Novel Superabsorbent Hydrogels Based on Polyacrylamide and White Angico Gum Enhanced with Kaolinitic Clay and Soapstone for Potential Agricultural Applications

Population growth and climate change demand technologies for the efficient use of water in agriculture. This study aimed to synthesize and characterize hybrid hydrogels of polyacrylamide and white angico gum (Anadenanthera colubrina), reinforced with kaolinitic clay and soapstone, for potential application as soil conditioners and nutrient carriers. The hydrogels were obtained via radical polymerization, followed by alkaline hydrolysis (0.1 mol L−1 NaOH) to convert amide groups into carboxylates. The results indicated that the HPAD formulation [constituted by white angico gum (1:1); 5% (w/w) kaolin and 5% (w/w) steatite (soapstone)] presented the best balance, with a maximum compressive force greater than 200 N, thermal stability up to 310 °C, and a swelling capacity of 60 g/g in saline medium, surpassing the limits of viability for use in soil. The kinetics followed the pseudo-second-order model, and the point of zero charge (pH 9.0–11.7) favored phosphate retention. It is concluded that the HPAD hydrogel, one of several hydrogel formulations developed in this study, is a viable and safe technical alternative, with non-toxicity exceeding 80% in Artemia salina assays and capable of optimizing water and nutrient efficiency in agricultural systems.