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  • 1.
    Adamopoulos, Stergios
    et al.
    Technological Educational Institute of Thessaly, Greece.
    Hosseinpourpia, Reza
    Georg-August-University Göttingen, Germany.
    Mai, Carsten
    Georg-August-University Göttingen, Germany.
    Tensile strength of handsheets prepared with macerated fibres from solid wood modified with cross-linking agents2015In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 69, no 8, p. 959-966Article in journal (Refereed)
    Abstract [en]

    This study was conducted to explain the tensile strength loss of wood due to the modification with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and glutaraldehyde (GA). Modified and control wood blocks were macerated to deliberate fibres, and handsheets were produced thereof. The nitrogen content of the fibres indicated that maceration removed the major proportions of DMDHEU. The stability of GA in wood during maceration was not assessed. Tensile strength determined at zero span (z-strength) and finite span (f-strength) was equal for the handsheets from DMDHEU-modified fibres and the control handsheets. The microscopic appearance of the tested finite-span paper strips from DMDHEU-modified fibres mainly indicated interfibre failure and did not differ from the fibre fracture mode of the control handsheets. In contrast, the z-strength of the handsheets from GA-modified fibres was lower than that of controls and decreased with increasing content of GA in the initial modified wood. The f-strength behaviour of the handsheets from GA-modified fibres was the opposite: it was higher than that of controls and increased with increasing GA content. The microscopic appearance of the rapture zones of the finite-span testing mainly indicated intrafibre failure for the GA-modified fibres. It was concluded that cross-linking is likely to be the major reason for tensile strength loss of GA- and DMDHEU-modified wood. In terms of DMDHEU-modified wood, the incrustation of the cell wall by the resin and the reduction in pliability could play an additional role.

  • 2.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Karlsson, Olov
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Uneven distribution of preservative in kiln-dried sapwood lumber of Scots pine: Impact of wood structure and resin allocation2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 251-258Article in journal (Refereed)
    Abstract [en]

    Scots pine (Pinus sylvestris L.) sapwood lumber was collected after kiln drying and preservative treatment with Celcure AC 800 (a copper-amine wood preservative). Distribution of the preservative throughout the lumber was visually examined. Not all, but some samples showed specific localized areas without any preservative distribution throughout their entire length. Those samples were assessed further for anatomical properties, specifically in impregnated and unimpregnated areas. Additional study was conducted on the morphological nature and redistribution of lipophilic extractives using three different histochemical staining methods. Intrinsic wood properties – especially the frequency of axial resin canals and the percentage of canals blocked – were found to be responsible for the irregular distribution of the preservative. Furthermore, the inability to create continuous and frequent interstitial spaces due to the collapse of thin-walled ray cells throughout the lumber resulted in un-even distribution of preservatives. Staining techniques were useful to localize places with more or less abundance of extractives (e.g., fats) in impregnated and unimpregnated wood, which varied considerably. Histochemical observations revealed information pertaining to the kiln dry specific distribution and redistribution of extractives between the areas. Moreover, resin reallocation and modification in ray parenchyma and resin canals induced by kiln drying would be another reason for the impregnation anomalies.

  • 3.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Uneven distribution of preservative in kiln-dried sapwood lumber of Scots pine: Impact of wood structure and resin allocation2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 251-258Article in journal (Refereed)
    Abstract [en]

    Scots pine (Pinus sylvestris L.) sapwood lumber was collected after kiln drying and preservative treatment with Celcure AC 800 (a copper-amine wood preservative). Distribution of the preservative throughout the lumber was visually examined. Not all, but some samples showed specific localized areas without any preservative distribution throughout their entire length. Those samples were assessed further for anatomical properties, specifically in impregnated and unimpregnated areas. Additional study was conducted on the morphological nature and redistribution of lipophilic extractives using three different histochemical staining methods. Intrinsic wood properties – especially the frequency of axial resin canals and the percentage of canals blocked – were found to be responsible for the irregular distribution of the preservative. Furthermore, the inability to create continuous and frequent interstitial spaces due to the collapse of thin-walled ray cells throughout the lumber resulted in uneven distribution of preservatives. Staining techniques were useful to localize places with more or less abundance of extractives (e.g., fats) in impregnated and unimpregnated wood, which varied considerably. Histochemical observations revealed information pertaining to the kiln dry specific distribution and redistribution of extractives between the areas. Moreover, resin reallocation and modification in ray parenchyma and resin canals induced by kiln drying would be another reason for the impregnation anomalies.

  • 4.
    Ahrenstedt, Lage
    et al.
    KTH, School of Biotechnology (BIO). KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Olksanen, Antti
    VTT Technical Research Centre of Finland.
    Salmien, Kristian
    VTT Technical Research Centre of Finland.
    Brumer, Harry
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Paper dry strength improvement by xyloglucan addition: Wet-end application, spray coating and synergism with borate2008In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 62, no 1, p. 8-14Article in journal (Refereed)
    Abstract [en]

    The polysaccharide xyloglucan as a wet-end additive improves paper properties. In the present study, paper strength improvement was analysed for dry handsheets made from chemical, mechanical and recycled pulps coated with xyloglucan in a spray application. Results are compared with sheets made from the same pulps treated with xyloglucan in the wet-end. Kraft pulp handsheets of bleached hardwood and softwood showed significant improvements of tensile, tear and Z-strength by xyloglucan spray treatment versus wet-end application, whereas handsheets of de-inked and thermomechanical pulp were improved only slightly. In both wet-end and spray applications, the effect of xyloglucan addition was intimately related to the presence of non-cellulosic components on the fibre surface. Further strength improvements were obtained for chemical pulps by addition of borax to the spray solution, which were likely to be due to the formation of borate-mediated xyloglucan cross-links. Spray coating of xyloglucan, with or without borax, thus represents a potential new application of this polysaccharide to increase paper dry strength.

  • 5.
    Aldaeus, Fredrik
    et al.
    RISE, Innventia.
    Schweinebarth, Hannah
    RISE, Innventia.
    Törngren, Per
    RISE, Innventia.
    Jacobs, Anna
    RISE, Innventia.
    Simplified determination of total lignin content in kraft lignin samples and black liquors2011In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, no 4, p. 601-604Article in journal (Refereed)
  • 6.
    Alfredsen, Gry
    et al.
    Norwegian Institute of Bioeconomy Research, Norway.
    Pilgard, Annica
    RISE, SP – Sveriges Tekniska Forskningsinstitut. Technical University Munich, Germany.
    Fossdal, Carl Gunnar
    Norwegian Institute of Bioeconomy Research, Norway.
    Characterisation of Postia placenta colonisation during 36 weeks in acetylated southern yellow pine sapwood at three acetylation levels including genomic DNA and gene expression quantification of the fungus2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 11, p. 1055-1065Article in journal (Refereed)
    Abstract [en]

    One way to protect timber in service against basidiomycete deterioration is by means of acetylation via reaction with acetic anhydride. The reason why acetylated wood (WAc) is resistant against decay fungi is still not exactly understood. The aim of this study was to contribute to this field of science, and Postia placenta colonisation after 4, 12, 20, 28 and 36 weeks was observed at three acetylation levels of Pinus spp. sapwood. Mass loss (ML) and wood moisture content (MC) data reflected the acetylation levels. The initial equilibrium MC (EMC) proved to be a good indicator of subsequent ML. Genomic DNA quantification showed P. placenta colonisation in all samples, also in samples where no ML were detectable. The number of expressed gene transcripts was limited, but the findings supported the results of previous studies: WAc seems to have some resistance against oxidative mechanisms, which are part of the metabolism of P. placenta. This leads to a delay in decay initiation, a delay in expression of genes involved in enzymatic depolymerisation, and a slower decay rate. The magnitudes of these effects are presented for each acetylation level. The data also imply that there is no absolute decay threshold at high acetylation levels, but instead a significant delay of decay initiation and a slower decay rate.

