Liquid uptake in Scots pine sapwood and hardwood visualized and quantified by neutron radiography

Abstract

Non-destructive neutron radiography is used to study the different processes of liquid transport in Scots pine sapwood and heartwood. The spatial and temporal changes in moisture content and saturation degree, measured at high resolution, are provided for water uptake in longitudinal, radial and tangential directions. Liquid uptake in sapwood, compared to in heartwood, is found to be faster and more homogeneous. Latewood cells are the preferential pathways for longitudinal and tangential uptake in both sapwood and heartwood resulting in strongly non-uniform water fronts. In radial uptake, water accumulates first in the border between growth layers. While the moisture content profiles vary strongly between earlywood and latewood layers, the corresponding swelling strain profiles change smoothly due to the mechanical interaction between the different layers. Long term experiments in laboratory show three phases of uptake: a first fast phase, a second slower phase and a third phase reaching capillary saturation. The main difference between sapwood and heartwood uptake takes place in the first phase when liquid is mainly transported in the lumen, until moisture reaches the top of the sample. After that, both wood types behave similarly, uptake is followed by a slower adsorption in the wood cell walls and liquid redistribution in perpendicular to the uptake direction until the sample is almost totally saturated. These findings are of interest for future studies on durability and treatability of pine sapwood and hardwood.

Impact of internal structure on water-resistance of plywood studied using neutron radiography and X-ray tomography

“…Density and moisture uptake are closely interrelated [8,21]. The high density, low porosity latewood becomes moisture saturated earlier than earlywood in water absorption test [22]. Hardwood species with high density have a high probability to have small cell lumens possibly acting as the preferential pathways for water transport in the longitudinal direction.…”

Removal of introduced inorganic content from chipped forest residues via air classification

“…Cambium concentrations of K, P, Ca, and Mg were found to be an order of magnitude higher than the concentrations found in sapwood, while most inorganic elements were lowest in the heartwood [33]. In addition to chemical differences between plant tissue types, there are also density differences, including measurable differences between bark, needles, heartwood, and sapwood [34][35][36][37][38]. These differences may be useful in separating these tissues into distinct fractions using methods that rely on material density, particle shape, and surface area.…”

Mechanisms of liquid imbibition in Douglas-fir inferred from 1H nuclear magnetic resonance methods

“…The pits are located regularly along the tracheid cells. Most of bordered pits of adjacent tracheid cells in heartwood are closed in the earlywood and opened in the latewood, whereas in sapwood they are opened both in the early and latewood (Almeida et al 2008, Sedighi-Gilani et al 2014. Through a quantitative analysis with Douglas-fir, it has been shown in (Elaieb 2014) that about 65% of pits are open in sapwood but only 23% in heartwood.…”

“…This model predicts that the total liquid uptake is proportional to the square root of time and that a uniform liquid front advances linearly with the square root of time. In wood, either in softwoods or in hardwoods, these characteristics have been observed, for example for the front of penetration (Kučerová 2012) or for the proportionality between the total liquid uptake and the square root of time (Sedighi-Gilani 2014). However, even if some deviations from the Washburn law are observed, capillary effects are usually considered.…”