Water beads produced

Many water-soluble vinyl monomers may be polymerized by the emulsion polymerization technique. This technique, which differs from suspension polymerization in the size of the suspended particles and in mechanism, is widely used for the production of a number of commercial plastics and elastomers. While the particles in the suspension range from 10 to 1000 nm, those in the emulsion process range from 0.05 to 5 nm in diameter. The small beads produced in the suspension process may be separated by filtering, but the latex produced in emulsion polymerization is a stable system in which the charged particles cannot be recovered by ordinary separation procedures. 

Features Thermoplastic small, glossy, spherical beads produces adhesive films which are clear, glossy, nontoxic, and water resist. resist, to attack by weak acids, alkalis, salts modified to obtain sol. in alkaline systems PVAL protection... 

FIGURE 1.7 The waxy coating on the surface cuticle of many leaves and flowers produces a hydrophobic surface. Water beads on the surface and runs off easily. 

To reduce the amount of dust produced, water can be added to the abrasive from a circular water sprayer around the no22le. Chemical corrosion inhibitors must be dissolved in the water to prevent flash msting of the steel. Newer methods to reduce dust include the use of ice, soHd carbon dioxide (dry ice), or plastic beads as abrasives. Blasting with dry ice is inexpensive and effective, but the accumulation of carbon dioxide must be avoided in enclosures. Plastic beads are inexpensive, but the cutting efficiency is low and paint removal is slow the beads can be cleaned of paint particles and reused. 

Packed Tubes Cocurrent flow of immiscible hquids through a packed tube produces a one-stage contact, characteristic of hne mixers. For flow of isobutanol-water through a 0.5-in diameter tube packed with 6 in of 3-mm glass beads, Leacock and Churchill [Am. Jn.st. Chem. Eng. J., 7, 196 (1961)] find... 

Suspension polymerization produces beads of plastic for styrene, methyl methacrviaie. viny l chloride, and vinyl acetate production. The monomer, in which the catalyst must be soluble, is maintained in droplet fonn suspended in water by agitation in the presence of a stabilizer such as gelatin each droplet of monomer undergoes bulk polymerization. In emulsion polymerization, ihe monomer is dispersed in water by means of a surfactant to form tiny particles held in suspension I micellcsK The monomer enters the hydrocarbon part of the micelles for polymerization by a... 

Suspension polymerization of water-insoluble monomers (e.g., styrene and divinylbenzene) involves the formation of an oil droplet suspension of the monomer in water with direct conversions of individual monomer droplets into the corresponding polymer beads. Preparation of beaded polymers from water-soluble monomers (e.g., acrylamide) is similar, except that an aqueous solution of monomers is dispersed in oil to form a water-in-oil (w/o) droplet suspension. Subsequent polymerization of the monomer droplets produces the corresponding swollen hydrophilic polyacrylamide beads. These processes are often referred to as inverse suspension polymerization. 

Beaded polymeric supports are produced by a two-phase suspension polymerization in which microdrops of a monomer solution are directly converted to the corresponding microbeads. The size of a microdroplet is usually determined by a number of interrelated manufacturing parameters, which include the reactor design, the rate of stirring, the ratio of the monomer phase to water, the viscosity of both phases, and the type and concentration of the droplet stabilizer. 

Because most widely used methods used to prepare classical styrene/divinylben-zene copolymers have always been based on suspension polymerization, it seemed logical that a series of porous PDVB gels using similar methodologies could be developed. In suspension polymerization, divinylbenzene is suspended as a dispersion of small droplets in a continuous phase of water and polymerized by classical free radical initiation. This process produces the spherical beads... 

Figure 12-5. The Lummus Crest Inc. process for producing polystyrene " (1) reactor, (2) holding tank (Polystyrene beads and water), (3) centrifuge, (4) pneumatic drier, (5) conditioning tank, (6) screening of beads, (7,8) lubrication and blending, (9) shipping product.

When the mesophase pitch is heated, tiny spherical beads having a radial orientation of the graphite embryo form and grows in the mother pitch. When the size of the beads in the pitch reaches an appropriate size (10-30 pm), the pitch is cooled down and the beads can be collected by dissolving the pitch matrix with an appropriate solvent. The beads are then heat-treated in an oxygen/water gas mixture to produce the protective skin, as for the MCF, and then graphitized, as depicted in Figure 10. 

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