Satoshi Shida

Effects of heat treatment on brittleness of Styrax tonkinensis wood

A new approach is proposed for the evaluation of the brittleness of heat-treated Styrax tonkinensis wood. Heat treatment made wood more brittle when wood was heated at a higher temperature or for a longer time. The brittleness increased to four times that of the control when wood was heated at 200°C for 12 h. For treatment at 160°C, the increase in brittleness without any change in weight is thought to be possibly caused by the relocation of lignin molecules. At higher temperatures, loss of amorphous polysaccharides due to degradation is thought to become the main factor affecting brittleness. The crystallites that were newly formed after 2 h of treatment showed brittleness that was different from that of the inherent crystallites remaining after 12 h of heat treatment. This inherent crystalline cellulose possibly plays a role in brittleness. There is also the possibility of using color to predict the brittleness of heat-treated wood.

Non-destructive Measurement of Moisture Distribution in Wood during Drying Using Digital X-ray Microscopy

The objective of this study was to develop a nondestructive method by which moisture distribution in wood during drying could be predicted. A newly developed digital X-ray microscope was used to measure the moisture content of wood and its accuracy and resolution was evaluated compared to the classic oven-dry method. Small green wood specimens of Sugi (Cryptomeria japonica D. Don) were cut and dried under constant temperature and humidity. As the weight was decreasing during drying, X-ray microscope images of cross section were obtained. From these digital images and specimen weight, the moisture content during drying was measured by the two methods. After the shrinkage of the specimen was canceled, the standard error achieved finally was about 1% moisture content within the experimental range. As the image was divided into small subimages, the clear moisture distribution can be seen. It was found that the image divided into 32 × 32 subimages in each size of 0.625 × 0.625 mm might be valid to determine the moisture distribution, and that the drying rate in early wood is larger than in late wood.

A Novel Method of Measuring Moisture Content Distribution in Timber During Drying Using CT Scanning and Image Processing Techniques

A new method for the nondestructive measurement of moisture content (MC) distribution in timber during drying was developed using X-ray computed tomography (CT) scanning and image processing techniques. The deformed cross section in the CT images due to shrinkage was corrected with the image registration, and the shrinkage was measured by digital image correlation analysis. The pixel-wise MC distributions during drying were measured and visualized successfully. The total timber MC estimated from the MC values of each pixel were strongly correlated with those measured by calculation without geometrical transformation of CT images. The coefficient of determination (R 2) and the standard error of prediction (SEP) were 0.99 and 0.18%, respectively, within the MC range of 19.2–47.3%. In addition, the measured shrinkage distribution during drying was in accordance with the diamonding deformation observed. The results suggest that CT scanning combined with image processing techniques is an effective tool for nondestructive assessment of MC distribution during drying.

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.

Predicting Thermal Efficiency in Timber Radio Frequency Vacuum Drying

Abstract In this work, the efficiency of transforming dielectric energy into evaporated water is analyzed for the case of timber radio frequency vacuum drying. Based on well-known heat and mass transfer equations, a simplified mathematical model is proposed that estimates the drying efficacy in regards to the thermo-physical properties of wood. Although not exact, the theoretical results are close to the experimental observations and elucidate some phenomena like the tendency of the timber to dry from inside to outside, and the drying rate increase with the rise of the timber gas permeability. The theoretical efficiency model also predicts a range of wood permeability values for which the drying efficiency changes from 100 to 0%, thus providing a quantitative scale for classifying the spectrum of “difficult-to-dry” all the way to “easy-to-dry” wood species when using radio frequency vacuum technology.

A PRELIMINARY STUDY ON ULTRASONIC TREATMENT EFFECT ON TRANSVERSE WOOD PERMEABILITY

Ultrasonic pre-treatment of small and pressure saturated Douglas-fir heartwood specimens at 20 kHz fixed frequency with an acoustic horn resulted in increased specific permeability coefficient in both radial and tangential directions. Statistical analysis revealed that there was a high correlation between ultrasonic treatment time and specific permeability coefficient. Improvement rate of permeability in both radial and tangential directions was nearly the same regardless of treatment time.

