Silicone surfactants antifoams

Production of Silicone Surfactants and Antifoam Compounds in Detergents... 

The unique properties of silicones make them ideal for formulating high-performance, versatile antifoam compounds. New modifications of silicone surfactants will continue to be developed. They will be optimized for particular functionality in detergent formulations. 

Whilst the migration of PDMS to liquid-air or liquid-liquid interfaces is well known and exploited commo cially in silicone antifoams and silicone surfactants , there is growing interest in the migration of sUoxane copolymers to solid interfaces which will be the focus of this review. 

At present, the most effective and versatile chemical antifoamers are mixtures. In fact, modem commercial formulations often contain mixtures of silicone oils, silicone surfactants or silica gels, with possibly two or more types of dispersed hydrophobic aggregates (with sizes around 1 micron, specific gravity 1.0-1.3, with rough fractal shapes). These mixed-type antifoamers are very effective at low concentrations (10-1000 ppm) and are widely used. The (hydrophobic) particles may be hydrophobized silica or glass and are often referred to as the activator, with the hydrocarbon or poly-dimethylsiloxane (PDMS) liquid or oil being referred to as the carrier. However, less expensive single-system antifoamers are commonly used, and these exist in many different forms such as soluble liquids, insoluble... 

Disperse the titanium dioxide 2190 ( Ex Kronos) in Orotan 165 (Rohm Haas, anionic dispersant) and Disperse Ayd W22 (Daniel Products, surfactant), with water as carrier. Antifoam (Byk 035 from Byk Chemie) and flash rust inhibitor (Emadox NA from Labema) are added. When dispersed, add the pigment paste to the let down mix. Add butyl benzyl phthalate plasticiser and Dehydran 1293 (modified polysiloxane defoamer from Henkel, to reduce foam formation on application) and mix well. Adjust viscosity with water. Neocryl A633 is a 42%nvc acrylic/styrene dispersion from Zeneca. Silwet L-77 (Osi) is a nonionic silicone surfactant to improve wetting. 

The theories of antifoam action are complex. Typical antifoam agents for silicone surfactants contain a silicone polymer and finely powdered silica [169]. A low surface tension of an antifoam agent, lower than that of the surfactant solution, is a necessary but insufficient condition. A siloxane surfactant solution cannot be defoamed by conventional siloxane antifoaming agents but is readily defoamed by an antifoam agent based on poly(methyl-3,3,4,4,5,5,6,6,6-nonafluo-rohexylsiloxane), [ CH3[CF3(CF2)3(CH2)2]SiO ], which has a low surface ten-... 

Approximately 70,000 tons of silicone polymers are produced each year In the United States. Silicones are used as greases, caulking, gaskets, biomedical devices, cosmetics, surfactants, antifoaming agents, hydraulic fluids, and water repellents. 

Intensive investigations have shown that specific silica-silicone mixtures or paraffin oil systems are considerably more universal in their applicability and that their effectiveness is independent of both water hardness and the nature of the surfactant-builder system employed [31-33]. Therefore, most heavy-duty detergents in Europe have silicone oil and/or paraffins as foam depressors. Soap has almost lost its importance as a foam regulator. Silica-silicone systems, frequently called silicone antifoams, are usually commercially available as concentrated powders. The key silicone oils used for antifoams are dimethylpolysiloxanes. 

Although silicone oils by themselves or hydrophobic particles (e.g., specially treated silica) are effective antifoams, combinations of silicone oils with hydrophobic silica particles are most effective and commonly used. The mechanism of film destruction has been studied with the use of surface and interfacial tensions, measurements, contact angles, oil-spreading rates, and globule-entering characteristics for PDMS-based antifoams in a variety of surfactant solutions.490 A very recent study of the effect of surfactant composition and structure on foam-control performance has been reported.380 The science and technology of silicone antifoams have recently been reviewed.491... 

Foam Control. Fermentations tend to froth because metabolites have surfactant properties. Prevention commonly is by addition of antifoam agents such as oils, heavy alcohols, fatty acids, or silicones. High-speed rotating impellers destroy bubbles by direct impact and by throwing them against the wall of the vessel. 

The most widely used in foam control are special materials called antifoams. They could be fats, oils, waxes, fatty alcohols and acids, ethers, organic compounds containing nitrogen and sulphur (alkylamines and amides, sulphides, thioethers, etc.), phosphorus organic compounds (in particular, tributylphosphate), silicon-organic compounds (silicon oils) and some non-ionic surfactants [e.g. 4,5]. 

The possibility to use Cm as a parameter characterising foam inhibition has been demonstrated for the first time in [60]. It was shown that the increase in the concentration of silicon oil Caf (antifoam) led to increase in Cm- That is why it was proposed to used the ratio Caf/Cm as a quantitative measure of the defoaming ability. However, it should be noted that the silicon oil concentrations at which inhibition of black spot formation was observed, were very low (10 5-10 9 %). For that reason it is difficult to conclude definitely whether the system was a real solution or represented a diluted emulsion of the antifoam in the surfactant solution. 

More convenient objects for the study of Cm(Caf) dependence have been found to be the low molecular compounds with relatively good solubility (compared to the silicon oil), for example, fatty alcohols, acids and hydrocarbons [48,55]. The experiments commented below were performed with these antifoams. First of all the Cm of films in the absence of an antifoam was determined by gradually increasing the surfactant concentration. Then small doses of the antifoam were introduced in a solution with surfactant concentration slightly above Cm, until the formation of black spots became impossible. At the same time the concentration of antifoam saturation in the solution was fixed. Table 9.2 presents the antifoam concentrations at which black spot formation in microscopic foam films is inhibited. 

FIGURE 5.64 Consecutive cycles of exhaustion and reactivation of mixed oU-silica compound in 10mM solution of the anionic surfactant sodium dioctyl-sulfosuccinate (AOT). An initially active antifoam (defoaming time 5 s) gradually loses its activity with the number of foam formation/destruction cycles in a standard shake test. The introduction of silicone oil results in a perfect restoration of the antifoam activity. Five exhaustion curves (indicated by roman numbers the symbols indicate the experimentally measured defoaming time) and the corresponding four reactivation events (the vertical dashed lines) are shown. (Adapted from Denkov et ah, Langmuir, 16, 2525, 2000.)... 

Fluid. [Dow Coming] Silicone fluid liq. dielectric, coolant antifoam, surfactant release agent water repellent for persond care prods., food pkg. and processing, release of acrylics, phendics and urethanes. 

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