V

Sodium dialkvl sulfosuccinate

Monoesters disodium salts are the most common sulfosuccinates used in cosmetic applications. Monoesters of alkanolamines (sulfosuccinamates) are milder than monoesters of fatty alcohols (sulfosuccinates). Monoesters derived from ethoxylated alcohols or alkanolamides are extensively used in personal products and especially in shampoos; they are known for their mildness and skin-irritation reduction when used in association with other anionic surfactants.

Sulfo Fatty Acid Esters. These surfactants are sometimes known under their abbreviated names: FES for fatty ester sulfonate, MES for methyl ester sulfonate, or ASME for alpha sulfo methyl ester. Most of a-sulfo fatty acid esters derive from fatty acid methyl esters. In general, alkyl esters of a-sulfo fatty acid have excellent detergency (i.e., oil dispersing and emulsifying properties) when the molecule is dissymmetric (as in the case of the a-sulfo methyl esters). On the other hand, the a-sulfo esters, in which the sulfonate group is in the middle of the molecule (as in the case of long-chain alcohol esters), deliver good wetting but poor detergency.

S03Na

Methyl ester of a-sulfo fatty acid, sodium salt

S03Na

Alkyl ester of a-sulfo fatty acid, sodium salt

Alpha-sulfo methyl ester surfactants deriving from Ci6-Ci8 fatty acid (e.g., ASMT, the tallowate) are appropriate for use in laundry detergents. ASME is also used in the formulation of syndet bars (laundry bars based on synthetic surfactants).

Fatty Acid Isethionates and Taurides. Fatty acid isethionates are usually prepared by reaction of a fatty acid chloride with sodium isethionate (HO-CH2-CH2-SO3-Na), itself resulting from the addition of sodium bisulfite to ethylene oxide. These surfactants are insensitive to water hardness and show good wetting, foaming, and emulsifying properties. In addition, they are very mild and have excellent compatibility with the skin. Taurides (or taurates) are acylamino alkane sulfonates that have chemical structures close to isethionates. They can be used in association with other surfactants to increase the viscosity.

R-C-N-CH2CH2-S03Na

Fattv acid isethionate

Sodium methyl acyl tauride

Acyl isethionates have been used in shampoos and personal cleansers. They are also incorporated in syndet bars together with various soaps. The most currently used is the cocoyl isethionate.

Taurides (or taurates), which have the same expected properties as soaps (except the sensitivity to water hardness), had been extensively used in shampoos but have been replaced by AEOS. Today they are limitedly used in cosmetics mainly in foam baths and toilet bars. Taurides are also used in soap bars especially designed for laundering with seawater, in agriculture, and textile dying.

Phosphate Esters

This class of surfactants includes alkyl phosphates and alkyl ether phosphates. O O

Alkyl phosphoric ester Dialkyl phosphoric ester

The use of phosphate esters as surfactants is especially useful in applications for which a particular tolerance to pH, heat, or electrolytes is required. They are also used in acidic cleaning products for household as well as industrial applications. Mild for the skin, alkyl phosphates sometimes enter the composition of facial and cleansing products.

Acylamino Acids and Salts

Acyl Glutamates. These surfactants are formed by acylation of a natural amino acid, the glutamic acid HOOC-CH2-CH2-CH(NH2)-COOH (or a-aminoglutaric acid). These surfactants are mild for the skin and the eyes, deliver improved skin feel, but are poor foamers.

NaOOC—CH2CH2CH—COONa

Acyl glutamates are mainly used in personal products such as shampoos.

Acyl Peptides. These surfactants are formed from hydrolyzed proteins (e.g., animal collagen). Depending upon the protein hydrolysis process (chemical or enzymatic), the average polypeptide molecular weight can vary from about 350 to 2000 and some free amino acids may be present in the hydrolysate. An acylation reaction occurs on the amine terminal functions and, possibly, on some side groups (e.g., the hydroxyls); it accordingly leaves free carboxyl groups which must be neutralized.

Products containing such surfactants are prone to be contaminated by various germs and have to be properly preserved.

Sodium acyl polypeptide (X- amino acids side groups)

Acyl peptides are mild surfactants designed for the personal-care area; they are especially used in shampoos because of their substantivity on the keratin of hair and, therefore, they effectively deliver the expected benefits of conditioning agents.

Acyl Sarcosides. Sarcosinates (or salts of acylamino acids) are the condensation products of fatty acids with N-methylglycine CH3-NH-CH2-COOH (or sarcosine).

