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  • 1.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Hansson, Lars
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    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.
    Bergsten, U
    et al.
    SLU.
    Lindeberg, Johan
    SLU.
    Rindby, A
    Evans, R
    Batch measurements of wood density on intact or prepared drill cores using x-ray microdensitometry2001In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 35, p. 435-452Article in journal (Refereed)
    Abstract [en]

    The performance of a batch scanning x-ray densitometer for measuring wood density without sample preparation, i.e., on intact drill cores, or on rectangular samples prepared from drill cores, was analysed. Effects of x-ray intensity, sample thickness and fiber direction, as well as extractives content, were evaluated for young (mainly sapwood) and old (mainly heartwood) wood from Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.). The x-ray power level used as standard (1.4 kW; 40 kV and 35 mA) seemed appropriate for the tested species and specimen thickness. The density of intact drill cores could be determined with a mean standard deviation of 1.6% for each sample, with a single machine run, if the cores were mounted with a fixed fiber direction and calibrations were made for each wood type. The corresponding precision for rectangular samples was 1.0%. Further improvements are attainable by using standard reference samples in each machine run and batch-wise analysis. For the chosen wood types and measurement technique, a sample thickness of 5 mm should give the best precision. However, for species with very narrow rings, thinner samples would improve the spatial resolution when ring boundaries are angled or curved. Extractives should be removed, especially for pine, but possibly also for spruce, if high precision in density determination is required.

  • 3.
    Esteban, Luis García
    et al.
    Ciudad Universitaria, Spain.
    Simón, Cristina
    Ciudad Universitaria, Spain.
    Fernández, Francisco García
    Ciudad Universitaria, Spain.
    Palacios, Paloma de
    Ciudad Universitaria, Spain.
    Martín-Sampedro, Raquel
    Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Spain.
    Eugenio, María Eugenia
    Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Spain.
    Hosseinpourpia, Reza
    Georg August University, Germany.
    Juvenile and mature wood of Abies pinsapoBoissie: sorption and thermodynamic properties2015In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 49, no 4, p. 725-738Article in journal (Refereed)
    Abstract [en]

    For industrial processes, it is important to study the hygroscopicity and thermodynamic properties of juvenile and mature wood. Samples of Abies pinsapo Boiss. collected in the natural areas of the species in Spain were used to study these properties in both types of wood. The equilibrium moisture contents were obtained, and the 15, 35 and 50 °C isotherms were plotted following the Guggenheim–Anderson–Boer–Dent model. The thermodynamic parameters were calculated using the integration method of the Clausius–Clapeyron equation. Chemical analyses, infrared spectra and X-ray diffractograms were applied to assess chemical modifications and possible changes in the cell wall structure. The chemical composition of the mature wood shows a decrease in the lignin and hemicelluloses content and an increase in the extracts and α-cellulose. The sorption isotherms for the three temperatures studied are higher in the mature wood than in the juvenile wood. Causes of this include the higher content of α-cellulose, the higher crystallinity index and the shorter crystallite length in the mature wood. No difference was found between the juvenile and mature wood in relation to the point of inflexion where the multilayer starts to predominate over the monolayer (approximately 30 %). In terms of the thermodynamic properties, the heat involved is greater in desorption than in adsorption, and more heat is involved in the mature wood than in the juvenile wood.

  • 4.
    Gamstedt, E. Kristofer
    et al.
    Uppsala University.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    de Borst, Karin
    University of Glasgow, UK.
    Mixed numerical–experimental methods in wood micromechanics2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 1, p. 183-202Article in journal (Refereed)
    Abstract [en]

    Mixed numerical–experimental methods are increasingly used in various disciplines in materials science, recently also in wood micromechanics. Having a relatively irregular microstructure, direct interpretation of mechanical tests is not always possible since structurally specific properties are quantified rather than general material properties. The advent of combined numerical–experimental methods unlocks possibilities for a more accurate experimental characterization. A number of examples of mixed methods pertaining to both emerging experimental techniques and physical phenomena are presented: nano-indentation, moisture transport, digital-image correlation, dimensional instability and fracture of wood-based materials. Successful examples from other classes of materials are also presented, in an attempt to provide some ideas potentially useful in wood mechanics. Some general pit-falls in parameter estimation from experimental results are also outlined.

