Nonisothermal moisture movement in wood

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. __________ 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]     

有限差分法逆求木材导热系数

【目的】提出一种基于有限差分法逆求木材导热系数的方法,以期弥补传统测量法设备复杂、价格高昂的不足,为后续建立导热系数的回归方程提供可靠数据。【方法】运用一维热传导控制方程描述木材升温过程中内部温度变化。以兴安落叶松弦切锯材为对象,通过试验获得锯材沿厚度方向的温度数据(温度检测：使用NEC Remote Scanner Jr． DC3100多点信号巡检仪通过埋入锯材的 T形热电偶获得),采用有限差分逆求法,合理化边界条件后编程求解其在不同含水率、不同温度下的径向导热系数(其中,控制方程离散后的导热系数差分矩阵采用追赶法求解,所有差分方程均在 Matlab2010b软件编程并运行),探讨并分析其随含水率、温度的变化规律。【结果】1)兴安落叶松锯材径向导热系数计算值沿厚度方向存在一定波动性,但其平均值0.1061 W·m －1 K －1(标准差0.0108)符合实际要求,且与理论计算值(0.1109,0.1252W·m －1 K －1)较为接近;2)含水率、温度对导热系数影响显著,且前者影响高于后者(含水率与温度的 F－检验分别为126.9421,99.0083);含水率、温度共同作用对导热系数亦存在显著影响(交互作用的 F －检验为164.2975);导热系数随含水率的升高而增大,随温度的升高亦增大;3)木材材性与内部含水率分布对导热系数的影响较大。【结论】通过试验获得木材内部可靠的温度分布与变化数据后,运用有限差分逆求法可快速、准确获得内部与测温点相对应位置的导热系数,尽管计算值存在一定波动性,但其平均值与理论计算值相吻合,说明运用该方法测算木材导热系数是可行的。相比传统导热系数测量方法,该方法最大优势在于经济且不受试样尺寸限制;同时,可以测算试样内部任意层位置导热系数。今后为提高测算精度,木材内部由于水分迁移产生的热量变化与材性差异应考虑使用该方法;同时,为推广此方法,将程序可视化亦是今后研究的方向。     

木材干燥机理和应用的研究

通过对木材干燥机理和应用的研究，提高木材的干燥速度并选择合理的干燥方法，从而实施科学的木材干燥作业。     

Thermal diffusion of bound water in wood

Summary There are few references in the wood science literature to nonisothermal moisture movement. Some experiments by Voight, Babbitt, and Choong indicate that thermal diffusion in wood may be very significant.Three equations are presented to represent nonisothermal moisture movement through wood in the transverse direction. The first, described in detail in a previous paper, is based upon two driving forces: Soret potential which results in thermal diffusion and chemical potential which results from a gradient of equilibrium relative humidity. All three equations include the same term for Soret potential and, in the second two equations, the thermal-diffusion term was derived by the application of activation theory. The isothermal term in these two equations utilizes moisture content gradient as the driving force and therefore a knowledge of the sorption isotherm is not necessary. The third equation contains an additional term for moisture-content activation to account for the increase in flux with an increased moisture content. All three equations give approximately the same result with the same input data at low moisture contents. The results diverge at high moisture contents and experimental data are required to determine which equation is most representative of the physical phenomenon of nonisothermal moisture movement.     

温度及水分状态对美国红松弯曲弹性模量的影响

应用温度控制系统,对美国红松小试样规格材进行测试,检验木材温度及水分状态对木材弯曲弹性模量的影响.结果表明:温度对木材的抗弯性能具有显著影响,随着温度的升高,木材的抗弯性能逐渐减弱;相同承载条件下,含水率越高,冻结木材的抗弯曲性能越强.对于纤维饱和材,冰点以下其弹性模量随着温度的降低而迅速增加,在冰点以上则增加缓慢;对于非纤维饱和材,其弹性模量受温度影响变化幅度在冰点两侧区别不明显.冻结木材弹性模量相对于常温(20℃)情况下(相对弹性模量)受温度和含水率变化的影响十分显著,而非冻结木材的相对弹性模量对温度变化均表现不敏感.通过建立的相对弹性模量-温度试验模型,能较好地预测不同温度及含水率下的木材弯曲弹性模量相对于常温的变化幅度.该研究为不同温度条件下尤其是低温时的木材弹性模量测量结果修正提供了试验依据.     

