Proton Spin–Lattice Relaxation in Wood—T1Related to Local Specific Gravity Using a Fast-Exchange Model
✍ Scribed by Yan Xu; C.D. Araujo; A.L. MacKay; K.P. Whittall
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 263 KB
- Volume
- 110
- Category
- Article
- ISSN
- 1064-1866
No coin nor oath required. For personal study only.
✦ Synopsis
The spin-lattice relaxation and cross relaxation of western redhemlock), there are three main reservoirs for lumen water: cedar sapwood (moisture contents 216 to 15%) and western hemearlywood and latewood tracheids, which are oriented longilock sapwood (moisture contents 144 to 15%) were investigated tudinally along the tree trunk, and ray cells which are oriusing proton magnetic resonance. Below the fiber saturation point ented radially. Figure 1 shows the scanning electron micro-(FSP), solid wood and cell-wall water were found to have the scope (SEM) image of a western red-cedar sapwood sample. same T 1 indicating a fast exchange of proton magnetization be-In this image, the cell walls are white and the cell lumens tween these two environments. Above the FSP, multiexponential are black. The earlywood tracheids, which grow during the T 1 decay was observed. A one-dimensional profile across the spring and early summer, are larger in radius than the lategrowth rings showed that the multiple components of spin-lattice wood tracheids, which grow in late summer and autumn.
relaxation in wood were due to variations in local specific gravity.
The latewood tracheids have a thicker cell wall and give
Within a small volume, a single T 1 was observed for protons in lumen water, cell-wall water, and solid wood. The mixing of proton the latewood region a higher wood-cell density. The radial reservoirs was attributed to water diffusion between the lumen alternation of these cell types results in the annual growth and cell wall, and cross relaxation between the protons in the cellrings. Tracheids vary in size from species to species. They wall water and the solid wood. This cross-relaxation time was range from 5 to 50 mm in radius and are 4 to 5 mm long. found to be a few milliseconds, which is fast on the T 1 time scale of Ray cells typically contain only about 3% of the total lumen tens of milliseconds. A fast-magnetization-exchange model which volume and have radii of about 8 mm. related T 1 values to local specific gravity was verified for protons Wood is a cellular material. The following characteristics in all environments in wood. Using this model, the distribution of play important roles in the physical and mechanical properlocal specific gravity was derived for the western red-cedar and ties of wood (3): (1) the moisture content; (2) the porosity hemlock samples.