Research Institution of University Forests, Faculty of Agriculture, Kyushu University
Abstract
Although a relationship between DC (direct current) conductivity and moisture content has been discussed by several researchers, it has not been clarified how the swelling and shrinkage of wood cell wall relates to the effect of moisture content on DC conductivity of wood. It is the purpose of this study to discuss the moisture content dependence of DC conductivity and the anisotropic electric behaviour for sugi (Cryptomeria japonica D. Don) wood, and to clarify the relationship between the mechanism of electrical conduction and \u22transient capillaries\u22 which relate intrinsically to the swelling and shrinkage of wood. It is shown through a discussion on the moisture content dependence of electrical conduction that the mechanism of electrical conduction above about five percent moisture content is related to the structure of transient capillaries as well as the mechanism of moisture adsorption in wood. Although the degree of dissociation of adsorbed ions is independent of the structure of transient capillaries, the mobility of ions relates to the structural difference of transient capillaries. Up to about five percent moisture content, it is shown that the dissociation and migration of adsorbed ions are considered not to be important, and tha t transient capillaries are considered to be important. As a result of a discussion on the time dependence of DC conductivity which relates intrinsically to the rate of ionic conduction, it is presumed as follows: I) the swelling is mainly due to the production of new transient capillaries and the enlargement of pre-existing capillaries up to fifteen percent moisture content, and 2) the swelling is mainly due to the increase in number of the transient capillaries being in nearly the saturated state above fifteen percent moisture content
