Rheological and Thermal Properties of Saponified Cassava Starch- g- Poly( acrylamide) Superabsorbent Polymers Varying in Grafting Parameters and Absorbency

Cassava starch-graft-poly(acrylamide) superabsorbent polymers (SAPs) with varying absorbencies were synthesized. Weight average molecular weight (M-w) of the hydrolyzed starch-graft-copolymers ranged from 1.6 x 10(6) to 2.8 x 10(6) g/mol, the largest being shown by the sample with highest percentage grafting. The storage (G) and loss modulus (G) of hydrogels were determined as a function of frequency. G was larger than G for the hydrogels with higher absorbencies and exhibited a liquid-like behavior. However, hydrogels with lower absorbencies showed a reverse viscoelastic behavior. The viscosity of hydrogels determined using a Brookfield viscometer at different shear rates was found to be larger for the hydrogels with higher absorbencies. The melting temperature (T-m) and enthalpy change of fusion (H-f) of the SAPs ranged from 149.7 to 177.7 degrees C and 65 to 494.9 J/g, respectively and showed a positive correlation with grafting parameters and M-w. Heavy metal ion removal capacity of hydrogel followed the order Cu2+>Pb2+>Zn2+. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40368.