Colloid and Surface Phenomena Aspects of Shampoo  

 

 

 

 


CE457/527

 

shampoo

(Photo courtesy of Reynolds metal company)

 

 

Submitted to:

 

Dr. P.Alexandirdis

Chemical Engineering Department

State University of New York at Buffalo

 

Submitted by:

Gregory Boehm

Vitor Dasilva

Daniel Fulcher

Jun Wang

 

April 9, 2002

 

 

Table of Contents

 

Introduction   ………………………………………………………………………….3

 

The Secrets of Human Hair Structure  ……………………………………………..4

 

Definitions / Descriptions of Shampoo  …………………………………………… 5

 

Chemistry of Shampoo  ……………………………………………………………   8

 

Surfactants Functions in Shampoo  ……………………………………………...  10

 

Testing Methods for Surfactants in Shampoo  …………………………………   15

 

Production Process  …………………………………………………………………17

 

Marketing considerations for Shampoo  …………………………………………  18

 

Conclusions  ………………………………………………………………………… 19

 

References   …………………………………………………………………………. 20

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Introduction

 

 

Colloid and surface phenomena is universally present in almost every surface interaction involving fluids and solids there is.  This phenomenon plays an important role in the study and understanding of various topics ranging from globe related occurrences to the processing and use of many industrial and ordinary household products such as shampoo. 

 

The focus of this report is to highlight the implications of colloidal surface effects in the manufacture of different types of shampoo and how this phenomena influence on their usage.  The interaction between these types of shampoo and the human hair will also be studied.

 

Chemical and physical properties of both human hair and different types of shampoo must be identified in order to understand how colloid and surface phenomena takes place on the production and use of this every day product.  Further sections of this report will define and discuss in detail such properties emphasizing on their colloidal behavior.  Human hair structured will be explained in order to picture the media in which this behavior occurs.  The composition of common shampoo types will be presented and their numerous agents identified.  Different types of shampoo processing will also be discussed in detailed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The secrets of Human Hair

Hair Structure

           


        Hair is composed primarily of proteins (88%), these proteins are of a hard fibrous type known as keratin. The typical structure of hair is showing in Fig. 1

 

 


Fig. 1. Structure of Hair [1]

 

        Below the skin is the hair root, which is enclosed by a sack –like structure called the hair follicle. Tiny blood vessels at the base of the follicle provide nourishment. A nearby gland secretes a mixture of fats called sebum, which keep the hair shiny and waterproof to some extern. Two sets of glands discharge secretions through the skin. Sebaceous glands arise from the walls of hair follicles and sweats glands embed in the subcutaneous layer which in the palms and soles. At the base of the follicle is the papilla; these cells play essential roles in regulating hair growth, hair cycle, and the size of the resultant hair. Surrounding the dermal papilla are epithelial keratinocytes and smaller number of melanocytes [2].

       

         Hair is structured in three basic layers.  Packed dead cells surrounding these structures are the cuticular layers of the hair.  In the center of these structures lies the medullar canal, which is actually apart of the excretory system and houses any foreign debris, heavy metals, synthetics and medications that are thrown off by the body and eventually released through the canal.  The first layer is the cuticle.  A second, thicker layer is called the cortex and sometimes a third, inner layer, called the medulla.  The cuticle is the outer layer of protective scales.  The cortex provides strength to the hair shaft, and determines the color and texture of hair.  The medulla is present only in thick, large hairs.  [3]

 

Hair Chemistry [1]

 

         When the hair is in its normal unstretched state, it is referred to as A of alpha kertin. The original configuration of the hair is held in place by the bonding found in the cortex layers of the hair. There are four types bond.

 

The Hydrogen Bond

         This bond is located between the coils of the alpha helix and is responsible for the ability of the hair to be stretched elasticity and return back to its original shape. These bonds are responsible for approximately 35% of the strength of the hair and 50% of the hair’s elasticity.

 

The Salt Bond

        The salt bond is also an ionic (electrolytically controlled) bond formed by the electron transfer from the side chain of a basic amino group to the side chain of an acidic amino acid. It is responsible for approximately 35% of the strength of the hair and 50% of the hair’s elasticity.

 

The Cystine Bond

The cystine bond also known as the disulfide bond, sulfur bond, or just S bond is formed by cross-links between cystine residues of the main polypeptide chains. This bond is perpendicular to the axis of the hair and between the polypeptide chains. It is responsible for the hair’s toughness or abrasion resistance.

 

The Sugar Bond

        The sugar bond is formed between the side chain of an amino acid having an OH group and an acidic amino group. It gives the hair toughness but little strength (5%).

Hair Life Cycle [1, 3]

      

        Hair is actually dead material when it leaves its root.  The root of a hair fiber sticks in a bag in the skin. The fiber is pushed out of this bag about 0.35mm per day, making an average growth rate of 1cm, or half of an inch, per month. The growth rate is however very much related to an individual’s age, diet and etc.  Healthy hair has an average lifetime of 2-6 years.  After a rest period of three months the single hair falls out, and a new fiber starts to grow out of the bag.  The lifetime also depends on circumstances and each person.  The lifetime of hair is responsible for the maximum of hair length one can have. 

