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  • 1.
    Adamopoulos, Stergios
    Aristotelian University, Greece.
    Flexural properties of black locust (Robinia pseudoacacia L.) small clear wood specimens in relation to the direction of load application2002In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 60, no 5, p. 325-327Article in journal (Refereed)
    Abstract [en]

    Values of pure moduli of elasticity (PMOE), experimental modulus of elasticity (MOE) in static bending and moduli of rigidity (GLR, GLT) were calculated in juvenile and mature black locust defect-free small wood specimens after loading in static bending alternately on true radial and tangential surfaces. For both juvenile and mature specimens, no significant differences (t-test, 95% probability level) were found between the radial and tangential moduli of elasticity and rigidity. Values of PMOE were found to be 27–32% higher than the corresponding values of MOE at the 15:1 span-to-depth ratio.

  • 2.
    Adamopoulos, Stergios
    Aristotelian University, Greece.
    Influence of hot-water extractives on radial and tangential shrinkage of black locust wood (Robinia pseudoacacia L.)2002In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 60, no 5, p. 377-378Article in journal (Refereed)
    Abstract [en]

    IntroductionRemoval of extractives increases the shrinkage and swelling of wood (Nearn 1955, Salamon and Kozak 1968, Cooper 1974, Taylor 1974). The effect of progressive extraction on the above properties has not been investigated much. In oak (Quercus conferta L.), a forest species rich in extractives, the shrinkage progressively increased with progressive extraction (Voulgaridis et al. 1980). In black locust (Robinia pseudoacacia L.), much of the main-stem volume is comprised of heartwood, characterized by the presence of dark yellow-brown extractives. While the extractives of black locust give the heartwood its distinctive color and decay resistance, they comprise only 6.2 to 8.3% of the dry weight of the main stem (Stringer 1992). Hot-water extractives range from 5.2 to 8.6% (Hart 1968, So et al. 1980). The present study was primarily undertaken to determine whether the progressive removal of hot-water extractives affects the radial and tangential shrinkage of black locust heartwood.

  • 3.
    Adamopoulos, Stergios
    et al.
    Georg-August-University Göttingen, Germany ; Technological Educational Institute of Larissa, Greece.
    Bastani, Alireza
    Georg-August-University Göttingen, Germany.
    Gascón-Garrido, Patricia
    Georg-August-University Göttingen, Germany.
    Militz, Holger
    Georg-August-University Göttingen, Germany.
    Mai, Carsten
    Georg-August-University Göttingen, Germany.
    Adhesive bonding of beech wood modified with a phenol formaldehyde compound2012In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 70, no 6, p. 897-901Article in journal (Refereed)
    Abstract [en]

    Untreated (controls) and phenol–formaldehyde (PF)-modified beech wood (10 and 25 % solid content) were glued with phenol resorcinol formaldehyde (PRF) and polyvinyl acetate (PVAc). Shear strength of PRF-bonded specimens was higher than that of PVAc-bonded ones under dry and wet conditions irrespective of the pre-treatment. Under dry conditions, only PVAc-bonded specimens exhibited reduction in shear strength due to PF-modification with 25 % PF concentration as compared to the controls. PF treated wood provided inferior bonding under wet conditions with the exception of 25 % PF concentration specimens glued with PRF adhesive. Modification with PF resulted in a decrease of adhesive penetration into the porous network of interconnected cells, especially at 25 % PF concentration.

  • 4.
    Adamopoulos, Stergios
    et al.
    Technological Educational Institute of Larissa, Greece.
    Milios, E.
    Democritus University of Thrace, Greece.
    Doganos, D.
    Democritus University of Thrace, Greece.
    Bistinas, I.
    Democritus University of Thrace, Greece.
    Ring width, latewood proportion and dry density in stems of Pinus brutia Ten2009In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 67, no 4, p. 471-477Article in journal (Refereed)
    Abstract [en]

    This study examined basic characteristics of stem wood produced in Pinus brutia Ten. reforestations in Northeastern Greece. Sixteen dominant trees growing at good and medium site qualities were felled at 14–22 years. Site quality classification was based on site quality surrogates and confirmed by using site index curves that were created for a neighbouring area. Discs were taken at three stem positions (base, middle, top) to study variations in ring width, latewood proportion and dry density. Generally, at both good and medium sites, ring width was found to increase towards the top of the stems while latewood proportion and dry density showed a negative relationship with stem height. Radial variability trends were similar at all heights, and at both sites, revealing a rapid increase for ring width in the first 3–6 annual rings followed by a decrease towards the bark, a gradual increase for latewood proportion and no specific change for dry density. Comparisons between wood material produced during the same growth period (2005–2001) showed statistically significant differences among sampling heights in all cases except for dry density in medium sites. At the base of the stems, mean ring width and dry density were significantly (P ≤0.05) higher at good sites (3.6 mm and 0.53 g/cm3) than at medium sites (3.0 mm and 0.50 g/cm3). However, the differences between the sites are of small magnitude and therefore have limited practical impact on wood processing. The availability of such data is useful in utilising small-dimension timber of brutia pine.

  • 5.
    Adamopoulos, Stergios
    et al.
    Technological Educational Institute of Larissa, Greece.
    Passialis, Costas
    Aristotle University, Greece.
    Relationship of the toughness and the modulus of elasticity in static bending of small clear spruce wood specimens2010In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 68, no 1, p. 109-111Article in journal (Refereed)
    Abstract [en]

    Unlike static bending, toughness is a mechanical property less commonly measured in clear wood. The paper presents results on the relationship of toughness and modulus of elasticity in static bending based on DIN standard tests on small, clear specimens of spruce, 2×2 cm2 in cross section.

  • 6.
    Adamopoulos, Stergios
    et al.
    Aristotle University, Greece.
    Voulgaridis, Elias
    Aristotle University, Greece.
    Dimensional changes of extracted and non-extracted small wood specimens of black locust (Robinia pseudoacacia L.)2003In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 61, no 4, p. 264-268Article in journal (Refereed)
    Abstract [en]

    From straight grained heartwood of black locust (Robinia pseudoacacia L.), specimens, 3 cm×3 cm in cross section and 0.5 mm (or 10 mm) in axial direction, were cut and used for the determination of dimensional changes and the rate of tangential swelling. Mean radial, tangential and axial shrinkage was 5.30%, 6.67% and 0.16%, respectively, while the coefficient of anisotropy was 1.26. Half of the specimens for the determination of the rate of tangential swelling were extracted for 48 h with distilled hot water. The tangential dimensional change and the time taken to attain half maximum swelling in air-dry and oven-dry specimens were assessed according to a common technique. Extractive removal resulted in an increase of the total magnitude of tangential swelling in both air-dry and oven-dry specimens. However, no significant differences in time taken to attain half maximum swelling between air-dry and oven-dry specimens were observed after extraction. The rate of tangential swelling was lower in air-dry specimens than in oven-dry specimens after 30 min of immersion in water when were non-extracted and after 5 min of immersion in water when were extracted. Extracted air-dry specimens had a greater rate of tangential swelling than non-extracted air-dry specimens and the same occurred for oven-dry specimens. Extraction resulted in a higher diffusion coefficient for air-dry specimens. The diffusion coefficient calculated for non-extracted air-dry specimens (0.901×10−4 cm2/min) showed that black locust is a difficult species to impregnate.

