The Change in Permeability of Larch Boxed-Heart Timber during Drying after High Temperature and Low Humidity Treatment

Japanese larch (Larix kaempferi) boxed-heart timbers with the dimension of 100 3 100 3 1,000 mm were dried after being steamed at 1008C and 08C wet-bulb depression for 5 hours, and then dried at 1208C and 308C wet-bulb depression for 8, 12, and 16 hours, respectively. The radial permeability of the surface layers of the timbers during drying was measured to discover the moisture movement mechanism in the transverse direction. The radial permeability in the surface layers of pretreated timbers decreased and tended to decrease as pretreating time increased. The decreased permeability can be attributed to the reduced distance between microfibrils inside the surface layers of pretreated timbers attributable to the pretreatment. This reduced distance decreases the moving rates of the bound water and water vapor from the inner part to surface layers of pretreated timbers during drying. Therefore, the average drying rate of pretreated timbers was decreased.