 

There are three phases in the hair life cycle:

Active growth phase, or anagen phase: the hair root produces the cells that form the living part of the hair. This pushes the cells that already exist up and out from the follicle.

Transition phase, or catagen phase: New cells are not created at this stage. Instead, the hair follicle actually shrinks about 82%;

Resting phase, or telogen phase: The protein hair strand remains connected to the hair follicle, but it doesn’t grow. After five or six weeks, the dermal papilla reconnects to the base of the hair follicle and the bloodstream. The hair reenters the active growth phase.

 

Definitions/Descriptions of Shampoo

 

What is Shampoo[4]

       

      In essence, shampoos are simply detergents.  They are a different type of cleaning media than ordinary laundry or hand detergents because of their application to different types of hair. Shampoos are used to remove excess oil, dirt and skin debris from the hair known as sebum.  A good shampoo will perform this function while leaving the hair manageable.  These products should possess rich foaming action and rinse out easily.  Various forms of shampoos are available, from clear liquids to opaque pastes.

        The primary ingredient of a shampoo is the detergent, either from an organic soap or a synthetic. Vegetable oil soaps, alkyl benzene sulfonates, sodium or triethanolamine alkyl sulfates, sulfated monoglycerides, sulfated oils and nonionics are typical.  The concentration used varies with the individual detergent and the shampoo type and will vary from about 10% to 50%.  Shampoos usually include modifying agents such as opacifiers, clarifying agents, antifreezes, conditioning and finishing agents, sequestrants, thickening agents, proteins, foam builders, and antidandruff agents.  The use level of these modifiers is usually about 1% to 10%.

 

Functions of Shampoo

     

         Depending on their functions, shampoos are used as cleaning agents for cosmetic purposes, antidandruff agents, antiseborrhoeic agents and keratolytic agents. [5]

As cleaning agents: these shampoos should be mild, effective, without causing irritation and should be used daily or on alternate days as needed. They remove dust and excess oil from the hair.

As antidandruff agents: these treat dandruff due to fungi like pityriasis versicolor. Rapidly relieves scaling and pruritis which are associated with fungal infections.

As antiseborrhoeic agents: they have cytostatic effect on cells of the epidermis and follicular epithelium, thus reducing corneocyte production.

As keratolytic agents: they remove ointment, pastes, which are used in the treatment of psoriasis. They also remove hard scales from the scalp.

Key features of different shampoos are showed in Table 1.[6]

 

Table1. Key Features of Shampoos

Type of Shampoo

Key Features

Clarifying Shampoo

Contain heavy – duty surfactants. Used to deep clean hair and remove the gunky build – up of conditioners, sprays, and gels.

Volumizing Shampoo

Add body to limp hair. Contain proteins that bond to hair and “pump it up”

Moisturizing shampoo

Best choice for dry, flyaway hair, make split ends look better, pull moisture onto hair to keep it from getting too dry.

Revitalizing Shampoo

Made for color – treated, permed, and damaged hair. Use as a gentler cleanser, protect color from fading.

Dandruff Shampoo

Contain medication that loosens and rinses away those annoying flakes.

2-in – 1 Shampoo

With conditioner, save time.

Swimmer’s Shampoo

Remove chlorine and other minerals.

 

 

Shampoo Design Consideration Factors

 

        The first step to understanding the chemical interactions that are present at a colloid level in a typical shampoo is to first understand the parts making up the entire mixture.  Shampoos rely on a selection of species, which are included in the design to further a specific design goal.  Within each of these categories is room for selection to tailor a product more closely towards the intended audience. 

 

       It is important to design a shampoo with its outcome clearly in view.  Desirable qualities for a shampoo are “Lathering in hard or soft water, easily and completely removable lather, without leaving a residue.  Safe for repeated use, non-irritating, chemically and physically stable, and not damaging to the eyes.”[13]

 

       Cleaning the hair is the primary purpose of any shampoo product.  This rudimentary practical function is what separates shampoos from the host of products, which are designed to increase the ability of hair to be styled or otherwise maintained.  Therefore one of the first steps to be undertaken is the selection of a proper detergent for the shampoo. Building foam is also important to the consumer, who without detailed information about the workings of a surfactant assumes that the more foam that is created the better the shampoo is working.  Working the lather into the hair is also used as a marketing tool for shampoos.  Most of the surfactants used for human hair are slightly acidic.  Some surfactants with caustic properties can be used like various chlorine salts.  These alkaline surfactants are typically more irritating to the scalp over prolonged periods then their slightly acidic counterparts like sodium lauryl sulfate, and other chains between 12 and 14 carbon atoms long with a hydrophilic head, empirical experience has lead to the choice of carbon chains of this length[14].  Solubility of the surfactant is sometimes an issue when the appearance of the shampoo is taken into account.  If a clear shampoo is desired then choosing a surfactant or blend of surfactants with a high solubility in water is essential. Examples of these are fatty alcohols, and stearate soaps. 

