Carlsson, A.
    et al.
    Söderberg, L. Daniel
    RISE, Innventia.
    Lundell, F.
    Fibre orientation measurements near a headbox wall2010In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 2, p. 204-212Article in journal (Refereed)
    Abstract [en]

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

  • 22.
    Carlsson, CMG
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Eriksson, I
    Lindström, E
    Ström, G
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Improved wettability of chemithermomechanical pulp by oxygen plasma treatment1994In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 9, p. 72-75,83Article in journal (Refereed)
    Abstract [en]

    Chemithermomechanical pulp has been treated by cold plasma of oxygen, nitrogen, argon or air. The wettability increases as a result of treatment by oxygen or air plasmas but decreases when argon or nitrogen plasmas are used. The initial water absorption rate can be improved by more than 100 % using an oxygen plasma. After subsequent ageing of the pulp the improvement was ca 200 %. Electron Spectroscopy for Chemical Analysis (ESCA) shows that the oxygen plasma treatment increases the oxygen content of the fibre surfaces due to oxidation and/or removal of fatty acids, resin acids, and probably also lignin. The amount of extractable material increases after the plasma treatment, probably due to oxidation and scission of the lignin and the carbohydrates. This oxidized low molecular weight material may act as a surfactant decreasing the surface tension of the absorbing liquid and thus enhance the absorption rate.

  • 23.
    Carlsson, G
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Ström, G
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Annergren, G
    Water sorption and surface composition of untreated or oxygen plasma-treated chemical pulps1995In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 10, p. 17-23Article in journal (Refereed)
    Abstract [en]

    Three kraft pulps and one bisulphite pulp have been studied. The surface chemical composition was determined by means of ESCA, and water sorption was studied using a dynamic contact angle tester. The surface coverage of lignin as well as dichloromethane (DCM) extractable material was found to be considerably larger than expected from bulk measurements. The results show that DCM extractable material decreases water sorption to a larger extent than lignin. Oxygen plasma-treatment improves water sorption of pulps containing large amounts of DCM extractable material and lignin due to oxidation of these compounds. Only a few seconds of exposure is needed. After ageing the improved water sorption is unchanged for kraft pulps. However, bisulphite pulp which contains larger amount of extractable material shows a decrease in rate of water sorption.

  • 24.
    Chinga-Carrasco, Gary
    et al.
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Aasrød, Kenneth
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Leinsvang, Berit
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Bouveng, Mikael
    RISE, Innventia.
    Johansson, Per-Åke
    RISE, Innventia.
    Structural effects on print-through and set-off2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 3, p. 596-603Article in journal (Refereed)
    Abstract [en]

    In this study the effect of paper structure on ink transfer and cold-set print quality was assessed. A factorial experiment involving 5 factors with two levels was designed. Several sheet structures were constructed. The sheets were made from three basic pulps, thermomechanical pulp (TMP), de-inked pulp (DIP) and stone groundwood (SGW). The designed structures were homogeneous and layered to verify the effect of sheet structure and fines content on print quality. A comprehensive multiscale characterisation of the sheet structures was performed. The analyses comprised scanning electron microscopy (SEM) and mercury porosimetry for bulk structure assessment. Parker Print Surf (PPS), laser profilometry and field-emission scanning electron microscopy (FE-SEM) were applied for giving a detailed description of the surface structure affecting ink transfer. The study revealed that the surface structure affects the ink demand and set-off. Increasing the micro-roughness leads to an increment of ink demand in order to achieve a given print density. The bulk pore structure affects the light scattering coefficients. Small pores are positive for increasing the light scattering and thus for reducing the print-through level. This was confirmed by SEM and mercury porosimetry measurements.

