Mechanism of microfibril contraction and anisotropic dimensional changes for cells in wood treated with aqueous NaOH solution

Anisotropic swelling of wood samples was observed upon treatment with an aqueous NaOH solution with 0–0.20 fraction concentrations. At NaOH concentrations less than 0.10, the swelling occurred only along the tangential axis (T) and not along the radial (R) or longitudinal (L) axes. At greater NaOH levels, the swelling was even more pronounced along T with shrinkage along the other axes. These anisotropic changes along R and L were closely related to the crystallinity of microfibrils in the wood cell wall and simulated with a cell structure model. This exercise revealed microfibril contraction and matrix swelling in the wood cell wall upon NaOH treatment. The observed anisotropy in cross section was caused by differences in the microfibril angles (LR and LT) with the cell wall.