8 - Thickening Agents (Book)

Thickening agents / viscosity-enhancing agents,

• raw materials that determine the final form and function of a personal care formulation

• primary function was to increase the viscosity of the formulation

Thickening agents / viscosity-enhancing agents

• Modify the rheology and the appearance of a product

• Improve sensory and on-skin performance properties

• Suspend insoluble ingredients including pigments and pearling agents

• Stabilize emulsions and suspensions

• Modify foaming properties in surfactant based formulations

• polymers (synthetic or natural)

• minerals

• waxes

• electrolytes

• nonionic materials

types of thickeners (5)

Hydroxyethylcellulose (HEC)

• nonionic water-soluble polymer derived from cellulose

• dissolves readily in water (cold or hot) to give clear, smooth, viscous solutions

• can thicken, suspend, bind, emulsify, form films, stabilize, disperse, retain water, and provide protective colloid action

• soluble in hot or cold water, used to prepare solutions with a wide range of viscosities

• outstanding tolerance for dissolved electrolytes

Hydroxyethylcellulose (HEC)

• soluble in both cold and hot water

• does not display a ‘cloud’ or ‘precipitation’ point

• nonionic and less affected by pH change, presence of anions and organic co-solvents

• used to produce pseudoplastic

• thicker at rest and thinner when stirred

• used as a highly efficient thickener and emulsion stabilizer

• in detergent systems it provides creamier and more lubricious foam

Hydroxypropylcellulose (HPC)

• nonionic water-soluble cellulose ether

• combines organic solvent solubility, thermoplasticity, and surface activity with aqueous thickening and stabilizing properties

• compatible with a wide range of anionic, nonionic, cationic and amphoteric surfactants

hydroxypropyl substitution

In HPC, ________ confers increased lipophilicity on HPC than other water-soluble cellulose derivatives, a key difference when formulating with alcohol-based formulations

2-11

viscosity of water-based solutions of HPC is not affected by changes in pH over the range of _____

Hydroxypropyl methylcellulose (HPMC)

• modified natural carbohydrate polymer derived from cellulose

• multifunctional additive

• most important properties include a foam-boosting effect, a significantly improved skin feel, and viscosity control in cleansing and conditioning personal care formulations

• reduces the required amount of certain ingredients, such as surfactants, other thickeners and emollients, without sacrificing performance

• hydroxypropyl

• methyl

In HPMC, the _____ and _____ group substituents impart water solubility and surface activity to the polymer

Methylcellulose (MC)

• acts as a film former, suspension aid, lubricant, lather enhancer/stabilizer, emulsion stabilizer, gelling agent and dispersant

• delivers luxurious foam and stabilization

• can be combined with xanthan gum or inorganic thickeners to achieve their suspension capabilities

• delivers light, nongreasy films

• In solid products, it functions primarily as a binder, but also adds humectancy and film-forming properties to improve the product shelf life and texture

• interfacial thermal gelation

MC offers a unique feature called ______ that reflects the combined effects of their surface activity and thermally gelling properties

Ethylcellulose (EC)

• oil-thickening and film-forming additive

• provides formulators with flexibility and new options

• film-forming properties, longer-lasting benefits compared to simple oil blends

• facilitates the inclusion and benefits of the oil properties in the final product

Carboxymethylcellulose (CMC)

• made by reacting sodium monochloroacetate with alkali cellulose

• synthesized by the alkali-catalyzed reaction of cellulose with chloroacetic acid

• used in detergents

• main application is gelling agent in toothpaste formulation due to its water retention capacity and rheological profile

• used for water binding, syneresis control, and to suspend pigments and active ingredients in solution

• carboxyl

• 60

• 40

• sodium glycolate

In CMC, the polar (organic acid) _____ groups render the cellulose soluble and chemically reactive. Following the initial reaction, the resultant mixture produces about ____% CMC plus ____% salts (_____ and _____)

intermediate ‘semi-purified’ grade

In CMC, this grade is used in paper applications such as restoration of archival documents

