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Frederick A Kamke - One of the best experts on this subject based on the ideXlab platform.
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Influence of temperature of thermal treatment on surface densification of spruce
European Journal of Wood and Wood Products, 2017Co-Authors: Mirko Kariz, Frederick A Kamke, Lauri Rautkari, Mark Hughes, Manja Kitek Kuzman, Milan Sernek, Andreja KutnarAbstract:Spruce ( Picea abies L. Karst) Wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface Densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface Densified Wood. The highest immediate springback occurred in Wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated Wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface Densified Wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface Densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature.
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Influence of the thermo-hydro-mechanical treatments of Wood on the performance against Wood-degrading fungi
Wood Science and Technology, 2013Co-Authors: Boštjan Lesar, Frederick A Kamke, Miha Humar, Andreja KutnarAbstract:Hybrid poplar ( Populus deltoides × Populus trichocarpa ) and Douglas-fir ( Pseudotsuga menziesii ) Wood specimens were Densified with three variations of thermo-hydro-mechanical (THM) treatment. The THM treatments differed in the steam environment, including transient steam (TS), saturated steam (SS), and saturated steam with 1-min post–heat treatment at 200 °C (SS+PHT). The bending properties, FTIR spectra, and colour of the THM Wood specimens were studied before and after exposure to two different Wood decay fungi, brown rot Gloeophyllum trabeum, and white rot Trametes versicolor . The results showed that the performance of Densified hybrid poplar Wood was considerably poorer than the performance of Douglas-fir heartWood. The FTIR spectra measurements did not show changes in the Densified hybrid poplar Wood, while some changes were evident in Densified Douglas-fir specimens. After fungal degradation, the most prominent changes were observed on the SS+PHT specimens. Colour is one of the most important parameter predominantly influenced by the Wood species and the intensity of the densification process for both Wood species, while after fungal exposure, the colour of all Densified Douglas-fir specimens obtained more or less the same appearance, and Densified hybrid poplar specimens resulted in lighter colour tones, indicating that the pattern of degradation of the Densified and non-Densified specimens are similar. The 3-point bending test results determined that the THM treatment significantly increased the modulus of rupture (MOR) and modulus of elasticity (MOE) of the Densified Wood specimens, while fungal exposure decreased the MOE and MOR in hybrid poplar and Douglas-fir specimens.
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Microstructure of viscoelastic thermal compressed (VTC) Wood using computed microtomography
Wood Science and Technology, 2013Co-Authors: Gernot Standfest, Frederick A Kamke, Andreja Kutnar, Bernhard Plank, Alexander Petutschnigg, Manfred DunkyAbstract:The paper describes for the first time the analysis of the structure of compressed Wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlyWood, while the compression of hybrid poplar mainly occurred in the vessels. In both Wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlyWood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, lateWood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir lateWood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC Densified Wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.
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Compression of Wood under saturated steam, superheated steam, and transient conditions at 150°C, 160°C, and 170°C
Wood Science and Technology, 2012Co-Authors: Andreja Kutnar, Frederick A KamkeAbstract:In this paper, the compressive deformation of hybrid poplar Wood ( Populus deltoides × Populus trichocarpa ) at high temperature (150, 160, and 170°C) and under various conditions of steam pressure was studied. Temperature and conditions of steam environment affected the relative density change and creep deformation during compression, as well as properties of the resulting Densified material. While the temperature significantly affected the compression deformation of specimens compressed under transient and superheated steam conditions, temperature within the range studied had little effect on the compressive deformation in saturated steam. In all tested conditions, compression deformation was achieved without cell wall fractures. Higher temperature of compression, regardless of steam condition, resulted in lower equilibrium moisture content. In specimens compressed under saturated steam, the modulus of rupture (MOR) and modulus of elasticity (MOE) were increased proportionally to the increase in density, while the compression under superheated steam produced lower increase in the MOE and MOR than expected based on the increase in density. Compression in transient steam conditions at 170°C produced Densified Wood with higher MOE and MOR than expected based on the increase in density.