Sodium acyl sarcosinaLt;

Sarcosinates are good surfactants for cosmetic usage because of their mildness to skin, substantivity on skin and hairs when incorporated in formulations around neutral pH, conditioning action, and foaming resistance in the presence of soaps or sebum. Incorporated in shampoos with alkyl sulfates, they boost the lather. Sarcosinates are also used as corrosion inhibitors.

Cationic Surfactants

From a very general standpoint, cationic surfactants differ from anionic and nonionic ones by the fact that they carry a positive charge. Their major interest in cosmetic industry resides in hair care; in this frame, they are use as hair conditioners and antistatic agents. Cationics are also found in the personal-care area as emulsifiers in some cosmetic preparations and as bactericidal agents.

Alkylamines

Primary, secondary, and tertiary alkylamines, and more especially their salts, are included in this surfactant class.

R —NHi R — N" R — C — NH —(CH2)3 —N "

Alkylamine Dimethyl alkylamine Alkylamido dimethyl propylamine

Amines and their salts are mainly used in textile treatment and occasionally in rinse fabric softeners. Salts of amines are used in cosmetics together with other surfactants. Their usage is restricted to specialties; they exhibit conditioning and antistatic properties in haircare applications. Amido-amines are also used in cosmetic products.

Alkylimidazolines

Reaction of a fatty acid with a substituted ethylene diamine forms imidazoline. Heating the resulting, amido-ethylamine yields the imidazoline with a five-member substituted ring. The tertiary nitrogen atom can be quaternized.

Imidazolines are cationic o/w emulsifiers. Considered to be irritating they are scarcely used in cosmetics as substantive hair conditioning agents.

Quaternary Ammonium Compounds

Quaternary ammonium compounds form a class of surfactants that contain a positively charged nitrogen atom linked to four alkyl or aryl substituents. The positive charge is permanent, regardless of pH.

Tetra-Alkyl(-aryl) Ammonium Salts. Tetra-alkyl ammonium salts have the structure [R1R2R3R4N+]X_ where R1, R2, R3, and R4 are alkyl or aryl groups and X~ represents an anion. The water solubility of quaternaries mainly depends upon the nature of R substituents. Low solubility quaternaries can adsorb on various substrates and impart various useful conditioning effects (e.g., softening, antistat, corrosion inhibition). With the exception of N-alkyltrimethyl ammonium salts, quaternary surfactants usually show poor detergency, wetting, and emulsifying capacities. Quaternaries are generally not compatible with anionics because of the formation of a water-insoluble complex.

Quaternary compound

The major usage of quaternaries is related to their ability to adsorb on natural or synthetic substrates and fibers. They are widely used as softening agents in rinse fabric softeners. Their softening and antistatic properties are similarly exploited in hair conditioning shampoos or after-shampooing rinses. It is worth noting that, in cosmetic applications, quaternaries may cause ocular and local irritation. Among quaternaries, some are used as germicides and disinfectants (e.g., benzalkonium chloride).

Heterocyclic Ammonium Salts. Heterocyclic quaternaries are derived from hetero-cyclic aliphatic or aromatic compounds in which a nitrogen atom constitutive of the cycle is quaternized.

The quaternaries derived from imidazoline and morpholine are used as hair conditioners and antistatic agents. Those derived from aromatic heterocycles are used as germicides.

Alkyl Betaines. Alkyl betaines, which are N-trialkyl derivatives of amino acids ([RiR2R3]N+CH2COOH), are classified as cationics because they exhibit a permanent positive charge. Because they also have a functional group able to carry a negative charge in neutral and alkaline pH conditions, they are often regarded—although this position is questionable—as ''amphoterics.'' The positive charge is always carried by a quaternized nitrogen while the anionic site can be a carboxylate (betaine), a sulfate (sulfobetaine or sultaine), or a phosphate (phosphobetaine or phostaine).

Betaines are good foaming, wetting, and emulsifying surfactants, especially in the presence of anionics. Alkylamido betaines deliver more stable foam and are better viscosi-fiers than alkyl dimethyl betaines. Betaines are compatible with other surfactants and they frequently form mixed micelles; these mixtures often deliver unique properties that are not found in the individual constitutive surfactants.

Betaines have low eye and skin irritation; moreover, the presence of betaines is known to decrease the irritation effect of anionics.

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