H-NMR STUDIES OF WATER INTERACTIONS IN SITKA SPRUCE AND WESTERN HEMLOCK - MOISTURE-CONTENT DETERMINATION AND 2ND MOMENTS

The purpose of this study was to examine the influence of the moisture level on the cell-wall material in wood using pulsed proton nuclear m agnetic resonance. The wood species used were western hemlock (Tsuga h eterophylla (Raf.) Sarg.) and sitka spruce (Picea sitchensis (Bong.) C arr.), distinguishing between heartwood and sapwood regions. The moist ure contents of the specimens were below the fibre saturation point an d they were conditioned to equilibrium moisture contents based on init ial desorption, adsorption and secondary desorption processes. From th e FID experiments, the NMR-based moisture contents and the solid-wood lineshape second moments were determined. Average relative proton-spin densities, which were needed to calculate the NMR-based moisture cont ents, were determined from known moisture contents and they were: heml ock sapwood: 0.616; hemlock heartwood: 0.537; spruce sapwood: 0.679; a nd, spruce heartwood: 0.446. The average RSD value, considering both h eartwood and sapwood, for western hemlock species was 0.577 and for si tka spruce was 0.563; these are close to published RSD values for othe r species. The condition as to how the equilibrium moisture content wa s attained did not influence the second moment for hemlock; however, f or spruce sapwood, the second moments were sorption dependent. The hem lock M(2) decreased from about 5.1 x 10(9) s(-2) at low M(NMR) to 4.5 x 10(9) s(-2) (heartwood) and 4.3 x 10(9) s(-2) (sapwood) at higher M( NMR). The adsorption and secondary desorption M(2) for the spruce sapw ood region decreased from about 5.0 x 10(9) s(-2) at low M(NMR) to abo ut 4.1 x 10(9) s(-2) near the M(F), whereas M(2) for the spruce heartw ood decreased from about 4.3 x 10(9) s(-2) at low M(NMR) to about 3.5 x 10(9) s(-2) near M(F). Extractives may have a key role in obtaining the RSD and second moments.