Minoru Masuda

Microscopic observation of transverse swelling of latewood tracheid: effect of macroscopic/mesoscopic structure

In order to study the transverse swelling/shrinkage of wood, the microscopic swelling behavior of latewood tracheid was observed using confocal laser scanning microscopy and the digital image correlation method. A microcrater structure was created on the surface of the specimen by using the ion sputter etching technique to obtain a pattern-rich digital image for image analysis. Douglas fir specimens were conditioned by two methods of absorption: rapid absorption of moisture from hot steam, and slow absorption of moisture from the water vapor of saturated solutions. Latewood tracheid near the surface of the specimen deformed only in the radial direction when the relative humidity of the surrounding air changed rapidly (rapid absorption of moisture from hot steam or absorption/desorption of moisture during the observation). In addition, the diameter of the lumen decreased upon rapid absorption of moisture, whereas it expanded upon slow absorption of moisture. These results indicate that the microscopic swelling behavior of latewood cells is strongly influenced by the macroscopic/mesoscopic structure, for instance, the cell arrangement or the alternation of latewood and earlywood.

Multiresolutional image analysis of wood and other materials

The gloss of wood is a unique texture compared to that of other materials. To express it quantitatively, two digital-image analyses were performed. One method was multiresolutional contrast analysis, which was the new method developed in this study. The other method was fractal image analysis. Twenty-four specimens, including solid woods, wood-plastic composites (WPCs), printed grains, and granites, were prepared. Digital images of specimens were obtained in five sizes and in two illuminant directions (perpendicular and parallel to the grain). The multiresolutional contrast values of perpendicular illuminated images were calculated and compared among specimens. The result of this quantitative analysis was that the gloss of wood was characterized by bright spots in a relatively small area. Using fractal analysis, the fractal dimension of a digital image was used as an index of brightness changes, not for expressing the self-similarity. These indices showed results similar to those of the multiresolutional contrast analysis.

Observation of microscopic swelling behavior of the cell wall

The swelling or shrinkage behavior of a cross section of wood is complicatedly affected by its anatomical structure and anisotropic elasticity. 1 Therefore, no theory that explains exactly the cause of swelling anisotropy has been reported. Recently, application of the digital image correlation method (DIC) to microscopic or mesoscopic strain measurements has been studied, 23 and DIC was found to be a promising tool for that purpose. We also observed the transverse swelling behavior of tracheids of Douglas fir by means of confocal scanning laser microscopy and DIC and succeeded in measuring the change of cell shape and distribution of expansion in cell walls with absorption of moisture. 4 However, the cross section surface planed by a sliding microtome was so smooth that we could not measure strain distribution in cell walls using DIC. In this study, therefore, the smooth surface of the cross section of cell walls was made rugged by sputter etching; and subsequently the minute swelling distribution of cell walls of latewood tracheids was observed with confocal scanning laser microscopy and DIC.

Changes of Color and Psychological Images of Wood Used for Exterior

Relations between psychological visual images of exterior wooden walls and their visual physical characteristics were investigated. Forty-two photos of different weathered wooden walls ware distributed to 18 male subjects and 19 female subjects and were arranged in orders according to “Furusouna (aged)”, “Yogoreta (dirty)” and “Kanjino yoi (good impression)”. These three words have high correlation between each other. Especially “Yogoreta (dirty)” and “Kanjino yoi (good impression)” have extremely high correlation between them (r=-0.983). Wooden walls with low lightness L* and low chroma C* give us “Furusouna (aged)” image. Average difference of hue between adjacent mosaics i. e. ΔH°12×12 has high correlation between these three phychological images. Prediction formula for “Furusouna (aged)” Ia obtained by multi-regression analysis isIa=2.492×log(ΔH°16×16)-0.027×L*av-0.555