Classification Of Emulgents

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Monovalent alkali metal and ammonium soaps

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They are the sodium, potassium or ammonium salts of long chain fatty acids 12-18 C e.g. oleic, stearic, ricinoleic.

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Monovalent soap preparation

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are prepared by saponification of the fatty acid glycerides in alkaline solution

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Monovalent soap uses

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o/w emulgents.

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Monovalent soap stable pH

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stable above pH 10 but are very sensitive to acids.

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Monovalent soap in hard water

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Not useful coz Multivalent ions e.g. Mg2+ , Ca2+, Al2+ and Zn2+ produce marked water insolubility

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Monovalent soap good properties

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excellent cleansing properties

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Monovalent soap limitations

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Toxicity
gastro-irritant properties
unpleasant taste

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Polyvalent alkali metal soaps

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Ca2+, Mg2+, and Zn2+ salts of fatty acids soaps

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Polyvalent alkali metal soaps uses

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w/o emulgents especially calcium
salts

They are relatively water insoluble

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Amine soaps

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amines form salts with fatty acids - oleic and stearic fatty acids. e.g. triethanolamine

o/w emulsions

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Amine soaps advantages

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stable, fine grained emulsions
non-irritant to the skin pH 7-8
resistant to heavy metals and pH changes than alkali soaps
produce clear gels with good detergent cleansing properties

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Amine soaps limitations

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Unsuitable for internal use.

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Alkyl sulphates and phosphates

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esters of fatty acids (usually from palm or coconut oil) reacted with sulphuric or phosphoric acid.
They are strongly hydrophilic and form o/w emulsions (e.g. sodium lauryl sulphate and sodium
cetostearyl sulphate).

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Alkyl sulphates and phosphates advantages

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strong wetting properties.
fairly stable to pH changes
Form complex films with fatty alcohols (cetyl or cetosteary alcohol) producing stable quality emulsion

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Sodium lauryl sulphate uses

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emulsifier and a solubiliser

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Sodium lauryl sulphate limitations

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susceptible to hydrolysis.

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CATIONIC SURFACTANTS

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quaternary ammonium compounds
o/w emulgents.

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CATIONIC SURFACTANTS advantages

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Can be used as emulgent and preservative
(cetrimide and benzalkonium chloride)

Form good, stable cleansing emulsion when combined with fatty alcohols (cetyl alcohol)

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pyridinium cationic surfactants e.g Cetylpyridinium bromide (a pyridinium salt)

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used as a disinfectant

bactericidal activity against a wide range of
gram-positive and some gram-negative organisms.

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cetrimide

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most stable emulgent in the pH 3-7 range.

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Stearyl trimethyl ammonium chloride

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good hair conditioning properties (cation is attracted
to the negative charge of the keratin)

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NONIONIC SURFACTANTS

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do not ionize to any great extent in solution
compatible with anionic and cationic substances.
stable in electrolytes and to pH changes.
In excess they tend to preservatives with phenolic or carboxylic acid groups.
low foaming and cleansing properties but are good emulqents

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Glyceryl monostearate

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excellent emollient and confers smoothness and fine texture on an emulsion.

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Glycol and glycerol esters e.g. glyceryl monostearate

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strongly hydrophilic nature.
Form stable complex film if combined with other agents e.g soaps to produce o/w emulsion

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Sorbitan esters (Spans)

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Formed by the dehydration of sorbitol to form the cyclic sorbitol moiety, and subsequent esterification with free fatty acids.
hydrophobic w/o emulgent

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Span 20, 40, 80 etc

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The lipophilic character is proportional to the length of the acid chain, allowing products of varying
character

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Sorbitan esters (Spans) uses

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are used alone to form w/o emulsions or in combination with polysorbates to form either o/w
or w/o systems.

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Polysorbates (Tweens) formed by

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condensation of the sorbitan esters (Spans) with polyoxyethylene.
(CH2-O- CH2)n - they are the polyethylene glycol derivatives of sorbitan esters.

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Tween advantages

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different character prod can be synthesized (# and polyoxyethylene groups length det hydrophylicity )
produce stable fine-textured o/w emulsions
no oral or topical irritancy.
suit oral emulsions of mineral, vegetable and fish liver oils
readily removed by washing
Can be combined with sorbitan esters produce different texture and consistency w/o or o/w emulsions

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Polysorbate 80

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used for parenteral emulsions and to emulsify dietary oils and fats (TPN).

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Polyoxyethylene Esters (macrogol esters)

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They are synthesized from long-chain ethylene oxide polymers.

They have a predominantly hydrophilic character and form o/w emulsions

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Polyoxyethylene Esters (macrogol esters) hydrophilicity and lyophilicity

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depends on the number of oxyethylene groups present
More groups confer greater hydrophilic character e.g. PEG-400 (stearic acid ester (n:17) and 400 oxyethylene groups)

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Polyoxyethylene Esters (macrogol esters) uses

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be blended with other emulgents to obtain a particular HLB character for emulsions

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Polyoxyethylene Ethers (macrogol ethers)

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These are condensation products of polyethylene glycol and fatty alcohols. O/W emulsion
tend to be mixtures of polymers of similar molecular weights eg. Cetomacrogol 1000 has n=15 or 17 and m= 20-24.

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Polyoxyethylene Ethers (macrogol ethers) advantages

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are compatible with many anionic, cationic and nonionic medicaments.
in gels and as cleansers in shampoos and cosmetics.
solubilising agent for volatile oils.

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Polyoxyethylene Ethers (macrogol ethers) limitations

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too hydrophilic to produce stable emulsions when used alone
Only produces an excellent emulsion when used with the hydrophobic cetostearyl alcohol

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AMPHOTERIC/AMPHOLYTIC SURFACTANTS

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This class includes natural phospholipids such as lecithin as well as various and proteins.

cationic in acid and anionic in alkaline, zwitterion in neutral.

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AMPHOTERIC/AMPHOLYTIC SURFACTANTS USES

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used as bactericidal detergents and nonirritant
shampoos.

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Acacia

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best emulgent for oral o/w emulsions at concentrations of between 5 - 10%

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Acacia Limitations

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emulsions are too sticky for external use
produces emulsions of low viscosity (thicken with tragacanth)
Susceptible to creaming because of low viscosity

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Tragacanth

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Used mainly as an emulsion stabilizer (0.5 - 1%), particularly for acacia emulsions.

produces coarse emulsions (high viscosity
of its mucilages.)

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Sodium alqinate

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Used mainly as an emulsion stabilizer (1 - 5%), particularly for acacia emulsions.

produces solutions of a high viscosity.

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Semisynthetic polysaccharides (Methylcellulose and Sodium carboxymethylcellulose )

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water-soluble cellulose resulting from the methylation of cellulose.
Name followed by a number viscosity of a 2% aqueous solution at 200C.

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STEROL-CONTAINING SUBSTANCES

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Derived from animal sources and include beeswax, wool fat, wool alcohols, lanolin cholesterol
and bile salts. All produce w/o emulsions.
Wool fat and wool alcohols both contain cholesterol and other sterols. W/O emulsion.

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FINELY DIVIDED SOLIDS

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Solids possessing both hydrophilic and hydrophobic properties
Include the natural clays e.g. bentonite and magnesium silicate and colloidal aluminium and magnesium hydroxides.

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FINELY DIVIDED SOLIDS USES

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clays form hydrated dispersions increasing viscosity and stability of the o/w emulsion.
used as emulsion stabilizers for external lotions and creams.
emulsifying agents for oral o/w preparations.

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Aluminium & magnesium hydroxides

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Finely divided solids used as emulsifying agents for oral o/w preparations.