Steric stabilization of cellulose nanocrystals by dextran grafting

Abstract

In this study, an enhanced dispersion stability of cellulose nanocrystals was achieved by terminal grafting of dextran (alpha-1,6 glucan) onto their surface. The carbon at the 6-position of the nanocrystal was first oxidized by the TEMPO method; then, the introduced carboxyl group on the surface of the cellulose nanocrystal was coupled with the 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 induced by grafting reached 184% of the carboxylated cellulose nanocrystal, resulting in a high dispersion stability. The dispersion stability was evaluated by calculating the change in viscosity before and after adding salt. Typically, cellulose nanocrystals are charged colloids; hence, adding salt reduces their dispersion stability and increases their viscosity. However, the addition of 0.05 M CaCl2 to a suspension of dextran-grafted cellulose nanocrystals did not cause a noticeable increase in viscosity or turbidity. This enhanced stability highlights the effectiveness of coating cellulose nanocrystals with water-soluble polymers.