Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

European Journal of Wood and Wood Products - Surface tension of solid wood surfaces affects the wettability and thus the adhesion of various adhesives and wood coatings. By measuring the contact...     

Monitoring wood moisture content using the WETCORR method

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Verfolgen der Holzfeuchte mit der WETCORR- Methode. Teil 2. Kalibierung und überprüfung

     

Influence of wood moisture content on bending and shear stiffness of cross laminated timber panels

The bending and shear stiffness of cross-laminated timber (CLT) made from softwood depend on the moisture content of the panel. In principle, the stiffness properties drop with increasing moisture content within the hygroscopic range. However, swelling provokes closing of open gaps of the middle layers and leads to an apparent increase of stiffness due to internal friction. This increase in stiffness is only relevant for low deflections and can provoke misinterpretation of measuring results when deriving stiffness properties of CLT by means of dynamic methods such as modal analysis. Drying, on the other hand causes cracking within CLT, which manifests itself in a distinct reduction of the bending stiffness perpendicular to the grain direction of the face layers. Calculating bending stiffness of CLT perpendicular to the grain direction of the face layers by means of the compound theory not taking into account the face layers therefore is a common and correct procedure.     

Small resistive wood moisture sensors: a method for moisture content determination in wood structures

The wood moisture content influences the service life of wood structures since wood is susceptible to decay by rot fungi if it is exposed to high moisture contents during long periods of time. In rain exposed structures, the moisture content close to end grain surfaces and joints can be significantly higher than the average moisture content, but moisture content determinations at such locations require small moisture content sensors. This paper presents small resistive moisture content sensors fastened by electrically conductive adhesive. The relationship between moisture content and electrical resistance was determined for Norway spruce (Picea abies (L.) Karst.) for a wide range of moisture conditions achieved both by equilibrating specimens over saturated salt solutions and by the pressure plate method. The error, i.e. the difference between the gravimetric moisture content and the moisture content from the regression equation, increased with increasing moisture content. Neither the wood type (heartwood/sapwood) nor the growth rate (southern or northern Sweden) influenced the resistance-moisture content relationship.     

木材强度无损检测的音频信号分析

介绍了利用快速傅立叶变换(FFT)分析木材受冲击激励后产生的响应信号频谱特征,探讨了木材强度与响应频谱特性和木材物理参数的相关性,提出了新的提取共振频率方法。     

含水率对木质材料切削力影响的研究

采用硬质合金锯齿刀具分别对三种实木(杉木、樟子松、水曲柳)和两种人造板(中密度纤维板、刨花板)进行闭式切削实验,研究不同含水率对木质材料切削力的影响。实验结果表明:含水率对木质材料切削力的影响显著。随着含水率的增加,杉木的主切削力和法向力都呈减小趋势,而樟子松和水曲柳的主切削力皆为先增大后减小,当接近纤维饱和点含水率时主切削力达到最大。对人造板,在5%～18%含水率范围内,随着含水率的增加,主切削力和法向力都不断增大。     

Novel polarization-type moisture meter for determining moisture content of wood above fibre saturation point

Resistance-type wood moisture meters are not reliable at moisture contents above the fibre saturation point. The aim of this study was to develop an alternative polarization-type wood moisture meter and to analyse the different calibration methods of this moisture meter in comparison with the traditional resistance-type wood moisture meter calibration method. A significant decrease (up to 3.5% of moisture content) in the tolerance interval of a single measurement was attained by introducing and integrating the original electrical wood charging number into the calibration model of the novel wood moisture meter with electric polarization effect for a high wood moisture content (MC) above 100%. The tolerance interval convergence was analysed using the traditional method of increasing the number of measurements and averaging the results and was compared to the novel method of compensating for random deviations, as used in this study. To calibrate the wood moisture meter, the wood’s electrical resistance and electrical capacitance timelines during the electrical charging cycle were registered in real time (online) with a preselected measuring speed and saved to the microcomputer memory. When the measurements were completed, the measurement data was processed by the device’s microcomputer. This novel polarization-type moisture meter allows for the moisture content of specific tree species to be predicted by selecting a suitable calibration model from a set of eight. The novel wood moisture meter can be used to monitor wood drying and to determine seasonal variations in the moisture content of growing trees.

