SYNTHESIS AND PROPERTIES OF NANOCELLULOSE-DYE CONJUGATES

Abstract

Synthesis of conjugates of cellulose nanocrystals (CNC) with chlortriazine reactive dyes (RD) has been developed.  The obtained CNC-RD conjugates were characterized using a complex of modern methods: UV-Vis, IR and 13C solid state NMR spectroscopy, thermogravimetric and elemental analysis, particle size and zeta potential analysis, scanning electron and polarization optical microscopy. IR spectra of CNC-RD films show absorption bands typical of cellulose. The formation of a covalent cellulose-dye bond is confirmed by the presence of characteristic absorption bands of the resulting ether bond in the region of 1000-1300 cm-1. Based on the analysis of solid-state 13C NMR spectra, it was concluded that the degree of crystallinity of the CNC-RD conjugates does not change compared to the CNC, i.e. the RD covalently bind to the surface of the CNC particles and do not affect the crystal structure of the CNC. Using a simple model of CNC with square cross-section, and based on the elemental analysis data, the amount of covalently bound dye on the surface of CNC particles was estimated. The results obtained allow us to conclude that covalent bound of RD occurs selectively at one of the ends of the cellulose nanocrystal (the so-called reducing end of the cellulose polymer chain). Successful CNC surface modification is confirmed by UV-Vis spectroscopy. It was found that aqueous suspensions of CNC-RD conjugates have indicator properties. The sizes and charges of the particles of CNC-RD conjugates in dilute aqueous suspensions were determined. High colloidal stability of the CNC-RD aqueous suspensions was confirmed. It has been shown that CNC-RD colloidal suspensions possess liquid crystalline properties, which is clearly demonstrated by their iridescent color in polarized light with stirring. CNC films modified with RD also possess birefringence properties and exhibit an iridescent color in polarized light. The morphology of CNC-RD particles was studied using scanning electron microscopy. The thermal stability of the CNC-RD conjugates was studied.