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Phenol–formaldehyde impregnation of Densified Wood for improved dimensional stability
Wood Science and Technology, 2010Co-Authors: Chris P. Gabrielli, Frederick A KamkeAbstract:To produce a highly stable Wood-based product with increased mechanical properties, phenol formaldehyde (PF) resin impregnation was combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending stiffness were evaluated. Two PF resins with weight average molecular weights of 172 and 780 were studied at three different concentrations, 5, 10 and 20%. After 24-h room temperature water soak and 2-h boil, both PF treatments at all concentration levels showed high levels of dimensional stability compared to non-impregnated VTC processed controls. The higher molecular weight PF provided greater stability with an average thickness swell value of 12% compared to 20 and 37% for the lower molecular weight PF resin treatment and control, respectively. High anti-swelling efficiency values were recorded for both low and high molecular weight resins, implying these modifications were effective at reducing the volumetric swelling which occurred in the unmodified control. PF treatments were also extremely effective at reducing irreversible swelling. The low and high molecular weight resin treatments had 1/5th and 1/7th the irreversible swelling than the unmodified VTC processed controls, respectively. All dimensional stability values improved as resin concentrations increased. Both resin types at all concentration levels reduced Young’s modulus.
Mark Hughes - One of the best experts on this subject based on the ideXlab platform.
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Influence of temperature of thermal treatment on surface densification of spruce
European Journal of Wood and Wood Products, 2017Co-Authors: Mirko Kariz, Frederick A Kamke, Lauri Rautkari, Mark Hughes, Manja Kitek Kuzman, Milan Sernek, Andreja KutnarAbstract:Spruce ( Picea abies L. Karst) Wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface Densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface Densified Wood. The highest immediate springback occurred in Wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated Wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface Densified Wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface Densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature.
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Surface densification of acetylated Wood
European Journal of Wood and Wood Products, 2016Co-Authors: Kristiina Laine, Kristoffer Segerholm, Magnus Wålinder, Lauri Rautkari, Mark Hughes, Chiel LankveldAbstract:The mechanical properties of Wood can be improved by compressing its porous structure between heated metal plates. By adjusting the process parameters it is possible to target the densification only in the surface region of Wood where the property improvements are mostly needed in applications, such as flooring. The compressed form is, however, sensitive to moisture and will recover to some extent in high humidity. In this study, therefore, acetylated radiata pine was utilised in the surface densification process in order to both reduce the set-recovery of Densified Wood and to improve the hardness of the acetylated Wood. Pre-acetylation was found to significantly reduce the set-recovery of surface Densified Wood. However, after the second cycle the increase in set-recovery of acetylated Wood was relatively higher than the un-acetylated Wood. The acetylated samples were compressed by only 1 mm (instead of the target 2 mm), yet, the hardness and hardness recovery of the acetylated samples significantly increased as a result of densification. It was also discovered that rough (un-planed) surfaces may be surface Densified, however, even if the surface became smooth to the touch, the appearance remained uneven.
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Wood densification and thermal modification: hardness, set-recovery and micromorphology
Wood Science and Technology, 2016Co-Authors: Kristiina Laine, Kristoffer Segerholm, Magnus Wålinder, Lauri Rautkari, 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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Micromorphological studies of surface Densified Wood
Journal of Materials Science, 2014Co-Authors: Kristiina Laine, Kristoffer Segerholm, Magnus Wålinder, Lauri Rautkari, Graham Ormondroyd, Mark Hughes, Dennis JonesAbstract:Scots pine ( Pinus sylvestris L.) Wood was surface Densified in its radial direction in an open press with one heated plate to obtain a higher density on the Wood surface whilst retaining the overall thickness of the sample. This study investigated the effect of temperature (100, 150 and 200 °C) and press closing speed (5, 10 and 30 mm/min, giving closing times of 60, 30 and 10 s, respectively) on the micromorphology of the cell-wall, as well as changes occurring during set-recovery of the Densified Wood. The micromorphology was analysed using scanning electron microscopy (SEM) combined with a sample preparation technique based on ultraviolet-excimer laser ablation. Furthermore, the density profiles of the samples were measured. Low press temperature (100 °C) and short closing time (10 s) resulted in more deformation through the whole thickness, whilst increasing the temperature (150 and 200 °C) and prolonging the closing time (30 and 60 s) enabled more targeted deformation closer to the heated plate. The deformation occurred in the earlyWood regions as curling and twisting of the radial cell-walls, however, no apparent cell-wall disruption or internal fracture was observed, even at low temperatures and fast press closing speed, nor after soaking and drying of the samples. In the SEM-analysis after soaking and drying, it was noticed that the cells did not completely recover their original form. Thus, part of the deformation was considered permanent perhaps due to viscoelastic flow and plastic deformation of the cell-wall components.