 

       Thickness of the shampoo solution is an important consumer design feature.  Shampoo is expected to behave in a certain manner when poured out of the bottle.  Viscosity greater then water makes it easier to pour the correct amount of shampoo.  It also helps it to stay in your hair when it is being used so it does not come out before the application is completed. [14]

 

            For the shampoos, which have a chance of precipitating earth, metals formally attached to the surfactants small amounts of chemicals to contain them are often added.  These are termed sequesterants, and are often used in the medical field to treat metal poisoning.  Tetrasodium diethanolamine is an example of one these compounds, they contain the loose metal ions and maintain the systems integrity.

 

            Shampoo is expected by the consumer to have a long shelf life and preservatives are added to the mixture to maintain this.  Two common additives for human shampoos are methyl paraben, and propyl paraben.  These prevent microbial infestation of the shampoo medium, which is otherwise so common in a warm moist environment like a bathroom. 

            Other ingredients can be added as well.  Shampoo is an excellent way to treat dandruff since the product is already in direct contact with the affected area.  Medication such as antimicrobial agents like salicylic acid and cadmium sulfide.  More recent has been the use of selenium sulfide.  Fragrances can also be included in shampoo.  The limit on these additives is largely determined by what the public will buy.  In the same manner common color additives are also used to give the shampoo a marketable appearance.  [15,16]

Chemistry of Shampoo

General Composition of Shampoo

 

        Shampoos are combinations of many chemicals and water, the general compositions of shampoos are:[7]

  1. Cleaning agents:  the prime ingredients in all shampoos are substances called surfactants. Responsible for cleaning action and laterring properties, they largely determine the hair’s condition after shampooing.
  2. Modifying agents: Shampoos contain far more components other than surfactants. There are thickeners (xanthan gum), preservatives (parabens), emulsifiers (glycol distearate), color additives and foam boosters (cocamide monoethanolamine). Some shampoos also include panthenol, which can diffuse into the hair shaft and bind to proteins, strengthening their structure. Humectants, which help to retain moisture, also are added. Ethyl alcohol, isopropyl alcohol and sodium xylene sulfonate can be used to maintain clarity in shampoo.
  3. PH adjuster: In healthy hair, the cuticle consists of translucent cells overlapping like shingles on a roof. In damaged hair, these shingles are more open and ragged.  As the rough adjacent hairs rub against each other, transfer of electrons can produce a static electrical charge.  The result is the dreaded affliction of flyaway hair.  Ideally, a shampoo should smooth down the cuticle and cover it with a clean coating of a sebum-like material.  The smoothing effect is readily achieved by controlling the shampoo's acidity.  All shampoos, whether they make the claim or not, are pH balanced.  The proper pH range is maintained by addition of buffering agents, such as citric acid.
  4. Fragrance:  Fragrance oils are added so that hair is left smelling fresh, which attracts consumers.

 

Good and Bad Ingredients in Shampoo

      

In shampoo, some chemical ingredients are rarely degradable or non – degradable, thus bad for environment, some ingredients are harsh for eye and skin, and some ingredients are necessaries for cleaning and conditioning. As showing Table 2, there is general guide to shampoo ingredients.

 

      Table 2.  The street Cents Guide to Shampoo Ingredients [8]

Good Ingredients

What it is

What it does

What it's called

Gentle Surfactants

Cleans your hair

sodium laureth sulfate and ammonium laureth sulfate

Silicone

Conditions

Dimethicone, cyclomethicone

Quarternary Ammonium Compounds

helps create manageable hair

Guar hyroxypropyltrimonium chloride, dicetyldimonium chloride, dihyrodenated tallow benqylmonium chloride, quaternium 18, stearalkonium chloride.

 

Continue Table 2.

Panthenol

adds lustre, movement, and keeps in moisture

Panthenol

Proteins

good conditioners, but might just wash out

collagen, elastin

Humectants

condition and keep moisture in, but are water-soluble and might just get washed away

glycerin, sorbitol, glycols, propylene glycol

Shampoo fillers

What it is

What it does

What it's called

Water

a large part of all shampoos

water, aqua

Preservatives

keep out contamination

Methylparaben, propylparaben, phenoxyethanol, DMDM hydantoin, 2-bromo-2-nitropropate-1, 3-diol, imidazolidinyl urea

Thickeners

make shampoo thicker

cetyl alcohol, stearyl alcohol, hydrogenated lanolin, polyethylene glycol (PEG), glycol stearate, palmitic acid

Citric Acid

keeps the pH level of the shampoo balanced

citric acid

Foam boosters

make more lather

cocamide MEA, lauramide MEA, lauric DEA, lauramine oxide, cocamidopropyl hydroxysultaine, polysorbate 20

Harsh Ingredients

What it is

What it does

What it's called

Surfactants that are harsh

will make matters worse if you have dry scalp or hair.

