Properties of Wood

Question 1

How is the structure represented?

Answer 1

Bundle of tubular cells (fibres) glued together by lignin.

Question 2

Which direction are cells aligned?

Answer 2

Usually longitudinal.

Question 3

What are Trackeids?

Answer 3

• Longitudinal aligned cells
• Softwood - 3 to 5mm long (aspect ratio (l/d) = 100)
• Hardwood - 1mm long
• Used for mechanical support and water/sap transfer.

Question 4

Cell make up

Answer 4

• Thin primary walls (forms first)

- Three layered secondary walls (forms second), provides most strength

Question 5

S1 (outside layer of three layer secondary wall)

Answer 5

• 15 degrees off horizontal
• Thin
• Almost perpendicular to cell axis
• Acting mainly perpendicular to grain

Question 6

S2 (middle layer of the three)

Answer 6

• Thick walls
• Microfibrils parallel to axis
• Providing strength in longitudinal direction

Question 7

S3 (inner layer of the three)

Answer 7

• similar to that of S1

Question 8

What is Cellulose?

Answer 8

= 50% of wood weight (about)

• Building block (glucose = sugar)
• With growth linear cellulose arrange into ordered strands, fibrils.

Question 9

What is Lignin?

Answer 9

= 23 to 33% of softwood weight
= 16 to 25% of hardwood weight
- mostly intercellular
- intractable, insoluable, materials (chemically)
- bounded to cellulose
- glue holding tube together
- longitudinal shear limited to strength of lignin

Question 10

What is Hemicellulose?

Answer 10

• Polymeric units made from sugar
• Different to cellulose (several sugars tied up in structure)
  = 20 to 30% hardwood
  = 15 to 20% softwood
• main sugar units xylose (hardwood) and mounose (softwood)

Question 11

What are Extractives?

Answer 11

= 5 to 30% of wood substance

• polyphenolics, colouring matters, essential oils, fats, resins, waxes, gums, starches, ad simple intermediates
• removed with water, alcohol, acetone and benzene
• some are toxic to resin, natural durability

Question 12

What is Ash?

Answer 12

= 0.1 to 3% of wood material

- Calcium, potassium, phosphate and silica

Question 13

What is the chemical composition of wood?

Answer 13

• 50% Carbon
• 44% Oxygen
• 6% Hydrogen
• 0.1% Nitrogen
• 0.1 to 3% Ash

Question 14

Specific gravity factors

Answer 14

• around 1.5
• float initially on water (voids of air), when saturated will sink (takes years)
• seasoned wood less than 2/3 weight water
• denser the wood the stronger it is

Question 15

Compression, is wood strong or weak under?

Answer 15

Stronger longitudinally

Traverse strong at 1/3 of og thickness

Question 16

Tension, is wood strong of weak under?

Answer 16

Strong parallel to grain

Weak perpendicular to grain

Question 17

No adjustment to allowable stress if average equilibrium moisture content is less than what?

Answer 17

15%

Question 18

Causes of deterioration in wood?`

Answer 18

• Fire
• Decay
• Termites
• Chemicals
• UV
• Moisture fluctuations
• Insects
• Mechanic abrasions

Question 19

Fungus on wood. What it does and how.

Answer 19

• Feeds on wood
• Spreads via spores
• Secrete enzyme that depolymerizes cellulose, resulting in rot.

Question 20

Fungus growth.

Answer 20

• Food (cell structure, cell content)
• Needs temperature of 5 to 40 degrees
• Moisture (fibre saturation, below 20% MC fungi is inhibited)
• Oxygen

Question 21

Fungus damage.

Answer 21

• Stains (sapstains) and decay damage.

Question 22

Prevent Fungus

Answer 22

• Minimise moisture

- Exclude air

Question 23

What termites do

Answer 23

• Feed off wood
• rest in soil (moist, warm)
• if moisture in wood is low they build shelter tubes for direct contact between soil and wood

Question 24

Protect from termites how?

Answer 24

• Block access to wood from soil

- Preservatives

Question 25

Moisture fluctuations

Answer 25

• Below FSP (fibre saturation point) results in dimensional changes

Question 26

What is shrinkage?

Answer 26

• Loss of moisture

- Relates to moisture fluctuations

Question 27

What is swelling?

Answer 27

• Gain of moisture

- Relates to moisture fluctuations

Question 28

Decay resistance in sapwood and hardwood?

Answer 28

• Sapwood lacks

- Heartwood does sometimes (species dependent) because of natural preservatives during formation.

Question 29

Wood preservation methods?

Answer 29

Treating
- Preservatives pressure treating cylinders, makes wood toxic to fungi, eliminates food.
Preserved food lasts 5 to 10 times longer.
Outside treated, inside not. If outside damaged, inside at risk.
Effectiveness depends on depth and amount of preserving.
Pressure of vacuum impregnation.

Question 30

What is Chromated Copper Arsenate and what is the process?

Answer 30

• fungicide.
• copper = fungicide, arsenic = fungicide + insecticide, chromium = uv resistance.
• water solution
• reacts with wood forming insoluable precipitate (virtually)
• reaction call fixation
• 1.5% of weight

Question 31

What is Alkaline Copper Quaternary?

Answer 31

• alernate to CCA
• quart = secondary fungicide
• preservative
  (might be missing info)

Question 32

What is Borates and process?

Answer 32

• deep penetration of green lumber
• non toxic (barely)
• colourless/oderless
• protect from rain/water
• preservative

Question 33

What is Cresote?

Answer 33

• black oil

- one of the oldest preservatives

Question 34

What are Tin compounds for?

Answer 34

• preservative

- organic

Question 35

How is fire prevented?

Answer 35

• fire retardant chemicals painted on surface
• works by limiting the gas released
• reducing heat in initial stages of fire
• pressure impregnation with water soluble salts

Question 36

How fire works?

Answer 36

• 100 degrees gas is released
• 250 degrees gas ignites with open flame
• 500 degrees self ignition