Enhancement of CO2/N2 Switchability and stability in cellulose nanofibers pickering emulsions by CO2-responsive rosin-grafted hydroxyethyl cellulose

The MPAN-g-HEC product exhibits CO 2 responsiveness. • CO 2 gas protonates MPAN-g-HEC to MPAN + -g-HEC. • MPAN + -g-HEC can enhance the stability of CNF-based Pickering emulsion. • Alternating CO 2 and N 2 in the system switches the emulsification and separation. Cellulose has been widely used in conventional Pickering emulsions, yet its application in stimulus-responsive Pickering emulsions remains relatively limited. In this paper, cellulose-based CO 2 /N 2 stimuli-responsive polymer compounds (MPAN-g-HEC) were prepared through the hydrophobic modification of hydroxyethyl cellulose using the maleopimaric acid 2-dimethylaminopropylamine imide with a tertiary amine group (MPAN). The grafting rate of MPAN-g-HEC was controlled by adjusting the HEC-to-MPAN mass ratio. Specifically, five grafted products (MPAN-g-HEC I∼V) were prepared, and the grafting rate increased from 9.24% to 48.43%. The addition of CO 2 resulted in the protonation of MPAN-g-HEC, converting it to the MPAN + -g-HEC. The critical micelle concentration (CMC) values of MPAN + -g-HEC ranged from 0.28 to 0.88 g/L, with corresponding surface tensions of 40.8–43.3 mN/m. The product with the best performance (MPAN-g-HEC IV, abbreviated as MPAN-g-HEC) is used to enhance the stability of Pickering emulsions of cellulose nanofibers. These stimuli-responsive Pickering emulsions exhibit stability due to the electrostatic interactions between MPAN + -g-HEC and CNF, as well as the formation of interfacial films at the oil-water interface. In addition, the alternating passage of CO 2 and N 2 can achieve the interconversion between emulsification and demulsification, and the process is reversible. Rheological tests show that the G′ and G″ tend first to decrease and then increase, indicating that the Pickering emulsion first undergoes damage and then reforms a network structure. Download: Download high-res image (192KB) Download: Download full-size image