Water states and migration in Xinjiang poplar and Mongolian Scotch pine monitored by TD-NMR during drying

Abstract The time domain nuclear magnetic resonance (TD-NMR) technique was applied to observe the water states, water migration and the T 2cutoff of sapwood (sW) and heartwood (hW) of Xinjiang poplar and Mongolian Scotch pine wood during drying. Three components in the T 2 spectrum could be observed for poplar and pine at room temperature, and a large, short time component and a small, long time component of free water was visible at the melting point of water. During drying, the long time T 2 component diminished rapidly above the fiber saturation point (FSP), and almost disappeared close to or below the FSP. The short time components of the T 2 distributions slightly enlarged with decreasing moisture content (MC) above the FSP but rapidly diminished and shifted to the left side below the FSP. The bound water content estimated based on the T 2cutoff is in agreement with previous findings. Free and bound water have been found to be in two primary states both in poplar and pine. The loss of free water was rapid and profound but the bound water slightly increased with decreasing MC above the FSP, and the free water evaporated completely close to the FSP, where the bound water began to disappear significantly.