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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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Cellulose content as well as alpha (α) and beta (β) celluloses were evaluated in 21 seaweed species belonging to different classes growing in Indian waters. The greatest yields of cellulose (crude) and β-cellulose were obtained from Caulerpa taxifolia (approx. 11.0% and 5.2%, respectively), whilst α-cellulose (approx. 8.2%) was the greatest in Padina tetrastromatica. The lowest cellulose (crude), α-and β-contents were recorded from the calcareous red alga Liagora ceranoides (approx. 0.85%, 0.62% and 0.18%, respectively). There was no variation in the yields of cellulose in the brown algae, whilst wide variations in the yields were found in the green and red algae.

Superior quality non-methylated and low-sulphated galactans were extracted from two Indian agarophytes namely Gracilaria debilis and G. salicornia growing naturally along the west coast of India, using an eco-friendly method developed in our laboratory. The galactans were characterised by FT-IR, 13 C NMR, GC-MS, ICP, GPC and rheological measurements. G. debilis produced exclusively nonmethylated galactan exhibiting the greatest gel strength of 650±25 g cm −2 and lowest sulphate of 0.21±0.06%. On the contrary, G. salicornia polysaccharide was composed of nonmethylated galactose (major) and mannose (minor), having gel strength of 510±25 g cm −2 and sulphate of 0.45±0.06%. Very low heavy metal contents were determined in both the galactan samples, which may thus be potentially useful in food and biological applications.

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Crude cellulose as well as α-and β-celluloses were estimated in thirty-four seaweed species of fifteen orders of Chlorophyta, Phaeophyta and Rhodophyta of Indian waters. The greatest yields of crude cellulose and α-cellulose were obtained from Chaetomorpha aerea (approx. 20.0% and 18.5%, respectively), and of β-cellulose (approx. 3.1%) from Caulerpa imbricata. The lowest crude cellulose, and α-and β-contents were recorded for the calcareous red alga Liagora indica (approx. 0.90%, 0.70% and 0.10%, respectively). There was little variation in cellulose content among the brown algae, while wide variations in the yields were found in the green and red algae. The present work contributes to the repertoire of 67 Indian seaweed species studied to now for their cellulose contents in our laboratory. The combined studies highlight that Chaetomorpha aerea, Acrosiphonia orientalis, Caulerpa taxifolia, Sargassum tenerrimum, Hydroclathrus clathratus and Gelidiella acerosa possess relatively high (>10%) cellulose contents, which could be of potential utility.