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1.
Jianxiong Lü Zhiyuan Lin Jiali Jiang Youke Zhao Jinghui Jiang Ruiqing Gao Yafang Yin 《Frontiers of Forestry in China》2007,2(2):222-226
Chinese fir plantation sapwood and heartwood boards were treated by three drying methods: radio frequency-vacuum drying (RFVD),
conventional kiln drying (KD) and high temperature drying (HTD). The maximum amount of dyeing solution uptake by the capillary
rising method was used to evaluate the liquid penetration of the treated wood. The pit aspiration ratio was determined by
a semithin section method. Changes in wood microstructure were investigated using scanning electron microscopy. The results
show that liquid penetration of Chinese fir sapwood after RFVD is significantly higher than that after KD and HTD. Liquid
penetration of Chinese fir heartwood after RFVD is higher than that after HTD. Liquid penetration of Chinese fir sapwood is
significantly higher than that of heartwood after three drying treatments. Low pit aspiration ratio and cracks of some bordered
pits are the main reasons for the increase in liquid penetration after RFVD treatment.
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Translated from Scientia Silvae Sinicae, 2006, 42(10): 85–90 [译自: 林业科学] 相似文献
2.
Summary
13C CP MAS NMR spectroscopy was used to characterize the structural changes of cell wall polymers in beech wood Fagus sylvatica during drying processes. The analysis of five wood samples, namely, untreated, untreated dried, pre-treated by steam and/or
NaOH subjected to drying showed partial depolymerization of lignin component as well as the change of the ratio of the crystalline
and of the amorphous parts of cellulose as the consequence of wood pre-treatment. In addition, T1ρ(1H) relaxation times were determined in beech wood sample pre-treated with steam at 135 °C and the lignin isolated from this
sample. The magnitudes of the relaxation times were found comparable in both samples as well as in the lignin-cellulose model
compound. These unique T1ρ (1H) values indicate that spin diffusion is complete and homogeneous due to spatial proximity of spins and confirmed the formation
of lignin-cellulose complex during thermal treatment of wood.
Received 30 June 1997 相似文献
3.
In order to understand the reason why glycerin pre-treatment can accelerate the deformation fixation of compressed wood, the
interaction between glycerin and wood at various temperatures was investigated in this study from stress relaxation approach.
The compression stress relaxation curves of poplar (Populus cathayana Rehd.) samples impregnated with glycerin were measured at temperatures ranging from 25 to 180°C, together with the curves
of oven-dry wood at temperatures between 100 and 180°C for comparison. The activation energy was calculated according to the
Eyring’s absolute rate reaction theory. The results showed that temperature had very obvious effect on stress relaxation for
both glycerin-treated wood (GTW) and oven-dry wood. The stress released very fast at higher temperatures. Glycerin showed
an accelerating effect on stress relaxation. At temperatures exceeding 120°C, a complete relaxation of the stress could be
expected. While for untreated wood, it cannot be reached until 160°C. By calculating the apparent activation energy (ΔE) of
GTW at different temperatures, it is clear that two mechanisms are responsible for different temperature ranges. From 40 to
100°C, ΔE is only 8.24 kJ/mol, which corresponds to the hydrogen bonds formed between wood and glycerin molecules; from 120
to 180°C, ΔE reached 81.38 kJ/mol, which corresponds to the degradation of hemicelluloses or lignin, and during this process,
new cross-linking would happen. 相似文献
4.
In order to analyze the effect of temperature gradient on moisture movement during highly intensive drying, such as microwave-vacuum
drying, the profile of the temperature and moisture content in sealed wood whose opposite faces were subjected to temperature
gradient for a short time was measured. The ratio of the moisture content (MC) gradient to the temperature gradient (dM/dT) was calculated and the factors influencing moisture movement under nonisothermal conditions were discussed. The results
indicate that moisture moved in wood from the warm surface to the cold one even if opposite faces of the sealed wood assembly
were exposed continuously to different but constant temperatures for a short period. The moisture content on the cold surface
was higher than that on the warm surface. The moisture content gradient opposite to the temperature gradient was established,
and the dM/dT was below 0.9%/°C. The temperature in the sample and the distance from the hot surface of the sample was strongly linearly
correlated. With an increase in temperature, initial moisture content and experimental time, the dM/dT was significantly increased.