  • 5.
    Hosseinpourpia, Reza
    et al.
    Georg-August-University Göttingen, Germany.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Mai, Carsten
    Georg-August-University Göttingen, Germany.
    Dynamic vapour sorption of wood and holocellulose modified with thermosetting resins2016In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 50, no 1, p. 165-178Article in journal (Refereed)
    Abstract [en]

    Micro-veneers of wood and holocellulose (HC) were modified with the thermosetting resins phenol formaldehyde and melamine formaldehyde. The dynamic water vapour sorption of the modified and untreated veneers was studied in a dynamic vapour sorption apparatus to assess the effects of resin modification. The adsorption of wood and HC as well as the desorption of wood was little affected by the modification in the low relative humidity (RH) range but decreased in the RH range above 60–70 %. The desorption isotherm of HC, however, was increased in the RH range of 15–80 % due to modification. Resin modification gradually decreased the EMC ratio of wood and HC and also influenced the moisture increment, equilibrium time and sorption rate in RH range above 50–60 % RH for wood and above 70–80 % RH for HC. HC exhibited a clearly lower hysteresis than wood. Modification of wood slightly reduced hysteresis compared to untreated wood, but modification of HC clearly increased hysteresis about to the same extent as that of wood. This indicates that the stiffening effect of lignin and thermosetting resins reduces the flexibility of the HC matrix, which results in increased hysteresis.

  • 6.
    Hosseinpourpia, Reza
    et al.
    Georg-August-University Göttingen.
    Mai, Carsten
    Georg-August-University Göttingen.
    Mode of action of brown rot decay resistance of acetylated wood: resistance to Fenton’s reagent2016In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 50, no 2, p. 413-426Article in journal (Refereed)
    Abstract [en]

    Acetylation is known to enhance the resistance of wood to brown rot fungi. As initial decay by some brown rot fungi is assumed to be caused by the Fenton reaction, pine micro-veneers acetylated to various weight percent gains (WPG) were exposed in a solution containing iron ions and hydrogen peroxide, i.e., Fenton’s reagent. Mass loss and tensile strength loss as well as the decomposition of hydrogen peroxide within the incubation time decreased with increasing WPG of the veneers. Incubation of untreated and acetylated veneers in acetate buffer containing ferric ions without H2O2 revealed that the modification strongly reduced the uptake of Fe ions by the wood cell wall. FT-IR analysis indicated oxidation of the unmodified control veneers but did not show predominant decay of specific cell wall components. Spectra of acetylated veneers did not reveal any significant changes induced by Fenton’s reagent. It was concluded that one possible reason for the enhanced resistance of acetylated wood to the Fenton reaction could be the reduced or almost completely prevented uptake of Fe ions by the wood cell wall.

  • 7.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Briggert, Andreas
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Säll, Harald
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Growth layer and fibre orientation around knots in Norway spruce: a laboratory investigation2018In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 1, p. 7-27Article in journal (Refereed)
    Abstract [en]

    The strength of structural timber largely depends on the occurrence of knots and on the local material directions in the surroundings of such knots. There is, however, a lack of methods for establishing a full dataset of the local material directions. The present research aims at the development and application of a laboratory method to assess the geometry of growth layers and the orientation of fibres in a high-resolution 3D grid within wood specimens containing knots. The laboratory method was based on optical flatbed scanning and laser scanning, the former resulting in surface images and the latter, utilizing the tracheid effect, resulting in in-plane fibre angles determined in high-resolution grids on scanned surfaces. A rectangular solid wood specimen containing a single knot was cut from a tree in such a way that it could be assumed that a plane of symmetry existed in the specimen. By splitting the specimen through this plane through the centre line of the knot, two new specimens with assumed identical but mirrored properties were achieved. On one of the new specimens, the longitudinal-radial plane was subsequently scanned, and the longitudinal–tangential plane was scanned on the other. Then, by repeatedly planing off material on both specimens followed by scanning of the new surfaces that gradually appeared, 3D coordinate positions along different growth layers and 3D orientation of fibres in a 3D grid were obtained. Comparisons between detected fibre orientation and growth layer geometry were used for the assessment of the accuracy obtained regarding 3D fibre orientation. It was shown that the suggested method is well suited to capture growth layer surfaces and that it provides reliable information on 3D fibre orientation close to knots. Such knowledge is of great importance for understanding the properties of timber including knots. The quantitative data obtained are also useful for calibration of model parameters of general models on fibre orientation close to knots.