Sodium lauryl sulfate, alkyl sodium sulpgate, and sodium oelfin sulfate, TEA-lauryl sulfate

Some "natural" ingredients or essential oils

May cause skin sensitivity on your scalp or sun sensitivity

almond extract, allspice, angelica, arnica, balm mint oil, balsam, basil, bergamot, chamomile, cinnamon, citrus, clove,

Typical Surfactants for Common Shampoo

 

       The major types of surfactants are anionic, cationic, nonionic, and amphoteric. Ions are molecules that have small electrical charges that may be positive or negative. Opposite charges attract and similar charges repel. Surfactants with a negative charge are called anionic. A surfactant with a positive charge is cationic.[9]

 

Anionic Surfactants:

        Anionic surfactants carry a negative charge when ionized. It provides a lot of the lather and detergency in the shampoo. Because of their excellent cleanings, foaming, and solubility properties. The most commonly used anionic are sodium laureth sulphate and sodium lauryl sulphate. Usually using a primary fatty alcohol and treating it with oleum, chlorosulfonic acid, or sulfuric acid make them. Sodium, ammonium, and triethanolammonium (TEA) lauryl sulfates are often found in shampoos. [10,11]A major disadvantage is that they can be harsh and irritating to the scalp.  Frequently, other surfactants and ingredients are added to reduce skin irritation.[9]

 

Cationic surfactants:

        Cationic surfactants carry positive charge when ionized. They are used less frequently due to their dangerous threat to eyes if used in large quantities. The gentleness of your shampoo depends on the surfactant found in its ingredients. Cationic molecules have the ability to cling to wet surfaces by static attraction. Consequently they are not easily removed during the rinsing process and form the basis of conditioning. Polyquarternium-10 is one of the most common cationic conditioners. It is based on a cellulose polymer that is then quaternaries to give the desired properties.[10,11]

 

Nonionic surfactants:

        Nonionic surfactant has no charge to the molecule, it isn’t used as a cleaning agent, but are often used in combination with the primary cleanser to change or modify it’s actions, they aid in solubility, modifying foam, and in some instances conditioning. They can strip the hair and lead to scalp irritation due to excessive defatting. These include laureth-3 or 4, cocamide DEA or coco glucosides.[10,11]

 

Amphoteric surfactants:

          Amphoteric surfactant carries both positive and negative charges when ionized. They are very useful for decreasing the irritancy of a formulation while increasing the active contents level of the product and quality of the lather produced. Each amphoteric surfactant has cationic and anionic charge groups, positive and negative. Most amphoteric shampoo surfactants are used in baby shampoos, because they are gentle and won’t burn the eyes. By far the most used is cocamido propyl betaine, or occasionally cocamido betaine. [10,11]

 

Surfactant Functions in Shampoo

Function of Different Surfactants

       

          Surfactants will influence six essential attributes of shampoo: cleansing, foam, condition, viscosity and aesthetic appeal combined with safety and mildness in use.

 

Cleansing:[12]

         Cleansing is a function of the primary surfactant. To be an effective cleansing agent the surfactant system must work quickly at a relatively low temperature. It must be effective in hard and soft water, be able to remove lipids and other soils and residues left after previous hair treatments and it must not leave any residues of its own. It must be non-toxic and reasonably non-irritant to skin and eyes. It is these requirements that have made ammonium lauryl sulfate (ALS) and sodium laureth sulfate (SLES) the dominant primary surfactants for so long.

 

Foam: [12]

          Foam is also a function of the primary surfactant and few materials can compete with ALS or SLES for quick flash foam. Additional materials may depress the foam or make it creamier and stabilise it. Dialkanolamides were the firm favourite for three decades but are increasingly being replaced by amphoteric surfactants.

 

Conditioning:[12]

         There are many ways of improving hair conditions. SLES and other anionic surfactants leave the hair feeling dry and difficult to manage. The introduction of a suitable secondary surfactant greatly reduces this.

 

Viscosity: [12]

         Products must have sufficient viscosity to stay on the palm of the hand prior to application but must not come out of the bottles as a globular lump. Anionic systems may be thickened by the addition of electrolytes or non – ionic compounds or by betaines. Sodium chloride and cocamidopropyl betaine (CAPB) are the materials of common choice.

 

Aesthetic appeal: [12]

       Although color, odor and pretty pictures on the label are essential factors for aesthetic appeal, the product appearance is also important. It must be either opaque or clear. Clarity requires complete solubilisation of all ingredients, something that can be surprisingly difficult despite the high level of surfactants present. Traditionally polysorbate-20 and PEG-40 hydrogenated castor oil have been used but several new materials have proved successful. PEG-6 caprylic/capric glycerides in combination with PEG-60 almond glycerides, is useful for solubilising essential oils and vitamin oils. PEG-18 Glyceryl Oleate/Cocoate is a good solubiliser and also adds viscosity.

 

Safety and mildness: [12]

        These are essential attributes of a product that may be used every day and which can come into contact with skin and eyes. Alkyl Sulfates and alky ether sulfates are aggressive surfactants that can irritate eyes and scalp and cause skin dryness. The effects are usually modified by the addition of amphoteric or non-ionic materials.

 

Mechanism and Theory in Cleaning Process

 

The colloid and surface phenomena in Shampooing

        Surfactants are molecules that have the ability to be both hydrophobic and hydrophilic. This is achieved by having two very different functional groups attached to each other. The hydrophobic part of the molecule usually consists of a hydrocarbon of variable length. Common chain lengths are between C8 and C18, the most used being C12 in cosmetics formulations. This strikes the balance between mildness and detergency or the ability to remove grease from the hair. Shorter chain lengths have stronger grease removing properties, longer chain lengths have greater mildness but less lathering properties and a balance has to be achieved in the formulation.

