Chemical Alterations of Hardwood Veneers Due to Thermal Treatment (original) (raw)
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Thermal modification beneficially alters several technological parameters of wood. The changes in the physical parameters are due to the significant alterations of the structure and the chemical composition of wood, which take place during the modification process. These changes are complex and some aspects are still far from being completely understood. Various industrially important hardwoods and softwoods have been treated in an autoclave in N 2 atmosphere. The physical (density, L-value, moisture content, bending strength, MOE) and chemical (pH, hemicellulose-, total phenol-and soluble carbohydrate content) parameters have been measured and evaluated. By establishing linear correlations between physical and chemical parameters the chemical changes affecting the physical properties could be investigated and tracked. Very good correlations have been found for hardwood samples, whereas for softwoods only poor correlations have been established. Results could contribute to a better understanding of the reactions of thermal modification, and could furthermore provide a basis for wood species dependent technology optimization in the future.
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The high temperature treatment of wood is one of the alternatives to chemical treatment. During this process, the wood is heated to higher temperatures than those of conventional drying. The wood structure changes due to decomposition of hemicelluloses, ramification of lignin, and crystallization of cellulose. The wood becomes less hygroscopic. These changes improve the dimensional stability of wood, increase its resistance to micro-organisms, darken its color, and modify its hardness. However, wood also might loose some of its elasticity. Consequently, the heat treatment conditions have to be optimized. Therefore, it is important to understand the transformation of the chemical structure of wood caused by the treatment. In this study, the modification of the surface composition of the wood was followed with Fourier transform infrared spectroscopy (FTIR) and inverse gas chromatography (IGC) under different experimental conditions. The effect of maximum treatment temperatures on the chemical composition of Canadian birch and aspen as well as the correlations between their chemical transformation and different mechanical properties are presented. FTIR analysis results showed that the heat treatment affected the chemical composition of birch more compared to that of aspen. The results of IGC tests illustrated that the surfaces of the aspen and birch became more basic with heat treatment. The mechanical properties were affected by degradation of hemicellulose, ramification of lignin and cellulose crystallization.
Changes in the chemical structure of thermally treated wood
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Changes in the chemical structure of hornbeam and uludag fir woods during thermal treatment were investigated at three temperatures (170, 190, and 210 oC) and three durations (4, 8, and 12 hours). After thermal treatment, the extents of degradation in the chemical structure of the samples were determined, and the effects on the chemical composition of hornbeam wood and uludag fir wood were investigated. The data obtained were analyzed using variance analysis, and Tukey’s test was used to determine the changes in the chemical structure of uludag fir and hornbeam woods. The results showed that heating wood permanently changes several of its chemical structures and that the changes are mainly caused by thermal degradation of wood polymers. It was found that decreasing of the cellulose and holocelluloses ratio had a favorable effect on the interaction of the wood with moisture. According to the obtained results, hornbeam wood is affected more than uludag fir wood. For each wood, the max...
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Due to environmental concerns the use of wood materials is becoming more extensive and is causing wood supply shortage, therefore the use of Populus genus wood species with a short rotation period is vital. Populus genus species wood has several shortcomings it is not durable, has low density and is hygroscopic. Thermal modification is a technology that can be used to improve the situation. In this study aspen (Populus tremula L.) was thermally treated using the Wood Treatment Technology (WTT) device for 50 min at 160 -160 WTT) and poplar (Populus x canadensis Moench) was vacuum-treated (VT) 120 min at 204 (120-204 VT), 120 min/ 214 -214 VT), 180 min 217 -217 VT) and 30 min 218 (30-218 VT). Mass loss (ML), colour change, density, tensile strength along the fibres, moisture exclusion efficiency and weight loss (WL) after brown rot fungus Coniophora puteana were determined and also light microscopy images were taken. Aspen veneers showed a ML of 5.3% between 120-214 VT (6.2%) and 30-2...
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Changes in chemical constituents and some physical properties such as swelling and water absorption of hornbeam (Carpinus betulus L) and uludag fir (Abies bornmulleriana Mattf.) wood were investigated after heat treatment at three different temperatures (170 oC, 190 oC, and 210 oC) for three different durations (4, 8, and 12 hours) by using thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectrometry. The results of TGA show that there was less weight loss in the main degradation region (300-500 oC) for the heat-treated samples as compared to untreated (control) samples. In addition, there was greater weight loss of hornbeam wood than of uludag fir wood in a similar degradation region. This difference could be due to the chemical constituents of softwoods and hardwoods. The results of FTIR spectrometry show that the chemical constituents of the hornbeam wood samples were more affected by heat treatment. All heat-treated samples exhibited lower water absorpti...
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In this study European ash wood (Fraxinus excelsior L.) was modified at 192oC and 202oC in Thermo-Drewno®, Poland; and at 212oC in Termogenik®, Spain. After modification, samples were characterized by wet chemistry according to standard methods (TAPPI) and by instrumental methods (FT-IR); in addition, surface and physical properties were measured (density, acidity, moisture, water uptake, contact angle, colour) in order to quantify changes due to treatment and temperature. The results showed that chemical composition of modified wood presents a gradual variation according to the heating regime, regardless of the industrial process applied; the greatest differences were obtained in treatment at 212°C compared to untreated wood. Furthermore, the density (< 0.68 g·cm) of modified wood decreased proportionally to treatment temperature. Colour measurements showed proportional changes to darker colours depending on the treatment temperature. On the other hand, some physical properties ...