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  • 1.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Effects of Cell Wall Structure on Tensile Properties of Hardwood: Effect of down-regulation of lignin on mechanical performance of transgenic hybrid aspen. Effect of chemical degradation on mechanical performance of archaeological oak from the Vasa ship.2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wood is a complex material and the mechanical properties are influencedby a number of structural parameters. The objective of this study has been toinvestigate the relationship between the structure and the mechanical propertiesof hardwood. Two levels were of special interest, viz. the cellular structureand morphology of the wood, and the ultra-structure of the cell wall. In thenext step, it was of interest to examine how the mechanical properties ofhardwood change with spontaneous/induced changes in morphology and/orchemical composition beyond the natural variation found in nature.

    Together, this constituted the framework and basis for two larger projects,one on European aspen (Populus tremula) and hybrid aspen (Populus tremulax Populus tremuloides), and one on European oak (Quercus robur). Amethodology was developed where the concept of relative density and compositemechanics rules served as two useful tools to assess the properties ofthe cell wall. Tensile testing in the longitudinal direction was combined withchemical examination of the material. This approach made it possible to revealthe mechanical role of the lignin in the cell wall of transgenic aspen trees,and investigate the consequences of holocellulose degradation in archaeologicaloak from the Vasa ship.

    The study on transgenic aspen showed that a major reduction in lignin inPopulus leads to a small but significant reduction in the longitudinal stiffness.The longitudinal tensile strength was not reduced. The results are explainableby the fact that the load-bearing cellulose in the transgenic aspen retained itscrystallinity, aggregate size, microfibril angle, and absolute content per unitvolume. The results can contribute to the ongoing task of investigating andpinpointing the precise function of lignin in the cell wall of trees.

    The mechanical property study on Vasa oak showed that the longitudinaltensile strength is severely reduced in several regions of the ship, andthat the reduction correlates with reduced average molecular weight of theholocellulose. This could not have been foreseen without a thorough mechanicaland chemical investigation, since the Vasa wood (with exception fromthe bacterially degraded surface regions) is morphologically intact and witha micro-structure comparable to that of recent oak. The results can be usedin the ongoing task of mapping the condition of the Vasa wood.

  • 2.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Mechanical behaviour of hardwoods: effects from cellular and cell wall structures2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The aim of this work was to investigate the mechanical properties of different hardwood species and relate the properties to the structure at the cellular and cell wall level. The species examined were European aspen (Populus tremula), hybrid aspen (Populus tremula x Populus tremuloides) and European oak (Quercus robur). The Populus species, including the fast-growing hybrid aspen, are used in a large number of projects using transgene technology, which also has raised the demand for a more extensive determination of mechanical properties of the species. Oak have been a popular construction material for thousands of years, esulting in a vast number of archaeological findings. Preservation of these often includes dimensional stabilization by polyethylene glycol (PEG), an impregnation agent which affects the mechanical properties. To which extent is not properly investigated, however. The study on European and hybrid aspen included development of a method for tensile testing of small, juvenile specimens in the green condition, where strain was measured using the digital speckle photography (DSP) technique. Mechanical performance of the species in terms of longitudinal tensile stiffness and strength were of special interest. Inferior mechanical properties of hybrid aspen corresponded well to mean values of density, which were lower for the hybrid aspen compared to European aspen.

    Oak was examined in the swollen state, where swelling was induced by PEG with molecular weight 600. Longitudinal tensile stiffness and strength as well as radial stiffness and yield strength in compression were compared. Longitudinal and radial strain was measured using video extensiometry and DSP, respectively. Additional characterization of the material included imaging from scanning electron microscopy (SEM), X-ray microtomography and determination of microfibril angle using wide angle X-ray scattering (WAXS). Tensile stiffness and strength in the axial direction were only slightly affected by PEG-impregnation. WAXS measurements showed that microfibril angles were close to zero which implicates that cell wall properties are strongly dependent on the microfibrils, and only marginally influenced by the plasticization effects from PEG on the lignin/hemicellulose matrix. In the radial direction, on the other hand, mechanical performance was strongly decreased by PEG-impregnation. This was believed to originate from softening of rays.

  • 3.
    Bjurhager, Ingela
    et al.
    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.
    Bardage, Stig
    Sundberg, Björn
    Mechanical characterization of juvenile European aspen (Populus tremula) and hybrid aspen (Populus tremula × Populus tremuloides) using full-field strain measurements2008In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 54, no 5, p. 349-355Article in journal (Refereed)
    Abstract [en]

    Functional analysis of genes and proteins involved in wood formation and fiber properties often involves phenotyping saplings of transgenic trees. The objective of the present study was to develop a tensile test method for small green samples from saplings, and to compare mechanical properties of juvenile European aspen (Populus tremula) and hybrid aspen (Populus tremula × tremuloides). Small microtomed sections were manufactured and successfully tested in tension parallel to fiber orientation. Strain was determined by digital speckle photography. Results showed significantly lower values for juvenile hybrid aspen in both Young's modulus and tensile strength parallel to the grain. Average Young's moduli spanned the ranges of 5.9-6.6 and 4.8-6.0 GPa for European aspen and hybrid aspen, respectively. Tensile strength was in the range of 45-49 MPa for European aspen and 32-45 MPa for hybrid aspen. The average density (oven-dry) was 284 kg/m3 for European aspen and 221 kg/m3 for hybrid aspen. Differences in mechanical properties correlated with differences in density.

