A comparative study on the preparation and characterization of cellulose nanocrystals with various polymorphs.

Polymorphic changes of cellulose nanocrystals (CNCs) are strongly associated with its properties and applications. In this study, CNCs with different polymorphs were produced by a simple polymorphic transformation treatment. Cellulose I nanocrystals were produced by typical sulfuric acid hydrolysis (CNC-I). Cellulose II nanocrystals were prepared by two different methods: (1) sulfuric acid hydrolysis of cellulose previously mercerized with 18.5 wt% NaOH (CNC-II), (2) mercerization of CNC-I with 18.5 wt% NaOH (MCNC-II). Cellulose III nanocrystals were prepared by ethylenediamine treatment of CNC-I (ECNC-III). The polymorphic changes of CNCs, and their properties including morphology, crystallinity, thermal stability, and re-dispersion ability were systematically investigated. The results showed that the other properties of CNC-II and MCNC-II were quite different from each other except for the morphology. The morphology of polymorphic transformed CNCs were strongly relate to the fashion of cellulose chains arrangement. Both CNC-II and MCNC-II exhibited a rod-like shape with short lengths, whereas the ECNC-III showed relatively long length, like CNC-I.