Interplay of colloidal stability of cellulose nanocrystals and their dispersibility in cellulose acetate butyrate matrix

Cellulose nanocrystals (CNC) prepared from eucalyptus cellulose CNCs were modified by the reaction with methyl adipoyl chloride, CNCm, or with a mixture of acetic and sulfuric acid, CNCa. The CNC were either dispersed at 0.1 wt% in the pure solvents ethyl acetate (EA), tetrahydrofuran (THF) and dimethylformamide (DMF) or in cellulose acetate butyrate (CAB) solutions prepared in these solvents at 0.9 wt%. The colloidal behavior of these dispersions was systematically investigated using a phase separation analyzer LUMiReader®. The mechanical properties and morphological features of the films resulting from the mixtures of CAB and CNC were determined by dynamic mechanical analysis, optical microscopy and atomic force microscopy, respectively. Regardless the functional group attached to the surface of CNC, the best colloidal stability was observed for dispersions prepared in CAB/DMF solution. Higher degree of substitution of modified CNCs favored the colloidal stability in EA and THF. Composite films prepared from CAB/DMF solutions were more homogeneous and presented better mechanical performance than those prepared in CAB/EA or CAB/THF. The mechanical performance of composites and neat CAB prepared from DMF was CAB/CNCs > CAB/CNCm > CAB/CNCa > CAB, indicating that the modification weakens the percolation process, which is mediated by H bonding.