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 (Chamaecy paris obtusa) wood were measured at various moisture contents in the temper ature range from -150 to 0 degreesC and in the frequency range from 1 kHz t o 1 MHz. Almost no volume change of the cell lumen due to water sorption wa s recognized. Using a parallel model composed of cell wall substance, adsor bed water and cell lumen for wood in the longitudinal direction and applyin g the sech law to the frequency dependence of the dielectric loss, the diel ectric constant at 10 kHz and -80 degreesC as well as the dielectric magnit udes 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 liqu id water. The dielectric constant of the adsorbed water at the limiting hig h frequency was about 4, which was almost equivalent to that of ice acid li quid water. With increasing temperature, the dielectric magnitude increased in the adsorbed water, but decreased in ice and liquid water. When compare d at the same temperature, the average relaxation time of the adsorbed wate r was comparable to that of liquid water at high moisture contents and to t hat of ice at very low moisture contents. The distribution of relaxation ti mes 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 t hat of liquid water and almost equivalent to that of ice.