European Journal of Wood and Wood Products最新文献

Surface charring is a wood modification process in which wood is charred by applying heat at high temperatures. Several tropical species from forest plantations have been widely studied for different wood modification processes in Costa Rica. This study aimed to investigate the effect of one-sided surface charring by using a heating plate at three different temperatures and determine the changes in the physical, mechanical, and chemical composition of Cupressus lusitanica, Gmelina arborea and Tectona grandis wood. The samples were placed between two metal plates and the bottom plate was heated at three target temperatures of 300 °C, 350 °C and 400 °C for 10 min, with a weight of 10 kg placed on the top plate to avoid deformations in the wood. The results demonstrated that the cellulose and lignin were not modified at 300 °C and 350°. FTIR spectrum showed a decrease in the peak associated with lignin (1434 and 810 cm^− 1), cellulose (1700 − 1600, 1206, 1032, 1111 and 780 cm^− 1) and hydroxyl groups of water (3400 and 2900 cm^− 1) and a slight difference in relation to the parent wood. These chemical changes increased ash content, carbon content, charring thickness and transition thickness, but decreased moisture content, density, oxygen content and volatile matter. The strain (MOE) in bending is governed by the charring thickness of the surface-charred wood, but the stress (MOR) in bending depends on the charring temperature and density.

This paper develops a process for the preparation of modified wood with low friction and low wear for tribological applications such as self-lubricating bearings. Two types of wood, beech (Fagus sylvatica) and robinia (Robinia pseudoacacia), have been studied and the results compared with naturally lubricated native lignum vitae. The process developed consists of plasticisation followed by compression in a mould, thermal modification and subsequent wax impregnation. Plasticisation was carried out by conditioning the samples to a low equilibrium moisture content of 10%, followed by heating to a sample core temperature of 80 °C. This process protects the internal wood structure from mechanical damage during densification. After plasticisation, the wood was compressed in a press mould. A low springback effect (SBE), resulting in compression of up to 40%, was achieved by unloading the mould without opening it. This step optimises compressive strength and hardness. Subsequent heat treatment reduces thickness swelling by up to 85%. Finally, a wax impregnation was applied to reduce friction. Sliding wear tests on modified beech wood have shown that the lowest wear occurs in the cross-sectional orientation (load perpendicular to the fibre ends; rxt orientation). Sliding friction studies using a steel ball on a ball-on-disc tribometer showed that compressed and thermally modified samples impregnated with rapeseed wax or beeswax exhibited coefficients of friction in a range of 0.08 to 0.09. These values are almost four times lower than those of plain compressed wood and even lower than those of lignum vitae, which was used for plain bearings decades ago. This study clearly demonstrates the high potential of compressed, thermally modified and wax-impregnated wood.

Activated carbons (ACs) were produced from stump wood of different tree species, such as pine, bearded birch, and American black cherry using chemical activation with KOH and NaOH. The activated carbons were characterized and evaluated as adsorbents for eliminating bisphenol A (BPA) from aqueous solutions. The kinetics of adsorption and equilibrium adsorption, as well as the impact of solution pH and ionic strength, were examined. The kinetics were analyzed using the pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Boyd kinetic models. The findings suggest that the adsorption kinetics followed the pseudo-second-order model. Additionally, the film diffusion was found to be the rate-determining step for the adsorption of BPA on all of the activated carbons. The data for adsorption equilibrium were tested using the Langmuir, Freundlich, and Sips equations, with results indicating that the Langmuir model was the most applicable. The capacity of activated carbons to adsorb BPA was dependent on their surface area. Higher BET surface areas resulted in increased adsorption. The birch-derived AC activated by NaOH had a monolayer adsorption capacity of 1.980 mmol/g, while the AC from black cherry activated with KOH had 2.195 mmol/g. The adsorption of BPA was pH-dependent, and no effect of ionic strength was observed. The activated carbons had very high adsorption capacities, indicating that stump wood is an excellent precursor for the production of highly effective adsorbents.

