Microwave treatment of <Emphasis Type="Italic">Eucalyptus macrorhyncha</Emphasis> timber for reducing drying defects and its impact on physical and mechanical wood properties

Microwave is a useful and proven tool for increasing permeability of refractory wood and, thereby, it can be used for reducing drying time and defects. However, strength loss is always a concern. In this study, green timber boards were treated with microwave in two intensities, low microwave (LMW), 89 kWh/m³, and high microwave (HMW), 95 kWh/m³, and compared with control boards. Samples of all three treatments were kiln dried together. Density and selected mechanical properties were also assessed after drying. LMW, the treatment which presented the best results, showed reduction in some drying defects, such as collapse (20%), surface check length (84%), internal check length (50%) and internal check width (70%). Density, MOE and MOR on static bending were unchanged, whereas reductions in shear strength (13%) and compression strength parallel to grain (10%) were observed. HMW, on the other hand, produced higher strength reductions and more drying defects than LMW. Fine adjustments of LMW microwave power might bring drying benefits without strength losses.