Module%201-%20Mixing.دادىاداىدداادىادادابنانبابنان

th 1
Module 1: Mixing
Mohammed Albarki, BSc.Pharm, PhD

Mixing
• This is a crucial step in the formulation of the pharmaceutical
dosage form.
majority
• The of pharmaceutical products contain more
than
one component so they do need a mixing or blending stage.
• Mixing can be defined as a process in which two or more
ingredients in separate or roughly mixed conditions are treated
so that each particle of any one ingredient is as nearly as
possible adjacent to a particle of each other ingredient.
• Good mixing is needed in all pharmaceutical products but it is
of special importance in some conditions such as drugs with
narrow therapeutic indexes.
• In this lecture:
Mixin
g
• or blendin
g
opposite to demixin
g
or segregatio
n 2
College of Pharmacy- Industrial Pharmacy I - 4t
h stage- Second Mixi

Mixing
randomizatio
n
• Mixing tends to result in a of dissimilar particles within a
system.
This is to be distinguished from an ordered system in which the particles are
arranged according to some iterative rule and thus follow a repetitive pattern.
Mixing is a fundamental step in most process sequences and is normally carried
out to:
appearance
1. Control heat and mass transfer.
2. Ensure the even of the final dosage form. This is to improve
single-
phase and multiphase systems.
3. Secure the uniformit
y
of the composition so that small samples withdrawn
from a bulk material represent the overall composition of the mixture. (even
distribution of components)
4. Promote physical and chemical reactions, such as dissolution, in which
natural
diffusion is supplemented by agitation. 3

Types of mixture
• Mixture are three types: positive, negative,
and neutral mixture.
• Positive mixtures:
• Such as gases and miscible liquids.
• Where spontaneous, irreversible, and complete
mixing would take place by diffusion, without
energy to keep the mixing
the expenditure of
state.
no
• This type of material will cause
problems during manufacturing.
4

Types of mixture
• Negative mixtures:
• They are demonstrated by biphasic systems (suspension,
emulsion).
• Negative mixtures are generally more difficult to form and
maintain and require a higher degree of mixing as compared
to positive mixtures.
• Any two-phase systems such as suspensions of solids in
liquids, emulsions, and creams tend to separate quickly unless
continually expended
energy is on them.
• Neutral mixtures: type of mixtures that are static in behavior,
will not mix spontaneously
that but when mixed will not
segregate spontaneously such as powders, paste, and ointments.
• Occurs when neither mixing nor de-mixing takes place unless
the system is acted upon by an external energy input. 5

Dosage Form Classification
6
• Dosage forms can be classified based on their
physical form into four types:
1. Gaseous
2. Liquids
3. Semisolids
4. Solids

7
h stage- Second Semester Mixing
Fluid Mixing

Flow Characteristics
• Fluids may be generally classified as Newtonian and non-
Newtonian, depending on the relationship between their shear
rates and the applied stress.
• The rate of shear may be defined as the derivative of velocity
with respect to distance measured normal to the direction of
flow
. viscosity
• The is the ratio of shear stress to the shear
rate.
• Forces of shear are generated by interactions between moving
fluids and the surfaces over which they flow during mixing.
8

Flow Characteristics
• Newtonian Fluid:
• The rate of shear is proportional to the applied stress,
and such fluids have a dynamic viscosity that is
independent of the flow rate.
constant
• Like water where viscosity;  the rate of
shear
increases with shear stress
• Non-Newtonian fluid:
• Apparent dynamic viscosity is a function of the shear
stress. Such as
thinnin
g
thickenin
g
1. Plastic flow: a fluid after a certain shear stress limit
2. Pseudoplastic flow: (shear behavior)
3. Dilatant flow (shear behavior)
9

Liquid Mixing Mechanisms
• Mixing Mechanisms: can be divided into four mechanisms and
usually more than one of them occurs in the mixing of liquid:
• First: Bulk transport
• Movement of a large portion of liquid to be mixed from one
location to another.
leaves a part
• However, this mechanism of the liquid within
the
moving material unmixed.
does not necessarily
•  A simple circulation of material
result in efficient mixing.
• This mechanism is usually accomplished using paddles, revolving
blades, and other devices.
10

