Amphoteric Polyacrylamide Prepared By Aqueous Dispersion Polymerization And Its Application On Newsprint

Amphoteric polyacrylamide is widely used in many fields due to its anti-polyelectrolyte effect and wide range of pH values in application, with both anionic and cationic groups on its polymer chain. As dry strength agent in papermaking, AmPAM take its advantage in wet end of deinked pulp, for its anionic group can protect the cationic group from anionic heteroion by electrostatic repulsion, and AmPAM can enhance the binding between fibers and strengthen the mechanical property of paper by the adsorption of cationic group to the fiber surface.As dry strength agent, the amphoteric polyacrylamide was prepared via the process of aqueous seeded dispersion polymerization in ammonium sulfate(AS) solution, in which the dispersion was composed of methacryloxyethyltrimethyl ammonium chloride(DMC) as cationic monomer, acrylic acid(AA) as anionic monomer, acrylamide(AM) as main monomer, poly dimethyl diallyl ammonium chloride(PDADMAC) as stabilizer and 2,2’-azobis(2-methylpropionamide) dihydrochloride(AIBA) as initiator. In this research, the chemical structure was characterized by FT-IR and 1H-NMR, while GPC, rotational viscometer and Malvern particle sizer were used to characterized molecular weight and its distribution, dispersion apparent viscosity and average particle size respectively. Also charge property and ionic degree of copolymers were investigated by colloid titration. In order to regulate and control the AmPAM property by optimizing the synthesis condition, the effects of types and molecular weight of stabilizer, initiator dosage, AS dosage and monomer ratio on dispersion appearance, stability, monomer conversion, molecular weight and average particle size were investigated.The effects of AmPAM monomer ratio and dosage on stability and drainage property of deinked pulp were investigated. The result shows that fiber converged and the Zeta potential of pulp reached peak value when AmPAM dosage was 2.5%~3.0%. Zeta potential didn’t change significantly from pH5.0 to pH 8.0. Besides, drainage and retention property were characterized by dynamic drainage jar(DDJ), UV-vis spectrophotometry and ash content. It indicates that 30-second drainage, first pass retention(FPR) and filler retention were enhanced by adding 0.30% AmPAM. Thus, AmPAM can improve drainage and retention property.AmPAM dry strength agent was applied to deinked pulp to simulate newsprint making. The effects of AmPAM dosage, molecular weight and monomer ratio on paper sheet tensile strength and tear were investigated in this research. The critical picking speed was tested by IGT printability tester to characterize surface strength, while the surface morphology of paper sheet was observed by SEM to study the reinforcement mechanism of AmPAM. The result shows that the tensile index and critical picking speed were improved after adding AmPAM strength agent by reinforcing the binding between fibers, and the morphology of paper sheet proved that AmPAM dry strength agent can improve paper mechanical property.