Study On The Relaxation Characteristics Of Waterin Wood By TD-NMR

Yello Poplar, Ash, Walnut and Red Oak were selected as the testing species of wood in this paper. Proton of water, as a probe, can be used to explore water states in wood through Nuclear Magnetic Resonance (NMR). Free Induction Decay (FID) and Transverse relaxation time(T2) were measured and comparative analyzed between ash walnut and red oak in adsorption and desorption process. Internal moisture migration process and the relaxation characteristics of water in different species of wood are explored. It is found wood moisture content(MC) can be measured with NMR by establishing a standard curve of wood MC and FID signal amplitude.Also take a comprehensive comparative analysis of Yello Poplar desorption and adsorption process.This study gets the following conclusions as follows:1. The relationship between wood sample MC and FID signal amplitude was highly linear in Ash, Walnut and Red Oak during desorption process, the curve of weighing method moisture content and NMR FID method measured moisture content in sorption process between the three kinds of wood almost overlap. Therefore, wood moisture content can be measured with NMR by establishing a standard curve of wood MC and FID signal amplitude.2. During the adsorption process of Ash, Walnut and Red Oak from the oven-dry state to the equilibrium state in40℃,31.6%±0.2RH environment,T2are between0.1ms to1ms,and increased rapidly with increase moisture content.Ash has the longest relaxation time and change fast,followed by walnut, the relaxation time of red oak is the shortest.During the adsorption process of Ash,Walnut and Red Oak from the31.6%±0.2RH equilibrium state to the66.1%±0.3RH equilibrium state in40℃environment,relaxation time of adsorbed water are about1ms, relaxation time increase slowly with the increase of MC. Ash has the longest relaxation time, more than1ms,followed by walnut for1ms,Red Oak are less than1ms. During the adsorption process of Ash,Walnut and Red Oak from the66.1%±0.3RH equilibrium state to the74.7%±0.2RH equilibrium state and from the 74.7%±0.2RH equilibrium state to96.4%±0.4RH equilibrium state in40℃environment,relaxation time of main adsorbed water is essentially the same,relaxation time of minor adsorbed water changes irregular. The total integral area of water was increased with the increase of MC.3. During the sorption process, below FSP, there was still a little free water in wood.4. The relationship between wood sample MC and FID signal amplitude was highly linear in Yello Poplar desorption and adsorption processes. There are six main water states in Yellow Poplar heartwood in desorption process. The relaxation time and peak area of free water are reduced above the fiber saturation point. Meanwhile the relaxation time and peak area of adsorbed water has little change. The value for relaxation time and peak area of bound water decreases rapidly below the fiber saturation point. The total integral area of Yello Poplar is reduced linear in two stages. T2distribution of Yello Poplar is similar with other three kinds of wood in adsorption process...