Viscosity Control Flashcards
Two primary purposes of adding thickeners
- Enhancement of product form/aesthetics/application properties
- Product Stability
Flow properties are determined by
- particle-particle interaction
- association structure disturbances
- polymer behavior in solution
Define rheology
How materials deform or flow in response to external forces
Define shear stress
External force applied over area
Pa = N/m^2
Define shear rate
velocity gradient (1/sec) HOW FAST
Define shear strain
Relative displacement
HOW FAR
Define viscosity
Measure of a material’s resistance to flow
Newtonian shear
linear response of flow rate to shear stress
Pseudoplastic refers to ______ rheology
Shear thinning
Dilatant refers to _________ rheology
Shear thickening
Thixotropic refers to _______ rheology
Shear thinning with time dependence
Slower return to original state
Thickening agents in external water phase in O/W emulsions
Hydrocolloids
Thickening agents in lipid phase in O/W emulsions
- Co-emulsifiers
- Solid amphiphiles that form liquid crystalline gel networks
Factors governing O/W emulsion viscosity
- Thickeners in water phase
- Thickeners in lipid phase dispersed in water phase
- Phase volume (Ratio—-Volume of dispersed phase: volume of continuous phase)
- Lipid composition of internal phase
Examples of synthetic polymer thickeners
- acrylates
- carbomers
- polyurethanes
Carbohydrates/plant/algal thickeners
- Xanthan gum
- Alginates
- Scleroglucan
- Carrageenan
- Guar
Example of fermentation derived microbiological by-product thickeners
Gellan-exopolysaccharide from Sphingomonas elodea
Cellulose derivative thickeners
Carboxymethylcellulose
Hydroxyethylcellulose
Examples of smectite clay thickeners
- Bentonites
- Hectorites
Dramatic viscosity increase occurs past the Critical Overlap Concentration due to
interaction of polymer molecules to form interpenetrating networks in the solvent
Associative rheology modifiers control rheology by
Association with:
- itself
- surfactant micelles
- water dispersible clays
- emulsified solvent phase
- dispersed solids
Nonassociative rheology modifiers control rheology by
chain entanglement of lightly cross-linked polymer molecules
Liquid Dispersion polymers used as self-emulsifying system consist of
Polymer thickener (anionic/cationic/nonionic)
Emollient Solvent
Nonionic emulsifier
What portion of Agar is Agarose
neutral gelling portion separated from sulfate non-gelling portion
What is agarose polymer made of
galactose and anhydrogalacose
Agarose gels are ___________ and are hydrated at _____ temperatures
thermoreversible
high
Agarose is derived from
Rhodophycae
Alginic Acid is derived from
Laminaria, Macrocystis, brown seaweeds
Acid sugars making up algal polysaccharides
Mannuronic, Guluronic
Form of alginic acid that acts as thickener
Sodium/Potassium alginate
Algin-derived thickeners exhibit __________ rheology, _____ sensitivity to heat, and _______ yield value
pseudoplastic shear thinning
high
little
Anionic forms of alginic acid complex with _______ to form _________
Divalent calcium ions
rigid gels
Having a high yield value leads to
increased stability at room temperature
Water swellable clays have ______ rheology
thixotropic
High solids dispersions tend to have ______ rheology
dilatant
What type of measurements does a viscometer give
Single point
What do rheometers measure
Give shear stress at a controlled shear rate
_______ phase is most important in finished product viscosity
Outer
Co-emulsifiers give
liquid gel network
Silicas work as thickeners by
hydrogen bonding
Hydrophobically modified polymers will act as thickeners by
associating with other hydrophobic materials OR have intermolecular bonding with other ingredients in solution
Which inorganic rheology modifier can also work in organic media
silica
greatest fault of carbomers
salt sensitivity
What is required for anionic polymers?
They must be neutralized with equivalent weight
What is difficult about carbomers once they have been neutralized?
Hard to thin out
Neutralizing Carbopol and Pemulen polymers in aqueous and hydroalcoholic solutions has this result
Hydroxyl groups associate to form cross links
Too much salt can break down the structure though
Describe the process of creating a liquid dispersion polymer
- Disperse polymer in liquid
- add in HLB emulsifier
- this thickens the water and inverts the emulsion
Croda’s Liquid dispersion polymers
- Polyacrylate polymers dispersed in carrier oil with an inverting surfactant
- Add to water–> turns into a w/o emulsion
- Polyacrylate molecules swell by osmosis, thickening the water phase
The three forms of Carrageenan depend on
levels of sulfation
Chitosan is a ________ polymer
cationic
Chitosan can be used for ________
coacervation encapsulation
Scleroglucan has ______ rheology
pseudoplastic
Locust Bean Gum retards ice crystal growth by
forming structured gel at solid/liquid interface for freeze/thaw stabilization
Gellan comes from
bacterium
Xanthan gum exhibits ______ rheology
shear thinning
______ are used in the scale-up process for processing gums
Eductors
Microcrystalline cellulose is a product of
partial cellulose depolymerization by mineral acid
Microcrystalline cellulose colloidal dispersion acts as
emulsion stabilizer
CMC is used as a
dispersion agent
Polyquaternium-10 consists of
cationic group attached to hydroxycellulose
Smectite clays can be used in low levels due to
synergy with organic thickeners
Synthetic polymers are synthesized with
free radical initiators
Synthetic polymers are ________ likely to be sensitive to salt and pH than natural gums
more
Thickeners for anhydrous systems
- Aluminum Stearate
- Trihydroxystearin
- SiO2
- Organoclays
- Polyethylene
Quat-18 is derived from
tallow
fatty quats react with smectite clay to
replace monovalent anions between clay platelets
Organic solvents have this effect on organoclays
interstitial space swelling