  • 7.
    Almkvist, Gunnar
    et al.
    Swedish Univ Agr Sci SLU, Dept Chem & Biotechnol, Box 7015, SE-75007 Uppsala, Sweden..
    Norbakhsh, Shahin
    Swedish Univ Agr Sci SLU, Dept Chem & Biotechnol, Box 7015, SE-75007 Uppsala, Sweden..
    Bjurhager, Ingela
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Varmuza, Kurt
    Vienna Univ Technol, Inst Stat & Math Methods Econ, Wiedner Hauptstr 8-10-E105, A-1040 Vienna, Austria..
    Prediction of tensile strength in iron-contaminated archaeological wood by FT-IR spectroscopy - a study of degradation in recent oak and Vasa oak2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 9, p. 855-865Article in journal (Refereed)
    Abstract [en]

    Oak from the Swedish warship Vasa and recent oak that was aged after impregnation with iron(II) chloride has been analyzed by FT-IR spectroscopy and submitted to tensile strength testing. The aim was to investigate correlations between FT-IR bands in the fingerprint region, chemical degradation, and tensile strength in iron contaminated oak. The concentration of carboxylic functions increased and the acetyl groups in the hemicellulose fraction were decreasing as a function of degradation time. These changes are accompanied by reduced tensile strength and elevated content of oxalic acid (OA) in both Vasa wood and the impregnated recent oak samples. To evaluate the possibility to predict tensile strength from spectral data, chemometric modeling by partial least-squares (PLS) regression was applied. The strategy of repeated double cross validation (rdCV) allowed a realistic prediction of tensile strength. Overall, chemical changes and mechanical performances of iron contaminated wood are strongly correlated and thus FT-IR spectroscopy is suited to predict the strength properties of the degraded wood.

  • 8.
    Almlöf Ambjörnsson, Heléne
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Östberg, Linda
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Schenzel, Karla
    Martin Luther University Halle-Wittenberg, Department of Natural Scinence III, Institute of Agriculture and Nutritional Science.
    Larsson, Per Tomas
    Innventia AB, Fibre and Material Science Business area Biorefining, Stockholm.
    Germgård, Ulf
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Enzyme pretreatment of dissolving pulp as a way to improve the following dissolution in NaOH/ZnO2014In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, no 4, p. 385-391Article in journal (Refereed)
  • 9.
    Almlöf, Heléne
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Kreutz, Bjørn
    Borregaard Chemcell, Norway.
    Jardeby, Kristina
    Borregaard Chemcell, Norway.
    Germgård, Ulf
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    The influence of extended mercerization on some properties of carboxymethyl cellulose (CMC)2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, p. 21-27Article in journal (Refereed)
    Abstract [en]

    Carboxymethyl cellulose (CMC) is produced commercially in a two stage process consisting of a mercerization stage in which the pulp is treated with alkali in a water alcohol solution and a second etherification stage whereby monochloro-acetic acid is added to the pulp slurry. In this study, the influence of the conditions of an extended mercerization stage was evaluated on the etherification stage concerning the degree of substitution (DS) and the filterability of the resulting CMC. The parameters studied were: (1) the ratio of cellulose I and cellulose II in the original pulp, (2) the concentration of alkali, (3) the temperature and (4) the retention time in the mercerization stage. The DS results indicate that the NaOH concentration in the mercerization stage is the most important among the parameters studied. When the NaOH concentration in the mercerization stage was high (27.5%), cellulose II showed a lower reactivity than cellulose I with respect to the DS obtained in the resulting CMC. The results from the filtration ability of CMC water solutions are interpreted that the amount of cellulose II in the original pulp and the temperature has a negative influence, while the NaOH concentration in the mercerization stage has a positive influence on the filtration ability. Retention time between 1 h–48 h in the mercerization stage had no effect on the DS or the filtration value. The filtration ability was assumed to be highly influenced by the presence of poorly reacted cellulose segments. The CMC samples with the lowest filtration ability at a given DS can be assumed to have the highest degree of unevenly substituted segments.

  • 10.
    Ambjörnsson, Helene Almlöf
    et al.
    Karlstad University, Sweden.
    Östberg, Linda
    Karlstad University, Sweden.
    Schenzel, Karla C.
    Martin Luther University Halle-Wittenberg, Germany.
    Larsson, Per Tomas
    RISE, Innventia.
    Germgård, Ulf
    Karlstad University, Sweden.
    Enzyme pretreatment of dissolving pulp as a way to improve the following dissolution in NaOH/ZnO2014In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 68, no 4, p. 385-391Article in journal (Refereed)
    Abstract [en]

    The dissolution of a softwood dissolving pulp in a NaOH/ZnO system was improved by means of a three-stage pretreatment with an initial xylanase treatment, followed by an alkaline extraction, and finally an endoglucanase stage. The solubility of the pulp increased from 29% to 81%, although the crystallinity and the specific surface area of the pulp did not change during the enzymatic treatment.

  • 11.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Calcium phosphate bonded wood and fiber composite panels: production and optimization of panel properties2017In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 71, no 9, p. 725-732Article in journal (Refereed)
    Abstract [en]

    The development of phosphate bonded composites with properties comparable with those of current Portland cement bonded products has been investigated. More precisely, the focus of the study was the optimization of calcium phosphate cements in combination with wood processing residues slash pine (Pinus elliottii Engelm.) planer shavings, Black wattle (Acacia mearnsii De Wild.) residues, Blue gum (Eucalyptus globulus Labill.) residues, hemp (Cannabis Sativa L.) hurds and dried crushed sugarcane bagasse (Saccharum officinarum L.) as well as pulp mill sludge and waste paper. A central composite design (CCD) for the response surface methodology (RSM) was applied for selection of the proper parameters. Mechanical tests were conducted on the composite products and the effect of the processing variables was evaluated based on the Pareto analysis of variance. The density of the wood-based panels ranged from 0.68 to 1.21 g cm−3, that of the agricultural fibers from 0.59 to 1.15 g cm−3 and that of the paper pulp panels from 0.81 to 1.21 g cm−3. The modulus of elasticity (MOE) data of the panels ranged from 1.63 to 4.92 MPa for wood, from 0.37 to 3.28 MPa for agricultural fibers and from 0.65 to 3.87 MPa for paper-pulp-based fibers. The physical properties of the composite products met the requirements for Portland-cement-bonded particleboards (EN 634-2, 2007).

