共查询到20条相似文献，搜索用时 46 毫秒
1.
Toni Antikainen Olli Paajanen Lauri Rautkari Andreja Kutnar Frederick A. Kamke Mark Hughes 《Wood Science and Technology》2014,48(2):325-336
In this study, birch (Betula pendula L.) veneers were simultaneously densified and dried using a contact drying method at pressures of 1.5 and 3 MPa at 130 °C and compared with veneer dried in a laboratory-scale convective type dryer. Compression rate, thickness swelling, and the density profiles of the veneers were investigated. Furthermore, the microstructure of densified veneers was studied by scanning electron microscopy (SEM). A maximum veneer compression rate of 9 % was achieved at a pressure of 3 MPa. Under these conditions, the veneers were, on average, densified from 504 to 574 kg m?3 (approximately 14 %). After water soaking, full set-recovery—recovery to the initial thickness—occurred. However, the swelling rate was lower for the densified veneer. Density profiles measurements showed that densification occurs throughout the veneers. The SEM images showed that the surface of the densified veneers were smoother, whilst no cracks were detected due to densification. Densification seemed to occur in vessels. Typically, rays were bent when there was a vessel nearby. 相似文献
2.
Charalampos Lykidis Katerina Kotrotsiou Antonios Tsichlakis 《Wood material science & engineering》2020,15(5):269-277
ABSTRACT Densification of resin impregnated wood under hot-pressing is a method that along with the potential for the reduction of set-recovery could additionally increase the density of wood and further improve other technical properties. In this study, the effect of the methylated melamine-formaldehyde modification on the shape memory effect of densified Populous nigra wood at various compression ratio levels was investigated. Furthermore, the effects on moisture content and compression ratio were also assessed. The most important conclusion drawn was that MF can act as a means for reducing set-recovery of compressed poplar wood since it is obvious that the use of MF significantly improved the stability of densified wood due to the formation of new bonds between cell wall components and MF. In the case of densification under stress of 10?kg/cm2, the stabilization was improved by the use of MF to about 50% compared to water-treated specimens. The effect of MF on the stabilization of densified wood was not very clear for stresses higher than 10?kg/cm2 since due to the outflow of MF solution during the first minutes of compression. 相似文献
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Effects of short-term thermomechanical densification on the structure and properties of wood veneers
Pavlo Bekhta Stanisław Proszyk Tomasz Krystofiak Jan Sedliacik Igor Novak Miroslava Mamonova 《Wood material science & engineering》2017,12(1):40-54
The effects of short-term thermomechanical (STTM) densification temperature and pressure on the changes in surface roughness, wettability, mass loss (ML), thickness and density of alder, beech, birch, and pine wood veneer with low moisture content (~5%) were investigated. The anatomical structure of veneers was also observed. Veneer sheets were densified using pressure levels of 4, 8 and 12 MPa at three temperatures: 100°C, 150°C and 200°C for 4 min. The results were compared with those of the non-densified veneers. The obtained results show that STTM densification of veneers similarly to long-term densification of solid wood causes irreversible changes in their properties. The STTM-densified veneer surfaces became smoother and more hydrophobic, ML increased slightly while roughness and thickness values decreased significantly, the cell lumens collapsed and a certain amount of fractures in cell walls developed with increasing densification temperature and pressure. All of the investigated wood species showed higher density values after densification. It was found that an even STTM densification of veneers provides stable properties under normal atmosphere conditions; in particular, the thickness and contact angle values were stable for 24 hours after densification, which is an important consideration for industrial applications. 相似文献
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L. M. C. C. Gil 《Wood Science and Technology》1996,30(3):217-223
Summary This work is related to a study about the densification of black agglomerate cork boards, through the development of a densification process and changing of different operational parameters. The densification allows a diversification of the fields of application for this material, shown by the densified products characteristics. The densification process is easy to use by the existing industries, and shows up and downstream advantages and a competing utilisation. This process gave rise to a patent application.This work was part of a research project with the financial support from the Commission of the European Communities, Contract No. MA2B-CT90-0006 (SMA) -Forest Programme 相似文献
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Semi-isostatic densification is a useful method to increase the density and to improve the mechanical properties of fast-grown
softwood species like radiata pine. A major disadvantage of this method is the almost complete recovery of the original dimensions
when densified wood is exposed to moisture. Heat treatment improves the dimensional stability of wood and might be a useful
method to prevent this shape-recovery after densification. However, no or only a limited effect on the shape-recovery was
