Wood Science and Technology最新文献

Bamboo exposed to variations in humidity is prone to cracking, which can reduce its usability. As a natural material, bamboo’s hygroscopicity causes dimensional changes, influenced by the gradient distribution of fibres throughout the wall thickness. This study evaluated the dimensional changes resulting from variations in moisture content. Hygroscopic coefficients were extracted and applied in a finite element model to assess the circumferential stresses generated during sorption and desorption processes. Conditioning tests showed that open ring samples tend to close during sorption and open during desorption, due to the predominant swelling and shrinking behaviour of the fibre cells. The developed finite element model successfully replicated the aperture behaviour and dimensional changes in the thickness of open ring bamboo samples. The optimized parameters were subsequently used to predict the stresses under varying humidity conditions in closed-ring samples The circumferential stresses ranged from 9.8 MPa to -12.5 MPa from the inner to the outer layer in the saturated condition, and from − 7.1 MPa to 11.4 MPa in the dried condition. The values achieved reflect stresses that can lead to cracks and the failure of bamboo, thereby demonstrating the model’s ability to predict the hygroscopic behaviour of the material.

This study proposes a novel method for wood species identification, that employs importance-based feature selection integrated with a multiple spectral fusion technique. Specifically, the fusion integrates near-infrared spectroscopy (NIR), hyperspectral imaging spectral information, and terahertz (THz) spectroscopy. The experimental samples comprised four conifers and one broadleaf wood. Preprocessing of the spectral data was conducted using a combination of Savitzky-Golay smoothing (SG), Standard Normal Variate (SNV) correction, and normalization techniques. A hybrid feature selection method, combining random forest (RF) and gradient boosting decision tree (GBDT) algorithms, was then employed to extract the most important spectral features. To enhance clustering stability and mitigate the risk of overfitting, data augmentation was performed using a variational auto-encoder (VAE) augmented with self-attention (SA) mechanisms. Subsequently, the fused multiple spectral data, containing the most significant features from both individual and combined spectra, were subjected to K-means clustering. The clustering performance was assessed using metrics such as accuracy (ACC), normalized mutual information (NMI), and adjusted rand index (ARI). The results revealed that the fusion of NIR features with the top 50 features with the highest importance of the top 60 THz features yielded the most optimal results. The clustering evaluation metrics demonstrated an ACC of 0.945, an NMI of 0.957, and an ARI of 0.959. The hybrid feature selection approach facilitates a deeper understanding of the critical features influencing the performance of wood species identification models, thereby enabling more effective feature selection during the development of machine learning models.

The heartwood of Dalbergia odorifera T. Chen (D. odorifera) is esteemed for its high flavonoid content. This study aimed to explore the spatial distribution of heartwood components in the xylem, analyze their accumulation patterns, and further discuss the synthesis and migration pathways of these components. To achieve this, DESI-MSI technology was employed, leveraging the specific interaction between flavonoids and the naturally derived compound Naturstoff A (diphenylboronic acid 2-aminoethyl ester), alongside Raman microscopy techniques to elucidate the in situ distribution of heartwood extracts in the xylem. Additionally, combined with microscopic observations of the pits, the study investigated the accumulation and migration pathways of heartwood components in D. odorifera. The findings indicated that the total flavonoid content increased from sapwood to heartwood and subsequently decreased, with the difference in fluorescence intensity before and after extraction displaying a similar trend. The distribution pattern of various flavonoids in the xylem was as follows: heartwood > transition zone > sapwood, and this distribution was uneven among different tissues within the same region. Notably, within the same region, the flavonoid accumulation in axial parenchyma cells was greater than that in ray parenchyma cells. Moreover, the cell corners were identified as the main sites of deposition for heartwood extracts. This research underscores the distribution patterns of heartwood constituents within the xylem, providing a scientific foundation for the conservation, enhancement, and utilization of D. odorifera heartwood resources.