          The hydrophilic part of the molecule can be of many and varied functional groups and will determine the nature of the surfactant and a lot of its properties. These include sulphate, ethoxy sulphate, succinates, polyhydroxylates, quarternerised groups and many more. [11]

      

          Cleaning action works like this:  The hydrophobic end secures itself in the oily layer of sebum while the hydrophilic end remains anchored in water. As the hair is rinsed, the soiled sebum is washed away.

 

        Most shampoos are synthetic surfactants and act by surrounding tiny oil and dirt globes in an aggregate called micelle.  These are spherical groupings of 40 to 100 molecules in which all hydrophobic ends point toward the center and all hydrophilic ends stick out in the surrounding water.  Cleaning action takes place as the hydrophobic end secures itself in the oily layer of sebum while the hydrophilic end remains anchored in water.  As the hair is rinsed, the soiled sebum is washed away as the micelle.  Removal of the sebum is facilitated by the ability of surfactant molecules to form these micelles.  Any tiny oil droplets removed from the hair by the surfactant will be attracted to the center of the micelle, keeping the oil drops from coalescing and re-depositing themselves on the hair before they can be rinsed away.[7]

 

       Surfactants have a polar and no polar region.  At low concentration, surfactant is evenly distributed. At high concentration, the surfactant form micelles. The most hydrophobic molecules will bind to hydrophobic region on the surfactant micelle. Less hydrophobic molecules will loosely bind to the micelle. Small molecules in the electrolyte move faster than molecules associated with the surfactant micelle. The voltage causes the negatively charged micelles to flow slower than the bulk flow (endoosmotic flow). This is known as micellar electrokinetic chromatography, as show in Fig. 2 [17]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


                                Fig2.[17]

 

        Surfactants also contribute to cleaning in a completely different way by affecting a physical property of water known as surface tension.  Water molecules are electrically charged with regions of positive and negative charge.  The reason is that the two hydrogen atoms are not symmetrically distributed around the oxygen atom but are on the same side.  As a result, the negative area of one molecule is attracted to the positive region in an adjacent one.  This is why water forms beads on a surface or drops in the air; the surface area of the water in contact with the air is minimized because water molecules are attracted to each other much more strongly than to the air.  To clean best, water needs a greater wetting ability.  Surfactants accomplish this because their molecules wedge between water molecules, reducing surface tension and allowing water to flow easily into every nook and cranny on a surface.[7,18]

 

          Lathering of a shampoo also is the result of the activity of surfactants.  Foam is nothing more than dispersion of a gas, in this case air, in a liquid.  A close look at foam produced by a shampoo reveals that it consists of air bubbles surrounded by a thin layer of water.  To achieve this effect, the liquid's surface tension must be reduced so it no longer needs to minimize the surface area exposed to air. The water can then stretch around the air bubble.  There is no clear link between a surfactant's ability to clean and to produce foam. Indeed, very effective shampoos that do not lather well can be formulated. But they do not sell well either.  Most shampoos incorporate surfactants with strong lathering properties although they may not be ideal in terms of conditioning or irritant potential. [7,18]

 

Mechanisms of Cleansing [12,18]

 

        The mechanisms of hair cleansing are complex. Undamaged hair has a hydrophobic surface to which lipids are strongly adsorbed. When hair is shampooed anionic surfactants are adsorbed to hair by their hydrophobic tails and the negatively charged heads orientate outwards. The fiber surface is thus wetted and non-polar materials are displaced. Semi-polar materials are solubilised into micelle structures and are removed by rinsing. Particulate matter adheres to hair through ionic and van de Waals forces, which are much reduced by the surfactant system and it is readily removed by rinsing.

 

         When comparing surfactant systems the different mechanisms involved in cleansing should be considered; they are mostly favored by anionic surfactants but non-ionic ones have an important part to play in solubilisation processes. The solubilisation process depends on the critical micelle concentration (CMC) and the number of micelles that aggregate together. Large micelles make large aggregates, which make it easier to absorb lipids within the micelle. Non-ionic surfactants and electrolytes pack themselves between the micelles of anionic surfactants, which increases the size of the aggregate and improves the solubilising of lipids. Thus ALS has a lower CMC and a higher aggregate number than SLS and is therefore a more effective cleanser. Ether sulfates have larger micelles and more are involved in micelle formation so they are more effective than non-ethoxylated alkyl sulfates.

 

Viscosity and Rheology properties in Shampoo [19,20]

 

         Shampoos are rather concentrated aqueous solutions of mostly anionic surfactants in combination with salts, particularly sodium chloride. In addition to foaming, detergency and mildness to the skin, the rheology of these liquids is of key importance. In use, the consumer expects the liquids to have non – Newtonian flow behavior, i.e. A slow flow from the bottle, indicating a high active content and allowing optimum dosage and easy distribution on hair. Flow behavior in which long thin threads or even cobwebs are formed when the bottle top is lifted is undesirable.

 

       The characterization of the flow behavior has hitherto been limited mainly to the measurement of flow curves, i.e. recording the shear viscosity as a function of the shear rate γ . Typical viscosity profile shows a pronounced pseudoplastic behavior. The shear rate ranges applicable to actual use are about 5-10 s-1 for flow from the bottle and about 50 – 100 s-1 for distribution on the hair.

