Real-time determination of wood moisture content using dielectric properties: A case study on Falcataria falcata

There has been a longstanding interest in developing a fast and accurate method for measuring moisture content in wood. The gravimetric method that is commonly used today is a widely accepted industrial standard but it is time consuming. In this study, we tested and evaluated Mantex Desktop Scanner that is based on dual energy X-ray absorptiometry as a potential technique for fast and accurate determination of moisture content at different temperatures in wood chips of Pinus sylvestris, Picea abies and a variety of mixtures thereof. The results of the study give similar results as the gravimetric method when determining the moisture content in wood. They further show that there was no significant influence on the result if samples were measured while frozen or at room temperature.

The paper describes a low-invasive experimental apparatus designed for the accurate determination of mechanical deformation and moisture content (MC) relationship on macroscopic wood samples. The device is particularly indicated for monitoring wooden handwork whose mechanical deformation is especially critical in relation to its role such as, for example, works of art or architectural works. The MC of wood is measured with a portable single-sided NMR probe and mechanical deformation by a fiber Bragg grating optical sensor. The data obtained are of high accuracy, despite the dimensions of the sample. The methodology provides an effective tool for investigating the dynamic relation between environmental relative humidity, MC, and shrinking-swelling of wood. Adsorption results collected for longitudinal deformation in silver fir (Abies alba Mill.) are presented to show the sensitivity of the optical sensor. Interesting findings include the detection of two different mechanisms of elongation and the time evolution of water mobility versus hydration and strain.

Laboratory studies have shown that wood has hygroscopic properties. When used as a construction material in buildings, it can thus influence indoor relative humidity and temperature. Ventilation can affect indoor climate if the temperature differ between indoor and outdoor air. The coating of indoor wood may also affect its hygroscopic properties. Few studies of wood in real buildings have been conducted. The main aim of this experimental study was to explore the association between moisture content in indoor air and wood in two classrooms. The floor plan of the two classrooms was identical. In one classroom, all wood surfaces were untreated, whereas, in the other, they were treated with a transparent varnish. Sensors measured indoor air relative humidity, moisture content in the wood, and temperature in the air and wood in both classrooms. Linear regression analysis was performed to explore possible associations. Strong positive associations between indoor air relative humidity and the moisture content in wood in the untreated classroom were found. Weak positive associations were evident in the classroom with treated wood. Ventilation reduced these associations.

ABSTRACTThe estimation of the pixel-wise distribution of the moisture content (MC) in wood using X-ray computed tomography (CT) requires two scans of the same wood specimen at different MCs, one of which is known. Image-processing algorithms are needed to compensate for the anisotropic distortion that wood undergoes as it dries. An alternative technique based on dual-energy CT (DECT) to determine MC in wood has been suggested by several authors. The purpose of the present study was to evaluate the hypothesis that DECT can be used for the determination of MC in real time. A method based on the use of the quotient between the linear attenuation coefficients (μ) at different acceleration voltages (the so-called quotient method) was used. A statistical model was created to estimate the MC in solid sapwood of Scots pine, Norway spruce and brittle willow. The results show a regression model with R2 > 0.97 that can predict the MC in these species with a RMSE of prediction of 0.07, 0.04 and 0.11 (MC in decimal format) respectively and at MC levels ranging from the green to the totally dry condition. Individual measurements of MC show an uncertainty of up to ±0.4. It is concluded that under the conditions prevailing in this study, and in studies referred to in this paper, it is not possible to measure MC with DECT.

Wooden façades are gaining in importance. Thermally modified wood is becoming one of the preferred materials for claddings. In spite of the fact that façades made of thermally modified wood have been in use for more than two decades, reports about long-term monitoring have been sparse. The results of three-year monitoring of a façade made of thermally modified wood in Ljubljana are reported. Moisture content measurements of thermally modified façades were taken at 22 locations and compared to the moisture content of untreated Norway spruce wood. Temperature and relative humidity were recorded in parallel. The moisture content of the wood was compared to the average relative humidity before the measurements. The results confirm the lower moisture content of thermally modified wood in comparison to reference Norway spruce. The moisture content of the wooden façade could be best correlated with the average relative humidity and temperature 48 h before the wood moisture content measurement was taken.

