Synthesis and characterization of zein-based superabsorbent hydrogels and their potential as heavy metal ion chelators

Superabsorbent hydrogels were synthesized by solution-based graft copolymerization of acrylic acid monomers on the hydrolyzed zein protein backbones in the presence of an acrylamide crosslinker, sodium bisulfite and potassium persulfate as initiators. The grafting was confirmed by Fourier transform infrared spectroscopy and the morphology was studied by scanning electron microscopy. A loose structure was observed in the hydrolyzed zein protein-g-polyacrylic acid. Moreover, differential scanning calorimetry and swelling tests were performed to evaluate the effect of the formulations on the thermal and swelling properties of the hydrogels. The highest equilibrium swelling value in distilled water reached 239.6 g/g of hydrogel. The potential of these materials as heavy metal ions chelator was also assessed. The preliminary results showed that the hydrogels had a good copper ion chelation capacity (maximum of 208 mg/g at pH 4.5), probably due to the presence of a large number of functional groups from the polyacrylic acid and the hydrolyzed zein protein.