Calcium soaps, precipitation, effect

It would therefore seem Ukely that these antifoam effects are largely associated with the formation of calcium soap precipitates. Curiously, Peper [195] ignores this possibility and interprets his resnlts in terms of formation of rigid islands of calcium soap monolayer interspersed with gaseous film of adsorbed surfactant. Peper [195] asserts that these islands wiU make the film unstable because of their inflexible brittle nature. No theoretical arguments are given for why these should be unstable. 

Practical laundry detergent formulations usually include builders for control of polyvalent metal ion activities so that the relevant salts of the anionic surfactant, which is usually present, are not precipitated out of solution. The presence of builders also has implications for the effectiveness of antifoam action because they may prevent the precipitation of calcium soaps. We can illustrate the relevant issues if we consider, for example, the concentration of calcium harduess uecessary to just initiate calcium soap precipitation in the case of a solution built by sodium tripolyphosphate at a pH >10.5. If we iguore the effect of solubilizatiou of soaps and calcium binding in anionic surfactant micelles, then, according to Irani and Callis [4],... 

Anionic Surfactants Early studies by Savins [1967] showed that sodium oleate soaps with potassium hydroxide and potassium chloride in aqueous solution had good DR effectiveness. Increasing the concentration of KCl from 5% to 10% gave better drag reduction results. Unfortunately, the soaps precipitate and are ineffective as DRAs in the presence of calcium ions, which are present in most aqueous systems. Solutions of anionic surfactants such as SDS and SDBS are not drag reducing. Little research on anionics as DRAs has been carried out. 

The role of calcium soap particles as antifoam additives is surprisingly poorly understood. Available evidence (which is scant) suggests that such particles may function simply as hydrophobic particles. However, measurements of the relevant contact angles are few and never combined with imaging and sizing of the particles. Moreover, there is evidence of transient antifoam effects accompanying the precipitation of such particles by reaction of calcium ions with soaps [198]. There is as yet no explanation for such transient effects. 

It is well known that precipitation of calcium soaps (i.e., calcium alkyl carboxylates) is often accompanied by reductions in foamability and foam stability of aqueous solutions of other surfactants. The available evidence, as we have discussed in Section 4.7.6, suggests that these effects concern the bridging mechanism of hydrophobic particles. 

Detergents are designed to be effective in hard water meaning water containing calcium salts that form insoluble calcium carboxylates with soaps These precipitates rob the soap of Its cleansing power and form an unpleasant scum The calcium salts of synthetic deter gents such as sodium lauryl sulfate however are soluble and retain their micelle forming ability even m hard water... 

Soaps react with the calcium and magnesium ions in hard water to produce soap curd that greatly reduces its effectiveness. The curds are actually insoluble calcium and magnesium salts. Synthetic laundry detergents have replaced soap for cleaning clothes in the last half century. Synthetic detergents are made from petroleum. They work like soap except they do not react with magnesium and calcium ions to form insoluble precipitates and salts. 

Hardness of a water sample is a measure of its capacity to precipitate soap. The presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. Their effect, however, is minimal, because these polyvalent ions occur in water often in complex forms and not as free ions. As a result, they cannot precipitate soap. Although calcium is not the only cation causing hardness, for the sake of convenience, hardness is expressed as mg CaC03/L. Similarly, anions other than carbonate, such as bicarbonate, also cause hardness in water. To distinguish the contributions of such anions from carbonates, hardness is sometimes termed as carbonate hardness and noncarbonate hardness. This can be determined from alkalinity. The relationship is as follows ... 

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