Starch-Acrylic Acid Hydrogel:Preparation and Swelling Characteristics

Hydrogels consisting of starch acrylic acid was prepared by using ceric ammonium nitrate as initiator and methylene bis acrylamide (MBAm) as crosslinker. The hydrogels were prepared by varying the amount of the crosslinker (0.5 mole %, 2 mole %, 5 mole %). The crosslinked hydrogels swelling properties were studied at different pH (1.2 and 7.4). The equilibrium swelling of the hydrogels at pH 1.2 was slow as compared to pH 7.4. This can be attributed that the -COOH group present within network remains almost intact, moreover there exist strong H- bonding interaction between -COOH groups of acrylic acid and -CONH₂ group of MBAm which are present within the network, thus resulting in movement of polymeric segment within the hydrogel. However, in the medium of pH 7.4 the complete ionization of COOH group result in extensive chain relaxation due to repulsion among similarly charged -COO groups present in macromolecule chain. This suggests that diffusion of the entrapped active agents will be greatly enhanced with a change in pH of the medium, thus making these copolymers as a potential candidate for the use in agriculture, biomedicine, pharmaceutics and controlled delivery of bioactive agents.