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 compressio n 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.

Hygroscopic swelling and shrinkage of latewood cell wall micropillars reveal ultrastructural anisotropy

“…Interface 11: 20140126 between MFA and longitudinal shrinkage is presented in the experimental study performed by Meylan [34] which shows that the longitudinal shrinkage is very low at small MFA and shows a rapid increase at MFA ≃ 30 W : On the other hand, in the transverse plane of the cell walls, the relationship between MFA and the swelling anisotropy is rarely investigated. The role of MFA can be observed by comparing the transverse swelling and shrinkage behaviour of normal wood with compression wood which has a much higher MFA in the order of MFA ≃ 45 W : Experiments on macroscopic samples show that the tangential swelling/shrinkage of compression wood is considerably smaller than normal wood while the longitudinal swelling is much larger in compression wood [35,36]. Dependency of the transverse shrinkage on the MFA in the range below MFA ≃ 30 W is not notable [37].…”

Wood identification of two anatomically similar Cupressaceae species based on two-dimensional microfibril angle mapping

“…The microfibril angle (MFA) is a reliable means of describing the characteristics of wood because this quantitative parameter can explain a number of important features, such as mechanical properties (Bendtsen and Senft 1986;Cave and Walker 1994;Cowdrey and Preston 1966) and shrinkage behaviors of wood (Abe and Yamamoto 2006;Barber and Meylan 1964;Meylan 1972). By contrast, features of the MFA specific to certain species of softwoods, such as MFA value itself and their transition from earlywood to latewood, remain undiscussed except for a few studies (Hori et al 2002;Lichtenegger et al 1999).…”