A nanocomposite interpenetrating hydrogel with high toughness: effects of the posttreatment and molecular weight

Previously, we prepared a tough nanocomposite interpenetrating hydrogel by chemical crosslinking of acrylamide (AM) with vinyl-modified silica nanoparticles (VSNPs), combined with physical crosslinking of polyvinyl alcohol (PVA). It is well-known that posttreatment method and molecular weight play important roles in the mechanical properties of the tough hydrogels. In this paper, different post-treatment methods, i.e., freeze-thaw and annealing-swelling and varying PVA degree of polymerization (500 and 1700) were used to prepare the nanocomposite interpenetrating hydrogels. The effects of posttreatment and PVA molecular weight on the mechanical and swelling properties were investigated in detail. Tensile tests showed that annealing-swelling process exerted a more pronounced influence on elevating the tensile strength of nanocomposite interpenetrating hydrogels, which arose from the increased crystallization degree of PVA and the denser network. Hydrogels with lower PVA molecular weight have higher tensile strength after freeze-thaw cycle than that with higher PVA molecular weight. Cyclic loading–unloading tests revealed that the gels with lower molecular weight of PVA can dissipate higher energy at 100% strain. The swelling kinetic study revealed that the swelling behaviors of nanocomposite interpenetrating hydrogels followed the pseudo-second-order dynamic equation.