Development of An Empirical Model for MDF Hot Press and Comparison with A Fundamental Model
Hot pressing is one of the critical operations during manufacturing of medium density fibreboard (MDF). In the hot pressing, moisture, mass transfer, heat transfer and fibre densification interact, resulting in continuing changes in mat physical, chemical and mechanical properties.
In order to better understand the hot pressing process, both empirical investigation and theoretical modelling have been performed. The advantage of the empirical approach is that it takes less time although the result is applicable only in the range of conditions tested. In the theoretical modelling, the behaviour of wood composites is mathematically expressed by applying the fundamental laws including heat and mass transfer within the panel, the stress and strain development, and creep behaviour of the fibre mat, and the curing kinetics of the resin. The fundamental model can be solved to predict the outcome for a wide range of raw material properties and pressing conditions, but the theoretical model needs validation before practical application.
This paper firstly presents an empirical model developed based on results for panels made under different pressing conditions in a pilot-scale press. This empirical model is used to determine the effects of mat material variables and pressing conditions on important panel properties. These properties include peak and core density, modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB). The core temperature and internal pressure are also quantified. The predicted properties from the empirical model are then compared with the simulation results from a fundamental model described in a separate papers. From the comparison, different modelling approaches in the field of wood composites are better understood and the advantages and disadvantages of each approach are analysed.