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Translated from Journal of Beijing Forestry University, 2005, 27(2): 96–100 [译自: 北京林业大学学报, 2005, 27(2): 96–100] 相似文献
5.
The structures of the solid state products formed by the partial combustion of Korean pine wood treated with fire-retardant
FRW were analyzed by microscopic FTIR. The volatile pyrolytic products of basswood (Tilia amurensis) specimens treated with FRW and its components guanylurea phosphate and boric acid were analyzed by GC-FTIR. The pyrolytic
and charring process, the effects of fire-retardant, and the structural characteristics of the pyrolytic products were discussed.
It was concluded that upon heating and by the catalysis of FRW and its decomposition products reactions of wood took place
successively, namely the dehydration of polysaccharide, the elimination of acetic acid from hemicellulose, the degradation
of polysaccharide, the degradation of lignin, the polymerization of the pyrolytic products of wood, reactions of oxygen-element-elimination
of aliphatic polymers and the structural change of the latter to form aromatic structures, and charring. The pyrolysis process
of wood was altered and the yield of volatile pyrolytic products was decreased by FRW treatment.
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Translated from Scientia Silvae Sinicae, 2005, 41(4): 149–154 [译自: 林业科学, 2005, 41(4): 149–154] 相似文献
6.
Structure and characterization of Chinese fir (Cunninghamia lanceolata) wood/MMT intercalation nanocomposite (WMNC) 总被引:2,自引:0,他引:2
Wenhua Lü 《Frontiers of Forestry in China》2008,3(1):121-126
With water-soluble phenol-formaldehyde resin as an intermediate, Chinese fir (Cunninghamia lanceolata) wood/montmorillonite nanocomposite (WMNC) was prepared through vacuum impregnation and characterized with XRD, SEM, FTIR
and TG-DTA analyses. The XRD analysis indicated that the wood crystallinity of WMNC decreased, the MMT exfoliated and some
nano silicate layers entered into the non-crystallized microfibrillar region of the wood cell wall. Wood structure is anisotropic
and its impregnation is anisotropic. Due to the nonuniformity of the MMT organic modification, PF intercalation and wood impregnation,
the MMT configuration and distribution in wood were diverse. The SEM graphs of WMNC showed that some silicate grains were
blocked in the wood cell lumen, some silicate layers adhered to the inner surface of the wood cell wall, and some exfoliated
MMT layers even penetrated the wood cell wall. The obtained hydroxyl of WMNC increased and its ether linking decreased. It
was considered that MMT and wood interacted not only with hydroxyl bonds, but also involved some chemical linking. Compared
with untreated wood and the PF-impreg, the pyrolysis process of WMNC changed; its starting decomposing temperature decreased
and its pyrolysis weight loss at high temperatures greatly decreased. The WMNC indicated certain nanoeffects of the composition
of the inorganic MMT nanolamellae.
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Translated from Journal of Beijing Forestry University, 2007, 29(1): 131–135 [译自: 北京林业大学学报] 相似文献
7.