 

        Surfactants are compounds, which, above a critical concentration, form micelles, i.e. aggregate which are undergoing a continuous dissolution and reformation process. Depending on the molecular structure, the concentration and or other additives, these micelles have a spherical or an isometric shape, in particular, rods. In contrast to the largely monodisperse spherical micelles, the rod – shaped micelles are polydisperse. Their average length increased with surfactant concentration.

 

As long as the rod – shaped aggregates are smaller than the average distance between them, the viscosity is low, similar to that of the solvent. Surfactant of electrolyte addition causes growth of the micelles until they overlap, whereupon the viscosity usually increased considerably, by many orders of magnitude. This is due to the formation of thread – like, flexible micelle, which entangle one another, separate, and hook together again, thus building up networks that are temporary, similar to the micelles themselves. These dynamic networks, in higher and lower magnification, are indicated in Fig. 3.

 

 

Fig 3. Temporary networks (a) Flexible rod-shaped micelles; (b) entanglement network.[19]

 

         The viscoelasticity typical for such polymer net works is also shown by certain aqueous surfactant solutions, sometimes even at low – to –emidilute concentrations, as is well documented for cationic surfactants complexes with strongly binding organic counterions such as substituted benzoic acids or in the presence of very high salt concentrations. The rheology of many viscoelastic surfactant solutions follows the behavior of Maxwell fluid. This means that its rheology can be described the simplest mechanical model. It consists of just one dashpot (for the lost energy equivalent to the viscosity) and one spring. (For the stored energy, equivalent to the elasticity).

 

          Instead of forming thread – like micelles, which build up a transient entanglement by shielding the micellar charge of the anionic surfactants, shampoos are also formulated with polymers in order to achieve suitable rheological properties. Viscosity is simply achieved through the addition of electrolyte, usually common salt. Salt thickens shampoo due to the ability of the sodium ions to lower the charge density on the outside of the micelles in the shampoo. This usually only applies to anionic species or anionic nonionic mixtures.

 

         The viscosity of a surfactant mixture is dependant upon the size of the micelles in the system. This is determined by several factors - concentration of surfactants, the type and ratio of species, temperature and charge density on the micelles. In mixed micelles the arrangement of the molecules is limited to some extent by the charge density on the surface of the micelle. This can be reduced in several ways. One is addition of more nonionic surfactant so that the ratio in the micelles rises and the negatively charged heads of the anionic surfactants are held further apart. Another is addition of a substance that reduces the charge density on the surface of the micelles.ie salt. By doing this charge density drops and the micelle size can increase. It also causes a rise in micelle aggregation number and the transition from spherical to cylindrical micelles. This transition also leads to a jump in the formulation viscosity as the threads can get knotted around each other. If this process continues a lamellar structure can be formed which is a gel. However it is very variable the response to salt addition in the system. If too much salt is added to a mixture then it can "crash". This is a sudden transition from thick back to thin liquid. In some cases this can be reversible with the addition of water. But too much salt reduces the solubility of the surfactant so much (again the equilibrium is forced to the left) that it comes out of solution and precipitates.

 

         Water – soluble polymers bear a sufficient number of hydrophilic groups that interact strongly with the water structure. They form solvation shells, which open the coil structure. Instead of conventional or high molecular weight polymers, cosmetic chemists often use thickeners that are efficient specifically in aqueous surfactant solutions such as PEG- (75-150) distearate or dioleate, PEG – 50 Ppo –1 – dioleate etc. those compounds are rather low molecular weight polymers, which display very low viscosity on their own, are likely non – ionic surfactants. As the mode of action, mysterious synergistic interactions between surfactant micelles and polymers happen. Synergism leads to nothing else but the formation of long thread – like micelles because of charge shielding.

 

Test methods for surfactants in shampoo

Ordinary methods[21]

       Generally, there are two types methods for surfactants analysis in shampoo, one is qualitative examination and the other is quantitative analysis.

 

Qualitative examination:

1.                  Behavior on acidification: the first step in the qualitative examination is to acidify an aqueous solution of the product with hydrochloric acid. If the later persists the presence of a surfactant is indicated.

2.                  Test for elements: if a surfactants is present, a filtered ethanol extract of the product is tested for sulphur, nitrogen, phosphorus and halogen either by the sodium – fusion method or preferably by the zinc – dust –sodium carbonate fusion method;

3.                  Test with mixed Dimidium Bromide –Disulphine Blue Dyes: in the presence of an anionic surfactant this indicator imparts a pink color to the chloroform phase. In the presence of cationic matter the chloroform phase is colored blue.

4.                  Test with methylene blue solution: depends on the chloroform phase color can determine cationic, anionic or nonionic surfactant may be present;

5.                  Test with Pontamine Fast Red 8NL:  reactions with this dye are carried out in an alkaline solution. Under these conditions the surfactant is anionic if the red color is initially in the aqueous phase. If the color is initially in the chloroform phase, the surfactant is cationic;

6.                  Paper chromatography: it permits the identification of a number of different types of active matter, of organic bases and of a number of additives which may be present;

7.                  Heating with Phosphoric Acid: when dry oxyethylene or oxypropylene adducts was heated with phosphoric acid, the oxyalkylene chain was degraded to give acetaldehyde or propionaldehyde respectively.

