Wood is an organic matter and is susceptible to microbial attack:
Biocides are chemical or microbiological substances, that are intended to neutralize harmful organisms in the nonagricultural sector. Among others, these harmful organisms may include fungi, bacteria, yeasts and algae. Microbial activity can cause discoloration, break down of emulsions, gelling or thinning, shifts in pH, bad odor and even gassing. On surfaces visible growth of fungi, bacteria and algae can occur. Biocides provide protection for health and protection of products. Therefore, biocides play a significant role in the maintenance of health and hygiene standards.
Bacteria only attack wood when it is extremely wet e.g. when stored in log ponds, buried in the soil or used in cooling towers. The most commonly found bacteria are:
1. Escherichia spp.
2. Pseudomonas spp.
3. Staphylococcus spp.
Fungi attack wood under damp conditions. This decay often originates in wood, which is in contact with the ground or where wood becomes damp. Two groups of fungi are found growing on timber; wood destroying fungi and wood discolouring fungi.
Wood destroying fungi cause decay of the wood, which results in a loss of strength as the wood, is destroyed. Wood destroying fungi may be further divided into brown, white and soft rots:
Brown rots are recognised by a darkening of the wood under attack. On drying the wood becomes brittle and often cracks. Fungi of this type commonly cause decay in buildings e.g. the dry rot fungus, serpula lacrymans and wet rot fungi, coniophora puteana.
White rots are characterised by a lightening of the attacked wood. Hardwoods are particularly susceptible. Fungi of this type commonly cause decay in external joinery e.g. donkioporia expansa.
Soft rots are characterised by wet wood being softened progressively from the surface. Wood used in water cooling towers or in the ground are prone to these fungi e.g. ascomycetes. Hardwoods are again particularly susceptible.
Wood discolouring fungi cause stains and moulds, which are surface growths that do not reduce the mechanical properties of wood but instead discolour it. In the case where appearance is important, there can be a loss of value. Softwood is more at risk than hardwood. Blue stain and sapstain fungi colonise and penetrate into wood to cause a blue or brown colouration in spots or streaks. Mould fungi can spread on the surface of wetted timber, where they feed on sugars and can cause different colorations e.g. black brown. The most common fungi are:
• Aspergillus spp.
• Aureobasidium spp.
• Trichoderma spp.
Wood boring insects are important pests in that they cause much damage in wood in structure and storage. The insects found damaging wood belong to the Cerambycidae, Anobiidae and Curculionidae families. Insects attacking wood in storage belong to the families Lyctidae, Bostrychidae, Platpodidae, Scolytidae and Cerambycidae.
Termites are a major problem in certain regions of the World such as France, Japan and parts of North America. If there is a termite problem, it normally requires the treatment of the whole building. The main termites found are: Coptotermes lacteus, Coptotermes formosanus, Nasutitermes exitiosus, Reticulitermus lucifugus, Reticulitermus flavipes, Kalotermes flavicollis.
Features of a Wood Preservative
Wood preservatives are used to control the above pests and the ideal wood preservative will have the following features:
• Have sufficient efficacy against wood destroying organisms • Be able to penetrate wood
• Be chemically stable
• Be able to be safely handled
• Be economical to use
• Not weaken the structural strength of the wood
• Not cause significant dimensional changes within the wood.
• Be toxicologically tested and approved
• Insecticide properties may be required
Target Product can be used :
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