     

含水率对落叶松材动态弹性模量的影响

在不同含水率下,利用应力波、纵波共振和横向弯曲振动三种方法对落叶松材试件进行了检测试验,研究了木材含水率对动态弹性模量等的影响,不同含水率下测试参数和动态弹性模量之间关系以及三种测试方法所得动态弹性模量之间的相关性.结果表明,含水率对动态测试结果影响显著;含水率对各测试参数和动态弹性模量之间的相关性影响不大;所得到的三个动态弹性模量之间相关程度相当高.     

Tokay wines as scavengers of free radicals (an EPR study)

Wines are increasingly considered to be beneficial to health, so we expanded our previous investigations of red and white wines to Tokay wines, employing electron paramagnetic resonance spectroscopy (EPR). Four sources of free radicals were used in scavenging experiments: thermally decomposed radical initiators, K₂S₂O₈ and 2,2′-azo-bis(2-methylpropionamidine) hydrochloride (AAPH), as well as the cation radical of 2,2′-azino-bis(3-ethylbenthiazoline-6-sulfonic acid) salt (ABTS), and the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). The radical-scavenging abilities of 30 samples of Tokay wines from the Slovak region were compared with 10 samples of red and 10 samples of white wines originating from various regions. Tokay wines show a very good scavenging ability, positioned between white and red wines expressed as trolox equivalent antioxidant capacities (TEAC) with 14.8 ± 1.5 for red, 8.1 ± 3.4 Tokay and 3.3 ± 1.6 for white wines in mmol dm⁻³ wine.     

Influence of moisture content of wood on sound velocity and dynamic MOE of natural frequency- and ultrasonic runtime measurement

This study comprises the analysis of the influence of the moisture content of wood on the dynamic properties—sound velocity and dynamic MOE (considering the density)—of green and dry sawn timber. The main objective was to find applicable functions or factors for the adjustment of the determined properties on the reference condition (moisture content u=12%) for the moisture content range below and above fiber saturation. Therefore, two dynamic measurement methods—measurement of the natural frequency and ultrasonic runtime—were considered. Possible differences in the results, pros and cons of both methods should be identified on the one hand. On the other hand, the applicability of already published moisture adjustments to the given data of both methods should be proved.     

Mechano-sorptive behaviour of wood and its use for moisture content determination

The enhanced ability of small wooden beams to deform under decreasing moisture content conditions when subjected to constant bending and torsional stresses, has been studied. Initially green samples of Eucalyptus grandis and Pinus sylvestris were used. The purpose of the study was to determine whether the increased deformation during desorption or drying conditions, as reported by other workers, could be used as an indicator of the instantaneous average moisture content. For both species, relative torsional and bending deformation (RTD and RBD) increased with decreasing moisture content and the deformation also increased with increasing temperature. In the case of E. grandis both RTD and RBD could be used to determine moisture content under drying conditions while for P. sylvestris the relationship between RBD and moisture content was more pronounced than that between RTD and moisture content.     

Detection of environmentally persistent free radicals at a superfund wood treating site

Environmentally persistent free radicals (EPFRs) have previously been observed in association with combustion-generated particles and airborne PM(2.5) (particulate matter, d < 2.5um). The purpose of this study was to determine if similar radicals were present in soils and sediments at Superfund sites. The site was a former wood treating facility containing pentachlorophenol (PCP) as a major contaminant. Both contaminated and noncontaminated (just outside the contaminated area) soil samples were collected. The samples were subjected to the conventional humic substances (HS) extraction procedure. Electron paramagnetic resonance (EPR) spectroscopy was used to measure the EPFR concentrations and determine their structure for each sample fraction. Analyses revealed a ～30× higher EPFR concentration in the PCP contaminated soils (20.2 × 10(17) spins/g) than in the noncontaminated soil (0.7 × 10(17) spins/g). Almost 90% of the EPFR signal originated from the minerals/clays/humins fraction. GC-MS analyses revealed ～6500 ppm of PCP in the contaminated soil samples and none detected in the background samples. Inductively coupled plasma-atomic emission spectrophotometry (ICP-AES) analyses revealed ～7× higher concentrations of redox-active transition metals, in the contaminated soils than the noncontaminated soil. Vapor phase and liquid phase dosing of the clays/minerals/humins fraction of the soil with PCP resulted in an EPR signal identical to that observed in the contaminated soil, strongly suggesting the observed EPFR is pentachlorophenoxyl radical. Chemisorption and electron transfer from PCP to transition metals and other electron sinks in the soil are proposed to be responsible for EPFR formation.     

