Soluble soap

The mechanisms by which an alkaline cleaner removes the soil are saponification, emulsification, and dispersion. These mechanisms can operate independently or in combination. Saponification occurs when alkaline salts react with fatty components of the soil, forming a soluble soap compound. 

The greatest industrial consumption of monobasic aluminum acetate has been as a solution in the preparation of red color lakes for the dyeing of cotton. Formation of a water-resistant coating on fabrics, paper, leather, or other materials is also an important appHcation. In this process, for example, cloth is dipped into a solution of water-soluble soap, then into the aluminum salt solution, forming an insoluble, water-resistant aluminum soap coating on the fiber surfaces (10). 

More frequently either methyl ethyl ketone peroxide or cyclohexanone peroxide is used for room temperature curing in conjunction with a cobalt compound such as a naphthenate, octoate or other organic solvent-soluble soap. The peroxides (strictly speaking polymerisation initiators) are referred to as catalysts and the cobalt compound as an accelerator . Other curing systems have been devised but are seldom used. 

Consideration will first be given to the inorganic builders used to produce the base material. The pH values of several commonly used materials are shown in Table 11.1. Hydroxides are the simplest, strongest alkalis and most commonly used. A major effect of hydroxides in cleaning is saponification the conversion of certain oils and greases to water-soluble soap-type materials. Hydroxides also produce solutions of high conductivity, as required for electrocleaning. 

Soaps are made by heating sodium hydroxide with a fat such as coconut oil, olive oil, or beef fat, which contain esters formed between glycerol and fatty acids (see Section 19.7). The sodium hydroxide attacks the esters and forms the soluble soap. In the case of beef fat, stearic acid forms the soap sodium stearate, seen in (3). Soaps, however, form a scum in hard water. The scum is an impure precipitate of calcium stearate. 

Water that contains significant amounts of Ca2+ or Mg2+ is said to be hard. These ions cause soluble soaps such as sodium stearate, palmitate, and oleate to precipitate as insoluble scums, which are an unsightly nuisance as well as a waste of soap ... 

Uses of the alkali hydroxides.—A soln. of potassium hydroxide is used in the laboratory as an absorbent for carbon dioxide, the sodium compound is not so often used because of the formation of less soluble sodium carbonate which is liable to choke the delivery tubes with crystals. Potassium hydroxide is used in making soft soaps the corresponding sodium compound gives the ordinary hard soaps. The hydroxide fused with a little lime is used as a cautery—pierre a cautere. The alkali lye is also used as a cleansing fluid, since it forms soluble soaps with many greases and fats. The lye also dissolves animal tissues. 

ALKALI. A term that was originally applied to the hydroxides and carbonates of. sodium and potassium but since has been extended to include tire hydroxides and carbonates of the other alkali metals and ammonium. Alkali hydroxides are characterized by ability to fomi soluble soaps with fatly adds, to restore color to litmus which has been reddened by acids, and to unite with carbon dioxide to form soluble compounds. See also Acids and Bases. 

Only molecules with certain specific types of configurations exhibit snrface activity. In general, these molecnles are composed of two segregated portions, one of which has low affinity for the solvent and tends to be rejected by the solvent. The other portion lias sufficient affinity for the solvent to bring the entire molecule into solution. Water-soluble soaps are probably the oldest surfactants. The long hydrocarbon chain has a low affinity for water and is referred to as the hydrophobic or nonpolar... 

Composition vs. properties. One of the key properties of a soap, key to determining applications, is solubility. As with other surfactants, the solubility of the soap is dependent upon the carbon chain distribution, which is, in turn, determined by the choice of raw material oils. C12-14 gives a more soluble soap with very high foam generation whereas Ci8+ soaps have much reduced solubility. The use of unsaturated acids, such as oleic, gives improved solubility compared to the saturated equivalents and, where high solubility is required, potassium salt or an amine salt may be used instead of sodium salt. 

Bhatnagar,2 following Donnan,3 thinks that electrical effects at the interfaces also are important, and finds that the formation of a water-in-oil or an oil-in-water emulsion depends on the ions present in the solution, which are no doubt adsorbed on the surface of the solid. The rule that monovalent ions promote oil-in-water emulsions, which are reversed by polyvalent ions, appears to hold good with solid emulsifiers as well as with soluble soaps. Developments of the theory in this direction will be of great interest. 

Detergents can also be very effective in helping grease and fats to be made soluble in water. An example of a soap is sodium stearate. It has a COO Na+ water-soluble end on a long carbon chain which is grease-soluble. Soaps can have a formula something like ... 

In this process the fabric is boiled with milk of lime which convert the fatty acid into insoluble lime soaps. The lime soap is then converted into free acids on acidification and calcium is washed away as calcium chloride. The deposited free acid is then converted to soluble soaps on subsequent boiling with sodium carbonate. This method is tedius and not economical as two boils are required to remove the natural impurities. 

Most builders also contribute significantly to detergency by providing alkalinity to the wash water. A high pH (>10) solution aids in the removal of oily soils such as sebum by saponification. The insoluble fatty acids found in oily soils are converted to soluble soaps under alkaline conditions, facilitating their removal during the washing process. 

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