Characteristics And Mechanism Of Poplar Wood During High-intensity Microwave Pretreatment

In this study, we take poplar wood as the object and reveal the mechanism of high-strength microwave pretreatment, Constructing theoretical model and its mathematical simulation system and use self-developed high-strength microwave pretreatment equipment to study the poplar’s drying and permeability characteristics after pretreatment. The main conclusions of this study showed as follows:1. A theoretical model to predict the critical pressure and temperature conditions of wood microwave explosion pretreatment has been developed, and the mathematical simulation has been conducted. The results show that:With the increase of pressure in the cell lumen, the tangential and longitudinal stress in wall of parenchyma cell increases, and its corresponding extension ratio increases, too. With the increase in radius, critical pressure and temperature to damage parenchyma cell decrease. When the microwave explosion pretreatment is conducted at the parenchyma cell level for E. urophylla, the minimum critical pressure and the temperature are184℃and2.03MPa respectively.2. During microwave pretreatment process, the effect of microwave feeding mode and the radius of the cylindrical resonant cavity on the temperature uniformity within wood and microwave energy utilization efficiency is significant; Compared with the other microwave feeding mode, the temperature distribution uniformity within wood and microwave energy utilization efficiency is the highest (up to87.48%) when the microwave radiation with3waveguides feeding is used to heat wood;The temperature coefficient variation and microwave energy utilization efficiency basically decrease and then increase with the increasing the radius of the cylindrical resonant cavity, and the optimizational radius for the cylindrical resonant cavity is in the range from0.186m to0.211m;The temperature distribution pattern in each cross section is consistent along the wood longitudinal;The farther away from the microwave feed entrance, the lower the average temperature on cross section, It means that the highest average temperature appears around the microwave feed entrance;When the thickness is2cm, the temperature distribution is the most uniform and the microwave energy utilization is the highest. 3. Compared with the untreated test wood,when the microwave power is5kw, lOkw,15kw and18kw, the drying rate is increased by8.32%,13.34%,18.53%and113.34%, the drying time is shortened by3.13%,9.38%,15.63%and53.13%; Compared with the untreated test wood, when the radiation time is30s,50s,65s and80s, as which drying rate increased by4.63%,17.33%,31.94%and66.74%, the drying time is shortened by6.45%,12.9%,25.8%and38.71%; The cross section deformation, distortion and deflection values of treated test wood is lower than the control wood.4. When the microwave power between10kw-15kw, compared with untreated wood, The absorption of transverse,tangential and longitudinal direction can be increased respectively by61.3%-73.8%,17.2%-43.3%and28.4%-38.7%, In particular when the microwave radiation power is18kw, the absorption is more obvious; When the irradiation time between50-65s, as compared to untreated wood, the absorption of transverse,tangential and longitudinal direction can be increased respectively by66.0%-19.2%46.2%-52.2%and19.7%-34.4%, Especially when the microwave radiation time above80s, the absorption is more obvious.