Gerard Janin

Natural wood colouring process in Juglans sp. (J. nigra, J. regia and hybrid J. nigra 23 ×J. regia) depends on native phenolic compounds accumulated in the transition zone between sapwood and heartwood

Abstract Radial distribution of soluble phenolics was investigated at different heights in stems of Juglans nigra, J. regia and hybrids J. nigra 23 × J. regia. Four major phenolic compounds were studied: hydrojuglone glucoside (HJG), quercitrin (QUER) and two unknown compounds characterized as two ellagic acid derivatives E1 and E2. HJG and E1 content increased gradually in the sapwood, peaked in the sapwood-heartwood transition zone, and decreased drastically in the heartwood. QUER was accumulated preferentially around the transition zone, and its content was relatively low in the outer part of the sapwood and in the inner part of the heartwood. E2 content was low in the sapwood and increased in the heartwood. The heartwood formation was marked by the accumulation of new soluble compounds. The relationship between wood extractives and wood colour were evaluated and discussed. HJG was considered to be a major precursor of heartwood colour providing chromophores through hydrolysis (deglucosylation), oxidation and polymerization processes.

ELLAGITANNINS IN EUROPEAN OAK WOOD : POLYMERIZATION DURING WOOD AGEING

Abstract Ellagitannins in acetone-water extracts of outer and inner heartwood of European oak were assayed and their M r distribution studied by gel permeation chromatography. Ageing of heartwood in the living tree induces darkening of the extract, a decrease in its solubility in cold water and polymerization of ellagitannins.

Colorimetry of wood specimens from French Guiana

The color of 97 species of wood specimens from French Guiana was measured on their radial and tangential surfaces with a colorimeter. We obtained the tristimulus values of X, Y, and Z of the 10° standard observer under the illuminant of D65, and the values of the CIELAB color system, L*, a*, b*, C*, and h. When the lightness index (L*) was <54, b*, C*, and h showed positive correlations against L*. When L* was >54, a* and C* showed negative correlations against L*. These results imply that wood color should be discussed by separating wood specimens into the high and low-lightness groups. A good positive correlation was found between the L* and h throughout the whole range of L*. It is thought that the value of h can be an important index, as can L*, for comparing of wood color because h shows a simple relation with L*.

Study of industrial boiling process on walnut colour: Experimental study under industrial conditions

Juglans regia) logs, measured during boiling water process under industrial conditions. The colour changes in sapwood and heartwood evolution were analysed according to the previous results obtained in laboratory. As it was expected, the sapwood color changes quickly during the first 10 hours and definitely after 30 hours of industrial treatment. Its colour is darker and redder. Heartwood behavior is quite different because its colour is changing slowly during the first 10 hours and important changes are occuring after the 39 first hours. These mean results were obtained on the four logs studied. This work precise the particular behavior of the color of wood during boiling and the efficient method used. This study may be used by industries, which are concerned by heating treatment before slicing, and applied to other species.Juglans regia), die während der Behandlung in kochendem Wasser bei Industriebedingungen entstehen. Die Verfärbungen im Splint- und Kernholz wurden analysiert unter Verwendung früherer Ergebnisse aus Laboruntersuchungen. Wie erwartet erfolgt die Verfärbung im Splintholz rasch während der ersten 10 Stunden. Nach 30 Stunden wird ein Endwert erreicht. Die farbe wird dunkler und rötlicher. Die Farbänderungen im Kernholz verlaufen ander; sie beginnen sehr langsam während der ersten 10 Stunden und deutliche Farbänderungen finden erst nach 39stündigem Kochen statt Die Ergebnisse werden als Mittel aus vier Rundhölzern genommen. Sie präzisieren die spezielle Verfärbungwährend des Kochens. Die verwendete Methode erwies sich als effektiv. Die Untersuchung könnte verwendet werden in Industrieprozessen, in welchen Erhitzen oder Dämpfen vor der Auftrennung des Holzes eingesetzt wird. Die Ergebnisse können auch auf andere Holzartn übertragen werden.

Modifications of hybrid Walnut (Juglans nigra 23 x Juglans regia) wood colour and phenolic composition under various steaming conditions

Summary The effects of steaming were studied on Walnut wood from a hybrid (Juglans nigra 23 × J. regia) tree in terms of wood colour and phenolic composition. Wood samples were subjected to treatments at 75, 100 and 125°C for 4, 8, 16 and 24 hours. Colour changes were measured in the CIELCh colour system and phenolics were characterized and quantified by means of HPLC. Steaming mainly resulted in a darkening of wood tissues. Colour changes increased as temperature increased from 75 to 125°C. Lightness L* gradually decreased from 0 to 24 h at 75°C, whereas with higher temperatures, most of the darkening occurred within the first 4 hours of exposure. Contrast in colour, between sapwood and heartwood in particular, could be reduced by steaming at 125°C. The best steaming treatment, leading to a colour of steamed sapwood close to that of natural heartwood, was at 100°C/16 h. Hydrojuglone glucoside (HJG), ellagic and gallic acid derivatives (E1, E2 and G respectively) were gradually degraded by steaming, whereas a new flavonol (F) and oxidation products (OP) increased. Relationships between wood colour and phenolic content are discussed.

