Preparation, swelling behaviors, and slow-release properties of a poly(acrylic acid-co-acrylamide)/sodium humate superabsorbent composite

A novel functional superabsorbent composite with slow-release fertilizer properties from acrylic acid (AA), acrylamide (AM), and sodium humate (SH), PAA-AM/SH, was prepared by aqueous solution polymerization, using N,N'-methylenebisacrylamide (MBA) as a cross-linker and ammonium persulfate (APS) as an initiator. In this article, the effects of the SH content on water absorbency and swelling rate were studied. In addition, the water absorbency in various saline solutions and the reswelling capacity of the superabsorbent composite were also systematically investigated. The results show that the water absorbency, salt resistance, and reswelling capacity of the superabsorbent composite are improved by introducing SH into the PAA-AM polymeric network. The functionality of the superabsorbent composite in practice was investigated experimentally by studying the release of SH and by testing the water-retention capability of the composite in sand soil. The superabsorbent composite shows slow-release fertilizer behavior after SH is introduced. Compared to sand soil without the superabsorbent composite, 33.45 wt % water was still retained on the 20th day when the sand soil was mixed with 1.0 wt % composite. These results indicate that the efficiency of SH utilization and water-retention capability of the superabsorbent composite are greatly enhanced at the same time by introducing SH into the PAA-AM polymeric network.