Study on Water Status and Distribution in 2 Fast-growing Woods During Drying Based on LF-NMR and MRI

In order to throw a light on the moisture state and migration in fast-growing wood during solar drying process, low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) were used to detect the moisture distribution, content change and its migration of Eucalyptus robusta and Populus tomentosa wood during the drying, and the scanning electron microscope (SEM) was used for the microscopic analysis. The results showed that the nuclear magnetic resonance (NMR) signal quantity was linearly correlated with the water content measured by weighing method, and the correlation was up to 0.99, making it possible for obaining the water content of wood in drying process via the equation constructed. According to the relaxation distribution of wood, there were 3 peaks in both Eucalyptus and Poplars during drying, including bound water and free water in 2 states, the relaxation time were 1.32, 32.75 ms, and 403.70 ms for the Eucalyptus and 2.66, 32.75 ms, and 352.12 ms for the Poplars, respectively. As the drying progresses, the relaxation time of water in different states decreased gradually, and the binding of wood to water increased. When the moisture content of the Eucalyptus and Poplars was about 27.28% and 35.71%, the loss of water was mainly composed of bound water. The moisture content could be distinguished by the density of hydrogen proton in magnetic resonance imaging (MRI), and the moisture movement in wood during drying could be observed. Therefore, the moisture states and distribution in wood can be quantitatively obtained by the LF-NMR and MRI.