Preparation of superabsorbent by graft copolymerization of acrylic acid onto corn starch using K_2S_2O_8 and rare earths as initiators

K2S2O8 and rare earths (RE) were used as initiators to prepare superabsorbents by graft copolymeri-zation of acrylic acid (AA) onto corn starch. The effects of monomer concentration, initiator K2S2O8 concentra-tion, cross-linker concentration, reaction temperature and the concentration ratio of RE and K2S2O8 on the graft copolymerization were studied in terms of the water absorption capacity of superabsorbents. Results indicate that the optimum conditions obtained for the grafting of AA onto 5g starch are as follows: AA of 75. 773 g/L, K2S2O8 of 0.437 g/L, RE of 0.874 g/L, cross-linker of 0.381 g/L and temperature of 70℃. The maximum water absorption capacity obtained is 740 g/g. The new method of graft polymerization is easily proceeded and controlled. The graft copolymers were characterized by infra-red spectroscopy, scanning electron microscopy and TG. Results characterized by IR and SEM give strong evidence for grafting of AA onto corn starch, and those characterized by TG reveal that the grafting of AA improves the thermostability of corn starch.