Preparation of Hypromellose-Graft-Polyacrylic Acid Superabsorbent Resin by Ultraviolet Polymerization and Its Slow-Release Performance

A hypromellose-graft-poly(acrylic acid) (HPMC-g-PAA) superabsorbent resin was synthesized through the graft polymerization of hydroxypropyl methylcellulose and acrylic acid in an aqueous solution by UV polymerization, with the addition of an initiator and cross-linking agent. Additionally, the HPMC-g-PAA/urea composite was synthesized by using a one-pot method to create a slow-release fertilizer by incorporating urea into the structure of superabsorbent materials. The structures of HPMC-g-PAA and HPMC-g-PAA/urea were characterized by FTIR, TGA and SEM. The effects of preparation conditions such as UV exposure time, HPMC content, neutralization degree, initiator amount, amount of cross-linking agent, and urea content on the water absorption capacity of the superabsorbent polymers were evaluated. Under optimal conditions, the HPMC-g-PAA exhibited a maximum absorption capacity of 1567 g/g in distilled water and 88.5 g/g in NaCl solution (0.9 wt %). Similarly, the HPMC-g-PAA/urea demonstrated a maximum absorption capacity of 1382 g/g in distilled water and 82.3 g/g in NaCl solution (0.9 wt %). The comprehensive investigation encompassed the assessment of slow-release and water-retention properties, as well as a growth experiment conducted on the samples. The slow-release period of sample reached 93% at the 26th hour. The obtained results unequivocally validate the effectiveness of the synthesized superabsorbent resin and slow-release fertilizer in significantly enhancing plant growth.