Lecture 5 - Viscosity Control

Question 1

Two primary purposes of rheology additives

Answer 1

Enhancement of product form
- Aesthetics, texture, processing, packaging control
- Flow & application properties
Product stability
- Preventing colloidal systems from breaking down
- Retard coalescence and creaming

Question 2

functions of thickeners

Answer 2

Control phase separation
Prevent syneresis
Suspend particulate materials
Form gels
Retard or eliminate crystal growth
Extend shelf life
Have a positive effect on product application

Question 3

The flow properties of cosmetic solutions, emulsions, and dispersions are a result of colloidal structures and/or thickening agents such as:

Answer 3

Particle-particle interaction
Association structure disturbances
Polymer behavior in solution

Question 4

define rheology

Answer 4

how materials deform or flow in response to external forces

“the branch of physics that studies the deformation and flow of matter”

Question 5

define shear stress

Answer 5

the external force applied over an area. Unit are Pascals (Pa) = Newtons per meter2 (1Pa= 10 dynes/cm2 )

Question 6

define shear rate

Answer 6

ratio of velocity of material to its distance from a stationary object -the velocity gradient (1/sec) –HOW FAST

Question 7

define shear strain

Answer 7

relative displacement of the faces of a sheared body (for example a layer of fluid)divided by the distance between them- (no units)-HOW FAR (relative measure of deformation)

Question 8

define viscosity

Answer 8

a measure of a material’s resistance to flow measured in Pascal seconds = 1 poise (P) in cgs system = 100 centipoise (cps)

Question 9

define newtonian flow

Answer 9

not variable with shear linear response of flow rate to shear stress

Question 10

define pseudoplastic flow

Answer 10

shear thinning

Question 11

define dilatant flow

Answer 11

shear thickening

Question 12

define thixotropic flow

Answer 12

shear thinning with time dependence (slower return to original state)

Question 13

4 Factors Governing O/W emulsion viscosity

Answer 13

Presence of thickening agents in external water phase (hydrocolloids)

Presence of thickening agents in lipid phase and dispersed in water phase (co-emulsifiers & solid amphiphiles that form liquid crystalline gel networks)

Volume ratio of internal- dispersed phase to external-continuous phase (phase volume)

Lipid composition of internal phase

Question 14

6 sources of thickeners

Answer 14

Synthetic polymers – acrylates, carbomers, acrylamides, polyurethanes etc…

Direct nature sourced carbohydrates: algal, plant exudates and seed gums

Fermentation derived microbiological
by-products - exopolysaccharides

Cellulosics - cotton linters, wood fiber

Smectite Clays – mined & purified silicate minerals – bentonites, hectorites
Inorganic silicas

Question 15

what is the Concentration- Response Function

Answer 15

The viscosity/thickness response of the solvent media versus concentration is dependent on interaction of gum molecules/particles with each other , the solvent and other ingredients

Question 16

what is the Critical Overlap Concentration

Answer 16

concentration above which dramatic viscosity increase occurs due to interaction of polymer molecules to form interpenetrating networks in the solvent.

Question 17

examples of Stabilizer polymers & gums, solids

Answer 17

Carbomers
Xanthan gum
Sclerotium gum
Cellulose derivatives : 				 - CMC (Carboxymethylcellulose)			- HEC (Hydroxyethylcellulose)
Bentonite/Hectorite clays
MgAl Silicate clay

Question 18

carbomers

Answer 18

Most popular aqueous phase thickener used in personal care emulsions

Must be neutralized -Equivalent Weight 76 ± 4

Ideal pH is 6.5-7.0 but high viscosities can be achieved
between pH 5.0-9.0

Salt sensitive (some grades less than others)

Maintains viscosity at Elevated temperature

Question 19

Liquid Dispersion Polymers

Answer 19

Polymer thickener dispersed in emollient solvent with nonionic dispersant/emulsifier
Used as self emulsifying systems- can emulsify additional oil
Disperses in water to form a thick emulsion
Anionic, cationic and nonionic polymers

Question 20

examples of Carbohydrates/ Polysaccharides

Answer 20

Plant, algal and microbial gums

• Xanthan
• Alginates
• Scleroglucan
• Carrageenan
• Guar – neutral polysaccharide
• Locust bean/ carob- neutral -branched chain thickener synergistic with other gums
• Gellan-exopolysaccharide from Sphingomonas elodea
• Pectin- galacturonic polymer with rhamnose – film former, clear gels
• Konjac –glucomannan
• Cellulose derivatives

Question 21

Agar/Agarose

Answer 21

Derived from red seaweed Rhodophycae
Agarose is the neutral gelling portion separated from the sulfate non gelling portion
Strong thermoreversible gels
Requires high temperature hydration

Question 22

Alginates: Alginic acid - Algin

Answer 22

Derived from brown seaweeds mainly Laminaria, Macrocystis
Algal polysaccharides composed of acid sugars:
Sodium and Potassium salts act as thickeners& stabilizers (Propylene glycol ester available)
Pseudoplastic Shear thinning solutions with little yield value/ heat sensitive
Thickening, emulsion & foam stabilizing
Anionic can complex with divalent Ca++ ions to form rigid gels

Question 23

Carrageenan

Answer 23

red seaweed (Rhodophycae) derived sulfated polysaccharide (Galactose units)