• Second: Turbulent mixing
turbulent fluid flow
• This resulted directly from the
which
is characterized by the random fluctuation of fluid
velocities at any given point within the system.
• In this mechanism, fluid movement (mixing) can be
visualized as a movement of portions of various sizes
(eddies) that move together.
Eddy
• is defined as a portion of fluid moving as a unit in a
contrary
direction often to that of the general flow.
tend to break up
• Larger eddies forming smaller eddies
until no longer distinguishable
they are .
11

• Third: Laminar flow (streamline)
• This type of flow happens when:
viscous
1. Mixing highly fluids.
2. It can also occur if stirring is relatively gentle
(moderate or slow)
3. May exist adjacent to stationary surfaces in vessels in
which the flow is predominantly turbulent.
layers of the fluid
• This can be described by moving
into another fluid.
• When two dissimilar liquids are mixed through laminar
stretches
flow, the shear that is generated the interface
between them.
• https://youtu.be/_dbnH-BBSNo?si=L-9q-ohIymEs998J 12

Liquid Mixing: Laminar Flow
• When 2 dissimilar liquids are mixed through laminar
stretches
flow, the shear that is generated the interface
between them.  If the mixer employed fold
s
the
layers back upon themselves, the number of layers &
hence the interfacial area between them increases
exponentially with time.
because
• This relationship is observed the rate
of
increase in interfacial area with time is proportional
to the instantaneous interfacial area.
13

Laminar Flow: Example
• Consider the case where the mixer produces a folding effect & generates a complete fold
every 10 seconds.
• Given an initial fluid layer thickness of 10 cm, a thickness reduction by a factor of 10-8
is
14
n
m
necessary to attain layers 1 thick (which approximate molecular dimensions ≈1 nm).
Since a single fold results in a layer thickness reduction of one-half, n folds are
required where:
• (12)n =10-8  take log of both sides (since Log (X)y = y Log X), Log 10=1
n log (1/2)= -8
• log(1/2)n = n log ½ and log 10-8 = -8 

• n= -8/(log ½) = -8 /-0.3 = 26.6 folds required to get 1 nm
Since each fold requires 10 seconds
•  total time required for mixing (equal to n times
10 seconds) = 26.6 * 10 = 226 sec or 4.43 minutes
require
s
• Good mixing at the molecular level a significant contribution by
molecularafter
diffusion the layers have been reduced to reasonable thickness by laminar flow.

Liquid Mixing: Molecular Diffusion
• Fourth: Molecular diffusion.
• Mixing of molecules of one fluid through another by random molecular motion.
primary mechanism
• The responsible for mixing at the molecular level
is
diffusion resulting from the thermal motion of the molecules when it occurs in
conjunction with laminar flow.
• In this mechanism, molecules move according to the
until they result in complete mixing.
concentration gradients
15

Liquid Mixing: Molecular Diffusion
reduce the sharp discontinuities
16
• Molecular diffusion tends to at the
interface
between the fluid layers and if allowed to proceed for sufficient time result in
complete mixing.
• The process described by Fick’s 1st law of diffusion (substances will diffuse from
areas of high concentration to lower concentration)
dm/dt= -DA
dc/dx
• The rate to mass transfer (dm/dt A
) across an interface of area is proportional to
dc/dx
the concentration gradient ( ) across the interface
• D (diffusion coefficient) depends on the viscosity and the size of the diffusing
molecules.
• The concentration gradients at the original boundaries are a decreasing function of
time, approaching zero as mixing approaches completion.

