European Journal of Wood and Wood Products最新文献

The use of cross-laminated timber (CLT) and laminated veneer lumber (LVL) in wooden structures including non-residential, tall and large buildings is increasing, even though they might be subjected to important horizontal forces. The asymmetric four-point bending test method, originally used for lumber and glulam, can be used to evaluate the in-plane shear performance of CLT. This test may have led to bending failure in the case of the CLT specimens. In this study, asymmetric four-point bending tests were conducted to evaluate appropriate shear strength and modulus. Span ratio of 0.5–1.0 is recommended for shear failure to occur as the latter is less affected by compression force. The shear strength exhibited a positive correlation with the ratio of the perpendicular layer, suggesting that the shear strength can be easily estimated. The diagonal measurement of shear deformation is a convenient method because it has less effect on deformation due to the direction of the grain.

In recent decades, the proportion of hardwoods in European forests has increased, and this trend is expected to continue in the future. Strength grading of hardwood is an important procedure to produce high-quality glued laminated timber and cross-laminated timber. The existing dataset lacks predefined thresholds and rules governing strength and stiffness indicators for hardwood. This study analyzes several visual and physical strength and stiffness-related parameters, including knot characteristics, density, and dynamic modulus of elasticity, focusing on their influence on the tensile strength and modulus of elasticity in tension parallel to the grain of European hornbeam (Carpinus betulus L.) timber boards. Destructive tensile tests were conducted on boards, and correlations between properties were analyzed. Additionally, the formulas for predicting the tensile strength and stiffness were derived with a coefficient of determination. The research findings can provide valuable insight into the behavior of European hornbeam, contributing to the standardization of strength grading and maximizing its mechanical utilization. Based on the research findings and compared with other tensile properties analysis, European hornbeam boards appear to have potential for use in the production of high-strength glued laminated timber.

Timber colour sorting is an important woodworking process in producing a homogeneously coloured and pleasant looking product. However, for multispecific timber such as light red meranti, LRM (Rubroshorea spp.), which spans a wide gamut of colours, there is an antagonistic compromise between having good separability of colour and the number of bins. This research attempts to solve this by intentionally overclustering the intensity gamut and then automating the selection of ideal colour sorting bins (CSB) for a given batch size to produce high-similarity coloured sorting. 178,327 unique LRM wood samples collected over 8 months of production were used. Machine learning clustering algorithms such as k-means and Otsu multithresholding were tested against percentile and equal spacing methods. Batch sizes of 250 (B250) and 1,000 (B1000) pieces were evaluated. Maximum likelihood estimation was tested against statistical methods to select the CSB, and ideal overcluster setups were determined using the average delta E ((Delta E^*_{00})) assessment. The ‘burn-in rates’ of 3–30 pieces were then evaluated. For the B250 four-bin setup, six overclusters (6C4) performed best, with a recommended ‘burn-in rate’ of 12 pieces. For B1000, 5C4 performed best with a ‘burn-in rate’ of 10 pieces. The 4C3 configuration and the ‘burn-in rate’ of 10 pieces were found to be the best for three-CSB for both B250 and B1000. This study shows the feasibility of using machine learning to automate the bin selection process when the overclustering technique is used to improve colour sorting in situations with a restricted number of bins.

Large parts of banks of canals in the Netherlands are protected by azobé timber sheet piles. Many kilometers of sheet piles in the province of Noord-Holland, are planned to be replaced or to undergo maintenance. Yet, there is insufficient knowledge on the current state of the azobé sheet piles and their residual service life. Based on this, a series of investigations on azobé sheet piles after 57 years of service were performed. Visual inspections showed surface deterioration on the water-exposed side for all boards. Nondestructive testing using micro drilling technique showed no signs of internal deterioration. A maximum reduction in thickness of 17% and an average thickness reduction of 6.7% of original thickness were observed. CT scanning showed that the remaining cross sections of the azobé boards were intact and had comparable density of new azobé boards. An exponential damage accumulation model was used to predict the residuals service life of the timber sheet piles subjected to earth stress. Conservative estimates based on physical measurements and residual bending strength indicate that the sheet piles have an additional service life of 22–43 years from the current state.

