title: Modelling of the hygroelastic behaviour of normal and compression wood tracheids.
abstract: Compression wood conifer tracheids show different swelling and stiffness properties than those of usual normal wood, which has a practical function in the living plant: when a conifer shoot is moved from its vertical position, compression wood is formed in the under part of the shoot. The growth rate of the compression wood is faster than in the upper part resulting in a renewed horizontal growth. The actuating and load-carrying function of the compression wood is addressed, on the basis of its special ultrastructure and shape of the tracheids. As a first step, a quantitative model is developed to predict the difference of moisture-induced expansion and axial stiffness between normal wood and compression wood. The model is based on a state space approach using concentric cylinders with anisotropic helical structure for each cell-wall layer, whose hygroelastic properties are in turn determined by a self-consistent concentric cylinder assemblage of the constituent wood polymers. The predicted properties compare well with experimental results found in the literature. Significant differences in both stiffness and hygroexpansion are found for normal and compression wood, primarily due to the large difference in microfibril angle and lignin content. On the basis of these numerical results, some functional arguments for the reason of high microfibril angle, high lignin content and cylindrical structure of compression wood tracheids are supported.
authors.affiliation: Uppsala University, Department of Engineering Sciences, Ångström Laboratory, Box 534, SE-751 21 Uppsala, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Joffre
authors.affiliation: Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: R Cristian
authors.initials: RC
authors.lastname: Neagu
authors.affiliation: SP Technical Research Institute of Sweden, SP Wood Technology, P.O. Box 5609, SE-114 86 Stockholm, Sweden.
authors.forename: Stig L
authors.initials: SL
authors.lastname: Bardage
authors.affiliation: Uppsala University, Department of Engineering Sciences, Ångström Laboratory, Box 534, SE-751 21 Uppsala, Sweden. Electronic address: kristofer.gamstedt@angstrom.uu.se.
authors.forename: E Kristofer
authors.initials: EK
authors.lastname: Gamstedt
mesh_terms: D002473:Cell Wall / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D008031:Lignin / Q000378:metabolism / Q000648:ultrastructure; D020894:Microfibrils / Q000378:metabolism / Q000648:ultrastructure; D011108:Polymers / Q000378:metabolism; D011312:Pressure; D014934:Wood / Q000502:physiology* / Q000648:ultrastructure*
chemical_list: D011108:Polymers; D008031:Lignin
keywords: Compression wood; Dimensional stability; Hygroelastic properties; Modelling; Reaction wood