Microstructural features assessment of different waterlogged wood species by NMR diffusion validated with...

Area of Science:

• Materials Science
• Wood Science
• Analytical Chemistry

Background:

• Wood is a complex, anisotropic natural material with a porous microstructure.
• Waterlogged wood, common in archaeological finds, requires microstructural analysis for conservation.
• Nuclear Magnetic Resonance (NMR) diffusion techniques offer insights into porous media but have limitations.

Purpose of the Study:

• To investigate the microstructure of waterlogged wood species using NMR diffusion.
• To validate NMR-derived parameters with complementary imaging and physical measurements.
• To establish diffusion anisotropy and tortuosity as key identifiers for wood species differentiation.

Main Methods:

• Pulse Field Gradient (PFG) Nuclear Magnetic Resonance (NMR) to quantify time-dependent diffusion coefficients (D(t)) and tortuosity (τ).
• Measurement of relaxation times and diffusion anisotropy (a_n) for water diffusing in wood.
• Complementary validation using micro-imaging NMR (μ-MRI), environmental-scanning electron-microscope (ESEM) imaging, dry density, and imbibition tests.

Main Results:

• NMR diffusion parameters, including D(t) and τ, were quantified along and perpendicular to wood axes.
• Pore size distribution and wood microstructure characterization were derived from NMR data.
• Diffusion anisotropy (a_n) versus tortuosity (τ) proved more effective in differentiating wood species than estimated pore size.

Conclusions:

• Diffusion anisotropy and tortuosity provide a robust method for characterizing and differentiating waterlogged wood species, especially when high-resolution imaging is unavailable.
• The combination of PFG-NMR and micro-MRI enhances the observable length scales in wood microstructure analysis.
• This study highlights the potential of NMR diffusion parameters as a primary tool for waterlogged wood investigation and conservation.