pH-Sensitive Crosslinked Guar Gum-Based Superabsorbent Hydrogels: Swelling Response in Simulated Environments and Water Retention Behavior in Plant Growth Media

Crosslinked guar gum-g-polyacrylate (cl-GG-g-PA) superabsorbent hydrogels were prepared to explore their potential as soil conditioners and carriers. The hydrogels were prepared by in situ grafting polymerization and crosslinking of acrylamide onto a natural GG followed by hydrolysis. Microwave-initiated synthesis under the chosen experimental conditions did not exhibit any significant improvement over the conventional technique. The optimization studies of various synthesis parameters, namely, monomer concentration, crosslinker concentration, initiator concentration, quantity of water per unit reaction mass, particle size of backbone, and concentration of alkali were performed. The hydrogels were characterized by wide-angle X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and solid-state C-13-NMR spectroscopy. Swelling behavior of a candidate hydrogel [GG-superabsorbent polymer (SAP)] in response to external stimuli, namely, salt solutions, fertilizer solutions, temperature, and pH, was studied. The GG-SAP exhibited significant swelling in various environments. The effect of GG-SAP on water absorption and the retention characteristics of sandy loam soil and soil-less medium were also studied as a function of temperature and moisture tensions. The addition of GG-SAP significantly improved the moisture characteristics of plant growth media (both soil and soil-less), showing that it has tremendous potential for diverse applications in moisture stress agriculture. (C) 2014 Wiley Periodicals, Inc.