Shrinkage stress of wood during drying under superheated steam above 100°C

In order to reduce the internal stress of wood during drying, an attempt was made to dry wood with superheated steam above 100degreesC. Sugi (Cryptomeria japonica D. Don) wood specimens were dried with radial restraint using superheated steam at up to 180degreesC, and the resulting restrained shrinkage stress was examined. A load cell capable of measuring shrinkage stress inside an autoclave was developed and the shrinkage stress was measured at temperatures from 80 to 180degreesC and a relative humidity of 0% to 80%. It was found that the shrinkage stress decreased dramatically with drying above 140degreesC and above 60% relative humidity. It was also found that the shrinkage stress above 140degreesC occurred even at 100% RH and was ascribed to the structural change in cell-wall components.