Formulation of Foams

A foam is a disperse system that consists of gas bubbles separated by liquid layers. Because of the significant density difference between the gas bubbles and the medium, the system quickly separates into two layers, with the gas bubbles rising to the top, which may undergo deformation to form polyhedral structures this process will be discussed in detail below. 

Several surface-active foaming materials may be distinguished, including surfactants (ionic, nonionic and zwitterionic), polymers (polymeric surfactants), particles that accumulate at the air/solution interface, and specifically adsorbed cations or anions from inorganic salts. Many of these substances can cause foaming at extremely low concentrations (as low as 10 mol dm ). 

In kinetic terms, foams may be classified as either unstable, transient foams (with a hfetime of seconds), or metastable, permanent foams (with lifetimes of hours or days). 

Formulation of Disperse Systems Science and Technology, First Edition. Tharwat F. Tadros. 

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I 76 Formulation of Foams Original state if thin film... 

Other uses are in formulations of foam typa extinguishers and in the production of protein hydrolyzates. 

Chem. Descrip. Linear alcohol ethoxylate Uses Detergent, dispersant, emulsifier, wetting agent for formulation of foaming detergents, leather, paint, textile, and pulp and paper specialties... 

Pentaerythritol is used in self-extinguishing, non dripping, flame-retardant compositions with a variety of polymers, including olefins, vinyl acetate and alcohols, methyl methacrylate, and urethanes. Phosphoms compounds are added to the formulation of these materials. When exposed to fire, a thick foam is produced, forming a fire-resistant barrier (see Elame retardants) (84—86). 

The avadabihty of PMDI also led to the development of polyurethane-modified isocyanurate (PUIR) foams by 1967. The PUIR foams have superior thermal stabiUty and combustibiUty characteristics, which extend the use temperature of insulation foams well above 150°C. The PUIR foams are used in pipe, vessel, and solar panel insulation glass-fiber-reinforced PUIR roofing panels having superior dimensional stabiUty have also been developed. More recently, inexpensive polyester polyols based on residues obtained in the production of dimethyl terephthalate (DMT) have been used in the formulation of rigid polyurethane and PUIR foams. 

With amine initiators the so-called self-catalysed polyols are obtained, which are used in the formulation of rigid spray foam systems. The rigidity or stiffness of a foam is increased by aromatic initiators, such as Mannich bases derived from phenol, phenoHc resins, toluenediamine, or methylenedianiline... 

Castor esters have been found to be nonirritating and noncomedogenic to the skin. Cetyl ricinoleate was found to be an effective noncomedogenic moisturizer (118). Castor-based quaternaries prepared by reaction of a castor fatty acid and a tertiary diamine are used for hair care. The ricinoleic quaternium is incorporated into clear shampoo formulations for foam enhancement and conditioning (119,120). 

In connection with a variety of disinsectants formulations (aerosols, foams, electric fumigators) on basis of pyrethroids the income of the given substances into air during application is possible as aerosols and as vapors, especially in case of electric fumigators application. 

Surface active agents are important components of foam formulations. They decrease the surface tension of the system and facilitate the dispersion of water in the hydrophobic resin. In addition they can aid nucleation, stabilise the foam and control cell structure. A wide range of such agents, both ionic and non-ionic, has been used at various times but the success of the one-shot process has been due in no small measure to the development of the water-soluble polyether siloxanes. These are either block or graft copolymers of a polydimethylsiloxane with a polyalkylene oxide (the latter usually an ethylene oxide-propylene oxide copolymer). Since these materials are susceptible to hydrolysis they should be used within a few days of mixing with water. 

After 8 h of reaction, the reactor was allowed to cool. A two-layer liquid formed. The top layer was found to contain mostly polypropylene ether triols with about 20% by weight diethylene glycol and 5% by weight toluene diamines. The top layer was purified by vacuum distillation at 2 mm Hg and 200° C to produce 320 g of a light brown liquid residue. This residue (polyols) was used as a replacement for 5% by weight of the Pluracol 535 polyol in the formulation of a flexible polyurethane foam. A flexible foam which had good resiliency and a density of 2.2 Ib/ft3 was obtained. At higher replacement levels, lesser quality foams were obtained. 

Experimental correlations have been established in a given LDL formulation between foam stability and interfacial tension [33]. For example, Fig. 15 shows the effect of increasing water hardness on plate washing performance of an LAS/AES blend. A small amount of Ca2+ ion helps substantially to stabilize the foam. Under the same conditions interfacial tension is also lowered substantially. The two curves show an inverse relationship where the minimum interfacial tension value corresponds to the optimum level of foam stability as measured by plate washing [33]. 

In comparison to U.S. wash conditions, European wash conditions are characterized by higher temperatures, higher surfactant concentrations, and longer agitation times. These differences as well as differences in washing machine design require more control of foam in European formulations than in U.S. formulations. 

Ammonium and alkanolamine salts of alcohol C12-C14 sulfates are used as foamers in the formulation of firefighting foams. 

Contact of surfactants with the skin and mucus membranes occurs either accidentally or as a consequence of normal use. Examples of this normal and everyday use are cleaning formulations, shampoos, foam baths, and toothpastes. Again this contact is seldom made with individual surfactants, in this case alcohol sulfates and alcohol ether sulfates, but through formulated products. It is known that surfactants present significant interactions, so that mixed systems are generally less aggressive than their individual components. However, the effect of pure surfactants merits attention, particularly sodium dodecyl sulfate, which is commonly used as a reference for many studies because of its high purity and availability. 

These higher foaming properties are very useful for such cosmetic formulations as shampoos, showerbaths, and so on. This is the same with the forming of fine bubbles and the improving of foam stability of other surfactants such as, for example, alkyl ether sulfates due to the combination with ether carboxylates [57,67-69] (Table 9). 

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