  • 7.
    Adamopoulos, Stergios
    et al.
    Aristotle University, Greece.
    Voulgaridis, Elias
    Aristotle University, Greece.
    Passialis, Costas
    Aristotle University, Greece.
    Variation of certain chemical properties within the stemwood of black locust (Robinia pseudoacacia L.)2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 5, p. 327-333Article in journal (Refereed)
    Abstract [en]

    From the bottom, middle, and top of three mature 35 to 37-year old black locust tree discs were cut and analysed to determine the variation within the stem of certain chemical properties. Hot-water extractive content was greater in heartwood than in sapwood, while the reverse occurred for the dichloromethane extractive content. Vertical stem analysis of hot-water extractives showed that they increased in heartwood but decreasedin sapwood from the bottom to the top of the stems while the reversal occurred for dichloromethane extractive content of sapwood. At the bottom and the middle of the stems, ash content was greater in sapwood than in heartwood, but at the top no difference was found between heartwood and sapwood. Ash content of both heartwood and sapwood was found to increase in the axial direction with respective values of 0.36% (bottom) and 0.76% (top) for heartwood and of 0.65% (bottom) and 0.76% (top) for sapwood. Ash analysis showed that considerable variations were found for the inorganic elements K and P being greater in sapwood than in heartwood. Heartwood was more acid than sapwood except for the top of the stems. Acidity mean values were found to increase from the bottom to the top of the stems in heartwood while they slightly decreased in sapwood. Total buffering capacity of heartwood was greater than that of sapwood and total buffering capacity of sapwood exhibited an inverse relationship to height. Very small acid equivalent values were determined only in sapwood. At the bottom, lignin content in heartwood (25.73%) was greater than in sapwood (18.13%). Lignin content of heartwood decreased from 25.73% at the bottom to 18.33% at the top, while that of sapwood was 18.13% at the bottom, 21.42% at the middle and 19.64% at the top.

  • 8.
    Adamopoulos, Stergios
    et al.
    Georg-August-University Goettingen, Germany ; Technological Educational Institute of Larissa, Greece.
    Xie, Yanjun
    Georg-August-University Goettingen, Germany.
    Militz, Holger
    Georg-August-University Goettingen, Germany.
    Distribution of blue stain in untreated and DMDHEU treated Scots pine sapwood panels after six years of outdoor weathering2011In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 69, no 2, p. 333-336Article in journal (Refereed)
    Abstract [en]

    Surface coating and bulk treatment of wood are two effective measures which can, individually or conjointly, protect exterior wood from deterioration. This paper reports on the blue stain attack in coated wood, untreated and modified with DMDHEU, after six years of natural exposure.

  • 9.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology.
    Sehlstedt-Persson, Margot
    Luleå University of Technology.
    Morén, Tom
    Luleå University of Technology.
    Development of a new rapid method for mould testing in a climate chamber: preliminary tests2013In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 71, no 4, p. 451-461Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to develop fast, simple and robust solid wood mould testing methods for the use in small-scale laboratory tests. The objective was to investigate mould susceptibility of different wood materials within the batches. The proposed method is based on natural contamination of non-sterile surfaces in climates conducive to mould growth. For this purpose, a climate chamber with regulated temperature and relative humidity was used. The conditioning chamber was divided into upper and lower chamber by a thin layer of stainless steel placed horizontally above the fan to minimise air circulation to the sample in the upper compartment. Mould-infected samples from outdoor tests were used as a source of mould inocula, and test trials were conducted on Scots pine (Pinus sylvestris L.) sapwood. Samples were suspended from the top of the upper chamber, and the chamber was exposed to different temperature and humidity levels. Severe mould infestation was observed after 12–14 days of incubation. Visual mould rating was then performed. Regardless of some constraints, this test method was very simple, fast, and effective. More importantly, unlike other test methods, it closely models mould infestation as it would occur under natural condition.

  • 10.
    Akter, Shaheda T.
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Bader, Thomas K.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Experimental assessment of failure criteria for the interaction of normal stress perpendicular to the grain with rolling shear stress in Norway spruce clear wood2020In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 78, p. 1105-1123Article in journal (Refereed)
    Abstract [en]

    The anisotropic material behavior of wood, considered as a cylindrically orthotropic material with annual rings, leads to several different failure mechanisms already under uniaxial stresses. Stress interaction becomes important in the engineering design of structural elements and is often predicted by failure criteria based on uniaxial properties. The prediction quality of failure criteria has been assessed with longitudinal shear stress interaction, though less is known on rolling shear stress in interaction with stress perpendicular to the grain. The study aims at investigating the corresponding mechanical behavior of Norway spruce (Picea abies) clear wood by validating failure envelopes for stress combinations in the cross-sectional plane, based on experimental investigations. For this purpose, a test setup that controls the stress interaction and loading of clear wood along pre-defined displacement paths needed to be developed. Experimentally defined failure states could then be compared to failure surfaces predicted by the phenomenological failure criteria. Material behavior was quantified in terms of stiffness, strength, and elastic and post-elastic responses on dog-bone shaped specimens loaded along 12 different displacement paths. A comparison with failure criteria for two nominal compressive strain levels showed that a combination of failure criteria would be required to represent the material behavior and consider the positive effect of compressive stresses on the rolling shear strength. The findings of this work will contribute to studying local stress distribution of structural elements and construction details, where stress interactions with rolling shear develop.

  • 11.
    Alfredsen, Gry
    et al.
    Norwegian Forest and Landscape Institute, Norway.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Dibdiakova, Janka
    Norwegian Forest and Landscape Institute, Norway.
    Filbakk, Tore
    Norwegian Forest and Landscape Institute, Norway.
    Bollmus, Susanne
    Georg-August-University of Göttingen, Germany.
    Hofstetter, Karin
    Vienna University of Technology, Austria.
    Thermogravimetric analysis for wood decay characterisation2012In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 70, no 4, p. 527-530Article in journal (Refereed)
    Abstract [en]

    The paper focuses on the use of thermogravimetric analysis (TGA) as a fast method for estimating the change of lignocellulosic materials during fungal degradation in laboratory trials. Traditionally, evaluations of durability tests are based on mass loss. However, to gain more knowledge of the reasons for differences in durability and strength between wooden materials, information on the chemical changes is needed. Pinus sylvestris sapwood was incubated with the brown rot fungusGloeophyllum trabeum and the white rot fungus Trametes versicolor. The TGA approach used was found to be reproducible between laboratories. The TGA method did not prove useful for wood deteriorated by white rot, but the TGA showed to be a convenient tool for fast estimation of lignocellulosic components both in sound wood and wood decayed by brown rot.

  • 12.
    Amiandamhen, Stephen
    et al.
    Stellenbosch University, South Africa.
    Montecuccoli, Zeno
    Stellenbosch University, South Africa.
    Meincken, Martina
    Stellenbosch University, South Africa.
    Barbu, Marius
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Phosphate bonded wood composite products from invasive Acacia trees occurring on the Cape Coastal plains of South Africa2018In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 76, no 2, p. 437-444Article in journal (Refereed)
    Abstract [en]

    The feasibility of manufacturing phosphatebonded wood composite board products from four locallyoccurring invasive acacia tree species (Acacia cyclops, A.saligna, A. mearnsii and A. longifolia) was studied usinga formulated magnesium oxide (MgO) and monopotassiumphosphate (KH2PO4) binder system. The optimizationfor the manufacturing process was studied using a centralcomposite statistical design, whereupon the following factorswere considered, i.e. KH2PO4:MgO ratio, the fly ashcontent as partial replacement for the binder and the woodcontent as a ratio of wood to the total inorganic content.A fitted response surface plot was used to show the effectof the main factors and their interactions on the measuredboard properties. A response surface model was developedto predict the parameters leading to the best board properties.All physical properties evaluated met or exceededthe minimum requirements for low density particleboards.The results showed that the variables considered have significanteffects on the physical properties of the boards.The optimum composite manufacturing process for makingdurable products within the scope of the studied specieswas found to be a KH2PO4/MgO ratio of 1.66, an ashcontent of 2.7% and a wood/inorganic ratio of 0.96 for theselected wood species.

