Surfactants for Industrial Purposes

More than one-third of all the surface-active compounds produced are used outside the extensive detergents and cosmetics sector, namely by industry [38]. 

Most industries require surfactants not so much for the manufacture of an end product, but rather as indispensable aid in a manufacturing step or in a chemical reaction. This also includes a number of processes which can be regarded as cleaning or washing steps. For textile manufacturing examples of the working steps are diagrammatically shown in Fig. 7. 

No less important, and certainly more problematic with respect to the environment, is the sector where, in addition to cleaning purposes, surfactants are also used for the formation of emulsions for manufacturing processes or chemical reactions. Emulsions are multi-phase systems of liquids which are not miscible with one another [39]. Since the inner, discontinuous phase and the outer, continuous phase in most cases contain water or oil, these types of emulsion are generally called an oil-in-water emulsion (milk type OW) or water-in-oil emulsion (butter type WO). 

Surfactants as emulsifiers ensure the stability of emulsions. They behave like polar substances which reduce the interfacial tension between the immiscible liquids. Their mode of action can be schematically illustrated as follows [39]  

There are a large number of emulsifiers of natural and synthetic origin, which fit into the surfactant classification given. The natural substances used as emulsifiers all fit into this system (See Table 4). 

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