European Journal of Wood and Wood Products最新文献

Drilling resistance (DR) measurements constitute a common method to evaluate the properties and internal conditions of wood. Generally, DR is used to monitor and assess the structural health of timber constructions. This study aimed at evaluating the influence of 3-mm holes left after drilling resistance measurements on the residual failure load of the wood specimens tested under the bending and compression conditions. Laboratory tests were performed using defect-free conditioned specimens of Scots pine (Pinus sylvestris L.) with various cross-sections. Drilling holes were made with an IML-RESI PD 400 tool and a new standard spade drill bit (IML System GmbH, Wiesloch, Germany) in different locations of the cross-section. We used a finite element modelling software to simulate the bending of drilled specimens and assess the accuracy of experimental data. For wood assessment, an orthotropic body model was used with regard to the non-linearity of the load deflection curve. The failure load in static bending was significantly influenced by the presence and location of holes in the specimens. However, this effect varied across the different cross-sections. It is recommended to use DR for the evaluation of structural timber in the areas of wood elements that are not exposed to the maximum tensile stresses. The influence of holes after DR measurements on residual failure load in compression was proportional to the wood cross-section loss and is minor for structural-sized wood constructions.

The frequency of Terahertz (THz) band is between microwave and infrared radiation. THz technology is widely used in non-contact nondestructive testing, material evaluation, security anti-terrorism, medical imaging and diagnosis, communications and other fields. Similarly, THz technology has been widely used in forestry. This paper analyzes the application progress of THz technology in forestry based on the research and application achievements of THz technology in recent years, such as tree species recognition, non-destructive detection of hidden defects in wood, wood moisture content measurement, wood density, some other important application areas (such as dendrochronology, crystalline structure, fiber structure) and summarizes the existing limitations and shortcomings. On this basis, the future application prospect and development trend of THz spectroscopy and imaging technology in forestry are projected. It is expected that this paper can play a positive role in promoting the application of THz technology in forestry, and provide new solutions and methods to solve the technical problems related to forestry.

Resin canals and ray cells in pine wood connect the interior to the exterior. The blockage of resin canals and ray cells by the resin, directly determines the water uptake of the wood. However, research on water uptake by resinous wood is lacking. Hence, this study aimed to explain how microwave (MW) or superheated steam (SS) treatment improves wood water uptake from the perspective of resin content (RC). Therefore, radiata pine sapwood and heartwood were treated with MW, SS, or microwave-superheated steam (MS) for different times. The results showed that MW and SS treatments expelled the internal resin of radiata pine. Owing to the low RC and high moisture content (MC) of sapwood, the effect of the MW treatment on the RC of radiata sapwood was insignificant. Heartwood has a markedly higher RC and lower MC than sapwood; therefore, MW treatment can drive part of the resin to migrate out of the wood. With increasing SS treatment time, the RC of the sapwood and heartwood decreased to varying degrees; however, the core layer resin could not be completely removed. In addition, MW treatment can accelerate the degreasing process as it discharges some part of the resin and opens some parts of the resin canals. Moreover, MS treatment can increase the porosity of sapwood and heartwood due to the expulsion of resin. MS treatment had no significant effect on sapwood water uptake; however, it increased that of heartwood by more than three times. The dye solution enters the wood through the open resin canals or ray cells and communicates with the axial resin canals. Therefore, the water uptake of heartwood is mainly related to the resin content and the blockage of the resin canals by the resin determines the entry of the dye solution to the interior of the wood.

