Preparation and property of high strength PVA-PEI- MWCNTs-COOH hydrogel using annealing treatment

Annealing is a heat treatment process for materials. In this study, a conductive hydrogel was synthesized by a one-pot method using three raw materials: polyvinyl alcohol(PVA), carboxylated carbon nanotubes(Multi-Walled Carbon Nanotubes-COOH, MWCNTs-COOH) and polyethyleneimine (PEI). Based on the traditional freeze-thaw method for the preparation of PVA-based hydrogels, the annealing treatment was further added here to enhance the mechanical properties and fatigue resistance of the hydrogels. The synthesized conductive hydrogels were annealed in oven at different temperatures for a certain time, and the optimized experimental conditions and results were: the mechanical properties of the conductive hydrogel were best improved under the condition of 100 ℃-20 min, with the ultimate stress of 30.8 MPa and toughness as high as 779.58 MJ/m³. A high-strength, fatigue-resistant conductive hydrogel was successfully prepared, and its mechanical properties far exceeded those of other conductive hydrogels. Through a series of tests such as X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), it was found that annealing promotes the orderly arrangement of PVA chains and crystallization through high temperatures, so as to enhance the mechanical properties of hydrogels. As a relatively simple and inexpensive annealing post-treatment technique, it is expected to be more widely used in improving the mechanical properties of hydrogels.