The Preparation Of Starch Grafting Dicyandiamide Formaldehyde Condensation Polymer And The Syudy Of Its Synthesis Mechanism

Cationic grafting starch is a kind of efficient,environmental,stable and affordable flocculants,but it is relatively hard to prepare and the types of vinyl monomer is less.In this paper a kind of flocculant made by starch grafting dicyandiamide-formaldehyde condensation copolymer was designed and prepared through analyzing the condensation mechanism of dicyandiamide and formaldehyde,and the molecular structure and the characteristic group of the new flocculant was confirmed by infrared spectrogram.The optimum preparation technology,which was confirmed through studying the factors such as material dosage,temperature and duration,is that the mole ratio of dicyandiamide,formaldehyde and ammonium chloride is 1:2:1,the reaction temperature is 70? and the reaction duration is 2 hours.It was found that the excess water would restrain the condensation reaction and cripple the flocculation effect.The degree of the reaction between formaldehyde and ammonium chloride would be different with different dosages of formaldehyde.The flocculant would lose its effect if it was reacted with alkali substances.A new mechanism of the dicyandiamide-formaldehyde condensation polymerization is that the hydrochloric acid,which is from the reaction of formaldehyde and ammonium chloride,initiates the reaction between cyanogroup and amidogen that formed an imidogen which is a strong exothermic reaction that will cause a boiling and splashing phenomenon.Then the remained formaldehyde reacts with amidogen and forms hydroxymethyl which can cause a condensation reaction and form a dicyandiamide formaldehyde molecule with a netty structure.The optimum preparation technology of starch grafting acrylamide is that:the mass ratio of starch,acrylamide and water is about 1:1:30,the concentration of ammonium persulfate is 5.0× 10-3mol/L,the reaction temperature is 80?,the gelatinization duration is half an hour and the reaction duration is 3 hours.The range of the the molecular weight distribution of the grating polymer is large,and the grafting polymer had a similar water-solubility with the homopolymer so it is difficult to separate the homopolymer of acrylamide from the grafting copolymer.Finally,a new flocculant made by starch grafting dicyandiamide-formaldehyde condensation polymer was designed and prepared,and its molecular structure was confirmed by infrared spectrogram and reaction mechanism.It was found that the optimum dosage is 15ml of the 5 times diluting solution of the new flocculant when it was used to treat 200ml dye water with a concentration of 2g/L and pulping and papermaking wastewater after biochemical treating,and the decolouring rate and the removal rate of COD were 98.3%and 83%,respectively.