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1.
Changes of crystallinity in wood cellulose by heat treatment under dried and moist conditions 总被引:8,自引:0,他引:8
The different effects of heat treatment on wood, especially on the cellulose crystallites of wood under ovendried and highly moist conditions, were investigated by X-ray diffractometer. Heat was found to increase significantly the crystallinity of wood cellulose; moreover, almost twice as much crystallization was observed after heat treatment of spruce and buna under a highly moist condition than under the oven-dried condition. In pure cellulose almost the same crystallization was observed under both the conditions, whereas more crystallization occurred in wood cellulose than in pure cellulose. Absolute crystallization was observed for the wood species and pure cellulose under both conditions, considering the thermal decomposition of the amorphous region in addition to crystallization. Our results suggested that other components accomparying wood cellulose were involved in the increase of crystallinity by heat treatment, and that wood cellulose contained more quasicrystalline regions than pure cellulose. Moreover, calculated apparent activation energies revealed that crystallization and decrystallization in pure and wood cellulose under heat treatment of highly moist condition were some-what easier than those under the oven-dried condition. The behavior of the piezoelectric modulusd
25 almost paralleled that of crystallinity. 相似文献
2.
Study of crystalline behavior of heat-treated wood cellulose during treatments in water 总被引:1,自引:0,他引:1
The crystalline behavior of heat-treated wood cellulose treated at 85% relative humidity (RH), in water, or boiled in water after heat treatment was investigated. The normal increased crystallinity was significantly depressed for samples that were oven-dried and then treated in 85% RH or in water. In the case of boiling-water treatment, a more pronounced increased in crystallinity was initially observed, which then decreased gradually. The crystallinity decreased more than untreated wood for samples that were heat treated for long periods and was slightly higher than the decreased crystallinity from the beginning of the above two treatments. On the other hand, no significant change in crystallinity was observed for samples of increased crystallinity or decreased crystallinity that were treated under high-moisture conditions, for all three treatments. The results show that the crystalline state of wood cellulose heat treated under oven dry or high-moisture conditions behave differently if treated in water after heat treatment. Results suggested that the mechanism of crystallization might be different for samples that are subjected to heat treatment under oven-dry and high-moisture conditions. 相似文献
3.
木材易产生吸湿变形和腐朽等问题,影响其应用效果。热改性处理可有效提升木材的尺寸稳定性和耐久性,并具有无毒、环保的特点,是一种极具潜力的木材改性方法。文中综述了木材组分(纤维素、半纤维素、木质素、抽提物)在热改性过程中发生的化学变化,以及木材树种和部位、处理介质、处理温度和时间对木材热降解的影响。经不同热改性工艺处理后,木材的化学成分变化存在较大差异。探明热改性工艺、热改性材化学成分变化和性能之间的响应机制,将有助于开发或优化热改性技术,从而得到性能优异的热改性材,拓宽其应用领域。 相似文献
4.
Effect of heat treatment intensity on some conferred properties of different European softwood and hardwood species 总被引:1,自引:0,他引:1
Mounir Chaouch Stéphane Dumarçay Anélie Pétrissans Mathieu Pétrissans Philippe Gérardin 《Wood Science and Technology》2013,47(4):663-673
Effect of heat treatment intensity on some conferred properties like elemental composition, durability, anti-swelling efficiency (ASE) and equilibrium moisture content (EMC) of different European softwood and hardwood species subjected to mild pyrolysis at 230 °C under nitrogen for different durations has been investigated. Independently of the wood species studied, elemental composition is strongly correlated with the mass losses due to thermal degradations which are directly connected to treatment intensity (duration). In all cases, an important increase in the carbon content associated with a decrease in the oxygen content was observed. Heat-treated specimens were exposed to several brown rot fungi, and the weight losses due to fungal degradation were determined after 16 weeks, while effect of wood extractives before and after thermal treatment was investigated on mycelium growth. ASE and EMC were also evaluated. Results indicated important correlations between treatment intensity and all of the wood conferred properties like its elemental composition, durability, ASE or EMC. These results clearly indicated that chemical modifications of wood cell wall polymers are directly responsible for wood decay durability improvement, but also for its improved dimensional stability as well as its reduced capability for water adsorption. All these modifications of wood properties appeared simultaneously and progressively with the increase in treatment intensity depending on treatment duration. At the same time, effect of extractives generated during thermal treatment on Poria placenta growth indicated that these latter ones have no beneficial effect on wood durability. 相似文献
5.
