EFFECTS OF THERMAL TREATMENT ON THE PHYSICAL AND MECHANICAL PROPERTIES OF IROKO (MILICIA EXCELS) WOOD

ABSTRACT

The aim of this research is to investigate the effects of thermal treatment on the physical and mechanical properties of a selected indigenous Nigerian wood. In order to achieve the research aim,  Iroko (MiliciaExcels) wood samples obtained from Ala forest in Akure, Ondo state, Nigeria were subjected to heat treatment at varying temperatures (80 oC, 100 oC, 120 oC, 140 oC and 160 oC) with constant treatment duration of 6 hours and for varying time durations at constant temperature of 120 oC. The following characteristics: moisture contents, density, dimensional shrinkages, shearing strength, compression strength, tensile strength, modulus of rupture in bending static (MOR) of the Iroko (Milicia excels) wood were studied. The results showed that all the values of the characteristics studied decreased with increasing treatment temperature and treatment time, except hardness that behaved otherwise. At 120 oC the Iroko wood has the best physical  and  Mechanical  properties  similar  to  that  of  Teak  that  makes  it  suitable  for technological applications such as Handles of Agricultural implements and tools, its durability makes it suitable for boat building piles, other marine work and rail road crossties. Iroko wood is also found suitable in many and most carpentry and joinery, flooring, furniture, veneer and cabinet works.

CHAPTER ONE

1.0     INTRODUCTION

This chapter provides the background information, the motivation for embarking on the thermal processing of Iroko wood (Milicia excels), the aims and objectives of this research, the limitation to this study, as well as the outline of this thesis.

1.1       Background

According to Korkut and co-investigators (2008), heat treatment of wood is considered as a viable alternative on ecological basis in comparison to chemically impregnated wood. Moreover, Rapp, (2001) reported that heat treated wood are suitable for fabricating garden, kitchen and sauna furniture, floors, ceilings, inner and outer bricks, doors and windows. A search through the available literature as well as a survey of the wood research activities carried out at Forest Research Institute of Nigeria (FRIN) in Ibadan and other Nigerian Universities revealed that there  are  no  information  on  the  effect  of  heat  treatment  on  the  mechanical  and  physical properties of Iroko wood (Milicia excels).

1.2 Problem statement

Jayeola et al., (2009) reported that only very few (e.g. Milicia excels – Iroko, Afzelia Africana – Apa, Anogeissusleiocarpus – Ayin, Antiaristoxicaria – Oro, Khayaivorensis – Oganwo, Mansoniaaltissima – Ofun, and Disopyros – Kanran) of the different species of trees in the Nigerian forests had been exploited economically on commercial scale. Most of the few that are exploited are large trees which are among the highly priced hardwood timbers of tropical Africa and are well known all over the world. An attempt to identify other species that are not exploited as well as the reason behind that is a subject to be research on. In an effort to draw the attention of the anatomists to engage in wood quality study, Jane (1967) recommended that the aspects of variation in wood structure are of practical importance in the industrial production sense. However, Bamiro (2004), pointed out that many Nigerian production engineers using wood know very little or nothing about its structure and properties. Jayeola, (2009) stressed that there is no doubt that the information obtained from the wood structures could provide a credible alternative for identification of timber species, even after processing. He believed that although there is a lot of promise in the use of wood structural information for timber identification in Nigeria, it could not be achieved as the level of information remains scanty. For the purpose of supplying more information and making Nigerian wood literature more available rather than scanty, the study of the properties of heat treated Nigerian  wood is therefore unavoidable. Considering these points, it is important that characterisation studies about heat treated Nigerian woods are carried out in an attempt to create a knowledge database to guide production engineers in the application of wood for appropriate technological purposes.

1.3 Aims and Objective of the Study

The aims and objectives of the study are summarised as follows: –

1.         To determine the effect of heat treatment processing parameters (temperature and time) on the physical properties, and mechanical properties, of Iroko (Milicia excels) wood.

2.         To  determine the optimum  processing  parameters as  well  as  optimum  technological properties of the Iroko wood.

3.         On the basis of the results obtained from 1 and 2, the Iroko (Milicia excels) wood will be characterised for suitable technological applications.

1.4       The Significance of the Study

It is expected that the outcome of this study would form part of database that would help students of wood technology, wood merchants, and production engineers to gain basic knowledge of Iroko wood (Milicia excels) with regards to its suitability for various applications in joinery, interior, furniture products and structural products. Furthermore, investigation of the heat treatment parameters would help determine the optimum physical and mechanical properties of Iroko (Milicia excels) wood. It is anticipated that this knowledge would help the Nigerian wood processing industries in the development of process parameters for their woods. An attempt to find out the physical and mechanical properties of wood in Nigeria, would not only help in establishing the level of the Nigerian woods quality but also assist in making an adequate, accurate and timely decision on the nature and quality of wood species available, which could lead to the effective utilisation of wood and its product in Nigeria.

Based on the argument that Nigeria does not export wood and wood products due to the high supply  and  demand  gap  being  experienced.  This  study  would  be  of  great  importance  in suggesting ways of increasing its supply to at least meet the high demands in Nigeria and probably lead to its exportation to other parts of the world and provide opportunity for Nigerian wood industrialists to invest their resources into the production of high quality wood products for exportation. This is expected to increase Nigeria’s foreign earnings.

1.5       Limitations of the Study

The study is generally about the effect of heat treatment parameters on the physical and mechanical properties of Iroko wood (Milicia excels). There are two basic techniques of identifying  the effects  of physical  and  mechanical  properties  of  a  wood.  However,  for the purpose of this study, thermal processing technique was used. Moreover, there are many timbers species in Nigeria but this study is specifically concerned about the Iroko (Milicia excels) species being one of the available timber species in Nigeria. The choice of Iroko (Milicia excels) was based on its availability, durability, easy workability in addition to the fact that it does not require regular treatment with oil or varnish. Sampling and observation techniques are the most crucial methods and techniques of carrying out this research study. The iroko (Milicia excels) wood sample will be subjected to different temperatures (80 oC, 100 oC, 120 oC, 140 oC and 160 oC) with constant treatment duration of 6 hours and for varying durations (2 hr, 4 hr, 6 hr and 8 hr) with constant temperature of 120 oC while the physical, and mechanical properties are to be systematically observed, prior and after the processing conditions.

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