Keisuke Kojiro

Micropores and mesopores in the cell wall of dry wood

To investigate micropores and mesopores in the cell walls of dry wood, CO2 gas and N2 gas adsorption onto dry wood were measured at ice-water temperature (273 K) and liquid nitrogen temperature (77 K). CO2 gas adsorption isotherms obtained were used for determining micropore volumes smaller than 0.6 nm by the HK method (Horvath-Kawazoe method), and N2 gas adsorption isotherms obtained were used for determining the mesopore volume between 2 nm and 50 nm by the Barrett-Joyner-Halenda (BJH) method. Micropores and mesopores existed in cell walls of dry wood, and the cumulative pore volume was much larger for micropores than for mesopores. Micropores in the cell wall of dry wood decreased with elevating heat treatment temperature, and the decreased micropore was reproducible by wetting and drying. Mesopores did not decrease so much with elevating heat treatment temperature. Micropore volumes for the softwood Hinoki and the hardwood Buna were compared. A larger amount of micropores existed in hardwood Buna than in softwood Hinoki, and this relationship was considered to correspond to the difference in thermal softening properties for lignin in water-swollen Hinoki and Buna. This result probably indicates that micropores in the cell walls of dry wood relate to the structure of lignin.

Changes in micropores in dry wood with elapsed time in the environment

To investigate the changes in microstructures of wood with elapsed time in the environment, CO2 adsorption onto dry wood was measured at ice-water temperature (273 K) for samples aged from 0.1 years to over 1000 years. The micropore size distribution was obtained using the Horvath-Kawazoe method. Micropores smaller than 0.6 nm in wood decreased in number with elapsed time in the environment, and a negative correlation was found between cumulative pore volume for pores smaller than 0.6 nm and elapsed time in the environment. Cumulative pore volume in the 1000-year sample was almost half of that in the 0.1- year sample. Micropores smaller than 0.6 nm in wood with a few decades or more of elapsed time increased in number after rewetting and drying. Consequently, microstructures of wood with longer time elapsed in the environment were considered to be more stable, because of longer-term thermal motion and possibly more repeated moisture adsorption and desorption and/or temperature variation in the environment.

Destabilization of wood microstructure caused by drying

Abstract To obtain new information about destabilization of wood microstructure caused by drying, effects of drying history on physical properties of wood were studied using the measurements of dynamic viscoelastic properties and gas adsorption. First, dynamic viscoelastic properties of dry wood in the radial direction were measured between 100°C and 200°C. Unstable states of dry wood still existed after heating at 105°C for 30 min and were modified by activated molecular motion in the first heating process to higher temperatures above 105°C, and dry wood subjected to higher temperatures showed larger dynamic elastic modulus (E′) and smaller loss tangent (tan δ). The phenomena thought to be caused by the unstable states reappeared after wetting and drying again. Secondly, carbon dioxide adsorptions onto dry wood at ice-water temperature (273 K) were measured, and micropore size distributions were obtained using the Horvath–Kawazoe (HK) method. Micropores smaller than 0.6 nm exist in dry wood. They decreased with elevating drying temperatures from 50°C to 160°C and increased again after rewetting and drying. In conclusion, it was confirmed that wood components in the microstructures were destabilized by drying and that physical properties of dry wood changed with drying histories.

Changes in the Crystalline and Amorphous Components of Moso Bamboo (Phyllostachys Pubescens) with Increasing Age as Determined by X-Ray Diffraction and MicroscopicFourier-Transform Infrared Spectroscopy

The crystalline and amorphous components qualities of moso bamboo (Phyllostachys pubescens) at various ages (43 days to 9 years) were measured by X-ray diffraction and Fourier-transform infrared spectroscopy. The crystal size, lattice spacing, microfibril angle and crystallinity remained almost constant during aging process. In addition, several infrared absorption peaks due to lignin became more distinct in the period that had been reported in previous study as the lignin content increased, and after the components ratio became constant, some peaks due to lignin became broader and shifted to lower wave number. In the previous study, using the samples taken from the same bamboo culms as the culms in this paper, the possibility was suggested that the degree of polymerization and/or the crosslinking density of lignin increased in the period after the components ratio had become constant. As a result of discussion in this research, it was suggested that the reduction of the distance between functional groups of lignin and some kinds of molecules around the lignin and/or the forming of new chemical bonds in lignin occurred in moso bamboo in the period after the components ratio had become constant. These results of discussion support the conclusion in our previous report

Enthalpy relaxation behavior of dry wood detected by temperature-modulated differential scanning calorimetry

Enthalpy relaxation of dry wood has been investigated by temperature-modulated differential scanning calorimetry. The reversing and non-reversing heat flow changes revealed that enthalpy relaxation occurred in dry wood, which did not exhibit any clear glass transitions. This enthalpy relaxation behavior seemed to differ significantly from those of previously reported isolated lignins, which implies that the microstructure of dry wood possesses a rigid amorphous state derived from interactions among wood components. The observed enthalpy relaxation is considered to be related to other components besides lignin, and the time-dependent physical properties due to unstable states or physical aging of wood originate not only from lignin but also from other components, such as cellulose and hemicellulose and the interactions between them.