Simulation of moisture transfer during wood vacuum drying

The influence of thermal treatment on moisture exchange between wood and natural environment with variable air parameters as well as on dimensional stability of wood samples was investigated. The experiments were carried out with oak wood samples indoors and outside. The thickness of samples was 30<strong> </strong>mm, width was 30<strong> </strong>mm and length was 20<strong> </strong>mm; conventional density varied from 500<strong> </strong>kg/m<sup>3</sup> to 580<strong> </strong>kg/m<sup>3</sup>. Initially, the wood was air-dried down to 7<strong> </strong>%<sub> </sub>–<sub> </sub>9<strong> </strong>% of moisture content. In order to decrease possibility of the both moisture absorption and evaporation during wood application thermal treatment must be applied. Due to that the samples were heated at temperature of 60, 80, 100 and 120<sup> </sup>ºC for 24, 48, 72 and 96 hours. The moisture content of wood and its variations after thermal treatment depends on the both heating temperature and duration. The higher temperature and the longer heating duration, the lower wood hygroscopicity can be achieved. The effect of thermal treatment on the moisture content and its changes were observed for wood samples stored indoor and outside. In dependence of thermal treatment conditions moisture content in wood samples independently on storing conditions (indoor or outside) can decrease down to 30<strong> </strong>% compare to the untreated ones. The change of moisture content<em> </em>during various seasons after 24 hours of storing indoor decreases down to 60 %, while outside that is only 39 %. Dimensional stability of wood samples also depends on the both thermal treatment temperature and duration. The higher treatment temperature and the longer duration, the higher dimensional stability can be obtained. The heat treatment of oak wood samples at selected regimes allows to decrease values of shrinkage and swelling coefficients down to 40 %.<p>DOI: <a href="http://dx.doi.org/10.5755/j01.ms.19.1.3825">http://dx.doi.org/10.5755/j01.ms.19.1.3825</a></p>

Root segments of loblolly pine (Pinus taeda L.) were decayed by Heterobasidion annosum (Fr.) Bref. (=Fomes annosus (Fr.) Karst.) over a broad range of wood (33–317%) and soil (36–259%) moisture contents in modified soil-block tests. Maximum weight loss occurred at 50–286% wood moisture content. Decay was inhibited at wood moisture contents over 290%. Water moved rapidly into the root segments by capillarity, and some decay occurred within 2 weeks. Water uptake was faster in inoculated segments than in noninoculated segments at a soil moisture content of 172% of the 0.2 bar (1 bar = 100 kPa) moisture content.

The novelty of this study is the development of an accurate wood moisture content (MC) estimation method based on a relatively brand-new, non-destructive testing technique (drilling chips extraction). The method is especially important in the assessment of existing timber structures, where non-destructive testing (NDT) results are affected by wood MC and should be adjusted to a reference MC, usually 12%. In the assessment of timber structures, it is not possible to determine MC by oven drying method and this should be estimated. Electrical resistance and capacitance are the conventional methods used for MC estimation. This research work aims to present an accurate MC estimation method based on the drilling chips extraction technique. For that, 99 specimens (90 × 65 × 38 mm3) from three softwood and hardwood species covering a wide range of densities (from 355 to 978 kg m−3) were tested after conditioning at five different MCs (5%, 10%, 15%, 20%, 25%). The Wood Extractor device based on the drilling chips extraction technique was used. The mass of the chips collected (drilling residue) from each drill was recorded. The results show that the MC of the chips extracted was statistically significantly different than the MC of the specimen and cannot be directly used as MC determination. However, the chips MC can be used as an estimator of specimen MC with high determination coefficients (R2 from 71% to 86%). As the main result, models to estimate density directly adjusted to a reference 12% MC from the wet and dry mass of chips extracted were developed with an R2 of 98%. In sum, the drilling chips extractor is a dependable and straightforward method to estimate MC and density from only one measurement. Density adjusted to a reference 12% MC can be directly estimated from a single model.

"Spruce wood was ground under certain fixed conditions to achieve data for interpretation of the grinding mechanism. For this purpose, wood moisture content, wood feeding rate and grindstone peripheral speed were given five, three and two different levels, respectively. The data obtained by application of a laboratory grinder were accordingly most reliable, because the grinder was run under well controlled conditions, and the wood samples represented one and the same wood quality, but at five moisture content levels. The grinding zone temperature was measured at the outlet from the grinding zone, and accordingly it would indicate the average grinding zone temperature. The grinding model suggests that the energy specific fibre production ( w/Pt) evaluated at various power friction levels (Pc/Pt) would help understanding the wood grinding mechanism. The energy specific fibre production showed significant dispersion, when evaluated as a function of the power friction. However, detailed analysis of the data revealed that there could be two linears, one representing moisture saturated wood, and one representing fresh wood that also contains free water in the lumina. Surprisingly, this linear also included data representing air-dry wood. Increasing wood moisture ratio from 0.2 kg to 1.4 kg per kg o.d. wood decreased the average grinding zone temperature significantly from about 98° to 88 °C. Further, there was roughly a difference of 8–12° C in grinding zone temperature due to the wood moisture, when evaluated as a function of the force friction coefficient (Ft/Fc). The two highest moisture ratios resulted in a low-level linear, as the other moisture ratios produced a high-level linear. The wood moisture content seems to affect the grinding process in different ways due to the moisture content level. Since moisture is absorbed in the fibre wall material and evidently linked to various lignin and cellulose components by hydrogen bonds, it will affect the grinding in a certain mode. However, the air-dry wood sample seemed to act as the fresh wood samples, which cannot be explained properly unless also considering fibrillation and fibre properties."

