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The wood of poplar (Populous sp.) species seem to be of low quality, mechanical resistance and is susceptible to microorganisms attacks, therefore, the application of thermal treatment is necessary, in order to improve some of its properties and increase its duration. Thermal modification of poplar (Populous sp.) wood was implemented at 180oC and 200oC, for 3, 5 and 7 hours in the presence of air and some of the most crucial mechanical properties were investigated. As the intensity of heat treatment increases, the mass loss of poplar boards is increased, attributed to moisture loss and the degradation and loss of chemical wood components. The bending strength decreased (2.05%-44.65%) compared to control, due to the treatments, while the elasticity decreased in all the treatment categories (5.66%-24.86%). The tangential hardness of poplar modified at 180oC for 3 and 5 hours, decreased by 10.24% and 14.59%, respectively and at 7 hours it grew by 2.35%, while at 200oC a decrease of 17.04-26.05% was recorded. The radial hardness decreased (2.81%-11.06%) at 180oC (3 and 5 hours) and when the duration reached 7h, it increased (9.28%), while at the treatments of 200oC radial hardness decreased (2.68%-18.86%). All the treatments reduced the impact bending strength of poplar specimens (24.27%-62.02%), even though they raised the resistance levels to compressive forces. Only the milder treatment achieved to decrease the roughness of poplar wood surface, while increasing further the treatment intensity, the degree of roughness showed a strong increase. [ABSTRACT FROM AUTHOR]

The effective specific heat of wood briquettes was determined by using a mathematical model developed for bulk pellets/briquettes and by measurements made in parallel and perpendicularly to the briquettes axis in the range of moisture contents below and above equilibrium moisture content. The mathematical model was based on the assumption that bulk pellets/briquettes are a porous system, consisting of solid particles and gas, with effective thermal properties. The model applied to the briquettes with the moisture content above the equilibrium moisture content is different to that applied to the briquettes with the moisture content below equilibrium moisture content, since alongside with wood fiber swelling, the magnitude and the number in the voids between chips increases. That is why, the briquettes density decreased in this moisture content range. New equations are proposed for this moisture content range considering a larger wood cell lumen that includes the chips interspaces. Experiments were performed at the temperature of briquettes ranging from 19 to 24°C and the average moisture content from 0 to 22.7%, dry basis. When increasing the moisture content above equilibrium moisture content, the briquettes expanded due to fiber swelling, but also due to the increase in the magnitude and number of chips interspaces. Both swelling and increase in briquettes voids influenced the effective specific heat. [ABSTRACT FROM AUTHOR]

Thermal modification of wood does not only change the color of the wood, it also changes wood properties that are closely related to its reaction to water (changes in dimensions, weight, density,...). These properties of thermally modified wood play an important role, limiting the use of thermally modified wood itself. These changes may be positive or negative depending on the wood species, thermal modification mode, the temperature used during the modification and other factors. The aim of this article is to broaden and collect knowledge about the effect of different thermal modification temperatures (160°C, 180°C and 210°C) on selected physical characteristics of spruce wood. The results of the study show that thermal modification at a temperature range of 160°C - 210°C has a statistically significant effect on the absorbability of thermally modified wood, as well as on tangential and volumetric swelling. Conversely, the effect of thermal modification on longitudinal swelling and a change in density during absorption was not proven. [ABSTRACT FROM AUTHOR]

The effect of thermo-hydro treatment (THT) on the durability of birch wood veneers and two plywood products - A and B was studied. THT was carried out in a multi-functional pilot scale wood modification device under elevated water vapour pressure at the following temperatures and treatment times (°C/min): 150/10; 150/50; 160/10 and 160/50. After THT, durability was examined according to the standards ENV 12038, EN 84 and EN 73. The durability class (DC) according to the CEN/TS 15083-1 was assigned to each treatment after fungal exposure. Water soluble extractives from THT samples were analysed with a UV-Vis Spectrometer in a range of 200 - 400nm, potentiometric titration and the Malaprade reaction. The best DC (2 - 3) for aged veneers was reached with the THT 160°C against the white rot fungus. The THT of industrial plywood A at 160°C enabled producing a material with improved durability (DC 1 - 3) after ageing. Plywood B with glued THT veneers showed lower decay resistance than plywood A. After ageing, better performance of plywood B was achieved at the THT 160°C assigning to DC 2 - 4. At the THT regimes under study, water soluble products (acids, sugars, aromatic compounds) were formed from both polysaccharides and lignin. [ABSTRACT FROM AUTHOR]

