Tablet compression student (2)
mizan00
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Jan 13, 2017
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About This Presentation
t
Slide Content
Tablet CompressionTablet Compression
Compression: Compression:
Compression is the process of applying Compression is the process of applying
pressure to the powder material for the pressure to the powder material for the
reduction of the bulk volume, to give a reduction of the bulk volume, to give a
solid matrix.solid matrix.
Compressibility:Compressibility:
It is the ability of the powder to decrease inIt is the ability of the powder to decrease in
volume under pressure (due to applicationvolume under pressure (due to application
of a given stress.)of a given stress.)
..
C o m p a c t io nC o m p a c t io n: C ompac tion is the s it uation in which powders are subjec ted to some lev el of mechanic al force.: C ompac tion is the s it uation in which powders are subjec ted to some lev el of mechanic al force.
Compression: Compression:
Compression is the process of applying Compression is the process of applying
pressure to the powder material for the pressure to the powder material for the
reduction of the bulk volume, to give a reduction of the bulk volume, to give a
solid matrix.solid matrix.
Compressibility:Compressibility:
It is the ability of the powder to decrease inIt is the ability of the powder to decrease in
volume under pressure (due to applicationvolume under pressure (due to application
of a given stress.)of a given stress.)
..
C o m p a c t io nC o m p a c t io n: C ompac tion is the s it uation in which powders are subjec ted to some lev el of mechanic al force.: C ompac tion is the s it uation in which powders are subjec ted to some lev el of mechanic al force.
CompactionCompaction::
Compaction of powder is the general term used Compaction of powder is the general term used
to described the situation in which powders to described the situation in which powders
are subjected to some level of mechanical are subjected to some level of mechanical
force.force.
That is, the transformation of a powder into a That is, the transformation of a powder into a
coherent specimen of defined shape by powder coherent specimen of defined shape by powder
compression compression
Compatibility:Compatibility:
It is the ability of the powder bed to cohere into It is the ability of the powder bed to cohere into
or to form a compact. or to form a compact.
Compaction of powder is the general term used Compaction of powder is the general term used
to described the situation in which powders to described the situation in which powders
are subjected to some level of mechanical are subjected to some level of mechanical
force.force.
That is, the transformation of a powder into a That is, the transformation of a powder into a
coherent specimen of defined shape by powder coherent specimen of defined shape by powder
compression compression
Compatibility:Compatibility:
It is the ability of the powder bed to cohere into It is the ability of the powder bed to cohere into
or to form a compact. or to form a compact.
The forces involved during compaction of The forces involved during compaction of
powders powders
Fa = Maximum upper punch force Fa = Maximum upper punch force
applied to compact.applied to compact.
Fb = Maximum force transmitted to Fb = Maximum force transmitted to
lower punch by compact.lower punch by compact.
Fd = Force lost to the die wall.Fd = Force lost to the die wall.
Fr = Maximum radial force at die wall Fr = Maximum radial force at die wall
during compaction.during compaction.
powders powders
Fa = Maximum upper punch force Fa = Maximum upper punch force
applied to compact.applied to compact.
Fb = Maximum force transmitted to Fb = Maximum force transmitted to
lower punch by compact.lower punch by compact.
Fd = Force lost to the die wall.Fd = Force lost to the die wall.
Fr = Maximum radial force at die wall Fr = Maximum radial force at die wall
during compaction.during compaction.
1. Particle rearrangement1. Particle rearrangement
2. Elastic deformation2. Elastic deformation
3. Plastic deformation of particles3. Plastic deformation of particles
4. Fragmentation of particles4. Fragmentation of particles
5. Formation of interparticulate bonds5. Formation of interparticulate bonds
6. Ejection6. Ejection
2. Elastic deformation2. Elastic deformation
3. Plastic deformation of particles3. Plastic deformation of particles
4. Fragmentation of particles4. Fragmentation of particles
5. Formation of interparticulate bonds5. Formation of interparticulate bonds
6. Ejection6. Ejection
Frictional forceFrictional force
Two major components to the frictional forces are:Two major components to the frictional forces are:
Interparticulate friction-: This arise at particulate Interparticulate friction-: This arise at particulate
contacts and can be expressed in terms of a contacts and can be expressed in terms of a
coefficient of interparticulate friction μ1. It is more coefficient of interparticulate friction μ1. It is more
significant at low applied loads.significant at low applied loads.
Materials that reduce this effect are referred to as Materials that reduce this effect are referred to as
glidants, colloidal silica.glidants, colloidal silica.
