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1.
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
2.
In this study heartwood from a Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] plantation was treated using a high-temperature drying (HTD) method at 115°C, a low-temperature drying (LTD)
method at 65°C, and freeze vacuum drying (FVD), respectively. The dynamic viscoelastic properties of dried wood specimens
were investigated. The measurements were carried out at a temperature range of −120 to 250°C at four different frequencies
(1, 2, 5, and 10 Hz) using dynamic mechanical analysis (DMA). We have drawn the following conclusions: 1) the storage modulus
E′ and loss modulus E″ are the highest for HTD wood and the lowest for FVD wood; 2) three relaxation processes were detected in HTD and LTD wood,
attributed to the micro-Brownian motion of cell wall polymers in the non-crystalline region, the oscillations of the torso
of cell wall polymers, and the motions of the methyl groups of cell wall polymers in the non-crystalline region in a decreasing
order of temperatures at which they occurred; and 3) in FVD wood, four relaxation processes were observed. A newly added relaxation
is attributed to the micro-Brownian motions of lignin molecules. This study suggests that both the HTD and the LTD methods
restrict the micro-Brownian motion of lignin molecules somewhat by the cross-linking of chains due to their heating history.
__________
Translated from Journal of Beijing Forestry University, 2008, 30(3): 96–100 [译自: 北京林业大学学报] 相似文献
3.
Summary The maximum torsional-shear stress of 5 softwoods and 4 hardwoods were tested in the radial and tangential planes. These tests
were carried out in glycerin which was preheated to different temperatures between 22°C and 150°C, inclusively.
The dense hardwoods possess 2.4 times higher shear stress than softwoods at 22°C. However, at elevated temperatures, the same
degree of shear stress reduction (77 %) is obtained for hardwoods and softwoods in both radial and tangential failure. Thus,
the reduction in shear stress is independent of physical and structural wood variables. 相似文献
4.
Spruce wood blocks were acetylated in the presence of potassium acetate (KAc) at 20, 40, 60, 80 and 120°C. At 20°C, the weight percent gain (WPG) due to the KAc-catalyzed acetylation reached 20% in 18 days, whereas that due to pyridine-catalyzed acetylation did not exceed 8%. The hygroscopicity and dimensional stability of the KAc-acetylated wood were the same as those of conventionally acetylated wood at the same WPG, irrespective of reaction temperature. These facts suggest that the KAc enables simplified acetylation of wood at room temperature. The activation energy (E a) of the KAc-acetylation in the lower temperature range (20–40°C, 121–131 kJ/mol) was comparable to that of the acetylation of wood meal (140–146 kJ/mol). It was speculated that diffusion became a minor factor at reduced reaction rates in the lower temperature range, thus requiring a greater E a. 相似文献
5.
Kaisu Leppänen Peter Spetz Andrey Pranovich Kari Hartonen Veikko Kitunen Hannu Ilvesniemi 《Wood Science and Technology》2011,45(2):223-236
Norway spruce saw meal was extracted with pressurized hot water at 120–240°C using a flow-through system. Only small amounts
of hemicelluloses were extracted at 120–160°C, but dissolution was significantly enhanced when higher extraction temperatures
were applied. All hemicelluloses but only 15% of lignin were removed from wood at 220°C, and even less lignin was extracted
at lower temperatures. Partial degradation of cellulose seemed to take place only at 240°C. Of the total amount of extracted
hemicelluloses, 4–22% was hydrolyzed to monosaccharides. Although the average molar masses of extracted hemicelluloses decreased
with increasing extraction temperature, even at 240°C the extracted carbohydrates occurred, on average, as polysaccharides.
Polysaccharides with an average molar mass of 31 kDa were obtained at 170°C. The molecular-mass characteristics and yield
of carbohydrates depend on the extraction temperature, which should be chosen based on the end use of the isolated hemicelluloses. 相似文献
6.