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Water vapour sorption behaviour of thermally modified Wood
International Wood Products Journal, 2013Co-Authors: Callum A S Hill, Kristiina Laine, Lauri Rautkari, James Ramsay, Mark HughesAbstract:The work presented in this paper reports on the water sorption properties of thermally modified Wood, Densified Wood and Wood modified using a combination of the two methods. The paper presents new findings concerning the sorption isotherms and sorption kinetics behaviour. The sorption kinetics is analysed in terms of the parallel exponential kinetics (PEK) model which has recently been introduced to the Wood science community as a better alternative to the often used Fickian models, at least where cell wall sorption behaviour is considered. The PEK model comprises two exponential sorption kinetic terms which are termed fast and slow sorption processes. The PEK model is then interpreted by using a relaxation-limited kinetics model consisting of two series-coupled Kelvin–Voigt elements.
Jonas Blomberg - One of the best experts on this subject based on the ideXlab platform.
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Swelling pressure of semi-isostatically Densified Wood under different mechanical restraints
Wood Science and Technology, 2006Co-Authors: Jonas Blomberg, Bengt PerssonAbstract:Semi-isostatically Densified and native Wood samples of Scots pine and European birch were soaked in water. The swelling coefficients as well as the swelling pressure, that arose when the specimens were restrained in some way prior to the swelling, were measured using a universal testing machine equipped with a high resolution load-cell and an external extensometer. As Densified Wood swells, the native structure is almost restored and the swelling pressure became twice as high as for native Wood in the most compressed directions (radial for pine and birch). That cell-shape recovery increases the swelling pressure can explain the problems with imbalance in laminated constructions where Densified Wood is used. The possibility to predict the swelling pressure from basic material properties was evaluated. The correlations between swelling pressure and material properties were strong enough to yield good predictive models.
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Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking
Holzforschung, 2006Co-Authors: Jonas Blomberg, Bengt Persson, Ulf BexellAbstract:Images obtained by scanning electron microscopy (SEM) helped to clarify the question as to how anatomy influences the deformation on compression and the spring-back of Densified Wood on water soaki ...
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mechanical and physical properties of semi isostatically Densified Wood
2006Co-Authors: Jonas BlombergAbstract:When Wood is Densified through semi-isostatical compression in a Quintus- press at pressures up to 140 MPa, the material properties change. The cells are flattened, size is decreased and shape is c ...
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Effects of semi-isostatic densification of Wood on the variation in strength properties with density
Wood Science and Technology, 2005Co-Authors: Jonas Blomberg, Bengt Persson, Anna BlombergAbstract:The variation in strength properties with density was compared between semi-isostatically Densified and non-Densified Wood. Strength properties were compared with published data from earlier studies using other methods for densification. Small clear specimens of eight species were analysed for compression strength in axial, radial and tangential direction, three-point bending and Brinell hardness. After densification, all tested strength properties increased with density, but especially strength perpendicular to grain became lower than expected from the density of non-Densified Wood. Strength of Densified Wood relative to what could be expected for non-Densified Wood of similar density was denoted as ‘strength potential index’. For axial compression strength and bending strength, strength potential index of individual Wood species varied between 0.7 and 1.0, i.e. Densified Wood is slightly weaker than what could be expected from its density. Strength potential index was lower for properties much determined by strength perpendicular to grain. In radial direction, Densified Wood was rubbery with low modulus of elasticity and nearly no proportional limit or modulus of rupture. Generally, Wood was apparently weakened in proportion to the degree of compression in respective direction. Strength potential index also increased with increasing original density of the species.
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compression mechanisms and strenght properties of semi isostatically Densified Wood
2004Co-Authors: Jonas BlombergAbstract:Since most strength properties increase with increased Wood density, densifying Wood through compression will increase strength and wear resistance. After densification, Wood with originally low de ...
Lauri Rautkari - One of the best experts on this subject based on the ideXlab platform.
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Influence of temperature of thermal treatment on surface densification of spruce
European Journal of Wood and Wood Products, 2017Co-Authors: Mirko Kariz, Frederick A Kamke, Lauri Rautkari, Mark Hughes, Manja Kitek Kuzman, Milan Sernek, Andreja KutnarAbstract:Spruce ( Picea abies L. Karst) Wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface Densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface Densified Wood. The highest immediate springback occurred in Wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated Wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface Densified Wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface Densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature.