  • 25.
    Coppel, L.G.
    et al.
    RISE, Innventia.
    Andersson, M.
    Edström, P.
    Kinnunen, J.
    Limitations in the efficiency of fluorescent whitening agents in uncoated paper2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, no 3, p. 319-328Article in journal (Refereed)
  • 26.
    Coppel, Ludovic Gustafsson
    et al.
    RISE, Innventia.
    Andersson, Mattias
    Mid Sweden University, Sweden.
    Neuman, Magnus
    Mid Sweden University, Sweden.
    Edström, Per
    Mid Sweden University, Sweden.
    Fluorescence model for multi-layer papers using conventional spectrophotometers2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 418-425Article in journal (Refereed)
    Abstract [en]

    We present an extension of a Kubelka- Munk based fluorescence model in which we introduce an apparent scattering (S UV) and absorption (K UV) coefficient for all wavelengths below 400 nm. We describe a method for modelling the total radiance factor of multi-layer papers and for estimating the optical parameters (S, K and Q) of each layer. Assuming that the fluorescent whitening agent only absorbs below 400 nm, we are able to determine S UV, K UV and the apparent quantum efficiency, Q(UV,λ) for 400 nm<λ<700 nm, from spectral radiance measurements in the visual part of the electromagnetic spectrum. We test the proposed method on different layered constructions made of three individual pilot paper layers. The proposed method allows the papermaker to determine the illumination independent fluorescence characteristics of single- and multilayer paper layers using a conventional singlemonochromator spectrophotometer operating in the visible part of the electromagnetic spectrum, and also to predict the radiance factor of fluorescing layered papers.

  • 27.
    Dahlgren, MAG
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Claesson, PM
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Audebert, R
    Interaction and adsorption of polyelectrolytes on mica1993In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 8, p. 62-67Article in journal (Refereed)
    Abstract [en]

    Interaction and adsorption of different polyelectrolytes onto mica was studied using the surface force technique. For highly charged polyelectrolytes in dilute aqueous salt solution, the adsorbed layer neutralizes the mica surface charge at a bulk concentration of 10-50 ppm. Upon dilution the adsorbed layers desorb slowly. When the indifferent salt concentration of the solution is increased at a constant polyelectrolyte concentration, additional adsorption takes place. Attractive interactions are present between two layers of adsorbed polyelectrolytes with a charge density of 30% or more as long as the substrate surface charge is not overcompensated strongly. This attraction, which is mainly due to bridging, is considerably stronger than the van der Waals interaction. For uncharged polyelectrolyte/surface systems, the thickness of the polyelectrolyte equilibrium layer increases with decreasing charge density. For the fully charged polyelectrolyte, the range of bridging and steric interaction indicates that the polyelectrolytes adsorb in a flat conformation on the mica surface. Desorption of the polyelectrolytes into a dilute aqueous salt solution is a slow process. For an initially slightly overcompensated system, the long-range and adhesive forces vary with time in contact with a polyelectrolyte-free solution. Initially, the adhesion force increases as the net surface charge decreases. This is due to an increased bridging attraction.

  • 28.
    Dahlvik, P
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Ström, G
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Eklund, D
    Variations in calcium ion concentration and pH influencing coating colour rheology, dewatering and immobilization1997In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 12, p. 61-66Article in journal (Refereed)
    Abstract [en]

    Interparticle interactions in a coating colour are largely influeced by electrolyte concentration and suspension pH. The degree of interaction is reflected in the rheological and dewatering properties of the colour as well as in the structural properties of the immobilized coating layer. In the present study an attempt is made to correlate the degree of interparticle interaction created within coating colours by variation in calcium ion concentration and pH with the atomic absorption spectroscopy were applied to gain further information about the degree of interaction. Results showed that coating colours of a mix of calcium carbonate and clay exhibit a pronounced elastic character. The elastic response increased with calcium ino concentration. This is due to calcium calcium ions binding to the dispersing agent, making it less effective. A further cauce is the decrease in the thickness on the diffuse layer of counter ions surrounding the pigment particles. A pH-reducation further strenghened the created intrinsic three-dimensional network structure. An increase in calcium ion concentration resulted in a reduced water retention, slightly pronounced by a higher pH. The immobilization solids content as did also a lower pH. Characterization of coated layers drawn down on polyester film confirmed that a combination of a high calcium ion concentration and a reduction of pH results in a pronounced pigment interaction, reflected in a thicker layer with lower density and higher roughness.

