Different Emulsion Recipes

The next two steps after the development of a mathematical process model and before its implementation to "real life" applications, are to handle the numerical solution of the model s ode s and to estimate some unknown parameters. The computer program which handles the numerical solution of the present model has been written in a very general way. After inputing concentrations, flowrate data and reaction operating conditions, the user has the options to select from a variety of different modes of reactor operation (batch, semi-batch, single continuous, continuous train, CSTR-tube) or reactor startup conditions (seeded, unseeded, full or half-full of water or emulsion recipe and empty). Then, IMSL subroutine DCEAR handles the numerical integration of the ode s. Parameter estimation of the only two unknown parameters e and Dw has been described and is further discussed in (32). 

For a single continuous reactor, the model predicted the expected oscillatory behaviour. The oscillations disappeared when a seeded feed stream was used. Figure 5c shows a single CSTR behaviour when different start-up conditions are applied. The solid line corresponds to the reactor starting up full of water. The expected overshoot, when the reactor starts full of the emulsion recipe, is correctly predicted by the model and furthermore the model numerical predictions (conversion — 25%, diameter - 1500 A) are in a reasonable range. 

The basic constituents of all commercial emulsion polymerization recipes are monomers, emulsifiers, and polymerization initiators. Other common components are modifiers, inorganic salts and free alkaH, and shortstops. The function of these different components and the mechanism of emulsion polymerization have been described (43,44). 

The human skin is a rather complex structure, which protects the body against the environment. The aim of the different cosmetics is to repair and restore the original balance of elements in skin structure. Cosmetic preparations would need to consider any reaction between them and the components of the skin. Skin creams are known to be composed of a variety of ingredients, which are based on end use (hands, feet, face, hair, etc.), and some speciality products that are applied to the skin to repair effects such as dryness. We will now consider some recipes for skin creams. Since the number of personal care emulsion creams is very large, only a few typical examples are given here. A variety of emulsion skin care products are found commercially that claim to exhibit properties for nurturing and protecting the skin. 

Although the early literature described the application of a tubular reactor for the production of SBR latexes(1), the standard continuous emulsion polymerization processes for SBR polymerization still consist of continuous stirred tank reactors(CSTR s) and all of the recipe ingredients are normally fed into the first reactor and a latex is removed from the last one, as shown in Figure 1. However, it is doubtful whether this conventional reactor combination and operation method is the most efficient in continuous emulsion polymerization. As is well known, the kinetic behavior of continuous emulsion polymerization differs very much according to the kind of monomers. In this paper, therefore, the discussion about the present subject will be advanced using the... 

Preparation of Carboxylated Latexes. Latexes were prepared by emulsion polymerization using recipes given in Table I. Several MMA-MAA copolymer latex samples were prepared with differ-... 

Figure 1. Conversion histories of the batch vinyl acetate emulsion polymerizations (similar recipes only the emulsifier concentration is different).

Polymerizations of the monomer emulsions were carried out with oil-soluble initiators. Oil-soluble initiators have often been employed in emulsion polymerization recipes and are generally used in suspension polymerization. Whereas in the latter case the initiation naturally takes place in the monomer droplets, the locus of initiation and growth of particles in emulsion polymerization with oil-soluble initiators has been open to some doubt. However, the fact that the particle size and size distribution is not very different from the results with water-soluble initiators and that the particles are generally much smaller than the droplets in the monomer emulsions indicates that with... 

To check the validity of this concept, the simplest and most straight-forward approach seemed to be to carry out rate studies of emulsion polymerizations with recipes of identical micellar sizes. Since, as mentioned previously, each specific value of surfactant ratio, r, of the mixed surfactant stands for a specific size of the mixed micelles, the experimental approach boils down to run several series of kinetic studies with different surfactant ratios between series, but with varying surfactant concentrations within each series. The standard recipe for such experiments was described in the Experimental Section. This standard recipe is essentially identical with the one used by Kamath ( ), Wang i9) and Letchford (15) with the exception of eliminating KOH. 

