The formulation basics for personal cleansers: for the beginning cosmetic chemist, here's a primer of the science, art and the secret tricks of the trade to create great hair shampoo, body wash and hand soap.
Primary surfactants perform two important functions--cleansing and foaming. Desirable personal cleanser properties may also include quick and easy miscibility with water; instant flash foaming; nice, creamy lather that feels silky soft upon application, effective cleaning of soils from the hair and/or skin, quick and easy rinseability, and soft and silky afterfeel.
Alkyl sulfates and alkyl ether sulfates such as sodium/ammonium lauryl sulfates and sodium/ammonium laureth sulfates, are cost-effective primary surfactants which are used in many personal cleansing applications. Alkyl sulfates and alkyl ether sulfates meet consumer demand for foam and lather as well as cleansing. These reasonably priced, high foaming surfactants have excellent cleansing properties.
Most formulators prefer to use a combination of lauryl sulfate and lauryl ether sulfate. Lauryl sulfates produce creamier foam with higher volumes of small bubbles compared to ether sulfates. Conversely, ether sulfates, particularly the two and three moles (EO), produce better flash foam. To develop a product with optimum yet balanced lather profile, lauryl and lauryl ether sulfates are added in a certain range of ratios.
For sodium lauryl sulfate and sodium laureth-2 sulfate a good starting ratio is 3:7 on an active surfactant amount basis. This combination of lauryl and laureth sulfate will give a nice, well-balanced lather profile that the consumer expects from a personal cleanser. This ratio is also a good starting point for viscosity response and short flow (non stringy) properties of the final product. Ammonium lauryl/laureth sulfates may be slightly better than their sodium counterparts in amount of foam generated, clarity at lower temperatures and viscosity response in certain formulas but they can release ammonia at higher pH.
Some of the attributes that secondary surfactants impart to a formula include increased viscosity, stabilized foam and reduced skin and eye irritation.
Personal cleansing systems based on alkyl sulfates and alkyl ether sulfates are relatively easy and cost effective for viscosity buildup. Generally speaking, a 10% active sulfate system will require about 1-2% of alkanolamide and 1-3% sodium chloride to reach or exceed a viscosity of 10,000 cps. Regarding rheology, this 3:7 lauryl to laureth sulfate ratio imparts a nice short flow for the system. Higher amounts of lauryl sulfates may cause stringy flow whereas the higher amounts of laureth sulfate will not have optimized creaminess of the lather and may not build maximum viscosity.
Developing a Shampoo Formula
In the past, cocamide DEA was a common alkanolamide for viscosity building and foam stability, and some formulators still use it. It is a liquid material and has balanced properties for viscosity building as well as stabilizing the foam. Higher chain amides such as oleamide DEA will generally build higher viscosities (on an equal active basis) than its coco counterpart but the foam stability will not be as good as that obtained by cocamide DEA. Some formulators use cocamide MEA to avoid the DEA. Cocamide MEA will generally build somewhat higher viscosities than cocamide DEA, but not as high as oleamide DEA. The foam stability provided by cocamide MEA is comparable to that provided by cocamide DEA. Cocamide MEA is a waxy solid and requires heat to make the finished product.
Salts, such as sodium chloride, increase the viscosity of sulfate-amide systems. It is always good to run a salt viscosity curve for each formula, which can be done by adding the salt to the formula in increments of 0.2% or so. After a certain amount of salt has been added, the viscosity peaks and any more salt will actually reduce the viscosity rather than increase it. This type of curve is useful for adjusting the viscosity of the product. Some formulators purposely exceed the curve in order to reduce the stringy character of the formula. Stringy flow can also be corrected by adding a little polysorbate 20 or propylene glycol to the formula. However, these materials will reduce the viscosity as well, which is why they are added in very low quantities such as 0.1-0.5%.
Betaines, like cocamidopropyl betaine (CAPB), are good secondary surfactants because of their high-foaming, viscosity-building and mildness-providing properties. In some formulas, CAPB acts as sole viscosity builder. So, for example, "amide free" formulas can be made with CAPB. When used in conjunction with alkanolamides, CAPB increases the viscosity more than can be achieved with the amide alone. As a general rule, 10-20% of alkanolamide and 10-20% of active CAPB based on the active amounts of the primary surfactants is a good starting point for formulation development. For example, with 10% total actives of alkyl/alkyl ether sulfates, 1-2% of an alkanolamide and 1-2% active CAPB (or about 3-6% as supplied) is needed. Therefore a starting formula for a simple medium grade shampoo can be as follows.