Xanthan gum

• natural-derived, high molecular weight polysaccharide used to thicken and stabilize suspensions, emulsions and foams against separation

• high viscosity; low shear rates; enables products to keep particles suspended or prevent oil droplets from coalescing

• pseudoplastic rheology, the viscosity drops when shear is applied, therefore the end product can be easily scooped, poured or squeezed

Xanthan gum

• thickening agent that is soluble in hot or cold water

• stable over a wide range of pH and temperatures

• resistant to enzymatic degradation

• excellent compatibility in the presence of anionic, amphoteric, nonionic surfactants and high concentrations of salt

Gellan Gum

• water-soluble anionic polysaccharide manufactured by microbial fermentation

• gelling agent

• effective at extremely low use levels, forming solid gels at concentrations as low as 0.1%

• used to form fluid gels (stabilizing suspensions and emulsions without adding viscosity)

Sphinomonas elodea

bacerium used to make gellan gum

gels

• stable over a wide pH range

• are compatible with anionic, amphoteric and nonionic surfactants

• easily combined with most other rheology modifiers

• high acyl content

• low acyl content

2 chemical forms of gellan gum

low

____ acyl products form hard, non-elastic gels.

high

____ acyl product form soft, elastic gels

Carrageenans

• extracted from red seaweed

• ability form stable gels under neutral and alkaline conditions

• kappa carrageenans

• iota carrageenans

• lambda carrageenans

3 forms of carrageenans

kappa carrageenans

this type of carrageenan forms strong, brittle gels

iota carrageenans

this type of carrageenan forms soft, elastic gels

lambda carrageenans

this type of carrageenans are non-gelling thickeners

Pectins

• family of partially methylated esterified polysaccharides produced from citrus peel and sugar beet pulp.

• adds structure through gelation and viscosity buildup

• can provide moisture absorption while being skin friendly

• used to formulate lotions and creams without the use of surfactants (if disrupted while processing)

• gel-forming component of fruits

• high methoxyl (HM) pectin

• low methoxyl (LM)

2 classifications of pectin

high methoxyl (HM) pectin

this class of pectin requires a minimum amount of soluble solids and a narrow pH range around 3.0 in order to form gels

LM pectin

this class of pectin requires the presence of a controlled amount of calcium or other divalent cations to form a gel

Hydroxypropyl Starch Phosphate

• specially processed pre-gelatinized starch that can create stable and elegant personal care emulsions

• delivered as a powder; ease of use and immediate dispersability in cold water; ideal for use in continuous manufacturing processes

• no pre-mixes needed; added to the oil phase or to adjust batch properties

Hydroxypropyl Starch Phosphate

• starch can aid in emulsion stabilization, enhance aesthetics and build viscosity

• outstanding stability over a broad temperature range (–30°C up to 50°C)

• brings body to the formulation and a conditioning after feel

• nonionic; flexibility to formulate over a wide pH range with high amounts of mono- and polyvalent salts (up to 20%)

Carbomers

• high molecular weight cross-linked polymers of acrylic acid

• when neutralized have the ability to absorb and retain water, resulting in a viscous gel or liquid

• (dried) comes in the form of a lightweight white powder

• provides viscosity, stabilization and suspension properties

• extremely efficient rheology modifier capable of providing high viscosity, and form sparkling clear, water-based or hydroalcoholic gels and creams.

Carbomers

• tightly coiled acidic molecules

• Once dispersed in water, the molecules begin to hydrate and partially uncoil, forming low viscosity solutions with an approximate pH range of 2.5–3.5

• polymers neutralized in order to achieve maximum viscosity

salt

most common way to achieve maximum thickening from these polymers (carbomers) is by converting the acidic carbomers to a _____

6.5–7.5.

