Influence of delignification on plastic flow deformation of wood

In this study, we elucidated the influence of delignification of wood on its plastic flow deformation caused by the shear sliding of wood cells. The delignified wood samples were characterized by attenuated total reflection-infrared (ATR-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, Raman imaging analysis, and dynamic viscoelastic measurements. Then, the effects of the chemical structure, distribution, and molecular motility of lignin on the deformability of wood were evaluated. The delignified wood in water-swollen state was significantly deformed without cell wall destruction at a lower pressure than the untreated wood. The deformability was evaluated from two perspectives: stress at flow starting point and deformed cross-sectional area of the wood sample. The deformability of the delignified and untreated wood increased with increasing temperature during compression. In the early stages of delignification, the lignin in the compound middle lamella decreased, especially at the cell corner, which reduced the stress at the flow starting point. However, the deformed cross-sectional area of wood varied slightly with delignification time in these stages. As the delignification proceeded, the lignin at the vicinity of the polysaccharides in the cell wall was removed and the deformability improved significantly. Additionally, the stress at the flow starting point increased linearly with the peak temperature of tan δ, corresponding to the glass transition temperature of lignin in water-swollen wood, regardless of the temperature during compression. The correlation between chemical and physicochemical properties and plastic flow deformability presented in this paper will aid in low-energy and highly productive formation of solid-state wood.