European Journal of Wood and Wood Products最新文献

Radiata pine is a valuable resource for construction and furniture manufacturing. However, its heartwood, which has a high resin content (RC), is limited in its applications. This is because the exudation of resin can cause issues such as unsightly appearance, degumming, or paint bubbling, posing a significant challenge to its use. Hence, the heartwood of radiata pine was taken as the research object, and the resin in wood removed and fixed by microwave-superheated steam (MS) treatment was studied. The moisture content (MC), RC, relative content of turpentine, and the anti-resin-exudation performance were determined; the changes in the morphology of resin in the resin canals, the Young's modulus of the latewood cell wall, and the chemical composition were analyzed. The findings show that MS can remove some of the pine resin in the wood, but not all. Microscopic observations confirmed that some resin remained in the resin canals of the MS treatment samples. In addition, the turpentine content decreased dramatically after MS treatment. For instance, the average turpentine content of latewood in samples after treatment at 120 °C was reduced to 9.7%, only 0.3% after treatment at 140 °C, and no turpentine was detected after treatment at 160 °C. This may explain why the wood after MS treatment showed good anti-resin-exudation, as the volatilization of turpentine would lead to the increase in softening point and thermal stability of resin. In addition, the Young's modulus of latewood cell wall increased with superheated steam (SS) treatment temperature. The resin was oxidized, dehydrogenated, and isomerized after MS treatment. These findings confirmed that MS treatment improves the anti-resin-exudation performance of radiata pine by increasing the softening point of residual resin and fixing it inside the wood. Through this strategy, the treated radiata pine heartwood shows greater potential for application.

Cross laminated timber (CLT) and glue laminated timber (glulam or GLT) are gaining attention given their use in high-rise buildings as climate mitigation concept. In most cases softwood is used to manufacture these engineered wood products, yet fast-growing and widespread hardwood species such as hybrid poplar have potential to meet the increasing demand. In addition to the mechanical performance, it is also key to investigate the fungal susceptibility and moisture dynamics of poplar, to gain insight into the service life of engineered poplar products. This paper therefore investigates the fungal decay resistance, as well as the moisture sorption properties of (thermally modified) hybrid poplar clones and Norway spruce. Fungal decay resistance was tested using the mini-block test. Moisture dynamics were evaluated using a floating test and dynamic vapor sorption (DVS). A higher fungal decay resistance and a significant decrease of moisture sorption was observed for thermally modified poplar. Our results show that the overall moisture properties of poplar and spruce are similar and that differences among the poplar clones are negligible, demonstrating the potential of poplar wood for engineered wood products. Together with findings on the mechanical properties in the literature, these results on durability and moisture performance give extra support for the potential utilization of poplar CLT in constructions.

By using basalt fibers as reinforcement materials, high performance particleboards could be produced by the wood-based panel industry. Due to the high strength of basalt fibers, the strength-to-weight ratio can be significantly increased, which would allow the use of these particleboards (PB) in high-load-bearing applications. In this study, a basalt grid with a grammage of 200 g m⁻² was implemented to reinforce PB and oriented strand boards (OSB). OSB were bonded with polymeric diphenylmethane diisocyanate (pMDI), while pMDI as well as melamine–urea–formaldehyde (MUF) and urea–formaldehyde resin (UF) were used for the PB. The target densities of the panel variants were 580, 650 and 720 kg m⁻³. The determination of the mechanical properties showed that the modulus of rupture (MOR) and modulus of elasticity (MOE) were increased up to 100% and 44% respectively, compared to panels without basalt grids. At the same time, the addition of the basalt reinforcement layer did not cause a decrease in internal bond strength (IB). Thus, the usage of basalt grid as a reinforcement material could be a good possibility to produce high-load-bearing panels without increasing the density of the PB.

The impact of extractives on the appearance and wettability changes of wood surface during artificial weathering was discussed from the aspect of chemical and structural changes. Un-extracted (CK) and extracted samples were subjected to UV irradiation or a combination of UV and water. The structural damage inflicted on the extracted sample by the combination of UV and water was more severe compared to the CK sample, corresponding to high roughness and the presence of visible cracks on the irradiated surface of the extracted sample. Analysis of FTIR spectra and overall color change (ΔE*) confirmed that ΔE* values correlated well with lignin decay and the generation of carbonyl groups. Furthermore, the wettability of samples aligned closely with changes in the hydrophilic hydroxyl groups determined by FTIR spectra. The presence of extractives in the CK sample retarded the rate of lignin degradation, and the additional carbonyl groups generated by extractives contributed to color changes. Overall, the extracted samples exhibited more pronounced structural deterioration, color changes, increased wettability, and composition degradation compared to the CK sample, underscoring the photo-stabilizing effect of extractives during UV irradiation. Additionally, the erosion of water exacerbated the degradation of chemical composition and structural deterioration, resulting in significant visible alterations and high wettability.