  • 12. Anugwom, Ikenna
    et al.
    Maki-Arvela, Paivi
    Virtanen, Pasi
    Willfor, Stefan
    Damlin, Pia
    Hedenström, Mattias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Treating birch wood with a switchable 1,8-diazabicyclo-[5.4.0]-undec-7-ene-glycerol carbonate ionic liquid2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 7, p. 809-815Article in journal (Refereed)
    Abstract [en]

    The suitability of a new switchable ionic liquid (SIL) has been investigated as a solvent for fractionation of lignocellulosic materials. SIL was prepared from inexpensive chemicals, e. g., glycerol, CO2, and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU). Fresh Nordic birch wood (B. pendula) was treated with the SIL for a time period of 1-5 days at 100 degrees C and under atmospheric pressure. Upon SIL treatment, at best, 57 % of the hemicelluloses were dissolved and 50 % of lignins were dissolved from the native birch. The slightly fibrillated SIL treated chips contained about 55 % cellulose. Up to 76 % of the recovered species removed from the spent SIL liquor was originating from hemicelluloses, mainly from xylan. The spent SILs were reused for fresh wood dissolution in four consecutive cycles and each time the wood dissolution efficiency was similar. SILs could offer affordable (easy-to-synthesize) solvent systems for partial elimination of hemicelluloses and lignin from wood. SILs can also be prepared in-situ and on-site.

  • 13.
    Areskogh, Dimitri
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Nousiainen, Paula
    University of Helsinki, Department of Chemistry.
    Gellerstedt, Göran
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Sipilä, Jussi
    Henriksson, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Oxidative polymerisation of models for phenolic lignin end-groups by laccase2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 1, p. 21-34Article in journal (Refereed)
    Abstract [en]

    The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5' and 4-O-5' bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the a-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.

  • 14. 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.

  • 15.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Changes in microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part II: Anisotropic stiffness properties2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 199-206Article in journal (Refereed)
    Abstract [en]

    Fungal decay considerably affects the macroscopic mechanical properties of wood as a result of modifications and degradations in its microscopic structure. While effects on mechanical properties related to the stem direction are fairly well understood, effects on radial and tangential directions (transverse properties) are less well investigated. In the present study, changes of longitudinal elastic moduli and stiffness data in all anatomical directions of Scots pine (Pinus sylvestris) sapwood which was degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks have been investigated. Transverse properties were found to be much more deteriorated than the longitudinal ones. This is because of the degradation of the polymer matrix between the cellulose microfibrils, which has a strong effect on transverse stiffness. Longitudinal stiffness, on the other hand, is mainly governed by cellulose microfibrils, which are more stable agains fungal decay. G. trabeum (more active in earlywood) strongly weakens radial stiffness, whereas T. versicolor (more active in latewood) strongly reduces tangential stiffness. The data in terms of radial and tangential stiffnesses, as well as the corresponding anisotropy ratios, seem to be suitable as durability indicators of wood and even allow conclusions to be made on the degradation mechanisms of fungi.

  • 16.
    Bader, Thomas K.
    et al.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Alfredsen, Gry
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Microstructure and stiffness of Scots pine (Pinus sylvestris L) sapwood degraded by Gloeophyllum trabeum and Trametes versicolor Part I: Changes in chemical composition, density and equilibrium moisture content2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 191-198Article in journal (Refereed)
    Abstract [en]

    Fungal degradation alters the microstructure of wood and its physical and chemical properties are also changed. While these changes are well investigated as a function of mass loss, mass density loss and changes in equilibrium moisture content are not well elucidated. The physical and chemical alterations are crucial when linking microstructural characteristics with macroscopic mechanical properties. In the present article, a consistent set of physical, chemical and mechanical characteristics is presented, which were measured on the same sample before and after fungal degradation. In the first part of this two-part contribution, elucidating microstructure/stiffness-relationships of degraded wood, changes in physical and chemical data are presented, which were collected from specimens of Scots pine (Pinus sylvestris) sapwood degraded by Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot) for up to 28 weeks degradation time. A comparison of mass loss with corresponding mass density loss demonstrated that mass loss entails two effects: firstly, a decrease in sample size (more pronounced for G. trabeum), and secondly, a decrease of mass density within the sample (more pronounced for T. versicolor). These two concurrent effects are interrelated with sample size and shape. Hemicelluloses and cellulose are degraded by G. trabeum, while T. versicolor was additionally able to degrade lignin. In particular because of the breakdown of hemicelluloses and paracrystalline parts of cellulose, the equilibrium moisture content of degraded samples is lower than that in the initial state.

  • 17. Baumberger, Stephanie
    et al.
    Abaecherli, Alfred
    Fasching, Mario
    Gellerstedt, Göran
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Gosselink, Richard
    Hortling, Bo
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Saake, Bodo
    de Jong, Ed
    Molar mass determination of lignins by size-exclusion chromatography: towards standardisation of the method2007In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 61, no 4, p. 459-468Article in journal (Refereed)
    Abstract [en]

    The reactivity and physicochemical properties of lignins are partly governed by their molar mass distribution. The development of reliable standard methods for determination of the molar mass distribution is not only relevant for designing technical lignins for specific applications, but also for monitoring and elucidating delignification and pulping processes. Size-exclusion chromatography (SEC) offers many advantages, such as wide availability, short analysis time, low sample demand, and determination of molar mass distribution over a wide range. A collaborative study has been undertaken within the Eurolignin European thematic network to standardise SEC analysis of technical lignins. The high-molar-mass fraction of polydisperse lignins was shown to be the main source of intra- and interlaboratory variations, depending on the gel type, elution solvent, detection mode, and calculation strategy. The reliability of two widespread systems have been tested: one based on alkali and a hydrophilic gel (e.g., TSK Toyopearl gel) and the other based on THF as solvent and polystyrene-based gels (e.g., Styragel). A set of practical recommendations has been deduced.

  • 18.
    Bengtsson, Andreas
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Bengtsson, Jenny
    Swerea IVF, Box 104, SE-43122 Molndal, Sweden..
    Olsson, Carina
    Swerea IVF, Box 104, SE-43122 Molndal, Sweden..
    Sedin, Maria
    RISE Innventia, Box 5604, SE-11486 Stockholm, Sweden..
    Jedvert, Kerstin
    Swerea IVF, Box 104, SE-43122 Molndal, Sweden..
    Theliander, Hans
    Chalmers Univ Technol, SE-41296 Gothenburg, Sweden..
    Sjoholm, Elisabeth
    RISE Innventia, Box 5604, SE-11486 Stockholm, Sweden..
    Improved yield of carbon fibres from cellulose and kraft lignin2018In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 12, p. 1007-1016Article in journal (Refereed)
    Abstract [en]

    To meet the demand for carbon-fibre-reinforced composites in lightweight applications, cost-efficient processing and new raw materials are sought for. Cellulose and kraft lignin are each interesting renewables for this purpose due to their high availability. The molecular order of cellulose is an excellent property, as is the high carbon content of lignin. By co-processing cellulose and lignin, the advantages of these macromolecules are synergistic for producing carbon fibre (CF) of commercial grade in high yields. CFs were prepared from precursor fibres (PFs) made from 70: 30 blends of softwood kraft lignin (SW-KL) and cellulose by dry-jet wet spinning with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) as a solvent. In focus was the impact of the molecular mass of lignin and the type of cellulose source on the CF yield and properties, while membrane-filtrated kraft lignin and cellulose from dissolving kraft pulp and fully bleached paper-grade SW-KP (kraft pulp) served as sources. Under the investigated conditions, the yield increased from around 22% for CF from neat cellulose to about 40% in the presence of lignin, irrespective of the type of SW-KL. The yield increment was also higher relative to the theoretical one for CF made from blends (69%) compared to those made from neat celluloses (48-51%). No difference in the mechanical properties of the produced CF was observed.

