An NMR determination of the physiological water distribution in wood during drying

Abstract

Proton magnetic resonance has been used to study water in Douglas fir and western red cedar. The free induction decay, when combined with a knowledge of chemical composition of the wood, gives an accurate measure of the absolute moisture content. Spin-lattice relaxation was found to be significantly different for the two species. In sapwood, three distinct spin—spin relaxation times, T2, were measured and assigned, with the help of anatomical data, to water in and on the cell wall, water in the ray and latewood tracheid lumens, and water in the earlywood tracheid lumens. This T2 behavior was explained by a model in which free water in a void exchanges with a small fraction of bound water on the lumen surface. The three T2's were almost independent of moisture content, suggesting physically separate compartments. The behavior of the three water components during drying was studied. The fiber saturation point could be determined from a single T2 measurement on a green sapwood sample. Magnetic resonance imaging of logs was investigated.