Costas Passialis

Physico-chemical characteristics of waterlogged archaeological wood

Waterlogged wood samples 300 to 100.000 years old of Picea abies, Pinus sylvestris and Quercus sp. from northern Europe (Norway, Sweden) that had been preserved in a glacier, burial grounds, house settlements, harbour installations and sunken ships in the sea were examined for changes in physico-chemical characteristics as compared to recent wood. The results showed that in waterlogged wood of all species the solubility in 1% NaOH (8.39-22.85%) was found to be higher than that of recent wood (3.84-5.57%). Ash content varied between 1.37-7.12% in old wood and was much higher than in fresh wood (0.31-0.65%). Klason ligin in old wood (25.71-72.40%) was higher than in fresh wood (20.31-30.95%) while crystallinity index (12.79-33.69%) was found to be lower than in fresh wood (34.56-40.20%). Increasing lignin content in old wood resulted in reducing the crystallinity index up to 3.1 times.

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%.

Water repellent efficiency of organic solvent extractives from Aleppo pine leaves and bark applied to wood

Summary Natural wax-like materials were extracted from leaves and bark of Aleppo pine (Pinus halepensis Mill.) by using toluene as organic solvent. Experimental water repellent formulations (WRFs) were prepared using 10% gum rosin as the resin constituent and 0%, 1% and 2% paraffin wax, pine needle/bark extracts or mixtures of paraffin wax and needle/bark extracts in proportion 1 : 1 as hydrophobic substance. All experimental WRFs applied to small, cross-sectional wood specimens of Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.). Wood specimens were impregnated by a simple immersion technique and the water repellent effectiveness (WRE) was assessed by using tangential swelling data. Toluene soluble extracts from needles and bark applied to wood provided hydrophobic properties to pine and beech wood specimens but to a lesser degree when compared to paraffin wax. Bark extracts appeared to be stronger hydrophobic materials than needle extracts. Both needle and bark extracts can be successful substitutes for paraffin wax in WRFs up to 50 %. The degree of protection provided by WRFs and the differences between treatments were smaller in pine heartwood and beech sapwood than in pine sapwood.

Experimental particleboards from Kenaf plantations grown in Greece

Hibiscus cannabinus L.) plantation grown in N.Greece during the period June–October 1996 provided the raw material for experimental particleboards. After harvesting, the kenaf stems were storaged under shelter for a week, the core of each stem was separated from bark and both were dried at about 20% and 10% moisture content, respectively, and chipped by a hammermill. Kenaf core, bast fibers and industrial wood chips were mixed in various proportions in order to produce three-layer E2 grade UF bonded particleboards. Kenaf core chips were characterized by a lower slenderness ratio than wood chips of the middle layer. Bulk density of both core chips and fibers was lower than that of wood chips. Substitution of wood chips with kenaf core chips in the middle layer up to 75% slightly affects static bending and internal bond of the boards, but reduces screw holding strength and increases water absorption and thickness swelling; a 100% substitution deteriorates all properties except static bending. In boards with surface layers from kenaf bast fibers or from fibers:wood chips (50:50), static bending and surface roughness are improved, while the other properties tested are deteriorated. Substitution of kenaf core chips in the middle layer with fibers in proportion 50% negatively affects the board properties except static bending. It can be concluded that core chips and bast fibers from kenaf stems may substitute industrial wood chips in the middle and surface layers of the boards, respectively, up to 50%.Hibiscus cannabinus L.) in N. Griechenland. Nach der Ernte wurden die Kenafstengel für eine Woche unter Dach gelagert, dann wurde das Holzgewebe im Stengelinneren von der Rindenschicht getrennt, anschliessend auf ca. 20% bzw. 10% Feuchtigkeit getrocknet und beides in einer Hammermühle zerkleinert. Die Herstellung dreischichtiger harnstoffharzverleimter (E2 Typ) Spanplatten erfolgte unter Verwendung verschiedener Beimischungen aus Kenafholzspänen, Kenaffasern und Industrieholzspänen. Kenafholzspäne und Kenaffasern zeichnen sich durch eine niedrigere Streudichte als Industrieholzspäne aus; darüberhinaus weisen Kenafholzspäne einen niedrigeren Schlankheitsgrad auf im Vergleich zu den Mittelschichtspänen der Industrie. Der Ersatz von Industrieholzspänen durch Kenafholzspäne in der Plattenmittelschicht bis zu einem Anteil von 75% beeinflusst unwesentlich die Biege-, und Querzugfestigkeit der Platten, hat aber eine negative Auswirkung auf das Schraubenhaltevermögen, die Dickenquellung und die Wasseraufnahme; ein Zusatz von 100% Kenafholzspänen zur Mittelschicht bewirkt eine Verschlechterung aller Spanplatteneigenschaften mit Ausnahme der Biegefestigkeit. Spanplatten, deren Deckschichten aus reinen Kenaffasern oder aus einer Beimischung von Kenaffasern und Industrieholzspänen in einem Verhältnis von 50:50 bestehen, weisen höhere Qualität bezüglich Biegefestigkeit und Oberflächenrauhigkeit auf, aber niedrigere hinsichtlich der übrigen Eigenschaften. Der Ersatz von Kenafholzspänen durch Kenaffasern in der Plattenmittelschicht hat, abgesehen von der Biegefestigkeit, einen negativen Einfluss auf alle Platteneigenschaften. In ihrer Gesamtheit führte die Untersuchung zu dem Resultat, dass der Zusatz von Kenafholzspänen und Kenaffasern in der Mittelschicht bzw. der Deckschicht von Spanplatten bis zu einem Anteil von 50% möglich ist.

