Preparation and Performance Study of High Water-Retention Recyclable Hydrogels for Landscaping

To meet the demand for superabsorbent, long-acting water-retentive, and recyclable hydrogel materials in landscaping applications, a series of AG-PAA/DA composite hydrogels were prepared using agarose (AG) and polyacrylic acid (PAA) as the network backbone, incorporating different mass fractions (2–30%) of dopamine (DA) via free radical polymerization initiated by ultraviolet light. The effects of DA content on the chemical structure, morphology, thermal stability, mechanical properties, water retention behavior, swelling kinetics, and cyclic water absorption–desorption performance were systematically investigated. The results show that DA is successfully integrated into the AG-PAA network through hydrogen bonding, electrostatic interactions, and covalent crosslinking, forming an amorphous homogeneous system. Thermal stability increases with DA content (residual mass at 800 °C rises from 77% to 88%). Mechanical properties exhibit a trend of increasing stress but decreasing strain, with optimal toughness (~670 kJ/m3) achieved at 10 wt% DA. Water retention performance is environment-dependent: in pure water, water retention increases with higher DA content, whereas in soil the opposite trend is observed. The kinetics of swelling conform to the pseudo-second-order model. The hydrogel with 10 wt% DA exhibits an equilibrium water absorption of 50 g/g in 0.9% saline solution and 1060 g/g in deionized water, and after 20 swelling–deswelling cycles the capacity retention fluctuates by less than 5%, demonstrating excellent cyclic stability. Considering all properties, AG-PAA/DA-10 is identified as the optimal formulation. This hydrogel combines high water absorption capacity, good environmental adaptability, and recyclability, showing great promise for water-saving irrigation in landscaping.