Assuming the use of semi-carbonized chips under the floor for thermal insulation, wood (Douglas fir heartwood) was semi-carbonized (torrefied) at heating temperatures of 270 to 300 ºC and oxygen concentrations of 1 to 4%. Changes in thermal insulation capacity, hygroscopicity, strength properties, and so on were investigated using the mass loss caused by semi-carbonization as an index. The thermal conductivity decreased linearly as the mass loss increased, and the rate of decrease was about 0.75% per 1% mass loss. The main cause of the decrease in thermal conductivity was the increase in porosity due to the decrease in density. However, the heat transfer model analysis revealed that the thermal conductivity of the substance (heat bridge) decreased by up to 5% due to the decreases in hygroscopicity and substance density. Although the compressive strength and shear strength decreased to about 1/4 when the mass loss reached 40%, the pulverization rate due to repeated drop impacts remained below 10%. Assuming that a mass loss of 20% or more ensures decay resistance, the semi-carbonization condition that achieves both thermal insulation and impact resistance was judged to be in the range of 20 to 40% in terms of mass loss.
In recent years, the number of wooden structures using screws which are expected to resist withdrawal forces are increasing. It becomes necessary to establish a design method based on a theoretical basis for the withdrawal performance. In this study, FEM (Finite element method) analysis using a 3D model reproducing the threaded part of the screw was conducted, and tensile stress concentration was observed at the tip of the thread under withdrawal force perpendicular to grain. Based on FEM analysis and fracture properties from experiments, an evaluation method of withdrawal strength of the screw embedded perpendicular to grain was proposed using linear fracture mechanics. The calculated values of that method were compared with experimental values of screw withdrawal tests of several woods, such as Japanese cedar, Japanese cypress, Japanese larch and Douglas fir. As a result, calculated values for Japanese cedar corresponded well to experimental ones and the values of Japanese cypress, Douglas fir and Japanese larch were evaluated to be on the safe side.
Trees of Enkianthus campanulatus (Ericaceae) are growing in colony in Uminokuchi shizengo, Yatsugatake kogen, Nagano Prefecture, Japan. In recent years, terrible bark stripping damage of the trunks by sika deer (Cervus nippon Temminck) happens frequently. However, many of them were repaired. In this study, the number of E. campanulatus stripped by sika deer was counted in a quadrat of 30 m square at 1550 m above the sea level. In the quadrat, we found 57 bundles with 184 trunks of which 83 trunks were stripped but 80 had been repaired. Dead trees due to bark stripping damage by sika deer were only three. Microscopic observation of repaired bark showed that the traumatic tissues in xylem appeared in the inner part of repaired bark, and no growth ring boundary was observed between cambial cells and the traumatic tissues. Additionally, living cells appeared on the surface of stripped trunk. From the results, it was assumed that the trunk of E. campanulatus can be easily repaired in a short period.
We investigated wood properties and variations in the stems of 10- and 16-year-old Melia azedarach trees of three clones (Type 1, Type 18, and M-type), to explore the potential of this species. All three clones had straight stems due to bud pruning. Diameter at breast height ranged from 21.9-24.8 cm in 10-year-old trees and 23.1-31.2 cm in 16-year-old trees. There were significant differences among clones in air-dry density, modulus of elasticity (MOE), and modulus of rupture (MOR) at 10 years, whereas at 16 years, air-dry density, MOE and MOR generally increased from the pith outward in all trees, regardless of elevation, but there were no significant changes in mean values by height. In the early stages of growth, air-dry density, MOE, and MOR were lower at lower elevations, but differences may have been less significant at lower heights because the lower the height, the better the growth of this species. Production targets were set at 30 cm for top end diameter and 4 m straight length, suggesting the possibility of harvesting materials from trees with similar heights, despite other differences, if trees attain target sizes.
Young's modulus of paperboard was obtained from tensile, static bending, longitudinal vibration, and flexural vibration tests under various specimen configurations, and the obtained values were compared with each other. There were significant differences among the Young's modulus values obtained by the four methods because the lamination construction and inelastic deformation of the paperboard affected the measurement of Young's modulus. Therefore, the method for measuring the Young's modulus should be carefully determined while considering the practical application of using the paperboard.
This study proposed eco-friendly chlorine-free bleaching as a method of pulp production for papermaking. As a wood species with excellent cooking ability, 12-year-old Eucalyptus globulus wood chips were kraft-cooked and oxygen (O)-bleached in a laboratory, and then the bleaching response was evaluated. In addition, these were compared with an O-bleached kraft mill pulp (LOKP), which was produced in a mill from mixed wood chips of E. globulus and Acacia spp. A five-stage bleaching sequence (O-Psa-Ep-Psa-Ep) using O-bleaching, peroxymonosulfuric acid (Psa) treatment and alkaline hydrogen peroxide (Ep) treatment was adopted. Produced E. globulus kraft pulp (yield: 50.1%, kappa number: 16.0, brightness: 33.3% ISO, viscosity 72.2 mPa·s) provided a bleached pulp with brightness of 88.6% ISO and viscosity of 10.8 mPa·s. Using a modified bleaching process by adding a small amount of ClO2 to the Psa stages in a sequence of O-(Psa+ClO2)-Ep-(Psa+ClO2)-Ep, viscosity of the bleached pulp was increased to 12.3 mPa·s with no significant change in brightness. The LOKP resulted in brightness of 90.1% ISO and viscosity of 8.7 mPa·s in the O-Psa-Ep-Psa-Ep sequence, and the viscosity was improved to 9.4 mPa·s in the O-(Psa+ClO2)-Ep-(Psa+ClO2)-Ep sequence.