Effect of Alkyl Grafting on the Interfacial Properties and Pickering Emulsifying Efficiency of Cellulose Nanocrystals

Abstract

This study investigates the effect of alkyl grafting on the interfacial properties and Pickering emulsifying efficiency of cellulose nanocrystals (CNCs). CNCs were modified with octylamine or dodecylamine through periodate oxidation, followed by reductive amination to tune their hydrophilic–hydrophobic balance while preserving their colloidal dispersibility in water. The introduction of alkyl chains significantly altered the surface characteristics of CNCs, leading to increased water contact angle, reduced ζ-potential, enhanced surface activity, and pronounced changes in rheological behavior associated with the formation of weak physical networks. These modifications strongly improved the interfacial performance of CNCs, resulting in enhanced adsorption at oil–water interfaces and superior Pickering stabilization efficiency. Compared with unmodified CNCs, alkyl-grafted CNCs produced oil-in-water emulsions with smaller droplet sizes, improved resistance to coalescence, and enhanced long-term stability. The modified CNCs also induced a stronger gel-like character in the emulsions, contributing to droplet immobilization and improved colloidal stability. As an example of application, surfactant-free emulsion based on epoxidized soybean oil (ESO) and stabilized by the amphiphilic CNCs was prepared and cured with triethylenetetramine (TETA) for possible application in coating. Beyond their emulsifying role, the modified CNCs acted as reinforcing agents, significantly increasing the stiffness of the cured films through the formation of a rigid nanocellulosic network within the cross-linked matrix. Overall, this work highlights the potential of hydrophobically modified CNCs as sustainable dual-function materials combining enhanced interfacial activity, efficient Pickering stabilization, and reinforcing capability for waterborne biobased coatings.