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Dynamic properties of bamboo, Phyllostachys pubescens, with moisture content (MC) ranging from −130 to 130°C, were studied by dynamic mechanical analysis (DMA). The results showed
that the hygrothermal effect on dynamic mechanical properties was negative. The storage modulus decreases with increasing
temperature and MC, and glass transition temperature decreases with increasing MC. The glass transition temperature and tan
delta of bamboo were 30.5°C, 0.02 and 10.61°C, 0.04, when MC was 10% and 34%, respectively.
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Translated from Journal of Nanjing Forestry University (Natural Sciences Edition), 2006, 30(1): 65–68 [译自: 南京林业大学学报(自然科学版), 2006, 30(1): 65–68] 相似文献
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Ultraviolet resonance Raman spectroscopy (UVRRS) was used to study the formation of aromatic and/or lignin-carbohydrate (LC)
structures at the reducing end groups of O-alkyl-substituted cellulose under conditions simulating the initial phase of kraft pulping. The derivatives studied were
methyl cellulose (MC) with degree of substitution (DS) of 1.64–1.95, carboxymethyl cellulose (CMC) with DS ∼0.6, and a lignin
model compound, creosol. The total alkali concentrations in the treatments were 0.1 M and 0.5 M and the sulfidities were 1%,
10%, and 30%. HS− ions and creosol are both strong nucleophiles and they compete for the hot-alkali-generated unsaturated electrophilic reaction
sites in the reducing end groups of the polysaccharides. The results indicated that conditions similar to those in the initial
phase of conventional kraft cooking (high OH− and low HS− ion concentrations) increased the aromatic nature of the end groups and conditions similar to those in the initial phase
of super batch cooking (low OH− and high HS− ion concentrations) partly inhibited the formation of aromatic and LC end groups. 相似文献
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Sudijono Dwianto Wahyu Yusuf Sulaeman Iida Ikuho Furuta Yuzo Minato Kazuya 《Journal of Wood Science》2004,50(4):371-374
Mechanical property changes due to the moisture content (MC) and/or temperature changes were examined for 15 Indonesian wood species. A static bending test was carried out at 20°C, 65% relative humidity (air-dry), and water-saturated at 20°C (wet-20) and 80°C (wet-80). For individual test conditions, modulus of elasticity (MOE) and modulus of rupture (MOR) increased linearly with specific gravity regardless of wood species; however, maximum deflection did not correlate with specific gravity for any MC or temperature conditions. The relative values of MOE and MOR measured in wet-20 to air-dry conditions were variously affected from slightly to strongly depending on the wood species. However, the relative values always decreased markedly when saturated in water at 80°C, regardless of wood species. The relative MOE, MOR, and maximum deflection values due to the change in MC or MC and temperature combined were independent of specific gravity but may be dependent on wood type: softwood or hardwood. 相似文献
7.
Hot-pressing is the main process in flakeboard manufacture. Studies in this field also emphasize the effect on the heat-transfer
process of the following factors: hot-pressing temperature, original moisture content (MC), target thickness and target density.
In this experiment, dynamic data of changes in temperature in mats can be logged through temperature transducers and a computer
data log system. The results of the experiment indicate that the core temperature-time curve can be divided into three stages:
a stage of a rapidly rising temperature, a stage of moisture vaporizing and a stage of a slowly increasing temperature. If
the hot-pressing temperature or the original MC increases during the first stage, the temperature will increase at an accelerated
rate. This rate of acceleration in thin or low-density boards is very high. During the second stage, increasing the hot-pressing
temperature or decreasing the original MC can shorten the time used to vaporize moisture. In thin or low-density board, this
time period is short. In the third stage the original MC does not affect the rate of temperature increase, while the effect
of the other factors is the same as that at the first stage. Given different conditions, vaporization temperature in the mat
changes.
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Translated from Journal of Beijing Forestry University, 2005, 27(2): 92–95 [译自: 北京林业大学学报, 2005, 27(2): 92–95] 相似文献
8.
In this study, molding moso bamboo strips to a curved shape using hot-press molding operation was explored. Bamboo strips with different thickness and moisture content (MC) were subjected to press molding under 120–210 °C for different time. Changes in the chemical components of bamboo were analyzed by Fourier-transform infrared spectroscopy (FTIR). Effect of MC on thermal mechanical behavior of bamboo was investigated using dynamic mechanical analysis (DMA). Results showed that the influencing degree of four variables on compression and recovery ratios decreased as: temperature?>?time?>?thickness?>?MC. Compression ratio increased and recovery ratio decreased dramatically when pressing temperature exceeded 180 °C. FTIR analysis indicated that polysaccharide (especially hemicelluloses) underwent a progressive thermal degradation during compression at 180 and 210 °C for 40 min, whereas relative content of lignin increased. DMA results showed that bamboo samples with a higher MC had a lower storage modulus value, confirmed water had a plasticizing effect. The loss factor of bamboo with higher MC (12 and 16%) exhibited two major transitions centred around 100 °C (α1) and 50 °C (α2), respectively. The temperature of these α transitions kept almost unchanged as moisture level increased from 12 to 16%. These findings provide fundamental information for the future preparation of curved bamboo as profiled components in engineered products. 相似文献
9.
