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Holger Militz - One of the best experts on this subject based on the ideXlab platform.
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Wood degradation affected by process conditions during Thermal Modification of European beech in a high-pressure reactor system
European Journal of Wood and Wood Products, 2016Co-Authors: Michael Altgen, Wim Willems, Holger MilitzAbstract:The degradation of beech wood during a Thermal Modification process in a high-pressure reactor system using steam as medium was investigated. The wood was modified at different peak temperatures (150–180 °C), peak durations (1–6 h) and maximum water vapor pressures (0.14–0.79 MPa), while wood mass loss and wood moisture content as well as soluble degradation products were analyzed. Wood degradation was found to be predominantly determined by the maximum pressure, rather than the peak temperature applied. However, accumulation of degradation products, i.e., carbohydrates and furfural, in wood modified at elevated pressure had to be considered when using mass loss as a marker for wood degradation. Mass loss and mass loss rate increased with the maximum pressure until reaching saturation at mass losses above 20 %, due to the limited amount of amorphous carbohydrates within the wood. Several factors have been discussed with regard to their impact on accelerated degradation reactions at elevated water vapor pressure, such as a better heat transfer in a compressed gas atmosphere, reduced evaporative cooling, the accumulation of organic acids as well as the presence of water in the wood during the process. However, none of these individual factors were completely consistent with the observed mass loss progression, which leads to the conclusion that the impact of elevated water vapor pressure, rather, is a combination of several factors that apply simultaneously. The application of elevated pressure might enable an effective process technique to generate sufficient wood degradation to upgrade dimensional stability and biological durability of wood at a low temperature range.
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wood moisture content during the Thermal Modification process affects the improvement in hygroscopicity of scots pine sapwood
Wood Science and Technology, 2016Co-Authors: Michael Altgen, Tamais Hofmann, Holger MilitzAbstract:Elevated wood moisture contents during the Thermal Modification process have been shown to adversely affect the improvement in dimensional stability and hygroscopicity. This study tested the hypothesis that the effect of elevated wood moisture content is based on the impact of water on chemical reactions which determine the cell wall matrix stiffness. Samples of Scots pine sapwood (Pinus sylvestris L.) were Thermally modified in saturated water vapor at different peak temperatures and durations starting either in oven-dry or in water-saturated state. For a given mass loss caused by the Modification process, the improvement in maximum swelling and equilibrium moisture content was stronger for oven-dry samples. After removal of water-soluble degradation products, which caused a cell wall bulking effect, the maximum swelling even increased after Modification in water-saturated state. Based on dynamic vapor sorption measurements, it was evidenced that the Modification in oven-dry state increased the cell wall matrix stiffness which improved dimensional stability and hygroscopicity. Enhanced bond formation in the polymeric network, i.e., via condensation and cross-linking reactions during the treatment of oven-dry wood, is suggested as a cause for this increase in matrix stiffness. In contrast, the Modification in water-saturated state enhanced the flexibility of the cell wall matrix, which increased the cell wall swelling and limited the improvement of hygroscopicity to the reduction in OH groups by removal of hemicelluloses. This enhanced matrix flexibility was potentially caused by predominant hydrolytic cleavage of bonds in case of water-saturated samples, evident from the chemical analysis of soluble degradation products, which increased the free volume between adjacent matrix polymers.
Michael Altgen - One of the best experts on this subject based on the ideXlab platform.
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Determining the degree of heat treatment of wood by light polarization technique
European Journal of Wood and Wood Products, 2018Co-Authors: Hariyadi Soetedjo, Daniel Zakrisson, Ilpo Niskanen, Michael Altgen, Göran Thungström, Eero Hiltunen, Lauri Rautkari, Jukka RatyAbstract:Thermal Modification of wood enables the use of non-durable wood species in exterior applications, but quality control methods are required to monitor the product variability. This study tests the potential of a light polarization technique where visible light (400–500 nm) is directed through a linear polarizer to the surface of Thermally modified wood to measure the reflectance. Besides an effect of the grain direction, the reflectance decreased with increasing temperature during the Thermal Modification process. The technique could be used for quality control, but further studies are required to understand its modes of action.
