Wood Science and Technology最新文献

Dynamic mechanical analysis and small-angle X-ray scattering (SAXS) measurements of hinoki wood swollen with water and/or ethanol in the temperature range of 20–78/95 °C were performed to clarify the relationship between swelling and microstructure in different swelling states. For the sample swollen in a water–ethanol mixture with an ethanol mole fraction of 0.2, a peak in tanδ, i.e., the ratio of the dynamic elastic modulus (E′) to the dynamic loss modulus (E″), was observed at around 50 °C. No clear peak was observed in the temperature range of the sample swollen with water or ethanol, but thermal softening behavior due to micro-Brownian motion of lignin was observed. The scattering behavior of the samples swollen with water and/or ethanol differed significantly from one solution to another. The SAXS intensity of samples swollen with water or mixture of water and ethanol increased with increasing temperature, while the SAXS intensity of samples swollen with ethanol changed little with increasing temperature. This suggested that the adsorption sites of ethanol were different. The position of the peak for the sample swollen with the water–ethanol mixture, observed in the Kratky plot, was shifted to the low-q side compared to the pure liquid. It was suggested that the aggregation state of the sample swollen with the mixture of water and ethanol was very different from those of the wood swollen with the pure liquid.

Cellulose nanocrystals (CNCs), derived from abundant natural cellulose, possess exceptional properties including low weight, bioavailability, and high mechanical performance. During shear loading, CNCs exhibit unique stick–slip behavior, making them excellent toughening materials for CNC neat films and nanocomposite. However, the failure behavior at the interface under specific conditions, particularly moisture and temperature, remains unclear. The study utilized molecular dynamics (MD) simulations to quantitatively investigate the hydrothermal effect on the degradation of CNC interface. The degradation mechanism induced by moisture and temperature was indicated through the reduction of adhesive energy and peak force with the consideration of hydrogen bonds. The simulation results showed that the role of water molecules in the interfacial failure depends their content. Water acted as a binder at low moisture levels, while at high moisture levels, it acted as a lubricant. Besides, temperature had a more pronounced impact on the interfacial shear performance. Our simulation results can be used as input in micromechanical models to bridge the gap between the macroscopic and microscopic behavior of films and nanocomposites.

The digital image correlation (DIC) system is a powerful tool for measuring distributions of displacement and strain on the surface of a specimen. DIC systems are employed not only for homogeneous materials such as metals but also for heterogeneous materials such as wood. Although numerous validations of DIC system accuracy for metallic materials exist, the accuracy verification for wood, especially under multiaxial stress conditions, is less common. This study investigated the accuracy of a DIC system equipped with a bilateral telecentric lens on wood (Douglas fir). The accuracy verification in uniaxial stress fields was conducted through full compression testing, while verification in multiaxial stress fields was performed through partial compression testing. Additionally, compression tests on A6063 (aluminium alloy) were conducted to examine the differences in the DIC system accuracy between homogeneous and heterogeneous materials. The accuracy of the DIC system was assessed by comparing the results with those obtained from strain gauges. The results from the full compression tests indicate that the accuracy of axial strain measured by the DIC system was comparable for the specimens of A6063 and Douglas fir in the longitudinal (L) direction but was inferior for Douglas fir in the radial (R) direction. This is because the differences in the mechanical properties of earlywood and latewood produce high strain gradients. Furthermore, the differences in Young’s modulus obtained from the DIC system and strain gauge for the specimens of A6063, Douglas fir (L), and Douglas fir (R) were − 1.23%, 2.26%, and − 12.5%, respectively. In the partial compression tests, the accuracy of strain components measured by the DIC system in the specimens of Douglas fir (R) was lower than that in A6063. In the partial compression tests, high strain gradients appear in multiple strain components, leading to a notable decrease in the accuracy of the DIC system compared to the full compression tests.

