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  • 1.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    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.
    Distribution of preservatives in thermally modified Scots pine and Norway spruce sapwood2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 3, p. 499-513Article in journal (Refereed)
    Abstract [en]

    Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170°C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species.

  • 2.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Perre, P.
    ENGREF - Laboratory of Forest Sciences.
    A microwave applicator for on line wood drying: Temperature and moisture distribution in wood1999In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 33, no 2, p. 123-138Article in journal (Refereed)
    Abstract [en]

    An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy, meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the position of each applicator in a larger scale microwave pilot plant.

  • 3.
    Blomberg, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Persson, Bengt
    Dalarna University.
    Swelling pressure of semi-isostatically densified wood under different mechanical restraints2007In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 41, no 5, p. 401-415Article in journal (Refereed)
    Abstract [en]

    Semi-isostatically densified and native wood samples of Scots pine and European birch were soaked in water. The swelling coefficients as well as the swelling pressure, that arose when the specimens were restrained in some way prior to the swelling, were measured using a universal testing machine equipped with a high resolution load-cell and an external extensometer. As densified wood swells, the native structure is almost restored and the swelling pressure became twice as high as for native wood in the most compressed directions (radial for pine and birch). That cell-shape recovery increases the swelling pressure can explain the problems with imbalance in laminated constructions where densified wood is used. The possibility to predict the swelling pressure from basic material properties was evaluated. The correlations between swelling pressure and material properties were strong enough to yield good predictive models

  • 4.
    Blomberg, Jonas
    et al.
    Luleå tekniska universitet.
    Persson, Bengt
    Högskolan Dalarna.
    Blomberg, Anna
    Högskolan Dalarna.
    Effects of semi-isostatic densification of wood on the variation in strength properties with density2005In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 39, no 5, p. 339-350Article in journal (Refereed)
    Abstract [en]

    The variation in strength properties with density was compared between semi-isostatically densified and non-densified wood. Strength properties were compared with published data from earlier studies using other methods for densification. Small clear specimens of eight species were analysed for compression strength in axial, radial and tangential direction, three-point bending and Brinell hardness. After densification, all tested strength properties increased with density, but especially strength perpendicular to grain became lower than expected from the density of non-densified wood. Strength of densified wood relative to what could be expected for non-densified wood of similar density was denoted as 'strength potential index'. For axial compression strength and bending strength, strength potential index of individual wood species varied between 0.7 and 1.0, i.e. densified wood is slightly weaker than what could be expected from its density. Strength potential index was lower for properties much determined by strength perpendicular to grain. In radial direction, densified wood was rubbery with low modulus of elasticity and nearly no proportional limit or modulus of rupture. Generally, wood was apparently weakened in proportion to the degree of compression in respective direction. Strength potential index also increased with increasing original density of the species.

  • 5.
    Boonstra, M.J.
    et al.
    Plato International AV, Arnhem.
    Blomberg, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Semi-isostatic densification of heat-treated radiata pine2007In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 41, no 7, p. 607-617Article in journal (Refereed)
    Abstract [en]

    Semi-isostatic densification is a useful method to increase the density and to improve the mechanical properties of fast-grown softwood species like radiata pine. A major disadvantage of this method is the almost complete recovery of the original dimensions when densified wood is exposed to moisture. Heat treatment improves the dimensional stability of wood and might be a useful method to prevent this shape-recovery after densification. However, no or only a limited effect on the shape-recovery was found when densified radiata pine was exposed to moisture.

  • 6.
    Brunow, G.
    et al.
    University of Helsinki.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lundquist, K.
    Chalmers University of Technology.
    Sipilä, J.
    University of Helsinki.
    On the distribution of the diastereomers of the structural elements in lignins: the steric course of reactions mimicking lignin biosynthesis1993In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 27, no 4, p. 281-286Article in journal (Refereed)
    Abstract [en]

    Stereochemical studies on the formation of the diastereomers of arylglycerol-β-aryl ether structures during lignin biosynthesis have been carried out with model compounds. The addition of water to quinone methides of the β-syringyl ether type gives arylglycerol β-syringyl ethers with a predominance of the erythro isomer when the pH of the medium is low. Since erythro forms of arylglycerol β-syringyl ethers are prevalent in hardwood lignins, this indicates that the pH of the medium in which lignin biosynthesis occurs is lower than has been assumed until now. Equilibration studies with non-phenolic model compounds of the arylglycerolβ-guaiacyl ether and β-syringyl ether types under acidolysis conditions indicate that the erythro predominance observed in the syringyl ethers in lignins does not correspond to equilibrium conditions. A remarkable resistance to acidolysis is observed in the model compounds of etherified syringylglycerol β-syringyl ether type.

