European Journal of Wood and Wood Products最新文献

High shape-stable phase change materials (PCMs) are critical for the application of thermal insulation or storage of building energy systems. In this work, the highly shape-stabilized PCM composites were prepared by using hierarchical porous bamboo supporting materials to stabilize polyethylene glycol (PEG). A rapid pretreatment method combining low-intensity microwave processing was employed for the first time to achieve porous bamboo with great structural integrity in which the PEG mass loading could be as high as 210%. The morphological, chemical, and hierarchical porous properties of bamboo supporting materials during the pretreatment process were systematically investigated. Due to the greatly developed pore structure and surface-active functional groups of bamboo supporting matrix, the formation of strong hydrogen bonds along with capillary actions between bamboo and PEG contributes to the excellent thermal storage properties of obtained bamboo-based PCM composites. The differential scanning calorimetry and liquid leakage tests of the composites exhibited high-stable shape and leak-proof performance with the phase change enthalpy high up to 100.6 J/g. This study provided a novel, rapid pretreatment method for bamboo and provided valuable insights for the future application of bamboo-based energy conservation materials.

Annual rings can record natural information such as regional temperature, humidity, and rainfall. However, they are often damaged by cracks, knots, and wormholes, making it difficult to obtain accurate data from them. In this study, O-Net is developed for the segmentation of annual rings in wood transverse sections containing cracks, wormholes, and knots. The O-Net framework is constructed by integrating parallel U-shaped encoder-decoder paths, utilizing convolutional kernels of two different sizes to capture multi-scale features of annual rings. Subsequently, the Efficient Channel and Spatial Attention (ECSA) mechanism is incorporated into the encoder to enhance the model’s ability to extract annual rings features near defects from both channel and spatial dimensions. Finally, a residual path is introduced through ablation experiments to refine the model’s architecture. The results demonstrate that O-Net effectively distinguishes between crack and knot boundaries and accurately segments annual rings, even in the presence of cracks and minor wormholes. O-Net is capable of extracting transverse sectional annual rings from wood containing cracks, wormholes, and knots, addressing the limitations of traditional methods in accurately extracting damaged annual rings with defects.

Wood samples treated with ultraviolet (UV) radiation (200 h, 80 °C) and mild thermal treatment (200 h, 80 °C) were stored under laboratory conditions in complete darkness for 14 years. 15 wood species used by the carpentry industry were involved in the tests. Colour changes were monitored and presented using the CIE L*a*b* colour measurement system. Samples with low extractive content (e.g. spruce, poplar, maple and ash) presented the greatest increase in redness and yellowness during UV irradiation. Cherry, larch and American cherry showed the best stability against photodegradation. These tree species have the highest natural extractive content responsible for redness. Both UV irradiation and the subsequent natural ageing in dark conditions resulted in a greater increase in redness than in yellowness. Long-term storage in total darkness resulted in much greater redness and yellowness increases for UV irradiated samples than for slightly thermally treated samples. Thermal treatment at 80 °C followed by the long-term storage in darkness produced only small alterations in lightness, redness and yellowness.

Wood-based panels bonded with urea-formaldehyde (UF) adhesive serve for construction and furniture manufacturing with excellent physical properties and cost-effectiveness. However, the moisture susceptibility of wood limits its applications and service life. The paraffin emulsions can provide waterproofing, whereas excessive paraffin weakens the bonding strength of wood-based panels. In this study, the modified paraffin with superior dispersion was prepared and the accompanying effects on the bonding performance was investigated. Results indicated that the modified paraffin emulsion with a mean particle size of 3.17 μm, which decreased by about 84.6% as compared to the commonly used paraffin. FTIR, XPS, SEM, and contact angle measurements showed that the modified paraffin reduced hydrophilic groups and enhanced the hydrophobicity. The commonly used paraffin particles are prone to agglomerate, which reducing the adhesive penetration depth of UF adhesive into wood. After modification, the penetration depth of UF adhesive into wood was increased by about 52.3%. The improved permeability of UF adhesive into wood contributed the highest tensile shear strength of glued wood with modified paraffin under both dry and wet conditions. Shear strain distribution during the test indicated that the modified paraffin enhanced stress transfer capacity within the glueline, improving mechanical performance. These findings are beneficial to develop the wood-based panels with high bonding performance and moisture-resistance for outdoor applications.