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Wood degradation affected by process conditions during Thermal Modification of European beech in a high-pressure reactor system
European Journal of Wood and Wood Products, 2016Co-Authors: Michael Altgen, Wim Willems, Holger MilitzAbstract:The degradation of beech wood during a Thermal Modification process in a high-pressure reactor system using steam as medium was investigated. The wood was modified at different peak temperatures (150–180 °C), peak durations (1–6 h) and maximum water vapor pressures (0.14–0.79 MPa), while wood mass loss and wood moisture content as well as soluble degradation products were analyzed. Wood degradation was found to be predominantly determined by the maximum pressure, rather than the peak temperature applied. However, accumulation of degradation products, i.e., carbohydrates and furfural, in wood modified at elevated pressure had to be considered when using mass loss as a marker for wood degradation. Mass loss and mass loss rate increased with the maximum pressure until reaching saturation at mass losses above 20 %, due to the limited amount of amorphous carbohydrates within the wood. Several factors have been discussed with regard to their impact on accelerated degradation reactions at elevated water vapor pressure, such as a better heat transfer in a compressed gas atmosphere, reduced evaporative cooling, the accumulation of organic acids as well as the presence of water in the wood during the process. However, none of these individual factors were completely consistent with the observed mass loss progression, which leads to the conclusion that the impact of elevated water vapor pressure, rather, is a combination of several factors that apply simultaneously. The application of elevated pressure might enable an effective process technique to generate sufficient wood degradation to upgrade dimensional stability and biological durability of wood at a low temperature range.
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wood moisture content during the Thermal Modification process affects the improvement in hygroscopicity of scots pine sapwood
Wood Science and Technology, 2016Co-Authors: Michael Altgen, Tamais Hofmann, Holger MilitzAbstract:Elevated wood moisture contents during the Thermal Modification process have been shown to adversely affect the improvement in dimensional stability and hygroscopicity. This study tested the hypothesis that the effect of elevated wood moisture content is based on the impact of water on chemical reactions which determine the cell wall matrix stiffness. Samples of Scots pine sapwood (Pinus sylvestris L.) were Thermally modified in saturated water vapor at different peak temperatures and durations starting either in oven-dry or in water-saturated state. For a given mass loss caused by the Modification process, the improvement in maximum swelling and equilibrium moisture content was stronger for oven-dry samples. After removal of water-soluble degradation products, which caused a cell wall bulking effect, the maximum swelling even increased after Modification in water-saturated state. Based on dynamic vapor sorption measurements, it was evidenced that the Modification in oven-dry state increased the cell wall matrix stiffness which improved dimensional stability and hygroscopicity. Enhanced bond formation in the polymeric network, i.e., via condensation and cross-linking reactions during the treatment of oven-dry wood, is suggested as a cause for this increase in matrix stiffness. In contrast, the Modification in water-saturated state enhanced the flexibility of the cell wall matrix, which increased the cell wall swelling and limited the improvement of hygroscopicity to the reduction in OH groups by removal of hemicelluloses. This enhanced matrix flexibility was potentially caused by predominant hydrolytic cleavage of bonds in case of water-saturated samples, evident from the chemical analysis of soluble degradation products, which increased the free volume between adjacent matrix polymers.
Lauri Rautkari - One of the best experts on this subject based on the ideXlab platform.
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THE INFLUENCE OF Thermal Modification ON VENEER BOND STRENGTH
2020Co-Authors: Kristiina Lillqvist, Lauri Rautkari, Anti Rohumaa, Susanna Källbom, Magnus WålinderAbstract:The purpose of this study was to investigate the effect of Thermal Modification on birchveneer properties relevant in plywood manufacture. The wood material used in thisstudy was a birch (Betula pe ...
