Drying wood using microwave energy is not very common, but could be a
complement to conventional air-circulation drying due to the possibility to dry
wood faster than the conventional drying methods with preserved quality.
Furthermore, this technique could be used to condition boards with too high
moisture content gradient. In this study, an industrial-scale, online microwave
drier for wood components has been used and adapted to wood treatment. The aim
of the present work was to investigate if the microwave drying method itself
affects such wood properties as bending strength, hardness and colour change.
Another aim was to explain, with finite element model simulations, the interaction
between microwaves and wood during heating and drying and to a lesser extent
also during microwave scanning of wood. Tests of the mechanical properties of
wood showed no difference in bending strength in comparison with the
conventional air circulation method. Nor was there any significant difference in
wood hardness (Janka) perpendicular to the grain between the drying methods or
between different temperature levels during the microwave drying. However, the
results showed that there is a significant difference in wood hardness parallel to
the grain between the methods when drying progressed to relatively lower levels
of moisture content; i.e. wood hardness becomes higher during microwave drying.
The developed multiphysics finite element model is a powerful evaluation tool for
understanding the interaction between wood and microwaves during heating and
drying as well as scanning. The model can be used for simulation of different
microwave treatments of wood.