Water hardness, surfactant sensitivity

In addition to their poor solubility in water, alkyl phosphate esters and dialkyl phosphate esters are further characterized by sensitivity to water hardness [37]. A review of the preparation, properties, and uses of surface-active anionic phosphate esters prepared by the reactions of alcohols or ethoxylates with tetra-phosphoric acid or P4O10 is given in Ref. 3. The surfactant properties of alkyl phosphates have been investigated [18,186-188]. The critical micelle concentration (CMC) of the monoalkyl ester salts is only moderate see Table 6 ... 

Resistance to water hardness Use nonionic surfactants, which are less sensitive to hard water ions than anionics, especially when solubility limitation imposed by the product restricts the use of high builder level... 

Suds suppressors (LD, DW, ADW, HC) Limit suds amount when suds will interfere with cleaning Sensitivity to wash temperature, water hardness, and builder system Efficiency on the surfactant system Alkyl phosphates Silicones Soap 0-5% 0-5%... 

Cosmetic Rinse off Preparations. In certain cosmetic products, tor example hair shampoos, it is not possible to use complexing agents because of the irritation of mucous membranes. Here a low sensitivity of surfactants to water hardness is a precondition for their application. Foam formation is generally considered to be a measure of shampoo quality (Table V). With increase in water hardness the foam volume of alkyl sulfates decreases very much, whereas with the corresponding alkyl ether sulfates this decrease is relatively small. For cosmetic applications, the good skin compatibility and low irritation to mucous membranes of alkyl ether sulfates is of high importance (37). 

Alcohol sulfates (AS) are usually manufactured by the reaction of a primary alcohol with sulfur trioxide or chlorosulfonic acid followed by neutralization with a base. These are high foam surfactants but they are sensitive to water hardness and higher levels of phosphates are required. This latter requirement has harmed the market for this type of detergent, but they are 2% of production for the major household surfactant market. Sodium lauryl sulfate (R = Cn) is a constituent of shampoos to take advantage of its high-foaming properties. 

They have high foam for shampoos and are kind to the skin. They are also used in light duty products such as dishwashing detergents. It is the least sensitive of the anionics to water hardness and therefore has benefited in the trend away from phosphates. They have 25% of the production for the major household surfactant market. 

Ionic surfactants are sensitive to water hardness whereas polyethoxylated surfactant are not. Hence the mixing of both types often result in formulations that are salt tolerant for applications such as detergency or enhanced oil recovery. 

The tt-sulfo fatty acid esters represent another class of anionic surfactants. Methyl ester sulfonates (MES) are surfactants that are derived from a variety of methyl ester feedstocks such as coconut, palm kernel, palm stearin, beef tallow, and soy. Palmitic and stearic acid derivatives lead to good detergency because of the long hydrophobic residues [3, 4]. The sensitivity of MES to water hardness is similar to AOS and small compared to LAS and SAS. MES have exceptional dispersion power with respect to lime soap. They have only been used in a few Japanese detergents [3, 4]. 

Alkyl ether sulfates (AES) are anionic surfactants obtained by ethoxy-lation and subsequent salfation of alcohols derived from feedstock or synthetic alcohol. AES, also known as alcohol ether sulfates, have low sensitivity to water hardness (Fig. 5.3), high solubility, and good storage stability at low temperature [4, 11]. 

Recent AOS synthesis leads to multifunctional surfactants that are less sensitive to water hardness than most anionics, and are better biodegradable than LAS. The C10-16 a-olefin-... 

The sodium salts of Q -sulfo fatty acid methylesters are soluble in water and resistant to hydrolysis in the pH range of 3-10. They are also only slightly sensitive to water hardness and offer good detergency in combination with other surfactants. Their foaming ability decreases strongly from the lauric methylester to the stearic methyl ester. 

The structures of some common nonionic surfactants are shown in Figure 3.2. Ethoxylated alcohols are produced from the reaction of fatty alcohols with ethylene oxide, which results in a broad distribution in the number of EO units per molecules. These surfactants are generally excellent detergents, very mild, and less sensitive to water hardness ions, and also act as solubilizers. A typical ethoxylated alcohol used in LDLDs has approximately 9 EO units and a carbon chain length distribution centered around Cll. 

The above dependence of the performance of ECs on water hardness and temperature may be related to the dependence of emulsifier properties on these parameters. This is discussed in more detail in Chapter 6. Nonionic surfactants are particularly sensitive to these parameters. For example, the solubility in water and, therefore, the effective HLB number of a typical nonionic surfactant decreases as the temperature or salt content of the solution increases. This is evident from the decrease in c.m.c. and cloud point with increasing salt concentration and/or temperature [10, 11]. 

Nonionics are especially useful because of their low sensitivity to water hardness and pH. Since they are compatible with charged molecules, they are easily used in mixtures with other ionic surfactants, which often result in beneficial associations. For instance, nonionics can help to solubilize calcium or magnesium salts of anionics. 

Description. These surfactants are formed by the reaction of sodium chloracetate with ethoxylated alcohols. Due to the addition of ethoxylated groups, ether carboxylates are more soluble in water and less sensitive to water hardness compared to conventional soaps. Also, keeping the best properties of nonionic surfactants, they do not exhibit any cloud point and show good wetting and foam stability. 

Description. Fatty acid isethionates are usually prepared by the reaction of a fatty acid chloride with sodium isethionate (HO-CHz-CHz-SOs-Na), itself resulting from the addition of sodium bisulfite to ethylene oxide. Like other esters, they are sensitive to hydrolysis. These surfactants are insensitive to water hardness and show good wetting, foaming, and emulsifying properties. In addition, they have excellent compatibility with the skin. 

An acylation reaction occurs on the amine terminal functions and, possibly, on some side groups (e.g., the hydroxyls) and thus leaves the carboxyl groups free, which must be neutralized. Because these surfactants contain amide functions, they are sensitive to hydrolysis. Also, they are prone to microbial degradation if they are contaminated and not appropriately preserved. They are rather tolerant to water hardness. 

Also, these surfactants are not only-much less sensitive tB the water-hardness ions than ionic surfactants, but also, if used in substantial concentration, they help to solubilize calcium or magnesium salts of LAS. 

In these surfactants, the numerous hydroxyls of glucoside groups ensure the solubility of the whole molecule in Water. Alkylpolygiucosides show good water solubility and have their cloud points at rather high temperatures (generally above 100°C) they are only slightly sensitive to the presence of electrolytes and are only very rarely influenced by water hardness. 

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