found when densified radiata pine was exposed to moisture. 相似文献
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《Wood material science & engineering》2013,8(3):132-139
Abstract A modified softwood product would enable the utilization of softwood in new areas. Densification is an old modification method to improve wood properties such as hardness and resistance to abrasion. A major problem with densified wood is, however, its ability to retain its original dimensions under the influence of moisture. Therefore, this study investigated the influence of surface to bottom layer thickness ratio on the shape stability of a modified and three-layered cross-laminated engineering wood product (EWP) subjected to moisture variations. The study describes a simple solid wood densification technique based on compressing a clear solid piece of softwood with vertical annual rings in the radial direction by restraining the tangential expansion. Three-layered cross-laminated EWP was manufactured with the densified wood as a surface layer. The recovery of the densified wood in the surface layer was then reduced to movements in the same level as the other two layers of unmodified wood. The EWP was subjected to climatic variations in order to investigate its shape stability. The results disclosed that an appreciable degree of shape stability was obtained by an increase in the surface to bottom layer thickness ratio of the EWP. 相似文献
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Effects of semi-isostatic densification of wood on the variation in strength properties with density
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. 相似文献
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Surface modification of wood using friction 总被引：1，自引：1，他引：0
Lauri Rautkari Milena Properzi Frédéric Pichelin Mark Hughes 《Wood Science and Technology》2009,43(3-4):291-299
The potential of linear vibration friction as an innovative means of producing increases in both surface density and surface hardness was explored. The influence of processing pressure and time on the degree of surface densification, surface hardness and surface elasticity was investigated. It was found that surface hardness (measured as Brinell hardness) was positively correlated with densification ratio. Furthermore, surface elasticity, that is the ability of the surface to recover elastically after indentation during the Brinell hardness test, could be increased by up to 33% depending on the degree of surface densification. The temperature rise due to friction was also studied. During processing, it was found that the temperature rise on both the radial and tangential surfaces was positively correlated with the processing pressure and time. 相似文献
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Effects of densification of poplar wood (Populus nigra) impregnated with nano-aluminum oxide (NA) and pre-treated with water vapor for 4 and 6 h were investigated in the present study. Physical and mechanical properties of treated poplar wood were measured according to the ASTM D-143 standard specifications, and then compared with the untreated specimens. Results showed significant improvement in all properties as a result of densification. A 4-h vapor pre-treatment improved effects on both physical and mechanical properties. When the duration of vapor-treatment increased to 6 h, wood polymers degraded to the extent that the improvements due to the vapor pre-treatment decreased substantially, though the final results were still significant improvements compared with the control specimens. High thermal conductivity coefficient of NA slightly but not significantly improved properties. Due to the high spring-back after 15 days, densified poplar is not recommended for applications in which densified wood will be exposed for long periods to high humidity or to direct water. 相似文献
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Pavlo Bekhta Stanisław Proszyk Tomasz Krystofiak Miroslava Mamonova Grzegorz Pinkowski Barbara Lis 《Wood material science & engineering》2014,9(4):233-245
The effect of short-term thermomechanical densification of veneer on the surface roughness and surface anatomical changes in four wood species – alder (Alnus glutinosa Gaertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) – was studied. Veneer sheets were densified at a temperature of 100, 150, or 200°C and at a pressure of 4, 8, or 12 MPa for 4 minutes. Seven roughness parameters such as Ra, Rz, Rq, Rp, Rv, Rsk, and Rku were determined. Profile surface was recorded using a modified Carl Zeiss ME-10 profile gauging profilometer. Surface anatomical changes of veneer were examined using scanning electron microscopy. The results showed that densification temperature and pressure affect surface roughness of veneer. The surface became smoother, and roughness values decreased significantly (except for Rku which increased slightly) with increasing temperature and pressure of densification. The effect of temperature on surface roughness changes is more pronounced compared with that of densification pressure. The lowest values of surface roughness were recorded for pine veneer samples followed by alder, birch, and beech samples. These results can be used to provide initial data for adhesive application processes in woodworking industry. 相似文献
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Gernot Standfest Andreja Kutnar Bernhard Plank Alexander Petutschnigg Frederick A. Kamke Manfred Dunky 《Wood Science and Technology》2013,47(1):121-139
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. 相似文献
15.