  • 13.
    Bastani, Alireza
    et al.
    Georg-August-University Göttingen, Germany.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Militz, Holger
    Georg-August-University Göttingen, Germany.
    Gross adhesive penetration in furfurylated, N-methylol melamine-modified and heat-treated wood examined by fluorescence microscopy2015In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 73, no 5, p. 635-642Article in journal (Refereed)
    Abstract [en]

    This study investigated the radial penetration of three conventional cold-set wood adhesives [emulsion polymer isocyanate (EPI), poly (vinyl acetate) (PVAc), one-component polyurethane (PU)] into various degrees of furfurylated and N-methylol melamine-modified (NMM) Scots pine, and heat-treated Scots pine and beech based on measurements of effective (EP) and maximum penetration (MP) from microscopic observations. EP of EPI adhesive decreased after modification with higher concentration of furfuryl alcohol while an improved penetration was recorded for PVAc into furfurylated wood. A deeper penetration was observed for all adhesives into wood treated with lower concentration of furfuryl alcohol. The EP of EPI and PU adhesives reduced after NMM treatment but it increased in the case of PVAc. In spite of reduction of EP of PU after NMM treatment, it represented a deeper penetration among all adhesives possibly due to its lower molecular weight. For Scots pine, increasing the treatment temperature improved EP of all adhesives while for beech, the EP of PU and PVAc increased largely in the case of samples treated at 195 °C. Visual analysis of fluorescence microscopy pictures provided more detailed information on modality of penetration. The results are useful for understanding the interaction among common adhesives and modified materials, and can be used in future research to explain the bonding behavior of modified wood.

  • 14.
    Bastani, Alireza
    et al.
    Georg-August-University Göttingen, Germany.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Militz, Holger
    Georg-August-University Göttingen, Germany.
    Water uptake and wetting behaviour of furfurylated, N-methylol melamine modified and heat-treated wood2015In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 73, no 5, p. 627-634Article in journal (Refereed)
    Abstract [en]

    This study reports on the water uptake (WU) and wetting properties of different modified wood materials; furfurylated and N-methylol melamine (NMM) modified Scots pine, and heat-treated (Vacu3 method) Scots pine and beech. All modifications caused a substantial reduction in WU in the longitudinal, tangential and radial directions both after short (24 h) and long contact times (168, 336 h) with a saturated sponge. The water uptake coefficient (w t ) was reduced by approximately 71–89 % in furfurylated wood, with the higher weight percent gain (WPG) providing a slightly greater reduction. The reduction in WU was not found to depend on the NMM solid content. The NMM treatment had the maximum effect on the reduction of tangential w t by 80–84 % and was much smaller in the longitudinal direction (31–68 %). The treatment temperature of 195 °C gave lower WU values than treatment at 210 °C, and the only exception was the radial direction of Scots pine. The longitudinal w t of heat-treated beech represented the highest reduction by 81–89 %, while radial w t was less affected in both species. Sessile drop apparent contact angles for water and diidomethane and corresponding surface energies on planed tangential and radial wood surfaces revealed an increased hydrophobicity and reduced polarity of modified wood. Furfurylated and NMM modified tangential surfaces had a higher increase of apparent contact angles than the radial surfaces but this was not observed in the case of heat treatment. Heat-treated wood showed reduced wetting of surfaces only with water. Apparent contact angles did neither differ with treatment temperature nor with the NMM resin load. The disperse component of surface energy was slightly increased by 20 % maximum in modified wood, while the polar components showed a dramatic decrease by −30 to −90 % with no major differences among treatments and intensities, and between surfaces. The results provide a better understanding of the hygroscopic behaviour of modified wood, which might be useful to predict its adhesion with various polymers such as glues, coatings and paints.

  • 15.
    Briggert, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Three-dimensional modelling of knots and pith location in Norway spruce boards using tracheid-effect scanning2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 5, p. 725-739Article in journal (Refereed)
    Abstract [en]

    Knots and the orientation of fibres in timber are decisive for the stiffness and strength of boards. Due to large property variations between members, strength grading is necessary. High resolution information of the orientation of fibres, both on surfaces and within members, would enable development of more accurate grading methods than those available today. A step towards three-dimensional (3D) models of the fibre orientation of the entire board volume is the establishment of 3D knot models based on scanning. The light from a dot laser illuminating the surface of a softwood board will, due to the tracheid effect, spread more along the fibres than across resulting in the dot entering an elliptical shape. In this investigation both the shape of the ellipse and the direction of its major axis were used to estimate the 3D fibre orientation on board surfaces. Knot surfaces were identified where the angle between the estimated 3D fibre direction and an approximated direction of the board’s pith exceeded a threshold value. By means of algorithms based on polar coordinates, knot surfaces which belonged to the same physical knot visible on different sides of the board were identified and as a result the position, orientation and volume of each knot were determined. Based on this information, a more accurate position of the board’s pith along the board was calculated. The established models showed good agreement with physical boards. The models constitute a promising starting point for further development of strength grading methods based on tracheid-effect scanning.

  • 16.
    Cristina, Simón
    et al.
    Technical University of Madrid, Spain.
    Francisco, García Fernández
    Technical University of Madrid, Spain.
    Luis, García Esteban
    Technical University of Madrid, Spain.
    Paloma, de Palacios
    Technical University of Madrid, Spain.
    Hosseinpourpia, Reza
    University of Göttingen, Germany.
    Carsten, Mai
    University of Göttingen, Germany.
    Comparison of the saturated salt and dynamic vapor sorption methods in obtaining the sorption properties of Pinus pinea L.2017In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 75, no 6, p. 919-926Article in journal (Refereed)
    Abstract [en]

    Several methods are available for obtaining the sorption isotherms of wood. Among these, the saturated salt and dynamic vapor sorption methods are the most frequently used  ones. For the first time, the hygroscopic response of wood obtained using these two methods is compared. This is done by determining the 35 and 50°C adsorption isotherms of juvenile and mature wood of Pinus pinea L. The hygroscopic behavior of the two types of wood is different, as the mature wood has a higher moisture content than the juvenile wood in the isotherms studied. Comparison of the static saturated salt method and dynamic vapor sorption shows few significant differences between the equilibrium moisture content obtained by each method during the adsorption process, both in a point by point comparison and in the comparison of quadratic polynomial forms of the Guggenheim Anderson-de Boer model. Moreover, in both methods the point of relative humidity from which multilayer sorption predominates over monolayer sorption is similar.

  • 17. Epmeier, Hannah
    et al.
    Johansson, Marie
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design. Byggteknik.
    Kliger, Robert
    Westin, Mats
    Bending creep performance of modified timber2007In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 65, no 5Article in journal (Refereed)
    Abstract [sv]

    The present study is a supplement to Epmeier and Kliger (2005), which investigated the effect of three different modification methods (acetylation, modification with methylated melamine resin and heat treatment in vegetable oil) on four material properties (density, modulus of elasticity (MOE), creep deflection and relative creep) and their inter-relations. In this study, another modification method (furfurylation) and four additional material parameters (“relative stiffness”, i.e. MOE/density, moisture content, change in moisture content and anti-creep efficiency) and their correlations are included. In addition, the creep curves were analysed to assess the development of bending creep performance. The properties were assessed by experimental work on 132 specimens of Scots pine sapwood with dimensions of 45×70×1100 mm3. It was found that modification leads to significant changes in material properties. Furfurylation increases density and reduces creep deflection, relative creep and moisture content. Modified timber tends to deflect and creep significantly less than untreated timber. However, the extent of reduction in relative creep appears not to be related to the extent of reduction in creep deflection. Initial deflection and/or modulus of elasticity are suitable for predicting the creep deflection of untreated and modified timber.

