Extraction of cellulose nanocrystals from microcrystalline cellulose for the stabilization of cetyltrimethylammonium bromide-enhanced Pickering emulsions

Abstract

The cellulose nanocrystals (CNCs) synthesized by sulfuric acid hydrolysis are highly hydrophilic and prone to form the agglomerations due to the hydrogen bonding, which limit their applications in the formulations of Pickering emulsions. For this reason, we selected microcrystalline cellulose (MCC) as the raw material for the extraction of CNCs through sulfuric acid hydrolysis and hydrogen peroxide oxidation, and then combined the surfactants of cetyltrimethylammonium bromide (CTAB) and CNCs to prepare the (O/W) Pickering emulsions by high-speed shearing method. The physicochemical properties of the resultant CNCs were evaluated by scanning electron microscopy (SEM), atomic force microscope (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The formed emulsions were characterized by fluorescent microscope (FM). And the effects of the CTAB concentration, pH and ionic strength on the stability of the formed Pickering emulsions were also investigated. Experimental results showed that the sulfuric acid hydrolysis of MCC induced the removal of the amorphous components and the cleavage of the crystalline microfibrils, making CNCs exhibit the curled and rod-like shape with the average hydrodynamic diameter of 460.5 nm (PDI = 0.585), zeta potential of -34.1 mV and the crystallinity index (CrI) of 77.3 %, which revealed good colloidal properties. In addition, the optimal emulsification conditions for CTAB concentration, pH and ionic strength were respectively 0.5 CMC, 11 and 20∼60 mmol/L. On the basis of the above results, the Pickering emulsions stabilized by CTAB/CNCs complex may have potential for large applications in foods, cosmetics and medicines.