EFFECT OF ENVIRONMENTAL CONDITIONS OF TWO NATURAL WOOD SEASONING MEDIA ABSTRACT
The versatility of wood is due to the level of moisture content in wood which determines the performance of wood in service. This performance is a result of the process used in the drying of the wood species. Wood can be dried through natural and artificial drying methods but the natural methods required little skill and cost in obtaining the desired results. 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.
TABLE OF CONTENT Page Title page i Certification ii Dedication iii Acknowledgment iv Abstract v Table of content vi - viii Chapter one 1.0 Introduction 1- 2 1.1 Statement of problem 3 1.2 Objectives of study 3 1.3 Justification of study 3-5 1.4 Scope of study 5 Chapter two 2.0 Literature review 6-7 2.1 physical properties of wood 7-82.2 Mechanical properties of wood 8-9 2.3 Dimensional changes in wood 9-10 2.4 Moisture content in wood 10-11 2.4.1 Equilibrium moisture content 11-12 2.4.2 Moisture movement directions for diffusion 12 2.4.3 Moisture content differences 12- 13 2.4.4 Moisture passageways 14 2.5 Influence of temperature, relative humidity, and rate of air circulation 14- 16 2.6. Reasons for splits and cracks during timber drying and their control 16 2.7. Shrinkage and swelling 17 2.8 Wood species used 17 2.8.1 Eku 17-18 2.8.2 Omo 18-19 2.8.3 Ure 19-20 Chapter Three 3.0 Materials and Methods 21 3.1 Sampling techniques 21-23 vi 3.2 Determination of Initial moisture content 233.3 Experimental design 23-243.4 Data analysis 24 Chapter four 4.0Result and discussion 254.1 Result 25-26 4.1.1 The moisture content of the two selected media25-26 4.2. Discussion 27-28 Chapter five 5.0 Conclusions 29 Reference30-31List of Tables 1 Initial and final moisture contents of the drying media 25-26 2 Differences in drying rates of each medium 26 Appendix32-33 1 The temperature of the drying media 32 2The diagram of the media 33
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 1 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.