An alternative approach for conditioning wood samples in nuclear magnetic resonance studies

A significant challenge in applying nuclear magnetic resonance (NMR) in examining the wood-water system is accurately and effectively conditioning wood samples before such tests. The common approaches, such as the saturated salt solution method, have drawbacks of long equilibrium time and significant moisture content deviations. The water-addition-equilibrium method proposed here is an alternative conditioning approach that adds liquid water directly to oven-dried samples following sealing and equilibrating at 45 ℃ for 72 h until obtaining the even water distribution in samples. The equilibrium time in the latter method was determined by analyzing evolutions of the spin-spin relaxation time (\(\:{T}_{2}\)) spectra with five equilibrium time durations, i.e., 0, 24, 48, 72 and 96 h. Compared with the salt solution method, it is much easier and faster to achieve target moisture content using the water-addition method. When the actual target moisture of the samples is similar, no apparent differences are observed between the \(\:{T}_{2}\) spectra obtained using the two methods. For this study, the water-addition method was applied to poplar samples with the moisture content target of 32% and below. The proposed method may be applied to other wood species and is expected to contribute to NMR examinations where the accurate and continuous control of sample moisture is required.