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Dependence of Poisson’s ratio and Young’s modulus on microfibril angle (MFA) in wood

Abstract Microfibril angle (MFA) is a major structural variable that describes the fine structure of the cell wall in wood. In this study, the relationships between the MFA of the S2 layer and the Poisson’s ratios and Young’s moduli (modulus of elasticity, MOE) of five wood species (agathis, larch, Japanese cedar, Japanese cypress and ginkgo) were determined by analyzing both their normal and compression woods. It was found that both the longitudinal MOE (MOEL) and MOE of the cell-wall substance (MOEW) decreased with increasing MFA, while the peaks values of Poisson’s ratio (νLT) were obtained at MFAs of ≈25°. In particular, at MFAs lower than 25°, the νLT increased with increasing MFA, and the opposite relationship was observed at MFA values exceeding 25°. This trend is in good agreement with the estimates obtained based on the theory of orthotropic elasticity with the underlying assumption that the orthotropic elasticity of materials is MFA-dependent. Hence, the MFA parameter incorporated into the orthotropic elasticity theory is useful for determination of the Poisson’s ratio.