D Pharmacy First Year

1. Mixing &
Homogenization
MR. G.A.SHETE

2.  Mixing is the most widely used operation in which 2 or more than 2 substances
are combined together.
 Objectives of Mixing May be
 Simple physical mixing of materials to form a uniform mixture
 To promote the chemical reaction to get uniform products
 Dispersion of solids in liquid to form suspension or paste
 Dispersion of 2 immiscible liquids to form an emulsion

3.  Types of Mixtures
 Positive Mixture-When two/more miscible liquids are mixed or
soluble solid is dissolved in water, the mixtures are called as positive
mixture .e.g. Solution. It is irreversible.
 Negative Mixture-Two immiscible liquids are mixed or insoluble
solids are mixed with water it forms negative mixture. E.g.
emulsion, suspension, mixtures. It is reversible.
 Neutral Mixture-The substances do not have tendency to mix but
once mix, don’t separate after mixing. E.g. ointment, paste, cream.

4.  Mixing Mechanism of powders
 Convective mixing : There is bulk movement of groups of particle from one
part of powder bed to another. It occupy by inversion of the powder bed by
means of blades or paddles.
 Shear mixing : When shear force occur it reduces the scale of segregation by
thinning of dissimilar layers of a solid particles.
 Diffusion mixing : It occur when random motion of particles within a
powder bed causes them to change position relative to one another. It
produced by any agitation of powder.
Factors affecting mixing of powders
 Particle size
 Particle Shape
 Particle Attraction
 Material Density
 Proportions of Materials

5.  Equipment's used for mixing of Solids
 In the laboratory, the mixing of powders is done by using mortar &
pestle or with the help of a drug spatula, this method is known as
Trituration.
 Following equipments are used in mixing of solids
 Tumbler Mixer
 Double cone blender
 Agitated powder mixer
 Air mixer

6.  Double cone blender
 Principle: Shear & Tumbling
 Construction: it is made up of stainless
steel & is available in different capacity
ranging from 5-200 kg. the efficiency of
blender is depends upon speed of rotation,
the common range is 30-100 r.p.m.
Working : The material is to be blended is loaded approx. 50-60 % of
total capacity the blender. As the blender rotates the material
undergoes tumbling motion & mixes material thoroughly. Agitator
blade are fixed to produce shear action. It is efficient for mixing
powders of different densities & mainly for small quantity of
powders.

7.  Agitated Powder Mixer
 It consists of Stationary vessel or through
in which an arm rotates & transmits
shearing action to the particles.the end to
end movement is required for genral
mixing which can be achieved by fitting
helical blades to the agigator.
The mixer is commonly used for mixing free flowing powdered
materials having uniform particle size & density.

8.  Mixing of Liquids
 Equipment's used in mixing of liquids
 Propeller mixer
 Turbine mixer
 Paddle mixer

9.  Propeller mixer
 Construction:
It consists of vessel and propeller, Propeller usually operates
at high speed which is up to 8000 rpm which gives lot of
turbulence. Propeller produced flow pattern parallel to their axis
of rotation. It is used when little shear is needed.
 Working:
Liquids to be mixed are placed in a vessel. During the mixing of
liquids, air gets entrapped in liquid or there is formation of vortex.

10. To avoid air entrapment and vortex formation ,position of propeller
shaft can be changed as follows:
i. Offset from center. ii. Mounted at angle.
iii. Enter the side of the vessel. iv. Using push-pull propeller
v. By the use of baffles
Diagram:

11.  Mixing of Semi-solids
 Equipment's used for Mixing
 Triple Roller mill
 Agitator mixer
 Planetary mixer
 Sigma mixer

12.  Triple Roller mill
 Construction:
 It consists of 3 rollers. Rollers are made up of hard abrasion resistant material.
Rollers are arranged very close to each other’s. Rollers are rotated at different
speed & in opposite directions. Material gets crushed when it comes in between
rollers.
Fig : Triple Roller Mill

13.  Working:
 Material want to be mixed put in to hopper. From hopper material
come between roller no.1 and roller no.2 and is reduced in size. The
gap between roller no.2 and roller no.3 is less than that between roller
no.1 and roller no.2 Due to which material is crushed and gets mixed.
A Scraper is provided to remove the material from roller no.3
 Uses:
 It is very useful for the purpose of mixing of solid powder in ointment
base.

14.  Silverson Mixer Homogenizer
 Construction
It consists of emulsified head which is covered with fine meshed stainless steel
sieve. The emulsifier head consist of a number of blades which rotates at a
very high speed, to produce powerful shearing action. The blades are rotated
by using an electric motor fitted at the top.
 Working:
The emulsified head is placed in the vessel containing immiscible liquid, in
such a way that it should get dipped into it. When the motor is started, the
liquid is sucked through the fine holes and the oil is reduced into fine globules
due to the rotation of blades. So a fine emulsion is produced which is then
expelled out.
 Use:
Useful for the preparation of fine emulsion and suspension.

15. Fig: Silverson Mixer Homonizer