Microencapsulation

Microencapsulation:

Definition: It is the process by which individual particles
or droplets of solid or liquid material (the core) are
surrounded or coated with a continuous film of
polymeric material (the shell) to produce capsules in the
micrometer to millimetre range, known as
microcapsules.

Microencapsulation
(Cont.):
Morphology of Microcapsules:
The morphology of microcapsules depends mainly on the core
material and the deposition process of the shell.

1- Mononuclear (core-shell) microcapsules contain the shell around
the core.

2- Polynuclear capsules have many cores enclosed within the shell.

3- Matrix encapsulation in which the core material is distributed
homogeneously into the shell material.
- In addition to these three basic morphologies, microcapsules can
also be mononuclear with multiple shells, or they may form clusters of
microcapsules.

Morphology of Microcapsules (Cont.):

Microencapsulation
(Cont.):
Coating material properties:
•Stabilization of core material.
•Inert toward active ingredients.
•Controlled release under specific conditions.
•Film-forming, pliable, tasteless, stable.
•Non -hygroscopic, no high viscosity, economical.
•Soluble in an aqueous media or solvent, or melting.
•The coating can be flexible, brittle, hard, thin etc.

Microencapsulation
(Cont.):
Coating materials:

Gums: Gum arabic, sodium alginate, carageenan.

Carbohydrates: Starch, dextran, sucrose

Celluloses: Carboxymethylcellulose, methycellulose.

Lipids Bees wax, stearic acid, phospholipids.
:
Proteins: Gelatin, albumin.

Microencapsulation
(Cont.):
Benefits of Microencapsulation:
1- microorganism and enzyme immobilization.
- Enzymes have been encapsulated in cheeses to accelerate ripening
and flavor development.
The encapsulated enzymes are protected from low pH and high ionic
strength in the cheese.
• The encapsulation of microorganisms has been used to improve
stability of starter
cultures.

Benefits of Microencapsulation (Cont.):

2-Protection against UV, heat, oxidation, acids, bases (e.g.colorants
and vitamins).
e.g. Vitamin A / monosodium
glutamate
appearance (white)
protection (water, T,
ligth)
3- Improved shelf life due to preventing degradative reactions
(dehydration, oxidation).
4-Masking of taste or odours.
5- Improved processing, texture and less wastage of ingredients.
- Control of hygroscopy
- enhance flowability and dispersibility
- dust free powder
- enhance solubility


6-Handling liquids as solids
7-There is a growing demand for nutritious foods for
children which provides them with much needed
vitamins and minerals during the growing age.
Microencapsulation could deliver the much needed
ingredients in children friendly and tasty way.
8- Enhance visual aspect and marketing concept.


9- Carbonless copy paper was the first marketable product to employ
microcapsules . A coating of microencapsulated colorless ink is
applied to the top sheet of paper, and a developer is applied to
the subsequent sheet. When pressure is applied by writing, the
capsules break and the ink reacts with the developer to produce
the dark color of the copy.


10-Today's textile industry makes use of microencapsulated materials
to enhance the properties of finished goods. One application
increasingly utilized is the incorporation of microencapsulated
phase change materials (PCMs).
Phase change materials absorb and release heat in response to
changes in environmental temperatures. When temperatures rise,
the phase change material melts, absorbing excess heat, and feels
cool. Conversely, as temperatures fall, the PCM releases heat as
solidifies, and feels warm.
it
This property of microencapsulated phase change materials can be
harnessed to increase the comfort level for users of sports
equipment, clothing, building materials, etc.


11- Pesticides are encapsulated to be released over
time, allowing farmers to apply the pesticides less
amounts than requiring very highly concentrated and
toxic initial applications followed by repeated
applications to combat the loss of efficacy due to
leaching, evaporation, and degradation.

Benefits of Microencapsulation
(Cont.):

12- Ingredients in foods are encapsulated for several
reasons.
Most flavorings are volatile; therefore encapsulation of
these components extends the shelf-life of these
products.
Some ingredients are encapsulated to mask taste,
such as nutrients added to fortify a product without
compromising the product’s intended taste.
Alternatively, flavors are sometimes encapsulated to
last longer, as in chewing gum.