Luis García Esteban Paloma de Palacios Francisco García Fernández Juan Antonio Martín Mar Génova Juan Ignacio Fernández-Golfín 《Wood Science and Technology》2009,43(7-8):679-690
The hygroscopicity and thermodynamic properties of buried juvenile Pinus sylvestris L. wood with an age of 1,170 ± 40 BP were compared with the corresponding values of juvenile wood of the same species from recently cut trees. The 35 and 50°C isotherms were plotted following the saturated salts method and subsequently fitted in accordance with the GAB model. The isotherms were then compared by means of the hysteresis coefficients. X-ray diffractograms were used to analyse the crystal structure of the cellulose. The effect of time on the buried wood caused hemicelluloses degradation and a decrease in the crystallinity index and the crystallite length, resulting in an increase in the proportion of amorphous zones. Because of this, the equilibrium moisture contents of the buried wood are higher than of the recent wood, both in adsorption and desorption. In terms of the thermodynamic properties, the heat involved is greater in the buried wood than in the recent wood. 相似文献
6.
高温炭化热处理对杉木XRD特征的影响规律 总被引:2,自引:0,他引:2
采用X射线粉末衍射仪研究高温炭化热处理对杉木XRD特征的影响规律。结果表明:高温炭化热处理对杉木纤维素结晶区002晶面衍射峰位置的影响不显著;不同处理温度水平下处理时间对木材X射线衍射峰强度的影响表现出不同的变化趋势;当处理时间相同、处理温度不同时,随着温度的升高,衍射峰强度呈现出先升高、后降低、再升高的趋势。 相似文献
7.
Tsunehisa Miki Hiroyuki Sugimoto Keisuke Kojiro Yuzo Furuta Kozo Kanayama 《Journal of Wood Science》2012,58(4):300-308
The thermal properties and transitions of solid and ground wood samples conditioned at different humidity conditions were investigated by temperature-modulated differential scanning calorimetry. A time-dependent transition was detected as an endothermic peak in the total and non-reversing heat flows and as a step change in the reversing heat flow during the first heating run of samples with moisture contents above 5?%, but it disappeared in the second heating run. These different thermal behaviors indicate that the effect of heat and moisture on the thermal properties of wood is history dependent. This step change in the reversing heat flow is considered to be a glass transition of moist wood. Other relaxation processes (e.g., enthalpy relaxation) occur simultaneously with this glass transition. The temperature ranges of the transition and the relaxation decreased drastically as the moisture content increased up to 11?%, while they remained almost constant at higher moisture contents. In addition, the transitions of the ground wood occurred at lower temperatures than those of the solid wood at similar moisture contents. Kissinger plots revealed that the apparent activation energy for the glass transition of the solid wood with a moisture content of 11?% was about 600?kJ/mol, whereas that of the ground wood was 220?kJ/mol. 相似文献
8.
The aim of this study was to determine changes in crystallinity and crystalline unit cell type of heat-treated Scots pine
(Pinus sylvestris L.) and Uludağ fir (Abies nordmanniana stev. subsp. bornmuelleriana Mattf.) wood samples by means of FT-IR spectroscopic method. Heat treatment was applied on the test samples in an oven at
three different temperatures (120, 150, and 180°C) and for two different periods of time (6 and 10 h) under atmospheric pressure.