This study explores the potential of using condensate generated during beech wood steaming (BSC) as an eco-friendly additive in urea-formaldehyde (UF) adhesives for wood-based panel (WBP) production. The research aimed to assess the hardening behavior of pure commercial UF resin and UF with added condensate (UF-BSC), investigating the potential catalytic effect of BSC on the hardening characteristics of UF adhesives. Changes in chemical structure after the curing process were observed with Fourier transform infrared spectroscopy (FTIR). The curing kinetics was studied by differential scanning calorimetry (DSC) under a dynamic scanning regime with heating rates of 5, 10, and 20 °C/min. Obtained data were analyzed using Kissinger-Akahira-Sunose (KAS) and Friedman (FR) kinetic iso-conversional methods to estimate the activation energy (E_a) of the curing reaction in the investigated UF adhesive systems. The results of DSC analysis imply that BSC lowers the temperature of the curing reaction of UF adhesive along with the prolongation of the curing reaction. The obtained kinetic data supported by FTIR and chemical analysis suggest that phenolic compounds present in BSC interfere with the main curing reactions leading to lower peak temperatures but higher activation energy. Тhis suggests that BSC increased the number of active sites involved in the reaction and, consequently, the number of collisions. BSC, as wastewater of the wood processing industry, can be efficiently utilized as an environmentally friendly, inexpensive substitute for deionized water in UF adhesive formulations for WBP manufacturing.

This work assesses the effectiveness of dilute inorganic alumino-silicate polymer suspensions in enhancing wood’s durability, fire resistance, and mechanical properties. Alumino-silicate polymer-treated wood exposed to Coniophora puteana lost less than 3% mass on average, compared to 20% for controls. The moduli of elasticity and rupture of treated specimens were nearly twice as high as those of the controls. Coating with the inorganic polymer was also effective as a fire retardant. Results indicate that inorganic alumino-silicate polymers are a very promising wood treatment.

To improve the reactive sites of lignin nanoparticles for use in phenol-formaldehyde resin (PF), a deep eutectic solvent (DES) composed of Choline Chloride–ZnCl₂ (ChCl-ZnCl₂) was employed to pretreat nanolignin. The modified and unmodified lignin nanoparticles were used to replace high proportions of phenol (50%, 60%, and 70%) to prepare the lignin-phenol-formaldehyde (LPF) adhesive. FTIR spectroscopy was used to characterize the changes in the functional groups of nanolignin during DES treatment. The changes in glass transition temperature (T_g) and the changes in curing temperature of the LPF resin were determined by Differential Scanning Calorimetry (DSC). The incorporation of modified nanolignin into the PF resin significantly increased the solid content, viscosity and accelerated the resin gel time. The phenolic hydroxyl content of DES-treated nanolignin increased and its methoxy content decreased moving away from the optimized experimental conditions. DSC curves show that DES-treated nanolignin has lower T_g value (81 °C) than unmodified nanolignin and virgin lignin (84 °C; 92 °C), respectively. The LPF resin with DES-treated nanolignin showed a lower peak temperature compared to those prepared using unmodified nanolignin. The shear strength of the LPF adhesive prepared by DES-modified nanolignin was higher than that of the control samples. When the substitution degree of modified nanolignin for phenol reached 70%, the bond strength of the plywood prepared by the DES pretreated nanolignin was 2.3 MPa and the free formaldehyde content was 2.9 mg/100 g, thus meeting the requirements of international standards. Based on the findings of this research, a high proportion of phenol can be substituted by nanolignin in LPF resins without changing their properties when nanolignins are treated by DES.

