• On small scale mortar and pestle can be used
but its efficiency is limited. To overcome this drawback small electric mixers
can be used although care must be exercised to avoid excessive entrapment of
air.
• For large-scale production mechanical
stirrers are used to provide controlled agitation and shearing stress to
produce stable emulsions.
• The methods commonly used to prepare emulsions can
be divided into two categories:
(A) Trituration Method: This
method consists of the dry gum method and wet gum method.
(1) Dry Gum Method
In this method, the oil is first triturated with gum
with a small amount of water to form the primary emulsion. The trituration is
continued till a characteristic ‘clicking’ sound is heard and a thick white
cream is formed. Once the primary emulsion is formed, the remaining quantity of
water is slowly added to form the final emulsion.
(2) Wet Gum Method
As the name implies, in this method first gum and
water are triturated together to form a mucilage. The required quantity of oil
is then added gradually in small proportions with thorough trituration to form
the primary emulsion.
Once the primary emulsion has been formed remaining
quantity of water is added to make the final emulsion.
(B) Bottle Method
This method is employed for preparing emulsions
containing volatile and other nonviscous oils. Both dry gum and wet gum methods
can be employed for the preparation.
As volatile oils have a low viscosity as compared to
fixed oils, they require a comparatively large quantity of gum for
emulsification.
In this method, oil or water is first shaken
thoroughly and vigorously with the calculated amount of gum. Once this has
emulsified completely, the second liquid (either oil or water) is then added
all at once and the bottle is again shaken vigorously to form the primary emulsion.
More water is added in small portions with constant agitation after each addition
to produce the final volume.
Formulae for Primary Emulsion
Dry gum method or continental method
|
|
Oil |
Gum |
Water |
|
For fixed oil |
4 |
1 |
2 |
|
For Volatile |
2 |
1 |
2 |
|
Oleo resins |
1 |
1 |
2 |