The Dielectric Properties of Wood V, On the Dielectric Anisotropy of Wood.

Abstract

This paper deals with the dielectric anisotropy of wood in relation to the structures of wood and the mechanism of the relaxation process due to the motion of CH_2OH group in the disordered region of wood substance. In very high frequency range in which only optical and infra-red polarizations contribute to dielectric constant, the value of dielectric constant of wood substance in parallel to grain direction was equal to that in perpendicular to grain direction. The dielectric anisotropy of wood, therefore, is mainly caused by the macroscopic structures. On the other hand, in the frequency range in which the relaxation process due to the motion of dipole contributes to dielectric constant, the value of dielectric constant of wood substance in parallel to grain direction was always greater than that in perpendicular to grain direction, and the frequency corresponding to dielectric loss factor maximum in parallel to grain direction was lower than that in perpendicular to grain direction. These results show that the transition probability of dipole jump to an adjacent site when the electric field applies to longitudinal direction is greater than that when the electric field applies to the other directions, and the heights of potential barriers among sites in longitudinal direction are higher than those in the other directions. The dielectric anisotropy of wood in low frequency range, therefore, depends not only upon the macroscopic structures but also upon the molecular structures and motions in wood substance.