Carrageenan-g-poly(sodium acrylate)/kaolin superabsorbent hydrogel composites: Synthesis, characterisation and swelling behaviour

A novel superabsorbent hydrogel composite based on kappa-carrageenan (kappa C) was prepared by graft copolymerisation of acrylic acid (AA) in the presence of kaolin using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The synthetic variables (i.e. AA, MBA and APS concentration, and the amount of kaolin) affecting the water absorbency of the resulting superabsorbent composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FTIR spectra of the initial substrates and of the superabsorbent composite. A new absorption band at 1722 cm(-1) in the composite spectrum confirmed the kaolin-organic polymer linkage. Increasing the amount of kaolin and the MBA concentration caused the water absorbency of the superabsorbent composite to decrease. The effect of various salt media and pH on the swelling of the superabsorbent was studied. The swelling kinetics of the synthesised composite was also investigated.