Synthesis and Characterization of Novel Smart Flocculant Based on Poly(MAam)-Pregelled Starch Graft Copolymers and Their Degraded Products

Poly(methacrylamide)-pregelled starch graft copolymers derived from native pregelled starch (substrate I) and hydrolyzed pregelled starches having different molecular weights were prepared and evaluated as flocculants for ferric laurate aqueous dispersions. This was done by subjecting substrate I as a starting substrate to acid hydrolysis to obtain three levels of hydrolyzed pregelled starch having different molecular weights (substrates II-IV). The latter were graft copolymerized with various amounts of methacrylamide monomers using an Mn(IV)-citric acid redox pair for initiating grafting to obtain copolymers having different graft yields. The flocculation efficiency was followed by estimating the transmission (%) and weight removal (%) of the flocculants. The grafted pregelled starches were characterized by estimating apparent viscosity, intrinsic viscosity, and elemental analysis. The major factors affecting the flocculation process such as the flocculent dose, pH of the flocculation medium, and molecular weight as well as the extent of grafting were studied in detail. It is observed from the obtained results that the flocculation efficiency of the prepared copolymers (a) increases by increasing the flocculants dose to reach a peak value then decreases thereafter; (b) increases by decreasing the pH values from 8 to 6; (c) increases by decreasing the molecular weight of the parent starch and follows the following order: substrate IV < substrate III < substrate II < substrate I; (d) increases by increasing the extent of grafting within the range studied; and (e) poly(methacrylamide)-graft copolymers derived from hydrolyzed pregelled starch (substrates II-IV) show a higher flocculation efficiency than polyacrylamide as a synthetic flocculant. (C) 2013 Wiley Periodicals, Inc.