One- and Two-Dimensional NMR in Studying Wood–Water Interaction at Moisturizing Spruce. Anisotropy of Water Self-Diffusion

Victor V Rodin

doi:10.3390/colloids3030054

Abstract

This paper examines how wetting the surface of wood affects characteristics of wood materials. An important question is how moisturizing wood has an effect on diffusion parameters of water, which will change conditions of the technological treatment of material. A fibrous structure of wood can result in different diffusivities of water in the perpendicular direction and along the wood fibers. The work explores how 1- and 2-dimensional NMR with pulsed field gradients (PFG) highlights an anisotropic diffusion of water when moisturizing spruce wood. The methods applied: T2-relaxation (CPMG) measurements with the application of inverse Laplace transform (ILT), cross-relaxation experiments (Goldman–Shen pulse sequence), 1D PFG NMR on oriented wood pieces or applying gradients in various orientation, and 2D diffusion-diffusion correlation spectroscopy (DDCOSY) with two pairs of colinear gradient pulses. The results showed anisotropic restricted diffusion correlating the size of tracheid cells. The experimental 2D diffusion-diffusion correlation maps were compared with model calculations based on parameters of 2D experiment on spruce and the theory of 2D DDCOSY with ILT. Moisturizing spruce wood resulted in anisotropic diffusion coefficient which can be monitored in 2D NMR to discover different diffusion coefficients of water along the axis of wood fibers and in orthogonal direction.

Highlights

Wood is a natural fibrous material with porous structure which allows a transfer of water through the pores [1,2]. This water transport corresponds to the wettability of the wood material, which changes for different kinds of wood and various surface and inner microstructures [3,4]
It is important to know how wetting the wood affects porous microstructure and how to find suitable methods for estimation of pore-water interactions and water transport during changing moisture of wood [3,4,5,6,7,8,9]. Different methods including those based on the phenomenon of nuclear magnetic resonance (NMR spectroscopy and NMR Imaging) have been applied and developed to monitor wettability and saturation of different porous materials with water [1,4,11,12,13,14]
Advantages of magnetic resonance methods are associated with quickness of measurement, and the result of the measurement can be obtained in real time [16]

Summary

Introduction

Wood is a natural fibrous material with porous structure which allows a transfer of water through the pores [1,2]. It was shown [18,21] that 2D correlation experiments with two pairs of gradient pulses applied in orthogonal directions to wood pieces can be valuable means to define an anisotropy of water self-diffusion.

Results

Conclusion