Die wall friction-:Die wall friction-:
This results from material being pressed against the die This results from material being pressed against the die
wall and moved down it. It is expressed as μ2., the wall and moved down it. It is expressed as μ2., the
coefficient of die wall friction. This effect is dominant coefficient of die wall friction. This effect is dominant
at high applied forces when particle rearrangement at high applied forces when particle rearrangement
has ceased and is particularly important in tabletting has ceased and is particularly important in tabletting
operation. operation.
Lubricant such as Magnesium stearate is used to Lubricant such as Magnesium stearate is used to
reduce.reduce.
Two major components to the frictional forces are:Two major components to the frictional forces are:
Interparticulate friction-: This arise at particulate Interparticulate friction-: This arise at particulate
contacts and can be expressed in terms of a contacts and can be expressed in terms of a
coefficient of interparticulate friction μ1. It is more coefficient of interparticulate friction μ1. It is more
significant at low applied loads.significant at low applied loads.
Materials that reduce this effect are referred to as Materials that reduce this effect are referred to as
glidants, colloidal silica.glidants, colloidal silica.
Die wall friction-:Die wall friction-:
This results from material being pressed against the die This results from material being pressed against the die
wall and moved down it. It is expressed as μ2., the wall and moved down it. It is expressed as μ2., the
coefficient of die wall friction. This effect is dominant coefficient of die wall friction. This effect is dominant
at high applied forces when particle rearrangement at high applied forces when particle rearrangement
has ceased and is particularly important in tabletting has ceased and is particularly important in tabletting
operation. operation.
Lubricant such as Magnesium stearate is used to Lubricant such as Magnesium stearate is used to
reduce.reduce.
Force distributionForce distribution..
Shown in fig X. Shown in fig X.
FA = FL + FFA = FL + F
D (1) (1)
Where FA is the force applied to the upper punch, Where FA is the force applied to the upper punch,
FL is that proportion of it transmitted to the lower punch, FL is that proportion of it transmitted to the lower punch,
FD is a reaction at the die wall due to friction at the surface. FD is a reaction at the die wall due to friction at the surface.
Because of the inherent difference between the force applied at Because of the inherent difference between the force applied at
the upper punch and that affecting material close to the lower the upper punch and that affecting material close to the lower
punch , a more compaction force, FM, has been proposed., punch , a more compaction force, FM, has been proposed.,
where where
FA + FLFA + FL
FM = --------------- (2)FM = --------------- (2)
22
Shown in fig X. Shown in fig X.
FA = FL + FFA = FL + F
D (1) (1)
Where FA is the force applied to the upper punch, Where FA is the force applied to the upper punch,
FL is that proportion of it transmitted to the lower punch, FL is that proportion of it transmitted to the lower punch,
FD is a reaction at the die wall due to friction at the surface. FD is a reaction at the die wall due to friction at the surface.
Because of the inherent difference between the force applied at Because of the inherent difference between the force applied at
the upper punch and that affecting material close to the lower the upper punch and that affecting material close to the lower
punch , a more compaction force, FM, has been proposed., punch , a more compaction force, FM, has been proposed.,
where where
FA + FLFA + FL
FM = --------------- (2)FM = --------------- (2)
22
In single –station presses, where the applied force In single –station presses, where the applied force
transmission decays exponentially, a more transmission decays exponentially, a more
appropriate geometric mean force, Fc, might be appropriate geometric mean force, Fc, might be
FG = (FA . FL)FG = (FA . FL)
0.5
Use of these force parameters are probably more Use of these force parameters are probably more
appropriate than use of FA, when determining appropriate than use of FA, when determining
relationships between compressional force and such relationships between compressional force and such
tablet properties as tablet strength.tablet properties as tablet strength.
transmission decays exponentially, a more transmission decays exponentially, a more
appropriate geometric mean force, Fc, might be appropriate geometric mean force, Fc, might be
FG = (FA . FL)FG = (FA . FL)
0.5
Use of these force parameters are probably more Use of these force parameters are probably more
appropriate than use of FA, when determining appropriate than use of FA, when determining
relationships between compressional force and such relationships between compressional force and such
tablet properties as tablet strength.tablet properties as tablet strength.
Development of Radial Force Development of Radial Force
As the compressional force is increased and any As the compressional force is increased and any
repacking of the tabletting mass is completed, the repacking of the tabletting mass is completed, the
material may be regarded to some extent as a single material may be regarded to some extent as a single
body. body.
In the case of an unconfined solid body this would be In the case of an unconfined solid body this would be
accompanied by an expansion in the horizontal accompanied by an expansion in the horizontal
direction of ∆D.direction of ∆D.