Natural weathering of Scots pine (Pinus sylvestris L.) wood treated with epoxidized linseed oil and methyltriethoxysilane

In this study, the effect of natural weathering on the performance of Scots pine sapwood treated with epoxidized linseed oil (ELO) and methyltriethoxysilane (MTES) was investigated by measuring water uptake, colour, check propagation and chemical changes. Boards were impregnated in a pilot-scale autoclave under various conditions. After the treatments, pairs of samples were cut from the treated boards and exposed at 45° angle facing south for a long-term test of natural weathering above ground in Uppsala (Sweden). The effect of solar radiation and humidity on the colour changes, water uptake, check propagation and chemical alterations was assessed during 20 months of exposure. The obtained results can serve as indication for the viability of the treatments. Samples impregnated with low retentions of ELO showed similar performance regarding check propagation and moisture uptake as samples with higher retentions. No significant difference between these samples was found regarding colour change which is mainly caused by blue stain fungi on the surface. In opposite, samples treated with MTES exhibited no consistent water uptake and check propagation unproportioned to the applied retentions. The spectra of ELO- and MTES-treated wood after weathering showed a significant decrease of the peak at 1510 cm^?1 indicating delignification of wood surface caused by weathering.     

Calorific values and ash contents of different parts of Masson pine trees in southern China

Calorific value of plants is an important parameter for evalu- ating and indexing material cycles and energy conversion in forest eco- systems. Based on mensuration data of 150 sample sets, we analyzed the calorific value （CV） and ash content （AC） of different parts of Masson pine （Pinus massoniana） trees in southern China using hypothesis testing and regression analysis. CV and AC of different tree parts were almost significantly different （P〈0.05）. In descending order, ash-free calorific value （AFCV） ranked as foliage 〉 branch 〉 stem bark 〉 root 〉 stem wood, and AC ranked as foliage 〉 stem bark 〉 root 〉 branch 〉 stem wood. CV and AC of stem wood from the top, middle and lower sections of trees differed significantly. CV increased from the top to the lower sections of the tnmk while AC decreased. Mean gross calorific value （GCV） and AFCV of aboveground parts were significantly higher than those of belowground parts （roots）. The mean GCV, AFCV and AC of a whole tree of Masson pine were 21.54 kJ/g, 21.74 kJ/g and 0.90%, re- spectively. CV and AC of different tree parts were, to some extent, cor- related with tree diameter, height and origin.     

Effect of high temperature heat treatment on pH value of Masson Pine wood

Heat-treated wood has good dimensional stability,corrosion resistance and visual quality,but it is prone to mold,which limits its application.Based on the pH value of heat-treated wood,this study examines the factors affecting the pathogenesis causing heat-treated wood mold.Normally,the pH value of the heat-treated wood is between 4.38 and 5.10,which is suitable for the growth of mold.However,the pH of the heat-treated copper-containing material is between 6.63 and 7.12,which deviates the treated wood from the comfortable growth conditions for the mold,thereby reducing the occurrence of mold.     

Impact of moisture content on dynamic mechanical properties and transition temperatures of wood

The dynamic shear modulus and the loss modulus of Betula alba, Ulmus parvifolia, Quercus robur, Acer platanoides, Tilia cordata, Fraxinus excelsior and Pinus sylvestris wood were measured using an inverted torsion pendulum within a wide temperature range. The glass transition temperature of the lignin–carbohydrate complex and the decomposition temperature of the wood cellulose were estimated. The temperature band from 170°C to 240°С shows the transition of the lignin–cellulose complex from the glassy to the rubbery state. Mechanical properties of different types of wood are affected by moisture and anatomical differences, but glass transition and decomposition temperatures are the same. More than 5% of moisture in the wood stored at normal conditions were found. After drying, the increase of dynamic shear modulus of wood over the entire region of the glassy state was observed. The intensity of maximum peak of dynamic loss modulus is also increased due to activation of the segmental motion of macromolecules of the ligno-carbon complex. The decomposition temperature of the cellulose crystallites was unchanged for specimens containing moisture and for dried specimens.     