Mixing Evaluation
•It is important to examine each mixture during the mixing
process to ensure that we have enough mixing (i.e.
random mixing).
•Danckwerts has suggested 2 criteria to describe the degree
of mixing (quality of randomness or goodness of mixing)
1. The scale of segregation:
• Scale of segregation is expressed in 2 ways either linear
or volume scale.
linear scale
• The represents the average value
of
the
diameter of the lumps whereas the volume scale
represents the average lump volume.
2. Intensity of segregation is a measure of the variation in
composition among the various portions of the mixtures.
will be zero
• Variation at the end of the
mixing
Bulk
17
Turbulent Diffusion

Equipment for Fluid Mixing
• Generally, fluid mixers consist of a:
1. Tank or a container to hold the material being mixed and
2. A suitable energy transfer tool such as an impeller, liquid
jet, or air stream.
• Besides supplying power, these tools also serve to direct
the flow of material within the vessel.
• Baffles, vanes, and ducts are also used to direct the bulk
movement of material in such mixers, thereby increasing
their efficiency.
limited in volume
• When the material to be mixed is so
that
it may be conveniently contained in a suitable mixer, batch
mixing is usually more feasible.
larger
• However, for
volumes, preferred.
continuous mixing is
18

Batch Mixers
• Batch mixers are used for small volumesand
impellers
they are either
or
jet mixers.
• Impellers: these are the main mixing units in
fluid mixers. It can be either propellers,
turbines, or paddles.
• The distinction between impeller types is on
the basis of:
1. The type of
2. The
flow pattern they produce, or
shape and pitch of the blades.
• These impellers cause turbulence and prevent
the formation of dead zones. 19

Types of flow in liquid
• The impellers create a current or stream
of liquid that moves in all places of the tank.
• The flow pattern may be analyzed in terms
of three components:
perpendicular
1. Radial: to the impeller shaft.
2. Axial or longitudinal (down and up):
parallel to the impeller shaft.
tangentia
l
3. Tangential: to the circle of
rotation around the impeller shaft.
• These may occur singly or in various
combinations
.
20

Impeller Batch Mixer: Propellers
Propellers
• of various types and forms are used.
• Also, like the machine screws, propellers may be either right- or
left-handed depending on the direction of the slant of their
blades
• The primary effect is due to axial flow, however, some
tangential flow does occur.
• Also, intense turbulence usually occurs in the
immediate vicinity of the propeller.
• Propellers are more efficient when they are run at high speed in
liquids with low viscosity.
21

Impeller Batch Mixer: Propellers
• Although any number of blades may be used, the
commonly used with fluids.
three-blade design is most
• The blades may be set at any angle or pitch but for most applications, the pitc
h
is
approximately equal to the propeller diameter.
22

Impeller Batch Mixer: Turbines
distinguished from propellers
• They are usually in that the
blades
of the propeller do not have a constant pitch throughout their
length
radial-tangential flow is desired, turbines with blades set
• When
at a90-degree angle to their shaft are employed
• With these types of impellers, a radial flow is induced by the
centrifugal action of the revolving blades
If
• the turbine blade is tilted  it will produce additional axial
flow similar to the propeller.
• Because they lend themselves to a simple and rugged design,
these turbines can be operated satisfactorily in fluids 1000 times
more viscous than fluids in which a propeller of comparable size
can be used.
• https://youtu.be/kobc3DdaofE
23

Impeller Batch Mixer: Paddles
• Normally operated at low speed (lower than 50 rpm).
blades have a large surface area
• Their as compared to the tank in which they
are
employed they pass close to the tank walls effectively mix viscous
and
fluids
semisolids
and which tend to cling to these surfaces.
• Circulation is primarily tangential, and consequently, concentration gradients
(not complete mixing) in the axial and radial directions may persist in this type of
mixer even after prolonged operation.
• Operating procedures should take these characteristics into account. With such
mixers, for example, ingredients should not be layered when they are added to
the mixing tank.
24

Batch Mixer: Jet Mixers: 1- Air
Jet
• Air Jets is a sub-surface stream of air or other
gasses used to mix the fluids.
• Fluids should be of:
1. Low viscosity,
2. Nonfoaming,
3. Nonreactive with the gas (or air),
4. And reasonably nonvolatile.
• The jets are usually arranged so that the
buoyancy of the bubbles lifts liquids from the
bottom to the top of the mixing vessel.
25

