Abstract: [Objective] 1) To explore the influence of die temperature on relaxation density, durability, and densification pressure of sawdust using the heating method. 2) To optimize the moisture content and heating temperature and find out proper process parameters for practical production.[Method] 1) Single factor design:the sawdust with the moisture content of 10%,12%, 14%, 16% and 18% was used as raw materials, the individual heating temperature of AC(ambient temperature), 50, 75, 100, 125, 150, 175, 200, 225 and 250℃ was applied, and pellets were produced by a self-developed single pellet extruder. The relaxation density, densification pressure and durability chart were drawn for further analysis. 2) The second regression general rotary combination design:the experiment was designed according to the result from single factor experiment. The charts of response surface of heating temperature and moisture content were drawn to analyze the interaction between relaxation density and densification pressure.[Result] 1) 10% moisture content:sawdust could be densified at the temperatures higher than 200℃, while the densification pressure was higher than 95.74 MPa;18% moisture content:the pellets were cracked, easily broken, and densification effect was bad. 2) When the heating temperature was controlled from 75℃ to 175℃, surface carbonization occurred and the higher the temperature was, the serious carbonization occurred on the surface. When the temperature reached 200℃ or higher, significantly decreased was found for the densification effect. 3) The densification pressure of pellets with different moisture contents generally decreased when the temperature increased from 75℃ to 225℃. 4) No significant difference was found among the durability of pellets with different moisture contents when the temperature was ranged between 75℃ and 200℃. When the temperature increased higher 200℃, the durability decreased sharply. 5) The results of ANOVA analysis showed that the model P of the relaxation density and the densification pressure were less than 0.001. The R² values were 0.93 and 0.99 respectively (both of them were more than 0.8), and the data of the equations were in accordance with the experimental result.[Conclusion] Heating method can effectively reduce the densification pressure, and thereby decrease the energy consumption in the densification process. 2) High-density pellets can be produced by sawdust with 14% moisture content using die heating method.3) When the relaxation density meets the requirement of medium density pellets standards (> 0.7 g·cm^-3) and the durability is above 90%, the densification parameters with minimum densification pressure are:heating temperature is 200℃, and moisture content is 12%.

Key words: densification, moisture content, heating temperature, relaxation density, densification pressure, durability