The synthesis and swelling behavior of a superabsorbent hydrogel based on starch (St) and polyacrylonitrile (PAN) were investigated. The physical mixture of St and PAN was hydrolyzed with NaOH solution to yield St—poly(sodium acrylate-co-acrylamide) superabsorbent hydrogels. The nitrile groups of PAN were completely converted to a mixture of hydrophilic carboxamide and carboxylate groups during the basic hydrolysis followed by in situ crosslinking of the PAN chains by the starch alkoxide ions. A mechanism for hydrogel formation was proposed and the structure of the product was established using FTIR spectroscopy. The effect of reaction variables, such as, base concentration, hydrolysis time, and temperature were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The optimized swelling capacity in distilled water was found to be >500g/g. The absorbency of the hydrogels indicated that the swelling ratios decreased with ionic strength increases. The St—poly(sodium acrylate-co-acrylamide) hydrogel exhibited a pH-responsive swelling—deswelling behavior at pH's 2 and 8. This on—off switching behavior provides the hydrogel with the potential to control delivery of bioactive agents. Release profiles of ibuprofen (IBU), a poor watersoluble drug, from the hydrogels were studied under both simulated gastric and intestinal pH conditions. The release was much quicker at pH 7.4 than at pH 1.2. The swelling rates of the hydrogels with various particle sizes were investigated as well.
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