Batch Mixer: Jet Mixers: 1- Air
Jet
• This is often accomplished with the aid of draft
tubes
. • These serve to 1- confine the expanding bubbles
2-
and entrained liquids, resulting in a more
efficient lifting action by the bubbles, and
inducing an upward fluid flow in the tube.
circulate fluid in
• This flow tends to the tank,

bringing it into the turbulent region in the vicinity of
the jet.
• The overall circulation in the mixing vessel brings
all parts
fluid from of the tank to the region of the jet
itself.
•  Here, the intense turbulence generated by the
jet produces intimate (deep) mixing
26

Batch Mixer: Jet Mixers: 2- Fluid Jet
• Fluid jet: liquid at high pressure is pumped into the tank.
power
• The required for pumping can often be used
to
accomplish the mixing operation, either partially or
completely.
• In such a case, the fluids are pumped through nozzles
arranged to permit a good circulation of material throughout
the tank.
• In operation, fluid jets behave somewhat like propellers
and they generate turbulent flow axially
.
do not
• However, they themselves generate
tangential
pumping liquid
flow, like propellers.
• Jets also may be operated simply by from
the
tank through the jet back into the tank
h stage- Second
27
Mixi

Continuous or In-line Mixers
Advantage
• : The process of continuous mixing produces
an uninterrupted supply of freshly mixed material and is
very large volumes
often desirable when of materials
are to be handled.
• It can be accomplished essentially in two ways:
1. In a tube or pipe (baffled pipe mixers) through
which the material flows and in which there is
very little backflow or recirculation,
2. Or in a mixing chamber mixers in which a
considerable amount of holdup and recirculation
occurs.
• To ensure good mixing efficiencies, devices such as
vanes, baffles, screws, grids, or combinations of these are
placed in the mixing tube.
28

Practical Considerations: Vortexing
center of the vessel
• Vortexing: a vortex develops at the
when
liquids are mixed by centrally-mounted vertical shaft
impellers.
turbine
• This particularly is characteristic of the with
blades
arranged perpendicular to the impeller shaft.
tangential flow
• The will cause a centrifugal force that
may
cause vortexing to happen. This is why tangential flow is not
recommended.
will not
• The tangential flow result in any mixing
except
possibly near the tank walls where shear forces exist.
very low impeller speeds
• Except in the case of or
at
very
high liquid viscosities (above 20000 cps). However, these
not common
cases are in the pharmaceutical industry. 29

Practical Considerations: Vortexing
• Vortexing is
30
not recommended in mixing due to:
1. Does not cause real mixing. The full power of the impeller is no
t
imparted to
the liquid.
2. Air is drawn onto the impeller and is dispersed into the liquid, which may
lead to foaming, especially if surfactants are present.
entrapped air may cause oxidation
3. The or it can reduce the mixing intensity
by reducing the velocity of the impeller relative to the surrounding fluid.

Vortex can be avoided by:
off-
center
1. Changing the arrangement of the impellers: mounting the impellers or
inclined or side position.
bu
t
2. Changing tank geometry. Asymmetric or angular geometry this will increase
time
the required for mixing since there will be areas in the tank in which the
circulation is poor.
opposite
3. Using a push-pull propeller: two propellers of pitch are mounted on the
same shaft to the rotary effects are in opposite directions  and cancel each
other.
31

Vortex can be avoided by
4. Using baffles: these plates will convert tangential
flow into an axial flow.
5. Use of diffuser/stator ring: that fits around the
impeller.
32

• Comparative mixing characteristics of various types of impellers
33

Mixer selection
• Selection will depend on:
34
Physical properties
1. of the materials to be mixed, such as density, viscosity, and
miscibility
.
Economic considerations
2. regarding processing for example the time required
for mixing and the power expenditure necessary.
Cost
3. and maintenance of the equipment.
• However, the selection of equipment depends primarily upon the viscosity of the
liquids and is made according to the mechanism by which intense shearing forces
can best be generated.

Mixer Selection 1- Monophasic System
•
35
Low Viscosity Systems:
• Fluids of relatively low viscosity encounter no problems during mixing except
when the operational scale is very large.
• Low-viscosity monophasic fluids are best mixed by the method that:
high degree of turbulence
1. Generates a &
2. At the same time circulates the entire mass of material.
• These requirements are satisfied by air jets, fluid jets & various high-speed
impellers.
10 poise
• A viscosity of approximately may be considered as a
practical
upper
limit for the application of these devices.