The ratio of these two dimensional changes is known as The ratio of these two dimensional changes is known as
the the poisson ratio λpoisson ratio λ of the material, defined as of the material, defined as
Λ = ∆D /∆HΛ = ∆D /∆H
As the compressional force is increased and any As the compressional force is increased and any
repacking of the tabletting mass is completed, the repacking of the tabletting mass is completed, the
material may be regarded to some extent as a single material may be regarded to some extent as a single
body. body.
In the case of an unconfined solid body this would be In the case of an unconfined solid body this would be
accompanied by an expansion in the horizontal accompanied by an expansion in the horizontal
direction of ∆D.direction of ∆D.
The ratio of these two dimensional changes is known as The ratio of these two dimensional changes is known as
the the poisson ratio λpoisson ratio λ of the material, defined as of the material, defined as
Λ = ∆D /∆HΛ = ∆D /∆H
This ratio is a characteristic constant for each solid This ratio is a characteristic constant for each solid
and may influence the tabletting . and may influence the tabletting .
Shown in fig-X, the material is not free to expand in Shown in fig-X, the material is not free to expand in
the horizontal plane, a radial die wall force Fthe horizontal plane, a radial die wall force F
R is is
developed perpendicular to the die wall surface.developed perpendicular to the die wall surface.
materials with larger poisson ratio giving rise to materials with larger poisson ratio giving rise to
higher Fhigher F
R. Then classic theory can then be applied . Then classic theory can then be applied
to deduce that the axial friction force FD related to to deduce that the axial friction force FD related to
the FR by the expressionthe FR by the expression
FF
D = μ = μ
ww . F . F
R (5) (5)
and may influence the tabletting . and may influence the tabletting .
Shown in fig-X, the material is not free to expand in Shown in fig-X, the material is not free to expand in
the horizontal plane, a radial die wall force Fthe horizontal plane, a radial die wall force F
R is is
developed perpendicular to the die wall surface.developed perpendicular to the die wall surface.
materials with larger poisson ratio giving rise to materials with larger poisson ratio giving rise to
higher Fhigher F
R. Then classic theory can then be applied . Then classic theory can then be applied
to deduce that the axial friction force FD related to to deduce that the axial friction force FD related to
the FR by the expressionthe FR by the expression
FF
D = μ = μ
ww . F . F
R (5) (5)
Where μw, is the coefficient of the die wall Where μw, is the coefficient of the die wall
friction.friction.
It is noted that FIt is noted that F
R is reduced when materials of is reduced when materials of
small poisson ratio are used and that in such small poisson ratio are used and that in such
case, axial force transmission is optimumcase, axial force transmission is optimum..
friction.friction.
It is noted that FIt is noted that F
R is reduced when materials of is reduced when materials of
small poisson ratio are used and that in such small poisson ratio are used and that in such
case, axial force transmission is optimumcase, axial force transmission is optimum..
A common method of comparing degrees A common method of comparing degrees
of lubrications has been to measure the of lubrications has been to measure the
applied and transmitted axial forces and applied and transmitted axial forces and
determine the Fdetermine the F
L / F / F
AA. .
This is called the coefficient of lubricant This is called the coefficient of lubricant
efficiency, or R value. The ratio efficiency, or R value. The ratio
approaches unity for perfect lubrication approaches unity for perfect lubrication
(no wall friction). Values below 0.8 (no wall friction). Values below 0.8
probably indicates a poor lubricationprobably indicates a poor lubrication
of lubrications has been to measure the of lubrications has been to measure the
applied and transmitted axial forces and applied and transmitted axial forces and
determine the Fdetermine the F
L / F / F
AA. .
This is called the coefficient of lubricant This is called the coefficient of lubricant
efficiency, or R value. The ratio efficiency, or R value. The ratio
approaches unity for perfect lubrication approaches unity for perfect lubrication
(no wall friction). Values below 0.8 (no wall friction). Values below 0.8
probably indicates a poor lubricationprobably indicates a poor lubrication
Die wall lubricationDie wall lubrication
Tablet formulation require the addition of a Tablet formulation require the addition of a
lubricant to reduce friction at die wall. Die wall lubricant to reduce friction at die wall. Die wall
lubricant function by interposing a film of low lubricant function by interposing a film of low
shear strength at the interface between tabletting shear strength at the interface between tabletting
mass and the die wall. mass and the die wall.
Perfectly there is some chemical bonding Perfectly there is some chemical bonding
between the boundary lubricant and the surface between the boundary lubricant and the surface
of the die wall as well as at the edge of the tablet.of the die wall as well as at the edge of the tablet.
The best lubricants are those with low shear The best lubricants are those with low shear
strength but strong cohesive tendencies In strength but strong cohesive tendencies In
directions at right angles to the plane of shear.directions at right angles to the plane of shear.