  • 8.
    Kielmann, B
    et al.
    Georg-August-University Göttingen, Germany.
    Adamopoulos, Stergios
    Georg-August-University Göttingen, Germany.
    Militz, H
    Georg-August-University Göttingen, Germany ; Technological Educational Institute of Larissa, Greece.
    Koch, G
    Federal Research Institute of Rural Areas, Forestry and Fisheries (vTI), Germany.
    Mai, C
    Georg-August-University Göttingen, Germany.
    Modification of three hardwoods with an N-methylol melamine compound and a metal-complex dye2014In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 48, no 1, p. 123-136Article in journal (Refereed)
    Abstract [en]

    This study evaluated the combined modification and staining of ash, beech and maple wood with a low molecular weight N-methylol melamine compound (NMM) and a metal-complex dye. Wood samples were treated with aqueous solutions of 10, 20 and 30 wt% NMM and 5 wt% of the dye. The treatment caused the fixation of the water-soluble dye by the NMM resin. Vacuum pressure impregnation of unsealed wood blocks did not result in different solution uptake and weight percent gain after curing among the three species, but sealing of the surfaces of the wood blocks to allow penetration only into one direction revealed easiest penetrability of beech followed by maple and ash. UV micro-spectrophotometry and light microscopy indicated that NMM was partly deposited in the cell wall and partly in the lumens. Penetration of the metal-complex dye was shown by means of X-ray micro-analysis (SEM–EDX). The study shows that a combined resin modification and staining of the three wood species tested is possible and that NMM causes fixation of the water-soluble dye.

  • 9. Kifetew, G
    Application of the deformation field measurement method to wood during drying1996In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 30, no 6, p. 455-462Article in journal (Refereed)
    Abstract [en]

    A method for measuring the deformation field on small wood specimens during drying using a regular grid pattern is described. Preliminary results showed a large variation in surface deformation in the range 0% to 6.2%. To explain the transverse deformation field on the radial face, the different deformation ranges were related to the macrostructure of wood. The latewood region was responsible for the higher deformation field range, while the earlywood layer explained the lower strain held range. The method described could provide important information regarding the history of a specimen which has not so far considered in previous studies on the dynamic behaviour of wood.

  • 10. Kifetew, G
    et al.
    Lindberg, H
    Wiklund, M
    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 on earlywood-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.

  • 11. Kifetew, G
    et al.
    Thuvander, F
    Berglund, L
    Lindberg, H
    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 pine Pinus 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.

  • 12.
    Larsen, Finn
    et al.
    Technical University of Denmark, Denmark.
    Ormarsson, Sigurdur
    Technical University of Denmark, Denmark.
    Numerical and experimental study of moisture-induced stress and strain field developments in timber logs2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 4, p. 837-852Article in journal (Refereed)
    Abstract [en]

    When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To obtain a better understanding of how stresses develop during climatic variations, the field histories of stresses (and strains) in cross sections in their entirety need to be studied. The present paper reports on experiments and numerical simulations concerned with analysing the development of strains and stresses during the drying of 15-mm-thick discs of Norway spruce timber log. The samples were dried at 23 °C and relative humidity of 64 % from a green condition to equilibrium moisture content. The moisture gradient in the longitudinal direction was minimised by use of thin discs simplifying the moisture history of the samples studied. The strain field history was measured throughout the drying process by use of a digital image correlation system. Numerical simulations of the samples agreed rather well with the experimental strain results obtained. The stress results also indicated where in the cross section and when fractures could be expected to occur during drying. More optimal drying schemes showed markedly reduced stress generation.

  • 13.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Oscarsson, Jan
    SP Technical Research Institute of Sweden, Videum Science Park, 351 96, Växjö, Sweden.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Källsner, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Prediction of timber bending strength on basis of bending stiffness and material homogeneity assessed from dynamic excitation2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 4, p. 667-683Article in journal (Refereed)
    Abstract [en]

    The potential of utilizing resonance frequencies corresponding to edgewise bending modes for predicting the bending strength of timber is investigated. The research includes measurements of axial and transversal resonance frequencies, laboratory assessment of density, static bending stiffness and bending strength of 105 boards of Norway spruce of dimensions 45×145×3600 mm. It is shown that Eb,1, (MOE based on the resonance frequency of the first bending mode) gives a higher coefficient of determination to the bending strength than what Ea,1 (MOE based on the first axial resonance frequency) does. It is also shown that resonance frequencies corresponding to higher bending modes can be used in the definition of a new indicating property, the measure of inhomogeneity (MOI). This is a scalar value representing the lack of fit between the true, measured resonance frequencies and the expected (assuming homogeneity) resonance frequencies of a board. The results show that using the MOI as a third indicating property, in addition to Eb,1 and density, increases the coefficient of determination with respect to bending strength from R2=0.69 to R2=0.75.

