Wood Science and Technology最新文献

This work is devoted to dimensional changes in oak wood induced by the adsorption of water and ethanol molecules during barrel aging of wine and spirits. A custom device has been developed to determine the deformations in the radial and tangential directions of samples soaked in liquid, through imagery and digital image correlation. Swelling measurements and residual shrinkage after subsequent drying are reported at eight ethanol contents, including pure water and ethanol. A synergistic effect is observed over a wide range of concentrations. This suggests a collaborative action of sorption sites when both water and ethanol are in sufficient quantity. In addition, sequential exposure tests were performed to assess the effect of history, showing that the order of exposure influences the swelling because of the irreversible alterations in the structure of the wood. All these data, including the residual shrinkage, were analyzed and the mechanisms are summarized in a graphical presentation.

This research paper studies the influence that the number of plies has on the identification of the mechanical properties of poplar Laminated Veneer Lumber (LVL) from tensile tests such as its stiffness. LVL poplar specimens were prepared with different ply configurations and subjected to uniaxial tensile tests. Both longitudinal and transverse stiffnesses were characterized in this research. The results show that the ply configuration influences the mechanical properties. The influence of the glued faces, the presence of lathe checks, and the compression ratio of veneers were studied during the manufacturing of the LVL. All these results provide valuable information for the design and optimization of laminated wood structures. An analytical modelling strategy is proposed to account for the effect of ply numbers, ply orientations, the compression ratio of veneers and the glue used on the stiffness of poplar laminate both in longitudinal and transverse directions.

The reaction mechanism of the Dakin reaction for three lignin model compounds was thoroughly investigated using density functional theory (DFT). A more comprehensive atomic and molecular level oxidation mechanism for the Dakin reaction was proposed, complementing the previously reported reaction process. The potential energy surface information for twelve possible channels was obtained at B3LYP/6–311 + G(d,p) level based on the geometry optimization together with the frequency calculation of the stationary points. The influence of substituent effects on the reaction energy barrier of Dakin reaction in lignin model compounds was estimated. The calculated results revealed that the rearrangement reaction of quinone structure primarily involves ring-forming and ring-opening of epoxy group, the ring-forming on O and C of benzene ring and ring-opening on C and C of benzene ring. The energy barriers of Dakin reaction decrease with an increase in the number of methoxy groups in lignin model compounds. Further elucidation of the Dakin reaction mechanism will provide a theoretical foundation for the development of more effective catalytic systems to enhance the valuable utilization of lignin in future applications.

There is currently no quality sorting of harvested hardwood timber in Norway on a national scale. Medium- and high-quality logs including those from birch (Betula pubescens Ehrh., B. pendula Roth) are thus not utilized according to their potential monetary value. Increased domestic utilization of quality birch timber requires that the quality of harvested logs be properly assessed for potential end uses. A preferred sorting procedure would use visually detectable external log defects to grade roundwood timber. Knots are an important feature of inner log quality. Thus, the aim of this study was to evaluate whether correlations between branch scar size and knot features could be found in Norwegian birch. Using 168 knots from seven unpruned birch trees, external bark attributes often showed strong correlations with internal wood quality. Both length of the mustache and length of the seal performed well as predictors of stem radius at the time of knot occlusion. The presence of a broken off branch stub as part of an occluded knot significantly increased the knot-effected stem radius, proving that the practice of removing branches and branch stubs along the lower trunk is a crucial measure if quality timber production is the primary management goal.

The histogenesis of reaction wood in woody plants is a promising area of exploration for emerging wood technology products and for a generalized understanding of stress physiology. The activity of total protein and antioxidant enzymes were measured during the development of normal and reaction wood (opposite wood and tension wood) in the bole of poplar trees (Populous alba L.) induced by two levels of sustained bending stress to produce moderate and severe reaction wood. Four-year-old poplars were induced to produce reaction wood by sustained bending to 0, 35 and 80° from the vertical position. The activity of antioxidant enzymes was studied with repeated sampling during one growing season. Severe reaction wood showed higher levels of H₂O₂ and enzymes than moderate reaction wood. Tension wood showed a higher accumulation of total protein than opposite wood at the beginning and end of the bending treatment and opposite wood showed higher enzymatic activity. H₂O₂ and antioxidant enzymes were also sensitive to mechanical bending stress; compared to normal wood, tension wood and opposite wood which showed higher enzymatic activity coupled with higher amounts of total H₂O₂. Ascorbate peroxidase was more active than glutathione peroxidase in both tension and opposite wood at some periods of sampling.