Benefits of Microencapsulation
(Cont.):

13- Controlled and targetted release of active ingredients.
Many varieties of both oral and injected pharmaceutical
formulations are microencapsulated to release over longer periods
of time or at certain locations in the body.
Aspirin, for example, can cause peptic ulcers and bleeding if doses
are introduced all at once. Therefore aspirin tablets are often
produced by compressing quantities of microcapsules that will
gradually release the aspirin through their shells, decreasing risk of
stomach damage.

14- Microencapsulation allows mixing of incompatible compounds.

Microencapsulation
Technologies

Microencapsulation processes with their
relative particle size ranges.

Physico - Chemical Physico - mechanical
Processes Processes
Coacervation (2 – 1200 um) Spray-drying (5 – 5000 um)
Polymer-polymer incompatibility Fluidized- bed technology
(0.5 – 1000 um) (20 – 1500 um)
Solvent evaporation Pan coating (600 – 5000 um)
(0.5 – 1000 um)
Encapsulation by supercritical Spinning disc (5 – 1500 um)
fluid

Co-extrusion
Encapsulation by Polyelectrolyte (250 – 2500 um)
multilayer (0.02 – 20 um)

Microencapsulation processes with their
relative particle size ranges (cont.).

Physico-Chemical Chemical Processes
Processes (cont.)
Hydrogel microsphere Interfacial polymerization
(0.5 – 1000 um)

Phase Inversion (0.5 — 5.0 um) In situ polymerization
(0.5 – 1100 um)

Hot Melt (1 — 1000 um)

Microencapsulation Techniques
(Cont.):

I. Physico-Chemical Processes:
1- Coacervation:
- Two methods for coacervation are available, namely
simple and complex processes.

-In simple coacervation , a desolvation agent is added for
phase separation.

- Whereas complex coacervation involves complexation
between two oppositely charged polymers.

1- Coacervation
(Cont.):

Complex coacervation:
1- First the core material (usually an oil) is dispersed into
a polymer solution (e.g., a cationic aqueous polymer,
gelatin).
2- The second polymer (anionic, water soluble, gum
arabic) solution is then added to the prepared
dispersion.
3- Deposition of the shell material onto the core particles
occurs when the two polymers form a complex.
4-This process is triggered by the addition of salt or by
changing the pH, temperature or by dilution of the
medium.

1- Coacervation
(Cont.):
5- Finally, the prepared microcapsules are stabilized by
crosslinking (with formaldehyde), desolvation or
thermal treatment.
Complex coacervation is used
to produce microcapsules containing
fragrant oils, liquid crystals, flavors,
dyes or inks as the core material.

(Cont.):

2- Polymer-polymer incompatibility:
- Also called phase separation.
1- This method utilizes two polymers that are soluble in
a common solvent, yet do not mix with one another
in the solution.

2- The polymers form two separate phases, one rich in
the polymer intended to form the capsule walls, the
other rich in the incompatible polymer meant to
induce the separation of the two phases. The second
polymer is not intended to be part of the finished
microcapsule wall.

(Cont.):

3- Solvent Evaporation:
- It is the most extensively used method of microencapsulation.
1-Prepare an aqueous solution of the drug (may contain a viscosity
building or stabilizing agent)
2- Then added to an organic phase consisting of the polymer
solution in solvents like dichloromethane or chloroform with
vigorous stirring to form the primary water in oil emulsion.
3- This emulsion is then added to a large volume of water containing
an emulsifier like PVA or PVP to form the multiple
(w/o/w).
emulsion
4- The double emulsion is then subjected to stirring until most of the
organic solvent evaporates, leaving solid microspheres.
5- The microspheres can then be washed and dried.

(Cont.):

4- Polymer Encapsulation by Rapid Expansion of
Supercritical Fluids:
- Supercritical fluids are highly compressed gasses that
possess several properties of both liquids and gases.
- The most widely used being supercritical CO2 and
nitrous oxide (N2O).
- A small change in temperature or pressure causes a
large change in the density of supercritical fluids .

