| 1. |
- Antão, Laura H., et al.
(author)
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Climate change reshuffles northern species within their niches
- 2022
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 12:6, s. 587-592
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Journal article (peer-reviewed)abstract
- Climate change is a pervasive threat to biodiversity. While range shifts are a known consequence of climate warming contributing to regional community change, less is known about how species’ positions shift within their climatic niches. Furthermore, whether the relative importance of different climatic variables prompting such shifts varies with changing climate remains unclear. Here we analysed four decades of data for 1,478 species of birds, mammals, butterflies, moths, plants and phytoplankton along a 1,200 km high latitudinal gradient. The relative importance of climatic drivers varied non-uniformly with progressing climate change. While species turnover among decades was limited, the relative position of species within their climatic niche shifted substantially. A greater proportion of species responded to climatic change at higher latitudes, where changes were stronger. These diverging climate imprints restructure a full biome, making it difficult to generalize biodiversity responses and raising concerns about ecosystem integrity in the face of accelerating climate change.
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| 2. |
- Čermák, Petr, et al.
(author)
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The effect of wetting cycles on moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) wood
- 2016
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In: Journal of Materials Science. - : Springer Publishing Company. - 0022-2461 .- 1573-4803. ; 51:3, s. 1504-1511
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Journal article (peer-reviewed)abstract
- The moisture behaviour of thermally modified Scots pine (Pinus sylvestris L.) exposed to cyclic conditions was analysed. Specimens of dimensions 15 × 15 × 5 mm3 were thermally modified at 180 °C (TM1) and 220 °C (TM2) using atmospheric pressure and superheated steam. Radial, tangential, volumetric swelling and anti-swelling efficiency (ASE) were calculated during six consecutive drying–soaking cycles. Afterwards, additional specimens were exposed to ten relative humidity cycles (0 and 95 %) at temperature 25 and 40 °C in order to analyse its influence on sorption behaviour. Application of thermal modification led to significant reduction of swelling from original 18.4–13.3 % for TM1 and to 10.5 % for TM2. However, after exposure to six consecutive soaking–drying cycles, the swelling of control specimens slightly decreased, whereas the swelling of thermally modified specimens increased. Due to the increased swelling after repeated cycles, the original ASE (28.6 and 42.7 %) decreased to 22.5 % for TM1 and to 36.88 % for TM2. The presence of leachable compounds and release of internal stresses are mainly attributed to that phenomenon. The EMC of the reference specimens decreases over the repeated humidity cycles for approximately 1 %–units. Same trend was found for the mild thermal modification TM1, but decreasing only in the range of 0.5 %–units. However, the EMC of the TM2 specimens during humidity cycles behaved differently. The results provide a better insight into details of thermal modification of wood and its behaviour under cyclic conditions.
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| 3. |
- Källbom, Susanna, et al.
(author)
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Surface chemical analysis and water vapour sorpion of thermally modified wood exposed to increased relative humidity
- 2015
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In: The Eighth European Conference on Wood Modification (ECWM8) 2015.
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Conference paper (other academic/artistic)abstract
- The increased interest in environmentally friendly building materials is accompanied with an increased need for research on thermally modified wood. Products made from recycling or reusing of thermally modified residuals will have advantages in terms of environmental aspects. Surface characteristics of thermally modified wood play an important role for the development of applications involving bonding processes, for example when using thermally modified wood residuals in biocomposites. Surface chemistry characteristics are important in developing such materials. A technique used for surface chemical analysis of the outermost surface is X‑ray photoelectron spectroscopy (XPS). Some surface chemical analyses of wood and modified wood can be found in Nzokou and Kamdem (2005), Inari et al. (2006), Bryne et al. (2010), Johansson et al. (2012), Rautkari et al. (2012). Furthermore, the influence of water and moisture has crucial effect on the properties of wood and wood products. Water vapour sorption properties of hygroscopic materials can be studied using a dynamic vapour sorption (DVS) instrument. Previous studies on thermally modified wood exposed to several sorption cycles using DVS have shown an increase in hysteresis during the first cycle, compared with unmodified wood (Hill et al., 2012). However, during the second and the third sorption cycle a reduction in sorption hysteresis was observed. The objective of this work was to study the surface chemical composition and water vapour sorption properties of thermally modified wood. In particular, an effort was made to study any influence on such properties due to a previous exposure to a high relative humidity (RH). Interpretations of the results indicate a decrease of extractable or volatile organic components and a relative increase of non-extractable components, for the high humidity-exposed samples. This could be due to remaining extractives migrating towards or redistribution at the wood surface layer as a result of moisture diffusion. The DVS results show that the thermally modified wood samples that had been exposed to the high relative humidity condition revealed a slight decrease of the hysteresis of the sorption isotherms. The opposite trend was furthermore seen for the unmodified wood.
