Constructing dual ionically cross-linked poly(acrylamide-co-acrylic acid) /chitosan hydrogel materials embedded with chitosan decorated halloysite nanotubes for exceptional mechanical performance

Abstract

Hydrogels with exceptional mechanical properties at high water content are crucial need for practical applications in various fields. However, achieving a hydrogel possessed splendid mechanical performance with well trade-off between tensile strength and toughness is highly demanded due to the mechanical weakness of conventional hydrogel. Herein, we report a novel kind of nanocomposite hydrogel developed by integrating chitosan decorated halloysite nanotubes (CS-f-HNTs) into dual cross-linked structure composed of chemical and Fe3+ induced ionically cross-linked network. Combining the nanoparticle reinforcement with physical interactions including hydrogen bonds among polymer chains and ionic coordination interaction between Fe3+ ions and functional groups on chitosan chains and the copolymer chains, the hydrogel exhibits extraordinary and balanced mechanical performance, including high strength (3.06 MPa), outstanding stretchability (>2000%) and superior toughness (47.6 MJ m−3) in which water content remains ~80 wt%. Based on microstructure observation and dynamic mechanical behavior analysis, we demonstrated that the addition of CS-f-HNTs effectively bridged polymer chains via physical interactions and strengthened dual cross-linked network, leading to significant improved mechanical properties. Moreover, the hydrogels also possessed remarkable self-recoverability (97.9% for small strain (200%) and 91.5% for large strain (1000%)) at room temperature and the related mechanism was discussed. The strategy developed herein may provide a newfound avenue in the design and development of strong and tough hydrogel for promising applications in loading-bearing structural materials. © 2020 Elsevier Ltd