To overcome the defects of longer curing times and higher curing temperatures for melamine urea formaldehyde resins (MUF) used in wood panel products, nanofluid MUF resin adhesives were prepared by dispersing SiO₂ and TiO₂ nanoparticles into the MUF resin at six concentration levels based on the overall mass of the adhesive, 0%, 0.2%, 0.4%, 0.6%, 0.8% and 1%, with the assistance of ultrasound. The excellent thermal conductivities of the nanofluid adhesives eliminated the defects of the MUF resins. When the SiO₂ and TiO₂ nanoparticles were incorporated, the viscosity increased as the nanoparticle concentration increased, the maximum viscosity increased by 13.4% with SiO₂ nanoparticles (1.0% level) and 11.4% with TiO₂ nanoparticles (1.0% level), the pot life, curing time, and free formaldehyde content of the MUF resins declined to varying degrees as the nanoparticle loading level was increased, the pot life maximum decreased by 38.5% with SiO₂ nanoparticles (0.2% level) and 36.0% with TiO₂ nanoparticles (0.2% level), the maximum reduction in curing time was 13.3% with SiO₂ nanoparticles (0.4% level) and 13.6% with TiO₂ nanoparticles (0.6% level), and the maximum content of free formaldehyde was reduced by 32.3% with SiO₂ nanoparticles (1.0% level) and 41.9% with TiO₂ nanoparticles (1.0% level). The nanofluid MUF resins showed much higher bonding strengths and lower formaldehyde emissions than pure MUF resins after being treated with the same hot pressing method used during plywood manufacturing. The maximum bonding strength was increased by 28.8% with the SiO₂ nanoparticles (1.0% level) and 25.4% with the TiO₂ nanoparticles (1.0% level) at a hot-pressing temperature of 100 °C and a hot-pressing time of 60 s/mm. The maximum formaldehyde emissions were reduced by 46.3% with the SiO₂ nanoparticles (1.0% level) and 46.3% with the TiO₂ nanoparticles (1.0% level) at a hot-pressing temperature of 110 °C and a hot-pressing time of 40 s/mm. Furthermore, nanofluid MUF resins used in plywood manufacturing decreased the hot-pressing temperature or shortened the hot-pressing time required.

Black liquor, a major by-product of the paper industry, is often underestimated in terms of its industrial value. Effective utilization of black liquor has become a pressing concern. In this study, electrode materials were prepared using activated carbon derived from black liquor and the optimal conditions for the preparation of black liquor activated carbon with high electrochemical performance was determined. The electrochemical performance of activated carbons obtained through the processes of evaporation and concentration of black liquor, extraction of lignin from black liquor, and direct utilization of industrial lignin, were compared. The results revealed that the optimal conditions for preparing activated carbon were a carbonization temperature of 500 °C and an activation temperature of 700 °C. The specific capacitance was measured to be 389 F/g at 0.5 A/g, with capacitance retention of 100%. Moreover, even after 5000 charge/discharge cycles at a current density of 2.0 A/g, the energy density reached 22.2 Wh/kg. The specific surface area of the activated carbon was determined to be 2147.77 m²/g. One notable advantage of the activated carbon prepared by evaporating the black liquor is that it retained hetero-atoms such as S present in the black liquor. This feature resulted in a higher capacitance compared to other preparation methods.

This paper describes the development and characterisation of wood-filled polylactic acid (PLA) composite filaments for application in fused filament fabrication three-dimensional (3D) printing. Four different wood-polymer composite filaments for 3D printing were prepared, and specimens were 3D-printed with the obtained materials. The composite filaments consisted of wood particles (10% or 20% mass ratio) and a PLA polymer matrix. Wood particles were prepared by grinding and sieving non-modified beech wood and thermally modified (TM) (at 200 °C) beech wood. Thermal modification of wood affected particle preparation and smaller particles with lower aspect ratios were obtained. Filaments with TM wood particles were extruded better than with non-modified wood particles, with lower surface roughness and lower porosity. With a higher wood ratio, the surface roughness and porosity of the filament increased. Non-homogenous filaments also affected extrusion in 3D printing and reduced the properties of 3D-printed parts. Parts 3D-printed from filaments with TM particles had better tensile strength than from filaments with non-modified particles, but were lower than from pure PLA filaments. The tensile strength of the injection-moulded specimens was 18–69% higher than that of the 3D-printed specimens, depending on the filament composition. The results indicate some positive effects of thermal modification of wood particles on the properties of filaments and 3D-printed parts. Nevertheless, further optimisation of particle preparation and extrusion parameters is needed to obtain quality filaments with this size of wood particles.