  • 29.
    Dang, Binh T.
    et al.
    Chalmers University of Technology, Sweden.
    Brelid, Harald
    Södra Innovation, Sweden.
    Köhnke, Tobias
    RISE, Swerea, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Effect of sodium ion concentration profile during softwood kraft pulping on delignification rate, xylan retention and reactions of hexenuronic acids2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, no 4, p. 604-611Article in journal (Refereed)
    Abstract [en]

    The objective of this investigation was to study how different concentration profiles of sodium ions influence the delignification rate, hexenuronic acid formation/degradation and xylan retention under kraft cooking conditions. The concentration of sodium ions was varied in time between 0.52 and 3.00 mol/kg solvent, taking two different routes by the controlled addition of sodium carbonate. The reaction rates of hexenuronic acid were found to increase when the sodium ion concentration was at the higher level. Furthermore, the results implied that the kinetics of hexenuronic acid reactions responds rapidly to changes in sodium ion concentration. Delignification and the removal rates of xylan decreased rapidly after the sodium ion concentration was increased. However, when the sodium ion concentration was decreased, the response to the change was delayed. These findings indicate that effects of ionic strength on the rate of delignification and removal of xylan arise as a consequence of changes in solubility and on mass transport phenomena rather than from the rates of chemical reaction. Furthermore, the results suggest that non-dissolved xylan located in the fibre wall matrix may also sorb on cellulose surfaces relatively early on in the cook if the concentration of sodium ions is at high level.

  • 30.
    Dang, Binh T.
    et al.
    Chalmers University of Technology, Sweden.
    Brelid, Harald
    Södra Innovation, Sweden.
    Köhnke, Tobias
    RISE, Swerea, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Impact of ionic strength on delignification and hemicellulose removal during kraft cooking in a small-scale flow-through reactor2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 3Article in journal (Refereed)
    Abstract [en]

    The effect of ionic strength/sodium ion concentration and type of anions on the delignification rate, the retention of xylan and the reactions of hexenuronic acid during kraft cooking has been investigated. A novel, small, flow-through digester was used in the cooking experiments in order to prevent the resorption of lignin and xylan and to maintain a constant concentration of active chemicals throughout the kraft cook. An increase in ionic strength/sodium ion concentration in the cooking liquor decreases the removal rate of both lignin and xylan during kraft cooking. In general, the removal rate of xylan tends to correlate with the delignification rate. However, the present investigation finds that the retention of xylan at a given degree of delignification increases at high ionic strength/sodium ion concentration. The addition of sodium salts of carbonate or chloride to the cooking liquor was shown to increase the rate of formation/degradation reactions of hexenuronic acids and the total amount of uronic acids substituted on the xylan backbone decreases when the concentration of sodium ions increases in the cooking liquor. This promotes a decrease in the dissolution of xylan and consequently an increase in the retention of xylan in the wood residues. The obtained results demonstrate that the xylan content in the fiber wall increases at higher ionic strength/sodium ion concentration, which leads to a slight increase in pulp yield.

  • 31.
    De Magistris, Federica
    et al.
    RISE, STFI-Packforsk.
    Salmen, Lennart
    RISE, STFI-Packforsk.
    Finite element modelling of wood cell deformation transverse to the fibre axis2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 2, p. 240-246Article in journal (Refereed)
    Abstract [en]

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

  • 32.
    Deshpande, Roghe
    et al.
    Karlstad University, Sweden.
    Sundvall, Lars
    RISE - Research Institutes of Sweden.
    Grundberg, H.
    Domsjö Fabriker, Sweden.
    Germgård, U.
    Karlstad University, Sweden.
    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.

  • 33.
    Duker, Elisabeth
    et al.
    RISE, STFI-Packforsk.
    Ankertors, Mikael
    RISE, STFI-Packforsk.
    Lindström, Tom
    RISE, STFI-Packforsk.
    Glad-Nordmark, Gunnel
    RISE, STFI-Packforsk.
    The use of CMC as a dry strength agent: The interplay between CMC attachment and drying2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 65-71Article in journal (Refereed)
    Abstract [en]

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

  • 34.
    Duker, Elisabeth
    et al.
    RISE, STFI-Packforsk.
    Lindström, Tom
    RISE, STFI-Packforsk.
    On the mechanisms behind the ability of CMC to enhance paper strength2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 1, p. 57-64Article in journal (Refereed)
    Abstract [en]