The influence of size effects on the shear strength and stiffness of glued-laminated timber (GLT) made from European ash (Fraxinus excelsior L.) was assessed based on a comprehensive experimental campaign. The experiments were performed on full-scale GLT beams with rectangular cross-sections width × height = b × h = 120 × 480-800 mm², shear lengths L_v = 720-1500 mm, and ratios between the shear length L_v and the beam height h, i.e. α = L_v/h = 1.2-2.5. The influence of the test configuration (3-point bending and asymmetric 4-point bending) was also assessed. The obtained shear strengths of European ash GLT had mean values f_{v, mean} = 10.2 N·mm^-2 (coefficient of variation CoV_fv = 14%) and 12.2 N·mm^-2 (CoV_fv = 15%), for the 3-point and asymmetric 4-point bending test configurations, respectively. The shear strength showed some size dependency, with an exponent 1/m = 0.2 0.4 for a strength modification factor (600/h)^1/m as a function of the beam height h. The shear modulus showed no size dependency and the obtained mean values were G_mean = 1162 N∙mm^-2 (CoV_G = 6%) and 1120 N∙mm^-2 (CoV_G = 6%), for the 3-point and asymmetric 4-point bending tests, respectively.

The durability of hybrid composites under environmental and biological stresses is a significant challenge for sustainable structural materials. This study assessed vacuum-infused hybrid composites made of Pinus elliottii veneers, unidirectional jute fabrics, fiberglass mats, and an unsaturated isophthalic polyester matrix. Manufactured via the Vacuum Infusion Process (VIP), composites with varied stacking sequences were tested against fungal decay and accelerated weathering. Decay tests using Trametes versicolor involved 16 weeks of incubation, monitoring mass loss weekly. Accelerated weathering in a QUV chamber exposed samples to cycles of UV radiation, simulated rain, and moisture for 15 weeks, with weekly evaluations including mass loss, colorimetric analysis (CIELab), and FTIR spectroscopy. Fiberglass-faced composites demonstrated superior T. versicolor resistance, with minimal mass loss due to protective polyester and fiberglass layers. Conversely, wood-faced composites were more vulnerable, showing greater mass loss and chromatic changes. Weathering caused significant reductions in chromatic parameters (a* and b*), especially in wood-faced composites, due to lignocellulosic degradation. FTIR analysis revealed carbonyl and ether bond breakdown in the polyester matrix, with more pronounced degradation in hydrophilic jute-layered composites. These results underscore the potential of hybrid composites as durable, sustainable materials for extreme environments, with tailored configurations enhancing resistance to environmental and biological stresses.

Black locust (Robinia pseudoacacia L.) has great potential for weathered exterior applications due to its natural durability and density. In particular, the narrow sapwood range and the crooked trunk areas with strong fiber inclination make the production of veneer lumber from shorter logs very interesting, except for logs with a tension back. This paper describes selected elasto-mechanical properties of robinia laminated veneer lumber, tested in a climate of 20 °C and 60% relative humidity and at the fiber saturation point. In particular the Young’s modulus (E_L, E_R, E_T) in tension, the Poisson’s ratios (µ_LT, µ_TR, µ_LR), and the strengths (σ_L, σ_R, σ_T). were determined experimentally by tensile tests, and the lateral strain coefficients µ_TL, µ_RT, and µ_RL were calculated from these values. The results show a significant decrease in Young’s modulus and modulus of rupture with increasing wood moisture content in the longitudinal, radial, and tangential directions. There was no notable dependence of the lateral strain coefficients on moisture content. Additionally, no significant correlations were observed between the investigated properties and gross density, nor between Young’s modulus and tensile strength. Unlike Young’s modulus and tensile strength, the lateral strain coefficients showed no clear trend with increasing wood moisture content. The strain coefficients are in good agreement with literature values, but further research with larger samples and different material sources is needed to complete the engineering constants. In addition, characteristic values of component size and material durability are of interest for future development.

