THICKNERS: Cosmetic Technology

D.P. Ghosh

Asst. Prof.

KSOP. Ghaziabad

THICKNERS:Viscosity imparting agents : These agents are used when it is desirable

to increase or decrease the viscosity of a liquid either to serve as adjacent for palatability or to improve pour ability. They are also called thickening agents.

Viscosity imparting agents are of two types:a) Viscosity modifier-Viscosity modifiers decrease the viscosity of a liquid to

improve pour ability and make it more palatable.

b) Viscosity enhancer- Viscosity enhancers increase the viscosity of a liquid to improve pour ability and make it more palatable.

Most commonly used viscosity imparting agents are :HydroxyethylcelluloseHydroxypropylmethylcelluloseMethylcellulosePolyvinyl alcoholPolyvinylpyrrolidone

THICKNERS:

THICKNERS:

RAW MATERIALS

THICKNERS:

• Many thickeners are polymers e.g cellulose

and carbopol.

• Carrageenan, pectin, and locust bean gum are

all examples of cosmetic thickeners.

Thickener types

THICKENERS

• Water and oils form the base fluids in which most personal-care and cosmetic products are formulated.

• These base fluids are generally classed as viscous or Newtonian fluids in that they possess a characteristic viscosity that is independent of the imposed rate of deformation.

• Newtonian fluids are also viewed as ideal fluids, in that they flow readily when subjected to very low deformations.

• Non-Newtonian fluids on the other hand possess viscosities that are dependent on the rate of deformation and may exhibit other properties

• such as elasticity, yield stress, and thixotropy not seen in Newtonian fluids.

Newtonian fluids

• The viscosity of these fluids can be modified by addition of particulates that may strictly change the viscosity .

• When non-interacting buoyant particles are used in these fluids, the viscosity of the dispersion can be predicted using the Einstein relation:

μ = μo(1 + 2.5φ+ . . .)• where μ and μo are viscosities of the dispersion and medium

respectively and φ is the volume fraction of the particles.

• Examples of such rheology-modifying substances include silica gels, fumed silica, carbon black, titanium dioxide and aluminum-magnesium-stearates

• when used at very small concentrations. Low molecular weight polymers also fit in this category and may be preferred if a smooth or fluid like formulation is desired.

Newtonian fluids

• Examples of such rheology-modifying substances include silica gels, fumed silica, carbon black, titanium dioxide and aluminum-magnesium-stearates when used at very small concentrations.

• Low molecular weight polymers also fit in this category and may be preferred if a smooth or fluid like formulation is desired.

Schematic of flow properties of Newtonian and non-Newtonian fluids

Non-Newtonian fluids• Unlike Newtonian fluids, non-Newtonian fluids possess shear-

rate dependent viscosities.• In addition to shear-rate dependent viscosities, non-Newtonian

fluids also exhibit elastic stresses when subjected to high shear

rates.

• The usefulness of the elastic response varies with application.

• Non-Newtonian rheology is more common in personal care formulations than Newtonian (viscous) rheology.

• The performance value of rheological additives that impart non-Newtonian characteristics to personal care formulations is demonstrated by the curve in Figure 2

Non-Newtonian fluids

• At low shear rates, i.e., near at rest conditions, non-newtonianfluids exhibit high viscosities that are relatively insensitive to shear rate and characterized by zero shear viscosity.

• At moderate shear rates the decrease in viscosity versus shear rate helps when pouring and pumping these fluids.

• The low viscosities exhibited by these rheological additives imply low resistance to rubbing and thus a smooth sensation of the substance during its application.

Elasticity

• It is generally observed that fluids that show more shear-thinning properties tend to show more elastic response.

• The desirability of the elastic response will vary with the intended use of the personal care product.

• In the case of toothpaste, an elastic force is needed to increase extrudate spring back during the tube filling operation in toothpaste production or while dispensing it at home.

• However, excessive elasticity might not be desirable, as it may make the toothpaste too stringy.

• High elasticity is needed to stabilize foams, for example in shaving creams, as it provides strength to film at the air/liquid interface in the matrix of bubbles.

• In the case of creams and lotions, a short texture with less elasticity may be desired.