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

  • 35. Enberg, S.
    et al.
    Rundlöf, M.
    Paulsson, M.
    Johnsen, I.A.
    Axelsson, P
    The influence of process conditions during pulp storage on the optical properties of Norway spruce high-yield pulps2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, p. 203-210Article in journal (Refereed)
  • 36.
    Enberg, Sofia
    et al.
    Norske Skog Saugbrugs, Norway; Mid Sweden University, Sweden.
    Rundlöf, Mats
    Mid Sweden University, Sweden; Capisco Science and Art, Sweden.
    Paulsson, Magnus
    Mid Sweden University, Sweden; AkzoNobel Pulp and Performance Chemicals, Sweden.
    Axelsson, Patrik
    Norske Skog Saugbrugs, Norway.
    Eriksen, Øyvind
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Engstrand, Per O.
    Mid Sweden University, Sweden.
    Some causes of formation of colour during storage of hydrogen-peroxide bleached Norway spruce mechanical pulp2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 2, no 29, p. 356-366Article in journal (Refereed)
    Abstract [en]

    The discolouration of hydrogen-peroxide bleached Norway spruce mechanical pulp during storage in mill systems was studied and the contributions of process water, iron and dyes were evaluated over the visible spectrum. Washing of the pulp made it less sensitive to storage, possibly due to the removal of extractives, lignin-like substances, iron and pulp fines. Storage in white water gave extensive discolouration with a shoulder in the absorption spectrum at around 550- 650 nm. Most of the colour was associated with pulp fines or filler but some colour was also found in smaller fractions and in the water phase. The addition of ferric ions increased the light absorption coefficient during storage, initially at short wavelengths and then over the whole spectrum, but could not explain the increased absorption at 550-650 nm and could not be the only cause of the darkening in the mill system. A cationic basic violet dye gave a shoulder in the absorption spectrum similar to that in the mill system, but the absorption in this area did not increase during storage. Model calculations indicate that ferric ions together with violet and red dyes could explain a major part, but not all, of the colour observed in the mill system after storage. The darkening not accounted for at longer wavelengths and around 550-650 nm is suggested to be related to fines and fillers including dissolved and colloidal substances associated with these particles.

  • 37.
    Enberg, Sofia
    et al.
    Norske Skog Saugbrugs, Norway; Mid Sweden University, Sweden.
    Rundlöf, Mats
    Mid Sweden University, Sweden; Capisco Science and Art, Sweden.
    Paulsson, Magnus
    Mid Sweden University, Sweden; AkzoNobel Pulp and Performance Chemicals, Sweden.
    Axelsson, Patrik
    Norske Skog Saugbrugs, Norway.
    Eriksen, Øyvind
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Engstrand, Per O.
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    The influence of process waters on optical properties during storage of hydrogen-peroxide bleached Norway spruce mechanical pulp2014In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 2, no 29, p. 344-355Article in journal (Refereed)
    Abstract [en]

    To evaluate the causes behind the formation of colour in mill systems, the effect of different process waters on the optical properties of hydrogenperoxide bleached Norway spruce mechanical pulp during storage was studied. The influence of process water type, temperature, time, pulp consistency and pH was evaluated over the visible range of wavelengths. The darkening was more pronounced when pulp was stored in process waters compared to in distilled water. Increased temperature and prolonged storage times increased the darkening as expected, whereas a higher storage consistency gave less darkening than a lower storage consistency (15% compared to 5%). The pH value that gave the lowest brightness reduction and a minimum in Δk460 was found to be 5.5-6.0. Storage of pulp in white water from the paper machine resulted in a broad shoulder in the k spectra indicating colour formation related to the particles in this water. Part of this shoulder in absorption spectra was related to added dyes, but the increase in absorption with time is likely to be caused by some other colour formation. The colour measured as a∗, b∗ showed that the storage changed the colour of the pulp towards red and yellow, and initially more towards red.

