Adhesive penetration of hardwood: a generic penetration model

An analytical model to predict the penetration of adhesives into hardwood is proposed. Penetration into hardwood is dominated by the vessel network which prohibits porous medium approximations. The model considers two scales: (1) a one dimensional capillary fluid transport of a hardening adhesive through a single, straight vessel with diffusion of solvent through the walls of the vessel; and (2) a mesoscopic scale based on topological characteristics of the vessel network. Given an initial amount of adhesive and applied bonding pressure, the portion of the filled structure could be calculated. The model was applied to beech samples joined with three different types of adhesive (PUR, UF, PVAc) under various growth ring angles as described by Hass et al. (2011). The model contains one free parameter that can be adjusted in order to fit the experimental data.     

Silylation of solid beech wood

This report presents a new derivative from the chemical conversion of hardwood. Silylation of hardwood was successfully achieved using trimethylsilyl chloride with pyridine as base. The new wood compounds were analyzed by FTIR spectroscopy. The FTIR spectra of the silylated wood compounds show new absorption bands derived from trimethylsilyl ether groups. Furthermore, the products were investigated by means of EDX analysis. The presence of silicon confirmed the conversion of wood into the corresponding silyl ether derivative. Electron microscopy, i. e. SEM, shows that the location of the silicon was not restricted to the surface of the wood fibres. Penetration of the reactants into the wood body occurred, when a solid wood sample (beads) was used.     

Moisture-dependent orthotropic elasticity of beech wood

Elastic material properties are one of the most important material characteristics in mechanical modelling. Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. In order to characterise beech wood as an orthotropic material, all of the independent elastic properties were determined at different moisture conditions. These characteristic properties have never been determined before as a function of moisture content yet are vital to the field of wood modelling. All elastic parameters, except for some Poisson’s ratios, show a decrease in stiffness with increasing moisture content. In comparison to available literature references at a moisture content of ω?≈?12%, the identified values were of the same order of magnitude. The determined material properties can be used to investigate the mechanical behaviour of beech wood structures including different moisture conditions.     

Liquefaction of beech wood in various supercritical alcohols

The liquefaction of Japanese beech (Fagus crenata Blume) was studied with various straight-chain alcohols in subcritical and supercritical states using a batch-type reaction vessel to obtain liquid fuel from lignocellulosics. Under the reaction condition of 270°C, beech wood was liquefied to some extent in all alcohols with about 50%–65% insoluble residue left after treatment for 30min. Under the condition of 350°C, however, more than 90% of wood was decomposed and liquefied in all alcohols. Alcohols with longer alkyl chains liquefied lignocellulosics in shorter reaction times. Because many kinds of alcohols, such as methanol and ethanol, can be produced from biomass, 100% biomass-based liquid fuel can be prepared by supercritical alcohol technology when using such bioalcohols. This study was presented in part at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, Japan, March 16–18, 2005     

Alkaline degradation of spruce and beech wood

Summary The alkaline delignification of spruce and beech wood is accomplished in three phases. The first phase results in a decrease of yield down to 83...80%, the second one in a decrease from 83...80% to 64...61% and the third one in a yeld drop from 64...61% to 50...46%. The amount of polysaccharides removed in the first phase was 22%, in the second phase 5...6% and in the third phase 10% of the total polysaccharides in the original wood. The amount of lignin removed in the first phase of delignification was 9...11% in the second phase 53...54% and in the third phase 28% of the total lignin in the original wood. The polysaccharides extracted in the second and third phase amounted to 70...78% of the polysaccharides removed in the first delignification phase. For an entire characterization of the delignification reaction not only the course of lignin removal is of importance but also the course of the polysaccharide extraction. The results show that for a two-stage alkali-oxygen-cooking technology the optimum yield after initial partial alkaline delignification lies in the range of 64...61%.     

Tartaric acid catalyzed furfurylation of beech wood

European beech (Fagus sylvatica L.) is a major tree species of European forest which is underexploited because of its low dimensional stability and durability. Similarly to what has been developed with radiata pine, furfurylation might be the answer to optimize the utilization of local beech wood. Beech wood furfurylation process was studied using five different catalysts: maleic anhydride, maleic acid, citric acid, itaconic acid, and tartaric acid. Optimization of the furfurylation process was investigated for different catalyst and furfuryl alcohol (FA) contents, and different duration of polymerization. The following properties were studied: weight percent gain (WPG), leachability, anti-swelling efficiency (ASE), wettability, modulus of elasticity, modulus of rupture, Brinell hardness, and decay durability. Tartaric acid, never investigated up to now, was retained as catalyst to perform furfurylation due to its efficacy compared to other catalysts and its novelty. Wood modification with FA and tartaric acid as catalyst led to samples with high WPG even after leaching, improved ASE, and lower wettability with water. Increasing the polymerization duration increased the fixation of FA in treated wood. Most of all, treatment gave a significant improvement in mechanical properties and resistance to wood decaying fungi.     

