Heat-treated and matched boards dried at 60°C of Scots pine (Pinus silvestris), Norway spruce (Picea abies) and Birch (Betula pubescens) were submerged into water, allowing for water absorption in the longitudinal direction during two weeks in room climate. Heat treatment was performed according to the Thermo-wood process at 170°C and 200°C. Boards from pine and spruce boards contained both sap- and heartwood. During water absorption computer tomography scanning, CT-scanning, was performed intermittently in order to measure the ascent of capillary water.
Longitudinal water absorption in heat-treated pine sapwood was substantial larger compared to untreated sapwood. In pine heartwood the ascent of water was low in heat- treated as well as in untreated boards. Spruce showed low water absorption in sap- and heartwood in heat-treated as well as in untreated boards. In birch the water absorption was lower in heat-treated wood compared to wood dried at 60°.
SEM-studies of the anatomical microstructure, pits and pit membranes were performed on heat-treated as well as on untreated material. SEM-studies revealed damages in heat- treated and dried pine sapwood mainly in pit membranes in the fenestriform cross-field pits connecting longitudinal tracheids with radial ray parenchyma cells. These damages are believed to play an important role in explaining the differences in water absorption between pine and spruce since the piceoid cross field pits in spruce seemed to be unaffected by heat treatment. In birch no striking, visible observations were found when comparing the three different treatment temperatures that could shed light to the observed big difference in capillary water absorption.
Keywords: Capillary water absorption, Heat treatment, Anatomical microstructure
Authors
Margot Sehlstedt-Persson
Luleå University of Technology, Wood Physics, Sweden
Dennis Johansson
Luleå University of Technology, Wood Physics, Sweden
Tom Morén
Luleå University of Technology, Wood Physics, Sweden
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