WOOD PRESERVATION

Slide 1: 

WOOD PRESERVATION PREPARATION OF TIMBER MECHANISM CHARACTERISTICS OF PRESERVATIVE N.KANAGARAJ BSF-06-007 BSC[FORESTRY]

Slide 2: 

For satisfactory treatment and good performance, the timber must be sound and suitably prepared. Except in specialized treating methods involving unpeeled or green material The wood should be well peeled and either seasoned or conditioned in the cylinder before treatment. It is also highly desirable that all machining be completed before treatment . Machining may include incising to improve the preservative PRETREATMENT

Slide 3: 

Peeling Peeling round products is necessary to enable the wood to dry quickly to avoid decay and insect damage To permit the preservative to penetrate satisfactorily. Even strips of the thin inner bark may prevent penetration. Patches of bark left on during treatment usually fall off in time and expose untreated wood. Processes in which a preservative is forced or permitted to diffuse through green wood lengthwise do not require peeling of the timber.

Slide 4: 

Drying Drying of wood before treatment is necessary to prevent decay and stain and to obtain preservative penetration. However, for treatment with waterborne preservatives by certain diffusion methods, high moisture content levels may be permitted How long the timber must be air dried before treatment depends on the climate, location, and condition of the seasoning yard, methods of piling, season of the year, timber size, and species

Slide 5: 

Conditioning of Green Products When green wood is to be treated under pressure, one of several methods for conditioning may be selected. The steaming-and-vacuum process is used In the steaming process, the green wood is steamed in the treating cylinder for several hours, usually at a maximum of 118ºC (245ºF). When steaming is completed, a vacuum is immediately applied. During the steaming period, the outer part of the wood is heated to a temperature approaching that of the steam; the subsequent vacuum lowers the boiling point so that part of the water is evaporated or forced out of the wood by the steam produced when the vacuum is applied.

Slide 6: 

Incising Wood that is resistant to penetration by preservatives may be incised before treatment to permit deeper and more uniform penetration. To incise, lumber and timbers are passed through rollers equipped with teeth that sink into the wood to a predetermined depth, usually 13 to 19 mm . The teeth are spaced to give the desired distribution of preservative with the minimum number of incisions. The incisions open cell lumens along the grain, which greatly enhances penetration. Incising is especially effective in improving penetration in the heartwood areas of sawn surfaces. Incising is practiced primarily on Douglas-fir, western hemlock,

Slide 7: 

MECHANISM OF WOOD PRESERVATION The preservation is mainly attributed to sap wood ( This is due to the fact that the pores are clear where in the heart wood pores are plugged with out growths …. TYLOSIS ) However the heart woods are also considered for its moisture content.

Slide 8: 

GENERAL MECHANISM It is a physico -chemical mechanism Before applying any preservative the cell sap should be removed on applying vaccum. This is done for easy penetration of preservative. ( PHYSICAL) On applying preservative, according to the relative vapour pressure in the lumen the chemical enters/ penetrates (PHYSICAL)

Slide 9: 

On applying pressure effective penetration is achieved Now again the cells are in saturated condition. It has to be again seasoned. On applying vaccum the excess preservatives and water are drained and hence the bounded preservative will react with free OH site of cellulose (CHEMICAL). The adhesive force and mono-molecular adsorption of cellulose between preservative and OH group of cellulose makes the preservative tightly bound (PHYSICAL).

Slide 11: 

CHARACTERISTICS OF IDEAL PRESERVATIVE 1. High level of lethal toxicity even in low concentrations against fungi, insects and marine organisms while low level of lethal effects for mammals. 2. High level of permanency under various conditions in which the treated timber would be used such as resistance to Leaching by water. Quick evaporation brought about by heat. Chemical transformation caused by oxidation, reduction polymerization.

Slide 12: 

3. High level of amenability to impregnation in the entire cross section of the wood that is being treated in order to give a more lasting effect. 4. The stability of the preservative during treatment of the timber must be high. In other words, it must not decompose at the high temperatures that are normally used during such treatments. 5. the preservative must be such that it does not increase the inflammability of the wood. On the other hand it would be advantageous to have a preservative which also functions as a fire retardant.

Slide 13: 

6. The health of the workers who use the preservative or even of those living in the area must not be adversely affected by it. 7. The cost of the preservative must not be prohibitive and it should be readily available. 8. Ease of transportation over long distances is another desirable characteristic.

Slide 14: 

9. The preservative must not cause corrosion in the metals that are used in the equipment used for wood preservation. 10. The preservative must not prevent the painting or varnishing of the treated timber. 11. The strength and other properties of wood should not be adversely affected by the preservative.

Slide 15: 

Thank you