Liquid penetration of precompressed wood VII: combined treatment of precompression and extraction in hot water on the liquid penetration of wood

The object of this study was to determine the cause of differences in the improvement in liquid penetration of precompressed wood species. The maximum amount of water uptake by the capillary rise method and changes in the aspirated pits seen with scanning electron microscopy before and after of preextraction and precompression were investigated using heartwood samples of four softwoods. The height of penetration and the weight by the capillary rise method for preextractive wood powders are discussed. Three wood species andLarix leptolepis showed marked increases in the amount of solution uptake after precompressed treatment only.Larix leptolepis wood required compression after extraction by boiling in water. These differences among wood species were caused by the accumulation of extractive material. It was also recognized that the accumulative material inLarix wood has plasticity and that inPseudotsuga is brittle. Based on these results it was found that it is difficult to destroy aspirated pits in the former and easy in the latter. On the other hand, the difference in penetration of each wood species was caused by the quantity and quality of the extraction material in addition to the extent of the wettability of the surface of the cell cavity as well as aspirated pit.Part of this report was presented at the 46th annual meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Chemical changes during the production of thermo-treated beech wood

Thermal treatments of beech wood with different temperature loads on the wood cause characteristic changes in the chemical composition. The determination of specific changes was carried out by means of suitable methods, both wet chemical and instrumental analyses. It could be confirmed that in addition to the degradation of polyoses, lignin, known as the thermally most stable compound, shows significant thermal alterations too.     

Impregnation of Scots pine and beech with tannin solutions: effect of viscosity and wood anatomy in wood infiltration

The impregnation process of Scots pine and beech samples with tannin solutions was investigated. The two materials involved in the process (impregnation solution and wood samples) are studied in depth. Viscosity of mimosa tannin solutions and the anatomical aspect of beech and Scots pine were analysed and correlated. The viscosity of tannin solutions presents a non-newtonian behaviour when its pH level increases, and in the case of addition of hexamine as a hardener, the crosslinking of the flavonoids turns out to be of great importance. During the impregnation of Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.), the liquid and solid uptakes were monitored while taking into consideration the different conditions of the impregnation process. This method allowed to identify the best conditions needed in order to get a successful preservative uptake for each wooden substrate. The penetration mechanism within the wood of both species was revealed with the aid of a microscopic analysis. Scots pine is impregnated through the tracheids in the longitudinal direction and through parenchyma rays in the radial direction, whereas in beech, the penetration occurs almost completely through longitudinal vessels.     

Identification of moisture-induced stresses in cross-laminated wood panels from beech wood (Fagus sylvatica L.)

The crosswise bonding of the layers in laminated solid wood panels results in internal stresses when the humidity varies. The layers hinder one another as a result of the anisotropy of wood. The purpose of this study was to determine the internal stress state in free and constrained swelling. The expansion properties in the three panel directions were measured. Furthermore, the swelling of samples was constrained while the resulting forces were recorded. Hygroscopic warping experiments were carried out inducing a climate gradient within the panels. Afterwards the stresses were calculated from released deformations and non-destructive measurements of the Young’s modulus. The materials used were untreated and heat-treated beech wood, the latter modified in two levels. In addition to homogenously structured panels, treated top layers were combined with an untreated middle layer. Swelling, swelling pressure, warping and internal stresses considerably decreased from untreated to treated wood. If layers from treated and untreated material were combined, stresses and deformations increased as compared to the variants produced only from treated wood. It was concluded that the lower equilibrium moisture content of heat-treated beech wood improves its dimensional stability, which results in smaller deformation differences between the layers. Hence, the stresses were less distinctive.     

Analysis of beech wood fatty acids by supercritical acetone extraction

Summary Soxhlet and supercritical fluid extracts of freshly cut oriental beech (Fagus orientalis) have been obtained using acetone. While the yield of the Soxhlet extract was 2.54% the yield of the supercritical acetone extract obtained at 240°C and 6.0–6.5 MPa was 9.55% (dry wood basis). The fatty acids present in the extracts were separated by chemical and Chromatographic methods and analysed by combined gas chromatography and mass spectrometry. Linoleic acid was the major fatty acid in both extracts.     