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| 4. |
- Källbom, Susanna, 1988-, et al.
(author)
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The influence of log soaking temperature and thermal modification on the properties of birch veneers
- 2016
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In: IRG Annual Meeting. - : IRG Documents.
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Conference paper (other academic/artistic)abstract
- In veneer manufacture the logs are routinely soaked in heated water baths in order to soften the wood prior to peeling. The temperature of the water may vary greatly between batches; however, the influence of log soaking temperature on veneer properties has had little research attention. Uncontrolled moisture is known to cause problems in wood-based materials, while thermal modification offers a method to control the interaction between wood and water. Therefore it might be beneficial to utilise thermally modified veneers in plywood manufacture. Yet, thermal modification is expected to also change other wood properties which might influence the possibility to utilise thermally modified veneers for wood-based-panels. The purpose of this study was to investigate the influence of log soaking temperature (70 °C and 20 °C) and thermal modification (8h in steam conditions) on selected properties of birch veneers, which are relevant in plywood manufacture. The surface area and surface free energy was studied with inverse gas chromatography (IGC). The surface free energy was found to be slightly higher for the unmodified veneers, however, no major difference was found in the dispersive part of the surface free energy between the log soaking temperatures or between unmodified or thermally modified veneers. The wetting of the veneers was investigated with the Wilhelmy plate method utilising the multicycling technique. It was found that lower log soaking temperature produced veneers with more hydrophobic nature. Also, thermal modification increased the hydrophobicity of the veneers. The bond strength was measured with an automatic bond evaluation system (ABES) using phenol formaldehyde (PF) resin. In general, the lower log soaking temperature resulted in slightly higher bond strength (however, the result was statistically insignificant), while thermal modification slightly lowered the bond strength. Based on these initial results thermally modifying the veneers prior to plywood manufacture might be useful.In veneer manufacture the logs are routinely soaked in heated water baths in order to soften the wood prior to peeling. The temperature of the water may vary greatly between batches; however, the influence of log soaking temperature on veneer properties has had little research attention. Uncontrolled moisture is known to cause problems in wood-based materials, while thermal modification offers a method to control the interaction between wood and water. Therefore it might be beneficial to utilise thermally modified veneers in plywood manufacture. Yet, thermal modification is expected to also change other wood properties which might influence the possibility to utilise thermally modified veneers for wood-based-panels. The purpose of this study was to investigate the influence of log soaking temperature (70 °C and 20 °C) and thermal modification (8h in steam conditions) on selected properties of birch veneers, which are relevant in plywood manufacture. The surface area and surface free energy was studied with inverse gas chromatography (IGC). The surface free energy was found to be slightly higher for the unmodified veneers, however, no major difference was found in the dispersive part of the surface free energy between the log soaking temperatures or between unmodified or thermally modified veneers. The wetting of the veneers was investigated with the Wilhelmy plate method utilising the multicycling technique. It was found that lower log soaking temperature produced veneers with more hydrophobic nature. Also, thermal modification increased the hydrophobicity of the veneers. The bond strength was measured with an automatic bond evaluation system (ABES) using phenol formaldehyde (PF) resin. In general, the lower log soaking temperature resulted in slightly higher bond strength (however, the result was statistically insignificant), while thermal modification slightly lowered the bond strength. Based on these initial results thermally modifying the veneers prior to plywood manufacture might be useful.