The modification by impregnation of veneers for the production of plywood with phenol–formaldehyde resins is a well-known method to improve the dimensional stability and fungal resistance. Because phenol is obtained from non-renewable resources, finding substitutes has been a topic of research. Due to similarities in chemical structure and availability, lignin cleavage products present a promising alternative. In this study, microwave-assisted pyrolysis cleavage products of softwood kraft lignin have been used to substitute 30% of phenol in phenol–formaldehyde resins. Scots pine veneers were impregnated with the resin, and five-layered plywoods were produced. The influence of the substitution on the bonding quality, the dimensional stability, and the leaching of resin from the specimens were studied. Mechanical properties such as the bending strength, the modulus of elasticity, as well as the dynamic impact bending strength of the plywood were analyzed. Both treatments led to plywood with good dimensional stability, and the resin was stable against leaching. The substitution of phenol with lignin cleavage products led to slightly reduced brittleness of the specimens compared to pure phenol–formaldehyde resin. This study presents a method to reduce the use of non-renewable resources, increase the use of currently underutilized lignin sources, and produce plywood with promising properties for exterior applications.

Abstract

The high demand for teak wood has driven efforts to achieve increased volumetric production in fast-growing plantations. However, the logs often exhibit higher proportions of sapwood and juvenile wood. This study was conducted to investigate how the age of teak trees in commercial plantations influences the heartwood proportion, wood density, and formation of mature wood. A total of 12 trees of both clonal and seed origins were harvested at the ages of 5, 10, 15, and 20 years old. Disks in the regions of the base, 2.3 m, and top of the trees were collected. Along the stem, we determined the total, heartwood, and pith diameters, as well as the proportions of bark, sapwood, heartwood, and pith. The base disks were used to analyze wood density and to demarcate the transition from juvenile to mature wood stages by X-ray densitometry. As teak wood aged, it exhibited higher heartwood percentages, with variations ranging from 7% (5 years old) to 56% (20 years old). The five-year-old wood had the mean highest density (0.74 g.cm⁻³). There was a trend of increasing mean wood density as the trees aged from ten years. The diameter profiles by X-ray densitometry indicate a higher wood density in the pith-bark direction. The density of 20-year-old wood ranged from 0.54 g.cm⁻³ (ring 1) to 0.78 g.cm⁻³ (ring 19). For all ages evaluated, juvenile wood is predominant, with the transition age occurring at approximately 11 years old. However, only 15- and 20-year-old trees had mature wood in their heartwood, but it was less than 2% of the total heartwood at those ages.

Abstract

The widespread utilization of fast-growing plantation timber in furniture and building construction is often hindered by defects such as insufficient mechanical strength, dimensional instability, and flammability. In this work, an effective and simple approach was presented to enhance the performance of fast-growing poplar wood, through surface impregnation with a mixed solution of biomass-derived furfuryl alcohol (FA) and flame retardants ammonium dihydrogen phosphate (ADP), followed by unilateral densification. Benefiting from the compressed surface structure and the addition of ADP, the densified wood impregnated with 8 wt% ADP exhibited superior fire resistance, achieving UL-94 V-0 rating and a high LOI value of 44.3%, and showed remarkably lower heat and smoke release in Cone tests. The incorporation of FA resin significantly enhanced the plasticizing effect of cell wall and the densification degree of surface layer, thereby improving the physical and mechanical properties of wood. The flame-retardant densified wood impregnated with 30 wt% FA and 8 wt% ADP exhibited a surface hardness of 4750.8 N, modulus of rupture of 106.3 MPa, and modulus of elasticity of 8.7 GPa. Moreover, the cross-linked network derived from FA resin effectively reduced the loss of ADP and suppressed the set-recovery of deformed cell walls, thereby enhancing the dimensional stability and durability of densified wood. The surface-impregnated and unilaterally densified wood exhibited exceptional comprehensive properties, showing a promising potential as a high value-added product for furniture and building construction.