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Overview: Location of Water in Wood Moisture Content

Wood and Water. Overview: Location of Water in Wood Moisture Content. Wood and Water. Importance: Utilization problems Water effect on properties - Strength - Dimensions - Heating Value - Electrical - Acoustical - Insulation - Decay Resistance. Water in Woody Cells.

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Overview: Location of Water in Wood Moisture Content

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

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

  3. 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 280 - Chapter 8: Wood and Water

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

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

  6. 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 280 - Chapter 8: Wood and Water

  7. 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 280 - Chapter 8: Wood and Water

  8. Moisture Content 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 280 - Chapter 8: Wood and Water

  9. 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 280 - Chapter 8: Wood and Water

  10. 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 280 - Chapter 8: Wood and Water

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

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

  13. Forestry 280 - Chapter 8: Wood and Water

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