CHEMICAL MODIFICATION, CROSS-LINKING AND CHARACTERIZATION OF SOME STARCH HYDROGELS

Modified starch hydrogels were prepared via the reaction of starch with acrylamide (AAm), under certain conditions and cross-linking with N,N'-methylenebisacrylamide (MBAAm). Rheological measurements of different ratios gels shows that both increasing of cross-linker or substrate concentration, lead to increase the elasticity of the gels. The molecular weight between two entangelement points (M(e)), was calculated from plateau modulus (G(p)') values. The effectiveness of the cross-linker was calculated by comparison between the number of elastically effective points rheologically [n(e)(r)] and that obtained from theoretical values [n(e)(t)]. The effectiveness has a maximum value 5.76% at the higher substrate concentration of 25% (w/w) gels. Swelling of different gels were studied in pure water and in different salt solutions. The curves show shrinking of the gels, however no collapsing occurs with increasing the concentration of salts. The maximum water absorption capacity were 140 g/g for 15/3 gels. The structure of the gels were interpreted with the guide of C-13 NMR spectrometry.