Surfactants, emulsion process

The emulsion process can be modified for the continuous production of latex. One such process (68) uses two stirred-tank reactors in series, followed by insulated hold-tanks. During continuous operation, 60% of the monomers are continuously charged to the first reactor with the remainder going into the second reactor. Surfactant is added only to the first reactor. The residence time is 2.5 h for the first reactor where the temperature is maintained at 65°C for 92% conversion. The second reactor is held at 68°C for a residence time of 2 h and conversion of 95%. 

A less rigid pavement can be created by blending an asphalt-water-surfactant emulsion with the upper soil layers. During the curing process, the asphalt-water emulsion deteriorates, leaving the asphalt to bind the hydrocarbon contaminants and soil to create a low-permeability pavement. Asphalt-soil pavements tend to be less rigid than pozzolanic-soil structures. 

Since relatively stable macroradicals are produced in the emulsion process, the termination rate decreases and a high molecular weight product is rapidly produced. It is customary to use a water-soluble initiator such as potassium persulfate and an anionic surfactant... 

The section on suspension polymerization indicated the differentiation between suspension and emulsion (or latex) polymerizations. Emulsion polymers usually are formed with the initiator in the aqueous phase, in the presence of surfactants, and with polymer particles of colloidal dimensions, i.e., on the order of 0.1 gm in diameter [17]. Generally, the molecular weights of the polymers produced by an emulsion process are substantially greater than those produced by bulk or suspension polymerizations. The rate of polymer production is also higher. As a large quantity of water is usually present, temperature control is often simple. 

Figure 11.15 Copper extraction by a liquid emulsion membrane process [52]. Feed, 200 ml, pH 2.0, 300 ppm Cu2+ membrane, 15 mL LIX 64N in kerosene, 3% Span 80 stripping solution, 15 mL H2S04. Reprinted from J. Membr. Sci. 6, W. Volkel, W. Halwachs and K. SchUgerl, Copper Extraction by Means of a Liquid Surfactant Membrane Process, p. 19, Copyright 1980, with permission from Elsevier...

A third type of emulsion process is the so-called microemulsion [123]. In microemulsions, the polymerization starts in droplets as well. However, these are thermodynamically stable and, in contrast to miniemulsions, they form spontaneously by gentle stirring. They consist of large amounts of surfactants or mixtures of them, and they possess an interfacial tension close to zero at the water/oil interface, with droplet sizes usually ranging between 5 and 50 nm. In... 

The major emulsion processes include the copolymerization of styrene and butadiene to form SBR rubber, polymerization of chloroprene (Fig. t -4) to produce neoprene rubbers, and the synthesis of latex paints and adhesives based mainly on vinyl acetate and acrylic copolymers. The product is either used directly in emulsion form as a paint or else the surfactants used in the polymerization are left in the final, coagulated rubber product. 

Kataoka T and Nishiki T. Development of a continuous electric coalescer of W/O emulsions in Uquid surfactant membrane process. Sep Sci Technol 1990 25 171-185. 

Emulsion polymerization is an important commercial process because, in contrast to the same free-radical polymerization performed in the bulk, molecular weight and reaction rate can be increased simultaneously (1-3). Furthermore, the lower viscosity of an emulsion system compared with that of the corresponding bulk process provides better control over heat transfer. Commercial emulsion processes usually use a surfactant/water/monomer system... 

One of the earliest uses of power ultrasound in processing was in emulsification. If a bubble collapses near the phase boundary of two immiscible liquids, the resultant shock wave can provide a very efficient mixing of the layers. Stable emulsions generated with ultrasound have been used in the textile, cosmetic, pharmaceutical, and food industries. Such emulsions are often more stable than those produced conventionally and often require little, if any, surfactant. Emulsions with smaller droplet sizes within a narrow size distribution are obtained when compared to other methods. 

PTFE is produced by free-radical polymerization mechanism in an aqueous media via addition polymerization of tetrafluoroethylene in a batch process. The initiator for the polymerization is usually a water-soluble peroxide, such as ammonium persulfate or disuccinic peroxide. A redox catalyst is used for low temperature polymerization. PTFE is produced by suspension (or slurry) polymerization without a surfactant to obtain granular resins or with a perfluori-nated surfactant emulsion polymerization) to produce fine powder and dispersion products. Polymerization temperature and pressure usually range from 0 to 100°C and 0.7 to 3.5 MPa. 

