Abstract

In this work, acrylonitrile (AN) and acrylic acid (AA) monomers were directly grafted onto chitosan using ammonium persulfate (APS) as an initiator and methylenebisacrylamide (MBA) as a crosslinking agent under an inert atmosphere. The hydrogels structure was characterized by Fourier transform infrared (FTIR)spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The effect of grafting variables, that is, AA/AN weight ratio and concentration of MBA and APS, was systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The water absorbency increased with increasing the AA amount in the monomer feed due to formation of polyelectrolyte. The swelling of the hydrogel samples in saline solution (0.15 mol/l NaCl, CaCl₂ and AlCl₃) was examined. The results indicate that the swelling capacity decreased with an increase in the ionic strength of the swelling medium. This behavior can be attributed to charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Furthermore, the swelling of superabsorbing hydrogels was examined in solutions with pH values ranging between 1 and 13.

Key words: Hydrogel, chitosan, superabsorbent, acrylonitrile, acrylic acid.