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  • 1. Backstrom, Marie
    et al.
    Jensen, Anna
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Influence of chip presteaming conditions on kraft pulp composition and properties2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 5, p. 393-399Article in journal (Refereed)
    Abstract [en]

    Presteaming is a well-established technique in pulp mills, which improves cooking liquor impregnation by removing air from within and between chips. The aim of the study was to investigate how conditions during steaming affect the subsequent kraft cook and properties of the obtained pulp. It was found that higher pressure and temperature during chip presteaming led to increased degradation and dissolution of hemicelluloses. Lower refinability and tensile index was obtained for pulps cooked after presteaming at high pressure and for a long time.

  • 2.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Aspects on Strenght Delivery and Higher Utilisation of the Strength Potential of Kraft Pulp Fibres2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Studies on strength delivery and related fields have so far concentrated on finding the locations in the mill where fibres are damaged and what the damages consist of. However, fibres will invariably encounter mechanical stresses along the fibreline and in this thesis a new concept is introduced; the vulnerability of fibres to mechanical treatment. It is hypothesised that fibres with different properties have different abilities to withstand the mechanical forces they endure as they are discharged from the digester and transported through valves, pumps and various washing and bleaching equipment.

    In the thesis, results are presented from trials where pulps with significantly different hemicellulose compositions were high-intensity mixed at pH 13, 70°C and 10% pulp consistency and pulp strength evaluated. By varying alkalinity and temperature, pulps with different carbohydrate composition could be obtained. High alkali concentration and low temperature resulted in high glucomannan content and low xylan content, whereas cooking at low alkali concentration and high temperature rendered a pulp with low glucomannan and high xylan content. The high alkalinity pulp was stronger, determined as tear index at given tensile index. The pulp viscosity was also higher for this pulp. However, when the pulps were subjected to high-intensity mixing, the high alkalinity pulp lost in tear strength and the re-wetted zero-span tensile strength was substantially reduced. The pulp cooked at high alkalinity was thus interpreted as being more vulnerable to mechanical treatment than the pulp obtained by cooking at low alkalinity.

    Another pair of pulps was manufactured at high and low sodium ion concentrations, but otherwise with similar chemical charges. The pulp obtained by cooking at low sodium ion concentration became stronger, evaluated as tear index at a given tensile index and the curl index was substantially lower, 8% compared to 12% for the pulp cooked at a high sodium ion concentration. The viscosity was 170 ml/g higher for the pulp manufactured at low sodium ion concentration. When the pulps were subjected to high-intensity mixing, the tear strength of the pulp manufactured at high sodium ion concentration was reduced. The re-wetted zero-span tensile index decreased also after mixing. The pulp obtained by cooking at higher sodium ion concentration was thus interpreted as being more vulnerable to mechanical treatment than the pulp manufactured at lower sodium ion concentration.

    In the thesis, two reasons for the low strength delivery of industrially produced pulps compared to laboratory-cooked pulps are put forward. Since the ionic strength of mill cooking liquor systems is much higher than is normally used in laboratory cooking, this can partly explain the difference in strength between mill- and laboratory-cooked pulp. A higher sodium ion concentration was shown in this thesis work to give a pulp of lower strength. Secondly, it is suggested that the difference in retention time of the black liquor in laboratory cooking and continuous mill cooking systems can explain the difference in tensile strength between laboratory-cooked and mill-produced pulp. The black liquor in a continuous digester has a longer retention time in the digester than the chips. This gives a longer time for the dissolved xylan to degrade and, as a consequence, the xylan deposited on the mill pulp fibres will be more degraded than the xylan deposited on the laboratory-cooked pulp fibres.

    In the thesis, results are also presented from studies using different strength-enhancing chemicals. The fibre surfaces of bleached never-dried and once-dried pulp were modified by the polyelectrolyte multilayer technique using cationic and anionic starch. Although the pulps absorbed the same amount of starch, the never-dried pulp reached a higher tensile index than the once-dried pulp. When the starch-treated never-dried pulp was dried and reslushed it still had higher tensile index than the never-dried untreated pulp. The starch layers were thus able to counteract part of the hornification effect. The never-dried starch treated pulps were subsequently dried, reslushed and beaten. Pulp with starch layers had a better beatability evaluated as the tensile index obtained after given number of PFI revolutions than dried untreated pulp. Hence, there is a potential to increase the tensile index of market pulp by utilising the polyelectrolyte multilayer technique before drying. Addition of CMC to bleached mill pulp and laboratory-cooked pulp increased the tensile strength to the same degree for both pulps. CMC addition had a straightening effect on the fibres, the shape factor increased and this increased the zero-span tensile strength also.