Kataoka, T. and Nishiki, T. (1990). Development ofa continuous electric coalescer of w/o emulsions in hquid surfactant membrane process. Sep. Sci. Technol., 25, 171-85. 

Surfactants or emulsifiers play an important role in the emulsion process. They are composed of ionic hydrophilic end and a long hydrophobic chain. Examples are ... 

Much of the work in this area has been done in emulsions having a droplet size of more than 1 pm, and the application of submicron (nano) emulsions in encapsulation of oils and flavors is relatively new in the literature. Some works have been carried out to determine the influence of submicron emulsions produced by different emulsification methods on encapsulation efficiency and to investigate the encapsulated powder properties after SD for different emulsion droplet sizes and surfactants. The process has been referred to as nanoparticle encapsulation since a core material in nanosize range is encapsulated into a matrix of micron-sized powder particles (Jafari et al., 2008). This area of research is developing. Some patents were filed in the past describing microemulsion formulations applied to flavor protection (Chung et al., 1994 Chmiel et al., 1997) and applications in flavored carbonated beverages (Wolf and Havekotte, 1989). However, there is no clear evidence on how submicron or nanoemulsions can improve the encapsulation efficiency and stability of food flavors and oils into spray-dried powders. 

HMIS Health 1, Flammability 1, Reactivity 0 Uses Perfumery surfactants lubricant for plastics processing resins antifoam food additive intermediate in mfg. of food additives surfactant, emulsion stabilizer, emulsifier, emollient, stiffener, astringent in pharmaceuticals cosolvent emulsifier, thickener, emollient, emulsion stabilizer, opacifier, vise, control agent in cosmetics in food-pkg. adhesives in food-contact coatings defoamer in food-contact coatings and paper/paperboard in cellophane for food pkg. food-contact textiles... 

Oleth-30 Oleth-80 surfactant, textile detergents Potassium oleate surfactant, textile dyeing PEG-2 hydrogenated tallowamine surfactant, textile emulsions Disodium nonoxynol-10 sulfosuccinate surfactant, textile finishing PEG-16 sorbitan tristearate surfactant, textile processing aids PEG-8 isostearate surfactant, textile scouring PEG stearate TEA-dodecylbenzenesulfonate surfactant, textile softeners Lauramine oxide... 

The process reduces the viscosity by addition of solvents, especially methanol, which stabilizes the bio-products. During the emulsion process, through the addition of surfactants, it permits the formation of micro-emulsions and stabiUzes the bioproducts, and facilitates its transport. 

The two-emulsion (reverse) method has been used recently by Lee etal, [185] in an attempt to synthesize spherical zirconia particles under controlled conditions. In the overall scheme, a non-ionic surfactant (Span 85, Span 80, Span 40 or Arlacel 83, i.e. Sorbitan sesquioleate see below for the choice of surfactant) was dissolved in n-heptane. The HLB values of the surfactants varied in the range 1.8-6.7. Aqueous solutions of zirconium acetate or ammonia were added to two parts of the surfactant-oil phase combination the two had identical volumes. Reverse emulsions were prepared by subjecting the above to ultrasonic agitation, and the two emulsions thus produced were then mixed under stirring. The gel particles that formed in the process were separated by using a modified Dean-Stark moisture trap. Figure 4.4 presents the two-emulsion process in which the two complementary emulsions are mixed to obtain gel precipitates in the spherical droplets. 

Micro-emulsion is another variant of emulsion polymerisation. Such emulsions are thermodynamically stable systems including swollen monomer micelles dispersed in a continuous phase. In general, they require fairly large concentrations of surfactants to be produced compared with the other dispersed polymerisation systems. Hence, the interfacial tension of the oil/water is generally close to zero. Polymers with ultra-high molecular weight, i.e. above 10 g/mol, can be obtained, as can copolymers with a very well-defined, homogenous composition. Whereas polymerisation can take 24-48 h in the normal emulsion process, it proceeds at a fast rate in micro-emulsion, as total conversion can be obtained in less than 30 min. Polymer particles of very small size (diameter < 100 nm) and narrow distribution can be obtained by this process. 

The emulsion process allows the production of particles with a diameter in the nanometer range (10-10 nm). The monomer is dispersed in water with a water-soluble initiator and a surfactant which forms uniform micelles. Polymerization occurs inside micelles, in which the monomer is able to diffuse, because the initiator is not miscible in the dispersed monomer phase. 

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