Wood Science and Technology最新文献

Ultrasonic-guided waves (GWs) have shown a high potential to be applied to the structural integrity of timber utility poles to detect and assess distinct types of defects. Yet, there are many challenges associated with this method, which may hinder its application, including the orthotropic nature of the timber, the presence of natural cracking, and the effect of environmental factors such as temperature and moisture content (MC) on the propagation of GWs. This study aims to scrutinize the effect of MCs ranging from 0 to 24%, and temperatures between − 20 and 100 °C on the propagation characteristics of GWs (longitudinal and circumferential) in cylinder timber structures excited over a range of frequencies between 10 and 20 kHz, experimentally and numerically. The numerical analysis was carried out using COMSOL Multiphysics, and Macro Fiber Composites were used to excite and sense the GWs. The anisotropic nature of timber poles was modeled using a transversely isotropic behavior. The results showed that the effect of timber’s temperature and MC on the GWs should be assessed simultaneously. Three-dimensional maps were generated to present the relationship between various wave modes, temperature, and MC. The work observed a larger critical role of MC than the temperature on the propagating GWs and timber’s material properties. The effect of temperature is more critical when timber’s MC increases above the fiber saturation point (FSP) due to high stiffness variations. This is seen as the group velocities of the longitudinal and flexural waves (as well as the bulk wave) shifted more at MCs above FSP than below FSP. When MC varies above FSP with no temperature variations the velocity difference is negligible with 1.5% due to complete timber saturation at all temperature values. The results showed that the change in the mode velocities in dry wood is not significant with varying temperatures, as the stiffness changes by 0.07%. Experimental validation, for the numerical results, showed low differences for the bulk wave, and flexural modes were within [7.1 15]% and [1.3 4.7]% for the 2nd flexural branch at 12.5 kHz, respectively. Based on the above results, the environmental conditions can highly impact the GWs characteristics in timber structures, hence this should be carefully considered in the application phase.

The crystalline characteristics, chemical composition, and thermal decomposition of elements in Quercus variabilis (Qv) virgin cork were investigated using X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric methods, respectively, and compared with those of elements in Quercus suber (Qs) reproduction cork. Samples of cork elements, including pure cork, lenticular filling tissue (LFT), dark-brown zone (DBZ), and sclereids, were prepared. The X-ray diffractograms of pure cork from both species showed an amorphous pattern, whereas those of LFT, DBZ, and sclereid showed a crystalline cellulose I pattern. The relative crystallinity of DBZ was significantly lower than that of Qv LFT and the sclereid. In the FTIR spectra, Qv pure cork tended to show weaker band intensities for the suberin, lignin, and carbohydrate compounds than Qs pure cork. The pure corks of both species showed stronger suberin bands than LFT, DBZ, and the sclereid. In the thermogravimetric analyses, the peaks of hemicellulose and cellulose decomposition in both pure corks were weaker than those in LFT, DBZ, and sclereid, whereas the peaks of suberin decomposition in both pure corks were the highest among all elements.

This paper focuses on the characterization of the three-dimensional elastic properties of wood materials using the propagation velocity of ultrasonic waves in the context of the inspection and diagnosis of timber structures. The scientific innovation consists in exploiting only the velocities of the compression (P) waves and using a single sample. From a three-dimensional formulation of Hankinson and an analytical development which allows to define the relations between the properties of elasticity and the velocities of ultrasonic waves, the twelve elastic constants are determined by means of an optimization procedure. The experimental validation on a Douglas fir cube allows to have the three moduli of elasticity (left( {E_{text{L}} ,E_{text{R}} ,E_{text{T}} } right)), the three shear moduli (left( {G_{text{LR}} ,G_{text{LT}} ,G_{text{RT}} } right)) and the six Poisson’s ratios (left( {nu_{text{LR}} ,nu_{text{LT}} ,nu_{text{RT}} ,nu_{text{RL}} ,nu_{text{TL}} ,nu_{text{TR}} } right)). The longitudinal modulus (left( {E_{text{L}} } right)) is more than eight times greater than the radial modulus (left( {E_{text{R}} } right)), which is more than two and a half times greater than the tangential modulus (left( {E_{text{T}} } right)). For the shear moduli, we obtain (left( {G_{text{LR}} > G_{text{LT}} > G_{text{RT}} } right)). The Poisson's ratios meet the requirements of energy deformation positivity and stiffness matrix inversion. The values of the elastic constants obtained are in line with those from the literature.

