| 1. |
- Adamopoulos, Stergios, et al.
(author)
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Adhesive bonding of beech wood modified with a phenol formaldehyde compound
- 2012
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In: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 70:6, s. 897-901
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Adamopoulos, Stergios, et al.
(author)
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Dimensional changes of extracted and non-extracted small wood specimens of black locust (Robinia pseudoacacia L.)
- 2003
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In: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 61:4, s. 264-268
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
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| 4. |
- Adamopoulos, Stergios
(author)
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Flexural properties of black locust (Robinia pseudoacacia L.) small clear wood specimens in relation to the direction of load application
- 2002
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In: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 60:5, s. 325-327
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Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Adamopoulos, Stergios
(author)
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Influence of hot-water extractives on radial and tangential shrinkage of black locust wood (Robinia pseudoacacia L.)
- 2002
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In: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 60:5, s. 377-378
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Adamopoulos, Stergios, et al.
(author)
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Relationship of the toughness and the modulus of elasticity in static bending of small clear spruce wood specimens
- 2010
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In: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 68:1, s. 109-111
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Journal article (peer-reviewed)abstract
- 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.
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| 7. |
- Adamopoulos, Stergios, et al.
(author)
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Ring width, latewood proportion and dry density in stems of Pinus brutia Ten
- 2009
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In: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 67:4, s. 471-477
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Adamopoulos, Stergios, et al.
(author)
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Variation of certain chemical properties within the stemwood of black locust (Robinia pseudoacacia L.)
- 2005
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In: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 63:5, s. 327-333
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
- Afshar, Reza, et al.
(author)
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Creep in oak material from the Vasa ship: : verification of linear viscoelasticity and identification of stress thresholds
- 2020
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In: European Journal of Wood and Wood Products. - : Springer Nature. - 0018-3768 .- 1436-736X. ; 78:6, s. 1095-1103
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Journal article (peer-reviewed)abstract
- Creep deformation is a general problem for large wooden structures, and in particular for shipwrecks in museums. In this study, experimental creep data on the wooden cubic samples from the Vasa ship have been analysed to confrm the linearity of the viscoelastic response in the directions where creep was detectable (T and R directions). Isochronous stress–strain curves were derived for relevant uniaxial compressive stresses within reasonable time spans. These curves and the associated creep compliance values justify that it is reasonable to assume a linear viscoelastic behaviour within the tested ranges, given the high degree of general variability. Furthermore, the creep curves were ftted with a one-dimensional standard linear solid model, and although the rheological parameters show a fair amount of scatter, they are candidates as input parameters in a numerical model to predict creep deformations. The isochronous stress–strain relationships were used to defne a creep threshold stress below which only negligible creep is expected. These thresholds ranges were 0.3–0.5 MPa in the R direction and 0.05–0.2 MPa in the T direction.
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| 10. |
- Ahmed, Sheikh Ali, et al.
(author)
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Development of a new rapid method for mould testing in a climate chamber : preliminary tests
- 2013
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In: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 71:4, s. 451-461
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Journal article (peer-reviewed)abstract
- 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.
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