SynopsisProton 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, T,, 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 T, 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 T,'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 T, measurement on a green sapwood sample. Magnetic resonance imaging of logs was investigated. INTRODUCTIONThe distribution and interactions of water in wood are of great importance in the commercial utilization of wood. Thus, the characterization of this water is essential for the sophisticated control of the chemical and structural properties of wood.'Proton nuclear magnetic resonance (lH-NMR) is not a new tool in the understanding of wood-water interactions2. or water-cellulose intera~tions.~ Pulsed NMR has been used to determine the moisture content (MC) of wood relative to a known ~t a n d a r d ,~ but no attempt has been made to directly *Work supported by the Canadian Forestry Service and the Natural Sciences and Engineering +On intersession leave from University of Alberta. *Author to whom requests for reprints should be addressed. (Mirb.) Franco], henceforth called fir, and western red cedar ( T h j a plicata Donn) was made. The behavior of three distinct mobile water components was studied during stepwise oven drying in order to identify where these components were physically located and to learn about the wood drying process. Anatomical data were obtained to determine the physical locations of the water. The work was done on both heartwood and sapwood. The NMR characterization of this water also allows optimization of parameters for imaging different types of water in logs by magnetic resonance imaging (MRI), which is being done in parallel with this work. MATERIALS AND METHODS SamplesThree rectangular cedar sapwood samples were cut from a 1 cm thick transverse slice of a green log. The resulting sample blocks measured approximately 1 X 0.55 X 0.55 cm with the long axis of the block parallel to the longitudinal tracheids in the wood. Each sample was placed at the bottom of a 18 cm long, 10 mm 0.d. NMR sample tube, and a 17 cm long teflon dowel, 8 mm in diameter, was then inserted just above the wood in order to minimize the air space with which the wood could equilibriate. A tight fitting plastic cap was used to seal the tube.Similarly, two samples each of ...

Two new proton magnetic resonance techniques, relaxation spectra and relaxation selective imaging, have been used to investigate the distribution of water in samples of normal white spruce sapwood, heartwood, and juvenile wood as well as two rehydrated heartwood samples containing incipient decay and compression wood respectively. It is demonstrated that the spin-spin (T2) relaxation behavior in wood is best presented as a continuous spectrum of relaxation times. Spectra of T 2 for white spruce show separate peaks corresponding to the different water environments. Bound water gives a peak with an T 2 time of about 1 ms and lumen water gives a distribution of T 2 times in the range of 10 to 100 ms. The lumen water T 2 time is a function of the wood cell radius. Consequently, the different cell lumen radii distributions for spruce sapwood, juvenile wood, and compression wood are readily distinguishable by the shape of their T 2 spectra. Water environments which are separable on a T 2 spectrum may be imaged separately. Imaging has been carried out in one dimension for bound water and lumen water of a spruce sapwood sample at four different moisture contents ranging from 100% to 17%. For the first time, we demonstrate that above the fibre saturation point the moisture density profile of the bound water is largely independent of moisture content. The feasibility and utility of using these techniques for internal scanning of logs and lumber is discussed. These techniques should provide new insights into the wood drying process.

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