Metal sorption and swelling characters of acrylic acid and sodium alginate based hydrogels synthesized by gamma irradiation

Hydrophilic hydrogels based on poly(acrylic acid) as synthetic polymer and sodium alginates as natural polymer (AG) were prepared by gamma irradiation. The AAc/AG hydrogels were characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The effect of temperature and pH on the degree of swelling in water was studied. In addition, the metal sorption affinity of the prepared hydrogels for Cu⁺², Co⁺² and Ni⁺² was investigated. The XRD spectroscopic analysis indicates the formation of interpenetrating polymer networks. The TGA study showed that the hydrogels based on AAc/AG hydrogels at different ratios displayed lower thermal stability than PAAc hydrogel. The kinetic study of swelling in water showed that PAAc and AAc/AG hydrogels reached the equilibrium swelling state after five hours. However, AAc/AG hydrogels showed degree of swelling in water greater than PAAc hydrogel. The degree of swelling of AAc/AG hydrogels was affected by temperature, it increases within the temperature range 25-40 °C and displayed pH sensitivity within the range 5.5-9 depending on composition. The metal sorption study showed that PAAc hydrogel possessed higher affinity for Cu⁺² ions than AAc/AG hydrogels, whereas AAc/AG hydrogels showed higher affinity for Co⁺² and Ni⁺² ions than PAAc hydrogel.