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Introduction

Medium density fibreboard (MDF) is a wood fibre composite material widely used in furniture manufacture, cabinet making, joinery and craft work. It acts as a substitute for an older generation of wood composite panel products including particleboard and hardboard, and to a lesser extent it is a substitute for solid timber. It's cost, mechanical properties, and ease of machining suggest that it could be used for a far broader range of engineering uses than at present. As MDF has only become widely available in the last ten years, research on it's properties and in particular treatments designed to improve its dimensional stability is limited. Because of this, results from the studies of particleboard and other timber products have been applied to make predictions of the behaviour of MDF. One disadvantage of MDF's are their susceptibility to moisture. Moisture sorption causes a loss of mechanical properties and increases in thickness swelling. The aims of this study were to construct sorption isotherms for two MDF types and to examine the effect of relative humidity on the mechanical properties of the boards. This study also aimed to relate changes, if any, in mechanical properties to the mode of failure of board specimens. Heat treatments have been used to increase the moisture resistance of particleboard [Suematsu, 1980], solid timber [Seborg et al., 1953] and waferboard [Hsu et al., 1989]. A further aim of this project was to examine the ability of a heat treatment or powder coating to reduce dimensional changes and loss of board properties on exposure to moisture. Ultimately, it was hoped that information generated in this study would be of use in developing MDF boards with enhanced resistance to moisture.