Modelling the economically viable wood in the crown of European beech trees

Long-term forest development programs in Germany aim on an increase of close-to-nature broadleaf forest stands. This means that the economic importance of European beech is expected to increase. The economic potential of a tree basically consists of the stem as well as the economically viable wood volume in the crown. Due to the high morphological variability of European beech crowns, taper models are often not satisfactory for predicting the economically viable wood volume arising from crowns. Prediction models with a higher precision are recently still lacking. Aim of this study is thus the development of prediction model for the economically viable crown wood volume of European beech trees.We determined the distribution of the wood volume in the crown over the branch diameters using the multistage ‘randomized branch sampling’ method (RBS). The tree-specific wood volume distribution on the branch diameters were used to cluster all sampled trees into 3 groups. Additionally, we developed a method able to distinguish between economically viable and unviable crown branches. Basing on the RBS measurements as well as revenues and processing costs, we modeled the economically viable wood volume from the crown for each tree. To calculate the wood volume under bark, we parameterized a bark thickness function from disk samples of the trees.We showed that the European beech crowns could be clustered into 3 groups differing in their wood volume distribution. The economically viable wood volume in the crown significantly depended on this grouping parameter as well as diameter at breast height (DBH). By contrast, the total amount of wood in the crown only depended on DBH. The differing viable wood volumes in the crowns were thus explained by different wood distributions and not by differing total crown wood volume. To make the results applicable in practice forestry, the modelling results were used to develop a regression formula able to predict the economically viable wood volume in the crown depending on the DBH and the crown type. As the crown type can also be predicted via measurable tree covariates, the regression model of the viable wood volume in the crown can be used as a support tool for the management of European beech stands. Sensitivity analysis quantifies how harvest revenues and costs translate into different viable tree volume.     

Estimating growth in beech forests: a study based on long term experiments in Switzerland

? This contribution presents a dynamic stand growth model for Beech (Fagus sylvatica L.) forests, based on a dataset provided by the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf. The dataset includes 143 research plots, covering a wide range of growing sites and providing up to 16 interval measurements per research plot.

? The objective of this research is to complement the range of existing beech growth models by bridging the gap between the historical yield tables and the single tree growth models. The specific aim is to develop transition functions which will project three state variables (dominant height, basal area and number of trees per hectare) at any particular time, in response to any arbitrary silvicultural treatment.

? Two of the transition functions were derived using the generalized algebraic difference approach (GADA), the third one was derived with the algebraic difference approach (ADA). All the functions were fitted simultaneously using iterative seemingly unrelated regression and a base-age-invariant method. The influence of thinnings on basal area growth was included by fitting different transition functions for thinned and unthinned stands.

? The overall model provides satisfactory predictions for time intervals up to 20 years. The new model is robust and its relatively simple structure makes it suitable for economic analysis and decision support.

     

Effect of severe thermal treatment on spruce and beech wood lignins

? The structure, proportion and mode of assembly of lignin, celluloses and hemicelluloses have marked effects on the reaction mechanisms during thermal treatment and therefore have a strong influence on the quality of the final product. The effect of treatment conditions, including severe conditions (up to 553 K) and treatment duration (up to 8 h) on the structure of native spruce and beech lignins was studied.

? Lignin content was determined by the Klason method and lignin structure was evaluated by thioacidolysis.

? The results highlighted the strong reactivity of the native spruce and beech lignins towards severe heat treatments. The distinct susceptibility of syringyl (S) and guaiacyl (G) units towards thermal treatment is confirmed by comparing the data for beech and spruce samples. The most severe treatment of spruce wood (280 °C) induced a dramatic enrichment in lignin content together with the almost complete disappearance of G lignin units, whereas a more moderate treatment substantially changed lignin structure by degradation reactions that affect the p-hydroxyphenyl (H) and G lignin units similarly.

? Thioacidolysis revealed that the thermal treatment induces the appearance of vinyl ether structures in spruce lignins. The decreased yield of the G and S thioacidolysis monomers reflects the progressive disappearance of G and S lignin units only involved in β-O-4 bonds and the formation of condensed linkages in proportions related to treatment severity. In severe conditions, β-O-4 linked S units are more degraded than their G homologues.

     

Dead wood in European beech (Fagus sylvatica) forest reserves

Data were analysed on the volume of dead wood in 86 beech forest reserves, covering most of the range of European beech forests. The mean volume was 130 m³/ha and the variation among reserves was high, ranging from almost nil to 550 m³/ha. The volume depended significantly on forest type, age since reserve establishment and volume of living wood. More dead wood was found in montane (rather than lowland/submontane) reserves, longer-established reserves (time since designation) and reserves with higher volumes of living wood.

On average, fallen dead wood contributed more to the total dead wood volume than standing dead wood. The percentage of dead wood that was standing was almost twice as high in montane than in lowland/submontane forest reserves (45% versus 25%). The volume of dead wood at selected sites changed considerably over time. The fluctuations were significantly higher in lowland/submontane than montane reserves, possibly connected with differences in the disturbance regimes and especially damage caused by windstorms. In NW Europe, the blow down of formerly managed, even-aged stands led to extraordinary high volumes of dead wood shortly after reserve establishment.

