The Influence Of Steaming Micro-Explosion Pretreatment On Eucalyptus Grandis×Eucalyptusurophylla Drying Characteristics

In this paper, eucalyptus grandisxeucalyptusurophylla was taken as experimental material, and heat transfer law inner eucalyptus during the pretreatment process, the influence of pretreatment schedule on the physical and chemical properties of eucalyptus, the influence of steaming micro-explosion treatment on eucalyptus weight gaining rate and the drying characteristics of eucalyptus were studied to get the mechanism of steaming micro-explosion pretreatment on eucalyptus drying characteristics. The results will provide guidance for the application of eucalyptus and improve its value. The conclusions are as follows:(1) During the pretreatment process, the internal temperature of the eucalyptus gradually increased with the increase of time, and the increase rate become slower and slower, and the influence of pretreatment condition on the outermost layer and outer layer temperature are not significant, but the influence of pretreatment condition on the center temperature are significant.(2) The relationship between temperature of outermost, outer and center layer and the pretreatment conditions was established, and the value of R2 is 0.990、0.984 and 0.990, respectively. The difference between the theoretical value and the practical value is small, thus, the theoretical formula can be used to simulate the eucalyptus wood pretreatment process.(3) After steaming pretreatment, eucalyptus wood moisture content has a certain degree of declining, and the higher the temperature, the more moisture content declined, and the declined content of 100℃,120℃ and 140℃ was 7.4%,10.9% and 15.7%. The relationship among the declining moisture content and the pretreatment time and temperature was established, and this formula could be used to simulate the declining moisture content.(4) The value of air-dry shrinkage and the dry shrinkage of untreated wood was 9.28%and 13.99%, and after steaming treatment, the value ranged from 5.21% to 7.98% and from 11.12% to 11.50%, which indicates the dimensional stability of eucalyptus is enhanced and the drying shrinkage resistance increase after steaming treatment. However, after steaming processing, the defects such as checking and crack were appeared, and at the same pretreatment time, the defects increase along with the increase of the steaming temperature; In addition, after steaming, all the extract content of eucalyptus was changed.(5) Considering the dimension stability, the extract content, and the drying defects, the optimum steaming temperature was 120℃, at which condition, the dimension stability was improved and the extract content was decreased.(6) The ultimate weight gaining rate increases with the increase of explosion pressure, and with the number of explosion times, the optimum micro-explosion pressure was 0.9 MPa, and the micro-explosion times is 5 times.(7) After the combination of steaming micro-explosion processing, the weight gaining rates of processed wood were all beyound 4.56%, much larger than the control group whose weight gaining rate was 0.89%, but steaming treatment is far greater than the effect of micro-explosion. The effect of micro-explosion is good when the moisture content of the specimen, which has been steaming treatment, is near to the fiber saturation point.(8) The formula of moisture changing value during the pretreatment process was got and the R2 was 0.983. This formula can calculate the moisture content changing value during the pretreatment process, thus, the moisture content changing value could be monitored, what’s more, the theory model of the steaming micro-explosion combined pretreatment sample were established, and this model can be used to predict the moisture content changing of the steaming micro-explosion combined pretreatment sample.