Eucalyptus globulus stumps are a by-product from the coppice pulp plantation after three generations. In this study a stump was fractionated in three discs (60 cm between them), and their constituent tissues—heartwood, sapwood and bark—were subjected to further chemical characterization by summative analysis, evaluation of the phytochemical profile and antioxidants activities, plus GC/MS and analytical pyrolysis aiming at their valorization. Wood density was similar between tissues and disc level: values ranging from 0.652 to 0.705 g/cm³ (Disc 1) and 0.605 g/cm³ (Disc 5). Bark had high ash (3.5%), extractives (7.5%) and holocellulose (68.4%) but lower lignin contents (22.0%). Original heartwood contained 0.7% ash, 7.0% extractives, 27.1% lignin, and 67.3% holocellulose. Heartwood showed high extractives (12.1–15.8%), less lignin (23.9–24.5%), and high holocellulose (61.7–64.7%) compared to sapwood which contained 3.9–5.4% extractives, 26.9–27.3% lignin and 68.6–71.5% holocellulose. Water extracts had poor antioxidant activity in contrast to ethanol extracts with high activities in heartwood. All tissues presented GS lignin type with S/G ratios varying from 3.0 to 3.4 (heartwood), 3.2–3.4 (sapwood), bark (3.5) and 3.8 (original heartwood). In wood, fibers and vessels were highly lignified with SG and G-lignin respectively; while rays had low lignin with G-type. Light and fluorescence macroscopic observation of the tissues in Disc 1 revealed a lower proportion and larger vessels in sapwood and high emission fluorescence at 488nm. Overall, these results show that stumps are valuable raw material to be used under the biorefinery context.

Compressive creep tests (CCTs) are widely used in viscoelastic characterisation of wood. However, the prevalent use of dry friction conditions in wood CCTs often introduces considerable uncertainties into the acquired creep data. To address this critical issue, this study proposes a simple yet more accurate CCT-based strategy for viscoelastic characterisation of wood. In this strategy, oil-lubricated conditions are first designed to reduce interfacial friction in CCTs, followed by optimally fitting of the obtained creep data using multi-element (generalised) viscoelastic models. To validate this strategy, comparative CCTs of typical pinewood samples under both oil-lubricated and dry-friction conditions are conducted, and numerical simulations of the CCTs are further performed. The results indicate that: (i) the axial deformation of pinewood in dry-friction CCTs can be significantly underestimated (by up to 28.45%), leading to unrealistic creep data and viscoelastic parameters. (ii) Viscoelastic parameters calibrated from lubricated CCTs can achieve the desired creep prediction accuracy (97.09%), demonstrating a 19.28% improvement over those from unlubricated CCTs. The findings of this study highlight the critical role of reducing interfacial friction in CCTs of the pinewood, with broader implications for the accurate characterisation and prediction of the creep behavior in various woods and timber structures.

This study investigates the dynamics of moisture transport in Scots pine (Pinus sylvestris L.) heartwood and sapwood, under alternating drying and wetting cycles, incorporating interactions between bound water, free water, and water vapor using a multi-phase model. Cylindrical specimens oriented longitudinally, radially, and tangentially were subjected to controlled relative humidity (RH) steps of 33%, 94%, and 64% at 23 (^circ)C. High-resolution X-ray computed tomography (CT) provided detailed, time-resolved measurements of moisture distributions within the wood. A multi-phase model was developed that couples Fickian diffusion (for bound water and vapor) with Darcy’s law (for free water), supplemented by phase-conversion terms that account for evaporation and sorption. Key parameters, including absolute and relative permeabilities, direction-dependent vapor diffusivity reductions, thermal conductivity tensors, and free water transport formulations, were determined by matching predicted moisture profiles to the CT measurements. Among concentration and mixed concentration-pressure formulations for free water model, the mixed approach produced the most accurate match. The CT images revealed a rapid depletion of free water during the initial drying step, followed by distinct variations in bound water content as the RH was raised and lowered. Numerical simulations closely replicated these trends, indicating that the calibrated model effectively represents moisture transport both above and below the fiber saturation point.

Scots pine was subjected to radial compression at 160 °C and heat treatment at 180–220 °C using hot pressing to produce compressed wood and thermally compressed wood (heartwood and sapwood). Then, the macromolecular structure changes of modified wood without destruction were analyzed using high-resolution 2D HSQC NMR. After heat treatment, the contour signals in NMR spectra evidently reduced. Its reduction mainly came from side-chain cleavage of O-acetylated galactoglucomannans (GGMs) and 4-O-methyl-gluconoxylans (MGXs) in hemicellulose. Moreover, the thermal stability of GGMs was lower than that of MGXs. Specifically, the thermal stability order of monosaccharides in heartwood and sapwood should be as follows: glucose > xylose > mannose > 2-O- and 3-O-Ac- Manp > galactose > 4-O-methyl-α-D-glucuronic acid ≥ arabinose. At 220 °C, hemicellulose only left minor xylan and mannan. Conversely, the change of cellulose structure was not obvious. NMR spectra indicated high temperature caused the breaking of β-O-4, β-5, and α-O-4 bonds, leading to the mass loss of lignin.