Mixer Selection 1- Monophasic System
•
36
High Viscosity Systems:
• Thick creams & ointments &pastes are of such high viscosity that is difficult if
generate turbulence
not impossible to within their bulk & laminar mixing.
• This means molecular diffusion is very important here.
• Mixing may be done with a turbine of flat blade design.
• The power consumption of these devices is insensitive to density and/or
viscosity.
• They are a good choice when emulsification or added solids may change these
quantities (viscosity and density) during the mixing.

Mixer Selection 2- Polyphasic System
37
subdivisio
n
• The mixing of 2 immiscible liquids requires the of one of
these
phases into globules, then distributed throughout the bulk of the fluid.
• These globules are successively broken down into smaller ones.
• Two primary forces play here:
The interfacial tension
1. of the globules in the surrounding liquid and
2. Forces of shear within the fluid mass.
• The first force tends to resis
t
the distortion of globule shape fragmentation to
opposite
small globules whereas the with the 2nd force.
viscosity
• The selection of equipment depends upon the of the liquids and this
is
made according to the mechanism by which intense shearing forces can best be
generated.

Mixer Selection 2- Polyphasic System
• In the case of low-viscosity systems, high shear rates are required and produced
by passing the fluid under high pressure through small orifices or by bringing it
into contact with rapidly moving surfaces.
38
• Highly viscous fluids
• Such as the ones encountered in the production of ointments, are efficiently
2 surfaces
dispersed by the shearing action of in close proximity and moving at
different velocities with respect to each other.
• This is achieved in paddle mixers in which the blades clear out the walls.
• These mixers generate shear to reduce globule size and induce sufficient
circulation of materials to ensure efficient mixing.

Mixer Selection
2- Polyphasic System
• The mixing of finely divided solids with a liquid of low viscosity in the
suspensio
n
production of a depends on the separation of aggregates & distribution
of these particles in the fluid.
single mixing operation
• This process occurs in a provided that shear forces
of
sufficient to disrupt aggregates.
• As the % of solids is increased or if highly viscous fluids are employed, the
solid-liquid system takes on the consistency of a paste or dough. 
knead or mull
• The choice of mixer is either the
materials.
Kneaders
• operate by pushing the material by squeezing & deforming them at
the same time. Such mixers take several forms.
counter-rotating blades or heavy arms
• Usually have that work the
plastic
mass. Shear forces are generated by the high viscosity of the mass & are
effective in the deaggregation & distribution of the solids in the fluid vehicle.
39

40
Semisolid Mixing

Semisolid Mixers
• Semisolids include ointments, paste,
creams, gels, etc.
41

Semisolid Batch Mixers: 1- Kneaders
A. Sigma-blade Mixer: contains counter-rotating
blades or heavy arms that work the plastic mass.
• The blades rotate tangentially in a 2:1 speed ratio (one
moves faster than the other).
• Mixing action is due to:
1. The shape and difference in rotational speed of the
blades facilitate lateral pulling of the material and
impart kneading and rolling action on the material.
2. Shear forces are also generated by the high viscosity
of the mass and are thus effective in de-aggregation
as well as distribution of solids in the fluid vehicle.
42
Top-loading Sigma-Blade Mixer

Semisolid Batch Mixers: Kneaders
B. Planetary Mixer: Provided planetary mixing action where the mixing arm
rotates around itself and around the circumference of the container.
1- 2-
• This two-rotation movement and offset position of the mixing
arm
reduces
or prevents the formation of dead zones of mixing and avoids vortex
formation.
43