Chemical reactivity of heat-treated wood 总被引：1，自引：0，他引：1
Chemical reactivity of heat-treated wood was compared with that of untreated wood. For this purpose, heat-treated pine or
beech sawdust was reacted with different carboxylic acid anhydrides in pyridine or with phenyl isocyanate in dimethyl formamide.
Compared to controls, weight gains obtained with heat-treated sawdust are smaller showing a lower chemical reactivity. FTIR
analyses of lignin and holocellulose fractions, isolated after acidic hydrolysis of polysaccharides or delignification with
sodium chlorite, indicate that both components are involved in the reactions. Compared to lignin, holocellulose exhibits important
infrared absorptions of about 1,730 cm−1, characteristic of ester or urethane linkages formed. Lower reactivity of heat-treated sawdust is explained by the decrease
in free reactive hydroxyl groups in holocellulose due to the thermal degradation of hemicelluloses, considered more reactive
than cellulose. 相似文献
10.
Yaguang Zhou Masami Fushitani Keiichi Sato Masayuki Ozawa 《Journal of Wood Science》2000,46(6):423-430
This study examined the bending creep behavior of hot-pressed wood during cyclic moisture changes. Sugi (Cryptomerica japonica D. Don) specimens were pressed in the radial direction under six combinations of nominal compressive strain (33% and 50%) and press temperatures (140°C, 170°C, 200°C). Creep tests were conducted at 20°C with three cyclic relative humidity changes between 65% and 95% under 25% of short-breaking stress. The effect of moisture content (MC) change on elastic compliance and mechanosorptive (MS) compliance was investigated. The relation between MS compliance and thickness swelling was studied. The results indicated that total compliance increased over the history of cyclic moisture changes; and its behavior was closely related to the changes in MC and thickness swelling. The total compliance increased during adsorption and decreased during desorption. Elastic compliance increased linearly with MC and was dependent on press temperature and compression. With increasing MC change, MS compliance increased during adsorption and decreased during desorption. The first adsorption led to greater MS compliance than did the subsequent adsorption with the same amount of MC change. In general, the elastic parameterK
E and the MS parameterK
Mincreased with compression and decreased as the press temperature increased. The MS parameterK
M was apparently greater than the elastic parameterK
E. The MS parameterK
M increased with swelling coefficient KSW of the hot-pressed specimen during adsorption and decreased with an increasing shrinkage coefficientK
SH during desorption. 相似文献
11.
Variation of stress wave velocity with MC and temperature 总被引：5，自引：0，他引：5
The effect of moisture content (MC) and temperature on the stress wave velocity and signal frequency spectrum through sapwood
has been investigated. It was discovered that in 2.5 m long green boards only low frequencies were present in the transmitted
signal, while for boards less than 500 mm long, the much higher resonance frequency of the transducer was dominant. For green
boards between 0.5 and 2.5 m both low and high frequency components were present. The frequency spectrum was monitored for
a 540 mm long board over a range of moisture contents and temperatures. When the MC was below 30% the transmitted signal waveform
consisted almost entirely of the transducer resonance frequency, while at higher moisture contents, low frequency components
predominated. The frequency spectrum of the transmitted signal was little affected by temperature, but it was affected by
the type of transducers used. The effect of temperature and moisture content on stress wave velocity was studied and is displayed
in the form of a three dimensional graph.
Received 3 May 1999 相似文献
12.
Wood exhibits a pronounced time dependent deformation behavior which is usually split into ‘viscoelastic’ creep at constant
moisture content (MC) and ‘mechano-sorptive’ creep in varying MC conditions. Experimental determination of model rheological
parameters on a material level remains a serious challenge, and diversity of experimental methods makes published results
difficult to compare. In this study, a cantilever experimental setup is proposed for creep tests because of its close analogy
with the mechanical behavior of wood during drying. Creep measurements were conducted at different load levels (LL) under
controlled temperature and humidity conditions. Radial specimens of white spruce wood [Picea glauca (Moench.) Voss.] with dimensions of 110 mm in length (R), 25 mm in width (T), and 7 mm in thickness (L) were used. The influence of LL and MC on creep behavior of wood was exhibited. In constant MC conditions, no significant
difference was observed between creep of tensile and compressive faces of wood cantilever. For load not greater than 50% of
the ultimate load, the material exhibited a linear viscoelastic creep behavior at the three equilibrium moisture contents
considered in the study. The mechano-sorptive creep after the first sorption phase was several times greater than creep at
constant moisture conditions. Experimental data were fitted with numerical simulation of the global rheological model developed
by authors for rheological parameter identification. 相似文献
13.