  • 7.
    Chen, Tingjie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Fujian Agriculture and Forestry University, Fuzhou, China.
    Wu, Zhenzeng
    Fujian Agriculture and Forestry University, Fuzhou, China.
    Niu, Min
    Fujian Agriculture and Forestry University, Fuzhou, China.
    Wang, Alice
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wei, Qihua
    Fujian Agriculture and Forestry University, Fuzhou, China.
    Rao, Jiuping
    Fujian Agriculture and Forestry University, Fuzhou, China.
    Xie, Yongqun
    Fujian Agriculture and Forestry University, Fuzhou, China.
    Effect of polyvinyl alcohol (PVA)/Si-Al hybrid composites on the mechanical properties of ultra-low density fiberboard (ULDF)2016In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225Article in journal (Refereed)
    Abstract [en]

    The microstructure and properties of ultra-low density fiberboard (ULDF) were affected by the different contents of polyvinyl alcohol (PVA). They were tested by using scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), X-ray diffractometer (XRD), thermogravimetric analyzer (TGA), and microcomputer control electronic universal testing machine, respectively. The SEM result showed that the microstructure of ULDFs was affected by the PVA. The FTIR and XRD results showed that there were two forms between PVA and Si-Al sol. They were combining with chemical bond and physical cross linking. The TGA results revealed that the thermostability of ULDF was decreased with the increasing content of PVA. Combined with the TGA and mechanical properties results, the reasonable content of PVA which was 30% was obtained. Under this condition, the modulus of rupture, modulus of elasticity, and the internal bond strength of ULDF were significantly improved from 0.13, 16.09, and 0.021 MPa to 0.35, 24.86, and 0.038 MPa, respectively.

  • 8.
    Hassan, Mohammad
    et al.
    National Research Centre.
    Mathew, Aji P.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hassan, Enas
    National Research Centre.
    El-Wakil, Nahla
    National Research Centre.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Nanofibers from bagasse and rice straw: process optimization and properties2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 1-3, p. 193-205Article in journal (Refereed)
    Abstract [en]

    Nanofibers (NF) were isolated from bleached bagasse and rice straw pulps. The pulps were refined using high-shear ultrafine grinder and then homogenized using high-pressure homogenizer. The efficiency of the used isolation processes was studied by optical microscopy (OM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and testing the tensile properties (wet and dry) of nanopaper sheets made from the nanofibers. In addition, opacity and porosity of nanopaper sheets made after different processing steps were investigated. The microscopy studies showed that the processes used resulted in nanofibers with diameters ranging from 3.5 to 60 nm. The results indicated that main isolation of nanofibers took place during refining using the ultrafine grinding process, while high-pressure homogenization resulted in smaller and more homogeneous size of nanofibers. Nanopaper sheets made from bagasse showed better wet and dry tensile strength properties than those made of rice straw

  • 9.
    Kifetew, Girma
    et al.
    Kungliga tekniska högskolan, KTH.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Wiklund, Martin
    Kungliga tekniska högskolan, KTH.
    Tangential and radial deformation field measurements on wood during drying1997In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 31, no 1, p. 35-44Article in journal (Refereed)
    Abstract [en]

    In a previous study, the deformation field measurement method on wood during drying was described. This paper discusses the deformation field measurement results during drying to 8.2% moisture content on the radial and tangential surfaces. It also attempts to explain the observations by an approximate expression based onearlywood-latewood interaction theory. The deformation on the radial surface varied between -0.7% and 7.5%. The actual measurements on the radial surfaces support previous work. Deformation measurements on the tangential surfaces were between -0.5% and 9.0%. Although the investigations were carried out on gross wood specimens, the results provide an insight into the extent to which local density variation within the early- and latewood layers may influence the magnitude of surface deformation.