The rank order of shear-thinning performance for these fluids is fluid (e)>(d)>(c)

Pseudoplastic Or Shear-thinning Rheology

• Examples of substances that impart viscosity as well as elasticity to a fluid are cellulose ethers, xanthan gum, and crosslinked polyacrylic acids.

• Clays can impart viscosity without elasticity.

• Water-soluble cellulose ether derivatives such as carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropyl cellulose, and methylcellulose impart pseudoplastic or shear-thinning rheology to formulations .

• This characteristic makes these polymers attractive candidates as thickening agents in personal care products.

Pseudoplastic Flow (Shear Thining)

• For instance, this flow characteristic enables a product to pour as a rich, viscous solution from the container, yet be easily applied to a substrate like hair, as its viscosity reduces with shear.

• These polymers tend to impart high viscosities at low shear.

• They exhibit moderate shear-thinning behavior, but possess little elasticity at a moderate range of deformation rates, similar to the rheology profile of fluid.

• Some of the applications where these polymers are used include shampoos, conditioners, hair spray, and hair-styling gels, toothpastes, and denture adhesives.

• For example, incorporation of 1% hydroxyethylcellulose into a TEA-lauryl sulfate luxury shampoo increased the formulation viscosity from a Brookfield viscosity of 460 cps to a gel with a viscosity of 5300 cps.

Suspending Agents

• Among the polysaccharides, xanthan gum has been widely used as a suspending aid.

• Xanthan gum has a double helical structure and undergoes significant hydrogen bonding in solution.

• At rest or when subjected to very low deformations, a weak three dimensional network structure is the prevailing structure which gives rise to the yield stress.

• When subjected to higher deformations, this structure can easily be broken down to give rheological behaviour similar to non-newtonian fluid.

Suspending Agents

• Other polysaccharides that exhibit yield stresses are kappa and iota carrageenans.

• Methylhydroxypropylcellulose has been shown to enhance shampoo lather by way of the water-binding.

• Carboxymethylcellulose imparts a high viscosity at low shear to formulations.

• Carboxymethylcellulose imparts a high viscosity at low shear to formulations, enabling it to effectively suspend solids.

• Hydrophobically modified cellulose ethers, such as modified hydroxyethylcellulose, viscosify aqueous phases through both hydrogen-bond network formation and through the formation of three-dimensional networks due to hydrophobic interactions.

• This dual thickening mechanism makes modified hydroxyethylcellulose particularly effective at suspending solids.

Thixotropy

• The thixotropy of a toothpaste system can be described by a rheogram representing a plot of shear stress against shear rate.

• The hysteresis area between the up curve and down curve is defined, as the energy required to break the network structure of the toothpaste.

• It gives an indication of the degree of thixotropy of the system.

Thixotropy

• Five major rheological additive types are currently used in toothpaste systems.

• They are generally classified into four main categories: 1) natural, 2) modified natural, 3) synthetics, and 4) inorganic.

• These classes are represented respectively by

• 1) xanthan gum, carrageenan; 2) cellulose ethers; 3) crosslinked polyacrylic acids; 4) clays and amorphous silicone dioxide.

GELLING AGENTS

• gel should be given to systems that display the following features:

• 1) coherent, two-component systems formed by a solid substance finely dispersed or dissolved in a liquid phase;

• 2) exhibit solid-like behaviour under the action• of mechanical forces; • 3) both the dispersed component and the solvent

should extend continuously throughout the whole system, each phase being interconnected.

GELLING AGENTS

• Rheological characterization divides gels into two major classes, strong and weak gels.

• Strong gels possess the canonical features of true gels.• They manifest typical behaviour of viscoelastic solids

and rupture beyond a certain deformation value rather than flow.

• Weak gels resemble strong gels at low deformation rates but their three dimensional networks get progressively broken down at higher deformation rates and they flow as a dispersed system.

• Gelatine, agar, pectins, alginates, and kappa carrageenans, Carbapol, alginate.

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Healthcare. Newyork

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Delhi.

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9. Indian Pharmacopoeia 2014(7th edition), Ministry of Health and Family Welfare, Published by

Govt. of India.