The present work has experimentally determined the specific fracture energy of the hardwood species silver birch (Betula pendula), which in recent times has caught increased attention for utilization in structural applications. The single-edge-notched beam loaded in three-point-bending was utilized for evaluating the fracture energy with the work-of-fracture method. In addition to birch, Norway spruce (Picea abies) was utilized as a reference material. The effect of two different geometries of the fracture area for each species was evaluated—one triangular and one rectangular fracture area. It should be noted that the geometry of the fracture area did influence the evaluated fracture energy, and this influence was not consistent between species. This was likely in part due to manufacturing difficulties with the triangular fracture area. In addition to the experimental testing, a numerical 2d-model including linear strain-softening behavior was used for comparative simulations. The numerical 2d-models showed reasonable agreement with the experimental results regarding the global load vs. displacement response, despite their relative simple nature. The specific fracture energy for the spruce specimens was evaluated to 221 J/(hbox {m}^2) and for the birch specimens to 656 J/(hbox {m}^2). Consequently, the present work implies a marked increase in specific fracture energy for birch, compared to spruce. This increase in specific fracture energy could potentially have a large influence on the failure behavior of birch when used in structural applications which is something that needs to be considered in future work.

Wood is a sustainable, benign, and high-performing green structural material readily available in nature that can be used to replace structural materials. However, insufficient mechanical performance (compared to metals and plastic), moisture sensitivity, and susceptibility to microorganism attack make it challenging to use wood as it is for advanced engineering applications. We here present an efficient approach to fabricating densified wood with minimal time and waste generation, demonstrating high mechanical strength, and decreased water penetration on the surface. Wood slabs were treated with deep eutectic solvents (DESs) to solubilize the lignin, followed by in-situ regeneration of dissolved lignin in the wood. Then, the slabs were densified with heat and pressure, turning the wood into a functionalized densified material. Lignin regeneration and morphological changes were observed via two-photon microscopy and Scanning Electron Microscopy (SEM), respectively. The final product is less susceptible to water absorption on the surface and has enhanced flexural strength (> 50% higher), surface hardness (100% increased), and minimal set recovery compared to natural wood. The improved mechanical performance is due to regenerated lignin which acts as a glue and fills spaces present within the interconnected cellulose network inside the wood, forming a highly dense composite during densification. Such enhancement in the properties of DES-densified wood composite makes it a favorable candidate for advanced structural and engineering applications.

Plant biomass, in particular forestry wastes, is a promising renewable feedstock for deep chemical processing. Organosolv methods allow the use of underutilized lignin. The synthesis of modified polymers by azo coupling with the use of aspen (Populus tremula) ethanol lignin and its sulfated modification is studied. The success of the synthesis has been proven and the features of the structure and properties of the synthesized samples were studied by the physicochemical techniques, including Fourier transform infrared and nuclear magnetic resonance spectroscopy, gel permeation chromatography and thermogravimetric analysis. It was shown that the new azopolymers have the ability to photoisomerize, which opens up prospects for their high-tech applications. The modified lignins are proven to be bioactive antioxidants.

Xuan paper is a classic Chinese handmade paper with long history and has been listed as a national intangible cultural heritage since 2009, which is mainly composed of wingceltis (Pteroceltis tatarinowii) phloem fibers and straw fibers. Due to the unique properties of wingceltis phloem fibers, Xuan paper is spotless, flexible, stable, and durable, and is widely used by calligraphers, painters, or museums for restoration. Uncovering the variation of phloem fiber properties throughout the traditional pulping process is essential for a comprehensive understanding of the special performance of Xuan paper. In this study, chemical, structural, and mechanical characterization was conducted on the raw bark (phloem fiber), treated phloem fiber, and pulp fiber at different steps of the traditional pulping process for making Xuan paper. The compositional and morphological analysis revealed the effective removal of the matrix polymers, while the phloem fiber almost retained the original fiber structure during the traditional process. Wide-angle X-ray scattering results indicated that the relative crystallinity of cellulose increased and crystals expanded after the lime cooking and exposure to sun and rain. Compared to the raw phloem fibers, the ultimate stress and tensile stiffness of pulp fibers decreased by 24.35% and 9.79%, respectively. However, the fracture strain and fracture toughness of pulp fibers showed a drastic promotion, which might be attributed to the energy dissipation caused by the cell wall structure, the breaking and reforming of hydrogen bonds, and the slipping and rearrangement of cellulose microfibrils.

