Water soluble polymer emulsifiers

When an emulsifier is used, its type and concentration primarily affects the number of latex particles formed, which in turn determines the rate of polymerization and, depending also on the rate of initiation, the molecular weight of the polymer formed. Although the physical properties of the polymer are primarily dependent on its molecular waght and molecular weight distribution, the properties of the latex depend on its concentration, average particle size, particle size distribution, and the viscosity of the aqueous phase, which may be enhanced by addition of a thickener—a water-soluble polymer not adsorbed by the polymer phase which does not affect the course of the reaction,... 

Emulsifier/stabilizer systems are normally used to make stable food emulsions. Thus, lecithin is generally not called on to handle the entire emulsification, but it works in combination with other emulsifiers and stabilizing polymers such as proteins, starches, and gums (31). Lecithin will break up (emulsify) the particles, and a stabilizer (water-soluble polymer, etc.) will hold the particles in a dispersed orientation when a stable emulsion is formed. 

Emulsion polymerization typically refers to the polymerization of a nonaqueous material in water. The polymerization of a water-soluble material in a nonaqueous continuum has been called inverse emulsion polymerization. The inverse emulsion polymerization technique is used to synthesize a wide range of polymers for a variety of applications such as wall paper adhesive, waste water fiocculant, additives for oil recovery fluids, and retention aids. The emulsion polymerization technique involves water-soluble polymer, usually in aqueous solution, emulsified in continuous oil phase using water in oil emulsifier. The inverse emulsion is polymerized using an oil- or water-soluble initiator. The product is a colloidal dispersion of sub-microscopic particles with particle size ranging from 0.05 to 0.3 pm. The typical water-soluble monomers used are sodium p-vinyl benzene sulfonate, sodium vinyl sulfonate, 2-sulfo ethyl acrylate, acrylic acid, and acrylamide. The preferred emulsifiers are Sorbitan monostearate and the oil phase is xylene. The proposed kinetics involve initiation in polymer swollen micelles, which results in the production of high molecular weight colloidal dispersion of water-swollen polymer particles in oil. 

In most cases, anionic water-soluble polymers such as poly(styrene-maleic anhydride), polyacrylic acid, etc., are apphed. These kinds of emulsifiers can influence the microcapsule preparation, mean particle size, and particle size distribution. By emulsification, an electric double layer generates on the dispersed phase. Then the electrostatic interactions between the protonated amino resin prepolymer and the negatively charged orgaific phase can act as a driving force, which enable the wall material polycondensate on the surface of the oil droplets but not throughout the whole water phase. ... 

Table 1.3 shows, for example, the surface tension of the solutions of some water-soluble polymers at 25°C (0.1% aqueous solutions of the polymers). Hydroxypropylcellulose (HPC) is a good example of a surface-active polymer. Water solutions greatly reduced surface and interfacial tensions. HPC functions as an assistant in both emulsifying and whipping. HPC combines organic solvent solubility, thermoplasticity and surface activity with the aqueous thickening and stabilizing properties of other water soluble cellulose pol miers. 

In contrast to these oil-in-water emulsions, it is possible that the emulsion polymerization can also be carried out with inverse emulsions. Inverse (water-in-oil) emulsion polymerization in which an aqueous solution of a water miscible hydrophilic monomer such as acrylamide, acrylic add, or methacrylic acid is dispersed in a continuous hydrophobic oil phase with the aid of a water-in-oil emulsifier such as sorbitan mono-oleate or -stearate. The emulsifier is ordinarily above the CMC. Polymerization can be initiated with either oil-soluble or water-soluble initiators. If an oil-soluble initiator is used, the system is an almost exact mirror-image of a conventional emulsion polymerization system. The final latex is a colloidal dispersion of submicroscopic, water-swollen particles in oil. This type of emulsion pol3unerization enables the preparation of high molecular weights water-soluble polymers at rapid reaction rates. It is also possible that the water-swollen polymer particles produced by this emulsion pol)nnerization transfer to aqueous phase rapidly by inversion of the latex. 

Polymers that themselves have substantial interfacial activity, such as synthetic hydro-phobically modified water-soluble polymers (HM-P) or natural proteins, acting alone (see Chapter 3) or, more especially, in concert with conventional surfactants, constitute a much more complicated, if very interesting, case. (See Chapter 4.) Although instances of such combined use may be found in the literature, this branch of emulsion science must still be regarded as relatively new and often empirical in the case of HM-P. On the other hand, as proteins, in combination with selected surfactants, have been a traditional emulsifier system for edible emulsions, their behavior at the oil/water interface with selected surfactants has been extensively studied. This area is rather specialized and the interested reader is referred to published treatises on the subject (62,63), and also to general technical literature in the field of latex paints. 

Initially, this chapter will begin with a description of the major factors influencing the formation, physicochemical properties, and stability of oil-in-water emulsions, as this will facilitate the understanding of the influence of water soluble polymers on emulsion characteristics. The physicochemical basis of the surface activity and film forming properties of water soluble polymers will then be covered. Finally, the characteristics of some of the most important water soluble polymers used as emulsifiers in the food industry will be discussed. 

The quality of the final encapsulated lipid powder depends on a number of factors including, the amount of Hpid encapsulated, the fraction of lipid exposed to the environment, the long-term chemical stability of the lipid, the flowability of the powder, the dispersibility of the powder, etc. These parameters can be controlled by selecting appropriate concentrations and types of components to make up the initial emulsion, as well as appropriate operating parameters for the spray dryer (e.g. flow rates, inlet, and outlet temperatures). Water soluble polymers (such as proteins and polysaccharides) are often used as emulsifiers to stabilize oil-in-water emulsions prior to spray drying, and after re-dispersion of the dried powder into liquid. Alternatively, water soluble polymers may make up part of the wall material that helps encapsulate and protect the lipid in the powder during storage. 

Common water soluble polymers used as emulsifiers in foods... 

Polymerizations of Methyl /r-Styrenesulfonate (MSS, 3). A batch emulsifier-free polymerization of MSS, VBC and styrene (25 25 50 wt %) gave a viscous dispersion that would not pass through a cotton plug. Reaction with trimethylamine did not reduce the viscosity, which was probably due to water-soluble polymer. 

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