Viscoelastic Behaviour of Wood Fibres during the Hot Pressing of Medium Density Fibreboard

Abstract

Summary Sufficient stress relaxation within a medium density fibreboard (MDF) mat during hot pressing is critical for producing a panel with acceptable mechanical properties and dimensional stability. This paper describes a series of load relaxation tests of wood fibres conducted at temperatures and moisture contents similar to those within an MDF mat during the hot pressing process (temperatures ranging from 80°C to 100°C with relative humidity levels ranging from 9% to 68%). The results clearly show an increase in relaxation when either the temperature or relative humidity is increased. The relaxation behaviour of MDF is also measured and the trends observed are comparable to those of the wood fibres. Taguchi experimental design is employed to analyse the effects of temperature, moisture content and initial stress on the viscoelastic behaviour of MDF.