Stergios Adamopoulos

Variation of certain chemical properties within the stemwood of black locust (Robinia pseudoacacia L.)

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. Zusammenfassung Vom unteren, mittleren und oberen Teil der Stämme von drei ausgewachsenen 35–37 Jahre alten Robinien wurden Stammscheiben herausgeschnitten und analysiert, um die Variation bestimmter chemischer Eigenschaften innerhalb des Stammes zu bestimmen. Insgesamt war der Heisswasser-Extraktstoffgehalt im Kernholz höher als im Splintholz, während für den Di-Chlormethan-Extraktstoffgehalt das Gegenteil der Fall war. Die senkrechte Stammanalyse der Heisswasser-Extraktstoffe ergab, dass der Extraktstoffgehalt im Kernholz vom unteren Stammende zum Zopf hin zunahm, aber im Splintholz abnahm, während der Di-Chlormethan-Extraktstoffgehalt im Splintholz zum Zopf hin zunahm. Die unteren und mittleren Stammteile wiesen im Splintholz einen höheren Aschegehalt auf als im Kernholz. Im oberen Teil unterschied sich der Aschegehalt zwischen Kern- und Splintholz nicht. Der Aschegehalt stieg sowohl im Kern- als auch im Splintholz in Stammlängsrichtung an, im Kernholz von 0.36% (unten) auf 0.76% (oben) und im Splintholz von 0.65% (unten) auf 0.76% (oben). Die Aschenanalyse ergab beträchtliche Schwankungen bei den anorganischen Elementen K und P. Im Splintholz waren diese höher als im Kernholz. Das Kernholz lag mit Ausnahme des oberen Stammbereichs mehr im sauren Bereich als Splintholz. Die durchschnittlichen Säurewerte nahmen im Kernholz in Stammlängsrichtung von unten nach oben zu und im Splintholz leicht ab. Die Gesamtpufferkapazität im Kernholz war grösser als im Splintholz, wo sie mit zunehmender Stammhöhe abnahm. Der Ligningehalt war im unteren Stammbereich im Kernholz höher (25.73%) als im Splintholz (18.13%). Im Kernholz verringerte sich der Ligningehalt von 25.73% im unteren Stammbereich auf 18.33% im Zopfbereich, während der Ligningehalt im Splintholz im unteren Teil bei 18.13% lag, in der Mitte bei 21.42% und im Zopfbereich bei 19.64%.

Topochemistry of heat-treated and N-methylol melamine modified wood of Koto (Pterygota macrocarpa K. Schum.) and Limba (Terminalia superba Engl. et Diels)

Abstract To broaden the knowledge about the chemical changes at the cell wall level of differently modified tropical hardwoods, heat-treated and N-methylol melamine (NMM)-treated samples of koto (Pterygota macrocarpa) and limba (Terminalia superba) were prepared. UV microspectrophotometry (UMSP) was applied at 278 and 240 nm as specific wavelengths to analyze chemical alterations of the samples caused by heat and NMM treatment, respectively. The absorbance of koto exceeded that of limba before and after treatment, potentially due to the higher extractive content of the former. Regardless of the wood species, the absorbance of the samples increased with increasing intensity of the NMM treatment. Additionally, the absorbance of lignin within the spectrum of 230–350 nm was altered due to the NMM treatment. The functionality of applying specific wavelengths for the analysis of different modification methods of wood was proven. However, the comparison with literature did not show differences in the absorbance, which could be assigned to the characteristics of tropical hardwoods.

WITHIN-TREE VARIATION IN GROWTH RATE AND CELL DIMENSIONS IN THE WOOD OF BLACK LOCUST (ROBINIA PSEUDOACACIA) *

Black locust (Robinia pseudoacacia L.) is regarded as an important natural resource almost throughout the world but relatively little is known about the within-tree variability of the anatomical characteristics of its wood. Discs 2 cm thick were cut at 2.25 m intervals, from the ground level to the top from ten black locust trees, 18–37-years-old, from the University Forest of Taxiarchi, Chalkidiki, Greece. The discs were used for the determination of growth rate and cell dimensions (fiber length and vessel member length and diameter) and their withintree variability (radial, oblique, vertical). Growth rate increased within the first 5–9 growth rings from the pith and then gradually decreased. Oblique variation of growth rate did not exhibit any clear tendency but a decrease at the top. In the case of vertical variation, growth rate decreased gradually with the year of cambium formation. Radial variability curves were found to be typical for the dimensions of cells (fibers, vessel members) especially for the fiber length. A rapid increase in cell dimensions was observed in the first 7–11 growth rings, the juvenile zone. Oblique and vertical variation of cell dimensions did not exhibit any clear tendencies.

Effects of nano-sized zinc oxide and zinc borate impregnation on brown rot resistance of black pine (Pinus nigra L.) wood

Abstract In this work, the brown rot resistance of black pine (Pinus nigra L.) wood, pressure-treated in an autoclave with nano-sized zinc borate and zinc oxide dispersions, was investigated. The two formulations based on zinc borate have given encouraging results, indicating fungicide effects of the metal nanoparticles on Coniophora puteana. In specific, mean weight losses for P. nigra sapwood exposed to this fungus (one without and one with the addition of a binder) were negligible, that is 0.54% and 0.34%, respectively. On the contrary, the impregnation of pine wood with nano-sized zinc oxide resulted in minimal protection, i.e. 35.9% weight loss. Therefore, nano-sized zinc borate can be utilised in new formulations to impart resistance to wood against the brown rot C. puteana.

