Shrinkage stress of wood during drying under superheated steam and its mechanism

为了减少木材干燥过程中的内应力，尝试了用100℃以上的过热蒸汽干燥木材。用高达180℃的过热蒸汽对日本柳杉木材试件进行径向约束干燥，并检测了所产生的约束收缩应力。研制了一种能够测量高压灭菌器内收缩应力的称重传感器，并在温度为80~180℃、相对湿度为0~80%的条件下测量了收缩应力。结果表明，干燥温度在140℃以上、相对湿度在60%以上时，收缩应力显著降低。实验还发现，即使在100%RH条件下，仍存在140℃以上的收缩应力，这归因于细胞壁成分的结构变化。

In order to reduce the internal stress of wood during drying, an attempt was made to dry wood with superheated steam above 100℃. Sugi (Cryptomeria japonica D.Don) wood specimens were dried with radial restraint using superheated steam at up to 180℃ 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 180℃ and a relative humidity of 0 to 80%. It was found that the shrinkage stress decreased dramatically with drying above 140℃ and above 60 percent relative humidity. It was also found that the shrinkage stress above 140℃ occurred even at 100%RH and was ascribed to the structural change of cell wall components.