Shampooing with pure anionic surfactants can leave hair difficult to comb while wet, and prone to ‘fly-away’ when combed after drying. Improvement of the wet-combability and reduction of static charge build-up can be achieved by addition of conditioning agents. These are especially effective if the formulation also contains amphoteric surfactants such as betaines or amine oxides. Cationic surfactants used in hair rinses are normally incompatible with anionic surfactants and cannot be used in shampoo formulations. This problem can be overcome by the use of quaternized polymers. An example is Polyquaternium 10, a quaternized hydroxyethyl cellulose, which is compatible with most of the anionic surfactants and can therefore also be used in clear formulations. It shows excellent conditioning properties and imparts manageability and body to hair. Due to its very high substantivity to hair, very low concentrations (below 0.5%) are sufficient. Use of high concentrations may lead to over-conditioning and build-up on the hair. Used in shower- or foam-bath formulations, polyquaternium 10 can improve skin-feel after use. Other important polyquats are Polyquaternium 7, Polyquaternium 23, Polyquaternium 8, and Polyquaternium II (CTFA nomenclature).
Small amounts of fatty components such as fatty alcohols or monoglycerides can support the conditioning effect of shampoos. Silicones can be very effective conditioners but are difficult to incorporate and may act as antifoaming agents.
Wednesday, May 28, 2008
Foam stabilizers
In the presence of oily soils such as sebum, the stability of shampoo foam can be drastically reduced. The so-called foam boosters act as stabilizers and also modify the foam structure to give a richer, dense foam with small bubbles. The alkanol amides are well known for this behavior. The most important types are the monoéthanolamides, which are obtained by amidation of fatty acids with monoethanolamine. Diethanolamides are usually obtained by amidation of fatty acid methylester, or triglycerides such as coconut oil, with diethanolamine. The latter are liquid products with a typical glycerol content.
The monoethanolamides are the most effective foam boosters but are difficult to incorporate due to their high melting points (approx. 800 C). The diethanolamide based on coconut oil is the most popular one, although the thickening effect is reduced, due to the glycerol. The price is relatively low and the product is easy to handle compared with pure amides based on methyl ester. Today, the diethanolamides are under discussion due to possible formation of carcinogenic nitrosamines. Consequently, EC regulations allow only alkanolamides with free diethanolamine below 4%.
Other well-known foam boosters are the amine oxides and betaines described previously. Protein hydrolysates and cellulose derivatives such as CMCs are recommended as foam stabilizers. Ethylene glycol mono- and distearates (EGMS, EGDS) are most often used as pearlescent agents in surfactant formulations. They have to be incorporated at high temperatures (approx. 70-750C), therefore ready-made liquid pearlescent bases are now very popular. A wide range of bases with different appearances, from turbid to real pearlescent, is offered on the market. Very effective opacity without pearlescent effect can be achieved with polystyrol dispersions. These are already highly effective at very low concentrations. Direct contact with perfume oils can result in coagulation of the polystyrol, and must be avoided.
Continuing of thickeners
A side-effect of all these thickeners is that they modify the flow properties, leading to increased Newtonian flow. This contrasts with salt- or polymer- thickened systems, which show typically pseudoplastic flow behavior.
Polymer thickeners like natural gums, cellulose derivatives (carboxymethyl cellulose, hydroxyethyl cellulse) and carbomers (CTFA name) are used more often in emulsions than surfactant-based formulations. Another type of rheological modifier is the inorganic bentonites, which can be used to obtain a yield point. This gives stability to shampoos carrying particles in suspension, e.g. pearlescent formulations or formulations containing zinc pyrithione, preventing sedimentation and separation. The systems are often thixotropic and will flow on shaking. In the absence of shear stress, such systems behave as solids.
Polymer thickeners like natural gums, cellulose derivatives (carboxymethyl cellulose, hydroxyethyl cellulse) and carbomers (CTFA name) are used more often in emulsions than surfactant-based formulations. Another type of rheological modifier is the inorganic bentonites, which can be used to obtain a yield point. This gives stability to shampoos carrying particles in suspension, e.g. pearlescent formulations or formulations containing zinc pyrithione, preventing sedimentation and separation. The systems are often thixotropic and will flow on shaking. In the absence of shear stress, such systems behave as solids.
Shampoo and bath additives
Shampoo and bath additives
Thickeners
A high viscosity is often very important both for product stability and for handling of a cosmetic product. For shampoos, shower and foam bath products, viscosities between 400 and 4000mPas are typical. Pearlescent products should have a minimum viscosity of 2000 mPas to avoid precipitation. In the case of ether sulphate as the main surfactant, the thickening can easily be achieved by addition of electrolytes (chlorides of sodium, ammonium or magnesium, for example) to the formulation. The mechanism is by an increase in the size of the micelles. The thickening effect of alkanol amides is similar. Due to possible contamination with nitrosamines, low ethoxylated fatty alcohols such as the laureth-3 are recommended as replacements. These products are also good thickeners but, unlike the alkanol amides, they increase the cloud point of the formulations.
A different principle of thickening is obtained by the use of special, high molecular weight thickeners such as PEG-6000 distearate, talloweth-6O myristyl glycol or PEG-120 methyl glucose dioleate. The structure of talloweth-60 myristyl glycol with its hydrophobic ends is very similar to that of PEG-6000 distearate. An advantage is that it is an ether product which remains stable against hydrolysis at higher temperatures or extreme pH values.
Thickeners
A high viscosity is often very important both for product stability and for handling of a cosmetic product. For shampoos, shower and foam bath products, viscosities between 400 and 4000mPas are typical. Pearlescent products should have a minimum viscosity of 2000 mPas to avoid precipitation. In the case of ether sulphate as the main surfactant, the thickening can easily be achieved by addition of electrolytes (chlorides of sodium, ammonium or magnesium, for example) to the formulation. The mechanism is by an increase in the size of the micelles. The thickening effect of alkanol amides is similar. Due to possible contamination with nitrosamines, low ethoxylated fatty alcohols such as the laureth-3 are recommended as replacements. These products are also good thickeners but, unlike the alkanol amides, they increase the cloud point of the formulations.
A different principle of thickening is obtained by the use of special, high molecular weight thickeners such as PEG-6000 distearate, talloweth-6O myristyl glycol or PEG-120 methyl glucose dioleate. The structure of talloweth-60 myristyl glycol with its hydrophobic ends is very similar to that of PEG-6000 distearate. An advantage is that it is an ether product which remains stable against hydrolysis at higher temperatures or extreme pH values.
Amphoteric surfactants
Amphoteric surfactants are surfactants where the charge changes as a function of the pH value of the formulation in which they are used. They are generally regarded a mild surfactants but this is not a simple matter and may not always be true. Amphóteric surfactants build complexes in combination with anionic surfactants and these complexes are milder than the individual surfactants.
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