Syndet

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. 

Manufacturers and specialist materials development associations publish extensive corrosion data in the form of monographs, and this form of presentation is also used in national standards. The most recent comprehensive text in this category is perhaps the publication by the Zinc Development Association . The work is important in that the section on chemicals also deals with common, though complex, chemical formulations, e.g. Are-extinguisher fluids, soaps and syndets, agricultural chemicals such as pesticides and fertilisers. This publication also demonstrates the mammoth task of recording all the available data for just one material. A comparable book for mild steel would probably be much larger, whereas for many other materials the information has not yet been determined. Thus at best, only very incomplete data are available in this form. 

Surface-active compounds, especially the anionic surfactants, are derived from fossil raw materials as well as from recent raw materials. The portion of the biomass on the production of anionic surfactants is about 75% if the soap, the quantitatively most important anionic surfactant, is included. Considering only the synthetic surfactants, the syndets, the portion of fossil raw materials in the production of these surfactants, is about 75%. Without the lignosulfonates (and the petroleum sulfonates) this portion is about 90%. Due to strong efforts... 

Generally ether carboxylates are not suitable for a syndet soap because they are waxy due to the ethylene oxide distribution. The solid ether carboxylates with a long alkyl chain and a low degree of ethoxylation have a bad foam. By use of nonethoxylated ether carboxylates, e.g., a carboxymethylated fatty acid monoethanolamide with the structure... 

Nontoxic effect on the skin flora was found by Schafer, which means that these amidether carboxylates can be well used in products which remain on the skin for a longer period [80]. A laurylamidether carboxylate based on digly-colamine has been described for the use in syndet soap with high mildness and good foaming effect [36]. 

For use in soap bars, a smooth feel after washing, mildness, lime soap dispersing effect, and foaming properties are important [36,104-106]. In transparent soap bars the clarity will be improved [104], in half-syndet soaps mildness and foam are increasing [105,106] combined with a smooth feel after use [105], With lauryldiglycolamidether carboxylate a good foaming and mild syndet soap has been formulated [36]. 

Syndet bar soaps were developed for sensitive skin. Their pH value usually is around 5-6, far less than that of the normal soaps (pH 9-10), which is the reason for the latter causing dermal fissures with people who need frequent washing of their hands. The manufacture of syndet bar soaps requires special attention to methodology. A typical raw material composition of a syndet bar soap is as follows ... 

Koch and Kligman s [70] assessment of syndet bar soaps will be discussed in Sec. VI. To repeat their conclusion, the syndet bar soap containing a sulfo-succinate elicited the weakest skin reaction. 

The reaction of step 2 is carried out by heating the reagents with various acid catalysts, such as orthophosphoric acid or its acid salts, bringing the pH down to 2.3-3.2 [4]. The Igepon A type of surfactant is quite susceptible to hydrolysis, particularly on the alkaline side, as is characteristic for most esters of carboxylic acids. It is therefore used most advantageously at a fairly neutral pH, such as combination soap-syndet toilet bars. 

The acid chloride route of the Schotten-Baumann reaction can be carried out continuously [6] while completeness of the reaction can be assured by rapid recirculation of the reaction product [7]. These compounds are used in specialty applications, such as shampoos or soap-syndet toilet bars [8]. 

M. Friedman, Chemistry, Formulation, and Performance of Syndet and Combo Bars, In L. Spitz ed., SODEOPEC, AOCS, Champaign, IL, 2004, pp. 147-188. 

Concerns about the effect of TPP on eutrophication have led many states, cities, and regional governments to ban the use of the compound in syndets. Such bans have caused serious problems for detergent manufacturers, however, because no entirely satisfactory substitute for TPP has yet been found. Two promising candidates are the sodium salt of nitrilotriacetic acid, 3Na, N(CH2C02)3 , or NTA and ethylenediaminetetraacetic acid (EDTA). Both of these compounds act in much the same way as TPP, that is, by sequestering metal ions. Other builders that have been incorporated into syndet formulations include sodium carbonate, synthetic zeolites, borates, and organic polymers known as polycarboxylates. 

Detergent manufacturers have been reluctant to stop using TPP in their syndet formulations, however. For one thing, they are not convinced that TPP is as much of an environmental threat as some scientists have suggested. Also, they point out that many of the alternatives available pose problems of their own. For example, there is some evidence that NTA may be carcinogenic in rats. In response to that information, the U.S. Environmental Protection Agency (EPA) banned the use of NTA in detergents in 1970. A decade later, however, the EPA reversed course and once more permitted its use in 1980. 

Environmental Response, Compensation, and Liabihty Act of 1980, designed to find and remediate toxic waste sites in the United States, syndet An abbreviation for the term synthetic detergent. synthetic detergent A cleaning product made of synthetic materials rather than natural soaps. 

Dissolve PVP-lodine in water, mix the solution with the fragrance and the syndet base. Pass the blend 4 x through a three-roller mill. Give the blend 3 times through a plodder with a narrow sieve hole disk. 

Synthetic detergents (syndets) belong to the group of surface active agents [which are substances which affect (usually reduce) surface tension when dissolved in water or in water solns] and have structurally unsymmetrical molecules contg both hydrophilic, or water-soluble, groups and hydrophobic, or oil-soluble hydrocarbon chains... 

Soaps form insoluble salts with metal cations frequently found in water such as calcium and magnesium. You may have seen these salts in the form of a tub ring after taking a bath. The magnesium and calcium salts of a good syndet will not precipitate from water. 

Branched chain syndets are less easily degraded by microorganisms in the environment than unbranched syndets. Therefore, it is for environmental reasons that syndets have mostly unbranched alkyl chains. 

The chemistry of soap manufacturing stayed essentially unchanged until World War II, at which time synthetic detergents (syndets) became available. There had been a search for cleansing agents that would foam and clean when added to seawater in response to the need of sailors who spent months at sea under severe freshwater restrictions. 

Thune, P. et al., The water barrier function of the skin in relation to the water content of stratum corneum, pH and skin lipids. The effect of alkaline soap and syndet on dry skin in elderly, non-atopic patients, Acta Derm. Venereol., 68, 277, 1988. 

Barel, A.O. et al., A comparative study of the effects on the skin of a classical bar soap and a syndet cleansing bar in normal use conditions and in the soap chamber test, Skin Res. Technol., 7, 98, 2001. 

FIGURE 31.3 Swelling of porcine skin SC in sodium cocoyl isethionate (SCI, syndet) and Na laurate (soap) solutions (l%wt). Soap treated SC shows significantly higher swelling than that treated with syndet. 

FIGURE 31.4 The amount of water soluble free amino acids (a) and cholesterol (b) removed from porcine skin after a single wash with a syndet bar versus a soap bar. Results show significantly higher removal from the soap washed site. 

The interaction of harsh surfactants on SC proteins results in an increase in skin surface water loss (SSWL). This is evident in the results shown in Figure 31.5. Water loss, measured using an evaporimeter immediately after a wash, show that harsher soap induces a higher rate of evaporation than milder syndet. The implications of this high rate of evaporation are examined further. 

---