  • 18.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Petersson, Hans
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    An experimental and numerical study of the shape stability in glued columns2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 6, p. 423-429Article in journal (Refereed)
    Abstract [en]

    The study concerns the question of how the shape stability features of laminated columns of Norway spruce can be improved in terms of twist through optimal orientation of the individual laminates. Both experimental testing and numerical simulations were employed for evaluating twist stability. In all the columns studied, deformations were measured experimentally at different moisture content levels. A number of columns were also selected for numerical analysis in order to obtain a more thorough understanding of the twist behavior involved, their geometries and material properties of interest being determined. The experimental results showed the twist stability of the columns to be highly dependant upon the internal orientation of the individual laminates. It was also found that high quality columns in terms of shape stability could be manufactured, even when the center-core material has a strong twist tendency. The numerical simulations performed were in close agreement with the experimental results.

  • 19.
    Eriksson, John
    et al.
    Chalmers University of Technology.
    Ormarsson, Sigurdur
    Chalmers University of Technology.
    Petersson, Hans
    Chalmers University of Technology.
    Experimental study of shape stability in glued boards2004In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 62, no 3, p. 225-232Article in journal (Refereed)
    Abstract [en]

    An experimental study of shape stability in wooden glued boards was performed to verify certain results of particular interest obtained earlier in numerical simulations. Possibilities for achieving products of good shape stability by gluing boards together in an optimal way are discussed. Since twist is often the most serious form of distortion defects for the user, it was the main type of board deformation considered. Three types of glued products were tested. The experiments show clearly that glued boards can be produced that remain stable in shape when exposed to extreme variations in moisture. The results agree well with the numerical simulations performed earlier. It was found that initial twist could be reduced by proper application of pressure during gluing and that through gluing the occurrence of cracking defects on visible surfaces could be substantially reduced.

  • 20.
    Grubîi, Victor
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    An image processing algorithm for detection and analysis of slicing checks2021In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 79, no 4, p. 999-1006Article in journal (Refereed)
    Abstract [en]

    In this paper, a new method of measuring slicing checks for flat-sliced veneers was evaluated. The method is based on image analysis of veneer cross-sections, having highlighted the slicing checks using surface staining. The segmentation of the checks consists of global thresholding followed by some morphological operations. The outputs of the algorithm are check depth ratio and check frequency. The method was tested on flat-sliced oak (Quercus robur L. and Quercus petraea (Matt). Liebl.) veneers of different thicknesses (1.5, 2.5, 3.5 and 4.5 mm). Two distinct wood qualities and two different cutting directions (lengthwise-sliced and plain-sliced veneers) were evaluated. The algorithm performance resulted in an overall accuracy of 85% enabling an accessible method for relatively fast and accurate measurements of slicing check characteristics in lamella cross-sections. Regression analysis indicated a lack of fixed bias but the presence of proportional bias with the presented method. Check measurements indicate that by varying cutting parameters, it is possible to achieve desired check characteristics independent of slicing thickness. The semi-automated slicing check detection method could benefit further research and optimisation of the slicing process parameters and pave the way towards industrial quality control of slicing checks. The intended area of application is veneer-laminated products for interior use with the focus on veneered wood flooring.

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  • 21.
    Grubîi, Victor
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Johansson, Jimmy
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Dagbro, Ola
    Linnaeus University, The University Library.
    Measurement of surface-checking in sliced lamellae-based engineered wood flooring using digital image correlation2023In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 81, p. 1427-1436Article in journal (Refereed)
    Abstract [en]

    The lack of quantitative methods for surface-checking measurements may hinder improving the product characteristics of engineered wood flooring products built with sliced top-layer lamellae. This study evaluated the digital image correlation method for its applicability to surface checking measurements in engineered wood flooring elements with the top-layer comprising the plain sliced lamellae of oak (Quercus spp.) species with nominal thicknesses of 1.5–4.5 mm. The method involves observing full-field surface displacements of the sliced lamellae-based wood flooring specimens subjected to an accelerated sorption/desorption cycle. Detection of surface checks relates to discontinuities in surface displacements which can be interpreted from the output strain data as strain peak regions. Additionally, a surface-checking index was defined to describe the extension of surface-checking. Exposure tests were performed on a combination of coating presence and a different number of testing cycles. The main findings provide insight into the method procedure parameters, such as exposure duration, climate conditions, analysis parameters and recommendations regarding the digital image correlation setup settings and specimen manufacturing.

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  • 22.
    Habite, Tadios
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Automatic detection of pith location along norway spruce timber boards on the basis of optical scanning2020In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 78, p. 1061-1074Article in journal (Refereed)
    Abstract [en]

    Knowledge of annual ring width and location of pith in relation to board cross-sections, and how these properties vary in the longitudinal direction of boards, is relevant for many purposes, such as assessment of shape mechanical properties and stability of sawn timber. Hence, the present research aims at developing a novel method and an algorithm, based on data obtained from optical surface scanning, by which the pith location along the length of sawn timber boards can be determined accurately and automatically. The first step of the method is to identify clear wood sections, free of defects along boards. Then time-frequency analysis, using the continuous wavelet transform, is applied to detect the surface annual ring width distribution of the four sides of the selected sections. Finally, the pith location is estimated by comparing annual ring width distributions on the different surfaces, and assuming that annual rings are concentric circles with the pith in the centre. The proposed algorithm was applied to a total sample of 104 Norway spruce boards. Results indicate that optical scanners and the suggested automatic method allow for accurate detection of annual ring width and location of pith along boards. For a sample of boards with the pith located within the cross-section, a mean error of 2.6 mm and 3.2  mm in the depth and thickness direction, respectively, was obtained. For a sample of boards of which 60% with pith located outside the cross-section, a mean discrepancy between automatically and manually determined pith locations of 3.9 mm and 5.8 mm in depth and thickness direction, respectively, was obtained.

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  • 23.
    Hameed, Mahmood
    et al.
    University of Göttingen, Germany.
    Behn, Claus
    University of Göttingen, Germany.
    Roffael, Edmone
    University of Göttingen, Germany.
    Dix, Brigitta
    Wilhelm-Klauditz-Institut (WKI), Germany.
    Benetzbarkeit von Recyclingspänen und ,,frischen“ Holzspänen mit verschiedenen Bindemitteln: [Wettability of fresh chips (chips obtained directly from wood) and chips obtained by mechanical disintegration (M-chips) and  thermohydrolytical degredation (T-chips) of particleboards with UF-, PF-resins and binders based on PMDI (polymers of diphenylmethan diisocyanates)]2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 5, p. 394-395Article in journal (Refereed)
    Abstract [de]

    Nach allen Messzeiten zeigten die „frischen“ Holzspäne eine bessere Benetzung mit UF-Harz, PF-Harz und PMDI-Klebstoff als die Recyclingspäne. Besonders durch mechanische Zerklei- nerung gewonnene Recyclingspäne weisen eine geringere Benet- zung auf als die „frischen“ Holzspäne. Dies ist womöglich auf das den Recyclingspänen anhaftende Binde- und Hydrophopie- rungsmittel zurückzuführen. Die bessere  Benetzung der durch thermohydrolytischen Aufschluss gewonnenen Späne ist möglicherweise darauf zurückzuführen, dass während des Aufschlus- ses Teile des Bindemittels chemisch abgebaut und wasserlöslich werden. Die Benetzung der Recyclingspäne mit PMDI ist auffallend besser als mit UF- und PF-Harz. Dies ist unabhängig davon, ob die zu benetzenden Späne durch mechanische Zerkleinerung oder durch thermohydrolytischen Aufschluss gewonnen wurden.

