Synthesis, characterization and effect of reaction parameters on swelling properties of acrylamide-sodium methacrylate superabsorbent copolymers

Superabsorbent copolymers (SAPs) based on acrylamide (AAM) and sodium methacrylate (NMA) were prepared by simultaneous free radical polymerization in aqueous solution using ammonium persulfate (APS) and N,N,N′,N′-tetramethylethylenediamine (TMEDA) as initiating systems at room temperature. Eight different copolymers were prepared by varying NMA with a fixed concentration of acrylamide and 1,4-butanediol diacrylate (BDDA) or ethyleneglycol dimethacrylate (EGDMA) as crosslinkers. The acrylamide-sodium methacrylate (AAM-NMA) SAP formation was confirmed by IR spectroscopy. The percentage of swelling, swelling and diffusion kinetic parameters (i.e., initial swelling network constant, swelling rate constant, maximum swelling equilibrium, network structure constant and type of diffusion, etc.) were investigated for all the SAPs at 25 °C. The swelling behaviour was also studied at different temperatures ranging from 10 to 50 °C. The effect of different reaction parameters, such as, crosslinker, initiator and activator concentrations on the swelling capacity was investigated. The effect of variation of crosslinker concentration on the copolymer network structure was studied by SEM analysis. Further the saline sensitivity of the copolymers was investigated at different saline concentrations. The effect of pH and de-swelling behaviour for AAM-NMA SAPs prepared at optimum reaction conditions was studied.