REVIEW ON GUIDELINES FOR FOAMING AGENTS
EMULSIFIERS & RHEOLOGY MODIFIERS:-
ASSOCIATE PROFESSOR OF PHARMACEUTICS
DEPARTMENT OF PHARMACEUTICS
GOVERNMENT COLLEGE OF PHARMACY
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FOAMING AGENTS/ SURFACTANTS:-
Foamability and stability of foam is related to surfactant structure
Production of reach and long lasting foamaccompanies all hygiene
activities and is perceived as a sign of cleansing action. Foamability and
stability of foam is related to surfactant structure and is a domain of
base surfactants. Products belonging to this class are a basic ingredient
of all wash-off formulations and make cleansing products what they are.
Surfactants as Cleansing Agents
The most common function of surfactants is to cleanse. Many consumers
still believe that the amount of foam a cleanser produces is an indication
of its cleansing efficiency, when, in fact, the amount of foam has much
more to do with the aesthetics of the product, rather than its cleansing
potential. Ingredient names containing the words sulfate, sulfocuccinate,
or the prefix sarco, indicate strong cleansing tendencies and provide
luxurious, thick foam
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•Sodium lauryl sulfate, sodium laureth sulfate, disodium lauryl sulfosuccinate, cocoyl
sarcosinate are all representative of this group. Milder alternatives to these
ingredients that contain words in their names like ampho or the suffix -taine, such as
cocoamphocarboxyglycinate and cocobetaine, are more suitable for barrier-
compromised skin that cannot tolerate strong surfactants.
•In recent years, the sulfate-free claim has become one of the most popular
marketing claims, promoting low-foaming cleansing options as healthier, barrier-
friendly alternatives to high foaming, potentially dehydrating cleansers. Likewise,
consumer demand for surfactants from sources other than petrochemical has
contributed to the development of greener alternatives, some of which are derived
from innovative sources such as cannabis sativa seed oil PEG-8 Esters.
•Other green surfactants include ingredients from oats, apples, coconut, sugar
beets and sweet almond seeds, such as sodium lauryl oat amino acid, sodium
cocoyl glutamate, sodium cocoyl hydrolyzed, amaranth protein, disodium
sulfosuccinate laurylglucoside crosspolymer, potassium olivoyl hydrolyzed oat
protein, sodium cocoyl apple amino acids, sodium, sweetalmondamphoacetate,
saponins, and betaine.
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•Differentiation of products and obtaining specific applications and
aesthetic properties is achieved through use of co-surfactants.
•Application of secondary surfactant can have a synergistic effect on
foaming, foam stability, rheology building properties and improve
mildness of the formulation.
• Dispersion of hydrophobic ingredients in water solution is achieved
through application of surface tension reducers.
• Emulsifiers arrange themselves at the water/oil interfaces and allow
solubilization of oils.
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Surfactants/Foaming agents:-
Surfactants are cleansing and foam forming agents. They form the base of
almost all cleansing products available. They mix with water and fat of the
skin to remove dirt. The term “surfactant” is broadly used to denote surface
activity, and is noted for its ability to reduce the surface tension between two
phases.
In general, surfactants may act as detergents, wetting
agents, emulsifiers, foaming agents, and dispersants. The lipophilic chain
is attracted by the soil and penetrates while the surfactant forces the soil to
an open surface area and then detach from the surface.
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the ability of cleansing agents to remove contaminants from a substrate,
should it be hair or skin. Surfactants are mainly used for their ability to
reduce the surface tension between two phases. In general, they may act
as detergents, wetting agents, emulsifiers, foaming agents, and
dispersants.
Surfactant Classification
Surfactant molecules rest at a water interface, forming a
thermodynamically stable system; such as micelles, lamellae, micro-
emulsions, emulsions and liquid crystals.
The non-polar component of a surfactant is hydrophobic and is
typically insoluble in water; based typically on linear or branched alkyl and
alkyl phenyl groups.
The polar component is hydrophilic; this region determines a
surfactant’s classification:
Nonionic (polyalkoxylate, glucose, sucrose, amine oxide)
Anionic (sulfate, sulfonate, carboxylate, phosphate)
Cationic (alkylammonium salts)
Zwiterionic (which contains both anionic and cationic groups)
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Portion and structure of hydrophilic and lypophilic parts of surfactant –
intrictic for every surface active agent enables classification into different
application function.