  • 3.
    Brännvall, Elisabet
    KTH, Superseded Departments, Pulp and Paper Technology.
    hydrogen sulphide gas pre-treatment prior to modified kraft cookingManuscript (preprint) (Other (popular science, discussion, etc.))
  • 4.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Overview of pulp and paper processes2009In: Pulping Chemistry and Technology, Walter de Gruyter, 2009, p. 1-11Chapter in book (Refereed)
  • 5.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Pulping technology2009In: Pulping Chemistry and Technology, Walter de Gruyter, 2009, p. 121-147Chapter in book (Refereed)
  • 6.
    Brännvall, Elisabet
    KTH, Superseded Departments, Pulp and Paper Technology.
    The effects of fines content and hydrogen sulphide gas pre-treatment on kraft pulping and the strength of polysulphide pulps2000Licentiate thesis, comprehensive summary (Other scientific)
  • 7.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The hemicellulose composition of pulp fibres and their ability to endure mechanical treatmentIn: TAPPI Journal, ISSN 0734-1415Article in journal (Refereed)
  • 8.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wood handling2009In: Pulping Chemistry and Technology, Walter de Gruyter, 2009, p. 13-34Chapter in book (Refereed)
  • 9.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Annergren, G.
    Pulp characterisation2009In: Pulping Chemistry and Technology, Walter de Gruyter, 2009, p. 429-459Chapter in book (Refereed)
  • 10.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Innventia AB.
    Backström, Marie
    Innventia AB.
    Improved impregnation efficiency and pulp yield of softwood kraft pulp by high effective alkali charge in the impregnation stage2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 11, p. 1031-1037Article in journal (Refereed)
    Abstract [en]

    A pulp yield increase up to 2% can be achieved by impregnation with a liquor containing 2 M effective alkali ( EA) concentration instead of 1 M. The yield increase is due to higher cellulose and glucomannan contents in the pulp, which can be rationalized by less yield loss by peeling, as impregnation is more effective at an elevated EA level. A rapid loading of chips with alkali can be realized due to a high diffusion rate. When the temperature becomes higher in the cooking stage, enough alkali is available for delignification reactions without the risk of alkali depletion in the chip core, so that the delignification is more homogeneous.

  • 11.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Eriksson, Malin
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Fibre surface modifications of market pulp by consecutive treatments with cationic and anionic starch2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 2, p. 244-248Article in journal (Refereed)
    Abstract [en]

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

  • 12.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Gustafsson, R.
    Teder, A.
    Properties of hyperalkaline polysulphide pulps2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 4, p. 436-440Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Hakanen, A
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Strykepotentialen hos massor från polysulfidkok: Del 1. Variationer i vätesulfid- och hydroxidjonhaltReport (Other academic)
  • 14.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Hakanen, A
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Strykepotentialen hos massor från polysulfidkok: Del 2. Massa- och fiberegenskaperReport (Other academic)
  • 15.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Characterisation of dissolved spruce xylan in kraft cooking2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 4, p. 380-385Article in journal (Refereed)
    Abstract [en]

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

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

  • 16.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A study on the difference in strength between industrially and laboratory-cooked pulp2006In: Nordic pulp and paper research journal, ISSN 0283-2631, Vol. 21, no 2, p. 222-226Article in journal (Refereed)
    Abstract [en]

    The tensile strength levels of industrially produced pulp and corresponding laboratory-cooked pulps were investigated. The industrial pulp had a lower tensile strength, which could not be explained by fibre form or fibre strength.

    It was concluded that bonding strength was the limiting factor for the tensile strength of the industrial pulp. The industrial pulp, despite of its higher hemicellulose content, had a lower surface charge. The xylan precipitated onto the fibres during the industrial cook was probably more degraded and consequently with lower degree of polymerisation and fewer charged groups.

