| Starch is a very important class of natural polymer materials.The research of natural polymer flocculants prepared with starch as raw materials in the treatment of wastewater has made significant progress.However,this type of flocculant still has a series of problems in the water treatment process such as complicated preparation process,high cost,strict reaction conditions and inability to achieve large-scale production.It has become an urgent need to prepare a starch-based composite flocculant that is cheap,highly efficient,short-flow and excellent in water treatment effect.In this paper,corn starch was modified by high-energy electron beams with different irradiation doses,and the ideal irradiation starch was selected.Under the action of the twin-screw basic process,the irradiation starch was combined with Methacryloxyethyltrimethyl ammonium chloride(DMC)and acrylamide(AM)monomer to prepare starch-based composite flocculant.and then the effect of irradiation on starch structure and the relationship between the preparation conditions of flocculant samples and their performance were studied,combined with the results of water treatment experiments to determine the optimal conditions.The specific research contents and conclusions are as follows:First,starch was treated in the range of 4-80 kGy with high energy ray irradiation,and the properties of starch at various irradiation doses were systematically studied.The results show that before the irradiation dose reaches 20 kGy,the viscosity of the irradiated starch decreases significantly,which shows that the molecular size of the starch decreases at this time.The effects of irradiation on starch are mainly chain scission and degradation,during the initial irradiation of 4kGy,the molecular weight content of 2 million grades in starch decreases from 19.8% to 6%.With the increases of irradiation dose,the overall molecular weight interval of starch shifts to a small molecular weight interval.After irradiation,the free radical content in starch gradually increases with the increase of irradiation dose.The ratio of amylopectin and amylose content in the original corn starch is 73:27,when the irradiation dose is increased to 10 kGy,the relative content of amylopectin decreases to 55.8% while amylose increases to 40.2%.As the radiation dose continues to increase,the starch molecules eventually break down into many short straight chains and a large number of glucose chain fragments.Secondly,the relatively ideal 4kGy irradiated starch was selected to be blended with DMC and AM monomers.Orthogonal experiment scheme was designed through initial exploration experiments,combined with a twin-screw extrusion process,starch-based composite flocculants were prepared and studied in various indicators.The results show that the appearance of the produced products shows a tight groove structure.The grafting rate of the products gradually increases with the increase of the DMC and AM monomer content in the sample ratio,and the content change of DMC has a greater effect on the grafting rate of the produce,after the monomer content of DMC and AM reach 10% and 5%,the change of the grafting rate of the products gradually become smaller.The water solubility of each product was measured and find that the water solubility of the products is strong,all reaching more than 93%.Based on the analysis of Cl ion and N element content in the product,it was concluded that the irradiation starch successfully grafted two monomers.The thermal stability of the products is similar to the weightless process of starch,and the stability is ideal.Finally,the various products were applied to water treatment experiments of printing and dyeing wastewater,and the effects of each product on the quality of wastewater were studied.The results show that the optimal dosage of the product is 0.5 g/L,and the samples No.6 and No.9 show the best performance,the turbidity removal rates are 97.8% and 92.6%,the chroma removal rates are 93.7% and 93.6%,the chemical oxygen demand(COD)removal rates are 88.7% and 88.8%.After water samples are irradiated,water treatment experiments can reduce the chromaticity and COD value to a certain extent.In addition,Moreover,adding appropriate amount of polyaluminum and mildly irradiating sewage can effectively reduce the flocculation sedimentation time.To optimize the flocculation sedimentation process,it is proposed to apply centrifugal separation technology to the water treatment process,it has little effect on the turbidity and color value of the water body.The research also finds that the flocculation effect of the prepared samples is the best when the pH is 6 to 8.According to the research in this paper,a method for preparing starch-based composite flocculant,which is a high efficiency,short process,can realize large-scale manufacturing and cheap,has been proposed.The flocculant prepared by this method has a good effect on water treatment,and it provides a reference for the industrial application of starch-based composite flocculants. |
