Dual Physically Cross-Linked Nanocomposite Hydrogels Reinforced by Tunicate Cellulose Nanocrystals with High Toughness and Good Self-Recoverability.

The weak mechanical properties of hydrogels usually limited their application in biomedical and industrial fields. Herein, we reported a nanocomposite network of poly(acrylic acid-co-acrylamide) (PAAAM) sequentially cross-linked by quaternized tunicate cellulose nanocrystals (Q-TCNCs) and Fe3+ . Q-TCNCs acted as both interfacial compatible reinforcements and cross-linkers in the nanocomposite hydrogels to form loose cross-linking, whereas compact cross-linking was built by ionic coordination between Fe3+ and -COO- of PAAAM. The toughness of dual cross-linked hydrogel (D-Gel) was 340 times that of mono-cross-linked hydrogel (m-Gel), which was 10 times that of PAAAM hydrogel. Moreover, the nanocomposite hydrogels exhibited excellent self-recoverability after treating the stretched samples in FeCl3 aqueous solution. This work provided a universal strategy for construction of tough nanocomposite hydrogel reinforced with cellulose nanocrystals.