ANATOMICAL CHARACTERISTICS AND PROPERTIES OF KENAF STEMS (HIBISCUS CANNABINUS)

From a kenaf plantation (Hibiscus cannabinus L.) established in North Greece, a number of stem sections were taken from three positions (base, middle and top) and cell morphology, anatomical appearance under SEM and basic technical properties were observed and determined. Kenaf plants had a maximum height of 2.53 m, with a mean basal diameter of 1.91 cm. The wood is the most abundant tissue with proportions up to 77% in cross-section area and up to 61.5% in weight. Wood proportions decrease, pith proportions increase and bark proportions remain constant from the base to the top of the stems. The dry density of stems ranged between 0.27–0.31 g /cm3, while that of wood ranged between 0.22–0.43 g /cm3 along the stems. The contents of hot water soluble extractives ranged between 10.6% and 20.4% and those of dichloromethane soluble extractives ranged between 0.7% and 1.2% for bark, wood and pith. Microscopic examination of stems and of macerated material showed that bark consists of thick and long (2,330 μm) fibres whilst pith consists of polygonal parenchymatous cells. Wood is diffuse- porous, fibres average 840 μm long, vessel members average 330 μm long and 45 μm in diameter and orthogonal parenchymatous cells are 90 μm long. Fibre lengths in both bark and wood increase from the base to the top of stem. Vessel diameters decrease from base to top, while vessel member lengths remain constant from base to middle but decrease at the top of the stem.

Juvenile and mature wood properties of naturally-grown fir trees

Introduction The production of a juvenile-type wood results from normal physiological processes. There is not much that foresters can do to avoid it. Wood characteristics change rapidly within the juvenile zone in the direction from the pith to the bark. Juvenile wood is characterized by faster growth rate, lower density and strength, shorter fibers and greater microfibril and fiber angle when compared with mature wood. Also, lignin and hemi-cellulose content are higher in the juvenile wood while alpha cellulose is lower. Juvenile wood adversely influences the quality of wood products. Higher proportions of juvenile wood are produced from fast growing plantations due to the faster growth rate and the shorter rotation time compared to natural stands. The age of transition from juvenile to mature wood formation can vary among different species and properties and is depended on genetic factors and silvicultural management (Robertson 1985).

Density and shrinkage of old wood

SummaryDensity and shrinkage were measured in samples of old wood preserved in a glacier, burial grounds, house settlements, harbour installations and ships sunk in the sea. Time of exposure ranged from about 300 to 100,000 years. Density was found reduced in most cases and shrinkage increased. In oak, density was reduced up to 0.13 gr/cm3 (at 12% m.c.) and a tangential shrinkage value of 62.16% was measured. Irrespective of time of exposure and loss of material, old wood retains its gross structural characteristics as long as it remains waterlogged.

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

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.

Characteristics of Briarwood

Briarwood a tumor-likc outgrowth of Erica arborea was investigated with regard to anatomical structure, propcrtics, chcmical composition, and effects of treatments (boiling in water, cxposure to high temperatures). Comparisons were madc with stem and root wood of Erica, and some othcr temperatc and tropical wood specics. Briarwood was found to have shorter and irregulär fibers in comparison to stem wood; tissuc arrangement is usually irregulär, but some cross sections appear normal; cnclosurcs (amorphous, crystal) arc prcscnt in cell cavities. The density and hardncss of briarwood are a l i t t le higher than that of stem wood, Volumetrie shrinkage is higher, but dircetional shrinkage tends to bc isometric. Extractivc eontent is vcry high. Ash is higher, and silica low. Boiling in water (removal of cxtractives) reduccd the Volumetrie shrinkage of briarwood (the effcct is normally opposite), did not affect thc drying rate, but rcsulted in higher dimensional stability, and eliminatcd drying defects. Exposure to high temperatures (150—600 °C) showcd a higher rcsistance of briarwood, which could be attributed to cxlractivcs.