Synthesis And Properties Of Quaternary Ammonium Type Cationic Starch Flocculation With Mechanically Activated

Flocculation process is one of the key links in the wastewater treatment.In China, the flocculation product is rich,but the cationic flocculant is rare.Cationic starch flocculants have a well prospect in practice,but have low production efficiency.In this paper,cationic starch flocculants were synthesized by wet process,wet process assistanted with ball-milling treatment,dry process and dry process assistanted with ball-milling treatment.The effect of preparation technologies on the flocculation efficiency,degree of substitution and reaction efficiency of products were discussed. Optimal procedure for cationic starch flocculant was obtained,and flocculation performance was analysised.Microstructure of starch and starch flocculation were elucidated by means of infrared spectrum(IR),x-ray diffraction(XRD) and scanning electron microscopical technique(SEM).The mechanism of flocculation was explored by charge density analysis,ubbelohde viscosimeter and zeta potentiometric analysis.The above analysis could provide a sound theoretical basis for good effect and low cost cationic starch flocculants preparation.1.Preparation process for starch flocculationThe effect of activation time,reaction time,starch concentration,initiator concentration,monomer concentration and reaction temperature on the etherify reaction were investigated.The degree of substitution and reaction efficiency of products synthesized by wet process,wet process assistanted with ball-milling treatment,dry process and dry process assistanted with ball-milling treatment were 0.03～0.07, 0.07～0.14,0.18～0.30,0.30～0.35 and 4%～10%,9%～20%,32%～42%,75%%～87% respectively.The dry process assistanted with ball-milling treatment was the best method for starch flocculation preparation.The degree of substitution,reaction efficiency,yield rate and flocculation efficiency of products synthesized by dry process assistanted with ball-milling treatment was the highest among the four processing methods and had less dependence upon the starch source.The optimal reaction conditions were as following: starches were mechanically activated by a stirring-type ball mill for 5h.Then the activated starches were used to fabricate etherify copolymer in the presence of monomer of 2,3-epoxypropyltrimethylammonium with the molar ratio of 0.40:1.00.Etherifying reaction was carded at 90℃for 2.5h with initial system moisture content less than 20%.2.Function of ball milling in starch modificationParticle size and gel permeation chromatography analysis results demonstrated that particle size,surface area of starch granule and molecular weight distribution of starch molecules exhibited major changes after ball milling.After subjected to ball-milling treatment,long chain and branch structure of starch molecules were broken,which resulted in a remarkable increase in small molecular segmer and decrease in large molecular segmer.XRD and SEM analysis revealed that the etherifying reaction occured not only in the amorphous region,but also in the crystalline region of the starch when ball-milling caused the molecular arrangement disorder,crystal structure destruction and lattice distortion.In addition,mechanical energy exchanging into chemical energy in polymer chain made the starch molecular groups be in an unstable state with high energy, and therefore enhanced the starch etherifying modification.3.Flocculation performance of starch flocculantsOptimal dose of flocculant in solution was slightly lower than the critical concentration,in which molecular chain had partly overlapped.Good flocculation performance existed in certain suspension solid content of kaolin suspension(1%). Excessively high or low kaolin suspension concentration could decrease the flocculation effect.It was found that the starch flocculation was comparatively more effective than potassium alum and polymeric aluminum chloride flocculant in kaolin suspension clarification.The starch flocculation had wide feasible pH and temperature range and small volume of floes afer flocculation.The best adsorption effect could be obtained when temperature was 15℃.4.Flocculation mechanism of starch flocculationComprehensive analysis showed its outstanding flocculation performance depended on its special molecular structure of amylose flocculation and amylopectin flocculation, and was the result that electriciy counteract was in cooperation with adsorption bridge building and the net rooling-sweeping action.Amylose flocculation was preferred to adsorb the colloidal particle at solid-liquid interface by train and taile type,while amylopectin flocculation was likely to adsorb by loop and tail type.