Crystalline stability of cellulose III nanocrystals in the hydrothermal treatment and NaOH solution.

To better understand the system and conversion of cellulose allomorphs, cellulose III nanocrystals (CNC-III) were used to investigate the crystalline stability of cellulose III in the hydrothermal condition and a lower concentrated NaOH-water system. It was shown that H2O or alkali played an important role in the process of polymorphic transformation. The CNC-III allomorph turned back to cellulose I with an extremely low crystallinity (similar to 4.18 %) during hydrothermal process at 90-95 degrees C, or cellulose II when the temperature excessed boiling point (>= 100 degrees C). Furthermore, CNC-III could be rapidly dissolved in an aqueous NaOH (similar to 7 wt.%) without a precooled treatment to obtain its stable solution. Afterwards, cellulose II with a steady average crystallite size (similar to 34) was acquired after the regeneration process via dialysis with distilled water. The polymorphic transformation was also analyzed by X-ray diffraction (XRD), solid-state C-13 nuclear magnetic resonance (C-13 NMR).