  • 14.
    Ormarsson, Sigurdur
    et al.
    Lund University,.
    Dahlblom, O.
    Lund University.
    Petersson, H.
    Chalmers University of Technology.
    A numerical study of the shape stability of sawn timber subjected to moisture variation: Part 1: Theory1998In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 32, no 5, p. 325-334Article in journal (Refereed)
    Abstract [en]

    A three-dimensional theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed, assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate and the mechano-sorption strain rate. Wood is assumed to be an orthotropic material with large differences between the longitudinal, radial and tangential directions in the properties found. The influence of the growth rings, the spiral grain and the conical shape of the log on the orthotropic directions in the wood is taken account of in the model. A finite element formulation is used to describe the deformation process and the stress development during drying.

  • 15.
    Ormarsson, Sigurdur
    et al.
    Technical University of Denmark.
    Dahlblom, Ola
    Johansson, Marie
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Finite element study of growth stress formation in wood and related distortion of sawn timber2009In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 43, p. 387-403Article in journal (Refereed)
    Abstract [en]

    Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.

  • 16.
    Ormarsson, Sigurdur
    et al.
    Lund University.
    Dahlblom, Ola
    Lund University.
    Petersson, Hans
    Chalmers University of Technology.
    A numerical study of the shape stability of sawn timber subjected to moisture variation: Part 2: Simulation of drying board1999In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 33, no 5, p. 407-423Article in journal (Refereed)
    Abstract [en]

    A theory for analysing the shape stability of sawn timber was implemented in a finite element program. To illustrate the types of results that can be obtained, the behaviour of a board during drying was simulated. The simulation yields information about unfavourable deformations and stresses during the drying process. To investigate factors that influence drying deformations, a parameter study was performed in which the influence of different constitutive models and different material parameters was studied. In addition, the influence of the spiral grain angle was examined.

  • 17.
    Ormarsson, Sigurdur
    et al.
    Chalmers University of Technology.
    Dahlblom, Ola
    Lund University.
    Petersson, Hans
    Chalmers University of Technology.
    A numerical study of the shape stability of sawn timber subjected to moisture variation: Part 3: Influence of annual ring orientation2000In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 34, no 3, p. 207-219Article in journal (Refereed)
    Abstract [en]

    Numerical simulations were performed to investigate how the annual ring orientation affects the shape stability of sawn timber. The influence of radial variations in the basic properties and the spiral grain is also studied. The knowledge obtained can contribute to more effective use of the raw material through allowing boards having properties that would yield bad shape stability to be sorted out. Possibilities for improving shape stability through gluing pieces of wood together are examined as well.

  • 18.
    Oscarsson, Jan
    et al.
    SP Technical Research Institute of Sweden, Videum Science Park, 351 96, Växjö, Sweden .
    Olsson, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Strain fields around knots in Norway spruce specimens exposed to tensile forces2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 4, p. 593-610Article in journal (Refereed)
    Abstract [en]

    Two-dimensional strain fields around knots in two Norway spruce specimens subjected to tension loading were detected using a contact-free measuring technique based on white-light digital image correlation. The first specimen included a traversing edge knot and the second one a centric knot. The development of strain fields as function of load level were measured by consecutive cyclic load tests in which one side of a specimen was studied during each test. The objectives were to examine to what extent the strain fields could be detected, to investigate the correlation between strain fields measured on different sides of a specimen, and to analyse the strain distributions around the knots. The results show that the applied technique is very useful for catching both overall and detailed information about the behaviour of knots in wood members exposed to loading. Clear wood defects that could not have been detected by neither visual inspection nor scanning were observed and conclusions could be drawn regarding release of internal stresses. The correlations between strain fields on different sides of the specimens were excellent and the correspondence between measurement results and comparative finite element calculations was surprisingly good, considering the fact that the employed FE models were fairly simple.

  • 19.
    Sint, KM
    et al.
    Georg-August-University Göttingen, Germany.
    Adamopoulos, Stergios
    Georg-August-University Göttingen, Germany ; Technological Educational Institute of Larissa, Greece.
    Koch, G
    Federal Research Institute of Rural Areas, Germany.
    Hapla, F
    Georg-August-University Göttingen, Germany.
    Militz, H
    Georg-August-University Göttingen, Germany.
    Impregnation of Bombax ceiba and Bombax insigne wood with a N-methylol melamine compound2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 1, p. 43-58Article in journal (Refereed)
    Abstract [en]

    Methylated N-methylol melamine (NMM) is known for its ability to enhance physico-mechanical properties, anti-fungal ability, and hydrophobicity and was therefore used to impregnate two less used and non-durable wood species from Myanmar, Bombax ceiba and Bombax insigne. Solution uptake, weight percent gain and nitrogen content were increased by increasing melamine concentrations with B. ceiba always achieving higher values compared with B. insigne. According to the leaching results, a higher degree of condensation after curing as well as a better crosslinking of NMM could be obtained at higher temperatures. However, both curing temperatures used (90 and 120 °C) resulted in almost the same amount of nitrogen fixed in the cell wall. UV microspectrophotometry confirmed the penetration of the NMM into different morphological regions of wood tissues, which was again supported by the analysis of point measurement spectra of treated and untreated specimens.