It was designated that crystallinity of both Scots pine and Uludağ fir wood samples increased during heat treatment depending
on the duration. However, monoclinic structure in crystalline unit cells of Scots pine and Uludağ fir wood samples converted
to triclinic structure when heat treated. It was estimated that monoclinic structure was dominant in the crystalline unit
cell. It was established that the crystalline structure of Scots pine wood samples was more affected by heat treatment than
that of Uludağ fir wood samples. 相似文献
9.
Strength properties of thermally modified softwoods and its relation to polymeric structural wood constituents 总被引:3,自引:0,他引:3
Michiel J. Boonstra Joris Van Acker Bôke F. Tjeerdsma Edo V. Kegel 《Annals of Forest Science》2007,64(7):679-690
Thermal modification at relatively high temperatures (ranging from 150 to 260 °C) is an effective method to improve the dimensional stability and resistance against fungal attack. This study was performed to investigate the impact of heat treatment on the mechanical properties of wood. An industrially-used two-stage heat treatment method under relative mild conditions (< 200 °C) was used to treat the boards. Heat treatment revealed a clear effect on the mechanical properties of softwood species. The tensile strength parallel to the grain showed a rather large decrease, whereas the compressive strength parallel to the fibre increased after heat treatment. The bending strength, which is a combination of the tensile stress, compressive stress and shear stress, was lower after heat treatment. This decrease was less than the decrease of only the tensile strength. The impact strength showed a rather large decrease after heat treatment. An increase of the modulus of elasticity during the bending test has been noticed after heat treatment. Changes and/or modifications of the main wood components appear to be involved in the effects of heat treatment on the mechanical properties. The possible effect of degradation and modification of hemicelluloses, degradation and/or crystallization of amorphous cellulose, and polycondensation reactions of lignin on the mechanical properties of heat treated wood have been discussed. The effect of natural defects, such as knots, resin pockets, abnormal slope of grain and reaction wood, on the strength properties of wood appeared to be affected by heat treatment. Nevertheless, heat treated timber shows potential for use in constructions, but it is important to carefully consider the stresses that occur in a construction and some practical consequences when heat treated timber is used. 相似文献
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ABSTRACT This article describes and explains a relatively unknown thermal wood modification process in pressurised unsaturated steam. Compared to other processes for the thermal conversion of wood, this hygrothermolytic (HGT) process has the unique feature of an additional independent and continuous process variable, enabling the full control of the water activity throughout the entire heating cycle. This process covers the technology gap between dry thermal and hydrothermal processes, offering a potential to optimise between the extreme processes, in search for improved material properties and improved process characteristics. The suitability of four different treatment intensity markers (mass loss, equilibrium moisture content, oxygen/carbon (O/C) atomic ratio and electron spin resonance signal) is tested on beech wood over the entire range from low-pressure (dry) to high-pressure (moist and wet) processes. Each marker has its own merits and different sensitivity for the broad palette of changing physicochemical wood properties during heat treatment, but all methods proved to be useful for routine production quality control. The O/C-ratio has the unique advantage that it provides an absolute thermal treatment level rating, neither requiring a control reference nor the knowledge of the wood species and any of the thermal treatment process details. 相似文献
12.
THE EFFECT OF HEAT TREATMENT ON DIFFERENT SPECIES WOOD COLOUR 总被引:2,自引:0,他引:2
Woodisnaturalmaterial,naturegivewoodsurfacecolor,g]oss,grain,qualitysenseetc-,whichconsititutedwoodaesthet-icfeeling.Forthisreson,peoplealwaysusedwide]ywoodtomakefurnitureanddecorating,andstlldiedonthequntitativetestingofwoodsurfacevisualphysicalmagnitude.tl-8jTreeswereprocessedoperationbyaseriesofworkingprocesstoformthewoodsurfacewhichwesawandtouchedonfur-nitureanddecorating.Inthesekindsofworkingprocess,whetherthevisualphysi-calmagnitudeofwoodsurfacehadvaria-tionsorthisvariationschangedwoodna… 相似文献
13.