  • 10.
    Kifetew, Girma
    et al.
    Kungliga tekniska högskolan, KTH.
    Thuvander, Fredrik
    Luleå tekniska universitet.
    Berglund, Lars
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    The effect of drying on wood fracture surfaces from specimens loaded in wet condition1998In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 32, no 2, p. 83-94Article in journal (Refereed)
    Abstract [en]

    The study describes the effect of drying on fracture surfaces of Scots pinePinus silvestris L. Microtomed specimens of isolated and combined early-and latewood, in green and oven-dried/resoaked state were loaded to failure in uniaxial tension parallel to the grain. The fracture surfaces were studied using scanning electron microscopy (SEM). Both green early- and latewood samples showed rough fracture surfaces, which in latewood was dominated by intrawall failure. In the resoaked state, transwall failure dominated and fracture surfaces were more flat, indicating a more brittle fracture process. Although variation in the data was large, the strength of the resoaked samples were generally lower than those of paired green samples. The observations support irreversible cell wall damage formed during drying which severely affects the failure mechanism.

  • 11.
    Källander, Björn
    Stora Corporate Research AB.
    Climate control in vacuum dryers for convective heat transfer: Part 1: Demands on climate control2002In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 36, no 6, p. 477-486Article in journal (Refereed)
    Abstract [en]

    The European Drying Group (EDG) proposal on a wood drying quality standard defines demands on final moisture content variation of the dried wood. The final moisture content variation will depend on material parameters as well as the production process and the wood will always show a “natural” moisture content variation after drying. Thus the drying process has to be defined well enough to allow for the natural moisture content variation in order to fulfil the demands of the drying standards. As the average equilibrium moisture content of the wood in a vacuum drying kiln with pure steam atmosphere is determined by the pressure and the temperature, the demands on the climate control system to fulfil the demands of the drying standard can be calculated with regard to the natural moisture content variation of the wood. In the first part of this contribution the demands on climate control in vacuum dryers are calculated based on the EDG-standard and the natural moisture content variation. In the second part of the contribution the demands on climate control are compared with climate and moisture content measurements from industrial production in vacuum kilns. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.

  • 12.
    Källander, Björn
    Stora Corporate Research AB.
    Climate control in vacuum dryers for convective heat transfer: Part 2: Actual climates in industrial kilns and suggestions to improve kiln design2003In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 37, no 1, p. 3-9Article in journal (Refereed)
    Abstract [en]

    The first part of this contribution determined the demands on climate control in vacuum drying kilns that are necessary to achieve the final moisture content variation stipulated in the European Drying Group (EDG) proposal on wood drying quality standards. In this second part of the contribution, these demands are compared with measurements of actual climates and the resulting final moisture content in vacuum kilns during industrial production. The measurements show that none of the studied industrial vacuum kilns are capable of controlling climate with acceptable accuracy. The variations in drying climate lead to large variations in final moisture content and reduced production capacities. Drying quality and drying capacity would be greatly increased with improved kiln design and improved climate control systems. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed.

  • 13.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Medical CAT-scanning: X-ray absorption coefficients, CT-numbers and their relation to wood density1991In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 25, no 5, p. 341-349Article in journal (Refereed)
    Abstract [en]

    This paper describes how X-ray absorption coefficients and CT-number in medical CAT-scanning can be calculated for dry and wet wood. A comparison with earlier recorded data for dry wood showed that the deviation between calculated and measured CT-numbers was not significant. Linear regression showed that wood density could be measured with an accuracy of +/- 4 kg/m3. Wood having the same green density but containing different amounts of water have different absorption coefficients and CT-numbers. A linear relationship between CT-numbers and density of wood containing water was developed. Wood density could be measured with an accuracy of +/- 13.4 kg/m3

  • 14.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    The accuracy of medical CAT-scan images for non-destructive density measurements in small volume elements within solid wood1991In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 25, no 6, p. 425-432Article in journal (Refereed)
    Abstract [en]

    A comparison between identically sampled CAT-scan images of five wooden test pieces (Pinus sylvestris) showed that the CT-number in each pixel varied with a standard deviation of ±3.9-11.1 CT numbers. This inaccuracy in CT-numbers is called "noise". As long as the direction of rotation can be controlled the noise in CAT-scan images of wood can be assumed to be approx. ±4 CT-numbers in each pixel. A calculation showed the average CT-number must differ ±1 unit to distinguish average CT-numbers in 2 × 2 × 1.5 mm volumes within solid wood. It has previously been shown that a change of ±1 CT-number corresponds approx. to a change in density of ±1 kg/m3. On the other hand, there is a difference in X-ray absorption coefficients between wood and water. Thereby dry wood densities in corresponding volumes must differ approx. ±2 kg/m3 to significantly be distinguished. The corresponding figure is approx. ±6 kg/m3 for wet wood densities with moisture content levels ranging from 6-100%.

