Synthesis, characterization and swelling behavior of gelatin-g-poly(sodium acrylate)/kaolin superabsorbent hydrogel composites

In the present paper, a novel superabsorbent hydrogel composite based on gelatin have been prepared via graft copolymerization of acrylic acid (AA) in the presence of kaolin powder using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. Certain variables of the graft copolymerization (i.e., the monomer, the initiator, and the crosslinker concentration as well as kaolin/gelatin weight ratio) affected on the ultimate water-swelling capacity were optimized. The composite structure was confirmed using Fourier transform infrared (FTIR) spectroscopy. A new absorption band at 1728cm(-1) in the composite spectrum confirmed kaolin-organic polymer linkage. The effect of kaolin amount and MBA concentration showed that with increase of these parameters, the water absorbency of the superabsorbent composite was decreased. The swelling measurements of the hydrogels were conducted in aqueous salt solutions. Results indicated that the swelling ratios decreased with an increase in the ionic strength of the salt solutions. This behavior can be attributed to 'charge screening effect' for monovalent cations, as well as 'ionic crosslinking' for multivalent cations. The effect of solutions with different pHs on the swelling of the superabsorbent was also studied and the hydrogels exhibited pH responsiveness, so a swelling-deswelling pulsatile behavior was recorded at pHs 2 and 8. Finally, the swelling kinetics of the synthesized composite with various particle sizes was preliminarily investigated as well.