Resistance based moisture content measurements on native,modified and preservative treated wood

Resistance characteristics were determined for a total of 27 wood-based materials containing native soft- and hardwoods, differently modified timbers and preservative treated timbers. A functional relation between measured electrical resistance and gravimetrical wood moisture content (MC) was established in a range between 15 and 50 % MC. Most precise MC estimation was found for salt-treated timber (±2.5 %), followed by native timber (±3.5 %) and modified timber (±7 %) in the hygroscopic range. As expected, preciseness decreased above fiber saturation, but was still sufficient for native timber (±8 %) and preservative treated wood (±5 %) at approx. 50 % MC.     

烟丝含水率对细支卷烟的影响

考察了烟丝含水率对细支卷烟烟支物理性能、烟支内部烟丝结构分布、烟支静燃速率、抽吸时燃烧锥落头率、卷烟主流烟气释放和感官质量的影响。结果表明,细支卷烟烟丝含水率为11.5%~13.8%,在卷烟单重一致的情况下,烟丝结构分布、卷烟抽吸时燃烧锥落头率以及感官抽吸品质受烟丝含水率影响大。烟丝含水率增大,烟丝抗造碎性能增强,烟支中大尺寸烟丝所占比例增加,烟末减少,卷烟抽吸时燃烧锥落头现象明显减轻;烟丝含水率从11.5%增加到12.9%,燃烧锥落头率可从65%降低至30%。烟丝含水率过高会导致卷烟烟气浓度减小,满足感降低。此外,烟丝含水率增大,细支卷烟的烟支硬度、烟支静燃速率、烟气焦油和烟碱释放量也会发生细微的变化。综上,建议细支卷烟生产过程中烟丝含水率尽量控制在12.5%~12.9%。     

Measurement of wood grain angle, moisture content and density using microwaves

In many wood products manufacturing processes, it is important to ensure that the physical properties of the raw material lie within acceptable ranges and are measured reliably. It is also important for practical use that the measurement process is robust, low-maintenance, fast and preferably non-contacting. This paper describes the development and demonstration of a microwave system for simultaneously identifying wood grain angle, moisture and density. The method involves propagating a microwave beam through the wood and measuring the resulting depolarization, attenuation and phase shift. The wood physical properties can then be identified from these measurements. In a series of measurements, the prototype microwave system successfully identified wood grain angles for hemlock and Douglas fir respectively with standard errors of 0.9° and 2.5° (measured range = -90° to +90°), moisture content 1.2% and 1.9% (measured range = 7–28%), moisture density 3.7 kg/m³ and 7.9 kg/m³ (measured range = 40–150 kg/m³, and dry density 16 kg/m³ and 30 kg/m³ (measured range = 325–625 kg/m³).     

水分含量对新鲜干酪贮藏特性的影响

对水分含量不同的4组干酪进行贮藏期水分含量、水分活度、pH、酸价、TBA值测定和感官评定。结果表明:干酪水分含量与水分活度随贮藏期呈递减趋势,并且呈正相关关系;酸价随着贮藏期的延长先增加后减少;pH则相反,呈先下降后上升的趋势;TBA值呈逐渐上升趋势。表明水分含量低的干酪,其耐贮藏性较好。感官特征测定在贮藏的第18d开始,干酪逐渐开始出现腐败特征,水分含量较低的干酪感官评分高。