         Also Thin – layer chromatography, Effect of Hydrolysis and Heat, Preliminary Deductions are qualitative examination methods.

 

Quantative analysis of anionic surfactants

        Depending on the different function groups of anionic surfactants, there are different quantative methods; one of general methods is volumetric titration. Titration techniques were among the earliest methods developed for the analysis of anionic surfactants. They included:

-          Acid base titration:

-          Single and two phase titration with cationic active matter

-          Double – decomposition reactions;

 Quantative analysis of cationic surfactants

Generally, there are small amounts cationic surfactants in shampoo; about five methods can be used to test them.

-          Gravimetric method;

-          Volumetric method;

-          Colorimetric method;

-          Chromatographic techniques;

-          Ultraviolet spectroscopic method

 

New methods:

 

1. Flow injection analysis:[22]

        The flow injection analysis (F I A) method based on the extraction of the CS with anionic dyes, i.e. Orange II, tetrabromophenolphthalien ethyl ester etc was not good enough. The selectivity and sensitivity of these methods are very poor with low sample throughput and precision. A new, simple and specific FIA method for the determination of CS in the term of cetylpyridinium chloride (CPC) based on the enhancement of color intensity of the Fe (III) –SCN – complex in the nitric acid medium was developed.

 

2. Prediction of ocular irritancy [23]

-  Isolated rabbit eye (IRE)

       The isolated rabbit test was first proposed by Burton et al (1981), as a means of screening for severe irritants without using live animals. The IRE confers the advantage that animals are not bred exclusively for the purpose. The method is capable of distinguishing between mild and moderate eye irritants, such as “baby” and normal “adult” shampoos.

 

- Bovine corneal opacity and permeability (BCOP) assay

       The BCOP assay was introduced by Gautheron et al (1992) as a method for screening process intermediates for worker safety. BCOP data correctly predicted whether a compound would be irritating or non – irritating.

        Both methods use the metric of corneal opacity, which in relation to accidental human exposure to an irritant is arguably the most important parameter, since it provides information on how visual acuity may be impaired accidental exposure.

   

Shampoo Production

General process

 

        Shampoo in terms of product consists of surfactants (cleaning agents) and conditioners. Surfactants, which are mainly detergents like AOS - alfa olefin sulphonate and LES (lauryl ether sulphate salt) are suspended in distilled water with perfume. Conditioning agents are added which could be different silicones or cationic polymers. For general production, fist dispersing thickener in deionized water, then add some PH – adjuster, then add surfactants, preservatives and other additives, at last final PH was adjusted to 5.0 – 6.0. After the system cool down, add fragrance. In all the process, continuing stir is needed in order to guarantee all chemicals and water mix completely. Shampoo is then filled in bottles or sachets. Packaging is technology intensive.

 

BRAN + LUEBBE System [24]

 

         BRAN + LuEBBE’s shampoo blending system is a compact, closed, multistream continuous proportioning system with variable delivery, positive displacement pump for each stream and a common drive for all the pumps. Drive speed can be fixed or variable to suit the application. The system was showed in Fig5.

 

Fig5 BRAN+LUEBBE system

 

Components:

Multi – gang Bran +Luebbe AREX metering pump

In line mixing

PH and viscosity monitoring system

 

Process

The typical system for the production of shampoos, supplied completed with instrumentation and pipe work, produces many variants. The process starts with the surfactants and the water being metered and passing through the first in – line mixer. The brine and one of the four additives to produce the required recipe are added just prior to the second in – line mixer. Immediately after this stage, the mixture passes through a small vessel, which contains the viscosity measurement.

 

      The PH measurement is carried out after this vessel. The finished product now goes to a buffer tank in which a level control automatically adjusts the total output of the blending unit according to the demand of the filling machine. Additional items are the glass suction vessels for each constituent. These are fitted with low-level alarm probes for loss of liquid. A three way valve, fitted up stream, enables, flushing water to be pumped through the system for rapid in – place cleaning and product change as necessary.

 

Key advantages

 

  The major advantages of the BRAN + LUEBBE proportioning systems are:

-          Substantial savings in production space, manpower and costs;

-          Product uniformity and total quality control;

-          Fast, easy recipe changing without wastage;

-          The option to automate any or all production functions;

-          Closed system produces a sanitary, air – free product.

 

Marketing consideration

 

         Shampoo is a high margin product and contribution margin is around 50-60% of realizations. Out of total direct cost, raw materials account for 40-45% and packaging materials account for 25-30%. The balance is accounted for utilities etc. Advertisement costs are substantial at about 15% for established brands. A nation wide launch costs about Rs100-150mn.[25]

 

       The direction of the hair care market, whether it is moisturizing or coloring, is heading towards making life easier. Another trend in the market is form more natural products.

 

       In 1997 in American, for years drug store and supermarket shelves have been filled with $1.99 shampoos and conditioners. To get the more expensive stuff, consumers had to strike out for the nearest salon. To meet consumer demand, many companies developed new, luxury products[26].

