Research On The Synthesis And Application Of The Polyampholyte P(DMDAAC-AM-AA)

A series of studies indicated that, large accumulation of the polyvalent metal ions in thepapermaking whitewater system, such as Ca²⁺and Mg²⁺, was one of the major problems whichresulted in the present situation that, the total closed cycle and “zero discharge” of the wastewaterstill can’t be achieved in papermaking industry. The continuous accumulation of those metals notonly exerts a negative influence on adsorption of the cationic chemical additives on the paperfibers, but also increases the damage of DCS. Hence, effective control and timely transfer out ofthe system of the metals in wet-end make a great significance to realize the cleaner production ofpapermaking, as well as promote the development of the theory of whitewater closed cycle.In this paper, the polyampholyte P （DMDAAC-AM-AA） composed of acrylamide（AM）,acrylic acid（AA） and dimethyl diallyl ammonium chloride （DMDAAC） was prepared.Coordination effect can be formed between the carboxyls, acylaminos and the hard acid metals,e.g. Ca²⁺and Mg²⁺, which palys a role in adsorption and cleaning. Meanwhile, the quaternaryammonium groups and acylaminos function with the paper stock components that carry negativecharges on the surfaces, e.g. fibers, and transfer the metals out of the system through staticelectricity and hydrogen bond effects. Moreover, the involved mechanisms and affecting factorsin the adsorption and transfer processes were also studied and discussed in this paper, which thus,provides the theoretical foundation and controlling method for resolving the problem.Single-factor method was used to optimize the systhesis process: initial molar ratio n（AM）:n（DMDAAC）: n（AA） was1:0.3:0.8, monomers mass fraction22.5%, initiator concentration0.2%, reaction temperature75°C, reaction time10h, which achieved over90%product yield andbetter applied properties. Using the combination way of batch and semicontinuous to feedmonomers, component proportion of the polymer was most near to the initial one, and Tgwas93.32°C, the sequence distribution of the polymer was good. The optimum adsorption conditionsof Ca²⁺on the polymer were investigated. The kinetic study showed that, adsorption equilibriumwas achieved at240min after the adsorption begun, and the kinetic curve was well represented bythe pseudo-second-order model, which meant chemisorptions. Langmuir and Freundlich modelswere used to describe the adsorption isotherms. The experimental results showed that theadsorption was well described by Langmuir model, and was monomolecular layer, easyadsorption process. Besides, the values of RLat different temperatures were all below0.5.The adsorption equilibrium of polymer onto the fibers was achieved at60min, and theequilibrium absorption capacity was ca.2.4mg/g oven dry stock. The optimum adsorptionconditions were30°C, stirring rate120rpm, concentration of the polymer and the stock1.0×10^-21.5×10^-2g/L and4⁵g oven dry stock/L, respectively. FT-IR difference spectra confirmed theadsorbed polymers at the surfaces of fibers.