From mixed surfactant systems of emulsion polymerization, monodispersed latices were usually obtained at fairly low conversions with rather wide variations in emulsifier compositions (j ). Therefore, samples for the determination of the particle size distribution in this system should be taken at relatively low conversions, otherwise, monodispersed latices will be obtained due to competitive growth from all samples regardless of the surfactant ratios in the recipe of polymerization. These particles will be different in size, but not in size distribution. 

Free-radical polymerizations are carried out by a variety of processes that require different design considerations with respect to recipe of polymerization and physical conditions for the process and process equipment. Generally free-radical polymerizations are carried out by four different processes (a) bulk or mass polymerization, (b) solution polymerization, (c) suspension polymerization, and (d) emulsion polymerization. 

Volume fraction of dispersed phase q>, since it determines some essential properties, such as rheological ones. For an emulsion, the value desired can mostly be predetermined by the proportions of oil and water in the recipe. This is often different for foams, especially when made by beating the value of q> obtained then depends on several conditions (see the next section). In foams one often speaks of the overrun, i.e., the percentage increase in volume due to incorporation of gas. The relation is percentage overrun = 100

[Pg.418]

Values for the propagation rate constant can be determined from bulk or solution experiments. Values of k have been published for a wide variety of monomers as a function of temperature. With standard emulsion polymerization recipes the value of [M]p is determined from equilibrium swelling measurements if a free monomer phase is present and by a mass balance if all the monomer is in the polymer particles. One normally assumes that [M] is not dependent on particle size in latexes comprised of different-sized particles. This assumption will be questionable in some systems, especially those involving high-swelling particles. 

Unlike PIC, which requires a precast structure, PCC has the advantage that it can be cast in place for field applications. Most of the PCC composites are based on different kinds of lattices obtained especially by emulsion polymerization. A latex is a stable dispersion of fine polymer particles in water, also containing some nonpolymeric constituents used in emulsion polymerization recipe. The lattices obtained through emulsion polymerization contain small polymer particles of 0.05-5 tm. 

A key consideration in conducting polymerization is maintenance of the proper recipe or ingredient mix. In most homopolymerizations and all copolymerizations, more than a single ingredient is required in the reacting mass. For example, in some emulsion polymerizations as many as 20 different components must be fed into the reaction at controlled concentrations. 

Anionic surfactants (such as sodium dodecyl sulfate), cationic surfactants (such as cetyltrimethylammonium bromide) (163), and nonionic surfactants (such as the polyoxyethylenated alkylphenols) (136,338) have been used in preparing emulsions. Different types of surfactants can be used in the same recipe (377) to provide additional stability under specific conditions. For example, mixtures of anionic and nonionic surfactants are common. The anionic surfactant controls the particle nucleation stage, and the nonionic surfactant imparts additional electrolyte tolerance, mechanical shear stability (345), and freeze-thaw stability. Mixtures of anionic and cationic surfactants tend to coagulate and are to be avoided. 

Very little has been reported about the use of spectroscopic methods for monitoring and control of other polymerization systems. Lenzi et al. [191] reported that the NIR spectra collected in a dispersive instrument with a transflectance probe may contain very useful information about the structure of core-shell polystyrene beads produced through simultaneous semibatch emulsion/suspension polymerizations. Lenzi et al. [192] developed a polymerization technique that combines recipes of typical emulsion and suspension polymerizations to produce core-shell polymer beads. More interesting, the appearance of the core-shell structure always led to qualitatively different NIR spectra that could not have been obtained with polymer suspensions, polymer emulsions, or mixtures of polymer suspensions and emulsions. As described by Lenzi et al. [191], different spectral peaks could be detected in the wavelength region constrained between 1700 and 1900nm when the core-shell structure developed. 

Due to the complex nature of the emulsion polymerization process and the associated set of distributed and lumped equations, the control vector parameterization approach can be adopted along with the -constraint optimization technique in a multiobjective form to account for the various control objectives. Several constraints should be included to define the desired final particle size and to account for different process and recipe limitations. 

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