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Determining the degree of heat treatment of wood by light polarization technique
European Journal of Wood and Wood Products, 2018Co-Authors: Hariyadi Soetedjo, Daniel Zakrisson, Ilpo Niskanen, Michael Altgen, Göran Thungström, Eero Hiltunen, Lauri Rautkari, Jukka RatyAbstract:Thermal Modification of wood enables the use of non-durable wood species in exterior applications, but quality control methods are required to monitor the product variability. This study tests the potential of a light polarization technique where visible light (400–500 nm) is directed through a linear polarizer to the surface of Thermally modified wood to measure the reflectance. Besides an effect of the grain direction, the reflectance decreased with increasing temperature during the Thermal Modification process. The technique could be used for quality control, but further studies are required to understand its modes of action.
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Wood densification and Thermal Modification: hardness, set-recovery and micromorphology
Wood Science and Technology, 2016Co-Authors: Kristiina Laine, Magnus Wålinder, Lauri Rautkari, Kristoffer Segerholm, Mark HughesAbstract:The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 % of the deformation in water-soaking. This phenomenon, termed set-recovery, was reduced by Thermally modifying the wood after densification. This study presents the influence of compression ratio (CR = 40, 50, 60 %) and Thermal Modification time (TM = 2, 4, 6 h) on the hardness and set-recovery of densified wood. Previously, set-recovery has mainly been studied separately from other properties of densified wood, while in this work, set-recovery was also studied in relation to hardness. The results show that set-recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 %. Hardness significantly increased due to densification and even doubled compared to non-densified samples with a CR of 50 %. Set-recovery reduced the hardness of densified (non-TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set-recovery. However, some reduction in hardness was recorded even if set-recovery was almost eliminated.
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Reducing the moisture sensitivity of linear friction welded birch (Betula pendula L.) wood through Thermal Modification
Journal of Adhesion Science and Technology, 2015Co-Authors: Jussi Ruponen, Petr Čermák, Martin Rhême, Lauri RautkariAbstract:Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding Thermal Modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, Thermal Modification under superheated steam at atmospheric pressure, internal bond (IB) and tensile-shear strength testing and soaking tests. As supposed, the non-modified reference specimens performed poorly after the seven days soaking test (on average 0.33 MPa IB strength), whereas the Thermally modified specimens yielded almost the same IB stre...
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Effect of extractives and Thermal Modification on antibacterial properties of Scots pine and Norway spruce
International Wood Products Journal, 2013Co-Authors: Tiina Vainio-kaila, Lauri Rautkari, Katrina Nordström, Marko Närhi, Olli Natri, Matti KairiAbstract:The effect of Thermal Modification and extracts of Scots pine sapwood and heartwood, and Norway spruce on the colonisation by the bacterium, Escherichia coli was studied. All wood samples caused more rapid decrease of bacterial numbers compared to glass, which was used as reference material. Pine sapwood caused somewhat faster decrease of bacterial count than the other wood types. On the other hand, both Thermal Modification and extraction increased the bacterial count on all the samples compared to untreated wood samples. Neither the amount of extractives nor the faster drying of the surface, to which the bacterial inoculum was added, could alone explain this result; rather it is likely that this is due to a combination of both factors.
André Wagenführ - One of the best experts on this subject based on the ideXlab platform.
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Thermal Modification of European beech at relatively mild temperatures for the use in electric bass guitars
European Journal of Wood and Wood Products, 2015Co-Authors: Mario Zauer, Anne Kowalewski, Robert Sproßmann, Holger Stonjek, André WagenführAbstract:The possibility of the use of Thermally modified European beech (Fagus sylvatica L.) in necks of electric bass guitars for the substitution of Hard maple (Acer saccharum) has been studied. The heat treatments were performed at relatively mild treatment temperatures of 140 and 160 °C for 12 h. The acoustic properties were determined by means of experimental modal analysis (EMA) and the mechanical properties by means of static and impact bending tests. The results show that both the acoustic and mechanical, static properties of beech improve significantly owing to Thermal Modification, being similar or better compared to Hard maple. The impact bending strengths decrease owing to Thermal Modification. Additional tests on complete necks of electric bass guitars by means of EMA and plucking tests on total instruments show that Thermally treated beech at mild temperatures can substitute Hard maple for the use as neck material in electric bass guitars.
