Preparation and swelling properties of a starch-g-poly(acrylic acid)/organo-mordenite hydrogel composite

A novel hydrogel composite was prepared via inverse suspension polymerization using starch, acrylic acid and organo-mordenite micropowder with the cross-linker, N,N'-methylenebisacrylamide and the initiator, potassium persulfate. Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy confirmed that the acrylic acid was grafted onto the backbone of the corn starch, that the organo-mordenite participated in the polymerization, and that the addition of organo-mordenite improved the surface morphology of the hydrogel composite. The swelling capacity of the hydrogel composite was evaluated in distilled water, and solutions with different pH values, and various salt solutions. It was found that the incorporation of 10 wt-% organo-mordenite enhanced the water absorbency by 144% (from 268 to 655 g.g(-1)) and swelling was extremely sensitive to the pH values, the concentration of the salt solution and cation type. Swelling kinetics and water diffusion mechanism of the hydrogel composite in distilled water were also discussed. Moreover, the hydrogel composite showed excellent reversibility of water absorption even after five repetitive cycles and the hydrogel composite exhibited significant environmental-responsiveness by changing the swelling medium from distilled water to 0.1 mol.L-1 NaCl solution. In addition, the loading and release of urea by the hydrogel composite were tested and the nutrient-slow-release capability of this material was found to be suitable for many potential applications.