Foaming and Antifoaming Agents

An important group of foaming agents which differ in their mode of action from surfactants are certain proteins. In this case soluble proteins are irreversibly denatured on adsorption and agitation. They become insoluble and form multi-molecular, rigid, surface layers which produce very long-lasting foams. Indeed many of the foams familiar in the kitchen are of this type, examples are beaten egg-white, whipped cream, and mousse. 

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The present review deals with the characterization of model protein foams and foams of various cultivation media. The suppression of foaming by antifoam agents and their effect on the oxygen transfer rate, microbial cell growth and product formation are discussed. The influence of process variables on the recovery of proteins by flotation without and with surfactants and mathematical models for protein flotation are presented. The effect of cultivation conditions, flotation equipment and operational parameters on foam flotation of microorganisms is reviewed. Floatable and non-floatable microorganisms are characterized by their surface envelope properties. A mathematical model for cell recovery by flotation is presented. Possible application areas of cell recovery by flotation are discussed. 

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. 

Boiler water foaming and frothing is undesirable because it contributes to overheating, carryover, and loss of operational control. As a result, antifoam and defoamer products are commonly employed in BW treatment programs. The same active ingredients are also widely used in all types of industrial processes (industrial grades), as well as in cosmetic, food, potable water, and kosher applications (all agents typically are odorless, colorless, and tasteless). 

In addition, even where foaming is not a specific problem in a boiler, carryover may occur, especially in lower pressure boilers with very high TDS (i.e., over 10,000 to 15,000 ppm TDS) because of the collapse of surface bubbles. This leads to BW aerosol generation and entrainment of the spray in steam. Under these circumstances, antifoam agents such as polyamides are useful in preventing these entrainment problems. Furthermore, the antifoaming action of polyamides is often enhanced by protective colloid materials such as tannins, and consequently, formulations containing polyamide emulsions in an alkaline tannin base are available. 

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