Moisture Dependence of Indentation Deformation and Mechanical Properties of Masson Pine (Pinus Massoniana Lamb) Cell Walls as Related to Microfibrilar Angle

To better understand how microfibrillar angle (MFA) and moisture content influence the mechanical performances of wood at the cell wall level, the nanoindentation technique was used to measure the indentation modulus, hardness, indentation creep rate (ICR), residual plastic deformation (RPD), and elastic recovery deformation (ERD) of Masson pine (Pinus massoniana Lamb) wood cell walls with small (16°), medium (27°), and large (38°) MFA values at 5, 8, and 11% MC, respectively. The results show cell wall elastic modulus was negatively correlated to moisture content, but the specific trend was to some extent affected by the value of MFA. MFA has a negative influence on cell wall elastic modulus across the range of all tested moisture contents. Cell wall hardness decreased significantly with increase of moisture content for all three MFA values, whereas the effect of MFA was insignificant. RPD and ERD of cell walls responded differently to the change of moisture content and MFA. In general, RPD is more sensitive to moisture content than MFA, whereas ERD and ICR are more sensitive to MFA than the low moisture content range as defined in this study