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1.
Mattos Bruno D. de Cademartori Pedro H. G. Missio André L. Gatto Darci A. Magalhães Washington L. E. 《Wood Science and Technology》2015,49(6):1281-1294
Wood Science and Technology - The aim of this study was to evaluate treatability, morphology and mechanical resistance of composites prepared by in situ polymerization of methyl methacrylate on... 相似文献
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Coloring characteristics of in situ lignin during heat treatment 总被引:1,自引:0,他引:1
To investigate the effects of lignin on the discoloration of Black locust (Robinia pseudoacacia) wood during heat treatment, chromatic indexes of the extractive-free wood samples are examined at different moisture contents (MC) under oxygen and nitrogen environment, respectively. The organic acids are produced during heat treatment, resulting in pH decrease in the samples. Components absorbing visible light are formed during heat treatment, and oxygen and moisture contents have obvious effects on the decrease in L*, increase in a* value, yellowness (b*) and total color difference (ΔE) of the samples. It is found that the β-5, C α C β unsaturated bond, the conjugated carbonyl group, quinones structures, α, β-unsaturated ketone and α-C?=?O in lignin increased after heat treatment. The formation of condensation products, the low-molecular-weight phenolic substances and the oxidation products in lignin result in the increment of the light absorption within the entire visible region. 相似文献
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This paper deals with the kinetics of the color changes of cellulose during heat treatment. The color of cellulose heated
at 90–180°C was measured by a spectrophotometer and expressed by CIELAB color parameters. The values of L* decreased and those of a*, b* and Δ
E*
ab
increased at all the treatment temperatures. Several kinetic models, namely, the zero-order, first-order, second-order and
autocatalytic model, were applied to the changes in the color values. Furthermore, the results of kinetic analysis using the
best-fit model were compared to the results obtained from conventional kinetic models. It was suggested that the kinetic analysis
using the best-fit model was the better way to accurately predict color changes during heat treatment. The values of apparent
activation energy calculated from the changes of L*, a*, b* and Δ
E*
ab
were 125, 124, 118 and 120 kJ/mol, respectively. These values were similar to the reported values calculated from other chemical
or mechanical properties. 相似文献
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Duygu Kocaefe Ramdane Younsi Bushra Chaudry Yaşar Kocaefe 《Wood Science and Technology》2006,40(5):371-391
A three-dimensional and unsteady-state mathematical model, which accounts for simultaneous heat and mass transfer taking place during the high temperature treatment of wood, has been developed. It was validated by comparing the predictions with the experimental data. In the model, the coupled heat and mass transfer equations proposed by Luikov are solved, and the temperature and moisture content profiles within wood are predicted as a function of time for different heating rates. For the model validation, an experimental study was carried out with aspen under different operating conditions. The samples were heated to high temperatures using a thermogravimetric system. The weight loss and the temperature distribution within the sample were monitored and registered during the experiment. The model can use constant or variable thermo-physical properties. The temperature and moisture content of the wood predicted by the model using variable properties were compared with those predicted by the same model using constant properties as well as with the experimental data. The experimental and model results are in good agreement, and it was shown that the accuracy of the model depends on the accuracy of the properties. After the model validation was completed, a parametric study was carried out. 相似文献
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INTRODUCTIONTheconventionaltwingmethodisgener-all3usedduringwoocldryinginChinaandothercountriesatpresent.Fluidvelocity,tem-peratUreandrelativehumidityofdryingmediaarecontrolledmainlybymoisbecontentofwood'dunngwtingprocess.Soitisveryim-portanttounderstandthephenomenonofheatandmasstransferinwoodduringdIyingproc-essformakingreasonablythewtingtechnoI-ogy-controlwtingprocess,heightenwtingquality'.decreasewtingenergyconsumptionanddiminishwtingtime.Thephenomenonofheatandmasstrans-ferinwooddurin… 相似文献