  • 24.
    Hameed, Mahmood
    et al.
    Göttingen University, Germany.
    Behn, Claus
    Göttingen University, Germany.
    Roffael, Edmone
    Göttingen University, Germany.
    Dix, Brigitta
    Wilhelm-Klauditz-Institut (WKI), Germany.
    Wasserrückhaltevermögen von Recyclingspänen und von direkt aus Holz gewonnenen Spänen: [The water retention value of dried wood particle (obtained directly from wood) was determinated and compared with that of particle obtained by mechanical disintegration (M) or thermohydrolytical degredation (T-) of UF-bonded particleboards]2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 5, p. 390-391Article in journal (Refereed)
    Abstract [de]

    Das Wasserrückhaltevermögen nimmt mit Verlängerung der Lagerungsdauer im Wasser zu, wobei die Zunahme im Falle der mechanisch gewonnenen Recyclingspäne (M) besonders ausge- prägt und im Falle der thermohydrolytisch gewonnenen Späne (T) auffallend gering war. Gegenüber den direkt aus Holz gewonnenen Spänen weisen die mechanisch gewonnenen (M) besonders niedrige WRV-Werte auf. Durch die thermohydrolytische Behandlung der Späne, bei der erhebliche Teile des Bindemittels abgebaut werden, nimmtdas  Wasserrückhaltevermögen  deutlich  zu  und  erreicht  sogar Werte,  die  höher  liegen  als  die  von  „frischen“  Spänen.  Für den Abbau des UF-Harzes infolge der thermischen Behandlung spricht auch der gegenüber den mechanisch gewonnenen Spänen (M) niedrigere Stickstoffgehalt der thermohydrolytisch erzeug- ten Späne (T). Es ist nicht auszuschließen, dass während der ther- mohydrolytischen Behandlung ebenfalls Acetylgruppen im Holz abgespalten werden, die zu einer zunehmenden Hydrophilie der Späne führen. Auf einen Abbau von Acetylgruppen deutet der vergleichsweise hohe Gehalt an Essigsäure in den Kaltwasserex- trakten der Späne hin, der nach der Thermohydrolyse festgestellt wurde.

     

  • 25.
    Hameed, Mahmood
    et al.
    Georg-August-Universität Göttingen, Germany.
    Roffael, Edmone
    Georg-August-Universität Göttingen, Germany.
    Eindringtiefe verschiedener Bindemittel in Splintholz- und Kernholzspänen der Kiefer (Pinus sylvestris L.): [On the penetrability of various glues from sap- and heartwood of Pine (Pinus sylvesteis L.)]2001In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 58, no 6, p. 432-436Article in journal (Refereed)
    Abstract [en]

    Investigation of the penetrability of various glues [urea-formaldehyde resin (UP-resin), phenol-formaldehyde resin (PP-resin), melamine-urea-phenol-formaldehyde made of pine sapwood and heartwood revealed: the various glues penetrate chips from pine sapwood regardless of tree age, height of the sample studied and surface structure deeper than in those made of heartwood. The various glues more deeply penetrate chips from sapwood and heartwood of the 48-year-old pine than chips from sapwood and heartwood of the 124-year-old pine. The penetrability of various glues in chips from sapwood and heartwood of the 124-year-old pine increases with increasing height of the sample studied. Moreover,  glues penetrate sanded surfaces of chips from sapwood and heartwood of the 48- und the 124-year-old pine to a lesser extent than unsanded chip surfaces.

  • 26.
    Hameed, Mahmood
    et al.
    University of Göttingen, Germany.
    Roffael, Edmone
    University of Göttingen, Germany.
    Veränderung des Gehaltes an Ethanol-Cyclohexan-Extrakten von Kiefernsplint- und kernholzspänen infolge thermischer Behandlung: [Decrease in the extractive content (ethanol-cyclohexane) of Chips from sapwood and heartwood of Pine (Pinus sylvestris L.) due to thermal treatment]1999In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 57, no 4, p. 294-295Article in journal (Refereed)
    Abstract [en]

    Decrease in the extractive content (ethanol-cyclohexane) of Chips from sapwood and heartwood of Pine (Pinus sylvestris L.) due to thermal treatment at 103 °C. 

  • 27.
    Hameed, Mahmood
    et al.
    University of Göttingen, Germany.
    Roffael, Edmone
    University of Göttingen, Germany.
    Voruntersuchungen zum Einfluß der anatomischen Schnittrichtung auf die Verleimbarkeit des Splint- und Kernholzes der Kiefer (P. sylvestris L.): [Influence of anatomical Wood section on the Gluing of Sap- and heartwood of Pine (Pinus sylvestris L.) with UF-resins]2000In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 58, no 5, p. 306-307Article in journal (Refereed)
    Abstract [de]

    Die Scherfestigkeitswerte von UF-Harz-gebundenem Kiefernsplint- und -kernholz sind in Abhängigkeit von der anatomischen Richtung in der Tabelle 2 zusammengestellt. Daraus geht hervor:

    1. Die Scherfestigkeit der Klötzchenpaare  aus dem Splintholz ist höher als die des Kernholzes  in den entsprechenden anato-mischen Richtungen.

  • 28.
    Hameed, Mahmood
    et al.
    Georg-August-Universität Göttingen, Germany.
    Roffael, Edmone
    Georg-August-Universität Göttingen, Germany.
    Über die Benetzbarkeit von Splint- und Kernholz der Kiefer, Douglasie und Lärche: [On the Wettability of sapwood and heartwood of various woods pieces (Pine, Douglas fir and Larch)]1999In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 57, no 4, p. 287-293Article in journal (Refereed)
    Abstract [en]

    On the wettability of sapwood and heartwood of various woodspecies (Pine, Douglas fir and larch) Results have established that the wettability of sapwood from three woodspecies (Pine, Douglas ®r and Larch) on the cross, radial and tangential section with water and various glues (UF-resins, PF-resins, MUPF-resins and PMDI-adhesive) is better than that of heartwood. In most cases, the tangential section in sapwood and heartwood was less wettable than radial and cross sections. Using alkaline phenolic resins which cause wood to swell, wettability in the tangential direction was improved.

  • 29.
    Hu, Min
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, Anders
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    SP Tech Res Inst Sweden, SP Wood Technol, Växjö.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Local variation of modulus of elasticity in timber determined on the basis of non-contact deformation  measurement and scanned fibre orientation2015In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 73, no 1, p. 17-27Article in journal (Refereed)
    Abstract [en]

    During the last decade, the utilization of non-contact deformation measurement systems based on digital image correlation (DIC) has increased in wood related research. By measuring deformations with DIC systems, surface strain fields can be calculated. The first aim of this study concerns the possibility to detect detailed strain fields along the entire length of a wooden board subjected to pure bending and the potential of using such strain fields to determine a bending modulus of elasticity (MOE) profile along a board. Displacements were measured over 12 subareas along a flat surface of the board. For each such area, a separate local coordinate system was defined. After the transformation of locally measured coordinates to a global system, high resolution strain fields and a corresponding bending MOE profile were calculated. A second method in establishing bending MOE profiles is to use fibre angle information obtained from laser scanning and a calculation model based on integration of bending stiffness over board cross sections. Such profiles have recently been utilized for accurate strength grading. A second aim of this study was to investigate the accuracy of the bending MOE profiles determined using the latter method involving fibre angle information. Bending MOE profiles determined using the two described methods agree rather well. However, for some patterns of knot clusters, the local bending MOE, calculated on the basis of fibre angles and integration of bending stiffness, is overestimated. Hence, this research adds knowledge that may be utilized to improve the newly suggested strength grading method.