Question 24

3 forms of Carrageenan available

Answer 24

Kappa- lowest sulfate – clear brittle gels with K+
Iota- moderate level sulfate forms softer gels
Lambda- highest sulfate, no double helix=no gel
helps stabilize freeze-thaw

Question 25

Chitosan

Answer 25

Chitosan is a partially deacetylated polymer of Chitin –a homopolymer of N-acetyl glucosamine Chitin is structural unit of fungi & invertebrates Commercial source –shrimp shells, also mushroom Hydrolyzed glucosamine residues are naturally cationic depending on pH – need acid neutralization for solubility Thickening and film forming depending on m.w. Used also for coacervation encapsulation

Question 26

Scleroglucan

Answer 26

Fermentation product of filamentous fungus Sclerotium rolfsii High molecular weight (~ 1 million) branched chain neutral glucose polysaccharide Fluid gels, high viscosity, good clarity - pseudoplastic with high yield values Suspension formation, emulsion and foam stabilization

Question 27

Guar

Answer 27

Cyamopsis tetragonoloba soluble fiber galactomannan polysaccharide from the endosperm of the Indian cluster bean a leguminous shrub Yields viscous pseudoplastic solutions of high low-shear viscosity at low concentration Functional derivatives (cationic, hydroxypropyl) use reagents that are usually disallowed by natural certifiers (Ecocert, NaTrue, NPA et.al.)

Question 28

Konjac Gum

Answer 28

Amorphophallus konjac tuberous root of subtropical Asia from which soluble fiber is used in foods to make jellies and noodles Synergistic gelation with other gums such as Xanthan and Carrageenan

Question 29

gellan

Answer 29

Sphingomonas elodea bacterial exopolysaccharide of four sugar moieties High molecular weight commercially partially de-esterified before use Gelling, texturizing and suspension hydrocolloid dependent on ion concentration for structure

Question 30

Locust Bean Gum

Answer 30

Carob seed source - extracted from the seed (kernels) of the carob tree (Ceratonia siliqua). A similar galactomannan to guar gum but less viscous because of less side chains Requires heat to fully hydrate (80-90℃) Retards ice crystal growth by forming structured gel at solid/liquid interface for freeze thaw stabilization Interacts with protein colloids like casein

Question 31

Rhizobium Gum

Answer 31

Biofermemntation exopolysaccharide from root nodule bacterium variant of Rhizobium sp discovered on a sunflower cultivar in France High molecular weight 1.5 million Dalton Complex branched partially acetylated polysaccharide Forms optically clear gels at low concentrations Emulsion stabilizer at low levels

Question 32

Tragacanth Gum

Answer 32

Astragalus gummifer plant exudates from a Middle Eastern leguminous plant Composed of a complex mixture of polysaccharide terpolymers, the sap dries into translucent hard ribbons The mucilage formed in water acts as an emulsifier, thickener, stabilizer, and texture additive

Question 33

Xanthan Gum

Answer 33

Biofermentation product of bacteria Xanthomonas campestris High molecular weight ~ 15 million polysaccharide of glucose, mannose, glucuronic acid Pseudoplastic flow with high viscosity at low concentrations – good yield value Solids suspension stabilization Emulsion stabilization against creaming and coalescence- surfactant compatible Specifically allowed in USDA NOP organic products

Question 34

Processing Basics- Gums

Answer 34

Potential for gel block dispersing gum particles in water Consistent even dispersion of particles into cold water- vigorous mixing vortex Heating may be necessary for quicker complete hydration Eductors used in scale-up process Premix with non-swelling solvent anhydrous glycerin, glycols, oils

Question 35

Imulsi-Fi : INCI Citrus Aurantium Sinensis (Orange) Fiber

Answer 35

Forms high viscosity hydrogels compatible with alcohol

Question 36

Microfibrous Cellulose

Answer 36

Chemically identical to vascular plant cellulose Biofermentation of sugar by Acetobacter xylinum Suspension properties enhanced in surfactant cleansers – shampoos , body washes

Question 37

3 types of smectite clays

Answer 37

Bentonite Hectorite Magnesium Aluminum Silicate

Question 38

Processing Basics- Clays

Answer 38

Consistent even dispersion of clay particles into water with vigorous vortex mixing High shear dispersion into water to open/separate mineral platelets for hydration: homogenizer or Cowles blade Heating to elevated temperature for complete hydration, usually > 70 ° C

Question 39

Natural Gums

Answer 39

Natural flora and micro sources Monomers are sugars coupled in enzymatic cellular processes Grown, harvested or fermented Extraction involves benign solvents mostly ethanol/ water Biodegradable and mostly ingestible Need relatively higher levels for effective use

Question 40

Synthetic Polymers

Answer 40

Synthesized with free radical initiators Monomers are low molecular weight reactive chemicals of variable safety Solvents may have toxicity issues Variable biodegradability Usually effective at low levels Can be salt and pH sensitive

Question 41

types of Surfactant Thickeners

Answer 41

Alkyl modified acrylate polymers Amides Associative thickening – hydrophobic interaction

Question 42

types of Thickeners for Anhydrous Systems

Answer 42

``` Aluminum Stearate Trihydroxystearin Fumed Silica or Si02 Organo-clays Polyethylene Fatty alcohols Waxes ```