Evaluation of thermally-treated wood of beech (Fagus sylvatica L.) and ash (Fraxinus excelsior L.) against Mediterranean termites (Reticulitermes spp.)

Termite resistance of thermally-treated ash (Fraxinus excelsior L) and European beech (Fagus sylvatica L) against subterranean termites (Reticulitermes banyulensis) was evaluated. A laboratory no-choice feeding test following the standard EN 177 was performed to assess the efficacy of this thermo-modification against subterranean termites in the Mediterranean area. After 8 weeks period of exposure, results showed that durability against termites was slightly improved for thermally-treated beech wood, which was classified as moderately durable. However, in case of thermally-treated ash wood, samples were highly biodegraded by termites, revealing no increase in their durability and being classified as non durable.     

Radial variation of total phenol content in beech (Fagus sylvatica L.) wood with and without red heartwood

A comparative study of the radial distribution of the total phenol contents has been carried out on two Beech (Fagus sylvatica L.) discs, one with red heartwood and the other without red heartwood. The wood disc samples were investigated immediately after felling and at the different stages of room-drying. In the disc without red heartwood the concentrations increased from the bark towards the pith. In the disc with red heartwood the total phenol concentration rose steeply in front of the colour boundary, but this could only be measured in the fresh tissues. This suggests, that in these tissues either the formation of phenols (accumulation) is more intense or that special phenols are also formed. Beyond the boundary the concentration decreased dramatically. After drying of the wood samples the concentration decreased in all wood parts of the discs, but the amount of this is the highest in the white tissues next to the red heartwood. The results prove that the transformation of the phenols in the white tissues next to the colour boundary takes place faster.     

Über den Keilwuchs und den welligen Jahrringverlauf in Buche (Fagus sylvatica L.)

The characteristic features of beech bark, namely the tight structure of the tissue, interrupted by dilating and sclerosed wide rays with crystal deposits, are brought into a casual relation with the wedge-growth and wavy growth of annual rings. It is shown that within the arcade-like pericycle and the sclerenchyma-pillar of the rays there exist undisturbed zones for the formation of the active phloem-tissue     

Gloss of thermally densified alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) wood veneers

Thermo-mechanical densification of wood is performed to improve physical and mechanical properties of wood. During this treatment aesthetic properties of wood, including gloss, also change. Therefore, the purpose of this study was to determine the effect of short-term thermo-mechanical (STTM) densification in different wood species (alder (Alnus glutinosa Goertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.)) on their gloss changes. Commercial wood veneers were densified in a hot plate press for 4 min at temperatures of 100, 150 and 200 °C, pressures of 4, 8 and 12 MPa. Gloss was evaluated at 20°, 60° and 85° angles of incident light using PICO GLOSS 503. Gloss measurements showed an enhancement of aesthetic properties of densified wood. Findings of this study indicated that both densification temperature and pressure have a significant effect on wood gloss. Gloss values of densified wood increased with increasing densification temperature and pressure for all investigated species. Compared to non-densified wood, gloss (85°) values (across/along the grain) for alder, beech, birch and pine increased after treatment to 2109.1/2376.9, 1728.6/2311.1, 2787.5/3000, and 2591.7/1216.7 %, respectively. The greatest gloss values were recorded at 200 °C and pressure of 12 MPa for all tested angles of incident light and for all densified wood samples. Gloss changes for birch were the highest, but the glossiest surface was observed for pine among all investigated species after wood densification.     

Investigation on bonding quality of beech wood (Fagus orientalis L.) veneer during high temperature drying and aging