Prevention of brown discoloration in European oakwood occurring during kiln drying by a vacuum process: Colorimetric comparative study with a traditional process

The efficiency of two kiln drying processes on brown discoloration developments ofQuercus robus (L) andQuercus petraea (Lieb) was studied. A traditional atmospheric pressure system, was compared with other using vacuum and super heated steam. 103 green boards from three different trees were used. After each cycle (6), we analysed and compared the color of the boards using a spectrocolorimeter fitted with the CIELAB analysis. With the traditional system (in moist condition) we obtained 100% brown discoloration, in contrast to vacuum and super heating which did not develop brown discoloration. The brown discoloration is characterised by a decrease in lightness (-6 to-8 units) and color angle (-1 to-2 units) compared to non discolored wood. The discoloration is probably independent of wood origin and can be prevented by quick kiln drying without oxygen.ZusammenfassungDie Auswirkung zweier Trocknungsprozesse auf die Verfärbung von Quercus robur (L) und Quercus petraea (Lieb) ist untersucht worden. Ein herkömmliches System mit atmosphärischem Druck wurde mit einem anderen verglichen, das Vakuum und Hei\dampf benutzt. Einhundertdrei waldfrisch geschnittene Bretter von verschiedenen Bäumen wurden verwendet. Nach jedem Zyklus kontrollierten und verglichen wir die Farbe der Holzschnittflächen mit Hilfe eines CIELAB Spektrocolorimeters. Im Gegensatz zur Vakuum- und Heißdampftechnik, die keine braune Verfärbung bewirkten, erreichten wir mit dem herkömmlichen System eine 100%ige Verfärbung. Die braune Verfärbung wird durch eine Verminderung der Leuchtkraft (-6 bis-8 Einheiten) und des Farbwinkels (-1 bis-2 Einheiten) charakterisiert. Die Verfärbung ist wahrscheinlich von der Holzherkunft unabhängig und kann durch einen sauerstoffreien Trocknungsprozeß verhindert werden.

Relations between the colorimetric values and densities of sapwood

Color measurements were made for sapwood specimens of 26 hardwood species. The densities of the specimens ranged from 258.5 to 945.6kg/m3. The colorimetric values and densities were compared among the species. The tristimulus values ofX, Y, andZ were poorly correlated with the densities. The chromaticity coordinatex had a good linear correlation with the densities of the wood specimens, especially in the transverse planes. The transverse plane of wood fibers is thought to emphasize the relative values in the long wavelength region of the visible ray.

Colour and chemical characteristics of moon rings in oakwood

The moon ring defect of oak wood is thought to occur during the transformation of sapwood to heartwood. This false sapwood can cause serious losses to the wood industry. Several oak samples containing this defect were studied, each separated into : sapwood, outer heartwood, moon ring and inner heartwood. Colour analyses were carried out by the CIELAB colour system, and phenolic and mineral components were also measured. The analyses show that moon rings are more red in colour, and contain higher concentrations of ellagic acid, than sapwood. Potassium concentrations are lower in the moon rings compared with other zones. Hierarchical and discriminant analyses of all the parameters studied confirm the differences observed between sapwood and moon rings. The results support the hypothesis that moon rings may be produced due to heartwood formation being interrupted by traumas, such as severe frost.

Effect of drying process on marupá wood color

This research was developed after consultations with tropical timber exporters, who were facing problems with the colors of the species under study. This work aimed at characterizing Simarouba amara tropical wood color and verifying possible differences between the colorimetric parameters determined for the tangential and the radial directions of the wood, kiln-dried and air-dried. S. amara wood presents a grayish-white color. This color is mainly characterized by the b* coordinate (yellow pigment). Depending on the drying method used, the wood may present different colors for both tangential and radial directions. In both drying methods conducted, the wood presented lighter color in the tangential direction. Kiln-drying appeared to reduce S. amara wood lightness.

Comparison of linear vibration welded joints in three different directions of wood tauari (Couratari oblongifilia)

Abstract Without any adhesive and other chemical additives, the mechanically induced welding can make good wood joints satisfying the relevant requirements for application. The bonding performances of the wood Tauari (Couratari oblongifilia) welded joints in three different directions were studied here: parallel to the wood grain, perpendicular to the wood grain and end grain to end grain. The results show that the compression shear bonding strength of the perpendicularly welded joints was the best, parallel welded joints took the second place while the strength of the end grain butt joints was so small that it could not resist the sewing machine. The figures of scanning electron microscopy and the density profiles show the different structures and density distributions of the welded joints which indicate the reasons behind the big differences of the compression shear bonding strength.