Water content measurement in black spruce and aspen sapwood with benchtop and portable magnetic resonance devices

Abstract

In this study, water content in black spruce (Picea mariana Mill.) and aspen (Populus tremuloides Michx.) sapwood samples was investigated with time-domain magnetic resonance (MR). Time-domain MR measurements easily distinguish water in different environments in wood according to the spin-spin relaxation time and provide quantitative information on water content. The MR techniques employed can distinguish and quantify the individual signal components. Both black spruce and aspen have two signal components at moisture contents above the fiber saturation point. These two signal components correspond to motionally restricted water, often referred to as bound water, and unrestricted, or free water. Bound water content is constant above 40% moisture content. No signal from free water was detected at or below 20% moisture content in either species. We also demonstrate the use of a recently developed portable unilateral magnet that can be employed as a powerful tool in the study and measurement of water content in wood.