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Surface densification of acetylated Wood
European Journal of Wood and Wood Products, 2016Co-Authors: Kristiina Laine, Kristoffer Segerholm, Magnus Wålinder, Lauri Rautkari, Mark Hughes, Chiel LankveldAbstract:The mechanical properties of Wood can be improved by compressing its porous structure between heated metal plates. By adjusting the process parameters it is possible to target the densification only in the surface region of Wood where the property improvements are mostly needed in applications, such as flooring. The compressed form is, however, sensitive to moisture and will recover to some extent in high humidity. In this study, therefore, acetylated radiata pine was utilised in the surface densification process in order to both reduce the set-recovery of Densified Wood and to improve the hardness of the acetylated Wood. Pre-acetylation was found to significantly reduce the set-recovery of surface Densified Wood. However, after the second cycle the increase in set-recovery of acetylated Wood was relatively higher than the un-acetylated Wood. The acetylated samples were compressed by only 1 mm (instead of the target 2 mm), yet, the hardness and hardness recovery of the acetylated samples significantly increased as a result of densification. It was also discovered that rough (un-planed) surfaces may be surface Densified, however, even if the surface became smooth to the touch, the appearance remained uneven.
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Wood densification and thermal modification: hardness, set-recovery and micromorphology
Wood Science and Technology, 2016Co-Authors: Kristiina Laine, Kristoffer Segerholm, Magnus Wålinder, Lauri Rautkari, 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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Micromorphological studies of surface Densified Wood
Journal of Materials Science, 2014Co-Authors: Kristiina Laine, Kristoffer Segerholm, Magnus Wålinder, Lauri Rautkari, Graham Ormondroyd, Mark Hughes, Dennis JonesAbstract:Scots pine ( Pinus sylvestris L.) Wood was surface Densified in its radial direction in an open press with one heated plate to obtain a higher density on the Wood surface whilst retaining the overall thickness of the sample. This study investigated the effect of temperature (100, 150 and 200 °C) and press closing speed (5, 10 and 30 mm/min, giving closing times of 60, 30 and 10 s, respectively) on the micromorphology of the cell-wall, as well as changes occurring during set-recovery of the Densified Wood. The micromorphology was analysed using scanning electron microscopy (SEM) combined with a sample preparation technique based on ultraviolet-excimer laser ablation. Furthermore, the density profiles of the samples were measured. Low press temperature (100 °C) and short closing time (10 s) resulted in more deformation through the whole thickness, whilst increasing the temperature (150 and 200 °C) and prolonging the closing time (30 and 60 s) enabled more targeted deformation closer to the heated plate. The deformation occurred in the earlyWood regions as curling and twisting of the radial cell-walls, however, no apparent cell-wall disruption or internal fracture was observed, even at low temperatures and fast press closing speed, nor after soaking and drying of the samples. In the SEM-analysis after soaking and drying, it was noticed that the cells did not completely recover their original form. Thus, part of the deformation was considered permanent perhaps due to viscoelastic flow and plastic deformation of the cell-wall components.
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Water vapour sorption behaviour of thermally modified Wood
International Wood Products Journal, 2013Co-Authors: Callum A S Hill, Kristiina Laine, Lauri Rautkari, James Ramsay, Mark HughesAbstract:The work presented in this paper reports on the water sorption properties of thermally modified Wood, Densified Wood and Wood modified using a combination of the two methods. The paper presents new findings concerning the sorption isotherms and sorption kinetics behaviour. The sorption kinetics is analysed in terms of the parallel exponential kinetics (PEK) model which has recently been introduced to the Wood science community as a better alternative to the often used Fickian models, at least where cell wall sorption behaviour is considered. The PEK model comprises two exponential sorption kinetic terms which are termed fast and slow sorption processes. The PEK model is then interpreted by using a relaxation-limited kinetics model consisting of two series-coupled Kelvin–Voigt elements.
Andreja Kutnar - One of the best experts on this subject based on the ideXlab platform.
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Densification of Wood
2020Co-Authors: Andreja Kutnar, Milan SernekAbstract:The paper treats the processes involved in Wood densification and provides a summary of the state-of-the-art, as presented in the literature, with regard to densification as achieved by compression, accompanied by some form of hydrothermal treatment. The viscoelastic nature of Wood is discussed, togetherwith its thermal softening and typical stress-strain relationships. The properties of Densified Wood products depend, apart from processing parameters, on various anatomical features such as density, the percentage of late Wood material, ray volume and the loading direction. The problems associated with Wood stabilization after densification are also treated. Relevant examples of Wood densification from fundamental research, and the results of applied studies significant for everyday practice, are presented. Aspecial focus is given on the process of viscoelastic thermal compression (VTC) of Wood.
