Lecture 5 - Viscosity Control Flashcards
Two primary purposes of rheology additives
Enhancement of product form
- Aesthetics, texture, processing, packaging control
- Flow & application properties
Product stability
- Preventing colloidal systems from breaking down
- Retard coalescence and creaming
functions of thickeners
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
The flow properties of cosmetic solutions, emulsions, and dispersions are a result of colloidal structures and/or thickening agents such as:
Particle-particle interaction
Association structure disturbances
Polymer behavior in solution
define rheology
how materials deform or flow in response to external forces
“the branch of physics that studies the deformation and flow of matter”
define shear stress
the external force applied over an area. Unit are Pascals (Pa) = Newtons per meter2 (1Pa= 10 dynes/cm2 )
define shear rate
ratio of velocity of material to its distance from a stationary object -the velocity gradient (1/sec) –HOW FAST
define shear strain
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)
define viscosity
a measure of a material’s resistance to flow measured in Pascal seconds = 1 poise (P) in cgs system = 100 centipoise (cps)
define newtonian flow
not variable with shear linear response of flow rate to shear stress
define pseudoplastic flow
shear thinning
define dilatant flow
shear thickening
define thixotropic flow
shear thinning with time dependence (slower return to original state)
4 Factors Governing O/W emulsion viscosity
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
6 sources of thickeners
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
what is the Concentration- Response Function
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
what is the Critical Overlap Concentration
concentration above which dramatic viscosity increase occurs due to interaction of polymer molecules to form interpenetrating networks in the solvent.
examples of Stabilizer polymers & gums, solids
Carbomers Xanthan gum Sclerotium gum Cellulose derivatives : - CMC (Carboxymethylcellulose) - HEC (Hydroxyethylcellulose) Bentonite/Hectorite clays MgAl Silicate clay
carbomers
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
Liquid Dispersion Polymers
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
examples of Carbohydrates/ Polysaccharides
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
Agar/Agarose
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
Alginates: Alginic acid - Algin
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
Carrageenan
red seaweed (Rhodophycae) derived sulfated polysaccharide (Galactose units)
3 forms of Carrageenan available
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
Chitosan
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
Scleroglucan
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
Guar
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.)
Konjac Gum
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
gellan
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
Locust Bean Gum
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
Rhizobium Gum
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
Tragacanth Gum
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
Xanthan Gum
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
Processing Basics- Gums
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
Imulsi-Fi : INCI Citrus Aurantium Sinensis (Orange) Fiber
Forms high viscosity hydrogels compatible with alcohol
Microfibrous Cellulose
Chemically identical to vascular plant cellulose
Biofermentation of sugar by Acetobacter xylinum
Suspension properties enhanced in surfactant cleansers – shampoos , body washes
3 types of smectite clays
Bentonite
Hectorite
Magnesium Aluminum Silicate
Processing Basics- Clays
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
Natural Gums
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
Synthetic Polymers
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
types of Surfactant Thickeners
Alkyl modified acrylate polymers
Amides
Associative thickening – hydrophobic interaction
types of Thickeners for Anhydrous Systems
Aluminum Stearate Trihydroxystearin Fumed Silica or Si02 Organo-clays Polyethylene Fatty alcohols Waxes
