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 × 10 6 to 2.8 × 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 (Δ H f ) of the SAPs ranged from 149.7 to 177.7°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 Cu 2+  > Pb 2+  > Zn 2+ . © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 40368.