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  • 1.
    Adamopoulos, Stergios
    et al.
    Technological Educational Institute of Larissa, Greece.
    Chavenetidou, Marina
    Aristotle University of Thessaloniki, Greece.
    Passialis, Costas
    Aristotle University of Thessaloniki, Greece.
    Span-to-depth ratio for shear free deformations in static bending of small wood specimens2011In: Wood research, ISSN 1336-4561, Vol. 56, no 3, p. 429-434Article in journal (Refereed)
    Abstract [en]

    Disregarding shear effects is a principal defect in predicting the bending strengths of small clear specimens of timber according to standards. The present study proposes a method to determine spans of 2 x 2 cm wood specimens of black locust and chestnut for shear free deformations in static bending. It was found that for both ring-porous species, spans of at least 40 cm in a bending test would ensure a negligible influence of shear on modulus of elasticity.

  • 2.
    Adamopoulos, Stergios
    et al.
    Technological Educational Institute of Larissa, Greece.
    Chavenetidou, Marina
    Aristotle University, Greece.
    Passialis, Costas
    Aristotle University, Greece.
    Voulgaridis, Elias
    Aristotle University, Greece.
    Effect of cambium age and ring width on density and fibre length of black locust and chestnut wood2010In: Wood research, ISSN 1336-4561, Vol. 55, no 3, p. 25-36Article in journal (Refereed)
    Abstract [en]

    The relationship between wood density (WD) and fibre length (FL) with cambium age (CA) and ring width (RW) was studied in two ring-porous species, black locust and coppice-grown chestnut, collected in the Sithonia Peninsula, Chalkidiki, Greece. Using regression analysis methods, models of WD and FL in relation to CA and RW were obtained. It was found that the effect of CA and RW on WD and FL was similar for both species examined. WD of black locust and chestnut was predicted better through a model using CA and RW. A model for FL variations was also obtained with CA and RW and was more accurate than the simple models based on the two factors, CA and RW, separately. The multiple regression models suggested that the use of cambial age of growth rings together with their width might explain better their effects on WD and FL of black locust and chestnut.

  • 3.
    Adamopoulos, Stergios
    et al.
    Technological Educational Institute of Larissa, Greece.
    Voulgaridis, Elias
    Aristotle University of Thessaloniki, Greece.
    Effect of hot-water extractives on water sorption and dimensional changes of black locust wood2012In: Wood research, ISSN 1336-4561, Vol. 57, no 1, p. 69-78Article in journal (Refereed)
    Abstract [en]

    The hygroscopicity and the dimensional changes of black locust heartwood were investigated in relation to the progressive removal of hot-water extractives. Extraction in the original specimen form removed only part of the total 8.434 % hot-water extractives, 3.601 % in first extraction and 4.642 % in second extraction. As a result, the adsorption and desorption behaviour of black locust wood was little affected by the extraction and only a small increase was observed in dimensional changes at every RH from 0 % to 97 %. The mean hysteresis coefficient was also little affected by extraction and increased from 0.75 at the unextracted stage to 0.77 at the second extraction. The initial dimensional change 3.76 % of unextracted black locust wood corresponding to RH changes between 43 % and 80 % increased after the first and second extraction to the respective values of 3.96 % and 3.97 %. Extraction had no effect on the significant, very strong linear relationships between swelling or shrinkage and equilibrium moisture content (EMC).

  • 4.
    Bastani, Alireza
    et al.
    George-August University, Germany.
    Militz, Holger
    George-August University, Germany.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Rohumaa, Anti
    Alto University School of Chemical Technology, Finland.
    Development of bonding strength of modified birch veneers during adhesive curing2016In: Wood research, ISSN 1336-4561, Vol. 61, no 2, p. 205-214Article in journal (Refereed)
    Abstract [en]

    This study investigated the bonding strength development of furfurylated, N-methylolmelamine (NMM) modified and thermally treated birch veneers glued with hot curing phenolformaldehyde (PF) adhesive in different pressing (20, 160 s) and open assembly times (20 s, 10min). For testing, the automated bonding evaluation system ABES was used with 2 N.mm-2applied pressure at 130°C. The bonding strength of both modified and unmodified samplesincreased significantly by prolongation of the pressing time from 20 to 160 s in all cases andfor both open assembly times. A deviation was observed for the samples treated at 220°C andat 20 s open assembly time. With the exception of NMM modified veneers, bonding strengthdid not change significantly by increasing the assembly time in the case of 20 s pressing forboth modified and unmodified samples. At 160 s pressing time, extension of the assembly timedeveloped a better bonding for controls, NMM modified and thermally treated veneers at 180°C.The combination of 10 min assembly time and 160 s pressing time proved as the optimal bondingcondition for controls, NMM modified and thermally treated veneers at 180°C while the highestbonding strength was noted in 20 assembly time and 160 s pressing time for furfurylated veneers.In most of the cases modification affected negatively the bonding performance of the veneers, inparticular for furfurylated and NMM modified samples.