The paper focuses on a multilevel analysis considering six species of bamboo of the Phyllostachys family (P. bambusoides, edulis, iridescens, viridiglaucescens, violacescens, and vivax) and Arundo donax grown in temperate climates, most of them not already studied in the literature. The analysis is divided into three levels. The analysis at the first level (the microscopic scale) includes an anatomical study to assess the shapes and dimensions of the vascular bundles and the sclerenchymatic and parenchymatic tissues. At the second mesoscale level, the percentage and distribution of the fibres, voids and parenchyma are calculated. At the third level, the macroscopic one, a discussion of the influence of the microscopical properties on mechanical properties is carried out. Despite the limited number of specimens analysed at the microscale level, differences between species emerged from the analysis and influenced the macroscopic characteristic values. In particular, the morphology of the components differs, especially in the case of Arundo donax, which presents a unique distribution of its components along the culm wall. Different contents of each component are observed for the species analysed. Moreover, an innovative analysis that focuses on the presence and distribution of voids is presented, which have a fundamental role in the mechanical behaviour of this material. The analysis did not account for the influence of the environment on composition or anatomical and physical characteristics.

Developing a moisture-stable structural material with high toughness is essential for improving the stability of packaging and building materials. Wood is a pervasive structural material with naturally good mechanical properties. However, insufficient moisture stability and toughness compromises its safety and structural requirements. Herein, we constructed a moisture-stable wood veneer with high toughness by assembling the choline chloride-ethanolamine delignified wood with alkali lignin, followed by hot-pressing to densify the material. Lignin can be assembled into the microchannel of the delignified wood as a filler and binder for reducing molecular transportation and increasing internal bonding. The enhanced tensile strength (582.0 MPa) and strain (3.6%) are accompanied by a significant increase in the toughness to 11.1 MJ/m³, which is 37 times higher than that of natural wood. The excellent mechanical property can be preserved to a large extent after retaining in tropic moisture conditions (38 °C, 90% RH) with retention of 66.2% and 60.8% for tensile strength and toughness, respectively. A stable water contact angle on the surface and limited water adsorption of reconstructed wood indicate a lowered water infiltration velocity, suggesting highly improved moisture stability as needed for structural materials.

The differential swelling seen between softwood opposite wood (OW) and its neighbouring compression wood (CW) developed in branches prompts several engineering issues such as dimensional instability and cracking. For a more efficient use of resources, the inevitable CW and OW should not be discarded or used as fuel, but incorporated into engineered wood products. Swelling is a hygroelastic phenomenon, where both the swelling and elastic properties of CW and OW are needed in order to make proper structural predictions. In this paper, swelling coefficients and moisture dependent elastic moduli for both CW and OW in the three principal material directions are provided along with measurements of moisture content, density, and microfibril angle. The small deformations necessitate the use of precise X-ray micro-computed tomography for measurements. The results indicate that CW and OW from Norway spruce branches differ in swelling, especially in longitudinal direction at low moisture content. It is noted that CW is a wood type with less pronounced anisotropic behaviour than both OW and normal wood from the stem, with the elastic moduli less sensitive to moisture changes in both longitudinal and transverse directions.

During the dehydration of waterlogged archaeological wood (WAW), shrinkage inevitably occurs due to capillary force and hydrogen bond recombination as WAW loses free and adsorbed water. Existing drying techniques, including solvent displacement, freeze-drying, and supercritical fluid drying, only take effect by reducing or eliminating the surface tension of liquid. Nonetheless, the contribution of hydrogen bond recombination in shrinkage has long been neglected and a countermeasure concerning this problem is needed. In this study, we propose a simple aqueous phenylboronic acid (PBA) treatment that can help improve dimensional stability and reduce hygroscopicity of WAW. Analysis by Fourier transform infrared spectroscopy, density functional theory calculation and dynamic vapour sorption reveal that PBA can incorporate with hydroxyl groups (–OH) on cellulose through coordination and hydrogen bonds, occupy the water-cellulose binding sites, and possibly inhibit the formation of hydrogen bonds between adjacent cellulose chains.

The transient dimensional changes during hygro-expansion and hydro-expansion of freely and restrained dried, softwood and hardwood sheets and fibers is monitored, to unravel the governing micro-mechanisms occurring during gradual water saturation. The response of individual fibers is measured using a full-field global digital height correlation method, which has been extended to monitor the transient hydro-expansion of fibers from dry to fully saturated. The hygro- and hydro-expansion is larger for freely versus restrained dried and softwood versus hardwood handsheets. The transient sheet-scale hydro-expansion reveals a sudden strain and moisture content step. It is postulated that the driving mechanism is the moisture-induced softening of the so-called ”dislocated regions” in the fiber’s cellulose micro-fibrils, unlocking further fiber swelling. The strain step is negligible for restrained dried handsheets, which is attributed to the ”dislocated cellulose regions” being locked in their stretched configuration during restrained drying, which is supported by the single fiber hydro-expansion measurements. Finally, an inter-fiber bond model is exploited and adapted to predict the sheet-scale hygro-expansion from the fiber level characteristics. The model correctly predicts the qualitative differences between freely versus restrained dried and softwood versus hardwood handsheets, yet, its simplified geometry does not allow for more quantitative predictions of the sheet-scale hydro-expansion.