In the present study, the effects of high drying temperature and UV light induced aging on bonding quality of plywood manufactured from untreated and treated veneer layers were investigated. Rotary cut veneers with dimensions of 500 mm×500 mm×2 mm produced from beech (Fagus orientalis Lipsky) log were selected for topochemical, chemical and mechanical analyses. The veneer sheets were oven-dried at 100°C and 180°C after the peeling process. Afterwards, the surfaces were exposed to artificial UV irradiation in an UV chamber for 24 h, 48 h and 72 h representing natural sun irradiation of 2, 4 and 6 months, respectively. Topochemical distribution of lignin and phenolic extractives of the treated and untreated veneers was investigated on a cellular level using UV microspectrophotometry (UMSP). For the chemical characterization of accessory compounds high performance liquid chromatography (HPLC) was used. Furthermore, the shear and bending strengths of plywood manufactured from the treated samples are determined in order to study the bonding quality. The UV microscopic detection shows that after high drying temperature and aging treatment, lignin condensation occurs. With increasing drying temperature and aging duration, more phenolic extractives are situated in parenchyma cells and vessel lumens which can be proved by increased absorbance at 278 nm. The HPLC analysis of the treated tissue showed distinct signals of polymerized compounds such as catechin and 2,6-dimethoxybenzoquinone which are chromophoric compounds in discolored beech wood. The mechanical properties of plywood showed that with increasing drying temperature up to 180°C does not negatively affect shear and bending strengths of samples. After exposure of the veneers to UV irradiation (especially 6 months), decreasing shear and bending strengths of plywood samples can be observed.     

Längenänderungen einiger Holzelemente der Rotbuche (Fagus sylvatica L.) in Abhängigkeit von Stammhöhe und Himmelsrichtung

In a selected annual ring the lengths of parenchyma strands, vessel members and wood fibres were examined, determined in different heights in the stem between 0 and 18 m and in four positions each round it. The relationship between measured values and height in stem as well as cardinals was ascertained and compared with statements in literature.     

A non-contact method for the determination of fibre direction of European beech wood (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.)

This paper introduces a non-contact method for the identification, quantification, and documentation of fibre direction of European beech wood (Fagus sylvatica L.). The developed approach is based on an automated visual analysis of the spindle pattern formed by the medullary rays, also termed wood rays. Each spindle is identified by means of image analysis technique, its position and orientation is determined, and the fibre direction of discretised elements is calculated. The individual process steps necessary to obtain an estimate of the fibre direction of a board are explained using the examples of five different failure types. In all examples, the estimated fields of fibre direction are congruent with the actual fibre direction determined by means of (1) the orientation of all present shrinkage cracks, which are established indicators for the fibre direction in wood, and (2) the fracture pattern after tensile testing. Employing the presented approach could open up new possibilities for the characterisation of European beech and other hardwood species with multi-row medullary rays in several fields of application, in particular regarding stress grading.     

Density profile and microstructural analysis of densified beech wood (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) plasticized by microwave treatment

This study was carried out in order to determine the efficacy of microwave (MW) plasticization for wood densification purposes. The plasticization process was carried out using a continuous feed laboratory MW at a frequency of 2.45 GHz. European beech (Fagus sylvatica L.) specimens measuring 50 mm?×?40 mm?×?8 mm were MW treated (plasticized) with an output of 3.5 kW at a conveyor speed of 0.4 m/min. Afterwards, MW plasticized specimens were densified with a ratio of 50%. Microscopic structure changes of densified wood were detected using a scanning electron microscope (SEM) and density profiles were measured using the X-ray densitography. An average density of 677 kg m^?3 and 771 kg m^?3 increased significantly to 951 kg m^?3 for radially densified and to 1194 kg m^?3 for tangentially densified specimens. X-ray densitography results show uniformity of density profiles through specimen thickness, which confirmed the evenly plasticized volume of wood. Microscopic structure observation revealed that the MW plasticization was not accompanied by any fractures, and deformations present in the densified wood were due to viscoelastic buckling of cell walls without crack propagation. Therefore, MW treatment can be considered as an effective method for wood plasticization.     