Manabendra Deka Miha Humar Gregor Rep Borut Kričej Marjeta Šentjurc Marko Petrič 《Wood Science and Technology》2008,42(1):5-20
A series of experiments were carried out to investigate the colour stability of chemically treated and thermally modified
wood compared to non-modified wood during long term artificial UV light irradiation. One set of wood samples was vacuum-pressure
impregnated with alkaline (pH 9.8) copper (II) ethanolamine aqueous solution, while another set of samples from the same wood
block was thermally modified at 210°C and −0.90 bar for 2 h. The treated and modified wood samples along with the non-modified
ones were exposed to artificial UV light with the wave length in the region of UVA (315–400 nm) and UVB (280–315 nm) intermittently
for 500 h. Colour measurements were carried out throughout the irradiation period at an interval of 100 h according to CIEL*a*b*
system, where the results are presented in terms of ΔE, ΔL*, Δa* and Δb* values. Better photo-stability in terms of colour changes was recorded for both treated and modified woods compared to the
non-modified one. By means of EPR and DRIFT spectroscopic study it was shown that some degree of colour stability of treated
and modified woods, achieved during artificial UV light irradiation, resulted from lignin modifications and monomers of phenolic
compounds. 相似文献
7.
Molecular sieving behavior of carbonized wood: selective adsorption of toluene from a gas mixture containing α-pinene 总被引:1,自引:0,他引:1
The adsorption properties of wood carbonized at various temperatures were investigated using a mixed gas containing toluene
and α-pinene. Hinoki (Chamaecyparis obtusa) samples carbonized at 500°–1100°C were exposed to gas mixtures of toluene and α-pinene at 20°C. The samples carbonized at 500°–700°C only adsorbed toluene, whereas those carbonized at 800°–1100°C adsorbed
both toluene and α-pinene. Analysis of the surface structure of the carbonized wood by nitrogen adsorption at liquid nitrogen temperature indicated
that the sample carbonized at 700°C had micropores mainly 0.6 nm in diameter and few mesopores, whereas the samples carbonized
at 900°C and 1100°C had mesopores and micropores larger than 0.8 nm in diameter. With the sample carbonized at 700°C, the
flat-shaped toluene molecules could probably penetrate into the narrower pores, 0.8 nm in diameter, whereas the bulky globular-shaped
α-pinene molecules could not. Carbonization at temperatures higher than 900°C probably enlarged the pore size and thereby reduced
the selectivity of adsorption. The results revealed that wood carbonized below activation temperature has a unique flat-pore
structure that seems to work as a kind of molecular sieving carbon, successfully removing only the harmful volatile organic
compound (VOC), toluene, and leaving behind a pleasant aroma of α-pinene in the atmosphere. 相似文献
8.
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
9.
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
10.
Influence of heating history on dynamic viscoelastic properties and dimensions of dry wood 总被引:2,自引:2,他引:0
To obtain new information about the mechanical and physical properties of dry wood in unstable states, the influence of heating
history on viscoelastic properties and dimensional changes of dry wood in the radial, tangential, and longitudinal directions
was studied between 100° and 200°C. Unstable states of dry wood still existed after heating at 105°C for 30 min and were modified
by activated molecular motion in the first heating process to temperatures above 105°C. This phenomenon is thought to be caused
by the unstable states reappearing after wetting and drying again. Dry wood components did not completely approach the stable
state in the temperature range tested, because they did not entirely surpass the glass transition temperatures in most of
the temperature range. In constant temperature processes at 135° and 165°C, E′ increased and E″ decreased with time regardless of the direction. This indicated that the unstable states of dry wood components were gradually
modified with time at constant temperatures. On the other hand, anisotropy of dimensional change existed and dimension increased
in the longitudinal direction, was unchanged in the radial direction, and decreased in the tangential direction with time
at constant temperatures.
Part of this report was presented at the 13th Annual Meeting of the Chubu Branch of the Japan Wood Research Society, Shizuoka,
August 2003 相似文献
11.
Cao Jin-zhen Yu Li-li You Xiao-di Kamdem D. Pascal 《中国林学(英文版)》2007,9(4):239-245
In order to clarify the interaction between copper and wood substances in wood treated with copper containing water-borne wood preservatives, the dielectric constant ε′ and dielectric loss factor ε″ of untreated wood and wood treated with four concentration levels of copper-ethanolamine (Cu-EA) solutions were determined within a temperature range from –100 to 40°C and a frequency range from 100 to 1 MHz. Three dielectric relaxation processes were observed in the ε″ spectrum; among them R-I is based on the reorientation of methylol groups in the amorphous region of wood cell walls and R-II is related to wood extractives. R-III appeared in Cu-EA treated wood, and its magnitude decreases with the concentration of Cu-EA solutions used in this experiment. This relaxation process was considered to be based on the reorientation of copper-ethanolamine-wood complexes in wood cell walls. At low copper retention, the hydrogen in the complex can form hydrogen bonding with adjacent hydroxyl groups, which results in a strong bonding state between copper and wood; at high copper retention, the numerous copper-ethanolamine complexes not only hinder them from forming hydrogen bonding with adjacent wood molecules due to steric hindrance, but also weaken the interaction between wood molecules themselves, which corresponds to reducing ε″ values of both R-I and R-III processes. The results explain the fact of in-creasing copper leaching in wood treated with high concentration copper-based water-borne preservatives. 相似文献
12.
