Q.
How can preservation of wood affects its use?
A.
PROPERTIES OF TREATED WOOD AFFECTING USES
Strength: Waterborne preservative treatments generally reduce the mechanical properties of wood. The treatment does not reduce the load carrying capacity to below acceptable levels. Incising may cause a slight decrease in strength but it gives an increased protection. Unless the steaming treatment period kept as short as possible, serious weakening of the wood can be observed. High pressure can brings about collapse of wood cells, especially with woods of low density. When the wood is treated to accepted chemical loading by normal industrial preservation methods any significant losses of strength is observed.
Flammability: Wood processed with water-borne salts has no greater flammability. However the wood treated freshly with creosote or heavy oil mixtures presents greater fire hazard. Therefore, mine props are processed with water-borne salts. After a few month creosote treated wood presents no fire hazard.
Electrical Conductivity: Creosote and organic solvent preservatives have no effect on the conductivity. Although water-borne chemicals change the electrical conductivity slightly, the differences are small and can be ignored for practical purposes.
Safety
Domestic and Industrial Buildings and uses: Creosote treated timber is not normally used in domestic buildings because of unpleasant and irritating odour. Timber used for domestic purposes is treated with water-borne chemicals by using pressure treatment or with organic solvent preservatives by double vacuum method. Wood treated with both creosote and water-borne preservatives is used as transmission poles, in warehouses and industrial and agricultural buildings.
Greenhouses, Seed and Mushroom Boxes: The timber treated with creosote or PCP are not recommended and the CCA processed timber can be used.
Children Playground Equipment and Garden Toys: Water-borne preservatives fixed in the wood can be used with absolute safety. Deposits seen on the surface are removed by redrying the wood to 22% moisture content, hosing down and drying again. Two coats of a water-repellent finish are also recommended as precaution. Creosoted wood is unsuitable.
Animal Pens: Most of the preservatives can be used with safety for animal pens. Timber treated with creosote should be air-dried and deposits on the timber treated with water-borne salts should be removed as described above. The use of PCP in preservatives should be avoided.
Food Containers: Creosoted timber must not be used as food containers. Copper 8-quinolinolate is recommended for the containers. The preservatives fixed in the wood, such as CCA, can be used with absolute safety on condition that surface deposits should be removed as described previously.
DIMENTIONAL STABILITY AND CHEMICAL MODIFICATION OF WOOD
One of the disadvantages of wood is dimentional instability by the changes in relative humidity of air. To prevent the different changes in different dimentions and improve some properties wood is treated with.
a) water-repellent formulations
b) phenolic resins
c) polyetlhylene glycol
d) monomers polymerising in the wood (wood-polymer composites)
e) acetic anhydride with catalyzer for acetylation of the material.
Ref:
Prof. Dr. Harzemşah HAFIZOĞLU
Z.K.Ü., Bartın Faculty of Forestry, Prof. Dr.