Why does wood absorb moisture?
Wood is a capillary porous body, in which there is a hyper-physics capillary system and a micro-Mao Yan tube system in the wood, it has a high void and a huge inner surface, and the saturated vapor partial pressure on the water surface of the capillary capillaries is smaller than that in the ambient air, so the wood has strong adsorption and Mao condensation. Dry wood on the surface of the basic filament adsorption of water vapor, first in the smallest capillary in the formation of concave meniscus, the formation of capillary condensation phenomenon and form Mao condensate. The Mao radius of condensation phenomenon of water vapor is suitable for certain relative humidity in air. The lower the air humidity, the smaller the capillary radius of condensation occurs.
Dry wood moisture absorption process is small, moisture absorption and stability water content is more or less less than in the same air state desorption stable water content. This phenomenon is known as hygroscopic lag. A6f expression.
Causes of moisture absorption lag
Moisture absorption of wood must be dry, in the drying process, the wood micro-capillary system inside the gap has been partially infiltrated into the air occupied, which prevents the wood to absorb water.
Wood in the previous drying process, used to absorb water from each other directly connected to form a hydrogen bond, reducing the absorption of water in the future of the drying chamber.
The value of hygroscopic lag is not related to tree species, but increases with the increase of wood size. Fine or thin wood moisture absorption lag is very small, the average is only about 0.2%, negligible. But sawn timber (plate, lumber) moisture absorption lag is larger, and increases with the previous drying temperature rise, its variation range is 1% "5%, the average value is 2.5%."