Topic 3: Properties of Timber Flashcards
(30 cards)
Define moisture content (M.C.) in timber.
M.C. is the percentage of water in wood, calculated as (M wet - M dry) / M dry x 100%.
How to determine the moisture content of timber?
Measure wet mass (M wet), oven dry at 105°C to get dry mass (M dry), then use M.C. = (M wet - M dry) / M dry x 100%.
Typical moisture content range for green wood?
30% to 200%, depending on species and season.
How does season affect moisture content of green wood?
Higher moisture in wetter seasons, lower in drier seasons.
Significance of oven drying at 105°C?
Removes free water for accurate dry mass measurement.
Properties of timber related to moisture content?
Weight, strength, stability, and decay susceptibility are affected by water content.
Define equilibrium moisture content (EMC).
EMC is the moisture level where wood neither gains nor loses water, balanced with surrounding air.
Why is wood hygroscopic?
Wood absorbs or loses water to reach equilibrium with the environment.
Types of moisture in wood?
Free water in cavities and bound water in cell walls.
What is the fibre saturation point (FSP)?
FSP is the moisture content where cell walls are saturated, but cavities are free of water.
How do temperature and humidity affect EMC?
Higher humidity increases moisture content; temperature affects moisture exchange rate.
Significance of FSP in wood?
Marks the transition of moisture from cell walls to cavities, affecting wood properties.
How does wood gain or lose moisture?
Through absorption or desorption until reaching EMC.
Role of adsorption forces in moisture content?
Hold bound water in cell walls, influencing moisture content and properties.
Effect of moisture content changes above FSP?
No significant dimension changes due to free water in cavities.
What happens when moisture content decreases below FSP?
Wood shrinks as water is lost from cell walls.
Define FSP in wood moisture context.
FSP is the moisture level where cell walls are saturated, cavities are free of water.
How is shrinkage related to moisture content changes?
Shrinkage occurs when moisture decreases below FSP.
Is shrinkage due to moisture loss reversible?
Yes, moisture reabsorption can restore original volume.
Define free water in wood.
Liquid filling the cavities of wood cells.
Explain bound water in wood.
Liquid or vapor chemically bound to cellulose in cell walls.
Describe the difference between free water and bound water in wood.
Free water fills the cavities of wood cells, while bound water is chemically attached to the cellulose in the cell walls.
Identify the source of the information about wood moisture.
The information is from http://timber.ce.wsu.edu/Supplements/Moisture/moisture%20page2.htm.
What is the role of hydrogen bonding in wood moisture content?
Hydrogen bonding chemically binds liquid or vapor water to the cellulose in the wood cell walls, creating bound water.
