Moisture-dependent orthotropic elasticity of beech wood

Elastic material properties are one of the most important material characteristics in mechanical modelling. Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. In order to characterise beech wood as an orthotropic material, all of the independent elastic properties were determined at different moisture conditions. These characteristic properties have never been determined before as a function of moisture content yet are vital to the field of wood modelling. All elastic parameters, except for some Poisson’s ratios, show a decrease in stiffness with increasing moisture content. In comparison to available literature references at a moisture content of ω?≈?12%, the identified values were of the same order of magnitude. The determined material properties can be used to investigate the mechanical behaviour of beech wood structures including different moisture conditions.     

杉木间伐材低浓纸浆流变特性

对不同浓度、温度、打浆度、剪切速率对低浓杉木间伐材机械浆流变特性的影响进行了实验研究,并对不同因素引起浆料表观粘度变化的机理进行了分析。结果表明:浆料浓度、打浆度、温度及剪切速率都会对浆料的表观粘度产生影响。随着浆料浓度的增加,浆料表观粘度呈指数式增加;随温度的升高,浆料表观粘度则缓慢下降;打浆度影响浆料的微观结构,随着打浆度的升高,纸浆的表观粘度呈下降趋势;低浓纸浆的表观粘度则随剪切速率提高而递减。在实验测量范围内,杉木间伐材低浓纸浆为满足幂律关系的非牛顿流体,拟合的本构方程的流变特性指数n<1,因此其在测量范围内为假塑性流体。低浓纸浆流变特性的研究纸浆模塑生产线流送系统设计提供了依据。图12表2参16。     

杉木生长与材性兼优无性系的选择

在江苏宁镇丘陵地区试验研究表明，杉木无性系生长与基本密度性状存在显著的遗传差异。按“两个阶段独立选择法”从供试材料中评选出013、026、027号等3个生长、材性兼优无性系，005、016、024、011号4个生长优、材性较优（与融水优良种源相近）无性系，和029号1代种子园最优家系子代。6年生时，它们的材积比对照（广西融水种源杉木）增加10.6%-144.9%，木材基本密度提高1.16%-20.26%，可作为优质、高产杉木优良无性系在低丘综合治理与开发中扩大应用，研究选出的021、014号等5个优质无性系，材积生长比对照差，但木材基本密度比对照高8.72%-19.68%，可作为育种材料用于杉木材性与生长杂交遗传改良。     

疏水改性对杉木微观力学性能的影响

为提高木材尺寸稳定性,利用烷基烯酮二聚体对杉木进行疏水改性处理,同时运用纳米压痕技术分析评价疏水处理对木材纳米力学性能的影响.结果表明,当处理剂的质量分数为5％、处理时间为30 min时,疏水效果最好,同时最节约成本;疏水处理会降低杉木S2层细胞壁的弹性模量,当处理剂质量分数为5％时影响较小;杉木S2层细胞壁蠕变值会随处理剂质量分数和处理时间的增加呈现上升的趋势.     

Prediction of mechanical properties of Chinese fir wood by near infrared spectroscopy

Mechanical properties and the visible and near infrared (NIR) (350–2500 nm) spectra obtained from longitudinal and transverse face of 155 small clear wood samples of Chinese fir (Cunninghamia lanceolata) were measured, and 103 of them were used to establish calibration models. Calibrations were tested on an independent set (52 samples). Differences between calibrations developed by using the longitudinal and transverse face were small. The calibrations developed by using NIR spectra (350–2500 nm) collected from transverse face were slightly inferior to those developed by using NIR spectra collected from longitudinal face. When reducing the spectral range to between 780 and 1050 nm, the calibrations developed by using NIR spectra collected from longitudinal face were slightly inferior to those developed by using NIR spectra collected from transverse face, and reducing the spectral range causes no decrease in the quality of the models developed using NIR spectra collected from transverse face. Partial lease square (PLS) modeling and test showed that calibrations developed using the visible and NIR spectra from transverse and longitudinal faces and calibrations developed by using the reducing spectral range (780–1050 nm) from the transverse face were moderate, and have a RPD range from 1.51 to 1.90. It is concluded that NIR spectroscopy can be used as an initial screening. __________ Translated from Journal of Northwest Forestry University, 2007, 22(5): 149–154 [译自: 西北林学院学报]     

