The Effects of Hygroscopic Behaviour of Entandrophragma cylindricum (Sapele) in South West Cameroon

ABSTRACT

This research work title, The effects of Hygroscopic Behaviour of Entandrophragma cylindricum (Sapele) in South West Cameroon was aimed at understanding the effects of moisture variation on mechanical properties of wood and to come out with possible recommendations that will help wood users and professionals to take good decisions about the moisture content of wood before its processing to avoid deformations. Static bending test was made to determine the flexural properties, such as modulus of rupture and apparent modulus of elasticity and when required, the stress at proportional limit and work – to – maximum load can be determined. In the case of this work, tests were conducted to determine the modulus of elasticity in the longitudinal direction, in dependence of the moisture content variation.

The compression tests parallel to the grain were performed in consonance with the recommendations of American Standard for Testing Material D 1037 – o6a. Sixteen samples were used for this test, 8 wet and 8 dry. The dimension of each specimen for compression was 20mm in the width 20mm in the thickness and 40mm in the length.

The data obtained were processed through the bending test perpendicular to grain and the compression test parallel to grain. Sixteen samples each were used for the bending test and the compression test. Eight wet and eight dry and from the findings it was seen that the moisture content of wood affects considerably the modulus of elasticity in both compression and bending test. To know the exact relation between the moisture content and the mechanical properties of wood, different levels of moisture content was taken into consideration. Throughout this work, it is seen that the modulus of elasticity increases when the moisture content is decreased. So, in this research, the samples were subjected to either the compression test or the bending test until rupture occurs. The samples were taken without any consideration for their moisture content and before the tests, the samples were first divided into two groups, A and B. Group A was submerged in water while Group B dried in an oven for 72hrs to vary the moisture content  inside the samples to 21% of moisture content. The tests were then done gradually on the samples with variation of their mechanical properties. Findings from the study shows that the moisture content has a very important effect on the mechanical properties of wood, we could see that sample 2 had the highest force with MOE 5570.776, MOR being 84.9955 and 221.7 as slope. From the bending and compression tests parallel to grain used in this study, these properties are more affected when the moisture content is high.

CHAPTER ONE

GENERAL INTRODUCTION

1.1 Background of the study.

          Wood and wood based materials are among the most important building materials in Cameroon. Wood is an organic material with a very complex composition. Due to its complex composition and its many-sided usage there are still many unanswered questions concerning wood use in buildings. In buildings wood is subjected to shrinkage, swelling, mould growth and rot if exposed to unfavorable environmental conditions. These phenomena are all related to moisture content and moisture conditions in a building structure. Rot may occur in wood which  is in contact  with  liquid  water  for  some  time,  while  shrinkage, swelling  and mould  growth  are mainly  related  to hygroscopic effects.

      Wood and wooden materials in buildings are continuously exposed to smaller or larger changes in climate. Outdoor climate changes are present throughout the day and night, and throughout the year. Indoor climate  changes  are  more  or  less  a result  of  the outdoor  changes in  addition to changes related to  the  inhabitants activities. There is still a need for improving and developing the basic knowledge of moisture in wood that is subjected to changing climatic conditions. Several large scale experiments on building envelopes ( e.g., walls  and roofs)  in order to investigate the heat,  air and moisture performance   have  revealed  that a more  thorough  investigation   on basic  moisture transport   in  wood   is  necessary. Poor agreement has been reported   between accepted   numerical   models   and measurements of moisture content in wooden materials in structures. More recently   recognized potential  health hazards  of mould  and other organisms  which  flourish  in buildings demand  basic knowledge  about moisture  transport  in wood.

1.2 Problem statement

Wood is a building material that is particularly susceptible to moisture damage, which may involve the building owners and users in considerable expenses. If the water content of wood is too high for longer periods of time, it may be attacked by fungus growth. Some types of fungus destroy the structure of the timber; the wood begins to rot. In view of the allergenic effects and the toxins produced by some varieties of mould fungus it may also impair the health, in particular, of the building’s inhabitants.

The informal sector which is constituted of the local market of sawn wood and other furniture or products from carpentry and joinery are largely dominated by their artisanal character. It is from this informal sector that many local constructions or furnitures are made. The artisanal character of the local use of wood is one of the reasons why wood is used without any study of its characteristics, many species of wood are then used for any purpose in the sense that for example, some wood that are good for covering of walls or ceiling because of their low mechanical properties and their sensibility to moisture change, are found in some constructions that are always exposed to higher level of mechanical stress and are affected. Changes in the moisture content is hardly noticed by the actors in the informal sector because they don’t have good equipments to control the level of moisture content in wood used for their construction. All these reduce the life span of their products. This is the reason why during when the furniture is being used, deformations like cracks, split, flexion etc, can be seen on some parts of the furniture which is a major problem of this research.

To carry out this research, the researchers have chosen Entandrophragma cylindricum one of the many wood species commonly used in the south west region of Cameroon for construction, to determine its hygroscopic behavior.

1.3 Research question

 Is there any influence of the hygroscopic behavior of Entandrophragma cylindricum on its mechanical properties?

1.4 Objectives of the study

1.4.1 General Objective

   – To contribute to the understanding of the mechanical properties of Entandrophragma cylindricum as a building material.

1.4.2 Specific Objectives

 – To analyze changes in mechanical properties of Entandrophragma cylindricum with variations in moisture content

 – To determine the mechanical properties of Entandrophragma cylindricum when pieces of the wood are soaked in water.

  – To determine the mechanical properties of Entandrophragma cylindricum when pieces of it are dried in an oven.

 – To do a comparative analysis of the mechanical properties of Entandrophragma Cylindricum of the dried and soaked pieces.