Guangjie Zhao Wensheng Luo T. Furuno Qiang Ren Erni Ma 《Frontiers of Forestry in China》2007,2(2):231-236
In order to investigate the pyrolytic characteristics of the burning residue of fire-retardant wood, a multifunctional fire-resistance
test oven aimed at simulating the course of a fire was used to burn fire-retardant wood and untreated wood. Samples at different
distances from the combustion surface were obtained and a thermogravimetric analysis (TG) was applied to test the prrolytic
process of the burning residue in an atmosphere of nitrogen. The results showed that: 1) there was little difference between
fire-retardant wood and its residue in the initial temperature of thermal degradation. The initial temperature of thermal
degradation of the combustion layer in untreated wood was higher than that in the no burning wood sample; 2) the temperature
of the flame retardant in fire-retardant wood was 200°C in the differential thermogravimetry (DTG). The peak belonging to
the flame retardant tended to dissipate during the time of burning; 3) for the burning residue of fire-retardant wood, the
peak belonging to hemicellulose near 230°C in the DTG disappeared and there was a gentle shoulder from 210 to 240°C; 4) the
temperature of the main peaks of the fire-retardant wood and its burning residue in DTG was 100°C lower than that of the untreated
wood and its burning residue. The rate of weight loss also decreased sharply; 5) the residual weight of fire-retardant wood
at 600°C clearly increased compared with that of untreated wood. Residual weight of the burning residue increased markedly
as the heating temperature increased when burning; 6) there was a considerable difference with respect to the thermal degradation
temperature of the no burning sample and the burning residue between fire-retardant wood and untreated wood.
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Translated from Journal of Beijing Forestry University, 2006, 28(3): 133–138 [译自: 北京林业大学学报] 相似文献
8.
For a better understanding of the binding between silicon dioxide and wood as well as the dielectric properties of silicon
dioxide/wood composite, dielectric relaxation was measured for untreated wood [Cunninghamia lanceolata (Lamb.) Hook] and for silicon dioxide/wood composite with different weight percentage gain (WPG). Cole–Cole’s circular arc
law, distribution spectrum of relaxation time and relation model were applied to the results of relaxation due to motions
of the methylol groups. The results were as follows. The generalized relaxation time and ε
s
− ε
∞
decreased with increasing WPG. The distribution spectrum of relaxation time decreased more and more and broadened with increasing
WPG. The methylol group in the amorphous region of the wood cell wall participated in hydrolysis reaction and condensation
reaction caused by tetraethylorthosilicate (TEOS), and there is a cross-link between silicon dioxide and wood. The value of
apparent activation energy (ΔE) increased for silicon dioxide/wood composite, and increased with increasing WPG. Activation enthalpy (ΔH) and activation entropy (ΔS) increased, while activation free energy (ΔG) decreased with increasing WPG. The number of hydroxyl groups cut in dielectric relaxation increased with increasing WPG. 相似文献
9.
Sub-alpine fir is characterized by its high proportion of wet pockets making it difficult to dry. Since it takes longer to
dry, mills experience reduced kiln productivity and increased energy consumption. High temperature drying (HTD) can be an
effective approach to accelerate the drying process. In this study, three drying schedules, namely, conservative (control),
HTD, and HTD and conservative combined (HTD/Cons), were evaluated when drying green sub-alpine fir 2″ × 4″ dimension lumber.
The results indicated that: (1) the drying rates in the HTD and HTD/Cons schedules were increased by 31–150% in comparison
to the drying rates obtained for the conservative schedule; (2) although drying stresses observed for the HTD schedule were
higher than those that were measured for the conservative schedule, no significant difference in drying stresses was found
between the HTD/Cons and conservative schedules; (3) warp was reduced in both HTD and HTD/Cons schedules; (4) neither the
HTD nor HTD/Cons schedule showed any significant reduction in modulus of rupture (MOR) and modulus of elasticity (MOE) when
compared to the values obtained for the conservative schedule. Diffusion coefficients during HTD for sub-alpine fir were determined
and it was found that diffusivity increases with temperature. A mathematical model describing the processes of heating and
drying under high temperatures was developed. The results of drying tests showed that the predicted drying curves by the model
satisfactorily agree with the experimental data. 相似文献
10.
