Factors influencing absorbent properties of saponified starch-g-(acrylic acid-co-acrylamide)

Mixtures of acrylamide (AM) and acrylic acid (AA) were grafted onto gelatinized maize starch by using eerie ammonium nitrate (CAN) as an initiator. These graft copolymers were hydrolyzed with alkali to yield hydrogels. The effects of different reaction variables, such as the concentration of the initiator and crosslinker, initial dilution of monomers, gelatinization conditions of starch, and the ratio of AM and AA in the monomer feed, on the water absorption capacities of these hydrogels have been examined. Absorption increases on gelatinizing starch at a higher temperature for a longer time as smaller granules gelatinize only under these conditions. The higher proportion of AA in the monomer feed enhances absorption due to formation of polyelectrolyte. The optimum conditions for obtaining maximum water absorbency established in the present study are granular maize starch = 2.0 g; gelatinization temperature = 95 degrees C; gelatinization time = 60 min; AM = 1.0 g; AA = 4.0 g; CAN = 0.008 mol/L; N,N'-methylene bisacrylamide = 1%. The product so formed was saponified with NaOH and then precipitated in excess of methanol. The dried and finely powdered product showed the maximum water absorbency of 510 g/g. (C) 2000 John Wiley & Sons, Inc.