Improved methodology of measuring moisture content of wood by a vibrational technique

A method of measuring moisture content of wood is introduced. This method uses a vibrational technique. A shaker driven by swept sine signals was used for the accurate generation of vibration. A cylindrical wood sample was used to verify the method of measuring the moisture content. Resonance frequencies of the wood sample decreased as its moisture content increased. An experiment was performed by measuring the vibration of a tree to explore the feasibility of applying the method to the measurement of the moisture content of trees. The circumferential mode, which is independent of the height of a tree, was identified using a white oak tree.     

Influence of moisture content on the vibrational properties of hematoxylin-impregnated wood

The vibrational property of hematoxylinimpregnated wood was investigated from the aspect of moisture content dependence. The specific dynamic Young's modulus (E/) and loss tangent (tan) of hematoxylin-impregnated wood were determined in the relative humidity (RH) range of 0%–97%, and were compared with those of the untreated and some conventional chemically treated woods. The changes in theE/ and tan of wood with increasing RH were suppressed by acetylation and formaldehyde treatment because of a marked reduction in the hygroscopicity of the wood. Although the hematoxylin impregnation did not significantly affect the hygroscopicity of the wood, its influence onE/ and tan were similar to that of formaldehyde treatment at low RH and of acetylation at medium RH. It was supposed that at low to medium RH hematoxylin restrains the molecular motion of amorphous substances in the cell wall because of its bulkiness and rigidity. On the other hand, at high RH it seems to work as a plasticizer with adsorbed water molecules.     

An improved technique for non-destructive measurement of the stem volume of standing wood

An improved technique, cheaper and less time-consuming, to measure standing wood volume by using an electronic theodolite was tested, by which greater information from the forest could be acquired accurately and non-destructively. This was achieved by recording the diameter at breast height and ground-level diameter of a tree as well as the included angle between the electronic theodolite and the left and right tangents of the stem at any point. The standing wood volume then was computed precisely by section. In addition, the factors that influence the precision of the method (observable distance and number of segments) were also analysed. In the study, 175 Larix gmelinii (Rupr.) Kuzen. trees and 190 Populus tomentosa Carrière trees chosen randomly for sampling were measured with the electronic theodolite, and then were cut down for measurement of the average cross-section volume. Based on the data acquired from 100 sample trees, a standard volume table was compiled, and then the data for the remaining random 10 sample trees in each group were selected for a comparison test. The results indicated that the optimal distance for indirect observation should be as high as the sample tree, and the optimal visual distinguished section was about 2?m. The correlation coefficient between the value measured non-destructively and the value of the felled trees of L. gmelinii was 0.97, with an average relative error of 1.62%. With regard to P. tomentosa, the correlation coefficient between the two values obtained by the two methods was 0.905 with an average relative error of 8.40%. It was concluded that the standard volume model based on the non-destructive measurement technique meets the requirements for precision in forest surveys. The precision of the standard volume model for L. gmelinii (a coniferous tree) was superior to that of the model for P. tomentosa (a broad-leaved tree). The electronic theodolite method provides an alternative technique for measuring trees without destructive sampling and is widely applicable for forest surveys.     

In situ measurement of wood moisture content in high-temperature steam

Changes in moisture content of sugi (Cryptomeria japonica D. Don) wood during high-temperature saturated and superheated steam treatments were investigated. A system for in situ weighing of specimens was used, and the reduction of wood substance by heating was taken into consideration. At 160°C the loss of wood substance due to heating was significant and influenced the moisture content values, but it was almost negligible at 120°C. Treatment time and temperature affected the moisture content in saturated steam but not in superheated steam. Excess water in a saturated closed system appears to promote the decomposition of wood and condensation in or on specimens.Parts of this work was presented at the 49th, 50th, and 52nd Annual Meetings of the Japan Wood Research Society in Tokyo, April 1999; Kyoto, April 2000; and Gifu, April 2002     

Assessment of high-frequency technologies for determining the moisture content of comminuted solid wood fuels