  • 19.
    Bengtsson, Andreas
    et al.
    KTH Royal Institute of Technology, Sweden.
    Bengtsson, Jenny
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, IVF.
    Olsson, Carina
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, IVF.
    Sedin, Maria
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Papermaking and Packaging.
    Jedvert, Kerstin
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Sjöholm, Elisabeth
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Biobased Materials.
    Improved yield of carbon fibres from cellulose and kraft lignin2018In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 12, p. 1007-1016Article in journal (Refereed)
    Abstract [en]

    To meet the demand for carbon-fibre-reinforced composites in lightweight applications, cost-efficient processing and new raw materials are sought for. Cellulose and kraft lignin are each interesting renewables for this purpose due to their high availability. The molecular order of cellulose is an excellent property, as is the high carbon content of lignin. By co-processing cellulose and lignin, the advantages of these macromolecules are synergistic for producing carbon fibre (CF) of commercial grade in high yields. CFs were prepared from precursor fibres (PFs) made from 70:30 blends of softwood kraft lignin (SW-KL) and cellulose by dry-jet wet spinning with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) as a solvent. In focus was the impact of the molecular mass of lignin and the type of cellulose source on the CF yield and properties, while membrane-filtrated kraft lignin and cellulose from dissolving kraft pulp and fully bleached paper-grade SW-KP (kraft pulp) served as sources. Under the investigated conditions, the yield increased from around 22% for CF from neat cellulose to about 40% in the presence of lignin, irrespective of the type of SW-KL. The yield increment was also higher relative to the theoretical one for CF made from blends (69%) compared to those made from neat celluloses (48-51%). No difference in the mechanical properties of the produced CF was observed.

  • 20.
    Bengtsson, Charlotte
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, AB Trätek.
    Kliger, Robert
    Bending creep of high-temperature dried spruce timber2003In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 57, no 1, p. 95-100Article in journal (Refereed)
    Abstract [en]

    In this paper, bending creep test results from high-temperature (HT) dried Norway Spruce timber are presented. The results are compared with creep tests of conventional low-temperature (LT) dried timber. The HT drying was performed at 115°C and the LT drying was performed at 70°C. The creep tests were performed in a varying climate with 20°C and 30–90% relative humidity. A total number of 24 specimens, 45 × 70 × 1100 mm, were loaded in bending during approximately 240 days. Both the HT-dried and the LT-dried material were cut from the same four trees to have as equal raw material as possible for the two drying methods. The results show smaller bending creep deformations of HT-dried timber (approximately 30%) as compared to the LT-dried timber. The variation in magnitude of creep for HT-dried timber was equal to or smaller than for LT-dried timber. Additionally, the variation in deformation between the moisture cycles was smaller for HT-dried timber. These observations indicate a less pronounced mechano-sorptive effect for HT-dried timber. The free shrinkage in the grain direction was significantly smaller for the HT-dried material than for the LT-dried material.

  • 21.
    Bengtsson, Jenny
    et al.
    RISE Research Institutes of Sweden, Materials and Production, Polymeric Materials and Composites.
    Bengtsson, Andreas
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Ulmefors, Hanna
    RISE Research Institutes of Sweden, Materials and Production, Polymeric Materials and Composites.
    Sedin, Maria
    RISE Research Institutes of Sweden, Bioeconomy and Health, Material and Surface Design.
    Jedvert, Kerstin
    RISE Research Institutes of Sweden, Materials and Production, Polymeric Materials and Composites.
    Preventing fiber-fiber adhesion of lignin-cellulose precursors and carbon fibers with spin finish application2023In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434XArticle in journal (Refereed)
    Abstract [en]

    Adhesion of fibers within a spun tow, including carbon fibers and precursors, is undesirable as it may interrupt the manufacturing process and entail inferior fiber properties. In this work, softwood kraft lignin was used together with a dissolving pulp to spin carbon fiber precursors. Lignin-cellulose precursors have previously been found to be prone to fiber fusion, both post-spinning and during carbon fiber conversion. In this study, the efficiency of applying different kinds of spin finishes, with respect to rendering separable precursors and carbon fibers, has been investigated. It was found that applying a cationic surfactant, and to a similar extent a nonionic surfactant, resulted in well separated lignin-cellulose precursor tows. Furthermore, the fiber separability after carbon fiber conversion was evaluated, and notably, precursors treated with a silicone-based spin finish generated the most well-separated carbon fibers. The underlying mechanism of fiber fusion post-spinning and converted carbon fibers is discussed. 

  • 22.
    Bengtsson, Jenny
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Biobased Materials. Chalmers University of Technology, Sweden.
    Jedvert, Kerstin
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, IVF.
    Hedlund, Artur
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, IVF.
    Köhnke, Tobias
    RISE - Research Institutes of Sweden (2017-2019), Materials and Production, IVF.
    Theliander, Hans
    Chalmers University of Technology, Sweden.
    Mass transport and yield during spinning oflignin-cellulose carbon fiber precursors2019In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 5, p. 509-516Article in journal (Refereed)
    Abstract [en]

    Lignin, a substance considered as a residue in biomass and ethanol production, has been identified as a renewable resource suitable for making inexpensive carbon fibers (CFs), which would widen the range of possible applications for light-weight CFs reinforced composites. Wet spinning of lignin-cellulose ionic liquid solutions is a promising method for producing lignin-based CFs precursors. However, wet-spinning solutions containing lignin pose technical challenges that have to be solved to enable industrialization. One of these issues is that a part of the lignin leaches into the coagulation liquid, which reduces yield and might complicate solvent recovery. In this work, the mass transport during coagulation is studied in depth using a model system and trends are confirmed with spinning trials. It was discovered that during coagulation, efflux of ionic liquid is not hindered by lignin concentration in solution and the formed cellulose network will enclose soluble lignin. Consequently, a high total concentration of lignin and cellulose in solution is advantageous to maximize yield. This work provides a fundamental understanding on mass transport during coagulation of lignin-cellulose solutions, crucial information when designing new solution-based fiber forming processes.

