Detersive surfactants

The solubihty characteristics of sodium acyl isethionates allow them to be used in synthetic detergent (syndet) bars. Complex blends of an isethionate and various soaps, free fatty acids, and small amounts of other surfactants reportedly are essentially nonirritant skin cleansers (66). As a rule, the more detersive surfactants, for example alkyl sulfates, a-olefin sulfonates, and alkylaryl sulfonates, are used in limited amounts in skin cleansers. Most skin cleansers are compounded to leave an emollient residue on the skin after rinsing with water. Free fatty acids, alkyl betaines, and some compatible cationic or quaternary compounds have been found to be especially useful. A mildly acidic environment on the skin helps control the growth of resident microbial species. Detergent-based skin cleansers can be formulated with abrasives to remove scaly or hard-to-remove materials from the skin. 

Although it is impossible to Hst all the practical detersive systems that might be encountered, a large proportion fall in a small number of classes. This classification disregards surfactant stmcture and type of substrate (fibrous or hard surface) and is restricted to a consideration of the soil present on the substrate, the mechanical action employed, the bath ratio, and the detergent used. Some of the more commonly encountered detersive systems are classified on this basis in Table 1. 

Surfactants. The most important components of detersive systems are, of course, the surfactants described elsewhere in the E,ntycIopedia. 

In a detersive system containing a dilute surfactant solution and a substrate bearing a soHd polar sod, the first effect is adsorption of surfactant at the sod—bath interface. This adsorption is equivalent to the formation of a thin layer of relatively concentrated surfactant solution at the interface, which is continuously renewable and can penetrate the sod phase. Osmotic flow of water and the extmsion of myelin forms foHows the penetration, with ultimate formation of an equdibrium phase. This equdibrium phase may be microemulsion rather than Hquid crystalline, but in any event it is fluid and flushable... 

From the anionic surfactants (Table 1.1) the most relevant is LAS with an annual global production volume of more than 3 X 1061 in 2001. LAS has a wide application because of its excellent detersive properties and cost-performance ratio. Commercial LAS is applied mainly in the formulation of powder and liquid laundry detergents. The calcium salts are used as an emulsifier in pesticide formulations their amine salts are used in dry cleaning and as degreasing agents in the metal industry [14]. 

Inter facial Parameters in the Detersive System. Three phases are present in the detergency system in this study a PEG (fiber), a hydrocarbon (soil), and an aqueous surfactant (bath) phase. These three phases meet to form three binary interfaces, whose interfacial energetic properties vary as a function of LAS homolog molecular weight. 

Cahn, A. and Lynn, J.L. Surfactants and Detersive Systems in Kirk—Othmer Encyclopedia of Chemical Technology, 3rd ed., Vol. 22, Wiley, New York, pp, 332 132, 1983. 

The most important components of detersive systems are the surfactants. Although a detailed discussion of surfactants and surfactant systems is beyond the scope of this chapter, and the reader is referred elsewhere for such (4), a limited discussion of oleochemicaUy derived surfactants is appropriate here. 

The chemical structure of the surfactant is an important factor in detersive effectiveness. When relating detersive power to chemical constitution, within limited series, certain regularities can be observed, but few if any general principles apply to the... 

The strong adverse influence of calcium ions on the stability of lyophobic suspensions is predicted by DLVO theory, and has been demonstrated with many types of simple soils. That calcium ions have an overwhelming effect on the redeposition of carbon soil onto cotton tends to support the idea that DLVO theory is a principal key in explaining detersive action. The redeposition of carbon onto cotton has been correlated quantitatively with the calcium ion content of the system, both in the presence and absence of surfactant (95). The adverse effect of calcium ions on wet soil removal in practical washing has also been well established (96). The effect of calcium in detergency cannot be explained solely, however, by its shrinking of... 

In addition to surfactants, a number of other materials are present in formulated laundry detergents. Among these are materials called builders. Their main purpose is to counter the detrimental effects of polyvalent cations on detergency. Polyvalent cations are introduced into the wash bath mainly by water hardness but may also come from soil or substrate. In addition, builders serve to increase the detersive effidency and effectiveness of surfactants and to supplement their beneficial effects on soil removal. 

A. Cahn and J. L. Lynn, Jr., Surfactants and detersive systems, in Kirk-Othmer Encyclopedia of... 

Builders. Builders are substances that augment the detersive effects of surfactants. Most important is their ability to remove hardness (i.e., soften the water) from the wash liquor and, thus, prevent them from interacting with the actives of detergents, that is, surfactants. 

Anionics are. historically the earliest and the most common surfactants. They are usually considered to be the workhorse in the detergency world. Accordingly, they are produced with the highest volumes and most of them are inexpensive. They are especially beneficial for their excellent detersive action and their efficacy to remove particulate soils. This benefit stems from the fact that many substrates are negatively charged anionics and derived molecular aggregates are not prone to firmly adsorb on such substrates, thereby hindering the redeposition of undesirable soils. 

Linear alkylbenzene sulfonate is also used in hand dishwashing, often in combination with AEOS (i.e., alcohol ethoxy sulfate) this surfactant association provides better foam resistance. Due to its very high detersive action, LAS has a low compatibility with skin and is scarcely used in cosmetics, except in antiseborrheic preparations. 

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