A model of anisotropic swelling and shrinking process of wood |
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Authors: | H Yamamoto F Sassus M Ninomiya J Gril |
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Institution: | (1) School of Bio-agricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan e-mail: hiro@agr.nagoya-u.ac.jp, JP;(2) Laboratoire de Mechanique et Genie Civil, Universite Montpellier 2 34095 Montpellier, CEDEX 2, France, FR |
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Abstract: | To elucidate the origin of the shrinking anisotropy of wood during the drying process, as well as to begin to gain an understanding
of the interaction between the moisture and the cell wall components, the shrinking process of a single wood fiber regarding
water desorption was simulated by using an analytical model which was developed in the previous report (Part 1). Resulting
data were compared with the experimental ones in this paper. The following conclusions were obtained: (1) The matrix substance,
as a skeleton in the secondary wall, tends to shrink isotropically. However, the cellulose microfibrils, as a rigid framework
of the cell wall, almost did not shrink at all due to the water desorption. As result, wood shrinks anisotropically during
a drying process. The microfibril angle in the S2 layer is one of the most important factors related to the degree of shrinking
anisotropy of the wood while drying. (2) According to the simulation, the expansive strain caused in the matrix skeleton by
the water sorption increases by 15% (= 150,000 micro-strains) from the oven-dried condition to the green condition. Based
on this value, the moisture content at the fiber saturation point is calculated to be about 35%, which is close to the experimentally
obtained one. These results give quantitative evidences that the hygroexpansion of the wood cell wall is controlled by the
mechanism of the reinforced matrix hypothesis.
Received: 28 July 1998 |
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