Study On Basic Condition And Destructibility Of Cell Collapse In Poplar Plantation

The collapse of poplar plantation occurres in the process of drying,which is show microscopically as deformation of cell,and macroscopically as subsidence of board surface.a terrible collapse would has influence on the dry quality,even leads to a taste of timber.At present,the research on the main reason and principle of wood cell collapse of poplar plantation is in the primary stage.In this paper,Populus beijingensis W.Y.Hsu and Populus alba var.pyramidalis bunge was taken as the research object,and the research was focused on the relationship between the collapse of cells and the basic condition and the outer condition in terms of drying of poplar plantation,and the relationship between the collapse of cells and the effection of pretreatment on the collapse of cells of poplar plantation.Beside that,in this paper,an emphatically research was made on the relationship between the collapse of cells and the character of microstructure and chemical composition of poplar plantation,as well as the character of relaxation time and the existing state of moisture content of poplar plantation,and the mastery of the establishment of the collapse of poplar plantation's cells.The details of the research is as follows.(1)Through the measurement of the character of microstructure of poplar plantation,a mastery of the relationship between collapse and each factor was made.The result showed that the state of collapse of mixwood of Beijing poplar and xinjiang poplar is serious.Beijing poplar and xijing poplar were similar in microstructure,but not in the factors that affect the collapse of cells.The collapse of Beijing popar was mainly affected by cell wall rate and parenchyma cell rate,while that of Xinjiang poplar was mainly affected by tyloses rate and parenchyma cell rate.(2)Through the measurement of the character of chemical composition of poplar plantation,made a grasp of the relationship between the chemical composition of poplar plantation and collapse of cells.The result showed that: the collapse of Beijing poplar was affected markedly by the composition of cell wall,and the cell's collapse of Xinjing poplar was affected markedly by the extractive content.(3)A analysis about the deviation of moisture content of poplar and a measurement of moisture content of heatwood,intermediate wood and sapwood by the way of unliabateralunclear magnetic resonance was made,the result showed that the deviation of moisture difference of intermediate wood was the largest among different parts of Beijing poplar and Xinjiang poplar,turned out to be 119.69% and 78.82% respectively,the moisture content and the collapse of poplar plantaion turned out to be an obvious positive correlation.(4)Through the cooperation between NMR-MOUSE and the annual ring workstation,a research on the saturated state of the growth ring boundary,and a grasp of the relationship between the saturated state of cross section and the collapse of cells was made.The result showed that the highest percent of moisture content saturation located in the part of intermediate wood of Beijing Poplar and Xinjiang Poplar,and turned out to be 97.45%and 79.5% respectively,it shows a positive correlation between the collapse and the deviation of moisture content of those two species.(5)With a custom-built shrinkage measurement equipment,a research on the change situation of the shrinkage stress caused by the shrinkage of wood in tangential and radial direction during the process of drying was made.The result showed that when dry temperature reached to 100?,just at the moment the shrinkage of Beijing poplar occurred,the shrinkage stress in tangential and radial direction turned out to be 0.046 MPa and 0MPa and Xijiang poplar tured out to be 0.177 MPa and 0.108 MPa respectively.(6)A research on the distribution and change laws of T2 of Poplar plantation in terms of dry condition with the way of low field-NMR was made,and the change situation of moisture content in terms of collapse of Poplar plantation revealed.The result showed that the occurrence of the collapse of Poplar was affected by the dry condition.As the temperature went up,the humidity went down,the collapse of poplar occurred more easily in terms of high moisture content.The collapse occurres at the moment of disappearance and transformation of the peak value of relaxation time,when the relaxation time was100? or above,the free water content of Beijing poplar and Xinjiang poplar turned out to be 38.33% and 29.10% respectively.(7)The collapse level of poplar can be reduced effectively by way of pre-freezing and microwave of Poplar.When the freezing temperature turned down and the freezing time extened,the volume shrinkage rate of Beijing poplar and Xinjiang poplar reduced When the microwave time extened and the power of microwave increased,the volume shrinkage rate of those two species reduced.