Mixi
Semisolid Batch Mixer: Kneaders.C- Mulling Mixers
Action
• : Mulling mixers provide forces that incorporate 1
kneading, 2- shearing, 3- smearing, and 4-blending of
materials for total uniform consistency.
• This process produces just enough pressure to move,
intermingle, and push particles into place without
crushing, grinding, or distorting the ingredients.
Uses:
• Mulling mixers are efficien
t
in the de-aggregation of
solids  These devices are suitable for mixing previously
mixed material of uniform composition but containing
aggregates of solid particles.
But
• are typically inefficien
t
in distributing the particles
uniformly throughout the entire mass.
• Note: In the event of segregation during mulling, a final
remixing may be necessary.
https://youtu.be/KLgq8rR34FE
h stage- Second Semester
44

Semisolid Continuous Mixer: 2- Mills
A. Roller Mills: Consists of one or more rollers.
triple roller
• Usually, a system is
preferred.
• The roller is made of hard abrasion resistance
materials and arranged to come into close
proximity to each other and rotated at different
rates
.
• Action: Depending on the gap, the material that
comes between the rollers is crushed, and also
sheare
d
by the difference in rates of movement of
heavy work
the two surfaces.
• This type of mixer is applied for
like
working with pastes. (example on next slide).
45

Semisolid Continuous Mixer: 2- Mills
• In extreme cases of solid-liquid mixing, a small volume of
large quantity
liquid is to be mixed with a of solids.
one of coating the solid particles
• This process is essentially
with
liquid and subsequent transfer of liquid from one particle to
another.
• In this type of mixing, the liquid is added slowly to reduce the
tendency of the particles to form a lump.
• However, the process is not for fluids mixing, but for solids
mixing. When the particles tend to stick together because of the
surface tension of the coating liquid, 
• The equipment used is the same as that for pastes (roller
mills).
• But: If the solids remain essentially free-flowing, the equipment
is the same as that used for solids mixing.
46

Solid Mixing
• Mixing is considered a critical factor, especially in the
case of potent drugs and low-dose drugs where
high amounts of adjuvants are added.
• Solid mixing is similar to liquid mixing.
• However, it shows some differences mainly come
after mixing
from that solid mixture (and sometimes
during mixing) is subjected to demixing or
segregation.
• The diverse characteristics of particles such as size,
shape, volume, surface area, density, porosity, and
flow charge contribute to the solid mixing.
48

Solid Mixing
• Solid mixing can be represented with the
following model where
• (A) is a complete segregation state.
• (B) is the Ideal mixing state (perfect
mix).
• (C) is Random Mixing.
• However, B (perfect mix) is virtually impossible
to get in practice with any mixing equipment.
• The best powder mixing process will result in a
case of the random mix where the probability
(chance) of finding one type of particle at any
is equal to its proportion in
point in the mixture
the mixture. 49

Practical Consideration in Working with Powder Mixing
• Segregation or demixing:
• Segregation is the central problem associated with the
mixing and handling of the solid particles,
1- 2-
• The powder can segregate during mixing and/or
during 3-
handling and processing after mixing.
• Causes: Solids tend to segregate by virtue of differences in
the particle size, density, shape, and other properties of the
particles of which they are composed.
• The second requirement for segregation can be met by the
Earth’s gravitational field, or by a centrifugal, electrical, or
magnetic field generated in the course of processing
50

Factors Affecting
Demixing
A. Particle size and size distribution: The difference in particle size between the
main cause
components is the of segregation in powder mixes.
• Small particle tends to fill the gaps (void) between larger particles and move toward the
bottom of the mass.
• The larger particle will have higher kinetic energy and will move to a larger distance
compared to small particles.
decreased
• This segregation problem can be
by:
1. Selection of a particle with a
remove fine or lumps).
close size range that can be achieved by sievin
g
(to
Milling
2. of the component before mixing to get a homogenous particle size below 30µm,
not
at which size segregation does tend to cause serious problems
3. Granulatio of the powder mix (enlarging the particle size). 51

Factors Affecting
Demixing
B. Particle shape:
• Particle shape is important because as the shape of a
deviate
s
particle more significantly from a spherical
form,  the free movement it experiences along its
major axis also decreases.
• Spherical particles exhibit the greatest flowability
easily
and are therefore more mixed but they also
segregate more easily than non-spherical particles.
Irregular or Needle
• shaped particles may become
interlocked decreasing the tendency to segregate
once mixing has occurred.
• Controlled crystallization during production of the
drug/excipients to give components of a particular
reduces the tendency
crystal shape or size range
to segregate. 52