Hygroexpansion of wood during moisture adsorption and desorption processes

In order to investigate the shrinking and swelling behavior of wood at a non-equilibrium state, the moisture sorptlon processes of wood under constant and changing conditions were studied. For the static sorption experiment, Chinese fir （Cunninghamia lanceolata） specimens were subjected to the adsorption processes at 25℃, 10 different relative humidity environments and the moisture contents were measured at distinct time intervals of adsorption processes. For the dynamic sorption experiment, the specimens were exposed to periodically and linearly varying relative humidity between 45% and 75% at 25℃. Moisture content as well as radial and tangential dimensional changes in response to the changing relative humidity were measured. The main results from the experiments indicated that： the moisture sorption isotherms of Chinese fir at equilibrium state and different stages of adsorption processes could be characterized by S-shape curves. From the non-equilibrium state to the equilibrium state, the sigmoid moisture sorption isotherms changed from smooth, gradually increasing values to a steep rise at 100% humidity. Furthermore, under dynamic conditions with a constant temperature and a linearly and periodically varying relative humidity, the moisture content as well as radial and tangential dimensional changes of the specimens generally waved but lagged behind the relative humidity change.     

Bending strength and toughness of heat-treated wood

The load-deflection curve for static bending and the force-time curve for impact bending of heat-treated wood were examined in detail. The effect of oxygen in air was also investigated. Sitka spruce (Picea sitchensis Carr.) was heated for 0.5–16.0h at a temperature of 160°C in nitrogen gas or air. The dynamic Young's modulus was measured by the free-free flexural vibration test, the static Young's modulus and work needed for rupture by the static bending test, and the absorbed energy in impact bending by the impact bending test. The results obtained were as follows: (1) The static Young's modulus increased at the initial stage of the heat treatment and decreased later. It decreased more in air than in nitrogen. (2) The bending strength increased at the initial stage of the heat treatment and decreased later. It decreased more in air than in nitrogen. (3) The work needed for rupture decreased steadily as the heating time increased. It decreased more in nitrogen than in air. It is thought that heat-treated wood was more brittle than untreated wood in the static bending test because W₁₂ was reduced by the heat treatment. This means that the main factors contributing to the reduction of the work needed for rupture were viscosity and plasticity, not elasticity. (4) The absorbed energy in impact bending increased at the initial stage of the heat treatment and decreased later. It decreased more in air than in nitrogen. It was concluded that heat-treated wood became more brittle in the impact bending test becauseI ₁₂ andI ₂₃ were reduced by the heat treatment.     

土壤水分梯度对阔叶红松林结构的影响

2002年8月,在吉林省白河林业局红石林场(12755E,4230N),沿着一个山坡设置了一个长宽为112m8m、包含14个样方的样带。调查了群落结构、0-10cm和10-20cm的土壤含水量、枯落物现存量及其C、N、P含量,主要树种的叶片和枝条的C、N、P含量。沿着山坡的不同位置土壤含水量的不同导致阔叶红松林的群落结构发生变化。蒙古栎的比例随着土壤含水量的下降而逐渐升高,而其他主要阔叶树种则逐渐减少乃至消失。枯落物的水分变化趋势与土壤一致。在不同坡位枯落物的分解状况不同,干重差异显著。坡下枯落物含量较坡上的丰富,部分原因在于群落结构的变化。水分和养分含量的变化影响了枯落物的成分、降解及其养分的释放,进一步影响了林木的生长速度和林分结构并最终影响整个生态系统。图7表2参14。     

马尾松天然林病虫害调查

通过对马尾松Pinus massoniana Lamb天然林及其速丰试验林、针阔混交天然林的调查，计有病虫19种，其中病害6种，害虫13种，天敌昆虫15种。调查表明，病虫种类和被害率，试验林较低，施肥区最低，混交林明显比纯林少。     

黔灵公署马尾松枯死原因的初步调查

本文通过对黔灵公园12个主要景点的马尾松林分调查和17株被害木的解剖，85株样木的取样，255个样本的镜检和分析，初步认为公园内马尾松枯死是诸多因素综合作用的结果，特别是以拟松材线虫Bursaphelenchus mucronatus与松墨天牛Monochamus alternatus的危害加速了马尾松树的死亡，马尾松平均被害株率，平均致死株率分别为21．7％，4．48％，提出了防治建议。     

Determination of wood moisture properties using a CT-scanner in a controlled low-temperature environment

Abstract

The aim of the present work was to examine an advanced image-processing algorithm for moisture content (mc) calculation and also to use this algorithm to analyse moisture loss data for low temperature drying. Since wood starts to shrink below the fibre saturation point during drying, the geometrical shape of the wood piece will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight mc. The results show that the algorithm for the dry weight mc on density data from the CT-scanning during low-temperature drying in the climate chamber is a powerful tool for analysing the moisture loss inside the wood piece. This method can make it possible to get a higher quality on the product.     

