Presentation on theme: "Chapter 9: Degradation and Protection Lecture 1: Degradation."— Presentation transcript:
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… No longer fit for its purpose Can be – Cosmetic or structural damage – Caused by biological or physical (abiotic) factors
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 Bio-based products are biodegradable – Part of the carbon cycle Potential to be burned for a “carbon-neutral” energy source
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
1)Water 2)Sunlight 3)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 Wood is actually pretty durable when exposed to high heat – At about 120 degrees, flammable gases become volatile – >200 degrees, rapid pryolysis occurs – 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 Requirements for fungi Temp Food O 2 Water Damage done Discolor Strength Toughness
Biotic Deterioration Decay fungi Brown rot White rot Soft rot Non-decay fungi Mold Stain Insects Many… Woodpeckers Marine borers Toredos Limnoria Most important
Fungi – 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 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 Wood residue is white and bleached All three polymer components metabolized Use enzymes to rode cell wall from the lumen outwards
White Rot (cont.) “Spalted wood” – Incipient white rot decay Spalted%20Wood.gif
Soft Rot In especially wet areas Treated wood susceptible Wood exterior becomes soft
“Dry Rot” – A Misnomer Serpula spp. – the true ‘dry rot’ – A brown rot fungus All rot needs water – Serpula needs less because it can move water Usually “dry rot” is brown rot that has (subsequently) dried out
Other Wood Discolorations Extractive bleeding – Species dependent Iron stain – Can react with extractives Enzymatic stains – Only in (recently) living wood
Types of Wood Destroying Insects – Carpenter Ants – Termites – Golden buprestid Beetle – Powder post Beetle – Wood house borer (old house, etc.)
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.
Termites 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 Can live in building components Not (usually) a structural problem Difficult to control A carpenter bee hole in a rafter.
Beetles 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.
BACTERIA 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 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 tents/Lab ‑ 05/Shipworms_1/shipworms_1.htm ‑ 05/Shipworms_1/Shipworms_1a/shipworms_1a.htm
Marine Borers Gribbles (Limnoria) – Small crustacean – Live in surface borrows for protection – Wave action erodes weakened wood producing an hourglass shape al/Limnoria.htm
Review Questions 1.Something good/bad about biomass deterioration 2.How can water damage bio-based composites? 3.What type of wood attacking fungi is the worst? The best?