Determining the Highly Anisotropic Cell Structures of Pinus sylvestris in Three Orthogonal Directions by PGSTE NMR of Absorbed Water and Methane

Abstract

The walls of solid matrix restrict the self-diffusion of a fluid absorbed in the matrix, and this is reflected in the echo amplitudes measured by PGSTE NMR. Hence, the pore size distribution of the matrix can be extracted from the echo amplitudes. We demonstrate that, when both liquids and gases (water and methane in this case) are used as probe fluids, the scale of the dimensions observable by PGSTE NMR may be over 4 orders of magnitude. This enables determining the dimensions of highly anisotropic pores. In the present case, the wood cell structures of Pinus sylvestris in three orthogonal directions were studied.

Time-of-flight remote detection MRI of thermally modified wood

“…The observed closing of the pits in the modification may play an important role in achieving such desired properties in thermal modification as reduced moisture content and improved dimensional stability. As the connections between tracheid cells could not be observed with PGSE NMR based methods in previous studies [19][20][21][22], TOF RD MRI increases crucially information given by NMR methods in wood research. The images also reveal that most of the gas flowed through early wood in both samples.…”

“…This method mainly provides information about the dimensions of lumens inside tracheid cells in the transverse direction. Combined PGSE NMR of liquids and gases extends the range of observable dimensions from two to over four orders of magnitude, making it possible to also determine the axial dimensions of tracheids and the dimensions of the other cell structures [22]. However, previous studies have not revealed the connections between cells and cell structures, even though it is known that tracheid cells are connected to each other by small pits (see Fig.…”

Wood Characterization by NMR & MRI of Fluids

“…Analysis of the echo amplitude decay using an appropriate theoretical model makes it possible to determine the structural dimensions. 13, 14 Consider the diffusion of fluid in pine. Because 93% of pine comprises boxlike tracheid cells (Figure 1), it is reasonable to use a model in which the probe fluid molecules are assumed to be confined within a rectangular box with perfectly reflecting walls.…”

“…Water (small D) is an optimal probe for measuring the transverse lumen dimensions (∼30 μm) because the pore size which water can probe with typical experimental parameters is about 10-300 μm, whereas methane gas (large D) is best suited for measuring lumen lengths (a couple of millimeters), as it can probe dimensions from 300 μm to 10 mm. 14 Pulsed-field gradient-stimulated echo (PGSTE) NMR 16 (a variant of PGSE NMR) amplitudes measured in the transverse directions from water and in the longitudinal direction from methane absorbed in pine are shown in Figure 8. Amplitudes decay faster in the radial direction than in the tangential direction (Figure 8a) because the average lumen size in the former direction is larger.…”

“…As the diffusion coefficient of moisture differs from that of methane gas, this component does not give quantitative information about the corresponding structures. 14 We have used PGSTE NMR for determining the changes in the lumen dimensions caused by thermal modification. By comparing the pore-size distributions measured from thermally modified sample and corresponding unmodified reference sample, we found that the lumen size decreased in all the three orthogonal directions (tangential, radial, and longitudinal).…”