Cationic Surfactants
Cationic Surfactants are not widely used in cleansers because they can
contribute an amine odor to a formula and potential irritants; salts are milder and
contribute to conditioning properties of a treated surface (e.g., alkylamidopropyl
amines)
Cationic Surfactant Advantages
Good for acidic systems, where they provide good conditioning properties.
Cationic surfactants have been under-utilized because of poor purity in the past
(as processes have improved, use of them is showing a resurgence); good foam
boosters; stable in amphiphilics; reduce irritation of sulfate systems; long-chain
alkyl amine oxides require a higher-than-normal salt concentration to form worm-
like micelles.
Historically used for their foam boosting properties and ability to increase viscosity;
can be used in low pH systems.
Cationic surfactants are used to reduce the irritation value of anionics; act as a
foam booster with improved substantive conditioning.
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The specific functionof the surfactant in theformulation stems from its
chemical structure.
Zwiterionic Surfactants:-
Zwiterionic Surfactants Advantages
Based on mono- or di-esters and an ethoxylated alcohol; milder than
sulfates but higher cost.
Head-group charge pH dependent; nitrogen becomes protonated at low
pH (positive charge-cationic).
Carboxylic acid become deprotonated at high pH (negative charge-
anionic).
Within this grouping are phospholipids, which can be used for their
physiological role and formation of liposomal structures to enhance
delivery of actives.
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Emulsions and Emulsifiers:-
An emulsion can be defined simply as two immiscible fluids in which one
liquid is dispersed as fine droplets into the other.
Homogenized milk is an example of a typical oil-in-water (o/w) emulsion.
Milk fat, representing oil phase, is dispersed in water by the
homogenization process.
Emulsifiers, in this case a milk protein called sodium caseinate, as well as
several phospholipids, prevent the fat and water from separating.
Micelle is the term frequently mentioned when emulsions are discussed.
It refers to the way water-loving heads and oil-loving tails arrange
themselves in a special way, depending on the environment.
They are usually driven to arrange either with the water-loving heads out
and the oil-loving tails in (o/w) or with the water-loving heads in and the oil-
loving tails out (w/o).
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The most common emulsions in the cosmetic industry (about 80 percent)
are the ones in which oil is dispersed in water (o/w).
They have high water content and, therefore, low in cost. These emulsions
are favored for their stability and flexibility, as well as their non-greasy, non-
oily feel.
On the other hand, w/o systems offer longer lasting emolliency, wash-off
resistance, and barrier protection.
They spread more easily on skin, and often leave a lubricious, rich or oily
feel, favored by mature clients and consumers with dry, barrier-
compromised skin.
These formulas tend to be less cost effective, as oils are always more
costly than water and these types of emulsions are generally more difficult
to produce.
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To create emulsions, typically a surfactant (emulsifier) is used.
Emulsifiers blend and hold together ingredients that would not normally
mix very well.
In cleansing products, the ability of an emulsifier to combine waters
and oils gives a final product the ability to both cleanse and condition
the skin at the same time.
Some commonly used emulsifiers in skin care are glyceryl stearate,
PEG-100 stearate, stearyl alcohol, cetyl alcohol, laureth-23, steareth
alcohol, cetyl/PEG/PPG 10 dimethicone, and stearic acid.
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Fatty acids are key components of many cosmetic emulsifiers, due to
their miscibility in a variety of natural and synthetic oils. They are
derived from natural oils such as coconut, palm kernel, sunflower,
wheat germ, and so on.
They are used as conditioning agents to improve the surfaces of hair
and skin, thickening agents to make thin products creamier, as
secondary emulsifiers to help create stable mixtures of oil and water,
and as opacifying agents to make formulas look more luxurious.
Emulsifiers have a hydrophilic or water-loving head and a lipophilic or
fat loving tail. The hydrophilic head clings onto the water phase of an
emulsion and the lipophilic tail creates a ball around the oil-based
ingredients, the oil phase of the emulsion.
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Being that close to 80 percent of all skin care ingredients are at least in
part derived from petroleum, it should come as no surprise that a great
number of emulsifiers are petroleum/hydrocarbon derived as well.
Esters, like polyethylene glycol or ethylene glycol, are called PEG esters
and represent the most prominent group of petroleum-related emulsifiers.
These emulsifiers make the creation of many beautiful, stable and unique
emulsions possible, yet they are constantly under the scrutiny of the
consumer.