Thermal conductivity and diffusivity of wood 总被引:5,自引:0,他引:5
Summary Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the
plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100 °C. The influences of temperature,
density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel
to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20
to 100 °C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The
effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such
as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types
of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity
by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases.
Received 7 May 1997 相似文献
13.
Vibrational properties and fine structural properties of wood were measured at high temperatures. Sitka spruce (Picea sitchensis Carr.) and Shioji (Japanese ash, Fraxinus spaethiana Lingelsh.) were used as specimens. The specimens, the system to support them, a magnetic driver, and a deflection sensor
were in an electric drying oven, where vibration tests were conducted. The heating temperatures ranged from room temperature
to 200 °C in 25 °C increments in both heating and cooling processes. X-ray diffractometry was carried out using positive sensitive
proportional counter (PSPC) at room temperature to 200 °C in 20 °C increments in both heating and cooling processes.
Received 13 December 1999 相似文献
14.
Colour responses from wood,thermally modified in superheated steam and pressurized steam atmospheres
《Wood material science & engineering》2013,8(3-4):211-219
Abstract In this study, two different methods were used to produce thermally modified wood. One was carried out in a typical kiln drying chamber using superheated steam (SS) and the other used pressurized steam in an autoclave cylinder (PS). Overall, both processes followed the same principles and the wood was not treated with any chemicals. Two wood species were studied, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Treatments in the autoclave were carried out under pressure using temperatures of 160°C, 170°C and 180°C. Temperatures of 190°C and 212°C were used in treatments in the chamber at normal air pressure. The colour was measured using L*C*H colour space. Results for both species showed that similar L* (lightness) can be reached at lower (20–30°C) temperatures using PS compared with SS treatment. The hue angle of PS-treated wood was smaller than that of SS-treated wood. No significant difference in C* (chroma) was detected. The difference in E value between PS- and SS-treated wood was smaller for Norway spruce than for Scots pine. The residual moisture content was about 10% higher in wood treated by the PS process compared with the SS process. 相似文献
15.
Method for measuring viscoelastic properties of wood under high temperature and high pressure steam conditions 总被引:3,自引:0,他引:3
A method for measuring the viscoelastic properties of wood under high temperature and high pressure steam was developed using a testing machine with a built-in autoclave. A newly developed load cell capable of resisting a steam pressure of 16kgf/cm2 and a temperature of 200°C was installed in the autoclave. This load cell could be used to determine precisely the loads while steaming at temperatures from 100°C to 200°C. In addition to load-detection problems, it was necessary to avoid the nonuniform thermal degradation of wood during the measurement process under steaming at high temperatures. This nonuniform degradation could be minimized by shortening the time required for the wood to attain thermal equilibrium using specimens conditioned to the fiber saturation point. According to this method, a stress relaxation curve for sugi (Cryptomeria japonica D. Don) wood being compressed while steaming at 180°C was obtained. The stress was seen to decrease rapidly with time, reaching almost zero at 3000s. 相似文献
16.
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
17.
The tensile stress relaxation of Chinese fir wood treated with copper–ethanolamine (Cu–EA) was compared with that of untreated control to investigate the influence of Cu–EA treatment on the dimensional stability of wood in long-term application, and also for a better understanding of copper–wood–water interactions in copper containing water-borne preservative systems. The results showed that temperature and moisture conditions play important roles in the stress relaxation behavior of wood with or without Cu–EA treatment. At 25°C, Cu–EA treatment has little influence on stress relaxation; while at 35°C, Cu–EA treatment can significantly reduce the stress relaxation of wood, suggesting that Cu–EA treatment can increase dimensional stability of wood at high atmospheric temperature in long-term application. The complicated effect of copper retention on stress relaxation further confirms that copper competes for hydroxyl groups as adsorption sites with water molecules, as put forward in the previous report. 相似文献
18.
