Coagulated polymers additives effects

Electrostatic stability plays a dominant role in many separation processes, such as filtration of industrial wastewaters. Coagulation aids (known as coagulants) are routinely used to improve the effectiveness of separation processes in such cases. Polymer-induced stability is often the method of choice, particularly in the case of concentrated dispersions for example, many pharmaceutical preparations, paints, inks, and liquid toners depend on surfactants or polymer additives for ensuring stable preparations. We see in Section 13.2 that in the case of concentrated dispersions both thermodynamic and kinetic issues often become very important. 

Homopolymers of DADMAC and copolymers of acrylamide and DADMAC are applied in the coagulation of fibers recycled from coated broke, a term used to describe a paper which cannot be sold for different reasons [ 176]. It is claimed that polymer solutions and water-in-oil emulsions containing DADMAC offer both superior performance and cost effectiveness compared to the traditional polymer additives used for this purpose [190,194]. 

Baxendale, Evans and coworkers reported in 1946 that the polymerization of methyl methacrylate (MMA) in aqueous solution was characterized by homogeneous solution kinetics, i.e. where mutual termination of free radicals occurred, in spite of the fact that the polymer precipitated as a separate phase. Increases in the rates of polymerization upon the addition of the surfactant cetyl trimethyl ammonium bromide (CTAB) were attributed to the retardation of the rate of coagulation of particles, which was manifested in a reduction in the effective rate constant for mutual termination,... 

Electron microscopy of the final latex of the experiments given in Table I showed almost no new nucleation. The particle size distributions were narrow and indicated no noticeable coagulation as well. New nucleation would lead to increased rates whereas coagulation would have the opposite effect. Any decrease in the rate therefore must be due to a decrease in [m], if we assume n to be constant. We therefore determined the tofuene/polymer ratio in the seed latex in the absence and presence of the various additives. Toluene was chosen as the solvent, because it is similar to styrene and allows the measurement of equilibrium solubilities without the risk of polymerization. Table II gives the experimental values of the toluene solubility in the seed as a function of time. The results indicate that the swelling is nearly complete within 5 to 10 min. 

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