The implications for forest management and biodiversity conservation are discussed. An increase in dead wood volumes must be carried out in accordance with the local/regional forest type and disturbance regime. Thus, in order to fulfil the requirements of as many wood-depending organisms as possible, it is important to preserve not only larger amounts of dead wood, but also dead wood of different types and dimensions as well as securing a long-term continuity of dead wood.     

Moisture content penetration in wood elements under varying boundary conditions

Knowledge of effects of moisture exposure on timber structures is important for serviceability and load bearing capacity of timber elements and systems. Varying climate affects the moisture content profiles in timber as the relative humidity changes in the ambient air. This paper presents methods for calculation of diffusion based moisture transport and corresponding results on how timber responds to varying moisture with regard to moisture penetration and distribution. The calculations are based on measured outdoor relative humidity and temperature at different climatic locations in Sweden. No remarkably large deviations between the different climatic locations were found in general, which is positive in a design code perspective.     

Liquid penetration of precompressed wood VI: Anatomical characterization of pit fractures

Pit fractures of refractory coniferous heartwoods caused by precompression in the radial direction were investigated and are discussed in terms of improved liquid penetration. Small cracks appeared at the boundary between the torus and margo, along the outer margin of the margo, and on the torus when specimens were compressed and deformation was fixed by drying. The remarkable cracks were generally observed for Cryptomeria japonica D. Don. Pseudotsuga menziesii Franco showed peculiar detachment of the torus from the pit border, and Larix leptolepis Gordon exhibited only small cracks on the torus. These fractures patterns were clearer when the precompressed specimens were recovered by water impregnation and then redried.This report was presented at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Microstructure,strength and structural integrity of heat-treated beech and spruce wood

Abstract

Heat treatment of wood is an effective method by which to improve the dimensional stability and biological durability, but the mechanical strength is decreased at the same time. Besides chemical modification of cell-wall constituents, physical weakening of the microstructure owing to heat-induced defects may also contribute to strength loss. Therefore, anatomical properties of heat-treated beech (Fagus sylvatica L.) and spruce (Picea abies Karst.), studied by light microscopic and scanning electron microscopic analysis, and their interrelation with strength properties and structural integrity were investigated. For determination of structural integrity, the high-energy–multiple-impact (HEMI) test was applied. Microscopic analyses showed frequent formation of radial cracks in heat-treated beech close to the rays as well as tangential cracks in the latewood of spruce. In addition, the modulus of rupture was more affected by the heat treatments than the resistance to impact milling (RIM) determined by the HEMI test, because RIM is based on multiple fractures on the microlevel that are not affected by the formation of intercellular cracks or other defects due to the heat treatment. It was concluded that heat-induced defects in the wood microstructure contribute to the substantial strength loss of thermally modified timber.     

Thermally initiated solvent-free radical modification of beech (Fagus sylvatica) wood

A procedure for rapidly modifying beech wood using a thermally initiated solvent-free grafting system was examined. In the modification, butyl acrylate and butyl methacrylate were used as vinyl monomers. Free radicals were generated from 2,2′-azobis(2-methylpropionitrile) or benzoyl peroxide at 103 and 180 °C by contact heating of the modified material. Chemical changes in the material were investigated by FTIR and X-ray photoelectron spectroscopies. The modification resulted in decreased surface wetting of the material manifested by increased water contact angles. The hardness of the resultant material decreased, while its color changed by the effect of temperature. It was shown that the approach allowed for efficient thermal-initiated modification of wood with rapid contact heating.     

Determining moisture-dependent elastic characteristics of beech wood by means of ultrasonic waves

The present study investigates the influence of moisture content on the elastic characteristics of beech wood (Fagus sylvatica L.) by means of ultrasonic waves. A set of elastic engineering parameters (i.e. three Young’s moduli, three shear moduli and six Poisson’s ratios) is determined at four specific moisture contents. The results reveal the significant influence of the moisture content on the elastic behaviour of beech wood. With the exception of some Poisson’s ratios, the engineering parameters decrease with increasing moisture content, indicating a decline in stiffness at higher moisture contents. At the same time, wood anisotropy, displayed by the two-dimensional representation of the velocity surface, remains almost unchanged. The results prove that the ultrasonic technique is suitable for determining the elastic moduli. However, non-diagonal terms of the stiffness matrix must be considered when calculating the Young’s moduli. This is shown experimentally by comparing the ultrasonic Young’s moduli calculated without, and allowing for, the non-diagonal terms. While the ultrasonic technique is found to be reliable to measure the elastic moduli, based on the measured values, its eligibility to measure the Poisson’s ratios remains uncertain.