Polymer Encapsulation by Rapid
Expansion of Supercritical Fluids
(Cont.):

Steps
:
1-Supercritical fluid containing the active ingredient and the shell
material are maintained at high pressure and then released at
atmospheric pressure through a small nozzle.

2-The sudden drop in pressure causes desolvation of the shell
material, which is then deposited around the active ingredient
(core) and forms a coating layer.

-Different core materials such as pesticides, pigments, vitamins,
flavors, and dyes are encapsulated using this method.
-A wide variety of shell materials e.g. paraffin wax and polyethylene
glycol are used for encapsulating core substances.
-The disadvantage of this process is that both the active ingredient
and the shell material must be very soluble in supercritical fluids.

Microencapsulation by rapid expansion of
supercritical solutions

Microencapsulation
Techniques (Cont.):
5- Hydrogel microspheres:
1- Microspheres made of gel-type polymers, such as alginate, are
produced by dissolving the polymer in an aqueous solution
2-Then, suspending the active ingredient in the mixture
3- Extruding through a precision device, producing micro droplets
4- Then fall into a hardening bath that is slowly stirred. The hardening
bath usually contain calcium chloride solution.

Advantage: The method involves an all -aqueous system and avoids
residual solvents in microspheres.

The particle size of microspheres can be controlled by:
A- using various size extruders or B- by varying the polymer solution flow
rates.

(Cont.):

II Physical Processes:
1- Spray-Drying & spray-congealing :
- Microencapsulation by spray-drying is a low-cost commercial
process which is mostly used for the encapsulation of fragrances,
oils and flavors.
Steps
:
1- Core particles are dispersed in a polymer solution and sprayed into
a hot chamber.

2- The shell material solidifies onto the core particles as the solvent
evaporates.

- The microcapsules obtained are of polynuclear or matrix type.

micro-encapsulation by spray-drying.

(Cont.):

Spray-congealing:
- This technique can be accomplished with spray
drying equipment when the protective coating is
applied as a melt.
1- the core material is dispersed in a coating material
melt.
2- Coating solidification (and microencapsulation) is
accomplished by spraying the hot mixture into a cool
air stream.
- e.g. microencapsulation of vitamins with digestable
waxes for taste masking.

(Cont.):

2- Fluidized-Bed Technology:
- Different types of fluid-bed coaters include top spray, bottom
spray, and tangential spray.
- used for encapsulating solid or liquids absorbed into porous
particles.
Steps
:
1-Solid particles to be encapsulated are suspended on a jet of air
and then covered by a spray of liquid coating material.

2- The rapid evaporation of the solvent helps in the formation of an
outer layer on the particles.

3- This process is continued until the desired thickness and weight
is obtained.

Schematics of a fluid-bed coater.
(a) Top spray;
(b) bottom spray;
(c) tangential spray

(Cont.):

3- Pan coating:
1- Solid particles are mixed with a dry coating
material.
2- The temperature is raised so that the coating material melts and
encloses the core particles, and then is solidified by cooling .

Or, the coating material can be gradually applied to core particles
tumbling in a vessel rather than being wholly mixed with the core
particles from the start of encapsulation.

(Cont.):

4- Co-Extrusion:
1- A dual fluid stream of liquid core and shell materials is
pumped through concentric tubes and forms droplets
under the influence of vibration.
2-The shell is then hardened by chemical cross linkings,
cooling, or solvent evaporation.
- Different types of extrusion nozzles have been
developed in order to optimize the process

Schematic presentation of the Co-extrusion process

(Cont.):

5- Spinning Disk:
Steps
:
:
1- Suspensions of core particles in liquid shell material are poured into
a rotating disc.
2- Due to the spinning action of the disc, the core particles become
coated with the shell material.
3- The coated particles are then cast from the edge of the disc by
centrifugal force.
4- After that the shell material is solidified by external means (usually
cooling).
- This technology is rapid, cost-effective, relatively simple and has
high production efficiencies.

Microencapsulation by spinning disc

Microencapsulation

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