  • 23.
    Bengtsson, Peter
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Sanati, Mehri
    Evaluation of hydrocarbon emissions from heart- and sapwood of Scots pine using a laboratory-scale wood drier2004In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 58, no 6, p. 660-665Article in journal (Refereed)
    Abstract [en]

    The subject of study is the emission of Volatile Organic Compounds (VOC) during the drying of wood. Heart-wood and sapwood from Scots pine were dried at different temperatures (50, 70 and 90oC) in a laboratory kiln.The sampling method, Solid Phase Microextraction was used to collect the different volatile organic compounds during the drying. The gas chromatograph and mass spectrometer was used to identify and quantify the organic matter. The total hydrocarbons were measured with a flame ionization detector. Primarily, different monoterpenes were released during the drying process. 3-carene and a-pinene were most common and were also analytically quantified. The diterpene, pimaral, was found in an estimated large amount in the later stage of the drying process but was not exactly quantified. Large differences in both release behavior and total amount of released hydrocarbon between heart- and sapwood were obtained. Emissions of VOC from heartwood were of a magnitude approximately three times higher than that from sapwood

  • 24.
    Berg, Jan-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Gulliksson, Mårten E.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Gradin, Per A.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    On the energy consumption for crack development in fibre wall in disc refining - A micromechanical approach2009In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 63, no 2, p. 204-210Article in journal (Refereed)
    Abstract [en]

    An analytical model has been applied to calculate the acquired strain energy density in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load. The energy density was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy is needed to create cracks at higher microfibril angles. The energy density was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy density was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data.

  • 25.
    Bjurhager, Ingela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gamstedt, E. Kristofer
    Keunecke, Daniel
    Niemz, Peter
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Mechanical performance of yew (Taxus baccata L.) from a longbow perspective2013In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 7, p. 763-770Article in journal (Refereed)
    Abstract [en]

    Yew (Taxus baccata L.) longbow was the preferred weapon in the Middle Ages until the emergence of guns. In this study, the tensile, compression, and bending properties of yew were investigated. The advantage of yew over the other species in the study was also confirmed by a simple beam model. The superior toughness of yew has the effect that a yew longbow has a higher range compared with bows made from other species. Unexpectedly, the mechanical performance of a bow made from yew is influenced by the juvenile-to-mature wood ratio rather than by the heartwood-to-sapwood ratio. A yew bow is predicted to have maximized performance at a juvenile wood content of 30-50%, and located at the concave side (the compressive side facing the bowyer). Here, the stiffness and yield stress in compression should be as high as possible.

  • 26.
    Bjurhager, Ingela
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Keunecke, Daniel
    Niemz, Peter
    Berglund, Lars A.
    Mechanical performance of yew (Taxus baccata L.) from a longbow perspective2013In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 67, no 7, p. 763-770Article in journal (Refereed)
    Abstract [en]

    Yew (Taxus baccata L.) longbow was the preferred weapon in the Middle Ages until the emergence of guns. In this study, the tensile, compression, and bending properties of yew were investigated. The advantage of yew over the other species in the study was also confirmed by a simple beam model. The superior toughness of yew has the effect that a yew longbow has a higher range compared with bows made from other species. Unexpectedly, the mechanical performance of a bow made from yew is influenced by the juvenile-to-mature wood ratio rather than by the heartwood-to-sapwood ratio. A yew bow is predicted to have maximized performance at a juvenile wood content of 30-50%, and located at the concave side (the compressive side facing the bowyer). Here, the stiffness and yield stress in compression should be as high as possible.

  • 27.
    Bjurhager, Ingela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ljungdahl, Jonas
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wallstrom, Lennart
    Gamstedt, E. Kristofer
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Towards improved understanding of PEG-impregnated waterlogged archaeological wood: A model study on recent oak2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 2, p. 243-250Article in journal (Refereed)
    Abstract [en]

    To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak (Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.

  • 28.
    Bjurhager, Ingela
    et al.
    Kungliga tekniska högskolan, KTH.
    Ljungdahl, Jonas
    Kungliga tekniska högskolan, KTH.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gamstedt, Kristofer
    Kungliga tekniska högskolan, KTH.
    Berglund, Lars A
    Kungliga tekniska högskolan, KTH.
    Towards improved understanding of PEG-impregnated waterlogged archaeological wood: a model study on recent oak2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 2, p. 243-250Article in journal (Refereed)
    Abstract [en]

    To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak (Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.

  • 29.
    Blom, Åsa
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Bergström, Mikael
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Elowson, Torbjörn
    Durability of Untreated Norway Spruce (Picea abies) Exposed Outdoors Above Ground for Nine Years.2004In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 58, no 2, p. 167-172Article in journal (Refereed)
    Abstract [en]

    Moisture dynamics and durability during weather exposure as affected by origin and production method were studied for nine years on 113 untreated spruce samples. The moisture content was measured on 67 occasions. The weight loss was determined for each sample at the end of the sampling period. The most important factors, affecting both moisture content and weight loss, were origin and drying technique. The samples originating from central Sweden had the best durability, followed by the southern stand, while the northern stand had the lowest durability in terms of weight loss. Airdrying had a negative impact on the performance of samples from all three stands, but to different degrees. Samples from the northern stand were most sensitive to airdrying, in terms of both weight loss and moisture content, followed by the southern stand, while the central stand was least sensitive. Why the samples from the northern stand were more sensitive to airdrying and showed the largest weight losses is unknown; it can only be suggested that the origin of the wood can be of importance for the durability.

  • 30.
    Blom, Åsa
    et al.
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Bergström, Mikael
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Elowson, Torbjörn
    Mass loss and moisture dynamics of Scots pine (Pinus sylvestris L.) exposed outdoors above ground in Sweden.2005In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 59, no 2, p. 183-189Article in journal (Refereed)
    Abstract [en]

    The durability of 566 Scots pine (Pinus sylvestris) samples was tested during a period of 9 years of exposure to weather in Sweden. The parameters investigated were heartwood/sapwood, origin, surface treatment, end-seal, storage and drying method, annual ring width and density. The weight was measured on 67 occasions during 9 years in order to assess the moisture content of the samples. The mass loss was determined for each sample at the end of the trial. Sapwood had a higher moisture uptake and a higher mass loss compared with heartwood. Even if sapwood was painted with an impermeable paint and then end-sealed, it still had higher average moisture content than heartwood. The results also demonstrated that sapwood was more sensitive to different handling conditions than heartwood. Sapwood was sensitive to air-drying and water storage, which was evident in the higher moisture uptake. In terms of mass loss, some differences were evident but they were not statistically significant due to the large standard deviation of the sapwood samples from water-stored logs. The only positive influence of water storage was on samples end-dipped in oil. One explanation could be that water storage led to increased permeability due to bacterial attack, which in turn enhanced the penetration of the oil. Heartwood had low and stable moisture dynamics during the test period, almost independent of treatment or handling conditions. No correlation with moisture uptake or mass loss was evident among annual ring width, origin or density.