The influence of moisture content (MC) on the dynamic modulus of elasticity of structural lumber was investigated using transverse
vibration testing methods. The flexural rigidity (EI) of a transversely vibrating beam was calculated as the modulus of elasticity (E) multiplied by the moment of inertia (I). The increase in E of lumber due to reduction in moisture content was computed by assuming that the flexural rigidity remains constant with
changes in moisture content. Reductions in I due to shrinkage were compensated by the increases in E which led to a proposal for a species-dependent MC adjustment model for modulus of elasticity. The model was validated using
38 mm × 89 mm × 4,290 mm western Canadian Spruce–Pine–Fir dimension lumber evaluated in the “as-received” and “dry” conditions.
Results obtained from the species-dependent model agreed closely with those from the E adjustment equation for dimension lumber given in ASTM D 1990. The results show that the ASTM moisture adjustment procedures
can be used to adjust dynamic E values for changes in moisture content also. 相似文献
14.
为探讨解结晶处理提高酶水解效率的机理,对比研究了高结晶度的微晶纤维素(MCC)和低结晶度的解结晶微晶纤维素(D-MCC)对纤维素酶的吸附过程。结果发现:酶吸附平衡后,样品的XPS和FT-IR分析表明纤维素酶通过酶蛋白的氨基(—NH_2)与纤维素分子链上的羟基(—OH)之间以氢键(C—OH…NH)力吸附在MCC上;相同条件下得到的MCC和D-MCC吸附率曲线的差异表明,底物结构的改善比提高温度更能提高酶吸附率;比较纤维素酶对MCC和D-MCC在35℃下的吸附动力学可知,通过降低底物的结晶度可促进酶吸附,刚性结构的MCC更满足准一级动力学的假设,D-MCC表面结构相对松散,其吸附过程需进一步分析,以得到更适合的动力学方程。 相似文献
15.
通过对黄土高原丘陵沟壑区26年生柠条植物篱不同部位(带间、带前、带内、带后)土壤水分的2年监测,对比分析了柠条植物篱不同部位土壤水分的分布特征及其动态,探讨了柠条植物篱对降水的再分配效应。结果表明:带状柠条植物篱内不同部位间土壤水分物理性质有明显的不同,其中,带内部位土壤密度(0.99 g·cm-3)、非毛管孔隙度(8.77%)、毛管持水量(58.89%)等均优于带间、带前、带后,土壤更为疏松,透水保水性能更良,而带前更加黏性化;随着土壤深度的增加,各部位土壤含水量均表现出逐层降低的趋势,依次为0~20 cm(25.51%±2.28%)40~60 cm(12.96%±1.34%)60~80 cm(10.03%±0.59%)80~100 cm(9.16%±0.81%)100~120 cm(8.76%±1.00%),但越接近表层,带前、带内部位土壤水分含量的优势更明显。根据对土壤水分的有序聚类分析,将柠条植物篱土壤层次划分为弱利用层、利用层和调节层3层,其中,带内的土壤水分利用层(20~120 cm)大于带前、带后(20~60 cm)和带间(40~60 cm),与柠条对土壤水分的主要利用层次相一致,带内的土壤水分调节层在120 cm以下,较带间(80 cm以下)和带前、带后(60 cm以下)均深,反映了带状植物篱带前、带内土壤含水率提高而带后表层土壤含水率降低的分异特征。 相似文献
16.
Experimental determination of the convective heat and mass transfer coefficients for wood drying 总被引：1，自引：1，他引：0
The knowledge of the convective heat and mass transfer coefficients is required for the characterization of the boundary
conditions of the heat and mass transfer equations of a wood drying model based on water potential. A new experimental method
for the determination of the convective mass transfer coefficient is presented. This method is based on the measurement of
the moisture content, and indirectly the water potential, at the surface of a wood specimen at different drying times. Drying
experiments were performed on red pine (Pinus resinosa Ait.) sapwood from nearly saturated to dry conditions at 56 °C, 52% relative humidity and air velocities of 1.0, 2.5 and
5.0 m s−1. The results show that the convective mass transfer coefficient is constant until the wood surface moisture content reaches
about 80% and then decreases more or less gradually as the moisture content decreases further. The convective mass transfer
coefficient increases with air velocity. A regression analysis shows that there is no significant improvement in considering
the water potential gradient near the wood surface when the difference in water potential between the surface and the surrounding
air (ψs − ψ∞) is used to determine the convective mass flux at the surface. Also, ψs − ψ∞ is more appropriate than the water vapour pressure difference (pvs − pv∞) as the responsible driving force of the moisture flux leaving the wood surface. The convective heat transfer coefficient
was determined during the same experiments. A plateau is observed at high values of moisture content corresponding to the
constant drying rate period.