  • 15.
    Megnis, Modris
    et al.
    Luleå tekniska universitet.
    Olsson, Tomas
    Luleå tekniska universitet.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Mechanical performance of linseed oil impregnated pine as correlated to the take-up level2002In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 36, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    The mechanical performance of pine sapwood (pinus sylvestris), impregnated with linseed oil to different take-up levels, is evaluated using several test methods. SEM is used to study morphological changes following the impregnation procedure. The reduction of mechanical properties is attributed to a) localized cell wall damage in the ray region that facilitates longitudinal inter-cell split in L-R plane (macrocrack) initiation and propagation; b) submicroscopical cracking in the S1 sublayer that reduces the resistance to Mode I and Mode II inter-cell splitting at any location where the oil front has passed. Mechanical testing shows the following effect of the impregnation on failure a) the Mode I fracture toughness GIc in L-T and L-R planes, determined in DCB test, is significantly lowered with no significant difference in fracture resistance reduction in between planes; b) 3-point flexural test for specimen geometry leading to cracking in R-L and T-L planes show that the flexural strength as well as flexural modulus are reduced due to impregnation; c) 3-point flexural tests on longitudinal specimens used to determine the impregnation effect on longitudinal modulus EL and shear moduli GLT and GLR, reveal only minor changes. Fracture surfaces in mechanical tests are analyzed using SEM, and differences are explained by described microdamage mechanisms.

  • 16.
    Oksman, Kristiina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Improved interaction between wood and synthetic polymers in wood/polymer composites1996In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 30, no 3, p. 197-205Article in journal (Refereed)
    Abstract [en]

    This article describes the properties of wood polymer composites consisting of linear low density polyethylene (LLDPE) and wood flour (WF). In an attempt to improve the interfacial adhesion between the matrix and the filler, different compatibilizers were used. The interaction between polymer and wood were studied by comparing LLDPE/WF composites with composites when compatibilizer was added. The experimental measurements were conducted by impact and tensile strength testing and Scanning Electron Microscopy (SEM). The mechanical properties of the composites were improved with SEBS triblock copolymer modified with maleic anhydride and with the ionomer polymer, Surlyn, as compatibilizers. SEM fractography confirmed better adhesion between wood particles and LLDPE matrix when SEBS was present

  • 17.
    Pahlberg, Tobias
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Johansson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Thurley, Matthew
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Wood fingerprint recognition using knot neighborhood K-plet descriptors2015In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 49, no 1, p. 7-20Article in journal (Refereed)
    Abstract [en]

    In the wood industry, there is a wish to recognize and track wood products through production chains. Traceability would facilitate improved process control and extraction of quality measures of various production steps. In this paper, a novel wood surface recognition system that uses scale and rotationally invariant feature descriptors called K-plets is described and evaluated. The idea behind these descriptors is to use information of how knots are positioned in relation to each other. The performance and robustness of the proposed system were tested on 212 wood panel images with varying levels of normally distributed errors applied to the knot positions. The results showed that the proposed method is able to successfully identify 99–100 % of all panel images with knot positional error levels that can be expected in practical applications

  • 18.
    Papadopoulos, Antonios N
    et al.
    Department of Wood and Furniture Technology-Design, Technological Educational Institute of Karditsa.
    Avrimidis, Stavros H.
    Department of Wood Science, University of British Columbia, Vancouver.
    Elustondo, Diego
    The sorption of water vapour by chemically modified softwood: Analysis using various sorption models2005In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 39, no 2, p. 99-111Article in journal (Refereed)
    Abstract [en]

    The sorption data for Corsican pine wood chemically modified with a homologous series of linear chain carboxylic acid anhydrides was analysed using various models, namely, BET, Dent, Le and Ly, Hailwood and Horrobin, Nelson, and Henderson. Hailwood and Horrobin resulted in the more appropriate model to represent the equilibrium data of chemically modified wood. In the present study, the parameter representing the molecular weight of the dry cell wall in the Hailwood and Horrobin isotherm was perfectly correlated with the weight percentage gain of anhydride. A linear relation was proposed between these two parameters in order to fit all experimental isotherms (the results showed an r 2=0.993).

