Transport of Polar and Nonpolar Liquids in Softwood Imaged by Neutron Radiography

The influence of the moisture capacity of cell walls on liquid transport in wood is studied using neutron imaging in combination with precision weighing. The time-dependent and spatial distribution of two liquids, one polar, water, and one nonpolar, decane, is documented during liquid uptake in the three orthotropic directions for samples of three softwood species: spruce and fir heartwood, and pine sapwood. Polar and nonpolar liquid uptake versus time is compared, the spatial distribution of the liquids within the samples is discussed, and the liquid volume and swelling profiles along the height of the samples are described in details. Water uptake is shown to be slower than decane uptake, due to water being adsorbed by the cells walls. Decane, due to its very low contact angle and high wettability compared to water, does not face much resistance from wood cellular features.