Combining decorative and functional elements is an essential trend in the value-added nature of fast-growing wood, which can promote its commercial application in wood-based boards, interior decoration, and furnishings. This study introduces a convenient method for preparing modified veneers that can replace the predominant market colors by adjusting the pH value and furfuryl alcohol (FA) concentration. The physical, mechanical, anti-mildew, and sound insulation properties were systematically evaluated. The results revealed that pH significantly affected color, and the surface bonding strength of all modified veneers met standard requirements. The shear strength, sound insulation properties, and dimensional stability of the plywood made from 70% FA-modified veneer at strong acid conditions were significantly improved, but the bending strength was reduced. Analysis of Variance revealed that pH values and FA concentration significantly affected the color changes. Combined with scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and Fourier-transform infrared spectroscopy (FTIR) results, it was shown that the distribution of the FA and the interaction between FA and cell wall chemical components were influenced by pH values and furfuryl alcohol concentration, which are likely responsible for the color and property changes.

Fungal growth and degradation of wood may be caused by damage in the surface coating. The larger the cracks, the greater in principle the possibility of moisture-induced problems. Measuring basic unknown material parameters and employing hygrothermal simulations, the suitability and the maximum acceptable vertical crack size in the surface coating for a given bottom window profile made of thermally modified (TM) spruce(wood) with that made of native spruce were compared for location Ljubljana. Validation with the field test data was the second objective of the respective research. The average calculated maximum moisture content in TM spruce is about 4% (kg/kg) lower than that of native spruce. The 3 mm wide crack in the surface coating of a window frame made of native spruce is of the highest concern, whereas a 9 mm wide crack in the coating of a TM spruce profile is still acceptable. As far as moisture content is concerned in our study the TM spruce window frames were proved to be significantly more suitable for installation than the corresponding frames made of native Norway spruce. It was shown that isopleth, VTT and biohygrothermal models for mould growth do not properly capture the comparison between both materials, mainly because they classify both in the same material class/substrate category and they do not consider the material moisture content.

In today’s environmental context, the use of glulam or Glued Laminated Timber (GLT) as an alternative to conventional building materials could reduce the carbon footprint of engineering structures. However, this material is sensitive to outdoor exposure with moisture content variations inducing internal stresses and cracks and high moisture content increasing the risks of decay. This study therefore focuses on the development of a protocol to evaluate the effect of climatic conditions on the mechanical performance of the material. For this purpose, GLT samples were equipped with embedded sensors. Moisture and deformation sensors can accurately track wet-dry (W/D) cycles and their effects on deformation at adhesive joints. Samples are stored outdoors and mechanical tests are carried out after 6 months of aging. The results show an average reduction in flexural strength of about 10% compared to unaged specimens. Shear tests on the adhesive joints show a decrease in strength of more than 20%. The study of the fracture mechanisms also indicates a link between the type of fracture and the aging conditions of the specimens. These tests also validated a monitoring protocol that will allow, in the long term, to evaluate the impact of these cycles on the mechanical performance of GLT.

A novel type of wood-based panel for structural applications is presented. Such panel named as alternated cross-laminated timber (aCLT) is based on the cross-laminated timber (CLT) panel concept but with a modified internal architecture, in which the cross-layers are replaced by hybrid layers composed of the traditional cross-lamellas alternated with in-line lamellas—as in glued laminated timber (GLT). Such modification aims to improve stiffness and strength in the main direction of the panel in comparison to the traditional CLT concept. To study the referred panel concept and its behavior, a series of panel stripes specimens (beams) of the new panel concept, as well as of CLT and GLT, were produced with 3 and 5 layers. An experimental campaign was performed to determine: (i) the Young`s modulus of the lamellas; (ii) the shear modulus and strength of the cross/hybrid layers of the panels and; (iii) the force vs. deflection of the beams in bending for the determination of bending and shear stiffness and strength. The data obtained in (i) and (ii) was inputted into a developed finite element (FE) model and the results from (iii) were used to validate the models. The FE model was later used to compare the performance of CLT and aCLT of equivalent thickness for a practical case. The results revealed a slight reduction in deflection (between 2 and 11%) and normal stress (1–7%) and a more substantial reduction in shear stress (between 28 and 94%) against the CLT solutions.