Studies on Water Absorbency of Polyacrylamide Hydrogels

Abstract

The polymerization was carried out under the different concentrations of acrylamide and crosslinker in an aqueous solution of NO 2 gas as initiator at 50 º C. The resulting polyacrylamide was saponified with NaOH solution. The hydrolysed polymers show high degree of water swelling (> 500) than that of unhydrolysed polymers (< 100). Swell ability of the gel decreases with the increasing concentration of N, N'-methylene bisacrylamide-a crosslinker which enhances the degree of crosslinking in the polymer chains. The increased crosslinking restricts the expansion of polymer network which causes the lowering of the water absorbency. It was observed that polymer hydration increased with the molar mass of polyacrylamide. The swell ability of polyacrylamide hydrogels is greatly lowered by the addition of ionic salts in the swelling medium. Both ionic strength and valency of the salts are responsible to decrease the water uptaking capacity of the gels which remain unaffected by nondessociating nature of urea. The hydrogels, so prepared, are stable and quite able to undergo swelling-deswelling cycles suggesting their reversible characters.