  • 17.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    A study on the difference industrially and in tensile strength between laboratory-cooked pulp2006In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 2, p. 222-226Article in journal (Refereed)
    Abstract [en]

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

  • 18.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The hemicellulose composition of pulp fibers and their ability to endure mechanical treatment2007In: TAPPI Journal, ISSN 0734-1415, Vol. 6, no 10, p. 19-24Article in journal (Refereed)
    Abstract [en]

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

  • 19.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The impact of ionic strength during kraft cooking on the strength properties of softwood kraft pulp2007In: Appita journal, ISSN 1038-6807, Vol. 60, no 1, p. 60-64Article in journal (Refereed)
    Abstract [en]

    A study was undertaken in order to investigate the influence of ionic strength during pulping (measured as sodium ion concentration) on pulp strength (evaluated as tear index vs. tensile index) and on the pulps ability to resist mechanical damage. Sodium chloride was added to the cooking liquor in order to control the ionic strength during the laboratory kraft cooking of soft-wood. The strength properties were compared to a conventional laboratory pulp, pulped at an ionic strength equal to that originating solely from the cooking chemicals added.

    It was shown that the ionic strength of the cooking liquor had an impact on pulp strength. Tear index at a certain tensile index decreased at higher ionic strength. The fibre strength, measured as rewetted zero-span tensile index, also decreased. Furthermore, high ionic strength during cooking rendered the fibres more vulnerable to mechanical damage.

  • 20.
    Brännvall, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Tormund, Disa
    Bakkstrom, Marie
    Bergstrom, Jonas
    Tubek-Lindblom, Anna
    Separate bleaching of pulp fractions enriched in earlywood and latewood fibers2007In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 27, no 2, p. 99-112Article in journal (Refereed)
    Abstract [en]

    Unbleached softwood kraft pulp was fractionated in hydrocyclones into a fine fraction, enriched in earlywood fibers, and a coarse fraction, enriched in latewood fibers. The response to individual bleaching chemicals and the bleachability in bleaching sequences of the pulp fractions was studied. The light absorption coefficient, light scattering coeffient, and brightness were higher in the unbleached fine fraction than in the coarse fraction. Hydrogen peroxide managed to reduce the light absorption coefficient of the earlywood enriched fine fraction more efficiently than that of the latewood enriched fraction. In the TCF-sequence the light absorption coefficient of the fine fraction was reduced to the level of the coarse fraction at a given consumption of bleaching chemicals. In the ECF-sequence the difference in light absorption coefficient remained between the fractions. At a given consumption of bleaching chemicals, the fine fraction had higher brightness than the coarse fraction, 2%- and 1%-units on the ISO-scale in the TCF and ECF bleaching sequence, respectively.

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

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

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

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

  • 23.
    Danielsson, Sverker
    et al.
    KTH.
    Brännvall, Elisabet
    KTH, Superseded Departments (pre-2005), Fibre and Polymer Technology.
    Lindström, Mikael
    KTH, Superseded Departments (pre-2005), Fibre and Polymer Technology.
    Xylan as a surface modifying agent in the kraft cook2006In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 231Article in journal (Other academic)
  • 24.
    Duker, Elisabet
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, T
    CMC addition to industrial and laboratory-cooked pulpManuscript (preprint) (Other academic)
  • 25.
    Duker, Elisabeth
    et al.
    STFI-Packforsk AB.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Tom
    STFI-Packforsk AB.
    The effects of CMC attachment onto industrial and laboratory-cooked pulps2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 356-363Article in journal (Refereed)
    Abstract [en]

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

  • 26.
    Henriksson, Gunnar
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lennholm, Helena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The Trees2009In: Pulp and Paper Chemistry and Technology: Wood chemistry and wood biotechnology / [ed] Monica Ek, Göran Gellerstedt, Gunnar Henriksson, Berlin: Walter de Gruyter, 2009, p. 13-44Chapter in book (Other academic)
  • 27.
    Karlström, Katarina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Extended Impregnation Cooking of Norway Spruce: Effects on Pulping Uniformity and Pulp Strength Properties2009Manuscript (preprint) (Other academic)
    Abstract [en]