In carbomers, once a neutralizer is added to the dispersion, thickening gradually occurs and the optimum viscosity is typically achieved at a pH of ____

• 5.0–9.0

In carbomers, high viscosities can be achieved in pH ranges of _____. At pH _____ viscosity will begin to decrease, caused by the dampening of the electrostatic repulsion caused by the presence of excess electrolytes

• sodium hydroxide (NaOH)

• triethanolamine (TEA)

In carbomers, neutralizing the polymer is achieved with a common base such ______ or _____

(amino-acid based)

• Dibutyl ethylhexanoyl glutamide

• dibutyl lauroyl glutamide

• 2 highly effective oil gelling agents based on l-glutamic acid

• provide hardness, strength and stability to the product, even at very high temperatures

• can form clear oil gels, as well as hard oil gel sticks

• used in anhydrous products as well as emulsions

• form nano-sized fibre networks that can suspend particles

• Polyamide-3

• Polyamide-8

• 2 polymers that are film formers, water repellency agents, pigment and polymeric emulsion stabilizers, structuring agents and rheology modifiers

• low colour and low odour, high-performance thermoplastic solids proven to form crystal clear, thermo-reversible gels

• work with a range of high to low polarity oils

Fumed silica

• synthetic, amorphous, colloidal silicon dioxide

• inorganic thickener

• Using this, cosmetic oils can easily be converted into highly viscous, largely transparent gels

• good thickener for non-polar systems

• not suitable for thickening aqueous systems

• incorporated at room temperature, without activation and using high shear equipment

• formulations show low sensitivity to temperature, electrolytes and pH

• 0.5 - 10

• 3

Depending on the desired effect, fumed silica can be used in a concentration range from ____% w/w. Concentration levels above ____% w/w can specifically counteract the oily or greasy skin feel of a formulation.

• hydrophilic

• hydrophobic

In fumed silica, _____ types are very effective as drying agents, while _____ types are particularly helpful as powder flow regulators

modified silica with hydrophobic properties

this type of fumed silica is perfect for creating or adjusting thixotropic properties, improving suspension without significantly increasing viscosity, and imparting stability and water-resistance to emulsions, especially for sunscreen and makeup formulations.

Hectorite

• hydrophilic clay with small-size, platelet-shape particles and large surface area to volume ratio

• very effective thickener of water, forming strong, stable viscous gels

• special properties including lower iron content, lighter colour, higher swelling capacity, greater gel strength and no crystalline silica

• not sensitive to temperature variations,

Hydrophilic clays

non-abrasive and have a pleasant silkiness that is quite different to that associated with the majority of cellulose, polymer and polysaccharide-based thickeners

Non-ionic surfactants

type of surfactant that can adsorb onto the clay surface if they are highly ethoxylated

can act as dispersing agents and weaken the gel structure

type of surfactant that can act as dispersing agents and weaken the gel structure in hydrophilic clays

Cationic surfactants

type of surfactant that interacts strongly and should be avoided in hydrophilic clays

• vegetable quaternary ammonium

• organoclays

Hectorite can be reacted with special ______ salts to produce ______ that are able to thicken and gel organic liquids

Organoclays

form thixotropic gels by developing hydrogen bonds between the edges of adjacent platelets

• high-shear equipment

• propylene carbonate

Hydrophilic clays or organoclays need to be efficiently dispersed using ______ and then activated with the optimum level of a chemical activator, such as _____

Magnesium Aluminium Silicate

• naturally occurring smectite clay that has been water-washed to optimize purity and performance

• swells in water

• used as a thickener, and an emulsion and suspension stabilizer due to its colloidal structure

• hydrophilic clay that has to be well dispersed with high-shear equipment in order to be effective.

