An Investigation of the Drying Rate of Water in Wood at Different Relative Humidities Studied by Time Domain Nuclear Magnetic Resonance

Xinyu Li, Ximing Wang, Minghui Zhang


The wood drying rate was determined at five different relative humidities (RHs) using time domain nuclear magnetic resonance (TD-NMR). The objective of this study was to obtain the drying rate of bound water and free water, and to also build a relation between RH and drying rate. Two kinds of wood species, Qingpi poplar (Populus platyphylla var. glauca) and Pinus sylvestris var. mongolica Litv. were employed for the spin-spin relaxation time (T2) measurement. The mass of free water and bound water during drying were obtained at the same time. The results indicated that the poplar specimens had a higher fiber saturation point (FSP). For both wood species, free water decreases quickly, which contributes to the main drying, especially at the beginning of drying, and still exists even when the moisture content (MC) is below the FSP. Bound water decreases slowly, and its equilibrium content ranges from less than 10% to more than 20%, in the order from lower RH to higher RH. In addition, the drying rate decreases linearly with increasing RH.


Drying rate; Relative humidity; Bound water; Free water; TD-NMR

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