    Extended impregnation kraft cooking is a demonstrated improvement of the kraft pulping process and offers a way to use softwood more efficiently. We demonstrate the possibility of producing Norway spruce (Picea abies) kraft pulp using a new cooking concept, producing a pulp that can be defibrated without inline refining at kappa numbers of approximately 90. The cooking concept uses the differences in reaction rate between the diffusion and consumption of hydroxide ions in the prolonged impregnation step. Lowering the impregnation temperature will favour the diffusion of cooking chemicals over neutralization reactions, thereby improving chemical distribution throughout the chips. Impregnation conditions in combination with cooking temperatures lower than those of conventional kraft pulping are demonstrated to produce pulp with a narrower kappa number distribution and comparable strength properties at a considerably higher yield.

  • 28.
    Li Jansson, Zheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Effect of Kraft Cooking Conditions on the Chemical Composition of the Surface and Bulk of Spruce Fibers2014In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 34, no 4, p. 291-300Article in journal (Refereed)
    Abstract [en]

    By varying cooking temperature, alkali charge, ionic strength, and cooking time in Kraft pulping of spruce chips, pulps ranging between kappa numbers 20-80 were obtained. The unbleached Kraft pulp fibers were subjected to mechanical peeling in order to separate the surface material from the bulk of the fibers and the carbohydrate composition and lignin content of the two fractions were analyzed. As expected, the lignin and xylan contents were higher on the fiber surface than in the fiber wall. The percentage of xylan on the fiber surface was fairly constant, independent of different pulping conditions or degree of delignification. The lignin proportion on the fiber surface gradually decreased with decreasing kappa number. At a given kappa number, pulping at a higher temperature resulted in less lignin on the fiber surface, probably because of the higher solubility of lignin at higher temperature. Cooking at lower alkali charge also resulted in lower lignin content on the fiber surface at a given kappa number. In this case, there was more time available for degradation of the surface lignin since the lower alkali charge resulted in longer cooking time needed to reach a certain kappa number.

  • 29.
    Li Jansson, Zheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Effect of kraft cooking conditions on the chemical composition ofthe surface and bulk of spruce fibers2011Manuscript (preprint) (Other academic)
  • 30.
    Svärd, Antonia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Corrigendum to “Rapeseed straw as a renewable source of hemicelluloses: Extraction, characterization and film formation” [Carbohydrate Polymers 133 (2015) 179–186](S0144861715006529)(10.1016/j.carbpol.2015.07.023)2017In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 174, p. 1240-Article in journal (Other academic)
    Abstract [en]

    The authors regret that the original version of this article unfortunately contained a mistake in Table 5. The correct Table 5 and associated text is given below. “The rapeseed hemicellulose films presented here had strain-at-break values of 70% (C) and 90% (H), even with no added plasticizers (Table 5).” The authors would like to apologise for any inconvenience caused.

  • 31.
    Svärd, Antonia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Rapeseed straw as a renewable source of hemicelluloses: Extraction, characterization and film formation2015In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 133, p. 179-186Article in journal (Refereed)
    Abstract [en]

    Polymeric hemicelluloses were extracted by autohydrolysis and alkali from a biomass feed consisting of the stems of rapeseed straw according to a full statistical factorial screening design. Water extraction yielded fractions rich in galactoglucomannan, while alkaline extraction yielded primarily xylan. The extracted galactoglucomannan and xylans had similar molecular weights, while the yield of xylan was higher than the yield of galactoglucomannan. The extracted hemicellulose fractions also contained some lignin (7-15%) and traces of Ca, K, Na, and Si. Free-standing films were prepared from the hemicellulose fractions with different xylan:galactoglucomannan ratios. The rapeseed xylan films showed strain-to-break values >60% without any added plasticizers.