They are often called ethoxylated surfactants, as ethylene or propylene
oxide is utilized in the chemical reaction. PEGs are either used alone or
linked to other ingredients to enhance solubility into a product.
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Depending on the manufacturing process, PEGs may be contaminated
with measurable amounts of ethylene oxide (a known carcinogen) and
1,4-dioxane (a possible carcinogen).
PEGs are still being reviewed for genotoxic effects that can lead to
mutations and cancer, but to date, nothing has been found.
Chemists are actively researching alternatives, but the only known
alternatives are either three to five times the cost of the current
emulsification system or do not provide long-term stability. This is an
ongoing issue for cosmetic chemists and product formulators
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Choosing an emulsifier is not only crucial for the stability of an emulsion,
but can also have a large impact on formula consistency, skin feel, and
perceived performance. The skin care market continues to be fast-paced
and highly competitive.
Consumers expect performance, convenience and superior aesthetics,
along with long-lasting, highly efficient moisturizers and age-fighting
creams that go on smoothly, without tackiness or residue. Innovative,
multifunctional, high performance products have the best chance of
success.
Silicone emulsifiers and silicone emulsions are emerging as an additional
option that can help bridge the gap between the o/w and w/o systems,
providing the best of both worlds, helping to produce stable and
aesthetically superior emulsions with high water levels, making them
relatively affordable.
These evolving surfactant and emulsion technologies are, and will continue
to be, at the core of innovative formulations, fully capable of satisfying
even the most demanding consumer requirements.
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Thickeners and rheology modifiers:-
Rheology Modifiers are ingredients that alter the flow of a product.
•In doing so they also alter the feel, offering increased slip and silkiness,
and behaviour, because of the way that they move, smoothly, across the
skin.
•They will usually improve the suspension capability of any gel while also
creating a more fluid product, that flows easily.
•Most rheology modifiers will also improve absorption rates, and depth,
while eliminating dryness.
.
•For some products, due to composition of surfactant system and/or
specific requirements of the formulation, use of special thickeners is
required. The example could be delicate formulations like baby care
products, where low concentration of sodium chloride and Sulfate free
formulations are a market standard.
•Rheology modifying products find an application where high viscosity of
the formulation is required in order to achieve desirable effect. These are
pearlizers, capsule or shimmer suspensions and soap dispensers.
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Rheology modifiers are often referred to as thickeners, and whilst
increasing the apparent viscosity will confer a feeling of “quality” to the
formulation, this is only one aspect of rheological control.
The product itself can be Newtonian or pseudoplastic, thixotropic, be a
ringing gel or a stringy flowable liquid.
This will then affect the way that the product appears in the bottle, how
easy it is to pour or scoop from the packaging, how easy it is to rub into the
skin or along the hair shaft, and how easy it is to rinse and remove the
product after use.
It will also be essential to choose the correct rheological characteristics to
ensure the stability of the finished formulation.
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The rate of recovery of a system when stress is removed is also very
important.
When a shear thinning system shows delayed viscosity recovery, it is
described as thixotropic (Fig.3).
This is one of the most important types of flow in cosmetics. Controlling the
degree of thixotropy enhances the application of a cream, eliminates
dripping of a roll-on antiperspirant or allows brushmarks in a coat of nail
lacquer to disappear, leaving a smooth film.
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•Activity in lowering surface tension between solids and liquids is achieved
by application of wetting agents.
•This is necessary in various types of formulations such as shampoos or
colourisation compositions.
•Better spreading of the dying product on hair ensures good pigment
distribution and better final effect.
•From the other side, good hair wetting efficiency results in satisfying
washing and supplementation as well if applied in hair care products
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To achieve such varied effects, a number of different types of
rheology modifier are available to the formulator. These include
natural gums such as guar and starch, modified naturals such
as cellulose derivatives, synthetics such as acrylic polymers
and inorganic such as clays.
Polymeric Rheology Modifiers:-
Polymeric rheology modifiers can be added to formulations to
control the rheology and the required effect can be achieved
with low concentrations of the polymer. The resulting solution
will have a rheology somewhere between the viscous behaviour
of water and the elastic behaviour of rubber.
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REFERENCES:-
Randy Schueller & Perry Romanowski. Beginning Cosmetic Chemistry,
2nd edition. (2003) Allured Publishing Corporation.
Internet sources
“Harry’s Cosmeticology”–edited by M. Rieger and
“The Chemistry & Manufacture of Cosmetics”– edited by M.
Schlossman
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THANK YOU
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