A DIFFUSION-MODEL FOR SPIN-SPIN RELAXATION OF COMPARTMENTALIZED WATER IN WOOD

A diffusion model for spin-spin relaxation of compartmentalized water with a surface relaxation was verified for lumen water in wood. Spin-spin relaxation measurements were carried out on water in redwood sapwood, spruce sapwood, and spruce compression-wood samples, which possessed different cell-lumen radius distributions as measured by scanning electron microscopy. For the redwood sample, NMR measurements were made for seven temperatures between 4 and 55°C over which the average lumen-water T2 decreased from 177 to 103 ms. The lumen-water theory and experiment were in agreement, and evidence of higher-order relaxation modes, theoretically predicted for low temperatures, was found. This model was extended to two water regions to characterize the surface relaxation in terms of the spin-spin relaxation and diffusion coefficient of the cell-wall water and the partition coefficient. Using the extension and measurements of the spin-spin relaxation times and relative populations of lumen and cell-wall-water, estimates for cell-wall-water diffusion in a maximally hydrated redwood varied from 0.92 × 10-6 cm2/s at 4°C to 5.89 × 10-6 cm2/s at 55°C. The activation energy for cell-wall-water diffusion in redwood sap-wood in this temperature range was 6700 cal/mol, about 40% higher than the free-water value of 4767 cal/mol. © 1993 Academic Press, Inc.