Wood Science and Technology最新文献

Multi-scale numerical homogenisation strategies have been used in the recent years to efficiently compute the effective elastic properties of heterogeneous materials. Coupled with a stochastic approach, they can be applied to natural material such as wood to take into account the variability of their properties. In the case of Pinus pinaster (Ait.), available elastic properties are based on those of generic softwood species due to a lack of data in the literature, reducing the overall precision of the results. This paper proposes an efficient numerical framework based on both a general numerical homogenisation method and the well-known Monte Carlo approach to determine the equivalent elastic properties at the macroscopic scale, with the associated variability, of the Pinus pinaster (Ait.) species. The coherence of the numerical model is established by comparison with analytical and experimental results available in the literature. The obtained results reveal very good accuracy in terms of equivalent elastic properties with a macroscopic behaviour characterised by an orthotropic symmetry. Moreover, the influence of the distance from the pith on the equivalent macroscopic elastic response is highlighted.

The stacking sequence of laminated wood significantly impacts the composite mechanical behavior of the material, especially when scaling down thermo-mechanical tests on plywood. In previous research, we developed a scaling methodology for thermo-structural tests on samples with similar cross sections, however this paper focused on testing plywood samples with different stacking sequences between the scales. Plywood samples at ½-scale and ¼-scale were subjected to combined bending and thermal loading, with the loading scaled to have the same initial static bending stresses. While the ¼-scale 4-layer [0°/90°]s laminate and the ½-scale 8-layer [0°/90°/90°/0°]s laminate had an equal number of 0° and 90° layers, as the char front progresses, the sections behave differently. Thus, modeling becomes essential to extrapolating the data from the smaller ¼-scale test to predict the behavior of the larger ½-scale test. Reduced cross-sectional area models (RCAM) incorporating classical laminated plate theory were used to predict the mechanical response of the composite samples as the char front increased. Three methods were proposed for calibrating the RCAM models: Fourier number scaling, from detailed kinetics-based pyrolysis GPyro models, and fitting to data from fire exposure thermal response tests. The models calibrated with the experimental char measurements produced the most accurate predictions. The experimental char models validated to predict the behavior of the ¼-scale tests within 2.5%, were then able to predict the ½-scale test behavior within 4.5%.

Coniferous forests in the European Union serve as crucial sources of roundwood, as well as contribute to various industries with different wood products. Harvesting of these trees leaves significant amounts of needles and small branches (logging residues). This underutilised forestry side-stream has the potential for various applications in the bioeconomy due to its chemical composition. Extraction of biomass involves various methods and solvents, including petroleum-based solvents, raising environmental and health concerns. This study aims to assess different extraction methods, with a focus on minimising or eliminating the use of hydrocarbon solvents, thereby refining valuable compounds for various applications, as well as evaluating the antimicrobial, antifungal and antioxidant activities of the obtained extracts. The most effective methods in extracting pine and spruce wood logging residues were determined to be maceration at boiling temperature with methanol and butanol, respectively. Extracts consisted of various compound groups such as fatty acids, resin acids, terpenes and more. The obtained extracts demonstrated antimicrobial and antifungal activity, as well as antioxidant activity.

Wood densification is a technique to enhance wood density and hardness, presenting a promising solution to expand wood use across various applications. However, current densification methods have cost and environmental impact limitations. This project introduces a potential environmentally friendly approach involving surface chemical densification through in-situ polymerization, using carbon Michael addition reaction between biobased acrylate and malonate monomers. This reaction, conducted in mild conditions with low energy and solvent consumption, aims to enhance wood densification while minimizing environmental impact. Various malonate-acrylate systems were formulated, and were optimized based on their viscosity, conversion rate, glass transition temperature, crosslinking density, and hardness. Then, sugar maple wood samples were densified with the best formulations. Monomers with lower viscosity demonstrated higher chemical retention. Density profile and penetration depth were also higher for the samples impregnated with lower viscosity formulations, which was confirmed by scanning electron microscopy. Confocal Raman spectroscopy confirmed that formulations successfully filled lumens and vessels without reacting with the cell wall components. Brinell hardness was used to determine the hardness of natural and densified woods. One-way ANOVA data analysis showed a significant increase in hardness of densified samples compared to untreated wood; however, based on TUKEY Anova analysis, no noticeable difference was reported between impregnated samples with different formulations. Overall, results showed the potential of the Michael addition reaction in wood impregnation.

