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….
Chapter 9:Degradation and Protection
Lecture 1: Degradation
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.
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
Requirements for fungi
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.
Wood inhabiting vs. wood eating
Drywood termite damage in a fence. Drywood termites inhabit the wood they are eating.
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.
A carpenter bee hole in a rafter.
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