The Relationship Between Load And Second Moment Of Wood Studied By Time Domain Nuclear Magnetic Resonance Technique

In this study,the relationship between load and second moment of wood was studied by changing load value,load acting time and load acting on wood cross,tangential and radial section with the time-domain NMR relaxation technique.The research focus on the relationship between loads,second moments,and internal wood structure.The results showed that:1.The second moment of Qingpi poplar and Pinus sylvestris increases with the load increasing,and the wood internal structure is denser.The second moment increases with the load increasing when the load applies to wood different sections.The second moment values of the wood was the largest when the tangential section was loaded,followed by the radial section and the cross section.2.The second moment of wood gradually increases with the loading time until equilibrium was reached.This shows that the internal structure of the wood gradually becomes denser under the load.And the second moment value reaches to constant.At the same time,the second moment increase with the loading time under the different section of Qingpi poplar and Pinus sylvestris.3.The trend for curve of the second moment for Qingpi poplar and Pinus sylvestris is the same with the trend for curve of wood density with loading time.The increase of second moment means that the internal structure of wood becomes denser.The result was confirmed by the density curve of wood with load.The change of wood density during compression is that the wood cells were crushed,and the compressed area was appeared.4.The second moment gradually decreased with the increase of adsorption time until the moisture sorption equilibrium was reached with load.During the process of cell-wall adsorption,the internal molecular anisotropic motion increased,wood structure loosens,shown by the second moments decreasing.The second moment of wood with load was higher than the one without load.And the second moment increases with load increases.In the process of moisture adsorption,the second moment values of the wood was the largest when the tangential section was loaded,followed by the radial section and the cross section.5.With the increase of load,the pore diameter of wood gradually decreases.This is result from the cell lumen of the wood is compressed and the slippage is occurred when the load applies to wood.And with the increase of load,the cell wall was crushed to a denser state.So the pore diameter of the wood cell wall was reduced.