Industries that trade in biomaterials require new and reliable methods for rapidly determining the moisture content (MC) of solid biomass. It is therefore important to develop and test alternative technologies that can fulfil the requirements of all parties in the wood fuel trading chain and provide real-time, accurate and representative MC measurements. The aim of this study was to evaluate the accuracy of a commercial high-frequency (HF) technology (originally developed to analyse potting soils) as a tool for determining the MC of comminuted solid biofuels. The measurements obtained using the HF technology were compared to measurements obtained using the gravimetric method from the European standard EN 14774-2:2009. The HF measurements were most accurate for feedstocks with homogeneous particle size distributions such as wood chips, sawdust and peat [root mean square error (RMSE) 3.1–4.5%]. Less accurate results were achieved for wood fuels with large particles and gaps between particles, such as crushed stem wood (RMSE 8.4%). If the system was adapted to improve its performance for heterogeneous particle size distributions, it should yield acceptably accurate MC estimates. Because of its potential in online analysis, it should therefore be regarded as a potential alternative to existing methods for MC measurement and merits further investigation.     

Evaluation of moisture content distribution in wood by soft X-ray imaging

A technique for nondestructive evaluation of moisture content distribution in Japanese cedar (sugi) during drying using a newly developed soft X-ray digital microscope was investigated. Radial, tangential, and cross-sectional samples measuring 100 × 100 × 10 mm were cut from green sugi wood. Each sample was dried in several steps in an oven and upon completion of each step, the mass was recorded and a soft X-ray image was taken. The relationship between moisture content and the average grayscale value of the soft X-ray image at each step was linear. In addition, the linear regressions overlapped each other regardless of the sample sections. These results showed that soft X-ray images could accurately estimate the moisture content. Applying this relationship to a small section of each sample, the moisture content distribution was estimated from the image differential between the soft X-ray pictures obtained from the sample in question and the same sample in the oven-dried condition. Moisture content profi les for 10-mm-wide parts at the centers of the samples were also obtained. The shapes of the profiles supported the evaluation method used in this study. Part of this work was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

Basic density determination for Swedish softwoods and its influence on average moisture content of wood packages estimated by measuring their mass

In this work, a set-up with a device measuring the mass of wood packages is examined as an aid to estimate the average moisture content (MC) of wood packages. As the basic density needs to be presumed in the set-up, an estimator of the basic density as a function of log diameter is determined for Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris). In total, 1920 specimens were collected at two different sawmills and analysed for this purpose. Specimens collected at the butt-end of pine had the greatest variation in basic density and it is recommended that they should be omitted when sawmills create their own functions for basic density estimation. Furthermore, the variation in basic density was shown to have the greatest impact on the estimated MC. A maximum error estimator of the MC became 14% at a MC of 70% and 9% at a MC of 10%. It was therefore concluded that the described method should not be used to estimate the MC of packages after drying but can serve as a valuable indicator of average green MC of a drying batch.     

Nondestructive testing method of wood moisture content based on a planar capacitance sensor model

For our research, a new hybrid experimental-computational method is presented. We applied a least squares fitting     

Effect of moisture content of a wood matrix on a small-scale biodegradation system for organic solid waste

The optimum working moisture content of a wood matrix for the garbage automatic decomposer-extinguisher (GADE) machine was investigated using a small-scale degradation reactor. A formula feed for rabbits was used as the model waste. The degradation experiment was conducted under controlled conditions such as moisture content, environmental temperature, and airflow rate. The degradation rate was estimated precisely from weight loss and the CO₂ evolution rate. The degradation rate were nearly constant at a moisture content of 30%–80% on a-wet-weight basis. Microorganisms from the environment propagated in the reactor with no inoculums added. The number of microorganisms showed a trend similar to that of the degradation rate. The microorganism community changed according to the moisture content of the matrix and were considered to attain a constant degradation rate at a wide range of moisture content of a matrix.Part of this report was presented at the 49th annual meeting of the Japan Wood Research Society, Tokyo, April 1999     

Feeding activities of Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe) as affected by moisture content of wood

The relationship between the moisture content (MC) of wood blocks and the feeding activities of two Japanese subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes speratus (Kolbe), was investigated with two choice tests. When three wood blocks with low MC (6%–12%), middle MC (79%–103%), and high MC (140%–182%) were exposed to workers of C. formosanus and R. speratus in a choice test, the feeding preferences were found in the middle MC blocks for C. formosanus, and the middle and high MC blocks for R. speratus, although wood blocks of low MC were also attacked. In a second choice test, wood blocks consisting of five pieces with water-impregnated (MC: 133%–191%) top, middle, or bottom piece were exposed to workers of both species. Higher consumptions were generally obtained in water-impregnated wood pieces and bottom pieces.     

