Behavior of the cellulose microfibril in shrinking woods

Abstract

We measured the longitudinal and tangential shrinking processes in wood specimens from Chamaecyparis obtuse Endl. with different microfibril angles (MFAs). The shape of the shrinking curve was compared with the MFA. Only the longitudinal shrinking process of specimens with a small MFA clearly showed nonlinearity, and the degree of nonlinearity increased as the MFA decreased. In contrast, the tangential shrinking process and the longitudinal shrinking process of compression wood with a large MFA were linear. The nonlinearity is probably caused by the longitudinal shrinkage of the noncrystalline region of the cellulose microfibril (CMF) in regions of low moisture content during water desorption. When the moisture content is high, the matrix substance in the cell wall begins to dry; however, the shrinkage in the chain direction is restrained by the rigid CMF. As the wood dries further, the noncrystalline region of the CMF embedded in the matrix substance begins to shrink. Because the longitudinal mechanical behavior of wood with a small MFA is greatly affected by a rigid CMF, longitudinal shrinkage increases suddenly at about 10% moisture content; as a result, the shrinking process shows nonlinearity.