| The microwave pretreatment of Eucalyptus urophylla Wood was studied in this article. The influence of microwave pretreatment on drying rate, drying quality, wood surface wettability, physical and mechanical properties of wood , and micro-structure of wood were revealed. It has important theoretical and practical value for increasing permeability of refractory lumber species such as E. urophylla. The main research results are as follows:(1) The influence of microwave pretreatment on lumber temperature: the higher the initial moisture content of lumber is, the slower the temperature rises; the thicker and wider the lumber is, the slower the temperature rises; the slower the feeding speed is, the faster the temperature rises. The temperature increasing rate is higher in flatsawn lumber than that in quartersawn lumber. The temperature increasing rate is remarkably affected by feeding speed, and there is extremely significant difference between 2mm/s and 4mm/s group, but there is no significant difference between 2mm/s and 3mm/s group and 3mm/s and 4mm/s group. The temperature increasing rate is rapid with feeding speed as 2mm/s.(2) Some defects may occurred in microwave treatment process, such as surface check, end check and internal check. The defects will differ in degree with different species, MC and dimension. Under experimental conditions, the defect is least with 55% MC. Defects is less with feeding speed as 2mm/s and 2.5mm/s. Various factors were considered synthetically, the optimized techniques are as following: the specimen's dimension is 505mm×48mm×27mm, and the feeding speed is 2mm/s.(3) The drying rate of microwave-treated lumber is higher than control samples, and the drying rate is improved by 2.6% for flatsawn lumber and 11.5% improved for quartersawn lumber. The difference of drying rate is small between flatsawn and quartersawn lumber after microwave treatment. As for control samples, the drying rate of flatsawn lumber is always higher than that of quartersawn lumber. All these can resulted that microwave pretreatment can increase drying rate, and the difference of drying rate was decreased between flatsawn and quartersawn lumber.As for the drying quality, the moisture content of treated lumber and control samples can reach grade II in accordance with national drying quality standard. The average final moisture content and mean square deviation of treated lumber are all lower than that of control samples. Regardless of the initial MC, the scale of warp and internal check of treated lumber is higher than that of control samples. (4) As for the physical and mechanical properties, the air-dry density of treated lumber is lower than that of control samples; The MOE/MOR value of treated lumber is lower than that of control samples, and the MOE of treated lumber reduced with MC increasing; The initial MC has significant effect to the value of treated lumber; The MOE of treated lumber is 25.3% higher than that of control samples when the initial MC is 45%.The hardness of cross-section is increased after microwave treatment, but the hardness of radial section and tangential section decreased. To treated lumber, the hardness of tangential section is higher than that of radial section, and there is no significant difference among different initial MC. The difference of initial MC hasn't significant effect to control samples. The contact angle of treated lumber is higher than that of control samples, but there is no significant difference.(5) The effects of microwave pretreatment on the microstructure of wood. The cell wall in treated lumber showed different degrees of rupture; the micro-cracks occurs in compound middle lamella between wood fibers; internal check and V-shaped crack occurs on the cell wall of wood fiber. The settlings in wood ray also break down.These cracks resulted in the decrease of mechanical property of treated lumber. The crack of wood fiber cell wall is universal and may lead directly to the decrease of hardness. There is no burst in ray parenchyma cell.
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