Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE The thermal-softening properties of softwood are tuned through sulfuric-acid-catalyzed organosolv treatment. Compositional analyses, including solid-state NMR, indicate that moderate organosolv treatment enables the in situ modification of lignin within the wood structure. Dynamic mechanical analysis demonstrates that the treated wood retains stiffness at ambient temperatures, while exhibiting thermal-softening behavior even under dry conditions.


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 H2O 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.