In this study the effect of heat treatment on some physical properties of Douglas fir (Pseudotsuga menziesii) was investigated. Wood specimens were subjected to heat treatment at 160, 180, 200 and 220°C for 1, 2, 3 and 4h. The results show that heat treatment resulted in a darkened color, decreased moisture performance and increased dimensional stability of wood. Compared with untreated wood, equilibrium moisture content (EMC), water absorption (WA) and volume swelling (VS) for treated wood decrease up to 42.63%, 34.93% and 67.47%. The higher the treatment temperature and the longer the treatment time, the lower EMC, WA and VS. The VS of treated specimens has a more significant reduction than EMC and WA when the heat treatment temperature is above 180°C. The visual color changes were more distinct after heat treatment above 180°C. Temperature has a greater influence than time on these properties of specimens.

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Microwave treatment is a newly developed technique to expel resin from pine wood by generating high internal steam pressure. To understand the mechanism of deresination process during the treatment, a mathematical model was developed and was used to predict its critical conditions. The model indicated that the critical pressure inside Masson pine wood was 1.17×105Pa and its corresponding critical temperature was 104 °C in order to expel the resin mixture from the interior to the surfaces. The experiment results showed that during microwave deresination large quantities of the resin overflowed to the wood surfaces when the temperature of the pine wood was controlled in the range 104-112°C. The result observed during the microwave treatment matched well with the critical temperature predicted from the simple mathematical model. The validated model could provide some understanding and improvement of microwave deresination process.