  • 31. Blomberg, Jonas
    et al.
    Persson, Bengt
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking2006In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 60, no 3, p. 322-331Article in journal (Refereed)
    Abstract [en]

    Images obtained by scanning electron microscopy (SEM) helped to clarify the question as to how anatomy influences the deformation on compression and the spring-back of densified wood on water soaking. Transverse sections of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), black alder (Alnus glutinosa), Swedish aspen (Populus tremula), European birch (Betula pubescens), European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) were studied. Wood is reinforced with rays in the radial direction and with dense latewood in the tangential direction. When strained radially, rays buckle or tilt tangentially. Softwoods were mainly compressed radially, owing to low number of rays and since latewood is much denser than earlywood. The diffuse-porous hardwoods with low density variation between latewood and earlywood were mainly deformed tangentially, except birch, which has high density at the annual ring border and is mainly compressed radially. The ring-porous hardwoods were relatively equally deformed in the radial and tangential directions because of the high number of rays and high latewood density. Moisture-induced spring-back (shape recovery) was proportional to the degree of compression. Rays remained deformed, which also influenced the surrounding wood. Longitudinal wood cells almost resumed their original shape. Wood with low density and a low degree of compression showed the highest structural recovery. Shearing deformation was particularly pronounced and permanent in woods with high strength anisotropy. Thin-walled and sheared cells, such as earlywood in softwood, tended to crack on compression. Cracks usually stopped at the middle lamella and had a lesser influence on strength properties than for lumen-to-lumen cracks.

  • 32.
    Blomberg, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Persson, Bengt
    Dalarna University, Borlänge.
    Bexell, Ulf
    Dalarna University, Borlänge.
    Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking2006In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 60, no 1, p. 322-331Article in journal (Refereed)
    Abstract [en]

    Images obtained by scanning electron microscopy (SEM) helped to clarify the question as to how anatomy influences the deformation on compression and the spring-back of densified wood on water soaking. Transverse sections of Norway spruce (Picea abies), Scots pine (Pinus sylvestris), black alder (Alnus glutinosa), Swedish aspen (Populus tremula), European birch (Betula pubescens), European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) were studied. Wood is reinforced with rays in the radial direction and with dense latewood in the tangential direction. When strained radially, rays buckle or tilt tangentially. Softwoods were mainly compressed radially, owing to low number of rays and since latewood is much denser than earlywood. The diffuse-porous hardwoods with low density variation between latewood and earlywood were mainly deformed tangentially, except birch, which has high density at the annual ring border and is mainly compressed radially. The ringporous hardwoods were relatively equally deformed in the radial and tangential directions because of the high number of rays and high latewood density. Moisture-induced springback (shape recovery) was proportional to the degree of compression. Rays remained deformed, which also influenced the surrounding wood. Longitudinal wood cells almost resumed their original shape. Wood with low density and a low degree of compression showed the highest structural recovery. Shearing deformation was particularly pronounced and permanent in woods with high strength anisotropy. Thin-walled and sheared cells, such as earlywood in softwood, tended to crack on compression. Cracks usually stopped at the middle lamella and had a lesser influence on strength properties than for lumen-to-lumen cracks. Copyright

  • 33.
    Bonarski, Jan T.
    et al.
    Polish Academy of Sciences, Poland.
    Kifetew, Girma
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Olek, Wieslaw
    Poznań University of Life Sciences, Poland.
    Effects of cell wall ultrastructure on the transverseshrinkage anisotropy of Scots pine wood2015In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 69, no 4, p. 501-507Article in journal (Refereed)
    Abstract [en]

    A hypothesis for explaining the differential anisotropicshrinkage behavior of wood has been proposed,and it was based on the differences in the cell wall ultrastructure.The starting point of the consideration is thatwood shrinkage is governed by its chemical composition,ultrastructure, and gross anatomy. It is also well knownthat the transverse shrinkage anisotropy of earlywood(EW) is more pronounced than that of the latewood (LW).In the paper, the cell wall ultrastructure and shrinkageanisotropy has been related to each other, and to thispurpose, a set of crystallographic texture descriptorswas applied. The descriptors are based on X-ray diffraction(XRD) experiments conducted on matched EW samplesfrom different growth rings of Scots pine. The rangeof the microfibril angle (MFA) was identified. The ratio ofthe maxima of inverse pole figures (IPFs) of both the tangential(T) and radial (R) directions was determined. Theratios quantify the inhomogeneity of the spatial arrangementof the ordered areas. The results of the study clearlyindicate that the transverse shrinkage of wood is governedmostly by a specific ultrastructural organization of moderatelyorganized cell wall compounds.

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  • 34.
    Brodin, Ida
    et al.
    Innventia AB, SE-11486 Stockholm, Sweden.
    Ernstsson, Marie
    YKI.
    Gellerstedt, Göran
    Innventia AB, Box 5604, SE-114 86 Stockholm, Sweden.
    Sjöholm, Elisabeth
    Innventia.
    Oxidative stabilisation of kraft lignin for carbon fibre production2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 141-147Article in journal (Refereed)
    Abstract [en]

    With the aim of investigating kraft lignin as a raw material for carbon fibre production, different lignins have been stabilised in air at conditions varied according to a full factorial experimental design. The lignins under examination were purified kraft lignin powders originating from birch, spruce/pine and Eucalyptus globules, as well as lignin fibres originating from birch with 5% poly(ethylene oxide) (PEO) added as a plasticiser. The influence of temperature, time and heating rate on yield and glass-transition temperature (Tg) was investigated. The highest yield was achieved after stabilisation at 280C during 2 h with a heating rate of 0.2C min-1. The Tg of all lignin powders was increased when stabilisation occurred under harsher conditions. X-ray photoelectron spectroscopy analysis (XPS) of both the outer surface and the cleaved cross-section of individual lignin/PEO fibres showed a clear gradient in the degree of chemical modification, with the major change occurring on the surface resulting in the appearance of a skin-core structure after stabilisation. The behaviour of the lignin fibres during stabilisation is similar to that of pitch-based fibres, indicating good possibilities for lignin as raw material for carbon fibre production.

  • 35.
    Brodin, Ida
    et al.
    RISE, Innventia.
    Ernstsson, Marie
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Gellerstedt, Göran
    RISE, Innventia.
    Sjöholm, Elisabeth
    RISE, Innventia.
    Oxidative stabilisation of kraft lignin for carbon fibre production2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, no 2, p. 141-147Article in journal (Refereed)
    Abstract [en]

    With the aim of investigating kraft lignin as a raw material for carbon fibre production, different lignins have been stabilised in air at conditions varied according to a full factorial experimental design. The lignins under examination were purified kraft lignin powders originating from birch, spruce/pine and Eucalyptus globules, as well as lignin fibres originating from birch with 5 poly(ethylene oxide) (PEO) added as a plasticiser. The influence of temperature, time and heating rate on yield and glass-transition temperature (Tg) was investigated. The highest yield was achieved after stabilisation at 280°C during 2h with a heating rate of 0.2°C min -1. The Tg of all lignin powders was increased when stabilisation occurred under harsher conditions. X-ray photoelectron spectroscopy analysis (XPS) of both the outer surface and the cleaved cross-section of individual lignin/PEO fibres showed a clear gradient in the degree of chemical modification, with the major change occurring on the surface resulting in the appearance of a skin-core structure after stabilisation. The behaviour of the lignin fibres during stabilisation is similar to that of pitch-based fibres, indicating good possibilities for lignin as raw material for carbon fibre production.