Thermal conductivity values for heat-treated wild cherry (Cerasus avium (L.) Monench) were measured for radial and tangential directions and compared with those for untreated cherry wood. The wild cherry was heat-treated at a temperature of 212°C for two periods of time: 1.5-2.5 hours, respectively. The thermal conductivity test was performed with a quick thermal conductivity meter based on the ASTM C1113-99 (2004) hot-wire method, and measurements were carried out at the room temperature of 20°C. The results show that the heat treatment caused an important decrease on thermal conductivity of wood compared to untreated wood and the thermal conductivity decreased with increasing heat treatment duration. The highest decrease in thermal conductivity was recorded for a treatment duration of 2.5h. Compared with untreated cherry wood, the thermal conductivity on tangential direction, and radial direction of 1.5h and 2.5h heat-treated cherry wood decreased with 22.21%, 19.76% and 29.43%, 29.67% respectively. Radial thermal conductivity was similar to the tangential thermal conductivity. The data are useful when calculating the energy required to kiln-dry lumber and predicting the thermal insulating qualities of log homes made from the species. [ABSTRACT FROM AUTHOR]

In this study the effects of thermal modification of beech wood (Fagus sylvatica) on color changes after heat treatment were determined. The heat treatment of beech wood was conducted in a temperature of 180°C and 200°C for five different durations ranging from 2 to 10h. It was observed a gradual color change of treated samples whereas after 4h treatment no significant changes were recorded, measured with a colorimeter. The greatest reduction of lightness indicator L* was observed between 2 and 4 hours whereas the most intense color differences compare to untreated samples were occurred in 8h and 10h treatments. Comparing the two treatment conditions there is an obvious colour difference. Moreover, at 4h treatments time the differences were approximately 27.92 units more. Finally, radial direction gave higher values regarding lightness and longitudinal the lowest. [ABSTRACT FROM AUTHOR]

Physical, chemical, biological and microscopic properties change in unprotected wooden material that is exposed to weathering conditions and so its structural and some characteristic properties such as colour, gloss and hardness are ruined. The aim of this study is to determine changing of colour, gloss and hardness values of heat treated wood exposed to weathering. For this purpose, Anatolian black pine, calabrian pine, sessile oak and chestnut woods have been used. The experimental samples were subjected to heat under atmospheric pressure at three different temperatures (130, 180 and 230°C) and two different time levels (2 and 8 h). Then, heat treated samples have been exposed to accelerated weathering conditions to two different time levels (120 and 240 h) according to related standards. After the accelerated weathering procedure, changes in the colour, gloss and hardness of the samples have been determined according to related standards. The hardness values of heat-treated wood increased at low heating temperature and time. Aged wood hardness and gloss decreased, compared to the control specimens. Also, results have been compared with values of control samples belonging to each group. [ABSTRACT FROM AUTHOR]

Boards of poplar wood were subjected to thermal treatment at 180°C and 200°C, for durations of 2, 4, 6, 8 and 10 hours, in order to investigate the effect of heat treatment on the hygroscopic properties. Specifically, the change of equilibrium moisture content, density, swelling and absorption of wood were examined, in order to determine the significance of treatment temperature and duration in the enhancement of wood hygroscopicity. Generally, swelling in tangential direction proved to be quite higher than swelling in radial direction, while thermal treatment enhanced in great extent swelling in tangential and radial direction and the absorption of the specimens as well. Swelling in tangential direction decreased within the range of 8.17% and 33.3% for specimens treated at 180°C and the range of 43.85% and 65.09% for specimens treated at 200°C for 2-10 hours, referring to the final measurement after 72 hours of water immersion. In radial direction, the swelling decrease ranged between 2.47% and 28.45% for specimens treated at 180°C and between 19.62% and 60.87% for specimens treated at 200°C for 2-10 hours, respectively, after 72 hours immersion. Most of the heat treatments resulted also in absorption decrease, attesting the improvement of the poplar wood hygroscopic behavior. Finally, as it was proved, the higher the treatment temperature that is applied, the shorter is the duration, needed for the same swelling and absorption decrease level to be achieved. [ABSTRACT FROM AUTHOR]

