Synthesis And Application Of Water-based Dispersion Cationic Polyacrylamide As Retention And Drainage Aid

Water-based dispersion cationic polyacrylamide (CPAM) used as retention and drainage aid is a new product by dispersion polymerization in recent years. Dispersion polymerization has the advantages of not only a fast reaction rate and a product with high molecular weight as emulsion polymerization but also simple polymerization process and operations as solvent polymerization. In addition, the dispersion polymerization process can be conducted with high solid content, low apparent viscosity, and good stability, and heat transmission and multiple selection of the dispersing agent are easy. The product prepared by using dispersion polymerization dissolves quickly, and no bulks and undissolved particles remain in the solution. The product can be applied instantly without the need for advance dissolution. The most significant advantage of dispersion polymerization is that no emulsifier and varsol, which would contaminate the environment, are used in the polymerization process. With these unique advantages, dispersion polymerization is a new direction in research and development of cationic polymerization.In present work, CPAM emulsion with high solid content, low viscosity, good stability and rapid dissolution was prepared from acrylamide (AM) and quaternary ammonium cationic monomer by dispersion polymerization in an aqueous solution of (NH4)2SO4. Different dispersing agents, cationic monomers and initiators were studied. The results showed that, the dispersion has the superior properties when methacryloyloxyethyl trimethyl ammonium chloride (DMC), poly(DMC) (PDMC), and 2,2'-azobis (2-methylpropionamide) dihydrochloride (V50) were used as cationic monomer, dispersing agent, and initiator, respectively.Effects of the amount of salts, comonomer, dispersing agent, initiator, and monomer mole ratio (DMC:AM), reaction time and temperature on dispersion polymerization were investigated. The results showed that, when the mass fraction of comonomers, (NH4)2SO4, PDMC and V50 was 14%,24%,4% and 0.10%, respectively, DMC:AM was 10:90, and reaction temperature was 56?, CPAM with low viscosity, good stability and application was obtained after 10h reaction. And its molecular weight was above 5×106g/mol.Changes in the apparent viscosity and particle morphology of the reaction mixture were measured during the dispersion polymerization process. A new particle formation mechanism during the dispersion polymerization process was proposed. The theory of reducing the apparent viscosity with NaCl was studied. The effects of dispersing agent and DMC:AM mole ratio on particle size,size distribution, and particle morphology were investigated. The results showed that increasing dispersing agent concentration resulted in a U-shaped variation in the particle size and widening after narrowing the particle size distribution; the particle morphology changed from smooth and round to rough and irregular at a higher dispersing agent concentration. With the increase in the DMC:AM mole ratio, the particle size increased, and such increase exhibited the same influence pattern as the dispersing agent on the particle size distribution and particle morphology.CPAM was applied in imitating fine paper production as retention and drainage aid. The dosage of CPAM, contact time with pulp and stirring rate were optimized. The filler retention was enhanced from 23.35% to 73.74% and the Schopper-Riegler beating degree, which reflected pulp drainability, was reduced 14° SR under optimum condition.