Optimization of preparing a high yield and high cationic degree starch graft copolymer as environmentally friendly flocculant: Through response surface methodology.

To pursuit effective and environmentally friendly flocculant, a bio-copolymer was prepared by starch grafting with acrylamide (AM) and dimethyl diallyl ammonium chloride (DMDAAC) through an initiator system KMnO4/HIO4. The initiation and grafting reaction were optimized by the Response Surface Methodology. In the initiation reaction, the optimum condition was KMnO4 at 0.28 mmol, HIO4 at 0.25 mmol, and the temperature at 67.64 °C, when the highest copolymer yield of 13.43 g was obtained from 4 g raw starch. In the grafting reaction, the optimum condition was the temperature at 68.71 °C, (AM + DMDAAC)/starch anhydroglucose units molar ratio at 2 and the AM / (AM + DMDAAC) molar ratio at 0.34, when the copolymer had the maximum cationic degree of 1.54 meq/g. The optimized preparing method had a high grafting efficiency of 97.12 ± 0.14% and high raw material utilization. The flocculation ability of the optimized graft copolymer was also tested. The result showed the graft starch was effective to remove reactive dyes and disperse dyes from wastewater. The dye removal efficiency of the graft starch was nearly 10% higher than polyacrylamide. Therefore, through the optimization of initiation and grafting reaction, the graft starch was a promising environmentally friendly flocculant.