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| 5. |
- Källbom, Susanna, 1988-, et al.
(author)
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Water vapour sorption characteristics and surface chemical composition of thermally modified spruce (Picea abies karst)
- 2016
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In: International Wood Products Journal. - : Taylor & Francis. - 2042-6445 .- 2042-6453. ; 7:3, s. 116-123
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Journal article (peer-reviewed)abstract
- The objective of this work was to study the hygroscopicity and surface chemical composition of thermally modified (TM) spruce. An effort was also made to study if those features were influenced by a previous exposure to a significant increase in relative humidity (RH). TM and unmodified Norway spruce (Picea abies Karst) samples, both in solid and ground form, were prepared. Water vapour sorption characteristics of the ground samples were obtained by measuring sorption isotherms using a dynamic vapour sorption (DVS). The surface chemical composition of the solid samples, both acetone extracted and non-extracted, were analysed using X-ray photoelectron spectroscopy (XPS). The DVS analysis indicated that the TM wood exposed to the 75% RH revealed a decrease in isotherm hysteresis. The XPS analysis indicated a decrease of acetone extractable or volatile organic components and a relative increase of non-extractable components for the samples exposed to the increased RH condition.
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| 6. |
- Laine, Kristiina, et al.
(author)
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Acetylation and densification of wood
- 2015
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Conference paper (other academic/artistic)abstract
- The purpose of this study was to explore the possibility to surface densify acetylated solid wood. The aim of surface densification is to improve mechanical properties, such as hardness, at the very surface of wood where the property improvements are mostly needed (e.g. in flooring and decking). However, when subjected to moisture, surface densified wood may swell back almost to the original dimensions. Therefore, acetylated and non-acetylated wood was surface densified in order to investigate whether the dimensional stability of densified wood may be improved by pre-acetylation. Surface densification was performed by compressing the acetylated radiate pine samples between metal plates with only one side heated (150°C) in order to target the deformation to one surface only. The original thickness of the samples was 20 mm and the target thickness 18 mm which was controlled by metal stops. The recovery of the deformation (set-recovery) was measured by soaking the samples in water and measuring the oven-dry thickness before and after soaking in repeated cycles. It was found that acetylated wood may be surface densified and indeed the set-recovery of the pre-acetylated wood was significantly lower (17.4 %) compared to non-acetylated wood (72.8 %). Further studies in adjusting the process parameters might lead to even higher reduction in set-recovery.
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| 7. |
- Laine, Kristiina, et al.
(author)
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Hardness, set-recovery and micromorphology studies of densified and thermally modified wood
- 2015
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Conference paper (other academic/artistic)abstract
- The purpose of the work reported in this paper was to increase the density of Scots pine wood in order to improve its hardness. Density was increased by compressing the porous structure of wood between heated metal plates in the radial direction by 40, 50 or 60% of the thickness. The compressed state was stabilised by thermally modifying (TM) the samples at 200 °C under steam conditions for 2, 4 or 6h. Set-recovery was almost eliminated (<1%) with TM of 6h for samples compressed 40 and 50%. It was discovered that hardness of densified wood was in some cases even three times higher compared to untreated wood. However, the hardness of the densified, non-TM wood was reduced after soaking and drying back to the original untreated level, while TM of 4 and 6h maintained an increased level of hardness.
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| 8. |
- Laine, Kristiina, et al.
(author)
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Micromorphological studies of surface densified wood
- 2014
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In: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 49:5, s. 2027-2034
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Journal article (peer-reviewed)abstract
- 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 A degrees 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 A degrees C) and short closing time (10 s) resulted in more deformation through the whole thickness, whilst increasing the temperature (150 and 200 A degrees 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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| 9. |
- Laine, Kristiina, et al.
(author)
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Surface densification of acetylated wood
- 2016
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In: European Journal of Wood and Wood Products. - : Springer. - 0018-3768 .- 1436-736X. ; 74:6, s. 829-835
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Journal article (peer-reviewed)abstract
- 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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| 10. |
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