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Grafting of agar and k-carrageenan with polyvinylpyrrolidone (PVP, average molecular weight 10,000 D) in an aqueous medium at a pH of about 7 produced agargraft-PVP and k-carrageenan-graft-PVP blends capable of forming hydrogels. The reaction was carried out with microwave irradiation in the presence of a water-soluble initiator, potassium persulfate. Optimum microwave irradiation conditions for obtaining hydrogels of the grafted products were achieved. The structural characteristics and thermal stability of the grafted blends were studied by Fourier transform infrared, 13 C-NMR, and thermogravimetric analyses. Appearance of new IR bands at 1661, 1465, and 1426 cm À1 in the grafted products indicated the insertion of PVP into the polysaccharide structure. Powder X-ray diffraction studies revealed the enhanced crystallinity in the products compared to in the control polysaccharides as well as PVP. Agar and k-carrageenan were grafted to a considerable degree, with 62.5 E % and 125 G % for agar-graft-PVP and 65.5 E % and 131 G % for k-carrageenan-graft-PVP. Optical micrographs of the grafted blends indicated considerable changes in the morphology of the agar and the k-carrageenan, substantiating the X-ray diffraction data. A plausible mechanism for the crosslinking of PVP to agar and k-carrageenan is proposed. These hydrogels exhibited enhanced water-holding capacity despite weaker gel strength than that in the respective control polysaccharides.

k-Carrageenan-graft-PAAm, a copolymer hydrogel of k-carrageenan (kC) and acrylamide (AAm), has been synthesized in aqueous medium at $ pH 7 in the presence of the initiator potassium persulfate (KPS), using microwave irradiation. The reaction conditions were optimized by varying the concentration of AAm and KPS to obtain copolymer hydrogels having different nitrogen contents e.g., %N 6.35, 10.56, and 11.05. It was observed that copolymer hydrogel having %N 11.05 gives superior adhesive properties whereas copolymer hydrogel with %N 10.56 produces superior absorbent properties in the presence of optimized concentrations of AAm (0.87 and 1.1428 mol/L respectively) and KPS (0.022 and 0.0296 mol/L respectively). The product with %N 6.35 is a soft gel (2-5% gel in 1% KCl) exhibiting low gel strength (135 g cm À2). The one with %N 10.56 showed superior swelling property and maximum swelling was observed in the alkaline pH (22 g/g). The swelling behaviors of the hydrogels were studied at different pHs (pH 1.2-12.5) as well as in 1% aqueous solutions of NaCl, KCl, and CaCl 2 . The 5% dispersion of the hydrogel having %N 11.05 in water had good binding properties with papers, polyethylene sheets, and wood pieces. To evaluate the measure of adhesive property, the viscosity and solid and liquid weights of the applied adhesive were measured. Characterization of the copolymer hydrogels was done by TGA, X-ray diffraction, 13 C-NMR, FT-IR, elemental analyses, and rheological studies.

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