OSB (oriented strandboards) made from Scots pine (Pinus sylvestris) were thermally post-treated at three different maximum treatment temperatures in the laboratory thermal treatment chamber of the Institute for Wood Technology Dresden (IHD). The OSB were supplied by a European manufacturer of OSB and bonded with methylene diphenyl diisocyanate (MDI). Post-treatment means that rather than thermally treating wood or strands before panel production, cut industry panels, i. e. 650mmx1200mm, were modified in IHD's lab kiln. The main goals of the thermal post-treatment of full-sized OSB were to improve the hygroscopic properties, i. e. to reduce the thickness swell (TS) and the equilibrium moisture content (EMC), as well as to improve the long-term properties creep behaviour and dimensional stability, without significantly reducing further mechanical properties like e. g. internal bond (IB) or bending properties, however. It was observed that the thermal post-treatment of the aforementioned OSB had a very positive effect on the moisture-related properties TS and EMC. The modified OSB showed far better values for said properties than the respective untreated ones. In can be concluded, that the thermal modification of OSB panels is possible and leads to very positive effects regarding their hygroscopic properties. [ABSTRACT FROM AUTHOR]

An overview on the mechanical and physical properties of cross laminated timber (solid wood panels) in the building industry and its use in timber construction is presented. Structure-property relations for solid wood based materials are discussed. Important properties, such as strength, sorption, diffusion, thermal conductivity in relation to the board structure are presented. By varying the structure, the properties can be optimized over a wide range. The focus of this publication lies on experimental works performed by Swiss researchers at the ETH Zürich. [ABSTRACT FROM AUTHOR]

Pannónia Poplar (Populus x euramericana Pannónia) and Robinia (Robinia pseudoacacia L.) were treated at 160°C and 200°C in different vegetable oils, in absence of Oxygen, using laboratory equipment. Three different vegetable oils were used, namely sunflower oil, linseed oil and rapeseed oil. Three different durations were chosen for the thermal treatment: 2h, 4h and 6h. The aim of the research work was to prove, in what extent the treatments influence some important characteristics of the wood. The investigated properties were: MOR, impact bending, compression strength, ASE and colour. Untreated samples from the same wood material served as control. The treatments decreased the impact bending in case of Robinia and poplar as well. Longer duration of the treatment delivered proportionally lower values in impact bending. The same could be observed regarding the MOR values for Robinia, whereas in case of Poplar the more intensive treatments (longer duration and higher temperature) caused a significant increase in MOR. Regarding the compression strength values the treatments resulted in higher strength values by Poplar, whereas in case of Robinia a clear increase could be observed at 160°C, and a significant decrease at 200°C. As a consequence of the treatments the dimension stability could be enhanced for both wood species, so the ASE values increased with increasing duration and temperature. The treatments caused significant darkening for both wood species by all temperatures. The colour coordinates L* and a* (lightness and red hue) shifted to the same direction for both species. The value b* (yellow hue) increased for Poplar, whereas a decreasing was observed for Robinia. Comparing the oils used for this research work, no significant differences in effectiveness could be proved for the investigated properties. An important observation for the practical use was done, as in Robinia wood numerous cracks could be observed in case of wet samples, while practically no damages (cracks, collapses) were observed in Poplar wood using wet samples. The treatments on laboratory scale enhanced the dimensional stability by acceptable decrease in mechanical stability for Robinia and in an increase for Poplar. The results encourage the authors to perform further investigations towards development of technologies for industrial application. [ABSTRACT FROM AUTHOR]