Wood fuel pellets are currently one of the ecological alternatives to fossil fuels for heat and power generation. These fuel pellets are produced through the densification/pelletizing process of a preconditioned sawdust material inside huge pellet mill presses, with dies made of multiple small cylindrical channels. While the industrial aspects of the fuel pellets are well understood and controlled, little knowledge was acquired on the flow of wood granular systems (sawdust) through circular dies. In this paper, such a flow was investigated by means of a capillary rheometer, in the case of a pretreated isotropic sawdust. Influences of the feedstock (water content and particle size distribution), extrusion parameters (piston speed, temperature), and die design (entry-cone angle, length of the cylindrical section) on the pellet density and aspect at the die exit were particularly discussed. Water contents were tested uncommonly until 40 wt%. Careful attention was paid to forces applied on the piston as an indication of power requirement in order to determine the best extrusion conditions. Low temperature and high moisture content appear to be the conditions that require lower power, while long capillaries increase density by 20% and give rise to a better aspect.

Permanent fixation of compressive deformation is one critical aspect of wood densification technology. In this study, heated and pressurized nitrogen gas (N₂), steam and their mixture were applied as the heating media to treat surface compressed poplar wood for the compressive deformation fixation. When steam was applied at 0.5 MPa, around 80% of the compressive deformation was permanently fixed. Although heat treatment in N₂ also caused hemicellulose degradation in wood as that caused by heat treatment with steam, yields of acetic acid and aldehyde compounds were significantly lower than that from heat treatment of surface compressed wood (SCW) with steam-N₂ mixture containing more than 50 vol % steam. Heat treatment with steam effectively reduced set recovery of SCW. Set recovery induced from hygroscopicity and water absorption were 2 to 4 times higher than those after treated with steam treatment. Additionally, heat treatment in N₂ resulted in the biggest wood hardness loss. When steam-N₂ volumetric ratio was 1:1, set recovery was over 50% lower than that obtained by heat treatment in N₂, while wood hardness was just slightly decreased. Steam introduction into N₂ for SCW heat treatment significantly reduced the compressive set recovery as well as mass loss. From the perspective of industrial manufacture and application, when the heating medium pressure exceeded 0.3 MPa, steam-N₂ mixture medium with over 50 vol % steam contributed to the permanent fixation of over 50% compressive deformation. Meanwhile, the set recovery of SCW after exposed to high temperature and high humidity was less than 5%, with no excessive hardness loss.

Sorbitol-citric acid (SorCA) modification is an eco-friendly wood treatment that demonstrates promising potential for enhancing dimensional stability and decay resistance of wood material. To improve the fire resistance property of SorCA (1:2; 30%) modified wood, fire retardants (FRs) such as diammonium hydrogen phosphate (DAP) and potassium carbonate (PC) were incorporated into the modification system at a rate of 10% and 15%, respectively. Scots pine wood modified with the combination of SorCA and FRs was subjected to mass loss calorimeter test to evaluate its flame retardancy. In addition, thermogravimetric analysis (TGA) was carried out for determining the thermal behaviour of modified wood at elevated temperatures. Fourier-transform infrared spectroscopy (FTIR) was used to identify the chemical bonds in the modified wood. The FTIR spectrum indicated an intensity enhancement at 1716 cm^− 1, resulting from the bonding with the cell wall or between the reagents. TGA analysis showed that the addition of DAP and PC to the SorCA system enhanced the thermal stability, yielding higher residual mass compared to SorCA alone and the untreated reference. The mass loss calorimeter revealed that SorCA with DAP 15% significantly improved flame retardancy, lowering the peak heat release rate by 65% and total heat release within 600 s by 82% compared to untreated wood. The combination of SorCA with DAP and PC contributed to the char formation and showed potential flame retardancy for modified Scots pine wood.