  • 36. Brodin, Ida
    et al.
    Sjöholm, Elisabeth
    RISE, STFI-Packforsk.
    Gellerstedt, Göran
    RISE, STFI-Packforsk.
    Kraft lignin as feedstock for chemical products: The effects of membrane filtration2009In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 63, no 3, p. 290-297Article in journal (Refereed)
    Abstract [en]

    The use of technical lignins as feedstock for chemical products will require improvements in purity, molecular mass distribution, and thermal behavior. Therefore, industrial black liquors from kraft pulping of softwood (spruce/pine) and hardwood (birch and Eucalyptus globulus) have been subjected to fractionation according to molecular mass by ceramic membranes. After acidification and isolation of the lignin fractions, a variety of analytical methods have been applied to help understand their structure - property relationships. From all types of lignin, the chemical and polymeric properties of fractions isolated from the membrane permeates were more homogeneous. This demonstrates that technical kraft lignins, irrespective of origin, may constitute an interesting feedstock for products, such as carbon fibers, adhesives, and phenol-based polymers.

  • 37.
    Brodin, Ida
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Sjöholm, Elisabeth
    Gellerstedt, Göran
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kraft lignin as feedstock for chemical products: The effects of membrane filtration2009In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 63, no 3, p. 290-297Article in journal (Refereed)
    Abstract [en]

    The use of technical lignins as feedstock for chemical products will require improvements in purity, molecular mass distribution, and thermal behavior. Therefore, industrial black liquors from kraft pulping of softwood (spruce/ pine) and hardwood (birch and Eucalyptus globulus) have been subjected to fractionation according to molecular mass by ceramic membranes. After acidification and isolation of the lignin fractions, a variety of analytical methods have been applied to help understand their structure - property relationships. From all types of lignin, the chemical and polymeric properties of fractions isolated from the membrane permeates were more homogeneous. This demonstrates that technical kraft lignins, irrespective of origin, may constitute an interesting feedstock for products, such as carbon fibers, adhesives, and phenol-based polymers.

  • 38. Bryne, Lars Elof
    et al.
    Lausmaa, Jukka
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SP – Sveriges Tekniska Forskningsinstitut / Funktionella material (KMf).
    Ernstsson, Marie
    Englund, Finn
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, Trätek.
    Wålinder, Magnus
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, Trätek.
    Ageing of modified wood. Part 2: Determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 3, p. 305–313-Article in journal (Refereed)
    Abstract [en]

    The main objective of this work was to study the chemical composition of surfaces and ageing effects on acetylated pine (Pinus sylvestris), heat treated spruce (Picea abies), and furfurylated radiata pine (Pinus radiata) in comparison to unmodified wood. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were the instruments of choice. Observation with a low-vacuum scanning electron microscope (LV-SEM) complemented the study. The spectroscopic information was also linked to a parallel wettability study on matched wood samples by the Wilhelmy method. The results show that XPS and ToF-SIMS are two powerful tools that in combination give complementary information, both quantitative and qualitative, and are well suited for observation of the ageing process of different wood surfaces. The hydrophobization process as a result of migration of extractives during ageing was well quantified by the XPS measurements and the results correlated well with wetting results. Several specific hydrophobic substances could be identified by ToF-SIMS measurements.

  • 39. Bryne, Lars Elof
    et al.
    Wålinder, Magnus
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, Trätek.
    Ageing of modified wood. Part 1: Wetting properties of acetylated, furfurylated, and thermally modified wood2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 3, p. 295–304-Article in journal (Refereed)
    Abstract [en]

    The main objective of this work was to apply contact angle analysis to predict work of adhesion (Wa) between some modified wood materials and certain thermoplastics and adhesives. Wetting properties, i.e., contact angles, were measured by the Wilhelmy method on both freshly prepared and aged veneer samples of unmodified and acetylated Scots pine, furfurylated radiata pine, and heat treated Norway spruce. The sessile drop method was used to measure contact angles on a phenol resorcinol formaldehyde, an emulsion polymer isocyanate, and a one-component polyurethane adhesive. Contact angle data were also collected from the literature on polyethylene, polyvinyl chloride, polymethyl methacrylate, polystyrene, and Nylon 6. Contact angle analysis based on the Chang-Qin-Chen model was then applied to determine so-called acid-base interaction parameters and Wa between the wood samples and the selected thermoplastics and adhesives. Results show that the ageing process led to an increased hydrophobic character of unmodified, heat treated, and furfurylated wood samples. The freshly prepared acetylated wood samples had a pronounced hydrophobic character which remained approximately constant after ageing. The predicted Wa between the wood and the adhesives was considerably higher than that between the wood and the thermoplastics. Furthermore, the predicted Wa between the acetylated wood and both the thermoplastics and water was approximately unchanged when comparing the fresh and aged samples. In contrast, the ageing of all other wood samples resulted in a dramatic decrease of the wood-water Wa and a moderate decrease of the wood-thermoplastics Wa. The wood-adhesives Wa, however, was unchanged for the unmodified and furfurylated wood when comparing the fresh and aged samples and even increased for heat treated and acetylated wood samples.

  • 40.
    Bryne, Lars-Elof
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Lausmaa, Jukka
    SP Technical Research Institute of Sweden, Chemistry and Materials Technology, Borås, Sweden.
    Ernstsson, Marie
    Institute for Surface Chemistry, Stockholm, Sweden.
    Englund, Finn
    SP Trätek, Technical Research Institute of Sweden, Wood Technology, Borås, Sweden.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Ageing of modified wood: Part 2: Determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 3, p. 305-313Article in journal (Refereed)
    Abstract [en]

    The main objective of this work was to study the chemical composition of surfaces and ageing effects on acetylated pine (Pinus sylvestris), heat treated spruce (Picea abies), and furfurylated radiata pine (Pinus radiata) in comparison to unmodified wood. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were the instruments of choice. Observation with a low-vacuum scanning electron microscope (LV-SEM) complemented the study. The spectroscopic information was also linked to a parallel wettability study on matched wood samples by the Wilhelmy method. The results show that XPS and ToF-SIMS are two powerful tools that in combination give complementary information, both quantitative and qualitative, and are well suited for observation of the ageing process of different wood surfaces. The hydrophobization process as a result of migration of extractives during ageing was well quantified by the XPS measurements and the results correlated well with wetting results. Several specific hydrophobic substances could be identified by ToF-SIMS measurements.