  • 19.
    Sandberg, Karin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Salin, Jarl-Gunnar
    Åbo Akademi University.
    Liquid water absorption in dried Norway spruce timber measured with CT scanning and viewed as a percolation process2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 1-3, p. 207-219Article in journal (Refereed)
    Abstract [en]

    Liquid flow in dried wood is complicated to study, since wood is a nonhomogeneous, hygroscopic-porous, anisotropic material. However, liquid flow is important to understand, since it has an influence on the durability of wood and on such processes like impregnation, drying, surface treatment, etc. In this study, simulations of liquid water absorption in wood as a fibre network, percolation, were compared with experimental water absorption in the longitudinal direction in spruce timber. With CT scanning, water distribution during liquid flow can be shown visually and measured by image processing. Liquid water absorption in end grain of spruce was measured with CT scanning after 1, 3, 7 and 14 days of liquid water absorption and shown as moisture content (MC) profiles in heartwood and sapwood. It was found that the amount of water absorbed could be expressed as a linear function of the square root of time. The slopes of the lines differed between sapwood and heartwood and also varied depending on the growth condition of the trees. The simulations according to the percolation method show generally good agreement with the measured results for sapwood

  • 20. Sundqvist, Bror
    et al.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Westermark, Ulla
    Determination of formic-acid and acetic acid concentrations formed during hydrothermal treatment of birch wood and its relation to colour, strength and hardness2006In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 40, no 7, p. 549-561Article in journal (Refereed)
    Abstract [en]

    Formation of benzyl esters from acetic and formic acids during heat treatment of birch at 160-200°C has been studied by gas chromatography. High concentrations of formic and acetic acids formed by the wood itself during hydrothermal treatment were found. The concentrations of acids increased with both treatment time and temperature. The maximum formic- and acetic acid concentrations found at 180°C and after 4 h of treatment performed in this work were 1.1 and 7.2%, based on dry-weight wood, respectively. The treated wood material was characterised by mechanical testing [bending tests perpendicular to the grain, modulus of rupture, modulus of elasticity, Brinell hardness, impact bending and colour measurements (CIE colour space)]. The experiments, where high concentration of acids was formed, showed severe losses in mass and mechanical strength. Indications of possible enhanced mechanical properties for the treated, compared with untreated birch wood were found around 180-200°C at short treatment times. This paper discusses possible degradation reactions coupled with the colour and mechanical properties in relation to acid formation, and suggestions for process optimisations.

  • 21.
    Thuvander, F.
    et al.
    Luleå tekniska universitet.
    Berglund, Lars A.
    Luleå tekniska universitet.
    A multiple fracture test for strain to failure distribution in wood1998In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 32, no 3, p. 227-235Article in journal (Refereed)
    Abstract [en]

    The tensile strain to failure of small wood samples is a desirable property in studies where the effect of small differences in microstructure on failure is of interest. However, the scatter in data is usually significant and only one data is obtained per specimen. For this reason, a new multiple fracture test for measurement of the strain to failure distribution was designed. Wood samples were bonded between two transparent PVC layers with higher strain to failure than the wood. Multiple fractures were then observed in single wood samples during tensile loading. This behavior is already utilized in tests in the field of synthetic composite materials. It was possible to conveniently register multiple fracture events as a function of strain by visual observation through the transparent PVC layers. The data were used to compare two different wood materials and to determine their Weibull distribution functions

  • 22.
    Thuvander, Fredrik
    et al.
    Luleå tekniska universitet.
    Kifetew, Girma
    Kungliga tekniska högskolan, KTH.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Modeling of cell wall drying stresses in wood2002In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 36, no 3, p. 241-254Article in journal (Refereed)
    Abstract [en]

    All applications of wood involve drying the material from the green state. The cell wall may be viewed as a laminate consisting of different layers. The layers have different orientations and therefore different moisture expansion characteristics. As a result, stresses will develop in the layers due to drying. Micromechanical models for fibre composite materials were used in combination with a laminate analogy in order to calculate these drying stresses in the cell wall layers S1, S2 and S3. Resulting stresses were very high. In reality viscoelastic effects will significantly reduce stresses at high moisture content. However, at lower moisture content irreversible cell wall damage is likely to form as a result of the stresses computed by the model.