Creep of Chinese fir wood treated by different reagents

In order to investigate the effect of different reagents on changes of the crystalline region and amorphous region (Matrix) in wood cell walls, the creep behavior of Chinese fir (Cunninghamia lanceolata) wood treated with dimethyl sulfoxide(DMSO) and diethyl amine, sulfur dioxide and dimethyl sulfoxide mixture (1)EA-SO2-DMSO), and the untreated wood at oven-dried, air-dry and water-saturated states during adsorption and desorption processes were all examined in air or in water. The measurements were carded out at ambient temperature and atmospheric pressure. The load is constant with 62 g or 0.607 6 N. The results obtained were as follows: 1) The instantaneous compliance J0 and the creep compliance J of specimens decrystallized with DEA-SO2-DMSO solution were bigger than those of DMSO swollen wood, and the latter was still much bigger than those of untreated wood. 2) For untreated wood, J0 and J increased with equilibrium moisture content (EMC) of wood, but there was not apparent correlation between wood EMC and the relative compliance. 3) Specimens treated with DMSO and DEA-SO2-DMSO mixture were recrystallized after immersion in water, and the degree ofrecrystallization of the former was larger. 4) For oven-dried specimens, the creep compliances in water were bigger than those in air. But for fiber-saturated and water-saturated specimens they were nearly equivalent to each other.     

Method for measuring viscoelastic properties of wood under high temperature and high pressure steam conditions

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.     

杉木冷冻干燥材和气干材液体浸注性的比较研究

A comparative study was conducted on liquid penetration of the freeze-drying and air-drying sapwood and heartwood lumber of plantation Chinese fir （Cunninghamia lanceolata）. The maximum amount of dyeing solution uptake by the capillary rise method was used to evaluate the liquid penetration properties of the treated wood. The pit aspiration ratio was determined by semithin section method. Changes in wood microstructure were investigated using scanning electron microscopy. The results showed that compared with air drying, the freeze drying had a significant effect on liquid penetration of sapwood and heartwood of Chinese fir. The liquid penetration of sapwood is significantly higher than that of the heartwood for both drying treatments. Low pit aspiration ratio and cracks of pits membrane of some bordered pits are the main reasons for increasing liquid penetration after freeze drying treatment.     

Changes of chemical composition and crystalline of compressed Chinese fir wood in heating fixation

The changes in relative crystalline, chemical composition and internal structure of compressed Chinese fir wood after different heating fixations were found strictly related to fixation conditions. The compressed wood powders were fixed either by heating at different temperatures all resulting in a 10% recovery, or by incubating at 180℃ for different periods with subsequent recovery levels. Both X-ray diffraction and infrared absorption of those samples have been measured. Relative crystalline increases at early stage of heating fixation, and then decreased gradually. Hemicellulose and lignin decomposition were induced by the fixation process, especially at 180℃, and lignin was degraded actively. Furthermore, absorbed water was lost after heating, but cellulose did not change markedly. Although different fixation pathways can result in the same recovery level, the major chemical reactions underlying them vary, which is consistent with the difference of fixation mechanisms.     

Effect of different drying methods on liquid penetration of Chinese fir plantation wood

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. __________ Translated from Scientia Silvae Sinicae, 2006, 42(10): 85–90 [译自: 林业科学]     

温度对杉木林土壤呼吸的影响(英文)

Soil samples collected from the surface soil (0(10 cm) in an 88-year-old Chinese fir (Cunninghamia lanceolata) forest in Nanping, Fujian, China were incubated for 90 days at the temperatures of 15°C, 25°C and 35°C in laboratory. The soil CO2 evolution rates were measured at the incubation time of 2, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80 and 90 days. The results showed that CO2 evolution rates of soil samples varied significantly with incubation time and temperature during the incubation period. Mean CO2 evolution rate and cumulative amount of CO2 evolution from soil were highest at 35°C, followed by those at 25°C, and 15°C. Substantial differences in CO2 evolution rate were found in Q10 values calculated for the 2nd and 90th day of incubation. The Q10 value for the average CO2 evolution rate was 2.0 at the temperature range of 15-25°C, but it decreased to 1.2 at 25- 35°C. Soil CO2 evolution rates decreased with the incubation time. The cumulative mineralized C at the end of incubation period (on the 90th day) was less than 10% of the initial C amounts prior to incubation.     

