1. Forestry 280 - Chapter 8: Wood and Water
Overview:
Location of Water in Wood
Moisture Content
Forestry Chapter 8: Wood and Water

2. Forestry 280 - Chapter 8: Wood and Water
Importance:
Utilization problems
Water effect on properties
- Strength - Dimensions
- Heating Value - Electrical
- Acoustical - Insulation
- Decay Resistance
Forestry Chapter 8: Wood and Water

3. Forestry 280 - Chapter 8: Wood and Water
Water in Woody Cells
Water Interacts with Woody Cells on Two Levels:
Fiber Level
– Water can reside in the cell lumen.
- Contain: sugars, inorganic components (sap)
- Free Water
Molecular Level
Hydrogen bonds to hydroxyl (OH) groups
Cellulose, Hemicellulose, Lignin?
OH groups called sorption sites
Bound Water
Forestry Chapter 8: Wood and Water

4. Forestry 280 - Chapter 8: Wood and Water
Water in Woody Cells
Forestry Chapter 8: Wood and Water

5. Forestry 280 - Chapter 8: Wood and Water
Water in Woody Cells
Forestry Chapter 8: Wood and Water

6. Forestry 280 - Chapter 8: Wood and Water
Water in Woody Cells
Clarification: Adsorb versus Absorb
Wood can aBsorb water like a sponge
- Capillary effects (surface tension)
- Free Water
Wood can also aDsorb water
- Intermolecular hydrogen bonds
- Reversible phenomenon
- Cause of wood hygroscopic character
Forestry Chapter 8: Wood and Water

7. Forestry 280 - Chapter 8: Wood and Water
Water in Woody Cells
Equilibrium Moisture content (EMC) – MC at which wood
has no net gain or loss of moisture when surrounded by air
at a given relative humidity and temperature.
Moisture In = Moisture Out
Forestry Chapter 8: Wood and Water

8. Moisture Content (MC): a measure of the amount of water in wood
MC = [ Weight of Wood plus Water – Oven Dry Weight of Wood ] X 100
Oven Dry Weight of Wood
= [ Weight of Water ] X 100
OD Weight
Since MC calculation is based on OD weight, it can have values greater than 100%
Forestry Chapter 8: Wood and Water

9. Forestry 280 - Chapter 8: Wood and Water
Moisture Content
Typically the weight of wood plus water is referred to as “Green Weight” (GW)
Therefore:
MC% = [ (GW – OD) / OD ] X 100
Several Definitions of green weight:
Weight of felled tree
Weight of wood above fiber saturation point (FSP)
Weight of wood at any MC above zero
Forestry Chapter 8: Wood and Water

10. Forestry 280 - Chapter 8: Wood and Water
Moisture Content Determination
Measurement of MC:
Typically accomplished by oven dry method:
American Society for Testing and Materials (ASTM) Standard D 2016
Gravimetric determination: Weigh / Heat / Weigh
Electronic moisture meters use electrical properties
to estimate MC
Forestry Chapter 8: Wood and Water

11. Forestry 280 - Chapter 8: Wood and Water
Moisture Content Determination
Dry in 103 ± 2oC
24 Hours
Weigh Wet Sample
Weigh Oven Dry Sample
Calculate MC per equation
For samples greater than 1 inch thick, the drying time
should be extended until sample weight is constant.
Forestry Chapter 8: Wood and Water

12. Forestry 280 - Chapter 8: Wood and Water
Moisture Content Determination
Oven Dry Method:
Advantages –
Simplicity
Relative Accuracy
Disadvantages –
Destructive
Duration
Volatile wood components
Forestry Chapter 8: Wood and Water

13. Forestry 280 - Chapter 8: Wood and Water