Bridging structure and energy in nanofibrillated cellulose production: Fibrillation mechanisms and machine...

Partially fibrillated(nanofibrillated) CNFs, despite their strong potential as eco-friendly nanomaterials, are difficult to quantify for their properties, which limits their industrial applicability. In contrast, fully individualized CNFs can be more clearly defined and allow direct correlations between particle structures and material properties, but they require high production energy. Therefore, there is a need for characterization methods specifically tailored to nanofibrillated CNFs to enable more energy-efficient production. In this study, the structural characteristics of CNFs produced using combinations of grinding and microfluidization were quantitatively evaluated, and the relationships among morphological changes, dispersion stability, and energy consumption were analyzed. Morphological observations demonstrated that different mechanical treatments induce distinct fibrillation mechanisms within the wood cell wall, which were closely associated with the sedimentation dynamics of the produced CNFs. Sedimentation behavior varied with the degree of fibrillation, showing rapid settling influenced by Stokes' law at low fibrillation levels and gradual linear settling influenced by Brownian motion at high fibrillation levels. Energy analysis revealed that combining moderate grinding (10-20 passes) with post-treatment microfluidization (5 passes) maximizes economic fibrillation. Furthermore, a CatBoost model accurately predicted energy consumption using structural indicators, demonstrating the feasibility of preliminary energy-consumption prediction using morphology-derived indicators.