ABSTRACT
The versatility of wood is due to the level of moisture content in wood which determine the performance of wood in service. This performance is as a result of the process used in the drying of the wood species. Wood can be dried through natural and artificial drying method but natural method required little skills and cost in obtaining desirable result. This project was based on the improvement of the natural method of wood drying, in order to reduce the cost of drying wood. Some wood species were selected and used for this project work and the result obtained at the end of the experiment, was presented in this report. Wood exchanges moisture with air; the amount and direction of the exchange (gain or loss) depend on the relative humidity and temperature of the air and the current amount of water in the wood. This moisture relationship has an important influence on wood properties and performance. This paper discussed the physical properties of most interest in the use of wood products. Some physical properties discussed are influenced by species as well as variables like moisture content; other properties tend to be independent of species.
CHAPTER ONE
1.0 INTRODUCTION
Drying, if carried out promptly after conversion of wood, protects timber against primary decay, fungal stain and attack by certain kinds of insects. Organisms, which cause decay and stain, generally cannot thrive in timber with moisture content which is below 20%. Several, though not all, insect pests can live only in green timber. Dried wood is less susceptible to decay than green wood which is above 20% moisture. Air drying is the drying of timber by exposing it to the air. The technique of air drying consists mainly of making a stack of sawn timber (with the layers of boards separated by stickers) on raised foundations, in a clean, cool, dry and shady place. Rate of drying largely depends on climatic conditions, and on the air movement (exposure to the wind). For successful air drying, a continuous and uniform flow of air throughout the pile of the timber needs to be arranged (Desch and Dinwoodie, 1996). The rate of loss of moisture can be controlled by coating the planks with any substance that is relatively impermeable to moisture; ordinary mineral oil is usually quite effective. Coating the ends of logs with oil or thick paint, improves their quality upon drying. Wrapping planks or logs in materials which will allow some movement of moisture, generally works very well provided the wood is first treated against fungal infection by coating in petrol/gasoline or oil. Mineral oil will generally not soak in more than 1–2 mm below the surface and is easily removed by planning when the timber is suitably dry (Rowell, 1983). It can be less expensive to use this drying method (there are still costs associated with storing the wood, and with the slower process of getting the wood to market), and air drying often produces a higher quality, more easily workable wood than with kiln drying. The drying rate of wood differs due to the amount of moisture content present in each wood cell. Hardwood is said to be more complex than softwood species, due to the types of different component parts contained in the hardwood cell (e.g. vessel, lignin, cellulose and hemicelluloses) and is discovered to require more drying period (Desch and Dinwoodie, 1996). The structural composition of wood and variation in the physical properties of different wood species are the reason for different seasoning period. Each wood species has different tendency to drying, when exposed to a particular drying phenomenon. There are various drying procedures which have been practiced over the years and the drying rate of these techniques differs from one another. Some have been discovered to be faster than the others during the process of subjecting the wood to drying. It is important to dry wood before subjecting it to any use, in order to reduce the moisture content (M.C %) of the wood. An artificial drying technique has been developed and it has been noted to be very fast in drying wood, than the natural drying techniques. The disadvantage of using this method is that the inner layers of the wood fail to dry properly, especially hardwood species (Innes, 1996). The cost of installation of the equipment for the artificial drying techniques are very expensive e.g. Kiln dryer. It is a more reliable means of drying techniques but when considering the cost required for installation of the equipment, it will be necessary to exercise some caution before embarking on it, especially by small firms. There is a need for modifying the natural process of wood seasoning, since it requires little capital.
1.2 STATEMENT OF PROBLEM
The problem with drying of wood artificially is on the cost for the seasoning. The different kilns for drying wood are costly to install. There is cost to be incurred during seasoning on electricity and heat generation etc. There is a need to find another workable and appropriate way in which we can bring about reduction in the cost required. This can easily be done by improving the natural means of wood seasoning. An enclosure with black polythene will be used to speed up the rate of natural drying techniques.
1.3 OBJECTIVES
To determine the drying time of wood in two different media.
To compare the rate of drying of wood in the two media.
1.3 JUSTIFICATION
Due to the problems of cost which can arise from seasoning of wood using artificial drying techniques, it became necessary to find a means by which wood can be properly seasoned. The major aim is to use a modified natural seasoning method in drying the wood, which is often at low cost. Since not most of the people or organisations can afford the price of setting up of equipment for artificial drying method (kiln seasoning), a certain procedures has been developed, to mitigate the problem of cost as well as uneven moisture content drying. It is essential to know the moisture content of wood in any wood industry before using it for construction, because too high moisture content cause movement in the wood. If such wood is used for construction without been seasoned, warping and curling later occur. It is therefore necessary to reduce the moisture content in wood, so as to avoid attack due to fungi and insects. This is done to ensured the satisfactory performance of wood in use, the amount of moisture content in wood is generally reduced before wood is put into service by the process of seasoning (drying). The reasons for drying wood before use can be summarized as follows:
1. Most strength properties of wood are improved by drying.
2. Nailed and screwed joints are stronger in seasoned wood.
3. Glued wood products perform better when assembled from dried wood.
4. Dried wood is better thermal insulating materials than wet wood.
5. Wood is dried to substantially reduce it shipping weight.
6. Dried wood is less susceptible to damage by insects than wet wood.
7. Prior drying usually makes treatment of wood with preservatives more successful.
8. The electrical resistance of dried wood is much greater than that of wet wood.
9. To dry wood to moisture content required for it use, because wood shrinks as its loss moisture.
10. To increase dimensional stability. Wood shrinks across the grain (not along the grain) when it dries. If wood is cut to size before it is seasoned, it will shrink during drying and thus be undersized in its final form.
11. To reduce or eliminate attack by decay or stain. Wood that is dried below 20 percent moisture content is not susceptible to decay or sap staining.
12. To increase the strength. As wood dries, the stiffness, hardness and strength of the wood increases. Most species of wood increase their strength characteristics by 50 percent or more during the process of drying to 15 percent moisture content.
Therefore seasoning of wood is of greater importance for economical utilization of wood. In summary, for efficient and economic utilization of all useable wood species, it is very important to dry the wood to the moisture content required in service.
1.4 SCOPE OF THE STUDY
This study was carried out to determine the moisture content of wood in two media. The difference in the moisture content of the two media is compared due to the difference in the climatic conditions of each medium.