The global textile fiber output increased five times from 1975 to 2020. Also, in 2010, the combined demand for man-made and natural fibers was projected to increase by 84% within 20 years. Clothing materials are largely made from cotton or petroleum-based synthetic fibers; both sources, however, have adverse environmental impacts. Thus, cotton requires vast amounts of land, water, fertilizers and pesticides, and synthetic fibers are not biodegradable. This scenario has raised the need for further exploration of cellulose polymers as sustainable sources for the textile industry. Cellulose, the most abundant renewable organic material on earth, is an outstanding polymer that by chemical derivatization or modification can offer a broad range of applications. Dissolving-grade pulp (DGP), which consists of highly pure cellulose, is the most suitable material for manufacturing cellulose derivatives and regenerated fibers. The latter are typically obtained by using the viscose process, which has considerable adverse environmental impacts. Although the textile industry has progressed substantially, further efforts are still needed to make its entire production chain more sustainable. This article provides an in-depth introduction to the potential of fibers with a high cellulose content, known as dissolving-grade pulps. It reviews the properties of DGP, the cooking and purifying methods typically used to obtain it, and the process by which paper-grade pulp can be converted into dissolving-grade pulp. Also, it discusses traditional and recently developed technologies for producing regenerated cellulose fibers. Finally, it examines the potential for recovering cellulose from textile waste as a novel sustainable practice.

Alkalization of plant or wood fibre (WF) is the most widely used method of chemical modification to improve reinforcement in thermoplastic composites. This process involves the complete or partial removal of extractives and or modification of lignocellulosic material. While research has shown that removal of the less thermally stable extractives results in an improvement in fibre thermal stability, in the current work it has been shown through single-factor analyses, Fourier transform infrared microscopy, scanning electron microscopy, thermogravimetric analyses and wide angle X-ray diffraction that meranti WF thermal stability is largely influenced by the holistic changes in the WF structure, which itself is affected by alkalization factors. After implementing stepwise regression on a central composite design, no empirical model could be established to explain or predict thermal stability due to interaction of treatment factors. As a result, single-factor analyses of temperature, time and alkali concentration were conducted. Single-factor analyses showed that different combinations of time, temperature and alkali concentration through a central composite design result in WF with different thermal stabilities, lignocellulosic content, crystallinities, crystallite sizes, extractives content and morphology. Alkali-treated meranti WF showed lower thermal stability compared to the untreated WF. Mild treatment conditions (e.g. 50 °C/30 min/5%) were seen to result in the most thermally stable WF. Increasing temperature, treatment duration and alkali concentration increased thermal stabilities except at harsh conditions (e.g. 50 °C/90 min/15%). A combination of high alkali concentration and long treatment times showed a combined detrimental effect on WF thermal stability. Changes in the lignocellulosic structure, crystallinity, crystallite sizes and surface features explain the observed changes in thermal stabilities.

For the utilization of silver birch (Betula pendula Roth) in load-bearing engineered wood products (EWPs), reliable bonding in production is a prerequisite. The current knowledge regarding the bonding of birch in EWP applications is limited. Extractives are considered a general factor of attention when securing bonding quality. Thus, in this study, the effects of hydrophilic extractives on several adhesion-related bulk and surface properties of silver birch wood were studied, e.g., vapor sorption, swelling behavior, microstructure, wettability, and mechanical properties. The extraction procedure slightly affected vapor sorption causing a reduction in swelling pressure. The extraction also led to a lower Young's modulus, as seen by compression tests. Control experiments with vapor-treated specimens, however, indicated that the effects were originating from the water imbibition and not due to the removal of extractives per se. This was supported by X-ray diffraction results, which were similarly affected by both vapor and extraction treatment. Therefore, the results indicate that the hygric history of the specimens was affecting the wood due to plasticization, increasing mobility, and thereby likely allowing biopolymer reconfiguration and subsequent quenching during re-drying, even though surface-free energy and wettability were not considerably affected. The extent to which these changes appear permanently or temporarily remains an open research question.