Ingredients %Wt. Water q.s. to 100 Sodium lauryl sulfate 10.0 (as supplied 30% active) Sodium laureth-2 sulfate 26.0 (as supplied 27% active) Cocamide DEA 2.0 Cocamidopropyl betaine 6.0 Preservative, perfume, dye q.s. Citric acid (if required) to pH 6.0
A wide variety of secondary surfactants improve the mildness properties of products such as shower gels, baby shampoos and baby bath products. Amphoterics, such as amphoacetates and amphopropionates, are used for mildness. Sulfosuccinates, alkyl polyglucosides, betaines, sultaines, sarcosinates, isethionates, taurates, ethoxylated sorbitan esters and amino acid-based surfactants improve mildness. An important aspect of a personal cleansing formula is a good lather profile. That is why it is important to keep some of alkyl/alkyl ether sulfate in the formula and incorporate one or a combination of some mild surfactants.
Specialty ingredients include a wide range of materials such as conditioning agents, special effect additives, proteins and vitamins. Conditioning shampoos, also called 2-in-1 formulas, use conditioning agents such as fatty amines, fatty quats, polydimethyl siloxanes, organo modified siloxanes (amino functional, quaternized silicones) and quaternized polymers (cellulose and guar). Conditioning shampoos using quats and amines must be compatible with any anionic surfactants in the formula. A formulator must carefully choose the quality and quantity of fatty quat and fatty amine to avoid heavy buildup, dulling, and flattening effects in the final product. Silicones are good for shine and luster. Small amounts of silicones will do a good job of light conditioning without heavy buildup. Quaternized polymers, such as quaternized cellulose, also provide a light conditioning effect and impart static control and easy combing, if used in proper amounts.
Additives to Consider
Shampoo formulas may also include special additives. Some of these materials include:
Proteins: Hydrolyzed vegetable protein, hydrolyzed wheat protein, hydrolyzed milk protein, hydrolyzed silk and hydrolyzed collagen.
Vitamins: Panthenol, biotin, vitamin E acetate, vitamin A and D palmitate.
Moisturizers/humectants: Glycerin, propylene glycol, sodium PCA, amino acid based surfactants and hylauronic acid.
Emollients: Esters like isopropyl myristate, decyl oleate and C12-15 alkyl benzoate.
Natural oils: Jojoba oil, aloe vera oil, safflower oil and almond oil.
Botanicals: Chamomile, aloe vera, rosemary and hops.
Aromatherapy: Lavender, ylang ylang, patchouli and other essential oils.
Minor ingredients include preservatives, perfume, dye, pH adjusters and chelating agents.
Developing a Shampoo Formula
In developing an economy shampoo formula with 6-8% surfactant solids, it is important to remember that the market is trending toward natural and biodegradable ingredients. Therefore it is important to find a surfactant system that is inexpensive yet high foaming, derived from natural, vegetable resources and biodegradable. Alkyl sulfates and alkyl ether sulfates fit the bill. You can get sodium and ammonium lauryl sulfates and sodium and ammonium laureth (or lauryl ether) sulfates that are derived from natural coconut oil. They are all biodegradable, high-foaming anionic surfactants.
A good starting point for an economy shampoo includes 7% active alkyl sulfates/alkyl ether sulfate, about 1% cocamide DEA and enough sodium chloride to get the maximum viscosity. As salt is added, the viscosity starts to increase up to a certain concentration of the salt after which any more salt will reduce the viscosity. The salt / viscosity curve get affected by the quality/quantity of anionic surfactants, and quality/quantity of alkanolamides among other factors. Generally speaking, the higher the amount of anionic surfactant and amide, the lower the amount of salt it will take to reach the peak viscosity. Formulators add betaines such as cocamidopropyl betaine in shampoos for mildness, viscosity building and to creaminess to the lather. Cocamidopropyl betaine also affects the salt viscosity curve. Other viscosity builders such as cellulosic polymers, polyacrylates and highly ethoxylated esters will also impact the curve. So the salt curve should be run on the final formula with all other ingredients in it. So far we have talked about increasing the viscosity but occasionally, a formula gets very thick and viscous. The formula may have a long, stringy flow problem as well.
