Defoamer breaker

Defoamers (foam breakers) destroy foams that have already occurred. 

In many applications we want to prevent the formation of foam or get rid of already existing foam (see, for example, Table 11.1). Usually chemicals are added to achieve this (see Ref. [564] for an introduction). We distinguish between antifoamers and defoamers. An-tifoamers are added to the liquid prior to foam formation and act to prevent or inhibit foam formation. Defoamers or foam breakers are added to eliminate existing foam. They can only reach the outer surface of a foam. 

Chemical Defoamers The addition of chemical foam breakers is the most elegant way to break a foam. Effective defoamers cause very rapid disintegration of the foam and frequently need be present only in parts per million. The great diversity of compounds used for defoamers and the many different systems in which they are applied make a brief and orderly discussion of their selection difficult. Compounds needed to break aqueous foams may be different from those needed for aqueous-free systems. The majority of defoamers are insoluble or nonmiscible in the foam continuous phase, but some work best because of their ready solubility. Lichtman (Defoamers, 3d ed., Wiley, New York, 1979) has presented a concise summary of the application and use of defoamers. Rubel (Antifoaming and Defoaming... 

Although many factors, such as film thickness and adsorption behaviour, have to be taken into account, the ability of a surfactant to reduce surface tension and contribute to surface elasticity are among the most important features of foam stabilization (see Section 5.4.2). The relation between Marangoni surface elasticity and foam stability [201,204,305,443] partially explains why some surfactants will act to promote foaming while others reduce foam stability (foam breakers or defoamers), and still others prevent foam formation in the first place (foam preventatives, foam inhibitors). Continued research into the dynamic physical properties of thin-liquid films and bubble surfaces is necessary to more fully understand foaming behaviour. Schramm et al. [306] discuss some of the factors that must be considered in the selection of practical foam-forming surfactants for industrial processes. 

Not all foams are wanted though. Foams, other than flotation froths, are generally not wanted in the process industries where they tend to interfere with process unit operations and may cause upsets. Some agents will act to reduce the foam stability of a system (termed foam-breakers or defoamers) while others can prevent foam formation in the first place (foam preventatives, foam inhibitors). There are many such agents and Kerner [327] describes several hundred different formulations for foam... 

Any substance that acts to reduce the stability of a foam it can also act to prevent foam formation. Terms such as antifoamer or foam inhibitor specify the prevention of foaming, and terms such as defoamer or foam breaker specify the reduction or elimination of foam stability. Example Poly(dimethylsiloxane)s, (CH3)3SiO[(CH3)2SiO]xR, where R represents any of a number of organic functional groups. Antifoamers can act by any of a number of mechanisms. 

Bubreak. [Buckman Labs] Defoamers and emulsion breakers. 

ClarUI lypure] Polymns, defoam-eis, eiruilsion breakers, fioihers, drying aids. 

Foam Breaker Any agent that reduces or eliminates foam stability. Also termed defoamer, but a more general term is Antifoaming Agent. 

Properties vary considerably, depending on the lengths and arrangements of these blocks. The block copolymers comprise unique and valuable surface-active agents. They can act as breakers for water-in-oil emulsions, as defoamers, and as wetting and dispersing agents. 

Bubble Breaker 259,260,613-M, 622, 730,737,746,748, 900,913,917 defoamer, aq. pigmented coatings Antibubble DF-181 defoamer, aq. pigmented dispersions Antibubble DF-181 defoamer, aq. pigmented systems TEGO Foamex 822 defoamer, aq. pigments Antibubble DF-181 defoamer, aq. preps. 

Although the presence of certain additives can enhance the foaming ability and persistence of a surfactant system, chemically similar materials may also significantly reduce foam formation or persistence. The same material can, in fact, function as both a promoter or inhibitor under different circumstances. Materials that reduce the amount of foam formed are termed foam inhibitors, which act to prevent the formation of foam, or foam breakers or defoamers, which increase the rate of foam collapse. A foam inhibitor may function by interfering with the adsorption of surfactant at the air-solution interface or by reducing the effectiveness of adsorbed surfactant as a stabilizer. 

A foam breaker that acts by spreading may do so as a monolayer or as a lens (Fig. 12.8). In either case, it is assumed that the spreading foam breaker sweeps away the stabilizing layer, leading to rapid bubble collapse from the outside of the foam. The rate of spreading of the defoamer will, of course. 

---