The properties of medium density fiberboard (MDF) panels manufactured by reconstituting wood fibers and binders under high temperature and pressure depend on various manufacturing variables, including wood-related parameters, adhesive-related ones, and process-related ones. This study focused on the analysis of big data (about 400 million data) of the manufacturing variables (1389 variables) of MDF panels to understand the influence of these variables on the properties of MDF, using Ridge, Lasso, and Elastic-net regression. Both Lasso and Elastic-net regression were better than Ridge one in predicting the properties of MDF. The analysis results also showed that flash tube dryer, mat forming, and hot-pressing variables were closely related to panel density while fiber bin, refiner, forming, press, and hot-press heating variables affected the modulus of rupture (MOR) of the MDF panel. The analysis of interactions between manufacturing variables and MDF properties showed that the panel density affected internal bond (IB) strength, core density, and moisture content while IB strength and moisture content were associated with the MOR of the MDF panel. However, it is not clear which variables are dominantly affecting the formaldehyde emission of MDF.

Four types of high-acidity carbon-based solid acid catalysts (CBSCs) were successfully synthesized from wood sawdust, sugarcane bagasse, coconut shell, and wood sawdust-derived lignin using fuming sulfuric acid (FSA) as the sulfonating agent. The synthesized CBSCs were successfully applied to the conversion of wood sawdust-derived glucose and fructose into levulinic acid. The findings show that FSA can provide the CBSCs with higher acidity (8.0–13.0 mmol/g) than conventional concentrated sulfuric acid. Under the suitable conditions established in this work, levulinic acid was formed with a yield of more than 50 wt% over glucose when using the synthesized CBSCs at a dosage of 30 wt% over the amount of sugar.

Birch plywood has superior mechanical properties compared with that made from most softwoods. However, durability-related issues still limit the application of birch plywood in outdoor structures. A means to enhance its durability is to acetylate birch veneers before processing them into plywood. An earlier study showed that such acetylated birch plywood has equivalent mechanical properties to unmodified ones. However, there is a need to better understand the moisture effect on the mechanical properties of unmodified and acetylated birch plywood for a better design of structural birch plywood elements. Moreover, due to the pronounced in-plane anisotropy of plywood, extra concern should be given to the weakest load angle due to the weakest chain theory. In this study, acetylated and unmodified birch plywood specimens were conditioned in climate chambers under three different environments with a temperature of 20 °C and increasing relative humidity (RH) from 35 to 65% to 95%. Thereafter, their in-plane edgewise flexural properties with load-to-face grain angles of 0, 45, and 90 degrees were tested. The influence of both RH and measured moisture contents on bending strength and stiffness are then presented. Prediction formulas of mechanical properties with moisture contents are derived by performing linear regressions among test results. Variations of brittleness factors and brittleness indexes under various RH conditions and load-face grain angles were also studied.

Ordinary coated abrasive belts (OCAs) are characterized by poor height consistency, irregular abrasive grit arrangement, and uncontrollable grit shape. These shortcomings lead to varying material removal rates, unstable surface quality, and shorter lifespans. To enhance the sanding process of wooden materials, a new precision-shaped abrasive belt (PSA) tailored to the attributes and cutting dynamics of wood was studied. In this study, PSAs were prepared using pyramidal structured abrasive grits with desired shape and angles between side-front faces (side-face angle). A sanding test was conducted on medium-density fiberboard (MDF) using OCA, as a control reference, along with PSAs. The sanding performance and service life of the PSAs with five side-face angles were evaluated through the analysis of the MDF removal amount by abrasive belts, surface roughness of MDF samples sanded using abrasive belts, and mass loss and surface morphology of the abrasive belts. The result revealed that PSAs exhibited a higher sanding stability than OCA. Moreover, both removal efficiency and surface quality of MDF depended on the side-face angle of PSA. A reduction in the side-face angle of PSA decreased its contact area with the MDF sample, resulting in an increased cutting depth and higher MDF removal rate with poor surface quality of sanded MDF face. Additionally, the side-face angle played a vital role in dust removal, with a smaller side-face angle being less susceptible to blockage by wood dust. PSA can easily adapt to various machining requirements depending on its grit structure and arrangement. This study provides theoretical support and practical guidance for PSA research and production.