| Flocculation is a simple, economic and widely adopted method in wastewater treatment. Because most of the wastewater's suspensions are negative charges, the cationic polyacrylamide (CPAM) flocculant has attracted much attention both in research and industry. Efforts have been made to modify CPAM with starch in order to reduce the high prices and slove its environmental pollution problems.CPAM has been synthesized by acrylamide (AM), dimethyl diallyl ammonium chloride (DMDAAC) with solution polymerization. Cationic polyacrylamide grafted starch (St-g-CPAM) has been synthesized by acrylamide (AM), dimethyl diallyl ammonium chloride (DMDAAC) and starch with a multiple initiator with solution polymerization. The effects of initiator ratio, reaction temperature, the monomer concentration and proportion of AM and DMDAAC on the molecular weight, the efficiency of grafting and the yield of grafting were investigated. The flocculation capability has been evaluated by turbidity reduction. The thermal behavior, chemical structure and microstructure of CPAM and St-g-CPAM were also characterized by thermal gravimetric (TG), IR and SEM.The results show that the optimal conditions of the polymerization on CPAM are as follows:the reaction temperature is 55℃, total mass fraction of (NH4)2S2O8 and NaHSO3.CH2O.2H2O is 0.0125%, mass ratio of NaHSO3.CH2O.2H2O/(NH4)2S2O8 is 4:3, mass fraction of C8H18N6.2HCl(V-50) compounds is 0.0125%, monomer concentration is 35%, cationic monomer concentration is 35%. The optimal conditions of the polymerization on St-g-CPAM are:the concentration of ceric ammonium nitrate is 0.5%, the mass fraction of C8H18N6.2HCl(V-50) compounds is 0.0125%, the reaction temperature is 60℃, the concentration of total monomer is 20%, the monomer ratio between acrylamide (AM) and dimethyl diallyl ammonium chloride (DMDAAC) is 7:3. It is suggested that CPAM with a molecular weight of 2.5×106 and St-g-CPAM with a grafting percentage of 92.5% and grafting efficiency of 99.7% have strong flocculation capability. |
