The ‘‘surfactant-free” character of the Pickering emulsions make them attractive for applications in cosmetic and pharmaceutical products, reducing some adverse effects (irritancy, hemolytic behavior, etc.). Besides, particle stabilization offers specific properties to these colloidal systems, such as high resistance to coalescence at low solid content due to the strong particle adsorption onto the oil/ water interface [1]. Among the wide range of nanoparticles that can be employed to stabilize emulsions, we highlight nanocellulose particles, both cellulose nanocrystals (CNC) and nanofibrillated cellulose (NFC). Pristine nanocellulose generally leads to O/W emulsions, and extra components (salts and/or surfactant) are often required to improve the macroscopic stability [2]. However, surface modification can enhance the colloidal stability besides promoting the formation of different types of multiphase systems (W/O and multiple emulsions). In this work, cationic NFCs with different degrees of cationization were used to stabilize O/W emulsions (O: W = 30:70), and their performance was compared with the emulsions prepared with negatively charged analogous, TEMPO-oxidized NFC (oNFC). The electrostatic attraction between the positively charged trimethylammonium groups and the negatively charged deprotonated oleic acid (present in the oil phase) reduced the interfacial tension and enhanced the colloidal stability of O/W Pickering emulsions prepared with cNFCs. Also, cationic nanofibers dispersed in the aqueous phase were found to increase the viscosity, decelerating the oil drops coalescence. Therefore, the stabilization of cNFCs Pickering emulsions had a synergistic effect from the electrostatic complexation at the liquid-liquid interface and network formation in the aqueous phase. To obtain other types of multiphase systems, we are now modulating the wettability of cNFCs through the grafting of thermoresponsive poly di(ethylene oxide) methyl ether methacrylate (PMeO2MA) on the surface of nanofibers.

Pickering emulsions stabilized by cationic nanofibrillated cellulose

ACS Spring Meeting 2021

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