  • 38.
    Eriksen, O.
    et al.
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Holmqvist, Claes
    RISE, STFI-Packforsk.
    Mohlin, Ulla-Britt
    RISE, STFI-Packforsk.
    Fibre floc drainage - a possible cause for substantial pressure peaks in low-consistency refiners2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 3, p. 321-326Article in journal (Refereed)
    Abstract [en]

    Is floc drainage a cause for substantial pressure peaks in low-consistency refiners? High-resolution pressure measurements using a sensor mounted in a stator bar have been performed. These show that during the initial stage of a bar crossing, a substantial pressure is sometimes generated, which can reach a level of several MPa. A theoretical model that explains the pressure pulses is presented. The analysis is based on the assumption that a floc of fibres is trapped between the leading edges of the approaching bar surfaces. Water needs to be expelled from the part of the floc that is compressed and enters into the refiner gap. The hydrodynamic resistance to expel the liquid from within the floc is shown to give rise to substantial pressures in the region close to the leading edge of the rotor bar. The estimated pressures are of the same order as the measured values.

  • 39.
    Eriksen, O.
    et al.
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Holmqvist, Claes
    RISE, STFI-Packforsk.
    Mohlin, Ulla-Britt
    RISE, STFI-Packforsk.
    Theoretical outline of the cause for observed cavitation in a low-consistency refiner2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 3, p. 315-320Article in journal (Refereed)
    Abstract [en]

    High-frequency pressure measurements in the refining zone have exposed features that strongly indicate that cavitation occurs regularly in low-consistency refiners. In order to explain the cavitation, it is assumed that pulp fibres are trapped between opposing bars on the discs in such a way that liquid is hindered to enter into the refining gap at the leading edge of the stator bar. In order to prevent a void as the rotor bar drags liquid away from the trapped fibres, a counter flow towards the trapped fibres then needs to be set up. This necessitates a low pressure in the gap, in order that liquid from the groove in front of the rotor is accelerated into the gap at the required rate. It appears that this mechanism can yield gap pressures several hundred kPa below that in the grooves. Cavitation bubbles may then form, which subsequently collapse and cause shock waves when the pressure rises after the bar passage.

  • 40.
    Eriksson, L
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Alm, B
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Effects of polyelectrolyte characteristics and flocculation conditions on fine particle floc properties1993In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 8, p. 153-159, 175Article in journal (Refereed)
    Abstract [en]

    Polystyrene latex was flocculated with cationic polyelectrolytes of different charge densities at low ionic strength and the effects of different flocculation conditions were studied. The flocs were characterized in an equipment with which the flocculation kinetics, the floc structure, the shear resistance and the ability for reflocculation after high shear can be studied in a single experiment. The structure was further investigated by SEM on freezedried flocs. With low charge density polymers the flocs had good shear resistance but limited ability to reflocculate after high shear. They consisted of compact microflocs connected into more open macrostructures and were formed by a bridging mechanism. Best floc properties seemed to be obtained with relatively mild stirring conditions during the initial flocculation. With somewhat higher charge density (≈10 %) a transition in mechanism was indicated since best shear strength and reflocculation was obtained with high intensity stirring during the initial flocculation. With medium charge density polymers the shear strength was lower and less dependent on the initial stirring rate. The size of the initial flocs was strongly decreased by in-creasing initial mixing intensity. On the other hand, the reflocculation was better than with low charge density polymers, and it also improved with increasing initial stirring rate. The flocculation was mainly due to charge neutralization with limited contribution of bridging and electrostatic attractions in the total attractive force. With high charge density polymers the shear resistance was somewhat better than for medium charged polymers and high initial stirring intensity seemed to be favourable also in this case. The good reflocculation however, seemed to depend on the initial stirring intensity in a non-monotonous way. The structure of the flocs had voids on all length scales because of a flocculation mechanism with strong and close contacts between the primary particles.

  • 41.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    The effects of high alkali impregnation and oxygen delignification of softwood kraft pulps on the yield and mechanical properties2022In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 37, no 2, p. 223-231Article in journal (Refereed)
    Abstract [en]

    This study investigated whether the yield improvement after high alkali impregnation (HAI) is maintained after oxygen delignification and whether the potential of oxygen delignification to increase the mechanical properties is affected by high alkali impregnation. The yield improvement achieved by high alkali impregnation (1 %) was preserved after oxygen delignification, particularly of glucomannan. The total fiber charge and swelling increased after oxygen delignification regardless of the type of impregnation in the cooking step. The tensile index improvement obtained by oxygen delignification was retained if this was preceded by high alkali impregnation. The stiffness index was higher and elongation slightly lower after HAI impregnation than after a standard (REF) impregnation. Fibers obtained through high alkali impregnation seem to be slightly less deformed and slightly wider than fibers obtained after a standard impregnation. 

