Ultraviolet-induced polymerization of superabsorbent composites based on sodium humate and its urea release behavior

This study was carried out to develop a superabsorbent composite for agriculture application, which is based on acrylic acid and sodium humate and prepared by ultraviolet (UV)-induced polymerization in the presence of crosslinker (N,N′-methylene bisacrylamide) and composite initiator (irgacure 651 and ammonium persulfate). The samples were characterized by means of FT-IR, SEM and TGA. The effects of sodium humate content, curing time and salt concentration on the water absorbency of composite were investigated. The swelling kinetics in distilled water, water retention capacity, biodegradability, re-swelling capacity and sodium humate release behavior of the composite were also investigated. The water absorbency of the superabsorbent composite synthesized under optimal conditions was 1425 g g−1 in distilled water. The results indicate that the superabsorbent composite incorporating with moderate amount of SH has good swelling ability and high gel strength. It can also significantly reduce the preparation cost, which are of great advantage to the widespread application in agriculture. Moreover, we synthesized a new coated controlled-release fertilizer employing poly(acrylic acid)/sodium humate (PAA/SH) with the urea slow release function. The urea release rate of 89.6 wt% was attained after buried in soil for 10 days, which can dramatically improve fertilizer efficiency comparing with directly applied urea to soil.