Swelling of superabsorbent acrylamide/sodium acrylate hydrogels prepared using multifunctional crosslinkers

Superwaterabsorbent acrylamide-sodium acrylate hydrogels were prepared by free radical polymerization in aqueous solutions of acrylamide and with sodium acrylate as comonomer. For each copolymerization, nine different compositions were used and in all systems a concentration of a multifunctional crosslinker such as trimethylolpropane triacrylate, ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate and N,N'-methylenebisacrylamide was employed. As a result of dynamic swelling tests, the influence of crosslinkers and the relative content of sodium acrylate on the swelling properties, the initial swelling rate and the swelling rate constant, swelling exponent, swelling coefficients and diffusional behaviour of water in the hydrogel systems were examined. Acrylamide-sodium acrylate hydrogels were swollen in the range 860-12870% in water, while acrylamide hydrogels swelled in the range 770-1420%. The equilibrium water content of acrylamide-sodium acrylate hydrogel systems was calculated in the range 0.8851-0.9922. The water intake of hydrogels followed a non-Fickian type diffusion.