The purpose of this study is to elucidate the factors related to improvement of the physical properties of bamboo as a material with increasing age. Moso bamboo (Phyllostachys pubescens) at various times (40 days∼9 years) since shooting were used for test samples in the green condition. The modulus of elasticity in bending (MOE) when loaded on the endodermis or the epidermis side was determined. In addition, at each endodermis and epidermis side, the thickness of parenchyma and fibrous cell walls and the percentages of cell walls of parenchyma and vascular bundles were measured. Results obtained are as follows. The MOE of bamboo is affected not only by the density of the entire woody substance but also by the types of cells in which the cell wall thickness increases, that is, parenchyma cells or fibrous cells, and by their radial location, that is, endodermis side or epidermis side. The MOE obtained by endodermis-side loading is greatly affected by the thickness of parenchyma cells and the percentages of cell walls of parenchyma, and the MOE obtained by epidermis-side loading is greatly affected by the thickness of fibrous cells and the percentages of cell walls of vascular bundles.

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Psychological evaluations were made to examine the visual effects of knots in softwood (todomatsu wood) interior wall panels. To examine the effect of knot quantity, the ratio of knot area to panel area (KA/PA) were set to four levels ranging from 0 to 1.32%. The effects of wall panel settings were also considered. A restaurant, a hotel, a hall, and a school were selected as settings wherein softwood interior panels were used. The evaluations on preferences for using softwood panels in the restaurant, the hotel, and the hall indicated a decrease in subject preference with increased KA/PA. The rate of decrease of preference indicated the same tendencies found for residential living rooms, as reported in our previous research. However, the rate decrease, when changing KA/PA from 0.86 to 1.32%, for softwood panel preference was less significant than that for living rooms, while there was no obvious relationship between KA/PA and preference in the school evaluation. Verified by analysis of variance (ANOVA), a significant difference was observed in the interaction between KA/PA and settings. This study indicated that the subjects were not only affected by knot quantity, but were also influenced by the context of the setting in which the interior wall panels were used.

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For the purpose of effectively utilizing low quality logs of short length, 24 mm-thick, 9-layer 9-ply plywood was produced with longitudinal scarf joint at the center of the strong-axis veneer. The effects of lamination number and arrangement of the veneer-joints on mechanical properties are discussed. Sugi (Cryptomeria japonica D. Don) was used for the veneer and hot-melt adhesive was used for longitudinal joints. A tendency for lowered bond quality was observed with increasing number of veneers with a longitudinal joint. Bending performance of specimens with longitudinal joints in face and back layers decreased significantly. The performance of plywood without longitudinal joints in face and back layers did not show a significant decrease and met the requirements of the JAS standard for structural plywood. The efficiency of veneer joints was calculated with parallel-ply theory. The efficiency for the layup where all strong-axis veneers were jointed showed the lowest values ; 60% for bending stiffness and 35% for bending strength. From the above findings, it was concluded that thick plywood with longitudinally jointed veneer can have practicable bending performance, if the longitudinal joints of veneer are restricted to the inner layers.

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