Received 27 February 1998 相似文献
17.
We performed desiccation and storage trials to better under- stand storage behavior of Knema attenuata seeds. Mature seeds with moisture content (MC) of 31% exhibited 73% germination. During the period of desiccation (open lab condition) seeds with MC 23% showed 40% germination. After further drying to MC 21% germination was reduced to 16%. Complete loss in viability resulted when seed moisture was reduced to 18%. The seeds stored at -10°C, 0°C, 10°C and 28±2°C (open lab condition) lost their viability within 10 days. Seeds stored in sealed polythene bags and moist sand retained viability for more days than did seeds stored under all other storage conditions. Sensitivity of seeds to lower temperature and desiccation suggest that the storage be- havior of K. attenuata seeds is recalcitrant. Seeds stored in moist condi- tions can, at best, be stored for a period of two months. 相似文献
18.
Summary The instantaneous profile method was used to establish the boundary desorption curve of the effective water conductivity
function of red pine (Pinus resinosa Ait.) sapwood in the radial and tangential directions from nearly saturated to dry conditions at 18, 56 and 85 °C. The results
obtained demonstrate that the effective water conductivity is a function of moisture content, temperature, and direction of
flow. The effective water conductivity increases by several orders of magnitude (104–105) as moisture content increases from dry to nearly saturated conditions at a given temperature. The effective water conductivity
also increases by a factor varying between 10 and 50 as temperature rises from 18 to 85 °C in the moisture content range considered.
The variation of the moisture content–water potential relationship with temperature can explain part of the temperature effect.
The effective water conductivity was generally higher in the radial direction than in the tangential direction in a ratio
varying from about 1/1 to 3/1 depending on moisture content and temperature. Finally, the flux–gradient relationships obtained
at given moisture contents were found to be linear, confirming the validity of using a moisture flux equation considering
the water potential gradient as the driving force for the experimental conditions considered in the present work. The knowledge
of the effective water conductivity function and of the moisture content–water potential relationship allows the utilization
of a two-dimensional model of moisture movement in wood during drying using the gradient in water potential as the driving
force for drying at temperatures up to 85 °C.
Received 27 February 1998 相似文献
19.
Rohny Setiawan Maail Kenji Umemura Hideo Aizawa Shuichi Kawai 《Journal of Wood Science》2012,58(1):31-37
This study examined the effects of moisture content (MC) on the manufacture of cement-bonded particleboard (CBP) using supercritical
CO2 in the curing process. Significant correlations were found between MC and the performance of CBP: the internal bond strength,
modulus of rupture, and modulus of elasticity values of CBP achieved their maximums, when the MC of boards was approximately
30%. This finding indicated that during the curing phase of manufacturing CBP, a MC of about 30%, which is nearly equal to
the water–cement (w/c) ratio of about 0.34, contributes to improved mechanical properties. However, the mechanical properties
decreased when the MC was below 30%, which had a negative effect on board performance, indicating that carbon dioxide could
not fully react and no carbonation occurred during the curing process. Maintaining a MC of approximately 30% as an ordinary
condition of the cement required in the curing of CBP could promote the reaction of carbon dioxide to form calcium carbonate
(CaCO3), which leads to increased final strength of CBP. Both X-ray diffractometry and thermal gravimetry observation agreed well
with these results and clarified that the increase of CaCO3 content caused by carbonation with increased MC of boards contributed to improving the mechanical properties of CBP. 相似文献
20.
The germination of common alder (Alnus glutinosa (L.) Gaertn.) and downey birch (Betula pubescens Ehrh.) seeds is often poor in bare-root nurseries. The effect of a variety of seed coverings and a few seed pretreatments
on seedling emergence was examined in this study in an attempt to address this problem. Seeds of each species were sown in
trays containing nursery soil, covered with grit, gravel, sand, combinations of these coverings, a hydromulch or a sealed
plastic cloche and then incubated for 6 weeks at 17–20°C. The grit combined with sand or gravel, the hydromulch and the cloche
increased seedling emergence when compared with the standard grit. In another experiment, seeds of each species were fully
imbibed (FI) (>50% moisture content, MC), as per standard practice, or adjusted to target MC (TMC) (30–35% MC) levels, and
then chilled to release dormancy. Some seeds of each MC treatment were primed at 20°C for 2 days following chilling, after
which all seeds were evaluated in laboratory tests and a nursery trial. Germination potential of the FI seeds declined in
the lab tests by the second test date, which was reflected in low seedling emergence in the nursery in birch. The primed FI
seeds of alder germinated most rapidly in the nursery, but other effects were not significant. Seedling emergence was better
in the nursery in response to the TMC than the FI pretreatment in birch.
相似文献
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