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Effects of Thermal Modification on the Properties of Two Vietnamese Bamboo Species. Part II: Effects on Chemical Composition
Bioresources, 2013Co-Authors: Martina Bremer, André Wagenführ, Steffen Fischer, T. C. Nguyen, L. X. Phuong, Vu Huy DaiAbstract:Bamboo is a very interesting bio resource for building materials because of its combination of strength properties and low density. However, its susceptibility to fungi and insects is problematic. Thermal Modification is used in Vietnam to improve the durability and dimensional stability of bamboo. Changes in the chemical composition during this Modification are the reason for such physical changes as color, equilibrium moisture content, and strength. This paper will describe the changes in the chemical composition depending on the Modification conditions. Furthermore correlations between chemical composition and physical properties, which are presented in Part I, are shown.
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THE EFFECTS OF Thermal Modification ON THE PROPERTIES OF TWO VIETNAMESE BAMBOO SPECIES, PART I: EFFECTS ON PHYSICAL PROPERTIES
Bioresources, 2012Co-Authors: Cong Trung Nguyen, André Wagenführ, Le Xuan Phuong, Vu Huy Dai, Martina Bremer, Steffen FischerAbstract:Bamboo is a very interesting bioresource for use as a building material because of its properties of strength in combination with low density. However, its susceptibility to fungi and insects is problematic for its usage. Thermal Modification is used in Vietnam to improve the durability and dimensional stability of bamboo. The Thermal Modification causes many changes related to the physical properties of bamboo, e.g., mass, color, and equilibrium moisture content (EMC). All these changes are dependent on the Modification conditions (Modification temperature and duration). The mass loss (ML), the color difference (ΔE*ab), and the reduction of EMC (ΔEMC) were due to the Thermal Modification increase with higher temperature and/or longer duration. Therefore the temperature had greater influence than the Modification duration. The changes were slight at 130 °C (ML: 0.3…0.6 %; ΔE*ab: 3…5; ΔEMC: 0.5…0.8 % ), moderate at 180 °C (ML: 1,5…4 %; ΔE*ab: 21…37; ΔEMC: 3.6…4.4 %), but very strong at 220 °C (ML: 14…16 %; ΔE*ab: 46…51; ΔEMC: 5.6…5.7%). There are close correlations between the changes mentioned above.
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Alteration of the unsteady sorption behaviour of maple (Acer pseudoplatanus L.) and spruce (Picea abies (L.) Karst.) due to Thermal Modification.
Holzforschung, 2010Co-Authors: Alexander Pfriem, Mario Zauer, André WagenführAbstract:Abstract The aim of the present investigation was to evaluate the influence of a Thermal Modification on the kinetics of the water vapour sorption of maple (Acer pseudoplatanus L.) and spruce [Picea abies (L.) Karst.] based on the assumption that the Fickian equation can be applied in this regard in the first approximation. The unsteady-state sorption process between two equilibria of humidity was modelled as a diffusion process. The rate of sorption was recorded by the gravimetric method, and then the diffusion coefficient was determined through inverse parameter identification. The Thermal Modification leads to an alteration of the unsteady sorption behaviour of both wood species. Transport of water vapour decreases with increasing degree of Modification. Depending on wood moisture, the trends of diffusion coefficients include all three levels of Modification. Furthermore, the diffusion coefficients decrease when the thickness of specimens decreases. The calculated diffusion coefficients showed a length dependency both for unmodified and Thermally modified spruce and maple. Accordingly, the results clearly show that these woods have a non-Fickian moisture transport behaviour. The results are nevertheless useful for comparative purposes.
