Tough and self-healable nanocomposite hydrogels from poly(acrylic acid) and polyacrylamide grafted cellulose nanocrystal crosslinked by coordination bonds and hydrogen bonds

Developing self-healable hydrogels with excellent mechanical performance is important for their potential applications. In this paper, tough and self-healable dual physically crosslinked nanocomposite hydrogels reinforced with polyacrylamide grafted cellulose nanocrystal (CNC-g-PAM) were fabricated by in situ free radical polymerization of acrylic acid (AA) monomers in the presence of FeCl3 (0.75% of AA mole) and CNC-g-PAM (1-3% of AA mass). The primary network of PAA/CNC-g-PAM nanocomposite hydrogels was constructed via coordination bonds between carboxylic groups from PAA and Fe3+ ions, while CNC-g-PAM served as both reinforcing nanofillers and physical crosslinkers via hydrogen bonds between PAA matrix and PAM chains on the surface of CNC. The nanocomposite hydrogels exhibited simultaneously improved elastic modulus, tensile strength and elongation at break with the increase of CNC-g-PAM loading. The dynamic nature of both coordination bonds and hydrogen bonds endowed the nanocomposite hydrogels with excellent energy dissipation, self-recovery ability and autonomous self-healing capacity. [GRAPHICS] .