Wood modification, an efficient approach to enhance the intrinsic properties of wood, has been extensively studied for decades. Due to growing environmental awareness, the sustainability of wood mo...

Environmentally Benign Wood Modifications: A Review

Improved TGA-MS measurements for evolved gas analysis (EGA) during pyrolysis process of various biomass feedstocks. Syngas energy balance determination

Pleating is an optimal way to increase bendability of wood used in diverse industrial applications. It results in the excessive buckling of cell walls and modifications of constitutive polymers. However, thoughtful understanding of the physical–chemical mechanisms of that modification process is very limited. The main purpose of the present study was to identify changes in functional groups of wood polymers induced by longitudinal compression. Four types of wood samples prepared from beech and sessile oak (untreated, steamed, longitudinally compressed and fixated for 1 min as well as longitudinally compressed and fixated for 18 h) were assessed by infrared spectroscopy. The spectra interpretation revealed that changes can be observed in hydroxyl as well as in carbon–oxygen single and carbon-hydrogen functional groups of polysaccharides and lignin. Beech wood seems to be more susceptible to investigated modification processes as compared to oak. Detailed interpretation of infrared spectra allows identification of changes in the hygroscopicity of wood as well as alterations in the linkage between structural elements in the polymer matrix of wood induced by the applied treatments.

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FTIR analysis of chemical changes in wood induced by steaming and longitudinal compression

Due to its good physical properties, softened wood (SW) has been widely used in the fields of home furnishing, interior decoration, and construction, such as decorative panels, softened wood flooring, wooden bricks, and softened wood furniture. However, traditional methods of wood softening often fail to meet the requirements of enterprises for softening wood. Here, inspired by the research related to wood softening, we propose a method for directly preparing softened wood (SW) using a new type of "ionic liquid" eutectic solvent (DES) owing to its low cost, environmental friendliness, recyclability, and other advantages. To improve the adaptability of the study, a total of five types of DESs were designed and prepared, and by the microwave-assisted DES treatment of natural wood (NW), the purpose of softening wood was achieved. Then, we conducted a series of comparative analyses and performance tests on NW and SW, including microscopic images, chemical composition, color difference, and mechanical properties. The results show that the wood softened by DES has become a highly porous network structure, and partial lignin, hemicellulose, and cellulose have been removed. At the same time, different degrees of color change, lower hardness, excellent mechanical flexibility, and a compression rebound rate of up to about 90% are obtained. The above-mentioned various properties of SW provide great potential for its application in wood products.

Softened Wood Treated by Deep Eutectic Solvents.

Since the properties of wood significantly change with its moisture content, it is important to know the effect of different moisture conditions on wood. A brief summary is provided on this topic in the first part of this article. The compression along the wood grain is a modification resulting in better pliability. The moisture dependence of mechanical properties of longitudinally compressed wood is not known yet. For this purpose, the results in this article are considered as basic research results. Bending- and compression tests on beech specimens compressed longitudinally by 20% were carried out at different moisture contents. Changing moisture content has almost no significant effect on the modulus of rupture of wood that has been longitudinally compressed, compared to the sensitivity to changes in moisture content of untreated wood. However, the effect of moisture content on the change of bending modulus of elasticity, compressive strength parallel to the grain and bendability coefficient diverges significantly. As a result of these changes, there is a great difference in the pliability with different moisture contents of treated wood. For the best pliability during bending, the moisture content of longitudinally compressed wood must be close to its fiber saturation point.

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Moisture-dependent mechanical properties of longitudinally compressed wood

Longitudinal compression induces changes in wood tissue resulting in better bendability. The main purpose of the present study is to identify the changes occurring at the microscopic level. Air-dried oak wood samples (Quercus petraea (Matt.) Liebl.) exposed to a thermo-hydro-mechanical treatment—combined with different longitudinal compression and relaxation treatments—were subjected to micromechanical (nanoindentation) and ultrastructural (scanning electron microscopy, atomic force microscopy) analyses at the wood cell wall level. The comparison of the various methods of treatments shows that the secondary cell wall S2 hardness decreased by 6% as a result of the compression and by 12%, when combined with a long relaxation period. Cell wall indentation modulus decreased by 25% and 51%, respectively. Relative elastic deformation work increased at the expense of plastic deformation work, while the relative proportion of viscoelastic work remained unchanged. Atomic force microscopic images revealed distinct disorientation of the normally straight microfibrils as a result of longitudinal compression, which was attributed to cause the weakening of the cell wall. The results indicate that changes at the ultra-structural level of the wood cell wall contributed to the changes in the macromechanical properties (for example modulus of elasticity and bendability) already reported previously, of the treated wood samples.

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Micromechanical properties of longitudinally compressed wood

Abstract Knowledge of hygroscopicity is extremely important both in the use of native wood and modified wood. In this study, the modification method was steaming at 100 °C, then longitudinal compression at a rate of 20%. The moisture content (MC) of treated and untreated green beech wood (Fagus sylvatica L.) was reduced in a climate chamber with gradual reduction of air humidity at 20 °C. The difference of calculated fibre saturation points between control samples and samples compressed for a long time was 6% (MC%). In the course of desorption, this difference decreased, and finally disappeared at 10% moisture content (40% relative humidity). In the second step of the research work, the speed of vapour adsorption was checked. The absolute dry samples were placed in air with 95% relative humidity. The highest deviation in the moisture content was 1% (MC%) between the control and the compressed samples. The compressed wood dries faster than the control samples under the same conditions. Furthermore, during adsorption, the moisture content of the compressed samples at room conditions is lower.

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Hygroscopicity of Longitudinally Compressed Wood

Abstract Longitudinal compression of wood and relaxation after compression (held compressed for a while) is called pleating and results in improved bending properties. The examinations conducted on the longitudinal compression of air-dried oak (Quercus petraea (Matt.) Liebl.) and beech wood specimens (Fagus sylvatica L.) revealed the effects of different compression rates (10, 20, 40, 60 mm/min). The comparison of the various treatment methods showed that the stress in wood specimens during longitudinal compression increases with the rising compression rate. The remaining length reduction due to pleating slightly decreases and the bending modulus of elasticity increases at higher compression rates. The highest deflection of the specimens during the 4-point bending tests lowers with the increasing compression rate, while the change of modulus of rupture is negligible. Taking into account the differences between these results and the industrial effectiveness of the treatment according to the compression rates, it can be stated that a procedure with a higher rate should be preferred.

Mátyás Báder

Papers

FTIR analysis of chemical changes in wood induced by steaming and longitudinal compression

Moisture-dependent mechanical properties of longitudinally compressed wood

Micromechanical properties of longitudinally compressed wood

Hygroscopicity of Longitudinally Compressed Wood

The Effect of the Rate of Longitudinal Compression on Selected Wood Properties