Emulsifying concentrates, effect

Figure 6 The effect of emulsifier concentration on the variation of monomer conversion by the polymerization time in the emulsion polymerization of styrene. Styrene-water = 1/3 KPS = 1,65 mM reaction volume = 300 ml stirring rate = 250 rpm temperature = 70 C,...

Achieving steady-state operation in a continuous tank reactor system can be difficult. Particle nucleation phenomena and the decrease in termination rate caused by high viscosity within the particles (gel effect) can contribute to significant reactor instabilities. Variation in the level of inhibitors in the feed streams can also cause reactor control problems. Conversion oscillations have been observed with many different monomers. These oscillations often result from a limit cycle behavior of the particle nucleation mechanism. Such oscillations are difficult to tolerate in commercial systems. They can cause uneven heat loads and significant transients in free emulsifier concentration thus potentially causing flocculation and the formation of wall polymer. This problem may be one of the most difficult to handle in the development of commercial continuous processes. 

Figure 8, Monomer conversion vs, polymerization time in the helical tubular reactor effect of varying initiator and emulsifier concentrations...

Experiments on the stability of the HIPEs indicated that one of the most important factors was the solubility of the emulsifier in the continuous (formamide) phase. Thus, the higher the surfactant solubility, the more stable the emulsion. The emulsifier concentration was also important stability increased to a maximum, then decreased, with increasing surfactant concentration. Surprisingly, the HLB number did not appear to have much effect on the stability of the emulsions, over the range studied (11 to 14). This was attributed to the high concentration of emulsifier in the continuous phase, although the narrow HLB value range is probably also a factor. 

Dr. A. Shaw at the University of Maryland Eastern Shore in Princess Anne, Maryland, is evaluating textile substrate for pesticide barrier effectiveness and comfort. Tests will be conducted to assess effectiveness of decontamination processes for these personal protection devices. Diazinon emulsifiable concentrates will be used to contaminate fabrics. Simulated wear studies will be conducted in the laboratory to assess the efficacy of these fabrics in protecting human health. 

At the lowest emulsifier concentration there is a long period of constant reaction rate which, however, is terminated at 70 to 80% conversion by a rather high maximum of the reaction rate owing to the strong gel effect (Trommsdorff effect) in the comparably large particles. 

In that publication a dependence of the shape of the rate-time function on such parameters as initial monomer concentration, emulsifier concentration, and dose rate was shown for the methyl acrylate system. The behavior of this system tentatively was explained by assuming a strong gel effect even at low conversions, of prolonged particle formation, and some kind of interparticle radical termination—all factors which are included neither in the Harkins view nor in the classical Smith-Ewart theory. 

Figures 6, 7 and 8 show experimental verification of Eq.(40) in batch emulsion polymerization of styrene ( 14). The number of polymer particles was measured by electron micrscopy, not at finite but at 1 hour after the start of polymerization. Figure 6 represents the effect of lowering the initial monomer concentration, Mq on the number of polymer particles formed at fixed initial initiator and emulsifier concentrations. The number of polymer particles formed is constant even if M is lowered to the critical value Mc. This is because normal°condition that micelles disappear before the disappearance of monomer droplets is satisfied in the range of monomer concentration above Mc. The value of Mc can be calculated by the following equation obtained by equating XMc, the monomer conversion where micelles disappear, to XMc2, the monomer conversion where monomer droplets disappear.

Figure 7. Effect of initial emulsified concentration when initial monomer concentration is very low ( 0 = 12.5 g/L H20 M0 g/cc H20)...

Figure 4 shows that higher concentrations of seed latex decrease the reaction rate, at constant mixed emulsifier concentrations, while Figure 5 shows that the smallest latex particle gave the lowest reaction rate. This effect is explained by the decreased availability of emulsifier to create micelles, since the small seed latex particle or high seed latex concentrations adsorb more of the surfactant, thus removing it from the water phase. 

Figure 3. Effect of mixed emulsifier concentration on conversion in tubular reactor ((E) (O) 2.2% (0) 4.4% (A) 6.9%)...

Quasi-elastic light scattering is an excellent technique for studying the formation and stability of submicrometer emulsions. Improvements in the methods of quasi-elastic light scattering data acquisition and analysis that enable full particle-size distribution studies of sub-micrometer emulsion systems are discussed. Using several oil/water emulsion systems as examples, we demonstrate the ability of these techniques to determine the effect of emulsifier concentration on the particle-size distribution produced by an inversion method of emulsification. Some of the benefits of obtaining the full distribution are also discussed. 

Effect of emulsifier concentration upon the number of polymer particles and the progress of polymerization ... 

Fig, 4 shows the effect of initial emulsifier concentration on the number of polymer particles produced. From the log-log... 

Initial emulsiffar concentration S I g/t-water ] Fxg 6 Effect of initial emulsifier concentration on the rate of polymerization. 

Fig 15 Effect of initial emulsifier concentration on particle size distribution(ExperimentaI conditions . 25 g/Z-water, Mo 0,2 g/cc-water )... 

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