Ultrasensitive moisture content characterization of wood samples by a cylindrical cavity resonator

ABSTRACTBranchwood is being exploited as a supplement to stemwood in wood products manufacturing, and the wood’s bending strength properties are vital for structural and non-structural applications. Non-destructive methods are being adopted in determining wood properties, and wood density and moisture content are two variables that could be useful. This study assessed the influence of density and moisture content (MC) on the Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) of branch and stem woods of Entandrophragma cylindricum (sapele) tested at two moisture levels (10 ± 4% MC and 17 ± 3% MC). Density was determined in accordance with ISO 3131. To determine bending strength properties, BS 373 was followed, using an INSTRON TCM Machine with a crosshead speed of 6.6 mm per minute. Results indicated that branchwood has higher density than its stemwood counterparts. MOE and MOR of both wood types were significantly higher at 10 ± 4% MC than their counterparts at 17 ± 3% MC. Differences in MOE and MOR between the wood types were not significant, although the branchwood had 87% and 93% respectively of the MOE and MOR of stemwood. From the two-way ANOVA, MC had a significant effect (P < 0.05) but wood type and the interactions of wood type and MC did not have a significant effect on MOE and MOR of stem and branch woods. The predictive powers of MC and density as a combined predictor for estimating bending strength properties were higher for branchwood than stemwood. Although density of E. cylindricum branchwood was significantly higher than its stemwood counterpart that did not translate into significant differences between MOE and MOR of branchwood and stemwood.

The moisture content (MC) of wood affects its industrial performance, but it is difficult to monitor spatial variations in MC. Here, a multivariate regression was developed to estimate the MC from near infrared (NIR) spectra and was used to monitor the spatial variation in the MC of wood during air- and oven-drying. The spectra and mass of wood pieces were measured at five stages during drying (at each 20% loss of initial water mass). Wood pieces were dried naturally and oven-dried at 60 °C. Initially, 25 spectra were recorded at equidistant points covering the entire longitudinal × radial surface of the sample. Then, a planing machine was used to access the inside of the wood, and NIR spectra were measured for each new surface, at a total of 100 points spatially distributed within the wood pieces. The wood pieces were analyzed in their original state, and when they had lost 20, 40, 60, and 80% of their initial water mass. An NIR-based regression (R 2 p = 0.90 and RMSEP = 10.51%) was applied to estimate the MC, and its spatial gradient during drying was then mapped. These analyses revealed the spatial variation in MC within wood pieces during drying.

It is known that compression wood by heat treatment needs approximately 20 hours at 180oC to attempt the permanent fixation of compressive deformation. On the other hand, even the permanent fixation of compressive deformation by steam treatment is reached in 10 minutes at the same temperature, this method needs expensive apparatus and inapplicable for large wood dimensions. These both problems can be solved by Close System Compression (CSC) method. CSC is a method to press the wood inside an airtight seal chamber, which is placed between the two hot press plates. Wood moisture contents, which evaporate due to heat from hot press, are trapped inside the CSC and produce steam. The wood species used in this research was Randu ( Bombax ceiba . L) with dimensions of 2 cm (L) x 2 cm (T) x 3 cm (R). The wood specimens were compressed into 2 cm in radial direction inside the CSC at 140oC, 160oC, and 180oC for 10 min, 20 min and 30 min. They were compressed in air-dried, water saturated and steam saturated conditions, because it was predicted that moisture content of wood and steam pressure, which was produced inside the CSC has significantly effects on the fixation of wood, beside the temperature. The result shows that moisture content of the wood has an effect on the decreasing of recovery of set. However, it was needed 180oC temperature and 10 kg/cm 2 steam pressure to attempt the permanent fixation. Therefore, it was necessary to add water to produce the steam pressure besides that was produced from the evaporation of wood moisture content.

One of the natural properties of wood and wood-based materials is their soaking capacity (hy­gro­sco­pi­ci­ty). The moisture content of wood and building constructions of wood and wood based materials significantly influences the service life and reliability of these constructions and buildings. The equilibrium weight moisture content of built-in wood corresponding to temperature/moisture conditions inside the cladding has therefore a decisive influence on the basic requirements placed on building constructions. The wood in wooden frame cladding changes its moisture content depending on temperature and moisture conditions of the environment it is built into. The water vapor condensation doesn’t necessarily have to occur right in the wooden framework of the cladding for the equilibrium moisture content to rise over the level permissible for the reliable function of a given construction. In spite of the fact that the common heat-technical assessment cannot be considered fully capable of detecting the effects of these factors on the functional reliability of wood-based constructions and buildings, an extension has been proposed of the present method of design an assessment of building constructions according to the ČSN 73 0540 standard regarding the interpretation of equilibrium moisture content in relation to the temperature/moisture conditions and their time behavior inside a construction.