Transcript Toxic Chemicals

Industrial Chemistry
Part VI
Principles Emulsions
2011
Importance of Emulsions
Many foods consist either partly or wholly as food
emulsions, or have been in an emulsified state
sometime during their manufacture.
milk, cream, salad cream, mayonnaise, salad
dressings, soups, sauces, butter, margarine,
beverages, ice cream and coffee whitener.
What is Emulsion?
Emulsions are mixtures of two immiscible liquids; in
which both the dispersed phase and the dispersion
medium are liquids.
Dispersed phase: is the liquid present in a small amount
(small droplets)
The dispersed liquid is known as the internal or
discontinuous phase
Continuous phase: is the liquid present in a large amount
(medium)
the continuous phase is known as the external or
dispersion medium
Classification (Types) of Emulsions
 Based on dispersed phase
Oil in Water (O/W): Oil droplets dispersed in water
Water in Oil (W/O): Water droplets dispersed in oil
More complex types consist of three or more phases,
which can be achieved by e.g. dispersing a w/o-emulsion
into a second watery phase, leading to a water-in-oil-inwater-(w/o/w-)emulsion.
In summary
1. oil-in-water (o/w)
2. water-in-oil (w/o)
3. water-in-oil-in-water (w/o/w)
4. oil-in-water-in-oil (o/w/o)
Types Based on Size of Liquid Droplets
0.2-50 µm Macroemulsion
0.01-0.2 µm Microemulsion
Mayonnaise: Oil in
Water emulsion
Milk: Oil in Water
emulsion
Water in oil emulsion
Sodas: Oil in Water
emulsion
Emulsion is Thermodynamically Unstable
W/O & O/W ONLY
Most oils are less dense in water, and if oil and water
are mixed then the oil will simply float to the surface.
In emulsions, the oil is dispersed as liquid droplets
through the continuous phase, usually but not
necessarily water. Those droplets want to combine
together again to form a single drop of oil this means
that an emulsion is thermodynamically unstable.
A difference in the densities of the two liquids may
cause undesired creaming of the dispersed droplets !!!
What we can do to prevent this unwanted physical process?
Stability of emulsions may be engineered to vary
from seconds to years depending on application.
How we can do that?
Compositions of Emulsion
Internal/Discontinuous/Dispersed phase (liquid)
External/Continuous phase (Liquid)
Emulsifying agent
Stabilizers
Emulsifying Agents
An emulsifier is a molecule with one oilfriendly and one water-friendly end i.e.
hydrophilic tail and hydrophobic head. (Do
you remember what is that?)
These agents surrounds the oil droplets in
water and reduces the tension between the
two liquids thus impart stability. Emulsifying
agents are often used to help the formation of
emulsions
Classification of Emulsifiers
Chemical Structure
Mechanism of Action
Synthetic Natural Auxiliary agents dispersed solids
Monomolecular
Multimolecular
Solid Particle Films
Synthetic
Anionics: alkali soaps (sodium or potassium oleate)
detergents (sodium lauryl sulfate, sodium dioctyl
sulfosuccinate, sodium docusate).
Non-ionics: Sorbitan esters (Spans®), polyoxyethylene
derivatives of sorbitan esters (Tweens®), or glyceryl
esters
Cationics: benzalkonium chloride, benzethonium chloride
Amphoterics
Natural Emulsifying Agents
Natural emulsifying agents are derived from plant
and animal tissues and mostly in the form of
hydrated lypophilic colloids. These emulsifiers make
the protective sheath around the droplets, give
droplets a charge so that they repel each other and
swell to step-up the viscosity of the liquid.
Although natural agents are inexpensive, safe and
non toxic but these are slow in action. So large
quantity of emulsifier is required for proper action.
Also the natural emulsifiers need preservatives as
these are subjected to microbial growth.

1) Carbohydrate Materials:
Acacia, Tragacanth, Agar, Pectin. o/w emulsion.

2) Protein Substances:
-Gelatin, Egg yolk, Caesin o/w emulsion.

3) High Molecular Weight Alcohols:
- Stearyl Alcohol, Cetyl Alcohol, Glyceryl Mono
stearate o/w emulsion, cholesterol w/o emulsion.
Finely divided solids:
These agents form a particulate layer around dispersed
particles. Most will swell in the dispersion medium to
increase viscosity and reduce the interaction between
dispersed droplets.
Most commonly they support the formation of o/w
emulsions, but some may support w/o emulsions.