The detailed anatomical and chemical features of the bark from endemic Quercus vulcanica in Turkey are reported here for the first time and discussed in the perspective of integration into a bark-based biorefinery system. The bark of Q. vulcanica trees was collected and studied through observations using light and scanning electron microscopy, wet-chemical analysis, inorganic elemental and FTIR analyses, GC–MS determinations of lipophilic extractives and suberin monomers, as well as TBARS antioxidant activity of hydroethanolic extracts. The bark of Q. vulcanica comprises phloem and a rhytidome with thin periderms and a few cork layers. The ash content is high (16.4%), primarily consisting of calcium oxalate crystals. Extractives were present in a high amount (23.1%) of which 88% corresponded to hydrophilic extractives (10.3% ethanol, and 10.1% water solubles). The suberin content is low (3.7%), which aligns with the small proportion of cork in the bark rhytidome. The composition of suberin is characterized by similar proportions of α, ω-alkanoic diacids and ω-hydroxyalkanoic acids, with 18-hydroxy-9-octadecenoic acid (26% of monomers) and octadec-9-enedioic acid (20.6%) as the main monomers. The lignin content is 21.9%, and the monomeric composition of polysaccharides includes glucose, xylose, arabinose, galactose, rhamnose, and acetyl groups. The lipophilic extractives are mainly composed of terpenoids (72.2% of all compounds), with friedelin and friedelanol as the main compounds. Hydroethanolic extracts, obtained under mild conditions with a yield of 10.2%, exhibited antioxidant activity (TBARS assay, EC₅₀ value of 55 μg/mL). The overall chemical and structural properties of Q. vulcanica bark indicate promising potential for biorefineries.

Poor dimensional stability, sensitivity to microorganisms, and flammability restrict the application of wood in certain areas where these properties are critical. Although furfurylation can improve the physical and mechanical properties of wood, the heat and smoke release of furfurylated wood during combustion are dramatic and need to be addressed. As a kind of halogen-free phosphorus flame retardant, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives exhibit excellent performance in polymer composites. In this study, DOPO was dissolved in furfuryl alcohol (FA) and used to modify wood. The effect of DOPO on the thermal stability, combustion behavior, and physical and mechanical properties of furfurylated wood was investigated. The chemical structure, morphology, and char residue after combustion were also characterized. The studies show that DOPO can react with the FA polymer and is incorporated and homogeneously dispersed in the wood structure. Compared to untreated wood, furfurylated wood has a much higher heat and smoke release during combustion. The addition of DOPO remarkably reduces the heat release of furfurylated wood, and this effect increases as the amount of DOPO increases. When the amount of introduced DOPO of furfurylated wood is 7%, its total heat release is reduced by 37.4% and becomes comparable to the untreated wood. However, DOPO does not suppress smoke production effectively. DOPO improves the thermal stability of furfurylated wood by promoting char formation and inhibiting the diffusion of oxygen and the escape of pyrolysis products. The addition of DOPO has little effect on the physical and mechanical properties of furfurylated wood. The results indicate that the combination of DOPO and furfurylation could be an efficient way to prepare highly stable and fire-resistant wood materials.

The resin impregnation treatment of wood is used as a pretreatment to improve the deformability of wood and the durability of its formed products. The objective of this study was to clarify the effect of solvent removal after resin impregnation on wood deformation. A solution of melamine formaldehyde (MF) resin was impregnated into the wood, and the solvent was removed from the wood under vacuum or different relative humidity (RH) conditions. The deformability of MF-resin-impregnated wood was evaluated based on the load required for molding. A higher RH during solvent removal allowed the MF resin to penetrate the cell wall, while the polymerization of the MF resin impregnated in the cell lumen and cell walls was accelerated. Polymerization of the impregnated resin significantly reduced the deformability. The cell orientation and distribution of the MF resin at the cellular level in the molded products were evaluated by X-ray diffraction and Raman mapping. The results showed that the higher the RH during the solvent removal process, the higher the cell orientation and amount of resin in the cell wall. These results suggest that the solvent removal process after resin impregnation has a significant effect on deformability during deformation processing and the formed products.

Ulmus pumila represents a promising lignocellulosic biomass source for biofuels and bioproducts production since it can grow in low rainfall and extreme temperature zones. A first step in the conversion process is biomass fractionation to enhance the performance of the hydrolysis and subsequent biological conversion steps. The aim of this work is to optimise the main variables (temperature, residence time and the addition or not of sulphuric acid) of steam explosion to pretreat Ulmus pumila biomass. The optimal conditions to maximise both glucose and xylose recovery were 204.8 °C and 30 mg H₂SO₄/g biomass, obtained through a multilevel factorial design of experiments. Additionally, enzymatic hydrolysis using high solid loads (15% and 20% (w/w)) and different enzyme doses was studied. As a result, steam explosion at optimal conditions followed by enzymatic hydrolysis with 20% solid loading and 60 mg protein/g cellulose of enzyme allow the recovery of 70% of the potential sugars.