These are materials incorporated into a shampoo formulation to enhance its aesthetics as well as improve its performance.
Thickeners comprise a broad variety of compounds that are used to increase viscosity of the formulations, modifying their consistency from viscous liquids to thick gels. Among the most frequently used are electrolytes, such as sodium chloride, alkanolamides and water-soluble cellulose derivatives, such as carboxymethylcellulose, hydroxyethylcellu-lose, carboxy vinyl polymers of the Carbopol type, polyvinyl alcohols, and natural gums, such as tragacanth. Magnesium aluminum silicates have found application as thickeners and suspending agents in antidandruff shampoos.
Opacifiers serve to impart to shampoo a pearlescent or opaque appearance. For this purpose, high-melting, wax-like materials are blended into formulations. Of particular utility in this respect are cetyl and stearyl alcohols and their esters as well as the latex emulsions of vinyl-, styrene-, and acrylic polymers.
The shampoo milieu offers itself as an ideal ground for microbial growth, particularly of the aerobic gram-negative organisms of Pseudomones. This may have a deleterious effect on the shampoo properties, posing at the same time a health hazard to the consumer. The function of preservatives is to inhibit such bacterial development. Although formaldehyde has been one of the most popular and effective preservatives, its use has declined as other compounds have come to the fore. Examples include methyl and propyl parabenes, DMDM hydantoin, quaternium-15, imidazolidynyl urea and others. The selection of a suitable preservative is made through a challenge test in which the product is subjected to the worst possible conditions anticipated during manufacture, shelf storage and actual use.
Other additives. Fragrance is an essential ingredient, often deciding the market appeal and success of the product. Addition of alcohols (ethanol, isopropanol) or glycols may be required to maintain the clarity of clear shampoos, while the presence of sequestering agents like EDTA prevents the formation of insoluble calcium or magnesium soaps when the shampoo is rinsed off the hair. FD&C and D&C dyes are commonly added to enhance the aesthetics of shampoo formulations. ''Squeaky'' clean feel of shampooed hair is frequently accompanied by difficult combing and substantial ''fly away.'' To overcome this, the shampoos contain ''conditioning'' additives that are substantive to hair remaining adsorbed on the surface after rinsing. A plethora of materials has been used to this end. To these belong amine oxides, protein hydrolysates, cationic surfactants, cationic polymers, lanolin and its derivatives, as well as natural materials, such as beer, honey, and egg.
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