Abstract
This review summarizes the development of the experimental technique and analytical method for using TD-NMR to study wood-water interactions in recent years. We briefly introduce the general concept of TD-NMR and magnetic resonance imaging (MRI), and demonstrate their applications for characterizing the following aspects of wood-water interactions: water state, fiber saturation state, water distribution at the cellular scale, and water migration in wood. The aim of this review is to provide an overview of the utilizations and future research opportunities of TD-NMR in wood-water relations. It should be noted that this review does not cover the NMR methods that provide chemical resolution of wood macromolecules, such as solid-state NMR.
Highlights
Characterization of Water in Wood byWood is a hygroscopic and porous material that constantly exchanges water with surrounding environment
We summarized the studies based on 1D (CPMG) and 2D (T1–T2 or T2–T2) pulse sequences for (a) identifying water components in wood over the whole moisture content (MC) region, (b) re-evaluating fiber saturation state, and (c) detecting the pore distribution in cell walls and
The results showed that hygroscopicity limit (HL) fiber saturation point (FSP) was aligned to the MC where volumetric shrinkage drastically changed; the cell wall water increased by around 10% from the HL state to cell wall saturation (CWS)
Summary
Wood is a hygroscopic and porous material that constantly exchanges water with surrounding environment. The characterization methods of water in wood have progressed [5], and there are various experimental techniques for qualitative analysis or quantitative calculation, covering a range of moisture content (MC) from the green state with liquid water to the absolute dry state. Among many experimental techniques for studying water in wood, time-domain nuclear magnetic resonance (TD-NMR) spectroscopy can cover the entire MC range from the absolute dry state to the fully water-saturated state [5]. It is capable of distinguishing water molecules within the hierarchical structure of wood, such as cell walls and cell lumina. By encoding the positional information with the NMR signal, magnetic resonance imaging (MRI) exhibits spatial information, providing an efficient method for monitoring water migration at cellular scale during wood drying and water uptake [8]
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