Novel fabrication of high-modulus cellulose-based films by nanofibrillation under alkaline conditions

We herein propose a novel continuous process for fabricating high-modulus films based on cellulose nanofibers. In place of a dissolution process, the pulps were mechanically disintegrated into nanofibers by ball-milling in an 8% NaOH solution. NaOH treatment loosened the hydrogen bonding between the cellulose microfibrils in the pulps, and a highly concentrated suspension (8%) of cellulose nanofibers with a uniform diameter of approximately 20-50 nm was prepared after ball-milling for 90 min. The resulting nanofiber suspensions prepared in the NaOH solution exhibited the crystal forms of both Cellulose I and Cellulose II, although the Cellulose II content gradually increased upon increasing the milling time. Finally, hydrogels were formed following neutralization of the suspensions, and the hydrogel sheets were hot-pressed into thin films at 120 °C. The Young's moduli of the films were significantly higher than those of typical regenerated cellulose films due to the presence of some remaining Cellulose I and a high crystallinity.