Emulsifier transfer

Emulsion Process. The emulsion polymerization process utilizes water as a continuous phase with the reactants suspended as microscopic particles. This low viscosity system allows facile mixing and heat transfer for control purposes. An emulsifier is generally employed to stabilize the water insoluble monomers and other reactants, and to prevent reactor fouling. With SAN the system is composed of water, monomers, chain-transfer agents for molecular weight control, emulsifiers, and initiators. Both batch and semibatch processes are employed. Copolymerization is normally carried out at 60 to 100°C to conversions of - 97%. Lower temperature polymerization can be achieved with redox-initiator systems (51). 

In addition to the monomers, the polymerization ingredients include an emulsifier, a polymerization initiator, and usually a chain-transfer agent for molecular weight control. 

Aqueous media, such as emulsion, suspension, and dispersion polymerization, are by far the most widely used in the acryUc fiber industry. Water acts as a convenient heat-transfer and cooling medium and the polymer is easily recovered by filtration or centrifugation. Fiber producers that use aqueous solutions of thiocyanate or zinc chloride as the solvent for the polymer have an additional benefit. In such cases the reaction medium can be converted directiy to dope to save the costs of polymer recovery. Aqueous emulsions are less common. This type of process is used primarily for modacryUc compositions, such as Dynel. Even in such processes the emulsifier is used at very low levels, giving a polymerization medium with characteristics of both a suspension and a tme emulsion. 

Aqueous emulsion polymerization is carried out using a fluorinated emulsifier, a chain-transfer agent to control molecular weight, and dispersion stabilizers such as manganic acid salts and ammonium oxalate (13,14). 

Tetiafluoioethylene—peifluoiopiopyl vinyl ethei copolymeis [26655-00-5] aie made in aqueous (1,2) oi nonaqueous media (3). In aqueous copolymerizations water-soluble initiators and a perfluorinated emulsifying agent are used. Molecular weight and molecular weight distribution are controlled by a chain-transfer agent. Sometimes a second phase is added to the reaction medium to improve the distribution of the vinyl ether in the poljmier (11) a buffer is also added. 

Basic Components. The principal components in emulsion polymerization are deionized water, monomer, initiator, emulsifier, buffer, and chain-transfer agent. A typical formula consists of 20—60% monomer, 2—10 wt % emulsifier on monomer, 0.1—1.0 wt % initiator on monomer, 0.1—1.0 wt % chain-transfer agent on monomer, various small amounts of buffers and bacteria control agents, and the balance deionized water. 

Chain transfer also occurs to the emulsifying agents, leading to their permanent iacorporation iato the product. Chain transfer to aldehydes, which may be formed as a result of the hydrolysis of the vinyl acetate monomer, tends to lower the molecular weight and slow the polymerisation rate because of the lower activity of the radical that is formed. Thus, the presence of acetaldehyde condensates as a poly(vinyl alcohol) impurity strongly retards polymerisation (91). Some of the initiators such as lauryl peroxide are also chain-transfer agents and lower the molecular weight of the product. 

Other additives that may be incorporated include sodium hydrogen phosphates as buffering agents to stabilise that pH of the reaction medium, lauryl mercaptan or trichlorethylene as chain transfer agents to control molecular weight, a lubricant such as stearic acid and small amounts of an emulsifier such as sodium lauryl sulphate. 

The function of emulsifier in the emulsion polymerization process may be summarized as follows [45] (1) the insolubilized part of the monomer is dispersed and stabilized within the water phase in the form of fine droplets, (2) a part of monomer is taken into the micel structure by solubilization, (3) the forming latex particles are protected from the coagulation by the adsorption of monomer onto the surface of the particles, (4) the emulsifier makes it easier the solubilize the oligomeric chains within the micelles, (5) the emulsifier catalyzes the initiation reaction, and (6) it may act as a transfer agent or retarder leading to chemical binding of emulsifier molecules to the polymer. 

Each cell in the extraction system presented in Fig. 122 is called a mixer-settler extractor and is made up of two parts. The role of the first part, the mixer, is to emulsify the incoming aqueous and organic phases and to transfer the emulsion to the second part of the extractor-settler cell. The purpose of the settler is to stratify the phases and enable the separation of the two liquids. 

Class QBlending Dissolving Suspending Solids GCaoking Emulsifying Heat Transfer Gas Dl sp ersion... 

A colloidal dispersion of oil-in-water. In BW systems where oil contamination has occurred, emulsifying agents from the oil can produce an emulsion which further adds to the total foulant load and impedes heat-transfer. Specific organic emulsifiers have both hydrophilic (water loving) and lipophilic (oil loving) groups in the same molecule. 

FIGURE 7.7 (See color insert) Adoptively transferred D011.10 transgenicT cells can be identified by expression of CD4+ and KJ-126 in spleen cell suspension from Balb/c mice after ovalbumin (OVA) immunization. Balb/c mice were injected iv with D011.10 spleen cells containing 3-5 x 1 06CD4+KJ-126+ cells and immunized by intraperitoneal injection of 2 mg OVA emulsified in complete Freund s adjuvant 2 days later. OVA immunization increases the frequency of KJ+T cells and alters the expression of various surface molecules consistent with T cell (Tc) activation. 

The solution is then transferred into the coupling vessel equipped with a mechanical stirrer and, possibly in the presence of a surfactant, precipitated with acetic acid, hydrochloric acid, or phosphoric acid. The coupling component may also be precipitated indirectly i.e., the appropriate mixture of acid and emulsifier is filled into the kettle first and the alkaline solution of the coupling component is then added gradually to the clear solution by gravity flow. The clarified solution of the diazonium compound is then introduced into or onto this coupling suspension. 

N. Garti, S. Magdassi, and D. WhitehUl Transfer Phenomena Across the Oil Phase in Water-Oil-Water Multiple Emulsions Evaluated hy Coulter Counter 1. Effect of Emulsifier 1 on Water Permeahihty. J. CoUoid Interface Sci. 104,587 (1985). 

P. Colinart, S. Delepine, G. Trouve, and H. Renon Water Transfer in Emulsified Liquid Membrane Processes. J. Membr. Sci. 20,167 (1984). 

Polymers may be made by four different experimental techniques bulk, solution, suspension, and emulsion processes. They are somewhat self-explanatory. In bulk polymerization only the monomers and a small amount of catalyst is present. No separation processes are necessary and the only impurity in the final product is monomer. But heat transfer is a problem as the polymer becomes viscous. In solution polymerization the solvent dissipates the heat better, but it must be removed later and care must be used in choosing the proper solvent so it does not act as a chain transfer agent. In suspension polymerization the monomer and catalyst are suspended as droplets in a continuous phase such as water by continuous agitation. Finally, emulsion polymerization uses an emulsifying agent such as soap, which forms micelles where the polymerization takes place. 

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