Tablet formulation require the addition of a Tablet formulation require the addition of a
lubricant to reduce friction at die wall. Die wall lubricant to reduce friction at die wall. Die wall
lubricant function by interposing a film of low lubricant function by interposing a film of low
shear strength at the interface between tabletting shear strength at the interface between tabletting
mass and the die wall. mass and the die wall.
Perfectly there is some chemical bonding Perfectly there is some chemical bonding
between the boundary lubricant and the surface between the boundary lubricant and the surface
of the die wall as well as at the edge of the tablet.of the die wall as well as at the edge of the tablet.
The best lubricants are those with low shear The best lubricants are those with low shear
strength but strong cohesive tendencies In strength but strong cohesive tendencies In
directions at right angles to the plane of shear.directions at right angles to the plane of shear.
Ejection ForcesEjection Forces
The force necessary to eject a finished tablet follows a a The force necessary to eject a finished tablet follows a a
distinctive patern of three stages:distinctive patern of three stages:
-The first stage involves the distinctive peak force required -The first stage involves the distinctive peak force required
to initiate ejection, by breaking tablet /die wall adhesion.to initiate ejection, by breaking tablet /die wall adhesion.
-A smaller force usually follows namely that required to push -A smaller force usually follows namely that required to push
the tablet up the die wall.the tablet up the die wall.
-The final stage is marked by declining force of ejection as -The final stage is marked by declining force of ejection as
the tablet emerges from the die wall.the tablet emerges from the die wall.
Variables on this pattern are sometimes found especially Variables on this pattern are sometimes found especially
when lubrication is inadequate and/or Slip-stick condition when lubrication is inadequate and/or Slip-stick condition
occur between the tablet and die wall.occur between the tablet and die wall.
The force necessary to eject a finished tablet follows a a The force necessary to eject a finished tablet follows a a
distinctive patern of three stages:distinctive patern of three stages:
-The first stage involves the distinctive peak force required -The first stage involves the distinctive peak force required
to initiate ejection, by breaking tablet /die wall adhesion.to initiate ejection, by breaking tablet /die wall adhesion.
-A smaller force usually follows namely that required to push -A smaller force usually follows namely that required to push
the tablet up the die wall.the tablet up the die wall.
-The final stage is marked by declining force of ejection as -The final stage is marked by declining force of ejection as
the tablet emerges from the die wall.the tablet emerges from the die wall.
Variables on this pattern are sometimes found especially Variables on this pattern are sometimes found especially
when lubrication is inadequate and/or Slip-stick condition when lubrication is inadequate and/or Slip-stick condition
occur between the tablet and die wall.occur between the tablet and die wall.
The forces involved during compaction of The forces involved during compaction of
powders powders
Fa = Maximum upper punch force applied Fa = Maximum upper punch force applied
to compact.to compact.
Fb = Maximum force transmitted to lower Fb = Maximum force transmitted to lower
punch by compact.punch by compact.
Fd = Force lost to the die wall.Fd = Force lost to the die wall.
Fr = Maximum radial force at die wall Fr = Maximum radial force at die wall
during compaction.during compaction.
powders powders
Fa = Maximum upper punch force applied Fa = Maximum upper punch force applied
to compact.to compact.
Fb = Maximum force transmitted to lower Fb = Maximum force transmitted to lower
punch by compact.punch by compact.
Fd = Force lost to the die wall.Fd = Force lost to the die wall.
Fr = Maximum radial force at die wall Fr = Maximum radial force at die wall
during compaction.during compaction.
Upper punchUpper punch
Fa ↓Fa ↓
. . . . . . . . . .. . . . . . . .. . ..
←←.Fr . .Fr . . . . . . . . . FdFd
compact ←. . . . ↓Fb. .compact ←. . . . ↓Fb. .
Lower punchLower punch
FigFig: : Forces involved in compactionForces involved in compaction
Fa ↓Fa ↓
. . . . . . . . . .. . . . . . . .. . ..
←←.Fr . .Fr . . . . . . . . . FdFd
compact ←. . . . ↓Fb. .compact ←. . . . ↓Fb. .
Lower punchLower punch
FigFig: : Forces involved in compactionForces involved in compaction
The physics of compaction is the The physics of compaction is the
compression and consolidation of two compression and consolidation of two
phases system (particulate solid-gas) due phases system (particulate solid-gas) due
to the applied force.to the applied force.