  • 32.
    Svärd, Antonia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Royal Inst Technol, Sch Chem Sci & Technol, Fiber & Polymertechnol, Stockholm, Sweden..
    Brännvall, Elisabet
    KTH. Royal Inst Technol, Stockholm, Sweden..
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Royal Inst Technol KTH, Fibre & Polymer Technol, Stockholm, Sweden..
    Rapeseed straw extraction yields hemicelluloses for renewable materials2016In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 251Article in journal (Other academic)
  • 33.
    Svärd, Antonia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Rapeseed straw polymeric hemicelluloses obtained by extraction methods based on severity factor2017In: INDUSTRIAL CROPS AND PRODUCTS, ISSN 0926-6690, Vol. 95, p. 305-315Article in journal (Refereed)
    Abstract [en]

    Rapeseed straw consists of a hard epidermis that is rich in hemicellulose and lignin and a sponge-like interior that consists mainly of cellulose. The stems were subjected to water, alkali or acid as extraction medium. The effects of the extraction conditions were quantified using severity factors and by comparing the effects of different extraction pHs, temperatures and times. Extraction with alkali resulted in a higher yield, 47 g/100 g straw in, compared to water, 6 g/100 g straw in, or an acidic, 5 g/100 g straw in, extraction process. An increase in temperature improved the extraction yield; in particular, more xylan was extracted at an elevated temperature and higher alkalinity. However, at high alkalinity, increased extraction temperatures led to a reduction in the recovery of glucomannan. The highest molecular weights (similar to 35,000 g/mol) of the extracted hemicelluloses were obtained using extraction procedures with 1.5 M NaOH at 110 degrees C and autohydrolysis at 150 degrees C. While these two parameter settings had very similar severity factors, extraction under basic conditions afforded an extract rich in xylan and low in lignin content, whereas autohydrolysis generated a glucomannan-rich extract.

  • 34.
    Svärd, Antonia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edlund, Ulrica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    The impact of extraction severity on polymeric hemicelluloses isolated from rapeseed strawManuscript (preprint) (Other academic)
  • 35.
    Svärd, Antonia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Sevastyanova, Olena
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Dobele, Galina
    Jurkjane, Vilhemina
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    COST Action FP1105: effect of raw materials and pulping conditions on the characteristics of dissolved kraft lignins2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 12, p. 1105-1114Article in journal (Refereed)
    Abstract [en]

    The composition, molecular weight (MW), and chemical structure of technical lignins as byproducts of pulping influence their application in terms of physical and chemical properties, reactivity, and performance. It is important to know how the analytical data of technical lignins are influenced by the wood species and the parameters of pulping. The present study focuses on kraft pulping and how the wood species (eucalyptus, pine, and spruce) and variable cooking times influence the characteristics of dissolved lignins. The black liquor (BL) was recovered after three different cooking times and the precipitated lignin was characterized by total acid hydrolysis including the determination of the acid insoluble part (Klason lignin, KL) and the sugars in the hydrolysate, elemental analysis, 31P NMR spectroscopy, analytical pyrolysis (Py-GC/MS), gel permeation chromatography (GPC), thermogravimetry (TG), and differential scanning calorimetry (DSC). The results indicate that the phenolic OH content, MW and glass transition temperature increased with longer cooking times for the softwood (SW) lignins. These lignins had also a higher MW (M-w 5500-8000 g mol(-1)), than the eucalyptus lignin (M-w 2200-2400 g mol(-1)). Eucalyptus lignin had higher sulfur content compared to SW.

  • 36.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Impact of Differing Time and Temperature during Impregnation on Kraft Cooking of Softwood ChipsManuscript (preprint) (Other academic)
  • 37.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Increased pulp yield by prolonged impregnation in softwood kraft pulping2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 1, p. 14-20Article in journal (Refereed)
    Abstract [en]

    The effect on kraft cooking proceeded by an impregnation stage performed at 130 degrees C for 30 min was compared to kraft cooking following prolonged impregnation at 105 degrees C for 60-120 min. The alkali consumed during impregnation varied depending on the temperature and time of the impregnation stage. In order to study the impact of the impregnation stage on the subsequent kraft cook, the initial concentration of effective alkali was adjusted to be initially the same in all cooks before cooking for 180-290 min. The alkali consumed in the impregnation stage affected the alkali profile of the cooking stage. The more alkali consumed in impregnation, the lower the demand in cooking. Higher alkali consumption in the impregnation stage also led to faster delignification in the cooking stage. Prolonged impregnation resulted in 1-1.5 percentage points higher yield compared to the reference case. The yield increment was due to a higher cellulose retention. Although the impregnation time was prolonged from 30 min up to 2 h, the higher delignification rate and higher yield only decreased the production rate with 11% compared to the reference.