Wood is a multiscale heterogeneous natural composite material with properties depending on its growing conditions and its genetic heritage. This variability is challenging for industries that work to perform homogeneous and reliable products. In industry, different non-destructive testing methods are in use to classify, grade, and select wood products to optimize their usage. Among them, the use of lasers to detect fiber orientation with different wavelengths. This orientation significantly influences the mechanical behavior of wood, including stress limits and stiffness. According to our knowledge, the use of laser diffusion still is limited to grain angle measurement. Our objective in this paper is to realize transmission light scattering maps for wood samples from several wood species (poplar, oak, Douglas fir, beech), and then identify the most suitable wavelength to study light diffusion in wood, depending on the property that will be measured. A supercontinuum laser is used over a wavelength range from 500 to 800 nm, allowing precise adjustment of the wavelengths. It was found that near-infrared light better scatters in the studied wood species than lower wavelength. However, the wavelength that gives the best contrast between earlywood and latewood depends on the sample studied and is not necessarily in the near infrared rays.

The present work investigated new sustainable opportunities for wood protection against xylophagous organisms (cellulolytic fungi and termites) based on the use of natural bioactive compounds present in Milicia excelsa wood and Nerium oleander bark. To achieve this, solid–liquid extractions by ethanol were carried out, obtaining extraction yields of 5.47 ± 0.78% for the extract of M. excelsa and 21.88 ± 0.53% for N. oleander. Gas chromatography coupled with mass spectrometry analyses were carried out to evaluate the chemical composition of both extracts, showing interesting compounds with biological activity such as pyrogallol, 4-acetylresorcinol, karanjin and scopoletin. Likewise, an evaluation of the cellulolytic capacity of different wood-isolated fungi (Aspergillus flavus, Penicillium chrysogenum, Trichoderma longibrachiatum, Mucor circinelloides and Mucor fragilis) was carried out through two screenings, based on their growth rate in carboxymethyl cellulose agar media, and their cellulose-degrading ability via filter paper rupture, being T. longibrachiatum the fungus with the highest growth rate in both substrates. Finally, a protective treatment for pine wood (Pinus sp.) was designed by using the ethanolic extracts separately and combined, respectively, against T. longibrachiatum and Reticulitermes grassei, comparing in both cases the biotic damage with a control. The results demonstrated that the impregnation significantly reduced T. longibrachiatum biomass consumption by over 70% for all treatments. Additionally, the M. excelsa impregnation notably decreased termite activity, with a 81% reduction in the long-term assays.

In this study we separated the chemical components of cork from Quercus variabilis by various solvent extraction and alcoholysis methods. We identified the content and chemical composition of suberin and dichloromethane extract with gas chromatography-mass spectrometry (GC-MS) and analyzed the antifungal effects of different cork extracts against wood-decaying fungi. The results showed that the main structural component of cork, suberin, averaging 36.34% of the total dry weight, exhibited a pronounced inhibitory effect on wood-decaying fungi, compared to the dichloromethane extract. By the end of the entire culture period, the colony diameter of white rot fungi was 5 mm in the 40 mg/mL suberin treatment group, 19 mm for brown rot fungi, both significantly smaller than the control group (90 mm). Hydroxy fatty acids, free fatty acids, and α,ω-diacids may be the key components contributing to the antifungal activity of suberin. The inhibitory mechanism of suberin components on wood-decaying fungi may involve suppressing the respiratory metabolism of the fungi and increasing the permeability of their cell membranes, thereby limiting their normal life activities.