  • 20. Thuvander, F
    et al.
    Kifetew, G
    Berglund, L A
    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.

  • 21.
    Wagner, Leopold
    et al.
    Vienna University of Technology, Austria.
    Almkvist, Gunnar
    Swedish University of Agricultural Sciences .
    Bader, Thomas K.
    Linnaeus University, Faculty of Technology, Department of Building Technology. Vienna University of Technology, Austria.
    Bjurhager, Ingela
    Uppsala University.
    Rautkari, Lauri
    Aalto University, Finland.
    Gamstedt, E. Kristofer
    Uppsala University.
    The influence of chemical degradation and polyethylene glycol on moisture-dependent cell wall properties of archeological wooden objects: a case study of the Vasa shipwreck2016In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 50, no 6, p. 1103-1123Article in journal (Refereed)
    Abstract [en]

    Cell wall measures allow for direct assessment of wood modification without the adverse effect of varying density and microstructure. In this study, cell wall properties of recent and archeological oak wood from the Vasa shipwreck were investigated for cell wall stiffness, hardness and creep with respect to effects of chemical degradation, impregnation with a preservation agent, namely polyethylene glycol, and moisture. For this purpose, nanoindentation tests were performed at varying relative humidity, leading to different moisture contents in the wood samples. Concurrently, microstructural and chemical characterization of the mate- rial was conducted. Impregnated and untreated recent oak wood showed a softening effect of both moisture and preservation agent at the wood cell wall level. On the contrary, increased stiffness was found for non-impregnated Vasa oak, which can be explained by aging-related modifications in cell wall components. These effects were counteracted by the softening effect of polyethylene glycol in the impregnated Vasa material, where a lower overall stiffness was measured. The reverse effect of the preservation agent and moisture, namely increased indentation creep of the cell wall material, was revealed. The loss of acetyl groups in the hemicelluloses explained the decreased hygroscopicity of the Vasa oak. In the impregnated Vasa oak, this effect seemed to be partly counteracted by the presence of low-molecular polyethylene glycol contributing to higher hygroscopicity of the cell wall. Thus, the higher overall sorptive capacity of the impregnated Vasa material, with respect to the non-impregnated material, was detected, which has resulted in a sorptive behavior similar to that of recent oak wood. The proposed approach requires only small amounts of material, making it especially suitable for application to precious historical wooden artifacts. 

  • 22.
    Xiao, Zefang
    et al.
    Georg-August-University of Gottingen, Germany.
    Xie, Yanjun
    Northeast Forestry University, Kina.
    Adamopoulos, Stergios
    Georg-August-University of Gottingen, Germany.
    Mai, Carsten
    Georg-August-University of Gottingen, Germany.
    Effects of chemical modification with glutaraldehyde on the weathering performance of Scots pine sapwood2012In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 46, no 4, p. 749-767Article in journal (Refereed)
    Abstract [en]

    Scots pine sapwood was treated with glutaraldehyde (GA) in aqueous solution using magnesium chloride as a catalyst in order to evaluate the durability towards weathering. Infrared spectroscopy suggested that GA treatment increased the photo-stability of lignin during artificial weathering of micro-veneers in a QUV over 168 h; photo-protection increased with increasing GA concentration. In comparison with the unmodified controls, GA-modified pine micro-veneer strips exhibited a lower tensile strength loss measured in a zero-span mode in the course of weathering. During 18 months of outdoor exposure, GA-modified pine wood boards exhibited a lower moisture content and water uptake than the unmodified ones. GA treatment also clearly restricted the penetration of blue stain fungi into deeper layers of wood. On the macroscopic scale, the surface of the GA-modified boards was significantly smoother due to less erosion, cracking and minor peeling of tracheids. Scanning electron microscopy further revealed that individual tracheids were detached from the cell compound and then washed away from the unmodified wood surface, whereas tracheids on surfaces of GA-modified wood remained in the tissue compound but displayed many axial and transversal cracks.

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