  • 42.
    Esteves, Claudia
    et al.
    RISE Research Institutes of Sweden, Bioeconomy and Health, Pulp, Paper and Packaging.
    Sevastyanova, Olena
    KTH Royal Institute of Technology, Sweden.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Brännvall, Elisabet
    RISE Research Institutes of Sweden.
    The impact of bleaching on the yield of softwood kraft pulps obtained by high alkali impregnation: Bleaching and high alkali impregnation impact2022In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 37, no 4, p. 593-608Article in journal (Refereed)
    Abstract [en]

    High alkali impregnation (HAI) increases the total yield of softwood pulps following kraft cooking. This yield improvement is also maintained after oxygen delignification. This study evaluates how bleaching with either chlorine dioxide or hydrogen peroxide affects the final yield of samples obtained with standard and HAI. The chemical composition, viscosity, brightness, mechanical and morphological properties were studied. Compared to cooking after standard impregnation the yield improvement achieved by HAI was preserved in both types of bleaching sequences (2 % units for chlorine dioxide and 4 % units for hydrogen peroxide). The introduction of charged groups into the cellulose fibers was higher with hydrogen peroxide bleaching than with chlorine dioxide however, no significant impact was seen on the swelling or mechanical properties. The brightness was higher for the pulps bleached with chlorine dioxide compared with hydrogen peroxide. Hydrogen peroxide bleaching resulted in similar brightness development for both standard and HAI. Fibers bleached with chlorine dioxide had the highest curl index (16-17 %) compared to the fibers bleached with hydrogen peroxide (15 %). © 2022 the author(s)

  • 43.
    Fellers, Christer N.
    et al.
    RISE, Innventia.
    Östlund, Sören
    KTH Royal Institute of Technology, Sweden.
    Mäkelä, Petri
    RISE, Innventia. Tetra Pak Packaging Solutions AB, Sweden.
    Evaluation of the Scott bond test method2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 231-236Article in journal (Refereed)
    Abstract [en]

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

  • 44.
    Ferritsius, Rita
    et al.
    StoraEnso, Sweden; Mid Sweden University, Sweden.
    Sandberg, Christer
    Mid Sweden University, Sweden; Holmen Paper, Sweden.
    Ferritsius, Olof
    Mid Sweden University, Sweden.
    Rundlöf, Mats
    Capisco, Sweden.
    Daniel, Geoffrey
    SLU Swedish University of Agricultural Sciences, Sweden.
    Mörseburg, Kathrin
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Fernando, Dinesh
    SLU Swedish University of Agricultural Sciences, Sweden.
    Development of fibre properties in mill scale high- And low consistency refining of thermomechanical pulp (Part 1)2020In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 35, no 4, p. 589-599Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to evaluate changes in fibre properties with high (HC)- and low consistency (LC) refining of TMP and determine how these contribute to tensile index. Two process configurations, one with only HC refining and another with HC refining followed by LC refining were evaluated in three TMP mainline processes in two mills using Norway spruce. An increase in tensile index for a given applied specific energy was similar for all LC refiners in the three lines, despite differences in the fibre property profiles of the feed pulps. Compared with only HC refined pulps at a given tensile index, HC+LC refined pulps had greater fibre wall thickness, similar fibre length, strain at break and freeness, but lower light scattering coefficient, fibre curl and external fibrillation. The degree of internal fibrillation, determined by Simons' stain measurements, was similar for both configurations at a given tensile index. The results indicate that the increase in tensile index in LC refining is largely influenced by a decrease in fibre curl and in HC refining by peeling of the fibre walls. Compared at a given tensile index, the shive content (Somerville mass fraction) was similar for both HC+LC and HC refining.

