Graft copolymerization onto starch. II. Grafting of acrylic acid and preparation of it's hydrogels

The grafting of acrylic acid (AA) onto granular maize starch in aqueous medium initiated by eerie ion has been studied gravimetrically under nitrogen atmosphere. The effect of concentration of eerie ion, concentration of AA, reaction temperature, polymerization time and material-to-liquor ratio on the grafting has been studied in terms of %GE and %Add-on. The optimum conditions obtained for the grafting of AA onto 2 g of granular maize starch were: [AA] = 0.2775 mol/L; [CAN] = 0.004 mol/L; time = 240 min; temp = 35 degrees C; material-to-liquor ratio = 1:10. The graft copolymers were characterized by infra-red spectroscopy, XRD, TGA and scanning electron microscopy. XRD showed that the crystallinity of starch decreases owing to grafting. SEM revealed that grafting is essentially a surface phenomenon. Grafting of acrylic acid affects the thermal stability of starch. Hydrogels were prepared by grafting AA onto gelatinized starch followed by neutralization with NaOH. The maximum water absorption obtained was 250 g/g. (C) 1998 Published by Elsevier Science Limited. All rights reserved.