Preparation And Swelling Properties Of Amphoteric Polyacrylamide Dispersion

Functional polyacrylamide (PAM) is one of the hot areas of materials in recently year. Amphoteric polyacrylamide (AmPAM) is a typical polyampholyte with their specific performance. Aqueous dispersion polymerization is the latest technology in the area of soluble polymer. The reaction carried out under mild conditions, while avoiding secondary pollution of organic solvents.In this paper, AmPAM with both anion and cation groups was prepared by dispersion polymerization, with acrylamide (AM) as the main raw material, acrylic acid (AA) as the anionic monomer, methacryloyl ethyl trimethyl ammonium chloride (DMC) as the cationic monomer, ammonium sulfate as the phase separation agent, DMC homopolymer (PDMC) as the dispersion stabilizer and 2,2'-azo-bis(2-methylpropion- amide) dihydrochloride (V-50) as the initiator. Effects of several factors were studied on dispersion polymerization, such as ammonium sulfate concentration, stabilizer concentration and molecular weight, monomer concentration and type, initiator concentration, NaCl concentration, ionic degree, pH value and temperature. Polymer structure was confirmed by NMR 1H spectrum and elemental analysis. Seeded dispersion polymerization was introduced to prepare dispersion with high polymer concentration. The equations of intrinsic viscosity and molecular weight were put forward by tests of several samples. Swelling properties of AmPAM dispersion were investigated by HAAKE rheometer and RheolabQC viscosity, comparing with cationic and anionic polyacrylamide dispersion. In addition, the application performance and effect mechanism of amphoteric polyacrylamide had been analyzed.With (N_H4)₂SO₄ aqueous solution as reaction medium, polymer dispersion with good stability and higher intrinsic viscosity can be prepared. Intrinsic viscosity of polymer would increase first and decrease with increasing of (NH4)2SO4 concentration, pH and temperature. It would increase with increasing of monomer concentration and ionic degree and decreasing of PDMC and V-50 dosage. Particle size and apparent viscosity of AmPAM dispersion would change with variety of all factors. The optical conditions are as follows: (NH₄)₂SO₄ concentration 28-33%, PDMC dosage 400mg·Kg^-1, molecular weight of PDMC 1.33-2.90×10⁶, monomer concentration 10%, V-50 dosage 400mg·Kg^-1, NaCl concentration 1%, pH 5-6 and the temperature 50-60With seeded dispersion polymerization, Weissenberg effect was weakened and the process was easy to control. Meanwhile, the dispersion of higher polymer concentration could be prepared.When there were some monomers in the continuous phase, these monomers could penetrate into the particle through the solvent channel. The particle would become bigger and apparent viscosity of dispersion would increase, too. (NH₄)₂SO₄ concentration had a great influence on the dispersion because the solubility of polymers was closely related with (NH₄)₂SO₄ concentration. Due to the properties'differences of ionic group in stabilizer molecule, swelling degree of anionic polymer dispersion was lower than that of cationic and amphoteric polymer dispersion. Due the difference of charge content in polymer molecule, swelling property of AmPAM dispersion was different from cationic and anionic polymer dispersion.If AmPAM dispersion was diluted by (NH₄)₂SO₄ solution with the concentration equal to original dispersion, the samples were the shear-thinning fluids when the polymer concentration was very high or low. Or, the samples were the shear- thickening fluids. If AmPAM dispersion was diluted by 20% (NH₄)₂SO₄ solution, apparent viscosity of these samples increased fast firstly, and then decreased. As the different role of (NH₄)₂SO₄ on macromolecules, swelling performance of AmPAM dispersion was different from that of cationic polyacrylamide dispersion.The application performance of AmPAM was good when it was used as flocculant and dewatering agent. It was better than ionic polyacrylamide.