Volume 76, Issue 10

A deep-learning-based semantic segmentation approach (U-Net) was used to partition the anatomical features in the cross-section of hinoki ( Chamaecyparis obtusa ) wood during a micro three-point bending test. Using the Crocker–Grier linking algorithm, thousands of cells were successfully extracted, and several parameters (area, eccentricity, fitted ellipse aspect ratio, bounding box aspect ratio) were used to evaluate the intensity of the cells’ deformation. Thus, the 2D map of the deformation intensity distribution was constructed. By analyzing flat-sawn, quarter-sawn, and rift-sawn specimens, it was confirmed that the annual ring orientation affects the flexural behavior of wood in the transverse direction. The quarter-sawn specimens exhibited the largest modulus of elasticity (MOE) and modulus of rupture (MOR). The ray tissue aligned against the load may have contributed to the restriction of cell deformation. The rift-sawn specimens exhibited the smallest MOE and MOR, possibly owing to the loading of the specimen in the in-plane off-axial direction, which induced the shear deformation of the cell wall. For all three specimen types, the fracture had high occurrence probability in the tension part of the specimen, which exhibited large cell deformation. Therefore, the proposed method can be adapted to the prediction of wood specimen fractures. With different test wood species, this approach can be of great help in elucidating the relationship between the anatomical features and the mechanical behavior of wood to improve the effective utilization of wood resources.

The mechanical properties of wood show a very high dependence on the moisture content (MC). A consideration of MC in numerical simulations increases the applicability of such prediction with respect to application and moisture states of the wood material. The goal of this work is to develop an accurate orthotropic elasto-plastic model for oak wood ( Quercus robur L.) at two different MC levels applicable for finite element analysis (FEA). To achieve this goal, the following steps were carried out: (a) in-house standard specimens tests in compression, tension, and shear and in all three orthogonal directions, followed by three-point bending, where all specimens were conditioned to a 12 and 25.6% MC, prior to the mechanical test; (b) integration of all obtained material characteristics into the consistent numerical material models; (c) validation of the developed material models by comparing the numerically predicted values with the experimental ones; and (d) iterative calibration of the material models by adjusting the individual material characteristics to minimize error using a reference. Material models were successfully developed with the following mean relative errors: 5.2% for 12% MC and 5.8% for 25.6% MC, respectively. Both numerical material models consistently predicted the oak elasto-plastic response that can be easily integrated into any FEA.

The wettability of wood affects some natural phenomena and applications in industry, such as the ascent of sap in the plant stem, wood drying, and impregnation processes for wood modification. Wettability is generally evaluated by measuring the contact angle using techniques such as the sessile drop method and the Wilhelmy method. However, these methods are not applicable to phenomena at the micro-scale such as liquid transport in hardwood vessels. In this study, micro-CT was used to measure the contact angle of liquid in a single wood vessel directly at the submicron scale. The wettability of a wood vessel was analyzed using contact angles of distilled water and diiodomethane. Conventional contact angles of the wood surface were measured using a fixed drop technique. The average contact angle in a vessel determined by the direct CT observation was significantly smaller than that on the wood surface measured by the sessile drop technique. This discrepancy is attributable to the higher total surface energy of the vessel compared to the free energy of a flat surface. The difference in surface energy is due to different chemical composition distributions in various cell wall layers, roughness and surface topography between the wood surface and vessels, and moisture state.

Fractal geometry describes the complex pore structure in natural and heat-treated wood and the relationship between pore structure and wood properties, such as strength, heat conductivity, and transport properties. However, the fractal types and the scale-dependent properties of natural and heat-treated wood remain unclear. In this study, comprehensive fractal analysis of the pore structure of natural and heat-treated spruce wood was carried out based on mercury intrusion porosimetry data. Both the volume fractal and surface fractal of natural and heat-treated wood were determined. The results showed that the two fractal types had different scale-dependent fractal properties. Four regions were identified in the pore structures. A volume fractal region was identified for pores in the region of 2–90 μm, while a surface fractal region was identified for pores in the region of 90 nm–7 μm. The pore structure in the region of 2–90 μm that corresponded to the large pore (the lumina in the cell) range showed strong volume fractal properties, and the fractal dimensions were 2.645–2.884. The pore structure in the region of 90 nm–7 μm that corresponded to the small pore (voids on or in cell walls) range showed strong surface fractal properties, and the fractal dimensions were 2.323–2.999. The range of fractal regions was hardly affected by the heat treatment atmospheres. These results showed that fractal geometry can be used to characterize the pore structures of natural and heat-treated wood. These findings are expected to explain the differences in properties between natural and heat-treated wood in the future.

Pressurized hot water extraction (HWE) treatment has the benefit of simultaneous extraction of hemicellulose-based carbohydrates and modification of the solid phase, but it does not drastically improve wood durability. However, removing hemicelluloses from the wood by HWE treatment creates water-filled spaces in the cell walls which could be filled with modification agent in order to improve the properties of the wood. Without drying, modification agent can be added into the saturated wood via diffusion. The esterification of wood with citric acid (CA) improves resistance to biological deterioration but increases brittleness. However, combining CA esterification with additional chemicals that form links with CA can mitigate brittleness. This study investigated esterification as a method for modifying HWE treated wood. HWE treatment with CA solution (4% w/v) was applied at 120 °C for 3 h to Scots pine ( Pinus sylvestris L.) sapwood specimens. The specimens were further modified by diffusion with CA and starch derivatives followed by curing. The applied method changed the moisture properties and chemical composition of the wood. The results showed successful wood bulking. The investigated method slightly improved decay resistance to Coniophora puteana and Trametes versicolor but did not change resistance to Rhodonia placenta .

In this study, two plant derived compounds, namely tannin acid (TA) and tung oil (TO) were used to modify southern yellow pine wood ( Pinus spp.) to enhance its durability. Wood samples were firstly impregnated with aqueous TA solutions at 5, 10 and 15%, respectively, and then impregnated with TO. Samples treated by TA or TO alone were also prepared. The dimensional stability, hydrophobicity, mold resistance, and thermal stability of both treated and untreated wood were evaluated. The results showed that the dimensional stability and hydrophobicity of wood treated with 10% TA and TO (T10+TO group) improved significantly. Compared with control group, the water absorption of T10+TO group decreased by 80.0% after 192 h immersion, and the antiswelling efficiency reached up to 90.7%, with the contact angle of 118° at 50 s. The mold resistance of wood after 5% TA and TO treatment presented an effectiveness of 87.5%. Meanwhile, T10+TO group presented better thermal stability. Overall, this study revealed that wood impregnated by TA and TO exhibited excellent dimensional stability and anti-mold properties, which could be applicable to indoor environment.

The present study used an atmospheric dielectric barrier discharge (DBD) plasma treatment to modify the interfacial properties of heat-treated wood (HTW). The changes in the wood surface characteristics, such as the microstructure, chemical structure, and wettability, were investigated using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Further, the fluorescent tracer technique was used to analyze the effect of plasma treatment on the adhesive penetration inwood. Results showed that the wettability of water and phenol-formaldehyde adhesives on the surface of HTW significantly improved after plasma treatment due to the increase in the hydrophilic and oxygen-containing functional groups. The average penetration (AP) and effective penetration (EP) of the phenolic adhesive into HTW also increased significantly after plasma treatment; the AP value of the E-E (earlywood bound to earlywood) HTW samples increased from 909 to 1674 μm, and the EP value from 60 to 183 μm upon plasma treatment. These observations indicate that the DBD plasma treatment is a promising method to improve the bonding properties of the glued HTW products.