Steric colloidal stabilization of cellulose nanocrystals by dextran grafting

In this study, enhanced dispersion stability of cellulose nanocrystal was achieved by terminal grafting of dextran (a-1,6 glucan) onto the surface of nanocrystals. The 6-position carbon of the nanocrystal was first oxidized by TEMPO method, and the introduced carboxyl group on the surface of cellulose nanocrystal was coupled with terminal amino group of terminally aminated dextran using N-hydroxysuccinimide and 1-ethyl-3-3-dimethylaminopropyl carbodiimide. Terminally aminated dextran was obtained by reductive amination using sodium cyanoborohydride and ammonium chloride. The weight gain by grafting reached 184% of the carboxylated cellulose nanocrystal, resulting in high dispersion stability. We evaluated the dispersion stability by the change in viscosity before and after adding salt. Cellulose nanocrystals are colloids, and adding salt reduces their dispersion stability and increases their viscosity. However, addition of 50 mM CaCl ₂ to the suspension of dextran grafted cellulose nanocrystal did not cause noticeable increase in viscosity or in turbidity. This enhanced stability indicates the effectiveness of coating cellulose nanocrystal by water-soluble polymers.