Antifoaming

The effect of the adsorbed surfactant-polymer complex on the rheology of the air-aqueous solution interface is easily detected by the talc particle test (Regis-mond, 1997). A small quantity of calcined talc powder is sprinkled on the surface of the aqueous solution in a 10-cm Petri dish. A gentle current of air is directed tangentially to the talc particles for 1-2 s and then removed. The observed movement is noted in the following categories fluid (F), viscous (V), gel (G) (= almost no flow), solid (S) (= no flow), and viscoelastic (VE) (= net movement, with some recovery upon removal of air current). 

The effect of interaction of sodium dodecyl sulfate with the polymer, polyvinylpyrrolidone, on the foaming of aqueous solutions of the former has been investigated by Folmer and Kronberg (2000). Depending upon the surfactant and polymer concentrations, the foaming can either be decreased or increased. Foaming increases when surface and/or bulk viscosities are increased by the surfactant-polymer concentration it decreases when surfactant-polymer interaction in the bulk phase causes desorption of them from the air-aqueous solution interface. 

When undesirable foaming of a solution cannot be reduced sufficiently by replacing the surfactant with a lower foaming one, or when the foam is caused partially or entirely by nonsurfactant components of the solution, then antifoaming agents are used to reduce the foam. Antifoaming agents act in various ways  

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Antiferromagnetism Antifoam Antifoam agents Antifoaming agents... 

Foam Control. Whereas some siUcones are known to be foam promoters, Dow Corning FS-1265 Fluid is a Hquid fluorosiUcone with effective antifoam properties. Petroleum industry appHcation of fluids and dispersions in gas—oil separators on offshore drilling platforms has been successful. Their use peaked in the early 1980s, coinciding with constrained cmde oil capacity and production. Diesel fuels are an excellent solvent for dimethyl silicones and render them ineffective as an antifoam. A new antifoam which does not require the use of added siUca is formulated from a fluorosiUcone copolymer. It has shown promise to antifoam (8) diesel fuel (see Defoamers). 

Antifoaming Agents. Foaming is a frequent problem in food manufacturing operations causing production inefficiencies. 

R, mst inhibitor O, oxidation inhibitor D, detergent—dispersant VI, viscosity-index improver P, pour-point depressant W, antiwear EP, extreme pressure F, antifoam and M, friction modifier. 

Questions and Answers Water-Based Antifoams, Nalco Chemical Co., Oak Brook, lU., 1983. 

Phosphoms trichloride is also used in the manufacture of antifoam agents, catalysts, dyes and pigments, as well as pharmaceutical and quaternary compounds, and is commonly used as a chlorinating agent. Phosphoms trichloride is used to make phosphoms oxychloride, which is used in the manufacture of adsorbents for air filters, antifoam agents, dyes and pigments, mineral-processing materials, pharmaceuticals (qv), and solvents. These uses represented 32,000 t of PCl in 1988 and 30,000 t in 1994. 

Many of the unique properties of siUcone oils are associated with the surface effects of dimethylsiloxanes, eg, imparting water repeUency to fabrics, antifoaming agents, release liners for adhesive labels, and a variety of poHshes and waxes (343). Dimethylsilicone oils can spread onto many soHd and Hquid surfaces to form films of molecular dimensions (344,345). This phenomenon is greatly affected by even small changes in the chemical stmcture of siloxane in the siloxane polymer. Increasing the size of the alkyl substituent from methyl to ethyl dramatically reduces the film-forming abiUty of the polymer (346). The phenyl-substituted siUcones are spread onto water or soHd surfaces more slowly than PDMS (347). 

Quahty control testing of siUcones utilizes a combination of physical and chemical measurements to ensure satisfactory product performance and processibihty. Eor example, in addition to the usual physical properties of cured elastomers, the plasticity of heat-cured mbber and the extmsion rate of TVR elastomers under standard conditions are important to the customer. Where the siUcone appHcation involves surface activity, a use test is frequently the only rehable indicator of performance. Eor example, the performance of an antifoaming agent can be tested by measuring the foam reduction when the sihcone emulsion is added to an agitated standard detergent solution. The product data sheets and technical bulletins from commercial siUcone producers can be consulted for more information. 

Other U.S. regulatory clearances for sorbic acid allow its use as an antimicotic in the manufacture of food packaging materials (159), as a pesticide adjuvant when appHed to growing crops (160), and with methylceUulose and dimethylpolysiloxane as an antifoaming agent (161). 

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