  • 38.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Brännvall, Elisabeth
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Henriksson, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Selectiveness and efficiency of combined peracetic acid and chlorine dioxide bleaching stage for kraft pulp in removing hexeuronic acid2011In: Cellulose Chemistry and Technology, ISSN 0576-9787, Vol. 45, no 1-2, p. 89-95Article in journal (Refereed)
    Abstract [en]

    Combined peracetic acid and chlorine dioxide bleaching stages of unbleached and oxygen delignified hardwood and softwood kraft pulps were compared with conventional chlorine dioxide and peracetic acid stages as to kappa number and viscosity reduction, selectivity and reduction of hexenuronic acid content. The combined stages were more efficient in kappa number reduction than those with only chlorine dioxide. Part of the increased kappa number reduction was due to an improved degradation of hexenuronic acid. The stages where chlorine dioxide was added before the peracetic acid (DT) showed a higher selectivity than those in which the chemicals were added simultaneously (D+T); in turn, the latter were more efficient than the "pure" chlorine dioxide (D, D-0) and peracetic acid stages (T). However, peracetic acid and chlorine dioxide seemed to react with each other, leading to the degradation of both bleaching chemicals. The mechanisms and practical implementation of these bleaching sequences are discussed.

  • 39.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Designing spruce xylan for higher tensile strength2011Manuscript (preprint) (Other academic)
  • 40.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Influence of spruce xylan characteristics on tensile strength of spruce kraft pulp2015In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 69, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The aim of the study was to investigate the possibility to use spruce xylan more efficiently by possible relocation of dissolved xylan with certain characteristics from the first part of the kraft cooking to the later part, when precipitation occur. The characteristics of re-located xylan was controlled by replacing half the black liquor (BL) at a late stage of a kraft cook, with the same amount of black liquor containing spruce xylan with known molecular weight and content of uronic acid (UA). Pulp with addition of xylan with high amount of UA groups responded strongly on beating, resulting in improved tensile strength. It is proposed that the best effect of xylan on tensile strength occurs when the xylan penetrates some distance into the subsurface of the fiber wall. Both low molecular weight (M-w) and a high degree of substitution decreases the tendency of xylan to aggregate, which enables the dissolved xylan to penetrate some distance into the exposed fiber surface. Upon beating, this xylan will be exposed thus facilitating improved fiber-fiber joint formation, which leads to increased tensile strength.

  • 41.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Mansoor, Zaheer Ahmad
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Xylan from Agro Waste As a Strength Enhancing Chemical in Kraft Pulping of Softwood2014In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, no 23, p. 9738-9742Article in journal (Refereed)
    Abstract [en]

    The possibility to use xylan from agro waste in order to improve the strength properties of spruce kraft pulp was examined. Xylan was extracted from wheat straw and rice husks, by subjecting the agro waste to kraft cooking. The extracted xylan was subsequently used at the end of a kraft cooking process of spruce, by replacing half of the black liquor with dissolved spruce xylan with white liquor containing agro waste xylan. The strength tests performed on the obtained softwood kraft pulps showed that even a small amount of rice husk or wheat straw xylan deposited on softwood fibers had a positive effect on the tensile index of the paper at given sheet density.

  • 42. Tormund, Disa
    et al.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Backstrom, Marie
    Olm, Leelo
    Delignification and bleaching response of earlywood and latewood2006In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 26, no 4, p. 325-337Article in journal (Refereed)
    Abstract [en]

    The delignification response in cooking and the impact of bleaching on earlywood and latewood were studied. Spruce earlywood and latewood chips were pulped by the kraft process and subsequently treated with one bleaching chemical at a time. In cooking, latewood required a higher alkali charge to reach the same kappa number. No difference in the light absorption coefficient between the different fiber types was observed. After oxygen delignification the earlywood fibers had a higher light absorption coefficient at the same kappa number. The difference in light absorbing material was maintained when bleaching was performed with chlorine dioxide, ozone, and peracetic acid. Hydrogen peroxide decreased the light absorbing structures in the earlywood to the same level as for latewood. The earlywood pulp had a higher brightness at a given kappa number than the latewood. The higher brightness remained through all bleaching operations and was primarily due to a higher light scattering ability.

1 - 42 of 42
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