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The scrimber is composed of the special elementary unit called fibrosis veneers. Study on chemical constituent changes of fibrosis veneers during heat treatment is helpful to expand the application areas of scrimbers. The objectives of this study were to investigate the effect of heat treatment on the chemical composition of poplar fibrosis veneers. The content changes of chemical composition and extractives after heat treatment were evaluated by chemical analysis. X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (NMR) were used to characterize the changes in the chemical structure of components. Untreated samples were also set for comparison. The results indicated that transformation of the material induced by this treatment led to an increase in the contents of lignin and extractives, while a decrease in those of holocellulose and α-cellulose. XPS spectroscopy results showed that the hemicelluloses and celluloses could be strongly affected by the atmosphere in the oven during the treatment. Relatively, the lignin was not very sensitive to the heating process to some extent. Solid-state NMR results showed that different degrees of transformations of the polymers took place during the heat treatment, resulting from the deacetylation of hemicelluloses, demethoxylation of lignin and changes in the cellulose structure. 相似文献
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Summary The transport of heat and moisture during the convective drying of southern pine was examined experimentally. Moisture distribution within the wood samples was measured using gamma attenuation. The accuracy of these measurements was found to be moisture content dependent with estimated uncertainties ranging from 29.5% at 10% moisture content to 6.8% at 120% moisture content. Local moisture content measurements reveal large inflections at high moisture contents. Peaks in moisture content are closely correlated with low fwood density and vice versa. Above the fiber saturation point the measured drying rate is not a well defined function of the moisture content. This is perhaps due to the biological variability of wood as well as grain orientation, although no definite conclusions could be drawn from the data with regard to the effect of grain orientation. The drying rate does not appear to be highly temperature dependent at high moisture contents. Below the fiber saturation point where diffusion is expected to be the dominant transport mechanism, the drying rate is less affected by biological variability and grain orientation, however, the effects of temperature are evident.The authors wish to acknowledge the support of this work by the National Science Foundation under Grant Number CME-7906367. We must also express our appreciation to staff members at Weyerhaeuser Technology Center who supplied us with wood samples. In addition to the authors, Mr. T. R. Brown, S. H. Moen, and D. Chow played a critical role in gathering much of the data 相似文献
9.
L. Awoyemi 《Wood Science and Technology》2008,42(1):39-45
Based on the already established mitigating potentials of borate salt on the negative effects of heat treatment on the strength
properties of wood (Awoyemi and Westermark 2005), the optimum concentration of the alkali buffer solution required to minimize strength loss was determined. Wood samples
were impregnated with 0.1, 0.3 and 0.5 M sodium borate solution and exposed to heat treatment for 4 h at 200°C. The mitigating
effect of borate salt on the degree of strength loss during heat treatment increases significantly with increasing concentration
from 0.1 to 0.3 M. Increasing the concentration of sodium borate from 0.3 to 0.5 M did not produce significant differences
in the degree of strength loss during heat treatment. The increase in the buffering effect observed with increasing concentration
of the sodium borate preservative is more pronounced on the modulus of rupture than on the modulus of elasticity. It is evidenced
therefore that the buffering effect of borate salt on the modulus of elasticity of wood exposed to heat treatment did not
start significantly until the 0.3 M concentration is reached and further increase in concentration beyond this point did not
produce any appreciable improvement in strength properties. 相似文献
10.
Jinghui Jiang Jianxiong Lu Yongdong Zhou Rongfeng Huang Youke Zhao Jiali Jiang 《Wood Science and Technology》2014,48(2):253-267
The properties of oak heat treated at temperatures of 160–220 °C, oxygen concentrations of 2–10 %, steam pressures of 0.1–0.4 MPa and treatment time of 2–4 h were investigated. Although modulus of elasticity (MOE), modulus of rupture (MOR) and equilibrium moisture content (EMC) of the heat-treated wood (HTW) were reduced, the value of $ \Updelta E^{*} $ was increased, and the dimensional stability [anti-swelling efficiency in radial (ASE-R), anti-humidity efficiency (AHE)] was improved considerably. Six regression equations (temperature, oxygen concentration, steam pressure and time as functions of MOE, MOR, ASE-R, AHE, EMC and $ \Updelta E^{*} $ ) were developed for the estimation and a nonlinear programming model was derived with operation research theory to obtain the most desirable HTW properties under some production constraints. 相似文献
11.