Brauns’ lignins present in the methanol extracts of fresh birch (Betula pendula) xylem and of sawn birch board subjected to vacuum drying were characterized by 1H and 13C NMR spectroscopy (1D and 2D), IR spectroscopy, gel permeation chromatography (GPC) and colour measurements (CIELab) in order to find out whether Brauns’ lignin could contribute to the colour change of sawn timber that occurred during vacuum drying. The two Brauns’ lignin samples contained about equal amounts of syringylpropane and guaiacylpropane units linked with β-O-4 and β–β side-chain structures. Molecular weight of the Brauns’ lignin of vacuum-dried birch board (acetylated: 5,200 g mol−1) was higher than that of the Brauns’ lignin of fresh birch wood (acetylated: 4,400 g mol−1). The Brauns’ lignin of vacuum-dried wood was also clearly darker and more prominently yellow and red;
between the Brauns’ lignin samples was 23.59. The differences in the molecular weights and colours suggest that the Brauns’ lignin underwent a chemical change during vacuum drying of the wood and that this change may have affected the colour of the wood. 相似文献
11.
Test samples of Japanese larch (Larix leptolepis) heartwood and Japanese beech (Fagus crenata) sapwood were heated for 22 h at constant temperatures (50°–180°C) under three water content conditions. Raman spectra of
the samples were recorded before and after the heat treatments, and spectral changes in the range from 1000 cm−1 to 1800 cm−1 were evaluated using the difference spectrum method. For both wood species, the Raman band intensity at 1655–1660 cm−1 due mainly to the C=C and C=O groups in lignin clearly decreased with increasing heat-treatment temperature (HTT). The spectral
change was thought to reflect the progress of condensation reactions of lignin molecules during the heat treatment. Moreover,
the decrease in band intensity was considerably facilitated by the presence of water in the cell wall, suggesting that the
condensation is closely related to the softening of lignin. From the spectral changes in the wavenumber region of 1200–1500 cm−1, it was considered that wood constituents are partially decomposed at the higher HTT.
Part of this article was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003 相似文献
12.
To analyze the effects of lignin on the destabilization of wood due to quenching, we examined the dielectric properties of
untreated and delignified wood before and after quenching at 20°C from 50 Hz to 100 MHz. For untreated wood, the inflection
points of log ε′ and log σ vs log f and the peak of log(tan δ) vs log f were attributed to interfacial polarization before quenching, and the location of the inflection point shifted to a higher
frequency with increasing moisture content because of changes in the water cluster. After quenching, the inflection points
of log ε′ and log σ and the peak of log(tan δ ) shifted to higher frequency; however, the values of log ε′, log σ recovered to those before quenching with the passage of time. For delignified wood, dielectric relaxation was observed at
a higher frequency than for untreated wood irrespective of quenching. It was inferred that the mobility of water molecules
was influenced by the cluster surroundings because of increased number of adsorption sites in hemicellulose. Moreover, after
quenching, the recovery process did not change greatly over time; it was shown that the matrix structure was affected more
by quenching with the loss of lignin. 相似文献
13.
Shuichi Doi Masakazu Aoyama Shigeru Yamauchi Yasuji Kurimoto 《Journal of Wood Science》2005,51(5):526-530
We investigated the effects of high-temperature drying schedules (120°–130°C) on decay and termite feeding of Japanese larch
timbers. Thermogravimetric analysis was conducted to investigate changes of the wood components. Decay and termite feeding
tests showed that specimens dried under high-temperature schedules were susceptible against a decaying fungus Fomitopsis palustris and attacks from termites Coptotermes formosanus and Reticulitermes speratus. These drying schedules changed chemical components, which were suggested by the thermal analytical result compared to the
control sample. The results of this study indicated that the acceleration of termite feeding takes place even under temperatures
that are comparatively lower than that used in our previous research in which 170°C steaming treatment was applied to Japanese
larch wood. Decay durability against a brown rot fungus also decreased, possibly from production of low molecular weight fragments
when hemicellulose decreased during the high-temperature drying processes. 相似文献
14.
