Mechanical and dielectric relaxations of wood in a low temperature range IV. Dielectric properties of adsorbed water at high moisture contents

The dielectric properties in the longitudinal direction of hinoki (Chamaecyparis obtusa) wood were measured at various moisture contents in the temperature range from -150 to 0 degreesC and in the frequency range from 1 kHz to 1 MHz. Almost no volume change of the cell lumen due to water sorption was recognized. Using a parallel model composed of cell wall substance, adsorbed water and cell lumen for wood in the longitudinal direction and applying the sech law to the frequency dependence of the dielectric loss, the dielectric constant at 10 kHz and -80 degreesC as well as the dielectric magnitudes between -90 and -60 degreesC for the cell wall and the adsorbed water at a moisture content of 21.5% were estimated. The dielectric constant and the relaxation magnitude of the adsorbed water were about 60 and 64 similar to 79, respectively, which were almost comparable to those of ice and liquid water. The dielectric constant of the adsorbed water at the limiting high frequency was about 4, which was almost equivalent to that of ice acid liquid water. With increasing temperature, the dielectric magnitude increased in the adsorbed water, but decreased in ice and liquid water. When compared at the same temperature, the average relaxation time of the adsorbed water was comparable to that of liquid water at high moisture contents and to that of ice at very low moisture contents. The distribution of relaxation times of the adsorbed water was much wider than that of ice and liquid water. The apparent energy of activation of the adsorbed water was greater than that of liquid water and almost equivalent to that of ice.