Dual physically crosslinked nanocomposite hydrogels reinforced by poly(N-vinylpyrrolidone) grafted cellulose nanocrystal with high strength, toughness, and rapid self-recovery

It remains challenging to develop hydrogels with comprehensive mechanical properties including ultrahigh strength, toughness and rapid self-recovery. Herein, dual physical crosslinking strategy was used to develop novel nanocomposite hydrogels reinforced by poly(N-vinylpyrrolidone) grafted cellulose nanocrystal (CNC-g-PVP). The hydrogels were fabricated via in situ copolymerization of acrylic acid (AA) and acrylamide (AM) in presence of CNC-g-PVP and subsequent introduction of Fe(3+)ions. CNC-g-PVP induced the first crosslinking through strong cooperative hydrogen bonds existing between PVP chains grafted onto CNCs and amide groups from P(AM-co-AA) chains. Fe(3+)triggered the second crosslinking by forming coordination bonds with -COO(-)groups. The cooperative hydrogen bonds enhanced the interfacial compatibility between CNC-g-PVP nanofillers and hydrogel matrix, and served as fast recoverable sacrificial bonds. As a result, the hydrogels exhibited high tensile strength (1.89-2.51 MPa), remarkable toughness (6.01-6.81 MJ/m(3)), rapid self-recovery (83.4-97.8% recovery of hysteresis loop within 5 min) and favourable fatigue resistance.