Dielectric Relaxation of Heat-Treated Wood
Hiroyuki SUGIMOTO and Misato NORIMOTO
Abstract:Changes in the dielectric relaxation of sugi (Cryptomeria japonica) specimens by heat treatment were investigated. Dielectric properties in the longitudinal direction for the oven-dried specimens were measured in the range from 20Hz to 1MHz and from |150 to 20. The relaxation due to the orientation of methylol groups was observed for the specimens treated at the temperature up to 300. The relaxation magnitude obtained from the Cole-Cole plots did not change by the heat treatment up to 200, but it decreased remarkably above 200 and became 0 at 300, showing the disappearance of methylol groups. Any relaxation was not detected within the range measured for the specimens treated at the temperature between 300 and 450. However, one relaxation was recognized for the specimens treated at the temperature between 500 and 600. Regarding the specimen treated at 500 as a system in which a small amount of ellipsoids of graphite disperses in the medium of an insulator, the applicability of the Maxwell-Wagner's theory to the tanΒ versus logarithmic frequency curve at 20 was examined. A good agreement between the experimental and calculated results was obtained in the case that long and narrow ellipsoids oriente to the direction of the electrical field. These results suggested that the relaxation was due to the interfacial polarization. Key Words:Dielectric Relaxation, Wood, Heat treatment, Methylol groups, Maxwell-Wagner's theory, Interfacial polarization