Sustainable preparation and characterization of thermally stable and functional cellulose nanocrystals and nanofibrils via formic acid hydrolysis

In this work, a sustainable method to prepare functional cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) using formic acid (FA) (a recoverable organic acid) was established. After FA hydrolysis, the obtained CNCs could be well dispersed in DMAC. Thus, the CNC products and fibrous cellulosic solid residue (FCSR) in DMAC could be easily separated by a conventional centrifugal process, and the collected FCSR could be further fibrillated to CNFs with relatively low-intensity mechanical fibrillation process. The isolated CNC products showed high crystallinity index (about 75%) and excellent thermal stability (with onset thermal degradation temperature of 325 ℃). Both the resultant CNCs and CNFs showed better dispersibility in DMSO, DMF and DMAC respectively because of the introduction of ester groups on the surface of the products. The presence of surface ester groups could increase the interface compatibility of nanocelluloses with polymeric matrices and enable their applications in reinforcing polymeric matrix materials (e.g. the composite films like PHVB+CNFs).