The authors reviewed the previous research results about the color changes in heat treated wood,and deeply analyzed the effect of heat treatment method and parameters including temperature and time of heat treatment,species and chemical composition on the color changes in heat treated wood.The relationships between color changes and chemical composition,physical and mechanical properties were found.The optical stability of the color of heat treated wood was studied.Some suggestions were proposed for the future research. 相似文献
14.
Effect of high temperature treatment on the mechanical properties of birch (Betula papyrifera) 总被引:1,自引:0,他引:1
Sándor Poncsák Duygu Kocaefe Mohamed Bouazara Andre Pichette 《Wood Science and Technology》2006,40(8):647-663
The thermal treatment of wood is an alternative to the chemical treatment for preservation purposes. The heat treatment process improves wood’s resistance to decay and its dimensional stability. However, mechanical strength decreases as a result of heat treatment. Therefore, the treatment parameters have to be optimized to keep this loss at a minimum while improving other properties. Thermal treatment is new in North America, and its parameters are not yet adjusted for the Canadian species. Carrying out the parameter adjustment in an industrial furnace requires many trials which are costly in terms of material and man-power. A laboratory study was carried out to determine the effect of different parameters of the heat treatment on the mechanical properties of birch in order to optimize this process. A thermogravimetric analyzer was built to carry out the laboratory tests. The impact of the process parameters–such as maximum treatment temperature, holding time at this temperature, heating rate, and gas humidity–on the mechanical properties of birch was investigated. Temperature distributions in wood and in gas as well as the weight loss of wood were measured during the experiments. Afterwards, hardness, modulus of elasticity, modulus of rupture, and resistance to screw withdrawal of the samples were measured. The relation between the process parameters and the resulting mechanical properties was examined. 相似文献
15.
高温热处理对木材颜色变化影响综述 总被引:3,自引:2,他引:1
通过总结热处理对木材颜色变化的研究结果,分析热处理方式、热处理工艺参数包括温度和时间、树种与化学成分对热处理材颜色变化的影响,颜色变化与化学成分以及物理力学性能的相互关系,以及热处理材颜色光稳定性能。对今后研究提出几点建议。 相似文献
16.
Data on thermal-death kinetics of bark beetles are essential to develop phytosanitary heat treatments for pine wood and pine wood packaging materials. Using a heating block system, effects of different heating rates between 44 and 50°C at 2°C intervals on destruction of Dendroctonus armandi adult insect were examined. Heat resistance of the insects was found to increase at low heating rates (0.1 or 0.5°C/min). Therefore, the thermal-death kinetics of the beetles were determined at a high heating rate of 5.0°C/min which simulated the rapid dielectric heating of wood products. Results showed that the thermal death curve of D. armandi followed a zero-order reaction kinetic model, indicating the heat destruction rate of the beetle at different treatment temperatures to be independent of their population size. The required thermal holding times to result in destruction of the entire population were 40, 8, 4, and 2?min at 44°C, 46°C, 48°C, and 50°C, respectively. The evaluated thermal-death kinetic data are useful in developing effective beetle elimination quarantine protocols for the wood. A 50°C ?2?min heat treatment with a heating rate of ~5°C/min can be effectively used for disinfesting bark wood materials. 相似文献
17.
圆盘豆木材力学强度对高温热处理条件变化的响应 总被引:1,自引:0,他引:1
以过热蒸汽为传热介质和保护性气体,在热处理温度为160℃、180℃、200℃、220℃,热处理时间为2h、4h、6h、8h的条件下对圆盘豆木材进行高温热处理,研究圆盘豆木材在不同热处理条件下的力学性能变化规律。结果表明,随着热处理温度升高和热处理时间延长,圆盘豆热处理材抗弯强度降低;弹性模量在160℃时最高,然后降低;硬度的变化趋势不明显。红外光谱分析表明,热处理使木材中的半纤维素、纤维素、木素发生降解反应,导致木材力学强度降低。 相似文献
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