Proton spin-lattice relaxation in wood - T-1 related to local specific gravity using a fast-exchange model

The spin-lattice relaxation and cross relaxation of western redcedar sapwood (moisture contents 216 to 15%) and western hemlock sapwood (moisture contents 144 to 15%) were investigated using proton magnetic resonance, Below the fiber saturation point (FSP), solid wood and cell-wall water were found to have the same T-1 indicating a fast exchange of proton magnetization between these two environments, Above the FSP, multiexponential T-1 decay was observed, A one-dimensional profile across the growth rings showed that the multiple components of spin-lattice relaxation in wood were due to variations in local specific gravity, Within a small volume, a single T-1 was observed for protons in lumen water, cell-wail water, and solid wood, The mixing of proton reservoirs was attributed to water diffusion between the lumen and cell wall, and cross relaxation between the protons in the cell-wall water and the solid wood. This cross-relaxation time was found to be a few milliseconds, which is fast on the T-1 time scale of tens of milliseconds. A fast-magnetization-exchange model which related T-1 values to local specific gravity was verified for protons in all environments in wood, Using this model, the distribution of local specific gravity was derived for the western red-cedar and hemlock samples. (C) 1996 Academic Press, Inc.