Cellulose nanocrystals as water-in-oil Pickering emulsifiers via intercalative modification

Abstract A novel water-in-soybean oil Pickering emulsifier based on CNCs was fabricated via the intercalative chemical reaction between n -octadecyl isocyanates and hydroxyl groups in CNCs. The structural variations of alkyl intercalated CNCs with different degrees of substitution for hydroxyl groups were studied by TEM, AFM, FTIR, XRD, elemental analysis and liquid DSC. It is shown that O(2)H/O(6)H instead of O(3)H in CNCs were substituted after intercalative modification. And the particle thickness was increased after the intercalation, due to the enlargement of the basal spacing of (200) lattice plane in CNCs. While their cross section dimensions were unvaried. The structural variations in alkyl intercalated CNCs on their emulsifying capacity were further studied. Particle length has the insignificant influence on the emulsifying capacity. Alkyl intercalated CNCs with different particle lengths failed to stabilize water-in-soybean oil Pickering emulsion droplets, if O(2)H/O(6)H hydroxyl groups were fully substituted with alkyls. Alkyl intercalated CNCs with appropriate amounts of substituted hydroxyl groups possessed a good emulsifying capacity. After the initial coalescence, the average droplet size and its distribution polydispersity remained nearly constant with one year of storage. Results shown that alkyl intercalated CNCs with different degrees of substitution for hydroxyl groups had the similar interfacial tension at the soybean oil-water interface, the similar molecular arrangement of internal intercalated alkyls but different contact angles. These indicated that emulsifying capacity was mainly related to their surface alkyl chains. Besides, water-in-soybean oil Pickering emulsions stabilized by alkyl intercalated CNCs were from steric hindrance rather than interfacial tension reduction mechanism.