  • 45. Furó, I
    et al.
    Daicic, J
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    NMR cryoporometry: a novel method for the investigation of the pore structure of paper and paper coatings1999In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 14, p. 221-225Article in journal (Refereed)
    Abstract [en]

    Many of the properties that paper coatings are designed to modify are determined to varying degrees by the nature of the pore space that interweaves the consolidated matrix. It is therefore highly useful to characterize the pore size distribution of paper coatings. Commonly used methods include mercury porosimetry, image analysis of scanning electron micrographs, and stain imbibition. Here, we describe a method, NMR cryoporometry, which is novel in its application to pores in paper and paper coating and is particularly suitable for measuring small pore sizes in the range of 1 to 100 nm. Such pore sizes are difficult to access with other techniques. The method is based on the principle of the freezing and melting temperature suppression of fluids entrapped within pores. A general outline of the technique is given, and an example of a cryoporometry measurement on a coated paper sample is described.

  • 46.
    Gimaker, M.
    et al.
    RISE, Innventia.
    Östlund, M.
    Östlund, S.
    Wågberg, L.
    Influence of beating and chemical additives on residual stresses in paper2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, no 4, p. 445451-Article in journal (Refereed)
  • 47.
    Giummarella, Nicola
    et al.
    KTH Royal Institute of Technology, Sweden.
    Henriksson, Gunnar
    KTH Royal Institute of Technology, Sweden.
    Salmen, Lennart
    RISE - Research Institutes of Sweden, Bioeconomy, Biorefinery and Energy.
    Lawoko, Martin
    KTH Royal Institute of Technology, Sweden.
    On the effect of hemicellulose removal on cellulose-lignin interactions2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 4, p. 542-549Article in journal (Refereed)
    Abstract [en]

    In a recent study, it was suggested that there could be direct associations between cellulose and lignin in mild alkaline cooked pulps. The observation was based on studies showing that the molecular straining of lignin was similar to that of cellulose. This finding has serious ramifications for technical production of pulps as it could expand on what is known about recalcitrant lignin removal during pulping. Herein, we investigate the possible interaction between cellulose and lignin discussing possible mechanisms involved at the nano- and molecular-scales, and present support for that the removal of hemicellulose by hot water extraction or mild kraft pulping causes strong interactions between lignin and cellulose. 

  • 48. Gorski, D.
    et al.
    Mörseburg, Kathrin
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Axelsson, P.
    Engstrand, P.
    Peroxide-based ATMP refining of Spruce: Energy efficiency, fibre properties and pulp quality2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, p. 47-63Article in journal (Refereed)
  • 49. Gorski, D.
    et al.
    Mörseburg, Kathrin
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Johansson, Lars
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Role of equipment configuration and process chemicals in peroxide-based ATMP refining of spruce2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, p. 233-247Article in journal (Refereed)
  • 50.
    Gorski, Dmitri
    et al.
    Norske Skog Saugbrugs, Norway.
    Mörseburg, Kathrin
    RISE, Innventia, PFI – Paper and Fiber Research Institute.
    Olson, James
    University of British Columbia, Canada.
    Luukkonen, Antti
    Andritz Inc., USA.
    Fibre and fines quality development in pilot scale high and low consistency refining of ATMP2012In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, p. 872-881Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to characterise and compare the development of fibre and fines properties in high consistency (HC) and low consistency (LC) refining of mechanical pulp. Primary refined pulp was produced using the Advanced Thermo-Mechanical Pulp (ATMP) refining process. Pulps were characterized to evaluate external and internal fibrillation, fibre shape and dimensions, surface area of fines and the proportion of split fibres. Based on the results, a different mode of fibre development was proposed for LC and HC refining. The LC refining resulted in a greater reduction in the shives content and R30 Bauer-McNett fibre fraction. The reduced R30 fraction considerably increased the middle fibre fractions; however it showed no further development in terms of surface fibrillation. While HC refining resulted in a significant reduction in fibre wall thickness associated with fibre collapse and increase in external fibrillation, LC refining mainly generated structural changes, seen in fibre straightening and increased flexibility. The HC and LC refined pulps had different property profiles compared at equal handsheet tensile index. The LC refined pulps contained less long fibres and fines but significantly more middle fraction particles. Extensive internal fibrillation of the straighter LC refined fibres appeared to have compensated for lower fines content and external fibrillation, producing well bonded sheets with good tensile strength.

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