  • 5. Blumer, Samuel
    et al.
    Niemz, Peter
    Serrano, Erik
    Växjö University, Faculty of Mathematics/Science/Technology, School of Technology and Design.
    Gustafsson, Per Johan
    Moisture induced stresses and deformations in parquet floors: An experimental and numerical study2009In: Wood research, ISSN 1336-4561, Vol. 54, no 1, p. 89-101Article in journal (Refereed)
    Abstract [en]

    The indoor climate in buildings has changed in the last decade due to more efficient climatic systems, floor heating systems and larger open floor areas with more natural light. All this has induced increasing ranges of relative humidity between different seasons. Also with decreasing relative humidity (in the winter 30-50% RH, in the summer 70-90% RH), floor-heating systems increase the temperature in wooden parquet planks for example. Such variations can result in troublesome deformations, delamination of the surface layer and development of cracks in the parquet flooring boards. Sometimes there is only deterioration of the appearance but the durability of the flooring system can also be reduced. Many laboratory tests have to be done before reaching an optimal design of the parquet elements. Due to high coasts and time constraints of experiments, other supplementary research methods should be tested and evaluated. The articles' main objective was to increase understanding of the behaviour of parquet floors exposed to different climatic conditions using numerical calculation. The use of the finite element models provides options for design purposes of wood flooring systems. Several finite element models for adequate design have been created, tested and applied. After calibration and validation of the calculation method, parameter studies on the influence of material properties, geometry of the parquet floors and the long-term behaviour of the wood and glue line were performed. The results show a strong relation between material and geometry choice on the deformation, for example the gap opening and on the stress distribution in glue line, which can induce delamination of the surface layer and distortional effects of the parquet boards

  • 6.
    Hosseinpourpia, Reza
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Mai, Carsten
    Georg-August-University Göttingen, Germany.
    Taghiyari, Hamid Reza
    Shahid Rajaee Teacher Training University, Iran.
    Properties of medium-density fibreboards bonded with dextrin-based wood adhesive2019In: Wood research, ISSN 1336-4561, Vol. 64, no 2, p. 185-194Article in journal (Refereed)
    Abstract [en]

    This study focuses on manufacturing of medium density fibreboard (MDF) panels bonded with dextrin-based wood adhesive and crosslinked in situ with various weight ratios of synthetic (e.g., polymeric-methane diphenyl-diisocyanate, pMDI) or bio-based (e.g., glyoxal) crosslinkers. The physical and mechanical properties of the panels were evaluated and compared with those from panels without crosslinker (control). Modulus of rupture (MOR) and internal bond (IB) strength of the MDF panels were considerably increased by increasing the crosslinkers’ content. While, slight improvements were observed in modulus of elasticity (MOE) of the panels as a function of crosslinker type and content. Addition of crosslinkers clearly reduced the thickness swelling (TS) and water absorption (WA) of the panels, whereas, the panels with pMDI showed superior performances than the control and glyoxal added ones within 4 h and 24 h immersion in water. The results indicate the potential of dextrin as wood panel adhesive along with the use of appropriate crosslinkers.

  • 7.
    Kielmann, B
    et al.
    Georg-August-University Göttingen, Germany.
    Militz, H
    Georg-August-University Göttingen, Germany.
    Mai, C
    Georg-August-University Göttingen, Germany.
    Adamopoulos, Stergios
    Technological Educational Institute of Thessaly, Greece.
    Strength changes in ash, beech and maple wood modified with a N-methylol melamine compound and a metal-complex dye2013In: Wood research, ISSN 1336-4561, Vol. 58, no 3, p. 343-350Article in journal (Refereed)
    Abstract [en]

    Ash, beech and maple wood was modified with aqueous solutions of methylated N-methylol melamine (NMM) and a metal-complex dye (BS) consisting of 10, 20, and 30 % NMM and 5 % BS. Static bending strength and stiffness, impact bending strength and hardness were examined to evaluate the suitability of modified wood for structural uses. The combined NMMBS modification resulted in significant higher dynamic (MOEdyn) and static (MOE) moduli of elasticity for all species. Beech and maple exhibited enhanced static bending strength (MOR), while that of ash was unchanged. The higher stiffness and strength of NMM-BS modified wood is attributed to its higher wood density and lower EMC and to the stiff character of NMM resin incorporated in the wood matrix. Impact bending strength decreased substantially after modification as a result of reduced pliability of treated wood. Brinell hardness significantly increased with the weight percent gain (WPG) due to modification, and, unlike the other properties, it was positively correlated with the WPG.

