Japanese cedar (Cryptomeria japonica) is a forest tree species, and widely distributed in Japan. The lumber of Japanese cedar has been used for building materials, furniture, and traditional crafts, but the “leaf” is rarely used for practical applications. In this study, the physiological activity in the water extracts of Japanese cedar leaf which extracted by the two-step hot/hot-compressed water percolation evaluated by the in vitro assay and the experiment using human keratinocyte, HaCaT cells. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and total polyphenol concentration in 180 °C extract were significantly higher than those in 80 °C extract. Additionally, the suppressive effects of 180 °C water extract of Japanese cedar leaf on the cellular reactive oxygen species (ROS) level were more effective than that of 80 °C water extract in HaCaT cells. Therefore, it was indicated that the 180 °C water extracts of Japanese cedar leaf contained more antioxidant compounds than that of 80 °C water extract.

Although researches on lateral resistance of timber joints have shown that joint movements are sometimes inhibited by friction generated between members, the effects of this resistance have not been clearly elucidated. Therefore, in this study, the influence of friction inhibition on the test results was analyzed. Bolted, nailed, and screwed joints were tested. Two methods of friction inhibition were applied: loosely tightening of fasteners, and inserting Teflon sheet and grease between members. It becomes clear that a static frictional appearing at the beginning of testing was sufficiently inhibited using the methods. In the case of loosely tightening, although the friction was sufficiently inhibited at the beginning of test, frictional resistance was gradually increased as the displacement of joint is increased. An effect of friction inhibition was clearly appeared in the mechanical characteristics. In particular, initial stiffness was strongly influenced as it decreased by 27-48%.

In this study, we produced aqueous vinyl polymer solution-isocyanate adhesives for wood (API) experimentally by mixing acrylic emulsion adhesives (AE) with different glass transition (T_g), acetoacetylated polyvinyl alcohol (AAPVA) and polymeric diphenylmethane diisocyanate (pMDI) to improve the adhesive performance of the adhesives added to wood-based materials for their vibration-damping properties. The relationship between film properties and wood bonding performance was investigated with regard to dynamic viscoelasticity and moisture absorption by the adhesive films, tensile shear strength, and wood failure rate using three-layer plywood. As a result, the decrease of the storage elastic modulus (E ') in high-temperature ranges was suppressed by adding AAPVA and pMDI in dynamic viscoelasticity. Additionally, AE with T_g near room temperature showed the highest values of tensile shear strength of the joints. Wood bonding performance was considerably improved by adding AAPVA and pMDI to AEs. Furthermore, the relationships between E ' and tensile shear strength of the joints were investigated, and an approximation curve based on a polynomial equation showed a strong correlation, with a coefficient of determination R ² = 0.876.

When out-of-plane loads are applied to cross laminated timber (CLT), shear stress occurs. If CLT results in shear failure, rolling shear in the transverse layer may occur because rolling shear strength is lower than that parallel to the grain. It then becomes important to evaluate the rolling shear strength of the lamina. However, how cross section size of laminae affect the rolling shear strength on Japanese larch (Larix kaempferi) has, to date, not been well examined. Therefore, we conducted compression type rolling shear tests on Japanese larch laminae with a thickness of 30 mm and widths of 60, 80, 100, and 120 mm. Laminae specimens comprising two pieces with a width of 60 mm were also tested. Results from the tests were as follows. The rolling shear strength was higher with increasing lamina width. In this study, the regression line of ratio of width to thickness and rolling shear strength was almost consistent with available data on Japanese larch lamina. The rolling shear strength of the specimen with two laminae was lower than that of specimens with 120 mm width.