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Influence of temperature of thermal treatment on surface densification of spruce
European Journal of Wood and Wood Products, 2017Co-Authors: Mirko Kariz, Frederick A Kamke, Lauri Rautkari, Mark Hughes, Manja Kitek Kuzman, Milan Sernek, Andreja KutnarAbstract:Spruce ( Picea abies L. Karst) Wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface Densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface Densified Wood. The highest immediate springback occurred in Wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated Wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface Densified Wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface Densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature.
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Influence of the thermo-hydro-mechanical treatments of Wood on the performance against Wood-degrading fungi
Wood Science and Technology, 2013Co-Authors: Boštjan Lesar, Frederick A Kamke, Miha Humar, Andreja KutnarAbstract:Hybrid poplar ( Populus deltoides × Populus trichocarpa ) and Douglas-fir ( Pseudotsuga menziesii ) Wood specimens were Densified with three variations of thermo-hydro-mechanical (THM) treatment. The THM treatments differed in the steam environment, including transient steam (TS), saturated steam (SS), and saturated steam with 1-min post–heat treatment at 200 °C (SS+PHT). The bending properties, FTIR spectra, and colour of the THM Wood specimens were studied before and after exposure to two different Wood decay fungi, brown rot Gloeophyllum trabeum, and white rot Trametes versicolor . The results showed that the performance of Densified hybrid poplar Wood was considerably poorer than the performance of Douglas-fir heartWood. The FTIR spectra measurements did not show changes in the Densified hybrid poplar Wood, while some changes were evident in Densified Douglas-fir specimens. After fungal degradation, the most prominent changes were observed on the SS+PHT specimens. Colour is one of the most important parameter predominantly influenced by the Wood species and the intensity of the densification process for both Wood species, while after fungal exposure, the colour of all Densified Douglas-fir specimens obtained more or less the same appearance, and Densified hybrid poplar specimens resulted in lighter colour tones, indicating that the pattern of degradation of the Densified and non-Densified specimens are similar. The 3-point bending test results determined that the THM treatment significantly increased the modulus of rupture (MOR) and modulus of elasticity (MOE) of the Densified Wood specimens, while fungal exposure decreased the MOE and MOR in hybrid poplar and Douglas-fir specimens.
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hardness and density profile of surface Densified and thermally modified scots pine in relation to degree of densification
Journal of Materials Science, 2013Co-Authors: Kristiina Laine, Lauri Rautkari, Andreja Kutnar, Sergej Medved, Mark HughesAbstract:Solid Scots pine (Pinus sylvestris L.) Wood was surface Densified to three different degrees of compression and hydrothermal post-treatment after surface densification process was performed. The study determined the significance of degree of compression and hydrothermal post-treatment on the density profile generated and the resulting improved Brinell hardness. It was found that different degree of compression resulted in only slightly different density profiles, when compared on the absolute thickness scale. Although the hydrothermal post-treatment lead to an average mass loss of 3.8 % in surface Densified specimens regardless of the degree of compression, density profile of surface Densified specimens was not significantly affected by hydrothermal post-treatment. Furthermore, the surface densification increased the Brinell hardness more than 90 %. Degree of compression had limited effect, which means that it did not matter if the specimens were compressed from 22 to 15 mm or 18 to 15 mm, the Brinell hardness was approximately the same. The hydrothermal post-treatment did not reduce the Brinell hardness of control and surface Densified specimens. Furthermore, the surface densification significantly increased the elastic recovery of surface Densified Wood, which was measured during hardness measurements and was affected by degree of compression. Additionally, the hydrothermal post-treatment reduced the elastic recovery, in control specimens and surface Densified specimens.
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Microstructure of viscoelastic thermal compressed (VTC) Wood using computed microtomography
Wood Science and Technology, 2013Co-Authors: Gernot Standfest, Frederick A Kamke, Andreja Kutnar, Bernhard Plank, Alexander Petutschnigg, Manfred DunkyAbstract:The paper describes for the first time the analysis of the structure of compressed Wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlyWood, while the compression of hybrid poplar mainly occurred in the vessels. In both Wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlyWood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, lateWood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir lateWood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC Densified Wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.