  • 23.
    Thuvander, Fredrik
    et al.
    Luleå tekniska universitet.
    Wallström, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Berglund, Lars A.
    Luleå tekniska universitet.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Effects of an impregnation procedure for prevention of wood cell wall damage due to drying2001In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 6, p. 473-480Article in journal (Refereed)
    Abstract [en]

    Drying of wood may lead to readily observable macroscale cracks. Recently observations were made indicating that also at the level of cell walls, damage occurs due to drying. A method is presented where green wood is impregnated using a solution of water and a bulking compound such as glycerol. Tensile strength parallel to the grain for wood impregnated in the green state was compared with that for ordinary dried wood and for wood impregnated after drying. Data demonstrate significantly higher strength for wood impregnated in the green state. It is postulated that this is due to damage in the cell walls of non-impregnated wood where the damage is induced by the drying stresses. Support for this hypothesis is also presented in the form of fractography results. For wood impregnated in the green state, damage development during drying is limited. This is because the impregnating chemical (glycerol in the present case) in the cell wall substitutes some of the moisture and therefore limits the drying stresses.

  • 24.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Diffusion, size and location of added silver grains in the cell walls of Swedish pine, Pinus sylvestris2000In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 5, p. 403-415Article in journal (Refereed)
    Abstract [en]

    The size and location of silver particles in K-glycerate/AgNO3 impregnated Swedish pine, green wood as well as high temperature dried, have been studied using TEM micrographs. The diameter of the silver particles was found to be 2-20 nm in the impregnated green wood and as large as 1000 nm (major axis) for the ellipsoid-shaped silver clusters in the impregnated dried wood. Studying the projected area of the silver particles in impregnated green wood indicated that there are a lot of particles (40%) in the compound middle lamella with fewer particles in the S2 (6-8%), S1 (4%) and S3 (2%) layers. The average distance between the silver particles, 50 nm (S2-layer), in impregnated green wood shows that the impregnant is distributed in the cell wall at the microfibrilar level. Experimental results show that the fastest diffusion path into the cell wall is from the lumen over the pit membrane through the compound middle lamella and not from the lumen through the secondary wall layer S3.

  • 25.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Distribution of added chemicals in the cell walls of high temperature dried and green wood of Swedish pine, Pinus sylvestris2000In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 4, p. 327-336Article in journal (Refereed)
    Abstract [en]

    High temperature dried and green wood of Swedish pine was impregnated with glycerate and silver nitrate. TEM and STEM/EDS on ultramicrotomed specimens was used to reveal the location of silver in the cell wall. The silver was precipitated by a new method using silver nitrate impregnated after which the wood had been impregnated with potassium glycerate. A significant difference in the distribution of the silver was observed. In the green wood, there was a homogenous distribution of the impregnant compared to the dried specimens. The inhomogenous distribution in the dried specimens is believed to be the result of damage inside the wood cell walls which in turn will have a negative effect on dimensional stabilizing results. The darker compound middle lamella observed is believed to be an artefact.

  • 26.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Measurement of cell wall penetration in wood of water-based chemicals using SEM/EDS and STEM/EDS technique1999In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 33, no 2, p. 111-122Article in journal (Refereed)
    Abstract [en]

    The penetration of bulking chemicals (glycerol, PEG 200, PEG 1500 and pentaerythritol) into the cell wall of wood, Pinus sylvestris, has been studied. A number of different methods for determining the distribution of chemicals in the cell wall were used. Measurements of the increase in cell wall thickness showed that glycerol and PEG 200 resulted in greater cell wall bulking compared to PEG 1500 and pentaerythritol. Examination with SEM/EDS-linescan confirmed these results. However, the better resolution possible with the STEM/EDS-linescan revealed an inhomogenous distribution of the chemical in the cell wall. This is believed to be due to microcracks in the cell wall which are the result of the initial drying of the wood. This general damage to the cell wall could be the reason for the failure to find a stabilizing chemical and method.

  • 27.
    Wallström, Lennart
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindberg, Henrik
    Luleå tekniska universitet.
    Wood surface stabilization with polyethyleneglycol, PEG1995In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 29, no 2, p. 109-119Article in journal (Refereed)
    Abstract [en]

    The possibilities of interaction between wood, Pinus sylvestris, (60% RH) and potassium stained PEG 1500 (polyethyleneglycol) have been investigated using Scanning Electron Microscopy (EDS-analysis), dynamical mechanical techniques (DMTA) and X-ray diffraction (WAX). The EDS-analysis shows an even distribution of potassium in the cell wall. On the other hand the predicted cell wall swelling associated with PEG absorption is absent. This indicates that the method of staining PEG with potassium does not work. The DMTA-measurements show interaction on the molecular level between wood and PEG 1500. EDS-analysis, SEM- and WAX-investigations show free PEG in the impregnated specimens.

1 - 27 of 27
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