Superabsorbent polyacrylamide grafted carboxymethyl cellulose pH sensitive hydrogel: I. Preparation and characterization

Abstract

Superabsorbent hydrogels were prepared by grafting copolymerization of cross-linked polyacrylamide chains onto carboxymethyl cellulose (CMC) via a free radical polymerization method. These graft copolymers hydrogel were characterized by infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Hydrogels with different chemical composition were obtained through variation of grafting polymerization conditions such as CMC concentration, Acrylamide (AM) concentration, N,N´-methylene bis acrylamide concentration, Ammonium per Sulphate concentration, reaction time, and reaction temperature. The impact of hydrogels’ composition on the water uptake capacity was monitored. Maximum water uptake, 158 g/g, was obtained with graft copolymer of 90% grafting percentage and 95% grafting efficiency compared to 37 g/g for the native polyacrylamide. Variation of CMC and AM concentration was found of determined effect. Direct impact of grafting percentage variation on the water uptake was observed. Sensitivity to pH of the swelling medium was recognized in both distilled and tap water. Sharp phase transition was recognized between pH 3.0 and 4.0 in swelling in tap water where this transition was broader in swelling in distilled water and recognized between pH 3.0 and 7.0. The hydrogel particle size was found also of determining effect where maximum swelling was observed with particles size ranged from 500μm to 1000 μm. Maximum swelling was obtained at 40°C after 4 h swelling time at both tap and distilled water.