Wood Microstructure Explored by Anisotropic ¹H NMR Line Broadening: Experiments and Numerical Simulations

Abstract

The cellular structure of wood, which is highly anisotropic along its main growth directions, is responsible for the observed anisotropy in its physical and mechanical properties that depend in a complex manner on the moisture content. Here, we demonstrate that the (1)H NMR spectra of wood from Norway spruce exhibit a strong and characteristic dependence on the direction of the sample relative to the applied magnetic field. By comparing spectra recorded at different magnetic-field strengths, we show that this variation is caused by the magnetic-field distribution created by the anisotropic and inhomogeneous distribution of matter and thereby magnetic susceptibility. On the basis of the observations that (i) the recorded spectral peak predominantly arises from translationally mobile water molecules and (ii) the spectral broadening is large if the long axis of the wood tracheid cells is perpendicular to the magnetic field, we set out to test the hypothesis that it is the susceptibility variation on the tracheid length scale that is responsible for the observed spectral features. To verify this, we numerically calculate in a discrete grid approximation the NMR line shapes obtained in realistic tracheid models, and we find that the calculated NMR line shapes are in good agreement with the corresponding experimental ones. We envisage the application of these findings for revealing the inhomogeneous distribution of water and its molecular properties in wood and wood-based materials at varying degrees of humidity.

Conservation process of archaeological waterlogged wood studied by spectroscopy and gradient NMR methods

“…It was reported that water bound to cellulose fibers below fiber saturation point is characterized by D ev ≥ 10 −12 m 2 /s (Topgard and Soderman 2001). Therefore, one can assume that the self-diffusion coefficient for bound water in wood cell walls is of the same order of magnitude (Engelund et al 2013;Terenzi et al 2013). Similar values can be expected for other solvents.…”

Surface Interactions and Confinement of Methane: A High Pressure Magic Angle Spinning NMR and Computational Chemistry Study

“…The other possible explanation for changes in resonance positions may be inhomogeneous distribution of methane within the silica matrix systems and local magnetic susceptibility. ,, The interfacial interaction of methane within the silica matrix systems could induce heterogeneity of the local magnetic susceptibility. Regions of different magnetic susceptibility at the interface of nonporous silica and methane may have local magnetic field strengths and Larmor frequencies changing the positions of isotropic 13 C NMR resonances from methane …”

The states of water in Norway spruce (Picea abies (L.) Karst.) studied by low-field nuclear magnetic resonance (LFNMR) relaxometry: assignment of free-water populations based on quantitative wood anatomy

“…Another possible explanation is that the ray cells are oriented perpendicular to the tracheid cells. For the cell wall water, the orientation of the wood sample during measurement has been shown to influence 1 H NMR data (Terenzi et al 2013). However, irrespective of how the dimensions are varied between the minimum and maximum values in Table 2, it is not possible to assign the ray cell lumen water to Peak 3 (Figures 2 and 5).…”