Syntheses And Applications Of High Molecular Weight Cationic And Amphoteric Polyacrylamides

With the rapid changing of papermaking technology, such as elevated paper-machine speed, increased use of twin-wire former, further closed water circuit and increased use of recycled fibers, highly efficient and shear-resistant paper chemicals are needed to meet the challenge.In this experiment, the cationic and amphoteric polyacrylamides (CPAM and AmPAM), with different molecular weights and different charge densities, were prepared through complex initiator systems in aqueous solution. Then, the products, used as retention and drainage aids and flocculants, were applied into the wet-end of papermaking and the treatment of papermaking waste water. The applied conditions were optimized. At the same time, the retention mechanisms using CPAM were probed through charge analysis. In order to provide the theoretical foundation for practical production and application, the feasible technical conditions were presented through mill trails.In the first part of this paper, the syntheses of high molecular weight CPAM and AmPAM were studied. According to the technology of radical polymerization, the CPAMs and AmPAMs with a series of different molecular weights and different charge densities were synthesized with AM, cationic monomer DMC and anionic monomer AMPS, through complex initiator systems in aqueous solution. In order to obtain the optimum process conditions, the effects of some factors, such as pH value, the dosage of initiators, the consistency of reactant and the temperature of initiation reaction, on molecular weight were studied.Secondly, the performances of high molecular weight CPAM were measured. The CPAM was characterized by Fourier transform infrared spectroscopy(FTIR) and 13C nuclear magnetic resonance spectroscopy(13C NMR), and its charge density was determined by colloid titration. All the results showed that the copolymerization technology used in this experiment was successful.Thirdly, a series of CPAMs and AmPAMs were used as retention and drainage aids for bleached wheat straw pulp. Their capabilities of retention and drainage increased as their charge density, molecular weight and dosage increased. CPAM and AmPAM are not sensitive to the change of pH. The filler retention and drainage were improved remarkably by using microparticle retention system. The effects of shear rate, contact time, CPAM dosage, pH value and bentonite dosage on the first pass retention(FPR) of dynamic conditions were investigated.In the fourth part, the retention mechanisms of CPAM were discussed. The technology of colloid titration, combined with the analysis of Zeta potential, was applied to measure the charge and Zeta potential of furnish under the conditions of only adding CPAM and both adding PAC and CPAM. The action mechanisms of each aid were explained theoretically.In the fifth part, high molecular weight CPAM and AmPAM were used as flocculants to treat papermaking waste water. Good results could be obtained when they cooperated with inorganic flocculants to flocculate the waste water from deinked pulp. When the ultrahigh molecular weight CPAM cooperated with PAC to treat the waste water from OCC pulp, the flocculating results were also good.Lastly, mill trials were conducted according to the synthesis process found in the laboratory. The molecular weight and cationic degree of substitution of products were measured. The results showed that the cationic degree of substitution of product accorded with the demands. The reason of diversity of product's molecular weight was found. Through mill trails, the feasible technical conditions were presented to meet the industrialization.