Wood moisture interactions

• Water uptake by sorption (bound water) —> in cell walls

• ater uptake by capillary forces (free water) —> lumina

• can absorb or release moisture from surrounding environment until it reaches equilibrium

• RH influences MC: the higher RH the higher MC

• Temperature influences RH: influence capacity of air to hold moisture

• Temperature and MC relationship: Increase in temperature —> decrease in MC

u=(m_u - m_dtr) / m_dtr * 100%

Resistance test: measuring electrical conduction

• Wood as a porous material with interconnected capillaries

• Water movements in microsystem and macrosystem

• Cell walls take up water from air

• Cell lumina transport liquid water

• Density

• Temperature

• Moisture content

• Cutting direction

• Chemisoption

• Adsoption

• Capillary condensation

• Hysteresis: 1-2%

• Previous history: some uptake of water is blocked by first water desoption

• Chemnistry of cell wall: Hemicellulose MC > Wood > Lignin

• Mechanical loading: MC is higher under tensile loading than under compressive loading

• Thermal pre-treatment: Lower moisture content with thermal treatment at higher temperature

• Chemical pre-treatment: salt impregnation —> lower MC

• Extractives:

• Reifholz: >30

• False heartwood: > 25

• coloured heardwood: >22

• The higher the density the lower the max. moisture content