Hydrolysable surfactants

Bronopol Antimicrobial preservative antiseptic (not oral) Sulfhydryl compounds, sodium thiosulfate, sodium metabisulfite, amine oxide or protein hydrolysate surfactants, aluminum... 

Sulfhydryl compounds cause significant reductions in the activity of bronopol, and cysteine hydrochloride may be used as the deactivating agent in preservative efficacy tests lecithin/ polysorbate combinations are unsuitable for this purpose. Bronopol is incompatible with sodium thiosulfate, with sodium metabisulfite, and with amine oxide or protein hydrolysate surfactants. Owing to an incompatibility with aluminum, the use of aluminum in the packaging of products that contain bronopol should be avoided. 

By analogy with solid particle dispersions, adsorption isotherms can be determined as a function of the chemical potential of the solute. An indirect, but rapid and powerful, example is given by surface tension measurements, which can detect very low amounts of surface-active solute in the form of contaminant. This property is used to determine purity in easily hydrolysable surfactants such as SDS or sodium bis(2-ethylhexyOsulfosuccinate (AOT). A minimum in the surface tension near the CMC directly detects the presence of a surface-active contaminant such as dodecanol or octanol, which will desorb from the interface at high surfactant concentrations. This desorption is the origin of the a priori counter-intuitive increase of surface tension with surfactant content (16). 

Acylated Protein Hydrolysates. These surfactants are prepared by acylation of proteia hydrolysates with fatty acids or acid chlorides. The hydrolysates are variable ia composition, depending on the degree of hydrolysis. CoUagen from leather (qv) processiag is a common proteia source. Acylated proteia hydrolysates (Maypoa, by laotex Chemical Company) are mild surfactants recommended for personal-care products (see Cosmetics). 

Further efforts to substantiate enantioselective micellar catalysis is now being continued. Yamada et al. (1979a,b) and Ihara (1978) found an enantiomeric rate ratio of 1.4 2.8 (l/d) for the combination of the surfactant [40] and D- and l- substrates [41]. Koga et al. (1977) also found slight rate differences between hydrolyses of D- and l- [42] catalyzed by micelles of [43]. 

In the development of the protein-fatty acid condensates it was possible to combine the renewable resources fatty acids (from vegetable oil) and protein, which can be obtained from both animal waste (leather) as well as from many plants, to construct a surfactant structure with a hydrophobic (fatty acid) and a hydrophilic (protein) part (Fig. 4.12). This was carried out by reacting protein hydrolysate with fatty acid chloride under Schotten-Baumann conditions using water as solvent. Products are obtained that have an excellent skin compatibility and, additionally, a good cleaning effect (particularly on the skin) and, in combination with other surfactants, lead to an increase in performance. For instance, even small additions of the acylated protein hydrolysate improve the skin compatibility. An... 

In contrast to nonionic surfactants, ionic surfactants build up a high zeta-po-tential at the water-oil interface which can also can influence the enzyme activity. Most investigated systems used AOT as the surfactant because its phase behaviour is well understood. However, AOT is often not very suitable, because it can totally inhibit enzymes (e.g. the formate dehydrogenase from Candida bodinii). The usage of lipases in AOT-based microemulsions is generally unfavourable as AOT is an ester that is hydrolysed itself. 

Acylated Protein Hydrolysates. These surfactants are prepared by acylation of protein hydrolysates with fatty acids or acid chlorides. 

Acylated protein hydrolysates are mild surfactants recommended for personal-care products. 

After dyeing, the liquor is usually drained off the material is rinsed and then washed off with addition of a surfactant. The washing intensity depends on the substantivity of the dye hydrolysate. With alkali-sensitive vinylsulfone dyes, soaping at the boil must be carried out in a neutral or weakly acidic liquor to prevent cleavage of the dye-fiber bond. 

As a class of surfactants, sulphosuccinates differ from most other sulphonates in their chemical stability and, due to the presence of the ester linkages, sulphosuccinates will hydrolyse at extremes of pH and with elevated temperature. Monoesters are more sensitive than diesters, with optimal stability of pH 6-8, whilst diesters are more stable and will tolerate pH of 1-10 at room temperature. This allows the use of diesters in a much wider range of environments, particularly under moderately acidic conditions. 

To obtain substantial yields of surfactant hydrophobes, especially in the most useful C12— 14 range, the choice is restricted to coconut, palm and palm kernel oils. In the C16-18 range, the same oils are also used but animal (normally beef) tallow can be used. The use of animal fats raises some ethical issues but these are not commonly used to produce anionic surfactants. The oils may be converted to methyl esters by transesterification which allows easier distillation to remove heavy/light fractions and the esters are finally hydrogenated to fatty alcohols. Alternatively, the fat or oil can be hydrolysed to fatty acid prior to esterification... 

This reaction yields surfactants in which the polar group is linked to the silicone through an SiOC linkage. These materials have found widespread use in nonaqueous applications such as manufacture of polyurethane foam (PUF) but in an aqueous system the SiOC linkage hydrolyses (rapidly away from pH = 7). 

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