Factors Affecting
Demixing
C. Particle charge:
• The mixing of particles whose surfaces are non-conducting (electrically)
often results in the generation of surface charges, as evidenced by a tendency of
clump
the powder to following a period of agitation.
• Surface charging of particles during mixing is undesirable, for it tends to decrease
the process of inter-particulate “diffusion.”
D. Particle density: (minor problem)
• If components are of different densities, the denser particles will have a tendency
to move downward regardless of their particle size.
• Most materials used in the pharmaceutical industry are of close densities and this
problem is not common in powder mixing.
53

Mechanism of Mixing (For Solids)
1. Convective Mixing: resembles bulk transport in fluid mixing.
• It includes moving a large bulk of solid at once.
inversion of the powder bed
• This can occur by by blades, paddle, a
revolving
screw, or by inverting the whole container such as in a V-shape mixer.
2. Shear mixing: As a result of forces within the particulate mass, slip planes are
set up and this gives rise to laminar flow.
• When shear occurs between regions of different compositions & parallel to their
interface, it reduces the scale of segregation by thinning the dissimilar layers.
3. Diffusive random motion
mixing: When a of particles within a powder bed
causes them to change position relative to one another. Such an exchange of
positions by single particles results in a reduction of the intensity of segregation.
• Diffusive mixing occurs at the interfaces of dissimilar regions that are
undergoing shear and therefore results from shear mixing. 54

Equipment
55

1- Tumbler/ Blender (batch mixers)
• Tumbler/blenders: consist of a container of different
rotated around its axis
geometrical shapes and cause movement
of materials in all planes.
• The resulting tumbling motion is accentuated through
baffles, lifter blades, or simply by the shape of the container.
• It can be in different shapes such as twin shells, double cones,
cubes, drums, and tetrahedral blenders are commercially
available.
twin-shape mixer (V-shape
• Of these types, the mixer) is
the
most preferred one, resulting in satisfactory mixing in a
reasonable time.
• These types of solid mixers are:
Efficient, not aggressive
• (good for friable powders),
• And preferable when mixing powders that have different
particle sizes 56

V-Shape Mixer (Twin Shell Mixer)
• It consists of two cylinders connected at a 45˚ angle.
• When rotates, the material is collected to the bottom and then
splits into two halves when rotated in the other direction.
because
• This is quite effective the bulk
transport
(convective) and shear, which occur in tumbling mixers,
generally are accentuated by this design.
should be adjusted
• The rotation speed depending
on
1- the size
2-
of the mixer and the amount of material existing.
Too slow
1. rotation results in no mixing (insufficient tumbling
and does not generate rapid shear rates).
Too fast
2. results in centrifugal action that holds the material
to one side of the mixer and results in no mixing.
57
• https://youtu.be/SOoOmhrPLdQ

2- Agitator Mixers (batch
mixers) fixed container
• Agitator mixers: consist of a
that
contains a moving screw, a paddle, or a plate to mix the
powder materials.
• These types of mixers are more effective in mixing wet
powders that do not mix well using tumbler mixers.
This is because these mixers do not depend entirely on
gravity.
high shear
• The forces that are set up are effective
in
breaking up lumps or aggregates.
• There are three types of agitato mixers:
58

Agitator Mixers: A- Ribbon mixer/blender
Design
• : Consists of a horizontal cylindrical tank usually
opening at the top and fitted with helical blades or
ribbons.
• Operation: The blades are mounted on the horizontal
axle by struts and are rotated to circulate the material to
be mixed
wound (turned)
• The helical blades are (in most
cases)
in opposite directions to provide for the movement of
material in both directions along the axis of the
tank.
• Although little axial mixing in the vicinity of the shaft
occurs, mixtures with high homogeneity can be
prolonged mixing
produced by even when the
components differ in particle size, shape, or density, or
there is some tendency to aggregate.
https://youtu.be/7JPSLKW5T_8
h stage- Second
59
Mixi

3- Rapid Mixer Granulator (batch mixers)
• Rapid mixer granulator:
• https://youtu.be/I-33cIrn8vc
h stage- Second
60
Mixi
Newer models
• that can perform both wet and dry
mixing efficiently in lesser time.
dual actions
• This means it can perform
like
1- mixing
2-
and tablet granulation which is an important process
in tablet formulation.
• An example of these mixers is the Lödige mixer.
high-shear
• It’s a mixer that consists of a
horizontal
cylindrical shell equipped with a series of plow-
shape
d
mixing tools and one or more high-speed
blending chopper assemblies mounted at the rear of
the mixer.