  • 30.
    Hu, Min
    et al.
    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.
    Modelling local bending stiffness based on fibre orientation in sawn timber2018In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 76, no 6, p. 1605-1621Article in journal (Refereed)
    Abstract [en]

    Strength of structural timber depends to a high degree on the occurrence of knots and on the local fibre deviation around such defects. Knowledge of local fibre orientation, obtained by laser scanning, has been utilized in a previously developed machine strength grading method, but rather crude assumptions regarding the fibre orientation in the interior of boards and a mechanical model that does not capture the full compliance of knotty sections were adopted. The purpose of the present study was to suggest and verify a model with which local bending stiffness can be predicted with high accuracy. This study included development of a model of fibre orientation in the interior of boards, and application of a three-dimensional finite element model that is able to capture the compliance of the board. Verification included bending of boards in the laboratory and application of digital image correlation to obtain strain fields comparable to those obtained by finite element simulation. Results presented comprise strain fields of boards subjected to bending and calculated bending stiffness profiles along boards. Comparisons of results indicated that the model suggested here was sufficient to capture the variation of local bending stiffness along boards with very high accuracy.

  • 31. KIFETEW, G
    THE EFFECT OF CROSS GRAIN ON THE TENSILE-STRENGTH OF PINUS-SILVESTRIS1992In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 50, no 10, p. 410-410Article in journal (Refereed)
  • 32.
    Lederer, Wolfgang
    et al.
    Vienna University of Technology, Austria.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Unger, Gerhard
    Vienna University of Technology, Austria.
    Eberhardsteiner, Josef
    Vienna University of Technology, Austria.
    Influence of different types of reinforcements on the embedment behavior of steel dowels in wood2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 6, p. 793-807Article in journal (Refereed)
    Abstract [en]

    In this study, dowel displacement-embedment stress relationships for different types, numbers and positions of reinforcements were experimentally investigated using a half-hole embedment test setup. Tests were performed parallel to the grain and in compression. Screws with a full or partial thread at different positions below the dowel and oriented strand board, plywood and nail plates on the loaded surfaces of the specimens, served as reinforcements. Test results underline their potential for an increased ductility of dowel-type connections. Comparison of reinforced and unreinforced specimens suggests premature failure of the unreinforced wood and consequently, an underestimation of the embedment strength as it is subsequently used in the design of dowel connections using the European yield model. This was supported by the investigation of cracks on the surface of the specimens visualized by means of a full-field deformation measurement system. It could be demonstrated that the strength in the embedment test even further increases if the reinforcement elements actively contribute to the load transfer. This property however cannot be considered as embedment strength, but represents the strength of a connection system. Test data is compared to the design equation in Eurocode 5.

  • 33.
    Olayiwola, H. O.
    et al.
    Stellenbosch Univ, South Africa.
    Amiandamhen, Stephen
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Meincken, M.
    Stellenbosch Univ, South Africa.
    Tyhoda, L.
    Stellenbosch Univ, South Africa.
    Characterization of unary precursor-based geopolymer bonded composite developed from ground granulated blast slag and lignocellulosic material residues2022In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 80, no 2, p. 377-393Article in journal (Refereed)
    Abstract [en]

    The excellent properties of geopolymer composites and their ability to be synthesized from various industrial waste streams make them promising green binders in wood-based composite manufacturing. The study characterized 100% slag unary precursor-based geopolymers reinforced with lignocellulosic material residue. The residue included sugarcane bagasse (SCB), Port Jackson (Acacia saligna) and Black wattle (Acacia mearnsii). The production process was established based on a mixed factorial design using Statistica 13.3. The factors considered included a curing pattern at 2 levels, sodium hydroxide concentration at 3 levels and lignocellulose material at 3 levels. Other parameters, such as precursor-activator ratio and sodium hydroxide-silicate ratio were constant. Statistical analysis revealed that curing temperature and sodium hydroxide concentration had a significant effect on the board properties and the addition of lignocellulose material improved the flexural strength. Curing at 40 degrees C influenced the reaction kinetics, enhanced microstructural properties, and produced a dense geopolymeric matrix which resulted in improved physical and mechanical properties. However, increasing the sodium hydroxide concentration beyond 6 M caused efflorescence and deteriorated the mechanical property of A. mearnsii and bagasse boards. Partial degradation of the fibres was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis, but the degraded products did not inhibit geopolymer setting. Scanning electron microscopy indicated a uniform board structure surrounded with micro crystals of calcium silicate hydrate (C-S-H). A. saligna boards produced with 6 M NaOH and cured at 40 degrees C met the technical specification of cement-bonded particleboards for outdoor applications according to the British standard EN 634-2.

  • 34.
    Olayiwola, Hamed
    et al.
    Stellenbosch University, South Africa.
    Amiandamhen, Stephen
    Stellenbosch University, South Africa .
    Meincken, Martina
    Stellenbosch University, South Africa.
    Tyhoda, Luvuyo
    Stellenbosch University, South Africa.
    Investigating the suitability of flyash/metakaolin-based geopolymers reinforced with South African alien invasive wood and sugarcane bagasse residues for use in outdoor conditions2021In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 79, p. 611-627Article in journal (Refereed)
    Abstract [en]

    The prevailing approach of total clearing to contain the spread of invasive plants (IP) in South Africa is generating enormouslignocellulosic wastes. This study examined the possibility of utilizing these wastes in the production of geopolymercomposites for use in outdoor environments. Untreated wood particles from Acacia mearnsii and A. longifolia, as well assugarcane bagasse residues, were incorporated into a geopolymer matrix developed from a binary precursor system of 75%fly ash and 25% metakaolin. The variables considered included precursor-activator ratio (PA), curing pattern (CP), lignocellulosicmaterial (LM), and alkali concentration (Mcon). The production process was established using a mixed factorialexperimental design. PA and CP were considered at 2 levels, while LM and MCon were considered at 3 levels. The densityof the boards exceeded 1 g cm−3 and are classified as high-density boards. The boards have comparable sorption propertiesto the cement-bonded particleboard according to the EN 632-2: 2007 standard. However, only A. longifolia boards producedwith 12 M NaOH and PA ratio of 2:1 met the mechanical strength requirements. Thermogravimetric analysis revealed thatthe boards are thermally stable. These results have shown that South African woody IPs are suitable for geopolymer woodcomposites, but there is still concern about their durability in the alkaline matrix. Scanning electron microscopy micrographsindicated mineralization of the particles and a partial degradation of hemicellulose was confirmed by Fourier transform infraredspectroscopy. Although the degraded components did not prevent geopolymer setting, there is need to further investigatethe extent and means of preventing degradation as this can derail the intended use of the product.

  • 35.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Briggert, Andreas
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Increased yield of finger jointed structural timber by accounting for grain orientation utilizing the tracheid effect2019In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 77, no 6, p. 1063-1077Article in journal (Refereed)
    Abstract [en]

    Finger joints in structural timber and glulam lamellae are often used to enable production of long members or to allow forre-connection of parts of a member after removal of weak sections. According to the European Standard EN 15497, certainmargins are required between knots and a finger joint in structural timber, which means that a considerable amount of clearwood becomes waste when finger joints are applied. The purpose of this paper was to investigate the possibility of reducingthe quantity of waste using different criteria for placement of finger joints. The investigation was based on (1) applicationof methods of colour scanning and tracheid effect scanning to detect knots and grain disturbance on board surfaces, and (2)interpretation of the requirements of EN 15497 regarding where finger joints may be placed. The standard’s requirementwhen producing finger joints is that the minimum distance between a knot and a finger joint is three times the knot diameter.The standard allows for the minimum distance between a knot and a finger joint to be shortened to 1.5 times the diameterwhen the local fibre orientation is measured. Utilizing this in simulated production resulted in reduction of waste from 7.4to 4.0%, when using finger joints simply to produce timber of long lengths. If finger joints are also used to re-connect partsof members after removal of weak sections, even larger savings can be made. Furthermore, it is concluded that knowledgeof fibre orientation obtained from scanning could be used not only to decrease the waste in production but also to increasethe quality of finger joints.