Bamboo has attracted widespread attention owing to its strong mechanical properties, availability in numerous regions, and green and low-carbon nature. However, the hydrophilic nature and susceptibility to mold growth limit its wide application. Therefore, this study uses green biological enzyme technology to improve the hydrophobic performance of bamboo, grafting hydrophobic monomer octadecylamine (OA) onto bamboo surfaces under the catalysis of laccase. The optimum reaction conditions such as the amounts of OA monomer and laccase, reaction time, and temperature were determined. Under these optimized conditions, the contact angle of treated bamboo reached 121°± 3°, which was six times higher than that of untreated bamboo, and its hydrophobicity is very stable compared to that of OA-bamboo, could withstand soaking and washing with hot water, ethanol and acetone, and the change rate of contact angle during 180s test was ∼1%. Moreover, as the water absorption rate of bamboo decreased, the defects of bamboo susceptible to mildew growth also considerably improved. The hydrophobic modification mechanism was studied using SEM (scanning electron microscopy), ¹H-NMR (nuclear magnetic resonance), and XPS (X-ray photoelectron spectroscopy), this analysis confirmed that OA grafting onto bamboo under laccase catalysis resulted in stable hydrophobicity. Moreover, OA chemically reacted with lignin in bamboo, possibly forming a C–N bond. This study provides valuable insights into the expanding applications of bamboo as sustainable materials.

This study utilized a self-developed gas permeability–porosity integrated analyzer to examine the gas permeability and porosity of pine, cypress, and Cunninghamia conifers across different wood orientations and parts. The findings reveal that the longitudinal permeabilities of conifers are higher than the radial and tangential permeabilities by factors of 14–100 and 275–600, respectively. A consistent exponential relationship exists between longitudinal permeability and porosity, irrespective of species. In the sapwood, the tracheid dimensions are 110.5–132.1% in radius and 103.6–116.2% in length compared to heartwood. A single tracheid exhibits higher longitudinal flow resistance than those in the radial and tangential directions. The primary longitudinal flow resistance stems from the lap surface of the upper and lower tracheids series connected with pits. In radial and tangential directions, the gas flow encounters a high density of pits from a series of connected tracheids. The number of series-connected tracheids in the longitudinal direction is only 1% of those in radial and tangential directions, whereas it reaches up to 600 times for parallel connections. This leads to considerably lower total flow resistance in the longitudinal direction compared to radial and tangential directions. The measured higher longitudinal gas permeability aligns well with the model calculations and the gas microseepage is predominantly related to tracheid structure, causing permeability variations.

Wood is a primary building tool for ancient buildings and structures, but for those that survive to date, naturally aged wood may pose a noteworthy fire hazard. There are potential risks to health, safety, and substantial cultural loss if fire risks in such buildings are not mitigated. We obtained several samples of aged wood commonly used in ancient structures (elm, pine, and aspen), and compared the kinetic and thermal characteristics to fresh wood examples to determine potential methods of enhancing safety. Differential scanning calorimetry was used to establish the heat release characteristics of the fresh and aged samples, and the characteristics of the thermal reaction stages were characterized using the temperature range and heat release laws for each reaction stage. The heat release characteristics during combustion were investigated for different heating rates, and the influence of aging on temperature change and heat release rate characteristics during different exothermic stages was assessed. Finally, using heat flow data, the apparent activation energy (AAE) of the samples and their distributions during different exothermic stages were calculated and analyzed via the Friedman differential iso-conversion method. Results showed that the exothermic energy of the aged samples was higher than that of the fresh samples, indicating that aging does impact the thermal reaction process. The aged samples in this study had a greater heat diffusion capacity, transmitted more heat, were more susceptible to burning (by spreading that heat), and generally posed a greater fire hazard. During the rapid exothermic phase, the AAE of aged wood increased as the reaction progressed, and exhibited lower AAE with a greater sensitivity to fire than fresh samples. A sound linear relationship between pre-exponential factor and AAE and the kinetic compensation effect was obvious. This study provided a rudimentary theoretical basis for the prevention of fires in timber-framed ancient buildings.