Formation of benzyl esters from acetic and formic acids during heat treatment of birch at 160–200°C has been studied by gas chromatography. High concentrations of formic and acetic acids formed by the wood itself during hydrothermal treatment were found. The concentrations of acids increased with both treatment time and temperature. The maximum formic- and acetic acid concentrations found at 180°C and after 4 h of treatment performed in this work were 1.1 and 7.2%, based on dry-weight wood, respectively. The treated wood material was characterised by mechanical testing [bending tests perpendicular to the grain, modulus of rupture, modulus of elasticity, Brinell hardness, impact bending and colour measurements (CIE colour space)]. The experiments, where high concentration of acids was formed, showed severe losses in mass and mechanical strength. Indications of possible enhanced mechanical properties for the treated, compared with untreated birch wood were found around 180–200°C at short treatment times. This paper discusses possible degradation reactions coupled with the colour and mechanical properties in relation to acid formation, and suggestions for process optimisations. 相似文献
19.
Ren Li Zhiqiang Gao Shanghuan Feng Jianmin Chang Yanmei Wu Rongfeng Huang 《Journal of Wood Science》2018,64(6):751-757
Sandwich compression of wood that can control the density and position of compressed layer(s) in the compressed wood provides a promising pathway for full valorization of low-density plantation wood. This study aims at investigating the effects of preheating temperatures (60–210 °C) on sandwich compression of wood, with respect to density distribution, position and thickness of the compressed layer(s). Poplar (Populus tomentosa) lumbers with moisture content below 10.0% were first soaked in water for 2 h and stored in a sealed plastic bag for 18 h, the surface-wetted lumbers were preheated on hot plates at 60–210 °C and further compressed from 25 to 20 cm under 6.0 MPa at the same temperature on the radial direction. The compressed lumbers were characterized in terms of density distribution, position and thickness of compressed layer(s). It was found that depending on preheating temperatures, sandwich compressed wood with three structural modes, namely, surface compressed wood, internal compressed wood and central compressed wood can be formed. Density of the compressed layer(s) in wood increased gradually as a result of the elevated preheating temperatures. Higher preheating temperatures gave rise to bigger distance between compressed layer(s) and the surface, and preheating temperature elevation from 90 to 120 °C contributed to a maximal distance increase of 2.71 mm. In addition, higher preheating temperatures resulted in bigger thickness of compressed layer(s) over 60–150 °C and temperature elevation from 120 to 150 °C lead to the layers integration from two into one. Further temperature elevation over 150 °C reduced the thickness of the compressed layer in wood. SEM scanning suggested that cell wall bucking rather than cell wall crack occurred in compressed layer(s) and transition layer(s). 相似文献
20.
Dynamic viscoelastic properties of wood acetylated with acetic anhydride solution of glucose pentaacetate 总被引:1,自引:0,他引:1
Spruce wood specimens were acetylated with acetic anhydride (AA) solutions of glucose pentaacetate (GPA), and their viscoelastic
properties along the radial direction were compared to those of the untreated and the normally acetylated specimens at various
relative humidities and temperatures. Higher concentrations of the GPA/AA solution resulted in more swelling of wood when
GPA was introducted into the wood cell wall. At room temperature the dynamic Young's modulus (E′) of the acetylated wood was enhanced by 10% with the introduction of GPA, whereas its mechanical loss tangent (tan δ) remained almost unchanged. These changes were interpreted to be an antiplasticizing effect of the bulky GPA molecules in
the wood cell wall. On heating in the absence of moisture, the GPA-acetylated wood exhibited a marked drop in E′ and a clear tan δ peak above 150°C, whereas the E′ and tan δ of the untreated wood were relatively stable up to 200°C. The tan δ peak of the GPA-acetylated wood shifted to lower temperatures with increasing GPA content, and there was no tan δ peak due to the melting of GPA itself. Thus the marked thermal softening of the GPA-acetylated wood was attributed to the
softening of wood components plasticized with GPA.
Received: March 29, 2002 / Accepted: May 21, 2002
Correspondence to:E. Obataya 相似文献