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  • 36.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Strength grading on the basis of high resolution laser scanning and dynamic excitation: a full scale investigation of performance2017In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 75, no 1, p. 17-31Article in journal (Refereed)
    Abstract [en]

    Effective utilization of structural timber requires grading and indicating properties (IPs) that are able to predict strength with high accuracy, and machines that are able to measure the underlying board properties at a speed that corresponds to the production speed of sawmills. The aim of this research is to assess the performance of a new machine strength grading method/procedure which was recently approved for the European market and to compare the performance of it with the performance of other available techniques. The novel method is based on laser scanning utilizing the tracheid effect, in combination with data from dynamic excitation and weighing. Applied indicating properties are defined in detail and results presented include assessment of the repeatability, coefficients of determination between IPs and grade determining properties, and examples of the yield achieved in different strength classes and combinations of strength classes. The investigated sample comprised more than 900 pieces of timber of Norway spruce (Picea abies) from Sweden, Norway and Finland. For this sample the coefficient of determination between the IP to bending strength and the measured bending strength was as high as R2 = 0.69, while the coefficient of determination between dynamic modulus of elasticity (MOE) and measured bending strength was R2 = 0.53. The yield in high strength classes, C35 and above, become about twice as high using the new method/procedure compared to machines using dynamic MOE as IP. A comparison of the performance with what have been presented for machines that are based on X-ray in combination with dynamic excitation indicates that the new method/procedure will surpass such machines as well. 

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  • 37.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Oscarsson, Jan
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology. SP Technical Research Institute of Sweden.
    Serrano, Erik
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Källsner, Bo
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Prediction of timber bending strength and in-member cross-sectional stiffness vartiation on basis of local wood fibre orientation2013In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 71, no 3, p. 319-333Article in journal (Refereed)
    Abstract [en]

    Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientation on face and edge surfaces of wooden boards was identified using high resolution laser scanning. In combination with knowledge regarding basic wood material properties for each investigated board, the grain angle information enabled a calculation of the variation of the local MOE in the longitudinal direction of the boards. By integration over cross-sections along the board, an edgewise bending stiffness profile and a longitudinal stiffness profile, respectively, were calculated. A new IP was defined as the lowest bending stiffness determined along the board. For a sample of 105 boards of Norway spruce of dimension 45 × 145 × 3600 mm, a coefficient of determination as high as 0.68-0.71 was achieved between this new IP and bending strength. For the same sample, the coefficient of determination between global MOE, based on the first longitudinal resonance frequency and the board density, and strength was only 0.59. Furthermore, it is shown that improved accuracy when determining the stiffness profiles of boards will lead to even better predictions of bending strength. The results thus motivate both an industrial implementation of the suggested method and further research aiming at more accurately determined board stiffness profiles.

  • 38.
    Olsson, Anders
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Schirén, Whokko
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Segerholm, Kristoffer
    Södra Skogsägarnas Ekonomiska Förening, Sweden.
    Bader, Thomas K.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Relationships between stiffness of material, lamellas and CLT elements with respect to out of plane bending and rolling shear2023In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 81, p. 871-886Article in journal (Refereed)
    Abstract [en]

    The use of cross laminated timber (CLT) for construction has increased greatly in recent years and the large volumes ofwood used for CLT means that it is important to optimize the use of the material. This requires relevant grading of lamellasand knowledge of relationships between lamella and CLT properties. In the present study, the relationship between dynamicaxial modulus of elasticity (MoE) of lamellas and the quasi-static out of plane bending stiffness of CLT is investigated. Bymeans of four-point bending test, it is shown that the effective quasi-static MoE of lamellas in CLT is only 2–6% lower thanthe average axial dynamic MoE of the individual lamellas. With this knowledge, producers of CLT can easily predict andcontrol the important out of plane bending stiffness of the produced CLT. Moreover, it is shown that effective rolling shearstiffness of layers in CLT can be accurately determined by means of digital image correlation performed in connection tofour-point bending of CLT, even for long test spans. For layers of lamellas of Scots pine of size 40 × 190 mm2the averageapparent or effective rolling shear modulus was determined to be 159 MPa. The average rolling shear modulus of the samematerial was determined to be 56 MPa.

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  • 39.
    Ormarsson, Sigurdur
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Gislason, Oskar V.
    Technical University of Denmark, Denmark.
    Moisture-induced stresses in glulam frames2016In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 74, no 3, p. 307-318Article in journal (Refereed)
    Abstract [en]

    Wood is a hygroscopic and moisture-sensitive material that seeks to achieve equilibrium moisture content (EMC) with its surrounding environment. For softwood timber structures exposed to variations in climate throughout their service life, this behaviour results in variable moisture-content gradients that cause moisture-induced stresses in the direction of and perpendicular to the fibres. Although Eurocode 5 (EC5) states that moisture-induced stresses should be considered, they are often not adequately dealt with in building design due to the difficulties in predicting the stresses involved by hand. Accordingly, there is a need for advanced computer tools to study how the long-term stress behaviour of timber structures is affected by creep and cyclic variations in climate. A beam model to simulate the overall hygro-mechanical and visco-elastic behaviour of (inhomogeneous) glulam structures is presented. A two-dimensional transient, non-linear moisture transport model for wood is also developed and linked with this beam model. The combined models are used to study the long-term deformations and stresses in a curved frame structure exposed to both mechanical loading and cyclic climate conditions. It is shown that the moisture-induced deformations and stresses are of such magnitude that the design codes employed should take them into account. Thus it is argued that climate-related loads should be treated as separate load contributions that can be included in different load combinations.

  • 40.
    Passialis, C
    et al.
    Aristotelian University, Greece.
    Adamopoulos, Stergios
    Aristotelian University, Greece.
    A comparison of three NDT methods for determining the modulus of elasticity in flexure of fir and black locust small clear wood specimens2002In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 60, no 5, p. 323-324Article in journal (Refereed)
  • 41.
    Passialis, Costas
    et al.
    Aristotle University, Greece.
    Voulgaridis, Elias
    Aristotle University, Greece.
    Adamopoulos, Stergios
    Technological Educational Institute of Larissa, Greece.
    Matsouka, Maria
    Aristotle University, Greece.
    Extractives, acidity, buffering capacity, ash and inorganic elements of black locust wood and bark of different clones and origin2008In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 66, no 6, p. 395-400Article in journal (Refereed)
    Abstract [en]

    Chemical properties of black locust wood and bark from Greece, Bulgaria and Hungary (clones NY, U and J) were investigated. Disks at breast height were taken from 25 black locust trees (five trees per origin and clone) and were divided into separate biomass components (juvenile heartwood, mature heartwood, sapwood and bark). Hot water soluble (HWSE) and dichloromethane soluble extractives (DSE), acidity (pH), buffering capacity, ash content and inorganic elements were determined according to standard laboratory techniques. Bark had the highest extractive content for both HWSE (9.25–13.49%) and DSE (3.09–4.03%). Differences of extractive contents in wood were found to exist between trees of different origin and between the three clones and ranged in heartwood between 5.04–10.10% for HWSE and 0.53–1.83% for DSE and in sapwood between 3.33–6.76% for HWSE and 0.48– 1.47% for DSE. The higher values of pH occurred in sapwood (4.92–5.35), while the differences between bark (4.44–5.12) and heartwood (4.35–4.92) were small. Acid (ABC) and base (BBC) buffering capacities from the initial to pH 10 for ABC and to pH 3 for BBC were greater in bark (ABC 0.0172–0.0219 ml/ml and BBC 0.0079– 0.0141 ml/ml) than in the other wood components (for heartwood ABC 0.0069–0.0159 ml/ml and BBC 0.0022– 0.0096 ml/ml and for sapwood ABC 0.00330.0066 ml/ml and BBC 0.00330.0049 ml/ml). The total ash content was greater in bark (7.24–8.56%) than in other biomass components (for heartwood 0.34–0.89% and for sapwood 0.72– 1.24%). The content of the main inorganic elements (Ca, K, Mg, Na, P) were also found to be much higher in bark while sapwood values were greater than heartwood.

