Preparation of pH/temperature-responsive semi-IPN hydrogels based on sodium alginate and humic acid as slow-release and water-retention fertilizers

Herein, a semi-interpenetrating network (semi-IPN) hydrogel (SH/PNA) was prepared by simple free radical polymerization using N-isopropylacrylamide and 2-acrylamide-2-methylpropanesulfonic acid as monomers, poly(ethylene glycol) dimethacrylate as a crosslinking agent, and sodium alginate and humic acid as filled biomolecules. Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and rheometer were used to characterize the structure and properties of the samples. The effect of feeding ratios on the gel mass fraction and swelling properties of the SH/PNA hydrogel was explored to optimize its preparation conditions. The swelling behavior under different pH and temperatures was investigated. The experimental result showed that the SH/PNA hydrogel had excellent water absorption capacity and pH/temperature dual responsiveness. Moreover, SH/PNA hydrogel was used as a carrier of urea to prepare slow-release and water-retention fertilizer by in situ loading method, and slow-release properties of urea in water and soil were measured. Taking into account its good ability for controlled release and water retention, the WSRF was expected to be a promising low-cost, environmentally friendly fertilizer that can be used in agriculture and horticulture.