Water–ethanol organosolv pretreatment of Japanese cedar (Cryptomeria japonica) for controlling fibrillation toward production of lignin-containing cellulose nanofibrils

Lignin-containing cellulose nanofibrils (LCNFs), which combine the high strength of cellulose with the hydrophobicity and ultraviolet stability of lignin, are promising materials for advanced applications. In this study, we developed an organosolv-based pretreatment strategy to control the fibrillation behavior of LCNFs derived from Japanese cedar ( Cryptomeria japonica ) by retaining lignin on cellulose fibers while facilitating mechanical fibrillation with a lower apparent energy requirement. The pretreatment was performed at 393 K using water-ethanol mixtures with water-to-ethanol molar ratios of 0.2, 1, 4, and 19. Compositional analysis revealed that lignin was largely retained, whereas hemicellulose was partially removed, particularly at a water-to-ethanol molar ratio of 4. These structural changes were supported by scanning electron microscopy, which revealed delamination of the woody cell walls, indicating enhanced structural accessibility. Mechanical fibrillation efficiency was quantitatively evaluated using classical comminution relationships. At a water-to-ethanol molar ratio of 4, the apparent work index, used here as a relative measure of the energy requirement, decreased by 66% compared to the untreated sample, indicating improved fibrillation efficiency and a lower apparent energy requirement under identical milling conditions. By applying classical comminution relationships as a common framework, this study provides a basis for comparing fibrillation efficiency across different pretreatment conditions.