Responses of cambium to warming were recorded three times (December 14-27, 1990, January 18-February 3 and February 27-March 13, 1991) on 14-year-old Cryptomeria japonica D. Don and four times (December 12-26, 1990, January 18-February 2, February 26-March 12 and March 28-April 13, 1991) on 27-year-old Larix leptolepis Gord., during a period of winter cambial dormancy. Stem surfaces at breast height, mid-tree height and the crown base were warmed to 25-30 degrees C for 2 weeks. After heat treatment, cambia in the treated regions and in untreated regions 1 m above each treated area were examined by optical and transmission electron microscopy (TEM). In C. japonica, heat treatment often resulted in cambial reactivation in the treated regions, and this response to heat gradually increased as the dormant season passed from winter to spring. Conversely, in L. leptolepis, no cell division was observed in the cambial region of warmed stems until natural resumption of cambial activity, which occurred after bud break. 相似文献
12.
本文分析了我国刨花板的生产、销售现状,说明了刨花板是人造板中使用范围最广、市场潜力最大的产品,是实体木材好的代用品。但在产品中存在着甲醛释放量过高的问题,只有解决这个问题,才能使刨花板有好的销售市场,有更大的发展空间。 相似文献
13.
Ing. J. Dobrý Ph.D. Dr. A. Dziurzyński Prof. Dr. V. Rypáček 《Wood Science and Technology》1986,20(2):137-144
Summary The results of respective investigations indicate that during white rot the combustion heat of wood (Qexp (J/g)) remained virtually unchanged and at the greatest extent of decomposition it was in the range also found in non-rotten wood. During brown rot the combustion heat of wood samples increased, beginning at a weight loss of 20–30%. The difference between Qexp and the weighted mean of combustion heat values of isolated chemical wood components (Qcal) were neglectable. If Qexp values measured for each sample were taken as 100%, then Qcal averaged from 101.1–105.6% and from 97.4–108.2% during white and brown rot, respectively. The Qcal calculation error is expressed as coefficient k; it varies depending on the accuracy and selectivity of the separation methods used. 相似文献
14.
Marjan Sedighi Gilani Julie L. Fife Matthieu N. Boone Karim Ghazi Wakili 《Wood Science and Technology》2013,47(5):889-896
The process of crack propagation in wood during pyrolysis is strongly linked to heterogeneities in its hierarchical porous structure. Fundamental understanding of this process is necessary for the analysis of the behavior of wood structural elements during fire exposure. Synchrotron-based X-ray tomographic microscopy combined with a recently developed laser-based furnace at the TOMCAT beamline of the Swiss Light Source provides a unique opportunity to study the heat-induced propagation of microcracks in hardwood in situ with high spatial and temporal resolutions. In this study, attention was focused on the 3D microstructure of beech and the interconnectivity between morphology and cracking patterns. It is shown that thermal cracks initiate mainly along the ray cells in hardwood and in the junction of seasonal growth layers. There is a clear indication of increased total porosity of the wood due to charring. 相似文献
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In this study the hydrological regime of Norway spruce (Picea abies) and birch (Betula pendula) growing on heavy soils in the south east of Austria was analysed. Results from the year 2003 characterised by an extremely hot and dry summer are presented in this paper. Due to the extreme weather conditions the soil water content in August 2003 was very low (0.10–0.25 m3 m−3) in the topsoil (0–50 cm) with no explicit difference between both tree species. 相似文献
19.
Summary The objective of this research is to study the moisture deformation of densified in technological pressing wooden composite materials. By generalizing Cosserat's couple-stress theory a structural model for determination of mid-surface strains and curvatures of composite board taking into account asymmetric structure and nonuniform distribution of moisture as well as nonlinear swelling functions of the wooden stuff and dependence of strain characteristics on moisture content is developed. On the basis of a laminate analogy the optimum flake or veneer alignment in board has been estimated for the real composite production process. According to analysis performed, the optimum alignment for hygromechanical properties may not coincide with that for mechanical properties, and for every type of loading, material with a definite structure should be used. 相似文献
20.
Thermophysical properties of wood-polymer composites 总被引:5,自引:0,他引:5
Michel F. Couturier Kenneth George Marc H. Schneider 《Wood Science and Technology》1996,30(3):179-196