Synthesis of the copolymer hydrogel κ-carrageenan-graft-PAAm:: Evaluation of its absorbent and adhesive properties

kappa-Carrageenan-graft-PAAm, a copolymer hydrogel Of K-carrageenan (kC) and acrylamide (AAm), has been synthesized in aqueous medium at similar to 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% KCI) exhibiting low gel strength (135 g cm(-2)). 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 CaCl2. 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, C-13-NMR, FT-IR, elemental analyses, and rheological studies. (c) 2006 Wiley Periodicals, Inc.