This paper evaluated the density and biological resistance of pinewood samples modified with thermo-mechanical densification and thermal post-treatment. The samples were densified with 20 and 40% compression ratios at either 110 or 150 °C. The thermal post-treatment was then applied to the pine samples at 185 and 212 °C for 2 h. These samples were exposed to white-rot (Trametes versicolor) and brown-rot (Coniophora puteana) fungi for twelve weeks and the resulting mass loss was determined. In the densified samples, the effects of the compression ratio on T. versicolor-initiated mass loss and of the compression temperature on C. puteana-initiated mass loss were found to be significant. The mass loss was less in the samples compressed at 150 °C with the 40% ratio, while the highest mass loss was observed in the undensified samples. In the thermally post-treated samples, the resistance to both decay fungi was significantly increased with the increase of the treatment temperature. The mass loss in the thermally post-treated samples at 212 °C after T. versicolor and C. puteana fungi testing was reduced by 73 and 67%, respectively. However, the effect of the densification processes on decay resistance in the thermally post-treated samples was insignificant. 相似文献
16.
Bruna Ugulino 《Wood material science & engineering》2018,13(2):64-72
Sanding is the most common machining process used to prepare wood surfaces prior to coating. Hence, to improve surface quality and coating performance during this process, an optimal set of machining parameters should be established according to wood species and its final use. The effects of grit size and feed speed on surface properties and coating performance of red oak wood were studied. Surface quality was assessed by surface roughness, scanning electron micrographs, and wetting analyses. Coating performance was evaluated using pull-off adhesion tests on coated surfaces before and after an accelerated weathering. The results showed that smoother surfaces are obtained as the grit size number of the abrasive increased. On the other hand, minor differences were observed on cell damages and surface roughness as feed speed changed. Also, there was little difference among treatments concerning wetting behavior and surface energy. Pull-off strength was more affected by changes in grit size than feed speed. A P100-grit size program with a feed speed of 7 m/min resulted in a suitable roughness which provided good adhesion and high pull-off strength after aging test. 相似文献
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Boštjan Lesar Miha Humar Frederick A. Kamke Andreja Kutnar 《Wood Science and Technology》2013,47(5):977-992
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. 相似文献
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《Wood material science & engineering》2013,8(3-4):98-104
Abstract End-grain surfaces of spruce wood specimens that were planed with a microtome knife were chemically modified by treatment with bleaching reagents, namely sodium hypochlorite and peracetic acid, and the effect of the surface modification on bond strength of end-grain joints was studied. The chemically treated samples were compared with sawn surfaces, microtome-planed specimens that were additionally irradiated by light, and surfaces that were solely planed with a microtome knife. Significantly higher bond strength compared with the microtome-planed specimens was observed for the sawn specimens and for hypochlorite-modified samples. These findings were ascribed on the one hand to an increased surface roughness resulting from the mechanical process of sawing leading to an enlargement of the bonding area. On the other hand, during the etching process with sodium hypochlorite a pulp of cell walls and cell wall fragments was formed, leading to a partially closed surface which prevented overpenetration of adhesive into the opened cells. 相似文献
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The effect of ultraviolet-visible light irradiation on changes in surface chemistry and morphology of moso bamboo (Phyllostachys pubescens Mazel) was investigated. Fourier transform infrared (FT-IR) and FT-Raman spectroscopy were used in combination to study chemical
changes induced by exposure to artificial sunlight (xenon lamp) for up to 160 h, and the resulting physical changes of cell
walls of bamboo surfaces were examined by scanning electron microscopy (SEM). FT-IR results showed that significant changes
occurred in the lignin component as indicated by considerable decreases in the intensities of the characteristic aromatic
lignin peak at 1512 cm−1 and other associated bands. This was accompanied by formation of new carbonyl groups at 1735 cm−1, resulting in photooxidation of bamboo surfaces. The photosensitive nature of bamboo lignin was also demonstrated by FT-Raman
analysis, in which obvious decreases in intensities of Raman bands at 1604 and 1630 cm−1 mainly derived from lignin and free and esterified p-coumaric and ferulic acids were observed. SEM micrographs of the irradiated cross sections of bamboo revealed that significant
damage occurred to the fiber walls, whereas the parenchyma cells exhibited slight distortion and some cracks occurred in the
cell walls. The structures of cell corners and middle lamellae were nearly intact after irradiation. 相似文献