  • 4.
    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.

  • 5.
    Bjurhager, Ingela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Halonen, Helena
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lindfors, E. -L
    Iversen, Tommy
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Almkvist, G.
    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. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    State of degradation in archeological oak from the 17th century vasa ship: Substantial strength loss correlates with reduction in (holo)cellulose molecular weight2012In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 13, no 8, p. 2521-2527Article in journal (Refereed)
    Abstract [en]

    In 1628, the Swedish warship Vasa capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the Vasa museum. Chemical investigations of the Vasa were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of Vasa oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, where the load-bearing cellulose microfibril is the critical constituent. The mean tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies.

  • 6.
    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.

  • 7.
    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.
    Wallström, Lennart
    Division of Polymer Engineering, Luleå University of Technology (LTU).
    Gamstedt, E. Kristofer
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Effects of polyethylene glycol treatment on the mechanical properties of oakManuscript (Other academic)
  • 8.
    Bjurhager, Ingela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Nilsson, H.
    Lindfors, E-L
    Iversen, T.
    Almkvist, G.
    Gamstedt, K.E.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Significant loss of mechanical strength in archeological oak from the 17th century Vasa ship: correlation with cellulose degradationArticle in journal (Refereed)
  • 9.
    Bjurhager, Ingela
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Olsson, Anne-Mari
    Innventia.
    Zhang, Bo
    Department of Biomaterials, Max Planck Institute of Colloids and Interfaces.
    Gerber, Lorenz
    Umeå Plant Science Center, Swedish University of Agricultural Sciences (SLU).
    Kumar, Manoj
    Umeå Plant Science Center, Swedish University of Agricultural Sciences (SLU).
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Burgert, Ingo
    Department of Biomaterials, Max Planck Institute of Colloids and Interfaces.
    Sundberg, Björn
    Umeå Plant Science Center, Swedish University of Agricultural Sciences (SLU).
    Salmén, Lennart
    Innventia.
    Ultrastructure and Mechanical Properties of Populus Wood with Reduced Lignin Content Caused by Transgenic Down-Regulation of Cinnamate 4-Hydroxylase2010In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 9, p. 2359-2365Article in journal (Refereed)
    Abstract [en]

    Several key enzymes in lignin biosynthesis of Populus have been down-regulated by transgenie approaches to investigate their role in wood lignification and to explore their potential for lignin modification. Cinnamate 4-hydroxylase is an enzyme in the early phenylpropanoid pathway that has not yet been functionally analyzed in Populus. This study shows that down-regulation of cinnamate 4-hydroxylase reduced Klason lignin content by 30% with no significant change in syringyl to guaiacyl ratio. The lignin reduction resulted in ultrastructural differences of the wood and a 10% decrease in wood density. Mechanical properties investigated by tensile tests and dynamic mechanical analysis showed a decrease in stiffness, which could be explained by the lower density. The study demonstrates that a large modification in lignin content only has minor influences on tensile properties of wood in its axial direction and highlights the usefulness of wood modified beyond its natural variation by transgene technology in exploring the impact of wood biopolymer composition and ultrastructure on its material properties.

  • 10. Leppänen, Kirsi
    et al.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Peura, Marko
    Kallonen, Aki
    Suuronen, Jussi-Petteri
    Penttilä, Paavo
    Love, Jonathan
    Fagerstedt, Kurt
    Serimaa, Ritva
    X-ray scattering and microtomography study on the structural changes of never-dried silver birch, European aspen and hybrid aspen during drying2011In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 65, no 6, p. 865-873Article in journal (Refereed)
    Abstract [en]

    The impact of drying on the structure of the never-dried hardwood cell wall was studied at nanometer level by means of wide- and small-angle X-ray scattering (WAXS, SAXS), and at micrometer level by X-ray microtomography (mu CT). Never-dried silver birch, European aspen and hybrid aspen samples were measured by WAXS in situ during drying in air. The samples included juvenile and mature wood, as well as normal and tension wood to allow comparison of the effects of different matrix compositions and microfibril angles. The deformations of cellulose crystallites and amorphous components of the cell wall were detected as changes in the cellulose reflections 200 and 004 and amorphous halo in the WAXS patterns. Especially, the width of the reflection 004, corresponding to the cellulose chain direction, increased due to drying in all the samples, indicating an increase of strain and disorder of the chains. Also, the cellulose unit cell shrank 0.2-0.3% during drying in this direction in all the samples except in hybrid aspen tension wood. According to the SAXS results of silver birch, the distance between microfibrils decreased during drying. It was detected by mu CT that the mean cross-sectional maximum width of the parenchymatous rays decreased from that of never-dried to air-dried birch by roughly 16%.

