Drying properties of Sugi round timber with microwave heating

Sugi round timbers injected with preservative are useful for outdoor playing and construction materials. To dry the Sugi round timbers for preservative injection, three drying methods including microwave drying, kiln drying and air drying were compared in this study. Using microwave drying, the timbers were dried within one day, but the other two drying methods required a much longer time. During most of the microwave drying process, the wood temperature appeared to be higher in the inner layer than in the outer layer. As a result, the inner layer moisture contents were significantly reduced by microwave drying, while kiln drying produced almost no decline in the inner layer moisture contents. In addition, although significant surface checks often occurred in timbers dried by kiln drying and air drying, microwave drying caused few surface checks. In contrast, internal checks were only observed in timbers treated by microwave drying. These results suggested that the microwave drying technique can improve the effectiveness of preservative injection in Sugi round timbers.