Yoh-ichi Matsushita Kazuhiro Sugamoto Kenji Miyakubo Chiaki Kurogi Takanao Matsui Hisato Oda Hideto Fujimoto 《Journal of Wood Science》2008,54(6):476-482
Sawdusts of sugi (Cryptomeria japonica) wood prepared before and after steam drying at 120°C in a kiln were extracted with n-hexane and ethyl acetate to give n-hexane extracts and ethyl acetate extracts. From gas chromatography-mass spectrometry analysis of the ethyl acetate extracts
from woods before and after steam drying, the components of 4-epi-cubebol, cubebol, and 2,7(14),10-bis-abolatrien-1-ol-4-one, which existed in the raw sugi wood, were proved to disappear
in the steam-dried wood. These components were also absent in the ethyl acetate extract of the steam-condensed solution of
waste steam from the kiln outlet. When these three components were treated with 0.2% (v/v) acetic acid solution at 120°C,
δ-cadinene was produced as a major product from both 4-epi-cubebol and cubebol by dehydration and cleavage of the cyclopropane ring, and cryptomerone from 2,7(14),10-bisabolatrien-1-ol-4-one
by hydration. The chemical changes of the three components presumably occur during steam drying of the sugi wood.
This study was presented in part at the 85th Spring Meeting of the Chemical Society of Japan, Kanagawa, Japan, March 26–29,
2005 相似文献
15.
对40 mm厚杉木锯材制定两个高温干燥工艺并进行试验研究,检测和分析干燥周期、干燥速率、锯材干燥质量等指标。干燥工艺I采用高温湿空气进行干燥;干燥工艺II在干燥前期高含水率阶段采用过热蒸汽条件,干燥后期低含水率阶段采用高温湿空气进行干燥。结果显示:两个干燥工艺在各阶段的干燥速率差异明显,干燥前期工艺II的干燥速率为1.30%/h,较工艺I低约37.2%;但干燥后期工艺II的干燥速率为1.89%/h,较工艺I高约70.27%。干燥工艺II可以有效避免锯材内裂的发生,干燥质量满足GB/T 6491—2012《锯材干燥质量》二级材的指标要求,干燥效率提高。 相似文献
16.
Relaxation mechanism of residual stress inside logs by heat treatment: choosing the heating time and temperature 总被引:1,自引:0,他引:1
Some methods to reduce residual stress inside logs have been reported, although the conditions for stress relaxation are
not yet clarified. Our study using precise experiments revealed that residual stress relaxation occurs only when both heat
and moisture exist inside the logs. We then determined the heating time and temperature required to relax the residual stress
inside the logs. Short air-drying treatments did not relax residual stress even though free water in the logs was greatly
reduced. The residual stress of the 33-h 80°C-heated bolts was relaxed, whereas that of the 48-h 70°C-heated bolts was not.
As for the influence of treatment time, bolts heated at 100°C were relaxed after 18 h of treatment. The 13-h heated bolts
did not show any relaxation. Therefore, residual stress relaxation occurred rapidly owing to the thermomechanical change of
the individual wood components comprising the cell wall. The moisture content inside all the bolts was much higher than the
fiber saturation point. This is because relaxation occurs only when the heating temperature is maintained above 80°C for a
particular duration of treatment.
Received: December 12, 2001 / Accepted: February 18, 2002
Present address: Institute for Structural and Engineering Materials, National Institute of Advanced Industrial Sciences and Technology, Independent
Administrative Institution, Nagoya 463-8560, Japan Tel. +81-52-736-7320; Fax +81-52-736-7419 e-mail: m.nogi@aist.go.jp
Part of this report was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000
Correspondence to:M. Nogi 相似文献
17.
In order to obtain the effects of acid catalysts on wood liquefaction in phenol, we investigated the liquefaction of wood
powder from Chinese fir (Cunninghamia lanceolata) and poplar (Triploid Populus tomentosa Carr) in the presence of phenol with the following weak inorganic acids as catalysts: phosphoric acid (85%), sulfuric acid
(36%), hydrochloric acid (37%) and oxalic acid (99.5%). Results show that phosphoric acid (85%) and sulfuric acid (36%) are
better than the other catalysts. It was found that lower residue ratios can be obtained under defined reaction conditions:
phenol/wood ratio is 4, a 10% catalyst based on the weight of phenol, a temperature of 150°C for 2 h and phosphoric or sulfuric
acid. The residue ratios are 3.2% and 4.0%, respectively.