 

       In 1998, with the economy still booming and Americans feeling comfortable disposing of their disposable income, pampering themselves has become commonplace, and hair care is one of categories benefiting from the high-flying economy. According to IRI, shampoo sales rose 7.6% to $1.6 billion. Unit sales were up only 2.8%, however, to 630 million. By brand, Pantene held the top spot with a dollar share of 14.7% and was second in unit share with 11.5%. Herbal Essence (9.1%) head and Shoulders (8.4%), Suave (7.6%) and Pert Plus (6.6%) rounded out the top five in dollar share.[27]

 

        In 1999, a combination of innovative technologies from research and development departments and the consumer’s desire for healthy hair has led to a boom in the hair care market. P&G power brand, led the shampoo category with annual sales of $237.3 million, respectively for the year ended July 18, 1999 by IRI.[28]

        In December 2000, markets kept $1.76 billion shampoo sale, according to IRI. Pantene, the mass-market sales leader in shampoo with $238 million, has ventured out in new bottle collections to give customers selections based on desired end – look.[29]

 

        Antioxidant, Vitamin –enriched and natural is the terms to which more and more consumers are responding when determining which hair care products to buy in 2001. According to information Resources Inc., shampoo sales for the year ended Aug. 12 rose 1.2% to $1.79 billion in supermarket, drug store and mass merchandisers.[30]

 

Conclusions

 

  1. Hair chemistry structure is the foundation of shampoo design
  2. Shampoo generally is composed by cleaning agents, modifying agents, PH adjuster and Fragrance oil etc. For all of the ingredients in shampoo, the most important are surfactants;
  3. The major types of surfactants are anionic, cationic, nonionic and amphoteric. Anionic surfactants are primary detergents and cationic surfactants have good condition properties. Nonionic surfactants aid in solubility, modifying foam. Amphoteric surfactants are gentle and won’t burn the eyes, are best choice for baby shampoo.
  4. Surfactants will influence six essential attributes of shampoo: cleaning, foam, condition, viscosity and aesthetic appeal combined with safety and mildness in use.
  5. Surfactants are molecules that have the ability to be both hydrophobic and hydrophilic. They affect the surface tension of water. The cleaning mechanism is the hydrophobic end secures itself in the oily layer of sebum while the hydrophilic end remains anchored in water. As the hair is rinsed, the soiled sebum is washed away.
  6. Above a critical concentration, surfactants form micelles. The viscosity of shampoo depends upon the size and shape of micelles. This is determined by several factors - concentration of surfactants, the type and ratio of species, temperature and charge density on the micelles. In mixed micelles the arrangement of the molecules is limited to some extent by the charge density on the surface of the micelle. This can be reduced in several ways. One is addition of more nonionic surfactant, another is adding electrolyte.

 

 

 

 

 

 

 

 

 

 

Reference:

1. http://www.geocities.com/HotSprings/4266/chem.html;

2. http://hometown.aol.com/hairbook/know.htm;

3. http://www.hairless.net/hairbiol.html;

4. http://www.surfactants.net/formulary/uniqema/pcm6.html;

5. http://www.fmhs.uaeu.ac.ae/females/shampoo.htm;

6. http://www.satisfied-mind.com/drugstore/shampoo.htm;

7. http://www.washingtonpost.com/wp-srv/national/horizon/dec98/shampoo.htm;

8. http://www.halifax.cbc.ca/streetcents/show/more/show_08_00/shampoo.html;

9. http://www.hair-shampoo.com/;

10. http://crystal.biol.csufresno.edu:8080/projects97/115.html;

11. http://www.hairscientists.org/article7.htm;

12. http://www.creative-developments.co.uk/

13. Ronni Wolf. MD, Clinics in Dermatology, 2001; 19: 393-397;

14. Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., volumes 1-24;

15. Estrin, Norman F., Crosley, Patricia A., Haynes and Charles R., CTFA Cosmetic Ingredient Dictionary, 3rd ed., Washington, D.C., Cosmetic, Toiletry, and Fragrance Association, c1982;

16. Robbins, Clarence R., Chemical and Physical Behavior of Human Hair, 3rd ed., New York: Springer-Verlag, c1994;

17. http://ntri.tamuk.edu/ce/surfactant.html;

18. Martin M. Rieger, Surfactants in Cosmetics, New York and Basel, 1985;

19. D.Balzer and M. Weihrauch, Colloids and Surfaces A: Physicochem. Eng. Aspects 99(1995) 233-246;

20. http://www.hairscientists.org/article15.htm;

21. G.F. Longman, The Analysis of Detergents and Detergent Products, 1975.

22. Rajmani Patel etc. Talanta,  48(1999) 923-931;

23. K.J. Cooper etc, Toxicology in Vito, 15(2001)95-103;

24. http://www.bran-luebbe.co.uk/shampoo.htm

25. http://www.indiainfoline.com/sect/pchc/ch06.html;

26. http://www.happi.com/special/GENERAL/aug972.htm;

27. http://www.happi.com/special/1208mm1.htm;

28. http://www.happi.com/special/dec993.htm;

29. http://www.happi.com/special/dec001.htm;

30. http://www.happi.com/specials/Deco11.htm;