  • 8.
    Sint, KM
    et al.
    Univ Gottingen, Germany.
    Militz, H
    Univ Gottingen, Germany.
    Hapla, F
    Univ Gottingen, Germany.
    Adamopoulos, Stergios
    Technol Educ Inst Larissa, Greece.
    Treatability and penetration indices of four lesser-used Myanmar hardwoods2011In: Wood research, ISSN 1336-4561, Vol. 56, no 1, p. 13-22Article in journal (Refereed)
    Abstract [en]

    Depletion of Myanmar's top commercial timbers has grown the attention towards lesser-used timbers, which present: low durability and require protection against biodegradation. This research tested the treatability of four nondurable Myanmar hardwoods: Bombax ceiba, Bombax insigne, Spondias pinnata and Tetrameks nudiflora. Conditioned heartwood samples were pressure-treated according to standard schedules using a staining solution. Solution uptake,penetration depths, and percent of each cell type penetrated were determined and discussed according to wood anatomical characteristics. B. ceiba, B. insigne and S. pinnata had high uptakes and good penetration making them promising for protective treatment. T nudiflora was also classified as easy to treat based on its penetration index but as generally difficult to treat according to retention and depth of penetration. This different behavior was attributed to the tyloses occluding its vessels. The results are useful for the development of specific treatment schedules to achieve the retentions and penetration required for the effective protection of these lesser-used hardwoods.

  • 9.
    Taghiyari, Hamid Reza
    et al.
    Shahid Rajaee Teacher Training University, Iran.
    Esmailpour, Ayoub
    Shahid Rajaee Teacher Training University, Iran.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Zereshki, Kurosh
    Shahid Rajaee Teacher Training University, Iran.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Shearn strenght of heat-treated solid wood bonded with polyvinyl-acetate reinforced by nanowollastonite2020In: Wood research, ISSN 1336-4561, Vol. 65, no 2, p. 183-194Article in journal (Refereed)
    Abstract [en]

    This study investigated the shear strength of heat-treated solid wood of three species (beech, poplar, and fir) bonded with polyvinyl-acetate (PVA) adhesive reinforced by nanowollastonite (NW). Wood specimens were heat-treated at 165°C and 185°C, and then bonded using PVA reinforced by 5% and 10% of NW. Shear strength tests parallel to the grain of bonded specimens were performed according to ASTM D143-14 (2014). The results demonstrated that the shear strength was significantly dependent upon the density of the specimens. Heat treatment decreased the shear strength of the bonded specimens considerably. This was attributed to several factors, such as a reduction in polar groups in the cell wall, increased stiffness of the cell wall after heat treatment, and a reduction in the wettability of treated wood. However, NW acted as a reinforcement agent or extender in the complex, and eventually improved the shear bond strength. Moreover, the density functional theory (DFT) proved the bond formation between calcium atoms in the NW and hydroxyl groups of cell wall polymers. The overall results indicated the potential of NW to improve the bonding strength of heat-treated wood.

  • 10.
    Voulgaridis, Elias
    et al.
    Aristotle Univ Thessaloniki, Greece.
    Passialis, Costas
    Aristotle Univ Thessaloniki, Greece.
    Negri, Martino
    Ivalsa Cnr, Trees & Timber Inst, Italy.
    Adamopoulos, Stergios
    Technol Educ Inst Larissa, Greece.
    Shear bond strength of black locust wood glued with three adhesive systems2012In: Wood research, ISSN 1336-4561, Vol. 57, no 3, p. 489-496Article in journal (Refereed)
    Abstract [en]

    Black locust wood was bonded with three commercial adhesives (PVAc, PU, epoxy) and tested for its shear bond strength against process (treatments I and II) and surface parameters (radial, tangential, roughness). For treatment I (applied pressure 8 bar, press time 1.5 h, curing time 24 h), the mean shear bondstrength was found to be 6.95 N.mm(-2), 5.54 N.mm(-2) and 10.53 N.mm(-2) corresponding to the three adhesives tested, respectively. Increase in press and curing time in treatment II (press time 3 h, curing time 7 days) significantly improved the gluing performance of adhesives, 9.58 N.mm(-2) for PVAc, 13.32 N.mm(-2) for PU and 15.03 N.mm(-2) for epoxy. Surface of gluing (radial, tangential) did not affect the shear bond strength significantly. Failure within wood was found to be up to 40 % for treatment I (PVAc, epoxy) and up to 85 % for treatment II (epoxy). Positive linear regressions were calculated between shearbond strength and wood failure only for PU and epoxy adhesives. Shear bond strength was not related to surface roughness for any adhesive.

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