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The polysaccharide, kappa-carrageenan (jC) was chemically modified to achieve a novel superabsorbent hydrogel via graft copolymerization of methacrylamide (MAM) onto the substrate followed by alkaline hydrolysis. Ammonium persulfate (APS) and N,N 0 -methylene bisacrylamide (MBA) were used as a free-radical initiator and a crosslinker, respectively. The saponification reaction was carried out using sodium hydroxide aqueous solution. Either jC-g-PMAM or hydrolyzed jC-g-PMAM (PMAM: polymethacrylamide) was characterized by FT-IR spectroscopy. The effect of grafting variables (i.e. concentration of MBA, MAM, and APS) and alkaline hydrolysis conditions (i.e. NaOH concentration, hydrolysis time and temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The swelling capacity of these hydrogels was also measured in various salt solutions. Results indicated that the swelling ratios decreased with an increase in the ionic strength of the salt solutions. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Absorbency of superabsorbing hydrogels was examined in buffer solutions with pH range 1-13. Also, the pH reversibility and on-off switching behavior, at pH values 3.0 and 8.0, makes the synthesized hydrogels good candidates for controlled delivery of bioactive agents. Finally, swelling kinetics in distilled water and various salt solutions was preliminary investigated. Results showed that the swelling in water was faster than in saline solutions.The tea bag (i.e. a 100 mesh nylon screen) containing an accurately weighed powdered sample (0.5 AE 0.001 g) with average particle sizes between 40-60 mesh (250-350 mm was immersed entirely in distilled water (200 ml), desired salt solution (100 ml), or buffer solution (100 ml) and allowed to Scheme 1. Proposed mechanistic pathway for synthesis of kC-based hydrogels.

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.