Petr Čermák - One of the best experts on this subject based on the ideXlab platform.
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Effect of hemp oil impregnation and Thermal Modification on European beech wood properties
European Journal of Wood and Wood Products, 2020Co-Authors: Jan Baar, Martin Brabec, Richard Slávik, Petr ČermákAbstract:Thermal Modification of wood is an environment-friendly method, which, among others, enhances wood water related properties, whereas the use of hot oil as a heating medium generally leads to better performance. In this study, European beech wood was hemp oil-impregnated, Thermally modified at 200 °C and both ways of treatment were combined. Analysis of the treated wood included the determination of the change in important wood characteristics—colour, hygroscopicity, dimensional stability, bending properties, and decay resistance against white rot. The results indicate that heat treatment combined with oil has influenced the properties of beech wood more than heat treatment itself. In certain cases, the high effectiveness is only relative with regard to mass increase caused by high oil retention.
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Reducing the moisture sensitivity of linear friction welded birch (Betula pendula L.) wood through Thermal Modification
Journal of Adhesion Science and Technology, 2015Co-Authors: Jussi Ruponen, Petr Čermák, Martin Rhême, Lauri RautkariAbstract:Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding Thermal Modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, Thermal Modification under superheated steam at atmospheric pressure, internal bond (IB) and tensile-shear strength testing and soaking tests. As supposed, the non-modified reference specimens performed poorly after the seven days soaking test (on average 0.33 MPa IB strength), whereas the Thermally modified specimens yielded almost the same IB stre...
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Numerical analysis of temperature profiles during Thermal Modification of wood: chemical reactions and experimental verification
Holzforschung, 2015Co-Authors: Miroslav Trcala, Petr ČermákAbstract:Numerical analysis of temperature profiles during Thermal Modification of wood was carried out. The numerical solution – based on finite element analysis, FEA – of the 3D problem of transient nonlinear heat transfer model is presented for wood as a typical anisotropic material. The numerical model was enhanced for describing chemical reactions of cellulose, hemicelluloses and lignin (pyrolysis model), which takes into account the exothermic reactions as an internal source of heat energy. Experimental as well as theoretical process schedules were applied and the influence of sample dimensions (sample geometry) and wood species was studied. The influence of wood species was negligible on heating time to reach the highest temperature, i.e., the temperature differences were about 2°C during the drying phase. A expected, the sample size played an important role in the heating duration and in terms of the exothermic reactions of wood. The experimental and numerical data are generally in good agreement. The numerical error increased in the range of higher temperatures. The results can be improved by consideration of wood species (mass of wood compounds) and boundary conditions in the pyrolysis model, thus, better insight into details of Thermal Modification of wood could be reached.
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Measured temperature and moisture profiles during Thermal Modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) wood
Holzforschung, 2014Co-Authors: Petr Čermák, Petr Horáček, Peter RademacherAbstract:Abstract The temperature and moisture profiles during Thermal Modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) wood have been investigated. Specimens with dimensions of 80×80×200 mm3 were heat treated based on ThermoWood technology. Heat transfer was continuously measured by several thermocouples placed into various positions of the samples. In the course of the treatment, samples were removed from the chamber at different times, and their moisture content (MC) was measured by the so-called slicing technique. The complete data of heat and moisture movement during the heat treatment process are presented. Significant temperature gradients occur in the initial and Modification stages of the process. In the latter, the chamber temperature was 200°C for 3 h, but exothermic reaction increased the sample temperatures to 240°C (beech) and 215°C (spruce). Thermodiffusion (Soret effect) at the beginning of the process was observed. Therefore, the MC under surfaces (in transverse and in longitudinal direction) was increasing ∼0.5%–3% for 5 h. The results provide a better insight into details of Thermal Modification of wood.