Development of sustainable bio-adhesives for engineered wood panels – A Review

Changes in both formaldehyde legislations and voluntary requirements (e.g. Germany RAL) are currently the driving factors behind research on alternatives to amino-based adhesives; moreover, consumer interest in healthy and sustainable products is increasing in bio-based adhesives. Sources of formaldehyde emissions in wood-based panels as well as different emission test methods have been discussed, and the main focus of this review is on the research conducted on sustainable bio-based adhesive systems for wood panels. Lignin, tannin, protein, and starch have been evaluated as both raw materials and adhesive alternatives to existing amino-based thermosetting adhesives. Adhesion improving modifications of these bio-based raw materials as well as the available and experimental crosslinkers have also been taken into account.

A comparison of three NDT methods for determining the modulus of elasticity in flexure of fir and black locust small clear wood specimens

A comparison of three NDT methods for determining the modulus of elasticity in flexure of fir and black locust small clear wood specimens

Flexural properties of black locust (Robinia pseudoacacia L.) small clear wood specimens in relation to the direction of load application

LR, 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.LR, GLT) wurden berechnet für juveniles und reifes Robinienholz. Die Berechnung erfolgte anhand von fehlerfreien Proben nach statischer Belastung, und zwar abwechselnd in genau radialer bzw. tangentialer Richtung. Für juvenile und Reifholzproben wurden keine statisch signifikanten Unterschiede gefunden zwischen den Werten des radialen MOE und der Schubmodule GLR und GLT (t-Test, 95% Niveau). Die Werte der reinen Biegemodule (PMOE) erwiesen sich als 27–32% höher als die entsprechende MOE-Werte bei einem Verhältnis von Spannweiten zu Tiefe von 15:1.

Wood defects during industrial-scale production of thermally modified Norway spruce and Scots pine

Abstract This research investigates wood defects, particularly the formation of surface cracks, during the production of thermally modified wood and its exposure to cyclic moisture changes. Boards of Norway spruce and Scots pine originating from different steps within the production of ThermoWood® were collected and wood defects were investigated at macroscopic and microscopic scale. Subsequently, the wood was exposed to capillary wetting cycles to record its sensitivity towards cracking. After the modification process, typical anatomical defects of conventional kiln-drying became more frequent and severe, with the magnitude being to some extent depending on the presence of defects in the raw material. At microscopic scale, damages to ray parenchyma and epithelial cells as well as longitudinal cracks within the cell walls of earlywood tracheids were evident in thermally modified wood. Despite a lower water uptake and higher dimensional stability, thermally modified wood was more sensitive to surface cracking during wetting cycles than unmodified wood, i.e. at the outside face of outer boards (near bark). For limiting surface cracking of thermally modified wood during service life, the use of high-quality raw material, the exposure of the inside face of the boards (near pith) and the application of a surface coating are considered beneficial.

Tracheid length – growth relationships of young Pinus brutia grown on reforestation sites

Brutia pine (Pinus brutia Ten.) reforestations have been successfully used for decades in restoration of degraded forest ecosystems in Greece. The future purpose of these reforestations might expand to include wood utilisation. This study provides information on tracheid length of juvenile brutia pine aged 14–22 years grown on good and medium sites in Northeastern Greece. In addition, relationships among ring width, latewood proportion, wood density, and tracheid length were evaluated by using Causal Correlation Analysis. Similar mean tracheid length values were found for good and medium sites. Radial variability of tracheid length was similar on the good and medium sites, showing the typical increase in the juvenile phase. On both site types, latewood proportion showed a strong and positive relationship with wood density. Unexpectedly and only on the good sites, a significant positive relationship was found between ring width and wood density. On the medium sites, tracheid length was negatively related to fast growth and positively to high wood density. Tracheid length on the good sites was correlated only with latewood proportion with a weak positive relationship. The overall results may provide opportunities to better understand the quality of small-dimension timber of brutia pine and to better utilise it.

Ring width, latewood proportion and density relationships in black locust wood of different origins and clones.

Cross-sectional discs were cut at breast height from 19 black locust trees aged 18–39 years of different clones and origin (Greece, Bulgaria and Hungarian clones J, U and NY). Ring width, latewood proportion and dry density were measured according to standard laboratory techniques in order to examine their relationships. Latewood proportion was found to increase (except for one tree from Bulgaria) with increasing ring width and logarithmic equations were calculated with relatively high correlation coefficients. A positive relation between dry density and latewood proportion was found in black locust of Bulgarian origin and in the Hungarian clone NY while in all other cases no meaningful relationship was observed. In mature wood, improved positive linear correlations were observed between dry density and latewood proportion with the exception of the Hungarian clone U. Regression analysis revealed low correlations between dry density and ring width and only black locust from Bulgaria had a high positive correlation. The positive correlations between dry density and ring width were slightly improved in mature wood with the exception of clone J from Hungary.