One way to reduce the viscosity and stringy character of the formula is to go over the peak of the salt curve and reduce viscosity by adding an excess amount of salt. This will also reduce the stringy flow property of the formula. Other techniques to reduce viscosity include adding alcohol (denatured ethyl alcohol) and/or glycols (propylene glycol). Surfactants with higher ratios of hydrophile (bulky hydrophilic group and relatively smaller hydrophobe) such as xylene sulfonates will also reduce the viscosity. Certain nonionic surfactants such as polysorbate 20 also tend to reduce the viscosity of anionic surfactant based formulas. Another important aspect of viscosity modifiers is the feel (and any other modification for example to the lather profile) of the formula, that they introduce. Temperature/viscosity and pH/viscosity curves are also important selection criteria for viscosity builders. Relatively flat curves would be preferable. In other words you would want the formula viscosity to remain relatively unchanged when the temperature or pH changes during storage or use.
Alkanolamides not only build the viscosity but also act as foam stabilizers. Alkanolamides also enhance "body" and provide lubricity to the formula, at relatively lower cost. Cocamide DEA will provide a relatively lower increase in viscosity but better foam stability as compared to oleamide DEA which will provide higher viscosity but less foam stability. Cellulose derivatives such as hydroxypropyl methylcellulose or hydroxyethyl cellulose provide viscosity building, foam stability and lubricity. The dispersion of these polymers may be tricky and takes time and certain kind of mixing equipment.
Polymers To Try
There are surface treated polymers available from suppliers that will be easier to disperse and hydrate in water. If there is salt and/or other electrolytes present in the formula, make sure the polymer will be able to tolerate that amount of salt. Natural polymers such as xanthan gum or guar can also be used as viscosity builders. Guar also comes as cationic active. Cationic guar will not only increase the viscosity but also add some conditioning properties to the formula. Similarly, polyquaternium-10, a cationic cellulose, adds conditioning and builds viscosity. These polymers, despite being cationic, are generally compatible with anionic surfactants. However, always run a stability test at various temperatures (room temperature, refrigerator, oven at 500[degrees]C and freeze thaw) for a new formula. Acrylates also build viscosity. Hydrophobically modified polymers that are available as 30% active liquids provide the ease of processing without all the trouble of getting a powdered polymer dispersed and fully hydrated in water. Highly ethoxylated materials such as PEG-120 methyl glucose dioleate, PEG-150 distearate, PEG-150 polyglycery1-2 tristearate and PEG-150 pentaerythrityl tetrastearate are also used as thickeners, particularly where there are nonionic surfactants or other hard to thicken surfactants involved. Some of these thickeners, like PEG-150 distearate for example, are waxy solids that must be dissolved with heat and mixed with the batch. They also add a heavy feeling that is slightly on the sticky side. Products thickened with PEG-120 glucose dioleate may have a relatively sharp temperature/viscosity curve; i.e., there may be a sharp viscosity drop with a relatively small increase in temperature.
Test and Test Again
No formulation work is complete without proper safety, physical, chemical, performance, stability and consumer panel testing. It is a good idea to have more than one or two final prototype formulas. Subject the formulas through these tests and then choose the final formula. But keep some formulas for back up. Another important aspect of product development is "product scale up." Any formula, no matter how good it looks in the lab, is worthless unless it can be reproduced in your plant.
The art of formulating a shampoo is the art of balancing the desirable properties in the formula and keeping the undesirables to a minimum, while achieving a specified raw material cost. In many formulas for example, an increase in viscosity can be associated with an increase in stringiness. The formulator's job is to reach a highly desirable viscosity without the undesirable stringiness.
The information contained herein is provided in good faith as starting guidelines to formulators and is based on the study in our laboratories and work of others. Pilot Chemical Company makes no warranties, expressed or implied, as to the accuracy of the information contained herein. Nothing contained herein grants or extends a license or permission in connection with patents of Pilot Chemical Company or others.
By Shoaib Arif
Pilot Chemical Co.
Shoaib Arif is manager, home and personal care applications at Pilot Chemical Co., Cincinnati, OH. Previously, he was manager of technology at Degussa Corp. He has also worked for Noveon, Witco and Olin Chemicals. The author has more than 30 years experience in formulating personal care and H I & I products and invite inquiries regarding formulation of such products. For assistance in formulating personal care or H I & I products please call Mr. Arif at 513-939-6150 or E-mail him at sarif@Pilotchemical.com
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|Publication:||Household & Personal Products Industry|
|Date:||Sep 1, 2009|
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