Facile Method to Fabricate Superstrong and Tough Poly(vinyl alcohol) Hydrogels with High Energy Dissipation
Jinlong Cao, Xiaowen Zhao, Lin Ye
Abstract
To enhance the intermolecular interaction of poly(vinyl alcohol) (PVA) hydrogels, after the freeze–thaw process, the primary formed PVA hydrogel was further annealed for a controlled time, followed by soaking in a CaCl2 aqueous solution. The evolution of a dual cross-linking bonding network structure in the hydrogels was studied, and it was found that the intermolecular hydrogen-bonding interaction was enhanced by the annealing process; the hydrogen-bond-component-abundant crystalline phase was formed, resulting in an increase in crystallinity and the crystalline domain size and a decrease in the crystalline domain distance. Thus, the formation of the dense network structure was accompanied by a perfect crystalline structure, significantly increasing the cross-linking density (υe) and decreasing the pore size for the PVA hydrogels. After soaking in the CaCl2 aqueous solution, a hydroxyl–Ca2+ coordination interaction was formed, leading to a much higher υe and a more compact network structure. As a result, the tensile strength and the fracture toughness of the PVA hydrogel with a dual cross-linking bonding reached 8.40 MPa and 14.16 MJ·m–3, which were roughly 6- and 12-fold higher than those of the nonannealed PVA sample, respectively. Meanwhile, the dynamic nature of hydrogen bonds and Ca2+-hydroxyl coordination bonds imparted hydrogel with energy dissipation. This work provided a facile method to fabricate a superstrong and tough PVA hydrogel without the incorporation of toxic additives for application in the load-bearing biomedical area.