High variations in juvenile wood properties in the radial direction and its worse performance than mature wood make it less suitable for some applications and often treated as waste material. This study aimed to assess how thermal modification affects the chemical composition and the physical, mechanical and swelling properties of Scots pine juvenile and mature wood. An additional goal was to evaluate if the modification can equalise the differences in selected properties of juvenile wood to those of mature wood so that from waste material, juvenile wood can become a fully-fledged raw material for various industrial applications. Thermal treatment at 220 °C influenced wood chemical composition, degrading mainly hemicelluloses but also affecting cellulose and lignin, which resulted in a reduction of hydroxyls and carbonyl/carboxyl groups. These changes were more pronounced for mature than juvenile wood. It reduced mass loss and swelling rate, and increased swelling pressure in the tangential and radial directions to a higher degree for juvenile than mature wood. Changes in mechanical properties in compression were statistically significant only for mature wood, while wood hardness remained unaffected. Although the applied heat treatment improved the performance of juvenile wood by reducing its swelling rate, it did not equalise the examined properties between juvenile and mature wood. Since higher juvenile wood proportion is expected in the wood supply from the future intensively managed forests, there is still a need to find suitable modification methods or better processing techniques so that instead of being thrown away as waste, it could be used broadly in various industrial applications.

Thermogravimetric analysis (TGA) was performed on five softwood and five hardwood thin wood samples in the longitudinal (L) and radial (R) directions. Dimensional changes were monitored using a charge-coupled device camera under a nitrogen flow. A comparison of the TG and derivative TG (DTG) curves revealed that shrinkage in the R direction began when the weight was reduced to 79–92% at 305–330 °C and 87–96% at 275–290 °C for softwoods and hardwoods, respectively. Hemicellulose is mainly degraded in this temperature range. In contrast, shrinkage in the L direction started at temperatures close to the DTG peaks, i.e., 360–380 °C and 345–370 °C, respectively, at which temperatures cellulose is mainly degraded. In general, the R/L shrinkage anisotropy was greater for hardwoods than for softwoods, but the species variation was large and the magnitude was directly related to the difference in the shrinkage onset temperatures between the R and L directions, regardless of the wood species. Therefore, shrinkage anisotropy can be attributed to the relative reactivity of hemicellulose and cellulose in wood cell walls. The shrinkage mechanism during carbonization is discussed in terms of the cell wall ultrastructure, in which cellulose microfibrils are covered by a hemicellulose–lignin matrix, and the orientation of the cells in the L and R directions.

The product of thermochemical processing of lignocellulosic biomass is biochar. It has a range of properties that make it suitable for a variety of economic applications. However, during pyrolysis and torrefaction, volatile organic compounds (VOCs) are released and may redeposit on the surface of the biochar. Some of these compounds may be harmful to the environment and humans. Bibliometric study shows that, to date, studies on the release of VOCs from biochar have been of an inventory nature and concerned with specific case studies of the specific types of biomass. To date, there has been no comprehensive and systematic analysis of the influence of lignocellulosic biomass properties and pyrolysis/torrefaction process parameters on VOC formation and redeposition on biochar. In this paper, the analysis is presented of the potential harmfulness of VOCs released during the thermochemical processing of lignocellulosic biomass components, based on cellulose, hemicellulose, and lignin pyrolysis/torrefaction chemistry data. 10 volatile organic compounds from cellulose, hemicellulose, and lignin pyrolysis were identified as potentially harmful due to the following properties: carcinogenicity, toxicity, flammability, skin corrosion/irritation, eye irritation, and mutagenicity, with different degrees of harmfulness. Additionally, the VOCs identified on biochar samples show a potential hazard. Among 140 identified compounds, 33 of them had harmful properties. Therefore, the redeposition on biochar of ketones, aldehydes, cyclic and aromatic hydrocarbons including polyaromatic hydrocarbons, and their derivatives, esters, and furans may lead to environmental contamination due to their release from biochar. A new niche for systematic research on the development of new knowledge regarding the biochars produced from biomass as a source of pollutant emission has been identified.