In the 1950s and 1960s, Eucalyptus camaldulensis trees were planted in the Lazio region (Central Italy) as windbreaks to protect crops. Nowadays, a maintenance plan has been implemented to manage these windbreak systems, resulting in a significant quantity of wood, currently used almost exclusively as biomass for energy. This study aims to explore the potential of this material for higher-value applications in industries beyond energy production. To this end, we conducted a classical technological characterization to establish preliminary knowledge of the physical, mechanical, and anatomical properties of E. camaldulensis specimens obtained from the management of windbreak belts in Tarquinia (Central Italy). The assessment considered radial and axial variations and compared the results with those of other Eucalyptus species to evaluate possible industrial uses. Physical characterisation included density, basic density, and radial, tangential, and volumetric shrinkages. Mechanical tests measured axial compression strength, bending strength, and hardness. Anatomical analysis examined fibre dimensions (length and diameter) and the proportions of heartwood, sapwood, and bark. The average density was 734 kg/m³ (12% MC) and the basic density was approximately 620 kg/m³. In general, the density seemed to increase with the increasing distance from the ground. Radial and tangential shrinkage were 5.6% and 8.7%, respectively; compression strength averaged 49.4 ± 7.9 MPa, bending strength 84.5 ± 22.8 MPa and hardness 30 MPa. Fibres length and diameter averaged 886 µm and 19 µm, respectively. A decrease in fibre diameter was observed with increasing distance from the ground, coupled with an increase in slenderness ratio. These characteristics suggest the feasibility of an alternative cascade use of the material, highlighting its potential applications beyond energy production.

This study was aimed at exploring the sheer creep behavior of wood through off-axis tensile creep and creep recovery tests. Using the creep recovery data, the shear creep properties of softwood (Japanese Hinoki cypress, Chamaecyparis obtusa) and hardwood (Japanese Buna beech, Fagus crenata) were compared. The trends of three components of strain, i.e., instantaneous elastic, delayed elastic, and permanent strains, during shear creep were predicted by decomposing the total strain during creep recovery, assuming that the rate of increase in delayed elastic strain is the same as the recovery rate during creep recovery. Fitting a Burger model to each predicted strain yielded more reliable material parameters compared with those obtained by simply mathematically fitting the Burger model to the total creep strain. The Burger model demonstrated excellent accuracy in fitting the measured creep curves of hardwood. However, it could not explain the shear creep behavior of softwood. This discrepancy in the fitting results was attributable to the differences in the behavior of permanent strain: The permanent strain of cypress exhibited a curvilinear trend, while that of beech displayed a more linear trend. To explain the curvilinear behavior of permanent strain, a modified Burger model, which assumes that the apparent viscosity of permanent strain changes in a strain-rate-dependent manner, was proposed. The modified Burger model yielded better fitting results than the conventional Burger model, suggesting that the viscous component of wood exhibits an apparent viscosity that depends on the strain rate rather than a constant value, as assumed in the conventional Burger model.

The Atkins model has been widely adopted for determining mechanical properties of wood, such as fracture toughness and shear yield stress, which are typically normalised by global density for cutting force and power predictions. This study explores the feasibility of determining these mechanical properties for knotty and clear Scots pine (Pinus sylvestris L.) using local densities revealed by X-ray computed tomography scanning. Six wood workpieces, three from Poland and three from Sweden, were scanned and subsequently cut on a custom single-tooth quasi-linear cutting machine. Cutting forces for both clear and knotty regions were recorded and normalised by local densities. Results indicate that clear Polish pine exhibits higher local-density-normalised fracture toughness and shear yield stress than Swedish pine, suggesting that wood origin influences mechanical properties beyond mere density differences. Knots display significantly lower local-density-normalised shear yield stress compared to clear wood, despite their higher density. The large variation in normalised fracture toughness observed in knots is attributed to differences in cutting direction relative to knot orientation. The study highlights the effectiveness of computed tomography scanning to provide detailed insights into wood density and structure, enabling more accurate normalization of cutting forces and enhancing the understanding of wood machinability across different origins and structural characteristics.