  • 11. Olsson, Anne-Mari
    et al.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gerber, Lorenz
    Sundberg, Björn
    Salmén, Lennart
    Ultra-structural organisation of cell wall polymers in normal and tension wood of aspen revealed by polarisation FTIR microspectroscopy2011In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 233, no 6, p. 1277-1286Article in journal (Refereed)
    Abstract [en]

    Polarisation Fourier transform infra-red (FTIR) microspectroscopy was used to characterize the organisation and orientation of wood polymers in normal wood and tension wood from hybrid aspen (Populus tremula x Populus tremuloides). It is shown that both xylan and lignin in normal wood are highly oriented in the fibre wall. Their orientation is parallel with the cellulose microfibrils and hence in the direction of the fibre axis. In tension wood a similar orientation of lignin was found. However, in tension wood absorption peaks normally assigned to xylan exhibited a 90A degrees change in the orientation dependence of the vibrations as compared with normal wood. The molecular origin of these vibrations are not known, but they are abundant enough to mask the orientation dependence of the xylan signal from the S-2 layer in tension wood and could possibly come from other pentose sugars present in, or associated with, the gelatinous layer of tension wood fibres.

  • 12. Svedström, Kirsi
    et al.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kallonen, Aki
    Peura, Marko
    Serimaa, Ritva
    Structure of oak wood from the Swedish warship Vasa revealed by X-ray scattering and microtomography2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 3, p. 355-363Article in journal (Refereed)
    Abstract [en]

    The degradation of oak wood of the historical warship Vasa was studied, focusing on cellular structure by X-ray microtomography (mu CT) and on the nanostructure of the cell wall by wide- and small-angle X-ray scattering (WAXS, SAXS). Solid samples [polyethylene glycol (PEG)-, impregnated and PEG-extracted] were submitted to X-ray analysis and the results compared to those of recent oak. The cellular structure of the Vasa oak was surprisingly well preserved at the micrometer level, according to the mu CT images. As revealed by WAXS, the fraction of crystalline cellulose was lower in the Vasa samples compared with recent oak, but the average length and width of cellulose crystallites (25 +/- 2 nm and 3.0 +/- 0.1 nm, respectively), and the mean microfibril angles (4-9 degrees), showed no significant differences. Accordingly, the crystalline parts of cellulose microfibrils are well preserved in the Vasa oak. The SAXS results indicated a declined short-range order between the cellulose microfibrils and a higher porosity of the Vasa oak compared with recent oak, which may be explained by modification of the hemicellulose-lignin matrix.

  • 13. Walther, Andreas
    et al.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Malho, Jani-Markus
    Pere, Jaakko
    Ruokolainen, Janne
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Ikkala, Olli
    Large-Area, Lightweight and Thick Biomimetic Composites with Superior Material Properties via Fast, Economic, and Green Pathways2010In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 10, no 8, p. 2742-2748Article in journal (Refereed)
    Abstract [en]

    Although remarkable success has been achieved to mimic the mechanically excellent structure of nacre in laboratory-scale models, it remains difficult to foresee mainstream applications due to time-consuming sequential depositions or energy-intensive processes. Here, we introduce a surprisingly simple and rapid methodology for large-area, lightweight, and thick nacre-mimetic films and laminates with superior material properties. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. They are forced to rapidly self-assemble into aligned nacre-mimetic films via paper-making, doctor-Wading or simple painting, giving rise to strong and thick films with tensile modulus of 45 GPa and strength of 250 MPa, that is, partly exceeding nacre. The concepts are environmentally friendly, energy-efficient, and economic and are ready for scale-up via continuous roll-to-roll processes. Excellent gas barrier properties, optical translucency, and extraordinary shape-persistent fire-resistance are demonstrated. We foresee advanced large-scale biomimetic materials, relevant for lightweight sustainable construction and energy-efficient transportation.

  • 14.
    Walther, Andreas
    et al.
    Molecular Materials, Department of Applied Physics, Aalto University.
    Bjurhager, Ingela
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Malho, Jani-Markus
    Molecular Materials, Department of Applied Physics, Aalto University.
    Ruokolainen, Janne
    Molecular Materials, Department of Applied Physics, Aalto University.
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
    Ikkala, Olli
    Molecular Materials, Department of Applied Physics, Aalto University.
    Supramolecular Control of Stiffness and Strength in Lightweight High-Performance Nacre-Mimetic Paper with Fire-Shielding Properties2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 36, p. 6448-6453Article in journal (Refereed)
    Abstract [en]

    Taking the heat: Hard/soft core/shell colloidal building blocks allow large-scale self-assembly to form nacre-mimetic paper. The strength and stiffness of this material can be tailored by supramolecular ionic bonds. These lightweight biomimetic materials show excellent and tunable mechanical properties and heat and fire-shielding capabilities.

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