chapter 9 degradation and protection
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Chapter 9: Degradation and Protection. Lecture 1 : Degradation . Learning Objectives. Define deterioration Understand the significance of the degradation of bio-based composites Identify the types of deterioration and some of the organisms involved. Deterioration is….

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learning objectives
Learning Objectives
  • Define deterioration
  • Understand the significance of the degradation of bio-based composites
  • Identify the types of deterioration and some of the organisms involved
deterioration is
Deterioration is…
  • No longer fit for its purpose
  • Can be
    • Cosmetic or structural damage
    • Caused by biological or physical (abiotic) factors
deterioration is important
Deterioration is Important
  • Scope of building products deterioration
    • 10% of wood used for replacement
    • Wood deterioration costs a lot per year
      • $500 million marine
      • $1 billion termites
      • $370 million in California decay
    • 512 wood preservation facilities produce $5.8 billion worth of ‘treated wood’ in US in 2007 (US Census)
deterioration is also good
Deterioration is Also Good
  • Bio-based products are biodegradable
    • Part of the carbon cycle
  • Potential to be burned for a “carbon-neutral” energy source

abiotic degradation
Abiotic Degradation
  • Warp & Thickness swell
    • Water swells lignocellulosics and can released trapped stresses
  • Creep
    • Deformation over long-term from relatively small load
  • High temp for long time can weaken
    • Can be exacerbated by chemicals (e.g. preservatives)
  • Fire
    • Chemicals can reduce risk/effects
  • Weathering
  • Water
  • Sunlight
  • Fire

The siding on this building is weathered. The darker areas are exposed to more sunlight. In protected areas under the eaves, the wood is closer to its original, light color. Finishes can be used to prevent weathering and improve the looks of exterior wood.

heat and fire
Heat and Fire

Wood is actually pretty durable when exposed to high heat

At about 120 degrees, flammable gases become volatile

>200 degrees, rapid pryolysis occurs

260-350 degrees, pryolysis accelerated and gases will ignite in the presence of oxygen

Carbon “char” residue during burning will insulate wood and decrease the rate of heat transfer. This slows fire in large wood members

agents of biological deterioration the fungi
Agents of Biological Deterioration – The Fungi

Requirements for fungi

  • Temp
  • Food
  • O2
  • Water

Damage done

  • Discolor
  • Strength
  • Toughness
biotic deterioration
Biotic Deterioration
  • Decay fungi
      • Brown rot
      • White rot
      • Soft rot
  • Non-decay fungi
      • Mold
      • Stain
  • Insects
      • Many…
  • Woodpeckers
  • Marine borers
      • Toredos
      • Limnoria

Most important

  • 1. Mold & Stain
    • Ascomycetes
    • Sapstain, bluestain
  • 2. Rot
    • Deuteromycetes
    • Brown, white
    • Soft rot

Bluestain has penetrated the sapwood of this pine log. The heartwood in the center is not affected. The stain cannot be removed but the wood is still structurally sound.

brown rot Rot
  • Selectively attack cellulose and hemicellulose
    • Modify lignin but do not metabolize it
    • Use a non-enzymatic mechanism to penetrate cell walls
  • Wood residue will have an abnormal brown to red color due to modified lignin
  • S-2 layer often first to be degraded due to high cellulose content
white rot Rot
  • Wood residue is white and bleached
  • All three polymer components metabolized
  • Use enzymes to rode cell wall from the lumen outwards
white rot cont
White Rot (cont.)
  • “Spalted wood”
    • Incipient white rot decay Spalted%20Wood.gif

soft rot
Soft Rot
  • In especially wet areas
  • Treated wood susceptible
  • Wood exterior becomes soft

dry rot a misnomer
“Dry Rot” – A Misnomer
  • Serpulaspp. – the true ‘dry rot’
    • A brown rot fungus
  • All rot needs water
    • Serpulaneeds less because it can move water
  • Usually “dry rot” is brown rot that has (subsequently) dried out
other wood discolorations
Other Wood Discolorations
  • Extractive bleeding
    • Species dependent
  • Iron stain
    • Can react with extractives
  • Enzymatic stains
    • Only in (recently) living wood

types of wood destroying i nsects
Types of Wood Destroying Insects
  • Carpenter Ants
  • Termites
  • Golden buprestid Beetle
  • Powder post Beetle
  • Wood house borer (old house, etc.)
insects types
Insects Types

Wood inhabiting vs. wood eating

  • Wood inhabiting
    • Some beetles
    • Carpenter ants, bees
    • Reinfesting vs. not
  • Wood for food
    • Termites
    • Some beetles

Drywood termite damage in a fence. Drywood termites inhabit the wood they are eating.

  • The most serious insect pest
  • Keeping dry helps
  • Integrated management
    • Risk reduction
    • Monitoring
    • Chemical control

Both termites (top) and ants (bottom) have flying reproductive forms (alates). Termites have straight antennae, equal length wings and abdomens that are as wide as the rest of their bodies. Ants have bent antennae, wings of unequal length and constricted waists.

carpenter ant bees
Carpenter Ant & Bees
  • Can live in building components
  • Not (usually) a structural problem
  • Difficult to control

A carpenter bee hole in a rafter.

  • Some attack only living trees
    • Some re-infest products
  • ‘Control’ depends on type

The surface of this log has numerous powderpost beetle entry holes. Powderpost beetles can attack and re-infest wood.


Generally limited because degradation slow

Can survive in anoxic or anaerobic environments

Affects bottomland forests and water-stored logs (can also affect marine pilings and buried wood)

Lumber can split when processed

After about six months bacteria begin to degrade pit and parenchyma structures

Bacteria highly adaptable so preservatives often fail

marine borers
Marine Borers
  • Shipworms (Teredos)
    • Mollusks
    • Larva borrow into wood leaving only very small entrance hole
    • Filter feed through entrance hole
    • Can reach ¾“ diameter hole that is two feet long‑05/Shipworms_1/Shipworms_1a/shipworms_1a.htm‑05/Shipworms_1/shipworms_1.htm

marine borers1
Marine Borers
  • Gribbles (Limnoria)
    • Small crustacean
    • Live in surface borrows for protection
    • Wave action erodes weakened wood producing an hourglass shape

review questions
Review Questions
  • Something good/bad about biomass deterioration
  • How can water damage bio-based composites?
  • What type of wood attacking fungi is the worst? The best?