Characterization of trembling aspen wood (Populus tremuloides L.) degraded with the white rot fungus Ceriporiopsis subvermispora and MWLs isolated thereof

Trembling aspen wood (Populus tremuloides L.) was treated with white rot fungus Ceriporiopsis subvermispora for 1, 2, 4, and 6 weeks. As fungal decay advanced, lignin contents were decreased gradually up to ca. 27.5% (based on the Klason residues of the control) after 6 weeks. Alkali solubility of cell wall residues was increased until 4 weeks of fungal treatment, but additional treatment did not cause any effects. Milled wood lignins (MWLs) were isolated from the decayed woods by Björkman’s procedure and subjected to thioacidolysis and analytical pyrolysis to investigate the modification of lignin structures during fungal degradation. Thioacidolysis revealed that the yields of trithioethylated C₆C₃ monomers, as a parameter for frequency of β-O-4 linkages in lignin, were substantially reduced (-20%, based on the control) in MWLs isolated from decayed woods. Analytical pyrolysis revealed that the relative amounts of coniferyl alcohol and sinapyl alcohol in the pyrolysates were lowered dependent on the biodegradation time, whereas an elevation of C₆C₁ and C₆C₂ pyrolytic phenols was observed. The results from both analytical methods strongly suggested that β-O-4 linkages were cleaved by C. subvermispora. Specially, degradation of syringyl-type lignin seems to be preferred.     

The effect of fine strands in core layer on physical and mechanical properties of oriented strand boards (OSB) made of beech (Fagus sylvatica) and poplar (Populus tremula)

This paper discusses the influence of three different content levels of fine strands in the core layers on the physical and mechanical properties of European beech and poplar oriented strand boards (OSB). The results show that increasing the fines content in the core layer from 10 to 50 %, based on total board weight has no significant effect on bending strength and modulus of elasticity (MOE). All panels exceeded the minimum requirement for bending strength and MOE set by EN standards. The highest modulus of rupture (MOR) and modulus of elasticity (MOE) was determined for panels solely made of poplar with different level of fines content. Increasing the amount of fines in the core layer raised the internal bond (IB). Panels made with 30 % fines in the core layer showed highest internal bond strength values. As the fines content increased from 10 to 50 %, thickness swelling decreased. Water absorption after 24 h showed the same declining trend as thickness swelling.     

The appearance of resin pockets in CT-images of Norway spruce (Picea abies (L.) Karst.)

Picea abies (L.) Karst.) was studied. The study also includes a comparison between measured and calculated CT-numbers of Norway spruce resin and wood. It was found that it should be possible to create algorithms that automatically detect large resin pockets in CT-images of Norway spruce. Compared to resin pockets in heartwood, resin pockets in green sapwood are more difficult to detect due to the high density of the surrounding wood. The study also showed that the correlation between measured and calculated CT-numbers was high and that it is possible to use the same function for conversion between CT-number and density for both green wood and resin.

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Genetics of bruchid (Callosobruchus maculatus Fab.) resistance in cowpea (Vigna unguiculata (L.) Walp.)

Bruchid resistance has been measured using a variety of techniques. Mean development period (MDP) and percentage adult emergence (PAE) are two of the more important traits measuring bruchid (Callosobruchus maculatus Fab.) resistance in cowpea. The objective of the study was to evaluate the genetic relationship between MDP and PAE in C. maculatus resistant cowpea. Seventy-two F₂ population plants were developed from the cross between C. maculatus resistant TVu-11953 (with delayed MDP and low PAE) and C. maculatus susceptible Ife Brown (with early MDP and high PAE) which were evaluated for resistance to cowpea C. maculatus. MDP at 45 days after infestation (DAI) and PAE at 60 DAI were taken as analysed measures for resistance to C. maculatus infestation. Data generated were subjected to chi-square analysis. Varied resistant response to C. maculatus infestation was observed among the F₂ generation plants but their responses showed inclination to the susceptible parent. A 15:1 ratio for susceptible to resistant genotypes was observed with MDP among the F₂ genotypes evaluated which is an indication of the presence of two recessive genes that control of MDP. The segregation of PAE also showed a 15:1 ratio goodness of fit (P > 0.05) for susceptible to resistant genotypes. Test of independence between MDP and PAE was not significant (χ² = 2.19, P = 0.19). This study revealed that the recessive genes controlling these two traits (MDP and PAE) were independently assorted and showed no linkage. This was also evident in the observed F₂ genotypes with C. maculatus resistance expressing either delayed MDP or low PAE and not both in the study.