Preparation And Flocculation Performance Of Natural Polymer Grafted Cationic Flocculant

With water pollution intensifies all over the world,flocculation,as an economical and simple wastewater treatment technology,has attracted more and more attention.The flocculant plays a decisive role in the flocculation process,and its quality determines the effect after treatment.Therefore,the preparation of efficient and inexpensive flocculants have been a research project for the majority of researchers.Natural polymers such as chitosan（CS）and starch（STC）have flocculation effect,but they have some shortcomings such as low molecular weight and poor solubility.In this paper,acrylamide（AM）and cationic monomer methacryloxyethyltrimethyl ammonium chloride（DMC）were grafted onto corn starch and chitosan substrates by graft polymerization to prepare natural polymer grafted cationic flocculants STC-g-PAD and CS-g-PAD.Two kinds of natural polymeric flocculants were prepared by aqueous solution polymerization using ammonium persulfate as initiator.The graphic efficiency is evaluation index,and the polymerization time,polymerization temperature,ammonium sulfate addition amount and the ratio of AM and STC on STC-g-PAD graft efficiency are studied.The optimum grafting efficiency of STC-g-PAD was obtained by orthogonal experiment when the mass of（NH₄）₂S₂O₈ was 0.25 g,the mass ratio of AM to STC was 2:1,and the grafting time was 3 h at 55℃.The influence of four polymerization conditions on the reaction was as follows:m _AM:m _STC>polymerization temperature>the amount of initiator is added>The polymerization time.Based on the preparation conditions of the starch-based flocculant,the effect of mass ratio of chitosan to acrylamide on the graft efficiency of CS-g-PAD was studied.The results showed that the graft efficiency of CS-g-PAD reached 83.15%when the ratio of chitosan to acrylamide was 1:4.The two natural based flocculants were characterized by FT-IR,it was proved that the target products were successfully prepared.The analysis of TG-DTG indicates that the thermal stability of the flocculant was improved;the analysis of XRD showed that the graft polymerization broke the original crystal structure of corn starch and chitosan,and made the synthesized flocculant changed into amorphous structure;SEM analysis showed that the surface roughness of the flocculant increased and many gullies were formed.Taking 1 g/L kaolin suspension as flocculation object,the effects of hydraulic conditions and the internal structure of two kinds of flocculants on the flocculation effect were studied.By testing the flocculating performance of flocculants prepared from two different sources of starch,it was proved that the flocculant effect prepared by corn starch with more amylose was better.It was proved that the transmittance of kaolin suspension could reach more than 95%under weak acidic and the optimized hydraulics conditions when the two natural grafting flocculants STC-g-PAD and CS-g-PAD dosages were 2 g/L,and the transmittance increased with the increase of grafting efficiency.