In Situ Lignin Modification in Softwood via Organosolv Treatments and Its Effect on Thermal‐Softening Behavior

ABSTRACT

Thermal molding is a common technique for fabricating wood materials. In this study, we aim to improve the thermal‐softening properties of softwood ( Cryptomeria japonica ) to increase its pliability during heating. This is achieved through in situ lignin modification within the wood structure via sulfuric‐acid‐catalyzed organosolv treatments using ethylene glycol (EG) or 1,4‐butylene glycol (14BG). The EG treatment results in lignin grafted with EG molecules within the wood structure; however, it also causes significant delignification. Conversely, moderate 14BG treatment modifies lignin within the wood structure and mitigates thermal instability by partially removing wood constituents that are more susceptible to pyrolysis. Dynamic mechanical analysis shows that the dynamic elastic modulus of wood samples after 14BG treatment at 120°C or 130°C, followed by H ₂ O washing, is comparable to that of the untreated sample at 50°C. However, the modulus rapidly decreases above 150°C, indicating enhanced thermal‐softening behavior. Partial removal of the modified lignin via NaOH washing weakens this behavior, supporting its contribution to thermal softening. Although these analyses are conducted within the elastic region, our results suggest that moderate organosolv treatment facilitates the thermal processing of wood materials by improving their thermal‐softening behavior.