Continuous mixers
• A characteristic of solids mixing equipment is that all else
being equal, but
:
• Mixtures produced by large mixers have greater variations in
composition than those produced by small mixers.
• This is an important consideration when relatively small
portions of the mixture are required to fall consistently within a
narrow composition range.  it is recommended to use batch
mixers for small quantities.
• Continuous mixing processes are somewhat analogous to those
discussed under fluid mixing.
Metered quantities
• of the powders or granules are passed
through a device that reduces both the scale and intensity of
segregation, usually by impact or shearing action.
61

Barrel Type Continuous Mixer
• In this mixer, the material is mixed under a tumbling
motion.
• The presence of baffles further enhances the mixing.
• Operation: When the material approaches the midpoint
of the shell, a set of baffles causes a part of the material
to move backward.
• Such a mechanism provides an intense mixing of
ingredients
62

Zig-zag Continuous Blender
• Design: It consists of several “V”-shaped blenders
connected in series.
• Operation: When the blender is inverted, the
material splits into two portions, one-half of the
material moves backward, while the other moves
63
forward.
• In each rotation, a part of the material moves
toward the discharge end.

Mixer Selection
• Mixer Properties:
ideal mixer
• An should produce a complete
blend
rapidly with as gentle (slow speed) mixing action
as possible to avoid product damage.
• It should be:
1. Dust-tight,
2. Cleaned easily,
3. Discharged easily, and
4. Requires low maintenance and low power
consumption.
64

• Tumbler Mixers:
1. Rotating shell mixers suffer from
65
poor cross-flow along the axis. 
• The addition of baffles or inclining the drum on the axis increases cross-flow
and improves the mixing action.
2. In cubical and polyhedron-shaped blenders, due to their flat surfaces, the
powder is subjected more to slidin
g
than a rolling action, a motion that is not
conducive to efficient mixing.
3. In double-cone blenders, the mixing pattern provides a good cross-flow with a
rolling rather than sliding motion.
4. The uneven length of each shell in a twin-shell blender provides additional
mixing action when the powder bed recombines during each revolution of the
blender. Twin-shell and double-cone blenders are recommended for precision
blending.

Mixer Selection Mixer Properties:
•
66
Agitator Mixers:
1. The shearing action that develops between moving blades and troughs (the
tank) in agitator mixers serves to break down powder agglomerates.
2. Ribbon mixers are not precision blenders and also suffer from the
disadvantage of being 1- more difficult to clean than tumblers and 2- having a
higher power requirement.
1- 2
-
3. The mechanical heat build-up and the relatively higher
drawbacks also associated with Sigma blades
power requirement are the
and planetary mixers.
However,
• the shorter time interval necessary to achieve a satisfactory blend
may offset these factors.
4. Blendex provides efficient batch and continuous mixing for a wide variety of
solids without particle size reduction and heat generation.

Mixer Selection: Material Property
1-
67
no
t
• Powders that are free-flowing or 2- that exhibit high forces of cohesion
or
adhesion between particles of similar or dissimilar composition are often
to mix owing to agglomeration.
difficul
t
can be broken down
• The clumps of particles in such cases by the use of
mixers
generate high shear
that forces or that subject the powder to impact.
planetar
y
• The use of agitators preferably and sigma blade mixers
is
recommended for such powders.
• For strongly cohesive materials, it is typically necessary to fragment
high shear,
agglomerates through the introduction of “intensification,” devices
such as agitators or mills that energetically deform grains on the finest scale.

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