Facile preparation of agar/polyvinyl alcohol-based triple-network composite hydrogels with excellent mechanical performances

Triple-network hydrogels have different network structures and diversified cross-linking methods, which make it expected to become a widely used soft material. In this work, the freezing method is used to form a hydrogen bond cross-linked physical network between the Agar molecular chains, and then acrylic acid (AAc) and a chemical cross-linking agent form a chemical cross-linked network using free radical polymerization. The polyvinyl alcohol (PVA) molecules in the hydrogel can increase the winding degree of the molecular chain and form the PVA semi-crystalline region. In addition, Fe3+ in the system is coordinated and cross-linked with the carboxyl group on the PAAc molecular chain, and the addition of carbon nanotubes (CNTs) increases the mechanical properties and stability of the composite hydrogel. The prepared Agar/PAAc-Fe3+/PVA/CNTs composite hydrogel shows good mechanical properties through the coexistence of chemical covalent bonds and dynamic reversible bonds. Furthermore, the Agar/PAMAAc-Fe3+/PVA/CNTs triple-network hydrogel based on agar/polyacrylamide acrylic acid/polyvinyl alcohol (Agar/PAMAAc/PVA) was also prepared. Among them, acrylamide (AM) monomer and AAc monomer form a chemical cross-linking network through radical polymerization. The prepared Agar/PAMAAc-Fe3+/PVA/CNTs hydrogel can realize rapid self-recovery after 5 consecutive and discontinuous compressions, respectively. This work provides a new idea for the preparation of multifunctional hydrogels with good thermal stability, mechanical properties and self-recovery.