The imbibition of water in the microstructure of cubic hardwood (oak and poplar) samples was followed by NMR, with sample faces either open to air or coated with paint, and along the different wood directions. Dynamic NMR relaxometry allows to clearly distinguish and quantify the amount of water appearing in fibers, in vessels, or as bound water, over time. It appears that the water penetrates first in the form of bound water in the wood sample. Subsequently, fibers are infiltrated at a slower rate, followed by vessels, which exhibit the slowest rate of invasion. For poplar, vessels even start to be invaded only after all the fibers have been filled. Furthermore, the invasion dynamics of the different phases are qualitatively similar when all open faces of the wood sample are coated with paint, preventing any air extraction by these faces. A simple capillary imbibition model fails to fully describe these processes, indicating that the wetting properties vary depending on the presence of bound water in the cell walls, and subsequently, on the presence of water in fibers. Finally, given that bound water penetrates prior to free water, the diffusion coefficient of bound water can be estimated from the data across different directions (L, R, T), which enables the characterization of moisture exchange between construction materials and ambient air under hygroscopic conditions.

The tendrils of Virginia creepers serve a crucial mechanical function in its attachment system, which may be subjected to environmental forces. In this study, a comprehensive experimental analysis of tensile tests was initially conducted on Virginia creeper straight tendrils, revealing their ability to deform with an elongation of approximately 50%. The investigation encompassed the tendrils of seasonal and locational variations, the moisture content, and the alterative weight ratio of the tendril core (peeled skin of the tendril) to the overall tendril. The findings indicated that the mechanical properties of the tendrils were significantly impacted by both moisture content and growth. The tendril microstructure was then examined by scanning electron microscopy (SEM), which revealed that a substantial presence of G-fibers with characteristic gelatinous helix and helical structures may play a significant role in the remarkable tendril elongation. The study may improve our understanding of the functional and structural aspects of climbers and their tendrils, and contribute to the development of new high-strength composite materials from plant fibers.

To develop a novel flame retardant that enhances the fire resistance of wood, a compound consisting of ammonium polyphosphate, tannic acid, and silica sol was integrated into Chinese fir. This study examined its effects on fire resistance and analyzed the dynamics of flame spread in flame-retardant wood using numerical simulations of the Fire Dynamics Simulator. The optimal flame retardant combinations, identified through orthogonal testing, were F-STA1 (Flame retardant silica sol: tannic acid: ammonium polyphosphate ratio of 2:1:1) and F-STA2 (Flame retardant silica sol: tannic acid: ammonium polyphosphate ratio of 3:1:2). Their corresponding limited oxygen index values were 34.2% and 33.6%, respectively, achieving a flame retardant classification of B1 level and a UL-94 rating of V-0. Thermogravimetric analysis revealed that the peak weight loss rates for F-STA1 and F-STA2 were substantially lower than those for the F-Ctrl (Control group), with increases in carbon residue rates of 83.33%, 114.22%, and 68.22%, at 800 °C for F-STA1, F-STA2, and F-TA (The flame retardant has no silica sol, and the tannic acid: ammonium polyphosphate ratio is 1:2), respectively. Cone calorimetric analysis indicated significant reductions in HRR (Heat Release Rate) and THR (Total Heat Release) for F-STA2, with decreases of 41.86% and 38.41% compared to the control. Raman spectroscopy demonstrated a reduction in the residual carbon ID/IG ratio by 34.63% for F-STA2. Furthermore, the addition of silica sol notably enhanced the mechanical properties of the wood; bending strength and modulus for F-STA2 improved by 55.47% and 45.33%, respectively, and compressive strength increased by 10.69%. Simulation outcomes suggest that flame retardant application reduces flame spread, smoke propagation, and the rate of temperature change in wood structure buildings, effectively inhibiting fire progression.