  • 42.
    Roffael, Edmone
    et al.
    Georg-August-Universität Göttingen, Germany.
    Hameed, Mahmood
    Damascus University, Syria.
    Behn, Claus
    Georg-August-Universität Göttingen, Germany.
    Einfluss der Alterung UF-Harz gebundener Holzspanplatten auf die Abgabe flüchtiger Säuren: [Influence of aging of UF-bonded Particleboards on the release of volatile organic acids]2009In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 67, no 2, p. 125-128Article in journal (Refereed)
    Abstract [en]

    Influence of aging of UF-bonded particleboards on the release of volatile organic acids Abstract The release of volatile organic acids from UFbonded particleboards made from Scots pine was assessed after production as well as after aging for 13 years. The results reveal that aging significantly decreased the release of formic acid and substantially increased the emanation of acetic acid. The change in the release of volatile acids by aging seems to be highly independent of the hardener type used (ammonium chloride, ammonium nitrate) as well as of the amount of added hardener.

  • 43.
    Sandberg, Dick
    University of Kalmar, Department of Technology.
    Distortion and visible crack formation in green and seasoned timber: influence of annual ring orientation in the cross section.2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 1, p. 11-18Article in journal (Refereed)
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  • 44.
    Sandberg, Dick
    Kungliga tekniska högskolan (KTH).
    Radially sawn timber.: Star-sawing - a new method for produring timber with vertical annual rings.1996In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 54, no 3, p. 145-151Article in journal (Refereed)
    Abstract [en]

    This work presents a new method of sawing to produce pith-free timber with vertical annual rings and without juvenile wood. The method, which is called star-sawing, gives sawn timber with two different shapes, viz, conventional timber with a rectangular cross-section and timber with a triangular cross-section. The volume yield for star-sawing has been determined with the help of computerized simulations and trial sawings. The results show that star-sawing is best suited for logs with a top diameter greater than 200 millimetres. Both a high volume yield and suitable dimensions of the sawn timber were then obtained. The volume yield of timber with vertical annual rings in star-sawing is about 0.70 calculated with regard to the top cylinder volume under bark.

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  • 45.
    Sandberg, Dick
    Kungliga Tekniska hgöskolan (KTH).
    Radially sawn timber: The influence of annual ring orientation on crack formation and deformation in water soaked pine (Pinus silvstris L) and spruce (Picea abies Karst) timber10.1007/s0010700502241997In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 55, no 3, p. 175-182Article in journal (Refereed)
    Abstract [en]

    This work describes deformation and crack formation in sawn timber of pine and spruce after first drying and subsequent cycles of resoaking in water and drying. The influence of annual ring orientation and the occurrence of juvenile wood was determined. In addition, the influence of compression wood, annual ring orientation at the edges of the cross section, the position of the board surface in relation to the pith, and the condition of the board surface i.e. whether wet or dry during resoaking were studied. When timber is exposed to repeated cycles of wetting and drying, warp, viz spring, bow, twist and cup, increases and is greater after the first cycle. The influence of annual ring orientation on spring, bow and twist depends on the type of deformation and on the kind of wood. Generally, the results indicated that timber with vertical and semi (half) vertical annual rings show less deformation (mean values) than plain sawn timber and timber containing pith. Cup is mainly caused by transverse anisotropy and is strongly influenced by the radius of the annual ring. Therefore, timber with vertical annual rings do not show any cup. Spring, twist and, especially bow are strongly influenced by compression wood. Large amount of compression wood in sawn timber increases such deformation. The distance between sawn timber in the log and the pith with surrounding juvenile wood is of vital significance for cracking. During moisture cycling, the amount of boards that develop cracks increased irrespective of their prior location in the cross section of the stem. Timber sawn from near the pith or distinctly containing pith has a higher relative crack length compared to timber sawn away from and lacking pith. In timber exposed to repeated cycles of wetting and drying the crack length increases irrespective of its prior location in the stem.

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  • 46.
    Sandberg, Dick
    University of Kalmar, Department of Technology.
    Radially sawn timber: the PrimWood Method for improved properies2005In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 63, no 2, p. 1-9Article in journal (Refereed)
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  • 47.
    Sandberg, Dick
    Kungliga tekniska högskolan (KTH).
    The influence of annual ring orientation on strength and dimensional changes during moisture variation in finger joints.1997In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 55, no 1, p. 50-50Article in journal (Refereed)
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  • 48.
    Sandberg, Dick
    Royal Institute of Technology.
    The influence of pith and juvenile wood on proportion of cracks in sawn timber when kiln dried and exposed to wetting cycles.1996In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 54, no 3, p. 152-152Article in journal (Refereed)
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  • 49.
    Sandberg, Dick
    et al.
    Kungliga Tekniska högskolan (KTH).
    Holmberg, Hans
    KTH.
    Radially sawn timber.: Gluing of star-sawn triangular profiles into form-stable products with vertical annual rings.1998In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 56, no 3, p. 171-177Article in journal (Refereed)
    Abstract [en]

    A method is presented for the gluing of star-sawn triangular profiles of pine (Pinus silvestris L.) into form-stable wood products with vertical annual rings. The triangular profiles are free from pith and from most of the juvenile wood. The method is based on dried and conditioned triangular profiles. Undesired defects are removed and the wood is finger-jointed into long lengths. In the finger-jointing, consideration is given to the appearance and annual ring orientation of the jointed materials. After the jointing, the triangular profiles are planed and glued into rectangular blocks with vertical annual rings. These blocks can then e.g. be used as construction beams or be sawn up into solid wood panels. A pilot plant has been built for the manufacture of knot-free solid wood panels based on the proposed method. Results show a total volume yield of 53.8%. Three critical production stages can be distinguished: removal of knots and defects, planing, and division of blocks into boards. These three operations are together responsible for more than 93% of the total losses in the manufacture. The removal of knots and defects meant a volume loss of 12.8%. 13% of the manufactured units were 2.1 m long without finger-jointing and free from knots and other defects. The average length of the remaining pieces used for finger-jointed units was 0.41 m.

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  • 50.
    Sandberg, Dick
    et al.
    Kungliga tekniska högskolan (KTH).
    Holmberg, Hans
    KTH.
    Radially sawn timber: Knots - number, type and size in star-sawn triangular profiles of pine (Pinus silvestris L) and spruce (Picea abies Karst)1996In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 54, no 6, p. 369-376Article in journal (Refereed)
    Abstract [en]

    This paper describes the appearance and number of knots in star-sawn triangular profiles of pine (Pinus silvestris L) and spruce (Picea abies Karst). The emphasis is placed on obtaining the volume yield of boards with a given knot appearance, together with the sizes of the fibre disturbances around the knots and how they affect the yield. The test material has been taken from three regions in Sweden and is made up of butt logs of pine and of normal and fast-growing spruce. The results show that a large proportion of the knots found in the triangular profiles from butt logs are unacceptable in further refinement of the timber and must be removed. Very few healthy knots can be found. To produce knot free boards, a volume reduction of on average 8 and 21 percent is obtained for pine and spruce respectively, calculated with respect to the original profile volume. If the fibre disturbance around the knots is also removed, a further volume loss of 5 percentage for pine and 6 percentage for spruce is obtained. The boards produced have a broad spectrum of lengths between 2 and 500 centimetres for pine and between 2 and 400 centimetres for spruce.

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