  • 41.
    Bryne, Lars-Elof
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Wålinder, Magnus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Ageing of modified wood: Part 1: Wetting properties of acetylated, furfurylated, and thermally modified2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 3, p. 295-304Article in journal (Refereed)
    Abstract [en]

    The main objective of this work was to apply contact angle analysis to predict work of adhesion (W-a) between some modified wood materials and certain thermoplastics and adhesives. Wetting properties, i.e., contact angles, were measured by the Wilhelmy method on both freshly prepared and aged veneer samples of unmodified and acetylated Scots pine, furfurylated radiata pine, and heat treated Norway spruce. The sessile drop method was used to measure contact angles on a phenol resorcinol formaldehyde, an emulsion polymer isocyanate, and a one-component polyurethane adhesive. Contact angle data were also collected from the literature on polyethylene, polyvinyl chloride, polymethyl methacrylate, polystyrene, and Nylon 6. Contact angle analysis based on the Chang-Qin-Chen model was then applied to determine so-called acid-base interaction parameters and W-a between the wood samples and the selected thermoplastics and adhesives. Results show that the ageing process led to an increased hydrophobic character of unmodified, heat treated, and furfurylated wood samples. The freshly prepared acetylated wood samples had a pronounced hydrophobic character which remained approximately constant after ageing. The predicted W-a between the wood and the adhesives was considerably higher than that between the wood and the thermoplastics. Furthermore, the predicted W-a between the acetylated wood and both the thermoplastics and water was approximately unchanged when comparing the fresh and aged samples. In contrast, the ageing of all other wood samples resulted in a dramatic decrease of the wood-water W-a and a moderate decrease of the wood-thermoplastics W-a. The wood-adhesives W-a, however, was unchanged for the unmodified and furfurylated wood when comparing the fresh and aged samples and even increased for heat treated and acetylated wood samples.

  • 42.
    Brännvall, Elisabet
    RISE - Research Institutes of Sweden (2017-2019), Bioeconomy, Biorefinery and Energy.
    Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose2018In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 10, p. 819-827Article in journal (Refereed)
    Abstract [en]

    Pulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1-1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.

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  • 43.
    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.

  • 44.
    Brännvall, Elisabet
    et al.
    RISE, Innventia. KTH Royal Institute of Technology, Sweden.
    Bäckström, Marie
    RISE, Innventia.
    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.

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    fulltext
  • 45.
    Brännvall, Elisabet
    et al.
    RISE - Research Institutes of Sweden, Bioeconomy, Biorefinery and Energy.
    Reimann, Anders
    RISE - Research Institutes of Sweden, Bioeconomy, Biobased Materials.
    The balance between alkali diffusion and alkali consuming reactions during impregnation of softwood. Impregnation for kraft pulping revisited2018In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 3, p. 169-178Article in journal (Refereed)
    Abstract [en]

    The purpose of the impregnation stage is to ensure that cooking chemicals reach all parts of the chips. However, as alkali comes into contact with wood, reactions take place, which alter the paths available for ionic transport and dissolve wood components. The aim of the present study is to establish the most favorable impregnation conditions, which result in an even alkali concentration profile through the chip at a sufficiently high level without extensive yield losses due to peeling. Softwood chips were subjected to different impregnation conditions. The progress of impregnation was assessed by analyzing the concentration of hydroxide ions in the bound liquor inside wood chips and the release of acetic acid. The extent of undesired reactions was measured as the amount of carbohydrate degradation products formed and amount of wood dissolved. Increased temperature and time lead to more degradation of the carbohydrates during impregnation. At high temperature, the concentration of alkali in the bound liquor was lower due to higher alkali consumption in degradation reactions. The most favorable process is to perform impregnation at an elevated initial effective alkali (EA) for a short time. This resulted in an increased alkali concentration in the bound liquor within the chip without extensive carbohydrate degradation.

  • 46. Buchert, J
    et al.
    Carlsson, G
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Viikari, L
    Ström, G
    Surface characterization of unbleached kraft pulps by enzymatic peeling and ESCA1996In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 50, p. 69-74Article in journal (Refereed)
    Abstract [en]

    Specific enzymes hydrolyzing pulp carbohydrates can be used for characterization of pulp fibres. By combining enzymatic peeling of fibre hemicelluloses with novel techniques of surface analysis, such as ESCA, new information can be obtained on the location of different components, i.e. xylan, glucomannan and lignin on the fibre surfaces. In this work unbleached kraft pulps were selectively peeled with purified Trichoderna reesi xylanase and mannanase and the structural modifications caused by the removal of the hemicelluloses were analyzed with ESCA. The removal of the accessible portion of the pine kraft xylan increased the amount of surface lignin, whereas mannan removal had no effect on the amount of lignin on the surface. In the case of birch kraft pulp the removal of accessible xylan did not enhance the amount of lignin on the surface. However, in birch kraft pulp the removal of xylan decreased the amount of extractives covering the surface.

  • 47.
    Bäckström, Marie
    et al.
    RISE, Innventia.
    Jensen, Anna
    RISE, Innventia.
    Brännvall, Elisabet
    RISE, Innventia. KTH Royal Institute of Technology, Sweden.
    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.

  • 48. Bäckström, Marie
    et al.
    Kolar, Marie-Claude
    Htun, Myat
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Characterisation of fines from unbleached kraft pulps and their impact on sheet properties2008In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 62, no 5, p. 546-552Article in journal (Refereed)
  • 49.
    Bäckström, Marie
    et al.
    RISE, STFI-Packforsk.
    Kolar, Marie-Claude
    RISE, STFI-Packforsk.
    Htun, Myat
    RISE, STFI-Packforsk.
    Characterisation of fines from unbleached kraft pulps and their impact on sheet properties2008In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 62, no 5, p. 546-552Article in journal (Refereed)
    Abstract [en]

    Fines are an essential component in the papermaking process because they have a profound influence on the behaviour of the wet web and on the mechanical properties of the final sheet. Primary fines are present in the pulp prior to refining, and secondary fines are produced during refining. In the present investigation, two commercially manufactured unbleached pulps with kappa numbers of 45 and 90 were studied in terms of how they responded to refining with respect to the quality of fibre and fines. Primary and secondary fines were collected and characterised and their impact on sheet strength was evaluated by addition of known amounts to a refined and decrilled pulp. All the measured paper strength properties improved when primary and secondary fines were added. The strength improvement was generally somewhat higher in the second case. The effect was more pronounced at a higher level of addition. We attribute the main strength improvements associated with fines to improved consolidation by the creation of capillary forces between the surfaces.

  • 50.
    Carlsson, Jenny
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Heldin, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Isaksson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Wiklund, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Investigating tool engagement in groundwood pulping: finite element modelling and in-situ observations at the microscale2020In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 74, no 5, p. 477-487Article in journal (Refereed)
    Abstract [en]

    With industrial groundwood pulping processes relying on carefully designed grit surfaces being developed for commercial use, it is increasingly important to understand the mechanisms occurring in the contact between wood and tool. We present a methodology to experimentally and numerically analyse the effect of different tool geometries on the groundwood pulping defibration process. Using a combination of high-resolution experimental and numerical methods, including finite element (FE) models, digital volume correlation (DVC) of synchrotron radiation-based X-ray computed tomography (CT) of initial grinding and lab-scale grinding experiments, this paper aims to study such mechanisms. Three different asperity geometries were studied in FE simulations and in grinding of wood from Norway spruce. We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding. We also correlate the strains obtained from numerical models to the integrity of the separated fibres in lab-scale grinding experiments. In conclusion, we found that, by modifying the asperity geometries, it is, to some extent, possible to control the underlying mechanisms, enabling development of better tools in terms of efficiency, quality of the fibres and stability of the groundwood pulping process.

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