Micromorphology,moisture sorption and mechanical properties of a biocomposite based on acetylated wood particles and cellulose ester

Abstract

One of the major issues in a long-term perspective for the use of wood–plastic composites (WPCs) in outdoor applications is the moisture sensitivity of the wood component and the consequent dimensional instability and susceptibility to biological degradation of the composite. In this work, the effects of using an acetylated wood component and a cellulose ester as matrix on the micromorphology, mechanical performance and moisture uptake of injection-moulded WPCs have been studied. Composites based on unmodified and acetylated wood particles, specially designed with a length-to-width ratio of about 5–7, combined with both cellulose acetate propionate (CAP) and polypropylene (PP) matrices were studied. The size and shape of the wood particles were studied before and after the processing using light microscopy, and the micromorphology of the composites was studied using a newly developed surface preparation technique based on ultraviolet laser irradiation combined with low-vacuum scanning electron microscopy (LV-SEM). The water vapour sorption in the composites and the effect of accelerated weathering were measured using thin samples which were allowed to reach equilibrium moisture content (EMC). The length-to-diameter ratio was only slightly decreased for the acetylated particles after compounding and injection moulding, although both the unmodified and the acetylated particles were smaller in size after the processing steps. The tensile strength was about 40% higher for the composite based on acetylated wood than for the composite with unmodified wood using either CAP or PP as matrix, whereas the notched impact strength of the composite based on acetylated wood was about 20% lower than those of the corresponding unmodified composites. The sorption experiments showed that the EMC was 50% lower in the composites with an acetylated wood component than in the composites with an unmodified wood component. The choice of matrix material strongly affected the moisture absorptivity of the WPC. The composites with CAP as matrix gained moisture more rapidly than the composites with PP as matrix. It was also found that accelerated ageing in a Weather-Ometer® significantly increased the moisture sensitivity of the PP-based composites.     

Influences of moisture content on the catalysis of sulfur dioxide and attainable properties in a vapor-phase treatment of wood with formaldehyde

Influences of moisture content on the catalysis of sulfur dioxide and physical properties of reaction products were examined for a vapor-phase treatment of spruce wood with formaldehyde. The reaction rate was strongly dependent on the amounts of water and sulfur dioxide in the reaction system, and this was consistent with a proposal that the hydroxymethylsulfonic acid (HOCH₂SO₃H) formed from sulfur dioxide, water, and formaldehyde acts as a catalyst for the reaction. However, not all water molecules contributed to the formation of HOCH₂SO₃H, because some were adsorbed by the wood components. When the initial moisture content was high, polymeric cross-linking was likely because the ultimate weight gain was much greater than the value estimated based on monomeric cross-links. The lower values of antiswelling efficiency and higher equilibrium moisture content at a specific level of weight gain also suggested the existence of polymeric cross-links. However, the difference in the length of cross-links did not significantly influence the mechanical properties.Part of this research was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, April 2003     

Predicting moisture content and density distribution of Scots pine by microwave scanning of sawn timber II: evaluation of models generated on a pixel level

The purpose of this study was to use images from a microwave sensor on a pixel level for simultaneous prediction of moisture content and density of wood. The microwave sensor functions as a line-scan camera with a pixel size of 8mm. Boards of Scots pine (Pinus sylvestris), 25 and 50mm thick, were scanned at three different moisture contents. Dry density and moisture content for each pixel were calculated from measurements with a computed tomography scanner. It was possible to create models for prediction of density on a pixel level. Models for prediction of moisture content had to be based on average values over homogeneous regions. Accuracy will be improved if it is possible to make a classification of knots, heartwood, sapwood, etc., and calibrate different models for different types of wood. The limitations of the sensor used are high noise in amplitude measurements and the restriction to one period for phase measurements.