Air Permeability Of Sugi (Cryptomeria Japonica) Wood In The Three Directions

To investigate the air permeability of sugi (Cryptomeria japonica) and the effect of grain directions on it, the air permeabilities of air-dried sugi sapwood and heartwood were determined along the three material directions of wood. The value of the longitudinal permeability was the highest and that of the radial permeability was the lowest. The permeability of heartwood was about an order of magnitude less than the permeability of sapwood in the same direction. The ratio between the tangential and radial permeability was approximately 10, which was similar to softwoods that have impermeable rays. These results suggest that sugi has ray tissues that are either impermeable or have very low permeability. The radial permeability of sugi was much lower than that of Pinus, Sequoia, Juniperus, Abies, and Tsuga measured with gases reported in the literature, indicating that sugi is one of the least radially permeable softwoods. These findings explain the reasons for the difficulties encountered in the drying and chemical treatment of sugi (Cryptomeria japonica).

Evaluation of Shear Strength of Japanese Wood Species as a Function of Surface Roughness

The objective of this study was to evaluate shear strength characteristics of four commonly used Japanese species, namely, Japanese cedar-sugi (Cryptomeria japonica D. Don), Japanese cypress-hinoki (Chamaecyparis obusta Endl.), false arborvitae-hiba (Thuobsis dolabrate Sieb. et Zucc.), and Japanese larch-karamatsu (Larix leptlepis Gordon), as function of their surface quality. Samples with radial and tangential grain orientations from each species were prepared using a planer and sanded with one of the sandpapers with 80-, 120-, and 240-grit size. A stylus type of equipment was employed to determine surface roughness of each sample before they were bonded in radial and tangential pairs using polyvinyl acetate (PVAc) adhesive at a spread rate of 260 g/m 2 . None of the samples showed any superiority from each other in terms of their surface quality based on three parameters: average roughness (R a ), mean peak-to-valley height (R z ), and maximum roughness (R max ). Average roughness value of both tangential and radial surfaces of the samples sanded with 80-grit sandpaper resulted in significant differences from those of the control samples. The highest shear strength value was 96.1 kg/cm 2 for the radial karamatsu samples sanded with 80-grit sandpaper followed by tangential hinoki samples with the value of 79.6 kg/cm 2 . In general, the samples finished with 80-grit sandpaper resulted in higher shear strength values than the others tested in this work. It appears that stylus-type equipment can be used to evaluate surface quality of such solid wood samples. Based on the results of this study, sanding of the samples with 80-grit sandpaper improved overall shear strength of the specimens by developing a better glue line between two pieces.

Infrared thermography for monitoring surface checking of wood during drying

Abstract Infrared thermography was used to explore more convenient ways to investigate the occurrence of checking during drying, which is indispensable for the development of the drying schedule and kiln operation. A small, constant-temperature chamber was combined with an infrared thermographic system. The occurrence of checking on cross-section was observed and the coefficient of variation of the surface temperature was measured by the system during drying. This research aimed to monitor surface checking in a wood drying process using infrared thermography, and this method is expected to a develop drying schedule. Thermographic measurement has the advantages of being non-destructive and prompt, and allowing detection over a wide area. Japanese cedar (sugi) boxed heart specimens were prepared and dried under a constant temperature of 105°C. During drying, infrared thermographic images were taken. The results indicate that the coefficient of variation of the surface temperature increased in the checked area of cross-section, whereas it decreased in the unchecked area. The change in surface temperature during drying showed some potential for detecting surface checking. Infrared thermography may be useful in the development of a kiln control system based on the surface temperature during drying.

Intercalation of wood charcoal with sulfuric acid

Intercalation of wood charcoal with sulfuric acid (H2SO4) was investigated. Carbonized sugi (Japanese cedar) samples were prepared by heating at various temperatures in the range 1700°–2700°C. Electrochemical oxidization was carried out in H2SO4 and the feasibility of intercalation was determined. In potentiometric analysis, plateaus appeared for samples carbonized at temperatures above 2300°C. In their X-ray diffraction profiles, the peak at around 26° was shifted to a smaller angle of about 22.4°. These results can be considered as signs of intercalation with acid molecules. Fourier transform infrared analysis of charcoal heated at 2700°C, following washing with water and drying of the sample, showed a band at 1220 cm−1 that was assigned to a sulfonate group. This band was not observed for samples heated at 1900°C. These observations suggest the occurrence of intercalation in the former charcoal, but not in the latter. It is concluded that wood charcoal can undergo intercalation when it has ordered stacking of hexagonal carbon layers.