木材干燥过程含水率和温度变化的数学模型研究

木材干燥过程存在着热质互换和能量的转移,这为从热力学的角度研究木材干燥过程提供了前提条件,因此提出利用热力学原理分析木材干燥过程含水率和温度变化规律的数学模型.首先建立描述含水率和温度变化的高阶非线性偏微分方程组,然后采用有限元分析原理将方程组离散化,再经过一系列数学运算得到方程的收敛解,具体方法为牛顿迭代法,最后通过对木材含水率和温度变化情况仿真结果的分析,验证该方法的可行性及数学模型的准确性.     

Effect of steam pretreatment on wood moisture content and characteristics of vacuum drying

The effects of high temperature steam pretreatment on the change in wood moisture content (MC) and characteristics of vacuum drying were investigated in this study. Poplar and manchurian walnut woods were pretreated with high temperature steam at 100°C and 140°C, prior to vacuum drying. A comparison of the characteristics of vacuum drying between steam pretreated wood and untreated wood was carried out. The results show that during steam pretreatment, the MC of wood decreased within a few hours. The reduction of MC varied with the temperature; the higher the temperature, the faster the MC dropped. During the vacuum drying stage, the rates of drying of pretreated samples were higher than those of untreated samples when MC was below the fiber saturation point. Furthermore, the total drying time of samples treated at a steam temperature of 140°C was lower than that of untreated samples. Therefore, a vacuum procedure after steam pretreatment can effectively shorten the drying time when drying wood.     

防治松材线虫病的室内药剂筛选

采用40％克线磷乳油、3％克百威颗粒剂、35％阿维菌素乳油及4．5％高效氯氰菊酯乳油4种药剂，分别以6种浓度梯度对松材线虫进行室内药剂生测，初步筛选出防效较好的药剂为40％克线磷乳油，其最佳的使用浓度为200mg／L。     

Evaluation of wood cutting forces in dry and wet conditions by small-scale chipping tests applying different analysis methods

ABSTRACT

The aim of this paper is to study the effect of high moisture content in comparison to dry timber on the resulting cutting forces based on experimental small-scale chipping tests. Therefore, a wood chipper for single cuts is designed and different species of Austrian locally growing trees are utilized. The test specimens are investigated in almost dry and soaked wet conditions. The resistance of wood is measured utilizing a force sensor and the signal during the cutting process is subsequently analysed by two different methods. The results reveal that the mean value of the acting force during cutting is 38–81% minor compared to the maximum force. Even though the peak of the dynamically acting load is measured for just a comparably small time range, it reveals an impact on the fatigue behaviour of the tool as well as the tool supporting material. Hence, an approach of evaluated load spectra is applied to include the load distribution of the chipping process. The effect of dry and wet wood on the cutting resistance is examined, whereby wood exhibiting a high moisture content of 30–40% changes the acting load up to 98%, depending on the method of analysis.     

松树根际高效解磷青霉发酵条件的优化

土壤磷素供应不足是导致松林地力衰退的重要因素之一,通过研制解磷微生物肥料来分解土壤中难溶磷是改善土壤磷素供应状况的有效途径.在分离获得两株解磷微生物(瓜纳卡斯特青霉JP-NJ2菌株和嗜松青霉JP-NJ4菌株)的基础上,通过正交试验分别对瓜纳卡斯特青霉JP-NJ2菌株及嗜松青霉JP-NJ4菌株的液体发酵培养基部分组分进行了优化,并对其适宜发酵条件进行了研究,得出JP-NJ2菌株适宜发酵培养基为蔗糖10 g+ (NH4)2SO4 0.3 g+MgSO4·7H2O 0.3 g+NaCl 0.3 g+KCl 0.5 g+FeSO4·7H2O 0.03 g+MnSO4·7H2O 0.03 g+卵磷脂0.4 g+CaCO3 5 g+蒸馏水1 000 mL,初始pH 5.0,发酵培养周期为9d,溶氧量为80％;JP-NJ4菌株适宜发酵培养基为蔗糖8 g+ (NH4)2SO40.5 g+MgSO4·7H2O 0.3 g+NaCl0.3 g+KCl0.7 g+FeSO4 ·7H2O 0.03 g+MnSO4 ·7H2O 0.03 g+卵磷脂0.8 g+CaCO3 5 g+蒸馏水1 000 mL,初始pH 6,培养周期为11d,溶氧量为90％.研究结果为两株解磷青霉工业化生产提供了参考.