The influence of microwave drying on the permeability of fir-wood

In this paper gas permeability of air dried fir sapwood is compared with gas permeability of microwave dried fir sapwood, and with alcohol dried fir sapwood; all wood was dried from green to under the fibre saturation point. The investigation showed that the longitudinal gas permeability of microwave dried fir sapwood is 10 times less (0.07 darcy) than the permeability of air-dried fir sapwood (0.77 darcy), while tangential gas permeability is nearly the same after air drying (0.0007 darcy) and microwave drying (0.00067 darcy). Tangential gas permeability of alcohol dried fir sapwood is 0.82 darcy. The permeability values of microwave dried fir sapwood show greater homogeneity (lesser dissipation) than the permeability values of air dried sapwood. The ratio between tangential and longitudinal permeability of microwave dried fir sapwood is significantly 10 times smaller than the same ratio for air dried fir sapwood. This indicates a reduction in anisotropy which should be investigated in more detail on a larger sample and on more species of wood. Further investigation should be followed by an examination of wood samples with an electron microscope.