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Translated from Journal of Beijing Forestry University, 2004, 26(5) [译自: 北京林业大学学报, 2004, 26(5)] 相似文献
18.
To investigate the influence of heating and drying history on the microstructure of dry wood, in addition to the dynamic viscoelastic
properties, CO2 adsorption onto dry wood at ice.water temperature (273 K) was measured, and the micropore size distribution was obtained
using the Horvath-Kawazoe (HK) method. Micropores smaller than 0.6 nm exist in the microstructures of dry wood, and they decreased
with elevating out-gassing temperature and increased again after rewetting and drying. Dry wood subjected to higher temperatures
showed larger dynamic elastic modulus (E′) and smaller loss modulus (E″). This is interpreted as the result of the modification at higher temperature of the instability caused by drying. Drying
history influenced the number of micropores smaller than 0.6 nm in dry wood not subjected to high temperature, although the
difference in the number of micropores resulting from the drying history decreased with increasing out-gassing temperature.
A larger number of micropores smaller than 0.6 nm exist in the microstructure of dry wood in more unstable states, corresponding
to smaller E′ and larger E″ than in the stable state. Consequently, unstable states are considered to result from the existence of temporary micropores
in the microstructures of dry wood, probably in lignin.
Part of this report was presented at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, March 2005, and at
the 56th Annual Meeting of the Japan Wood Research Society, Akita, August 2006 相似文献
19.
Dielectric properties in three main directions for hinoki wood (Chamaecyparis obtusa) specimens conditioned at various levels of relative humidity were measured in the frequency range from 20 Hz to 10 MHz over
the temperature range from −150°C to 20°C. Three relaxations were observed in the specimens conditioned at high levels of
relative humidity. The relaxation in the highest frequency range was ascribed to the motions of adsorbed water molecules.
The relaxation in the middle frequency range remained unchanged by the ethanol–benzene extraction of specimens. The relaxation
location was independent of measuring directions. The relaxation in the lowest frequency range was not detected in the specimens
impregnated with methyl methacrylate (MMA). This result suggested that the relaxation was due to electrode polarization. The
Cole-Cole circular arc law applied well to two relaxations recognized in the specimens impregnated with MMA. The relaxation
magnitude in the middle frequency range was extremely large, and the distribution of relaxation times was very narrow. These
characteristics suggested relaxation of the Maxwell-Wagner type resulting from the interfacial polarization in the heterogeneous
structure, which included adsorbed water with large electrical conductivity within the insulating cell walls. 相似文献
20.
Eiichi Obataya Sakae Shibutani Kensuke Hanata Shuichi Doi 《Journal of Wood Science》2006,52(2):111-114
Japanese cedar wood specimens were steamed at 80°, 100°, and 120°C over 14 days, and their equilibrium moisture content (M)
at 20°C and 60% relative humidity, longitudinal dynamic Young’s modulus (E), bending strength (σ
max), and breaking strain (ε
max) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater
reduction in M, σ
max, and ε
max. The E of wood was slightly enhanced by steaming at 100°C for 1–4 days and 120°C for 1–2 days, and thereafter it decreased. The
slight increase in the E of sapwood was attributable to the reduction in hygroscopicity, while sufficient explanation was not given for a greater
increase in the heartwood stiffness. Irrespective of the steaming temperature, the correlations between M and the mechanical properties of steamed wood were expressed in terms of simple curves. M values above 8% indicated a slight reduction in E and s max, whereas M values below 8% indicated a marked decrease in the mechanical performances. In addition, the e max decreased almost linearly
with a decrease in the value of M. These results suggest that hygroscopicity measurement enables the evaluation of degradation in the mechanical performances
of wood caused by steaming at high temperatures. 相似文献