Waxes

• mixture of hydrophobic organic substances of medium-chain length

• melt at temperatures in the range of 40°C up to 140°C without decomposition and will re-solidify unchanged

• solubility and consistency is strongly temperature-dependent

• animal

• vegetable

• mineral

3 classifications of waxes

Beeswax

• secretion of the abdominal glands of the honeybee

• white and colourless

• moderately hard, and somewhat sticky, plastic and kneadable at body temperature

• one of the best oil-binding waxes known

• often used in lipstick and lip balm to produce creamy textures, favorable adhesion to the skin and films

• oil-gelling properties are helpful for stabilizing water-in-oil emulsions and for texturizing effect

• used as a means of enhancing texture and adding volume in mascara and make-up

cera flava

yellow-grade beeswax is defined as ______

cera alba

white-grade beeswax is defined as ______

61–65°C

melting point of beeswax

Carnauba Wax

• secretion of the Brazilian palm, produces the wax in the cuticula of the fronds

• extremely narrow melting curve

• exhibits high crystallinity and a high degree of contraction, is very hard and brittle

• highly favorable emulsification properties

• excellent capacity for binding ester oils and mineral oil

• raises the melting point of oil gel

• preferred additive in lipsticks and lip balms

• highly suitable for use in mascaras

• provides glossy and lustrous surfaces.

Copernicia cerifera

scientific name of carnauba wax

84°C

melting point of carnauba wax

Candelilla Wax

• hard but exhibits low crystallinity and a degree of tackiness at higher temperatures

• excellent capacity for binding ester oils

• provides high surface gloss when applied in lipsticks and exhibits satisfactory contraction properties – important for demolding lipsticks

Euphorbia cerifera

scientific name of candelila wax

• dark brown

• pale yellow

Crude candelilla wax is _____ in color and then refined to a _____ wax

72°C

melting point of candelila wax

• resin

• sitosterol

these 2 chemicals of candelila wax combines with esters to give it oil binding ability

Sunflower Wax

• wax obtained from sunflower oil

• forms hard and very homogeneous thermally stable oil gels

• excellent for light-coloured, practically odorless and tasteless lip balms, lipsticks and other oil gels.

• long chain (about C60) wax ester mainly from monovalent alcohols and acids

• narrow melting curve with no molten contents

• oil gels are very heat resistant

80°C

melting point of sunflower wax

Rice Bran Wax

• main components are long-chain wax esters with chain lengths of around C60

• very hydrophobic character

• forms soft oil gels

• highly preferred for emulsions like mascaras and skin care products

Microcrystalline Wax

• solid obtained by extracting the oil from petrolatum

• complex mixture composed mainly of C31–C70 isoparaffins

• microcrystalline structure, high adhesive power, good extensibility

• not susceptible to low temperatures and has a high melting point

• When mixed with other waxes, it suppresses crystal formation

Ozokerite Wax

• white, crystalline, odorless and tasteless solid

• most often made from blends of paraffin and microcrystalline waxes

• increase viscosity, assist in emulsion stability and enhance gel strength in liquid and semi-solid systems

• hard wax with a relatively high melting point

• used to promote structure and stick strength.

• sodium

• potassium

• magnesium

surfactants are often co-formulated with inorganic electrolytes, like _____, ____, and _____ salts that are included as inexpensive thickeners

Salts

affect the surfactant’s aggregative and functional behaviour

Electrolytes

• thickening effect depends on the presence of an anionic surfactant and it works up to a concentration maximum

• After this maximum is reached the viscosity collapses, as further increase of this thickener leads to a destruction of the micelle network

• 1–2

• aqueous solution

electrolytes thickeners should be added on the order of ____%, and generally in the form of an _____ to prevent poor electrolyte distribution

• hydrophobic

• hydrophilic

2 groups of non-ionic thickening agents for surfactant systems

Hydrophobic monomeric or oligomeric type

• low molecular weight that are mostly non-ionic surfactants

• provide a shear thinning flow

• viscosity decreases with increasing shear rate and at lower temperatures, but have stable viscosity at higher temperatures

Hydrophilic polymeric types

• high molecular weight

• based on highly ethoxylated oleochemical derivatives

• provide a Newtonian flow behaviour; viscosity is independent of the shear rate.

• lower

• higher

For hydrophilic polymeric types, at _____ temperatures the viscosity increases significantly, while at _____ temperatures the viscosity decreases dramatically