High-density wood is crucial for interior applications, especially for engineered wood flooring, as mechanical properties such as hardness are correlated with density. However, high-density wood is scarce and expensive. Densification methods allow low or moderate-density woods to replace harder species, transforming them into high-performance, high-value products. The objective of this project was to increase the surface hardness of three abundant North American hardwoods, sugar maple (Acer saccharum Marsh.), yellow birch (Betula alleghaniensis Britt.), and red oak (Quercus rubra L.), through lateral impregnation of the Michael Addition formulations. Samples were densified using three formulations based on Michael addition reactions with acrylate and malonate components. Results showed that the pattern of formulation penetration into lumens and vessels depends on viscosity over curing time. Chemical retention was higher in red oak, and formulations with lower initial and overtime viscosity retained more chemicals. As expected, an asymmetric density profile was observed via X-ray densitometry and microtomography in comparison to bulk densification methods. Passive chemical densification was confirmed by confocal Raman spectroscopy in densified wood. All densified woods showed a significant increase in Brinell hardness compared to untreated wood, although no significant differences appeared between samples with different formulations. The highest hardness was reported for sugar maple, which has a higher initial hardness, while the increase in surface hardness was greatest for red oak. Overall, samples densified with formulations containing a mixture of diacrylate and triacrylate with moderate viscosity (around 27 cP) and a glass transition temperature (around 55 °C) showed slightly higher surface hardness.

In this study, a brand new bamboo scrimber–rubberwood CLT (BRCLT) has been proposed, along with one-component polyurethane (PUR) adhesive. Three processing factors were considered, pressure (1.5 MPa and 2.0 MPa), glue spread rate (150 g m⁻² and 200 g m⁻²), and application of a water-based surface modifier. The bonding performance of BRCLT was examined by conducting block shear, delamination, short-span flatwise shear and four-point bending tests. It was found that (1) the optimal gluing process for fabricating BRCLT was a pressure of 2 MPa, a glue spread rate of 150 g/m⁻², and the application of a water-based surface modifier. (2) The modifier significantly reduced the delamination rate of BRCLT. (3) BRCLT produced using the optimal bonding parameters can meet V1-grade CLT in terms of maximum shear stress, modulus of rupture (MOR), and modulus of elasticity (MOE), as stipulated in the American standard ANSI/APA PRG 320, suggesting BRCLT had a great potential to be a new member of CLT family.

Particleboard properties result from a variety of material and process-related parameters. While many of them have been extensively investigated, there is a notable lack of knowledge regarding the influence of the particle geometry. This is due to a longstanding lack of suitable measurement technologies and, in the investigation, unintentional overlapping of other interference factors. In the present study, the influence of particle size and surface-specific adhesive amount (SSAA) on the formation of particleboard properties was investigated. Laser-based 3D scanning technology was used to determine the dimensions and the specific particle surface area of particles of different sieve fractions, from which different types of boards were produced. This approach allowed the SSAA to either be maintained at a constant level for boards made from different sieve fractions (influence of particle size) or to be specifically adjusted for boards made from a single fraction (influence of SSAA). To further isolate the influence of particle size and SSAA from the interfering influences of an uneven distribution of particles of different size, adhesive and density, the boards were produced with a single-layer structure and a homogenous density profile. As particle size increased, a statistically significant reduction (all statistical tests were carried out at a significance level of α = 0.05) in modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond strength (IB) was observed, accompanied by an also statistically significant increase in thickness swelling (TS) and water absorption (WA). As the SSAA increased, the MOR, MOE and IB showed a corresponding statistically significant rise, while TS and WA significantly decreased. This knowledge of basic coherences (since significant interference factors were excluded) provides the basis for targeted process optimization in the production of particleboards.