Examples
Magnesium Hydroxide, Aluminum Hydroxide o/w
emulsion
magnesium trisilicate.
Mechanism of action of emulsifying agents:
Monomolecular
- Coherent monomolecular film
- flexible film formed by SAA,
- depend on lower the d o/w ,
- can prepare o/w and w/o emulsion
Examples: Synthetic SAA, K laurate
Mechanism of action of emulsifying agents:
Multimolecular
Strong rigid film formed, mostly by the hydrocolloid,
- which produce o/w emulsion,
- d is not reduced to any extent ,
- the stability due to strength of the formed interfacial
film
Examples: Hydrophilic colloid ( acacia, gelatin)
Mechanism of action of emulsifying agents:
Solid particles
Film formed by solid particles that are small in size
compared to the droplet of the dispersed phase.
- Particles must be wetted by both phases in order to
remain at the interface and form stable film,
- can form o/w and w/o
Examples: Colloid clays(bentonite, Mg(oH)2)
Tests Used To Identify Emulsion Type:
Dilution test: based on the solubility of external
phase of emulsion.
- o/w emulsion can be diluted with water.
- w/o emulsion can be diluted with oil.
Conductivity Test:
water is good conductor of electricity whereas oil is
non-conductor. Therefore, continuous phase of
water runs electricity more than continuous phase
of oil.
Dye-Solubility Test:
when an emulsion is mixed with a water soluble
dye such as amaranth and observed under the
microscope.
¡ if the continuous phase appears red, then it
means that the emulsion is o/w type as water is
the external phase
¡ if the scattered globules appear red and
continuous phase colorless, then it is w/o type.
Fluorescence test:
Fluorescence test: oils give fluorescence
under UV light, while water doesn’t. Therefore,
O/W emulsion shows spotty pattern while W/O
emulsion fluoresces.
Theory of emulsification
Droplets can be stabilized by three methods
i. By reducing interfacial tension
ii. By preventing the coalescence of droplets.
a. By formation of rigid interfacial film
b. By forming electrical double layer.
Theory of emulsification –reduction
of interfacial tension
Phase A
Phase B
A
B
Change from A to B
increases surface area of
phase A, hence the Due
to increased surface
energy, the system is
thermodynamically
unstable.
Emulsifying agents are needed to decrease the
interfacial tension and to24stabilize the emulsion.

Oriented-Wedge Theory:
- mono molecular layers of emulsifying
agents are curved around a droplet of
the internal phase of the emulsion.
Multimolecular films
Theory of emulsification -Formation
of electrical double layer
+
- +
Oi
l
-
- +
- +
-+
-
-
+
+
Water
+
+
Emulsion
made with
sodium
soap.
-
Electrical double layer at oil-water interface
Interfacial films
Solid particle film: These agents form a 
particulate layer around dispersed particles.
Most will swell in the dispersion medium to
increase viscosity and reduce the interaction
between dispersed droplets.
Most commonly they support the formation 
of o/w emulsions, but some may support w/o
emulsions.

Methods of emulsion preparation:
On small scale:
¡ Porcelain mortar and pestle
¡ On large scale:
Mechanical stirrer
Methods of emulsion preparation:
Emulsifier is triturated with the oil in perfectly
dry porcelain mortar
water is added at once
triturate immediately, rapidly and continuously
(until get a clicking sound and thick white cream
is formed, this is primary emulsion)
the remaining quantity of water is slowly added to
form the final emulsion
English or Wet Gum Method
triturate gum with water in a mortar to form a mucilage
oil is added slowly in portions the mixture is triturated
after adding all of the oil, thoroughly mixed for
several minute to form the primary emulsion
Once the primary emulsion has been formed remaining
quantity of water is added to make the final emulsion.
Bottle or Forbes Bottle Method
It is extemporaneous preparation for volatile oils or oil
with low viscosity.
gum + oil (dry bottle)
Shake
water (volume equal to oil) is added in portions with
vigorous shaking to form primary emulsion
remaining quantity of water is added to make the final
emulsion
Auxiliary Emulsifying Agents
A variety of fatty acids (e.g., stearic acid), fatty alcohols
(e.g., stearyl or cetyl alcohol), and fatty esters
(e.g., glyceryl monostearate) serve to stabilize emulsions
through their ability to thicken the emulsion. Because
these agents have only weak emulsifying properties, they
are always use in combination with other emulsifiers
 Be stable .
 Be compatible with other ingredients .
 Be non – toxic .
 Bossess little odor , taste , or color .
 Not interfere with the stability of efficacy of the
active agent .
Emulsion Stability:
The instability of pharmaceutical emulsions may be
classified as the following:
a) Flocculation and creaming
b) coalescence and breaking
c) Phase inversion
d) Miscellaneous physical and chemical change
Emulsion Stability
Flocculation and creaming:
¡ Flocculation - The small spheres of oil join
together to form clumps or flocs which rise or
settle in the emulsion more rapidly than
individual particles.
¡ Creaming - it is a concentration of the floccules
of the internal phase formed upward or
downward layer according to the density of
internal phase.