Preparation of Chinese fir wood/MMT nanocomposites and the factors affecting it

The nano intercalation compounding of wood and MMT has important implications for the modification of wood and for the development of new materials. With water-soluble phenol formaldehyde resin as an intermediary, the nanocomposites of Chinese fir (Cunninghamia lanceolata) wood and montmorillonite (MMT) were prepared via three impregnation methods, i.e. normal pres-sure, once and twice vacuum methods. Based on the weight percent gain (WPG) of impregnated wood, the effects of compounding wood and MMT in term...     

Influence of histories on dynamic viscoelastic properties and dimensions of water-swollen wood

The influences of heating history, cooling method, and cooling set on microstructures and the mechanical properties of water-swollen wood were studied by measuring viscoelastic properties and dimensional changes while elevating temperatures between 20°C and 90°C. Both the viscoelastic properties and dimensional changes of waterswollen wood in the first heating process were quite different from those in the other heating processes. The results revealed that the molecular state of green wood around room temperature was stabilized and could not return to this state if drying or heating was carried out. Cooling methods greatly affected the viscoelastic properties, while they hardly affected dimensional changes when the temperature was elevated. Localized stress in the microstructures of water-swollen wood produced by quenching affected the mechanical properties in the heating process, while external stress less than the proportional limit caused by a cooling set had no effect. This revealed that much greater localized stress linked to the instability of waterswollen wood than the external stress in relation to the cooling set occurred. Part of this report was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

杉木间伐材生产胶压木工艺的初步研究

本文探讨了利用小径杉木间伐材生产建筑结构用材——胶压木的生产方法与工艺条件,并研究了各种工艺参数对产品性能的影响,确定了生产胶压木的较佳工艺条件。     

Preliminary study of viscoelastic properties of MAPP-modified wood flour/polypropylene composites

Viscoelastic properties of maleated polypropylene (MAPP)-modified wood flour/polypropylene composites (WPC) were investigated by both a compression stress relaxation method and dynamic mechanical analyses (DMA). Three wood to polymer ratios (40:60, 60:40, and 80:20) and five MAPP loading levels (0, 1, 2, 4 and 8%) were used to study their effects on the viscoelastic properties of MAPP-WPC. The results show that: 1) higher wood to polymer ratio corresponds to higher stress relaxation levels for unmodified WPC. The modification with MAPP has an obvious effect on the stress relaxation of MAPP-WPC at higher wood to polymer ratios (60:40 and 80:20), but almost no effect at the 40:60 wood to polymer ratio. The optimal MAPP loading level for the wood to polymer ratio of 60:40 appears at 1%; 2) the storage modulus reaches its maximum at a MAPP loading level of 1% for wood to polymer ratios of 40:60 and 60:40, while for the 80:20 wood to polymer ratio, a higher storage modulus is observed at higher MAPP loading levels, which is quite consistent with the stress relaxation results. The results suggested that a suitable loading level of MAPP has a positive effect on the viscoelastic properties of WPC at higher wood to polymer ratios. Excessive MAPP loading would have resulted in adverse effects.     

Variation of the viscoelastic properties of wood as a surface finishes substrate

The variation of the viscoelastic properties of wood during exposure to sunlight-type radiation of thin specimens of Abies grandis as a model of the thin surface film of solid timber was followed by thermomechanical analysis (TMA) tests in compression and in tension. For all the types of tests carried out, the TMA traces obtained present only a single inflexion point, which has been assigned to lignin softening. Sunlight radiation was found to have a degrading effect on lignin while the cellulose to hemicelluloses interactions do not appear to be worsened during exposure to the same. The softening temperature variation as a function of sunlight radiation exposure appears to be a parameter which can be used both to observe wood degradation as well as to control the effectiveness and durability of wood stabilization treatments. Received 17 June 1997     

Characterisation and categorisation of the diversity in viscoelastic vibrational properties between 98 wood types

Context   

Increased knowledge on diversity in wood properties would have implications both for fundamental research and for promoting a diversification of uses as material.     

Dynamic viscoelastic properties of wood acetylated with acetic anhydride solution of glucose pentaacetate

 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