Study On The Microwave Treatment Mechanism Of Pinus Sylvestris Linn.var.mongolica Litv.

Microwave treatment technology has attracted wide attention for its fast and efficient improvement of wood penetration and impregnation performance.However,due to the lack of wood equipment development and mechanism research,it has not been well promoted and applied in the wood industrial.In this paper,Pinus sylvestris Linn.var.mongolica Litv.was used as the research material,the anatomical and dielectric properties were studied,and the effect of wood moisture content(MC),density and position on the power loss density(LPD)were investigated by CST.At the same time,the temperature characteristics with different microwave processing parameters were online-monitored,and the impregnation characteristic,microstructure and porosity of microwave pretreatment wood were researched.Finally,the thick wall cylinder model was established,and the destructive stress of ray parenchyma and tracheids were calculated.The main conclusions were shown as follows:(1)The wood LPD in continuous tunnel microwave treatment equipment is related to initial moisture content,position in the equipment and wood thickness.The distribution of LPD on the wood section with different MC was basically the same,the LPD of the wood center was the highest,and the edge was lower.In the section close to the microwave source,power loss density decreased with the decrease of MC.The maximum LPD increased first and then decreased with the increasing of wood height in the cavity and the wood thickness.(2)In the process of high intensity microwave treatment,two types of temperature characteristics were found.Type one is divided into the following 3 stages,namely,the first heating stage,the momently constant temperature stage and the subsequent sharply heating stage.Type two is divided into heating stage and constant temperature stage.The maximum temperature and heating rate increase with the increase of microwave power,and decrease with the increase of initial MC.However,the duration of wood constant temperature decreased with the increase of microwave power,and increased with the increase of initial moisture content.The order of highest temperature and heating speed was the surface point,the center,the lower surface and the end point;in the wood thickness direction,the closer to the generator,the faster the temperature increased.(3)Microwave treatment could significantly improve the impregnation characteristics of wood,the dye absorption rate of weight gain was significantly affected by microwave irradiation time and microwave power.Microwave processing time is the most important factor,followed by microwave power.And in the 20-40% content range,the dye absorption rate of weight gain is not significant affect by wood moisture.The gain rate of dye absorption and dye permeability in the wood were best,when treated with power of 20 kW and processing time of 90 s.(4)The dye uptake rate of weight gain was significantly affected microwave irradiation time and microwave power,which was not significantly affected by wood moisture content,and the microwave processing time was the significant factor.The pit structure of wood was destroyed by high intensity microwave treatment.At the same time,some resin canal was destroyed,and macroscopic cracks were produced along the direction of wood ray parenchyma.Micropores on pit membrane and intercellular space on the cell wall were damaged by high intensity microwave treatment,resulting in the number of microporous material within the range of less than 200 nm reduced,the cumulative pore volume and cumulative pore area within this range decreased compared with that of the control.And the damage of the resin canal,pit aperture and part of cell wall,make the number of pore diameter bigger than 8?m increased compared with the control one.(5)The damage pressure of Pinus sylvestris Linn.var.mongolica Litv.ray parenchyma was 0.38 MPa,and the corresponding temperature of saturated steam in the wood was 146.3?.The yield and damage pressure of Pinus sylvestris Linn.var.mongolica Litv.earlywood tracheid were 1.28 MPa and 3.19 MPa,and the corresponding temperature of saturated steam in the wood were 185? and 223?.