Consolidation:Consolidation:
Due to particle-particle interaction, the Due to particle-particle interaction, the
mechanical strength of the material is mechanical strength of the material is
increased, which consolidates the material increased, which consolidates the material
into a single solid matrix. This phenomena into a single solid matrix. This phenomena
is called consolidation. is called consolidation.
compression and consolidation of two compression and consolidation of two
phases system (particulate solid-gas) due phases system (particulate solid-gas) due
to the applied force.to the applied force.
Consolidation:Consolidation:
Due to particle-particle interaction, the Due to particle-particle interaction, the
mechanical strength of the material is mechanical strength of the material is
increased, which consolidates the material increased, which consolidates the material
into a single solid matrix. This phenomena into a single solid matrix. This phenomena
is called consolidation. is called consolidation.
Decompression:Decompression:
#During tablet manufacturing, the #During tablet manufacturing, the
compressional process is followed by a compressional process is followed by a
decomposition stage when the applied decomposition stage when the applied
force is removed.force is removed.
# So as a result of elastic recovery, a new # So as a result of elastic recovery, a new
force is developed within the tablet which force is developed within the tablet which
is augmented by the forces necessary to is augmented by the forces necessary to
eject the tablet from the die wall.eject the tablet from the die wall.
#During tablet manufacturing, the #During tablet manufacturing, the
compressional process is followed by a compressional process is followed by a
decomposition stage when the applied decomposition stage when the applied
force is removed.force is removed.
# So as a result of elastic recovery, a new # So as a result of elastic recovery, a new
force is developed within the tablet which force is developed within the tablet which
is augmented by the forces necessary to is augmented by the forces necessary to
eject the tablet from the die wall.eject the tablet from the die wall.
Deformation:Deformation:
When a solid body is subjected to an When a solid body is subjected to an
opposite force, its geometry is changed opposite force, its geometry is changed
depending on the nature of the force and depending on the nature of the force and
the change in geometry is called the change in geometry is called
deformation.deformation.
There are 2 types of deformation-There are 2 types of deformation-
Elastic deformationElastic deformation
Plastic deformationPlastic deformation
When a solid body is subjected to an When a solid body is subjected to an
opposite force, its geometry is changed opposite force, its geometry is changed
depending on the nature of the force and depending on the nature of the force and
the change in geometry is called the change in geometry is called
deformation.deformation.
There are 2 types of deformation-There are 2 types of deformation-
Elastic deformationElastic deformation
Plastic deformationPlastic deformation
Powder particlesPowder particles
RepackingRepacking
Deformation particles(due to compressionDeformation particles(due to compression
if compressive force is removedif compressive force is removed
Elastic deformationElastic deformationplastic deformationplastic deformation
particles return to theirparticles return to theirparticles retain in particles retain in
deformation conditiondeformation condition
Powder particlesPowder particles
RepackingRepacking
Deformation particles(due to compressionDeformation particles(due to compression
if compressive force is removedif compressive force is removed
Elastic deformationElastic deformationplastic deformationplastic deformation
particles return to theirparticles return to theirparticles retain in particles retain in
deformation conditiondeformation condition
Elastic deformation:Elastic deformation:
In elastic deformation, the deformed In elastic deformation, the deformed
materials return to their initial shape. materials return to their initial shape.
( deformation disappears completely)( deformation disappears completely)
All solids undergo / show elastic All solids undergo / show elastic
deformation when external force is deformation when external force is
applied but the force must be within the applied but the force must be within the
range.range.
Example:Example: Aspirin, Aspirin,
Cohesion is lost.Cohesion is lost.
In elastic deformation, the deformed In elastic deformation, the deformed
materials return to their initial shape. materials return to their initial shape.
( deformation disappears completely)( deformation disappears completely)
All solids undergo / show elastic All solids undergo / show elastic
deformation when external force is deformation when external force is
applied but the force must be within the applied but the force must be within the
range.range.
Example:Example: Aspirin, Aspirin,
Cohesion is lost.Cohesion is lost.
::
Plastic deformationPlastic deformation
Here, the deformed materials don’t return to Here, the deformed materials don’t return to
their initial shape (deformation doesn’t their initial shape (deformation doesn’t
completely recover after release of stress).completely recover after release of stress).
Time independent, permanent deformation of a Time independent, permanent deformation of a
particle. Degree of deformation is thus particle. Degree of deformation is thus
controlled by applied pressure and controlled by applied pressure and
independent of the time of loading.independent of the time of loading.
Deformation occurs without a change in particle Deformation occurs without a change in particle
volume.volume.
Plastic deformationPlastic deformation
Here, the deformed materials don’t return to Here, the deformed materials don’t return to
their initial shape (deformation doesn’t their initial shape (deformation doesn’t
completely recover after release of stress).completely recover after release of stress).
Time independent, permanent deformation of a Time independent, permanent deformation of a
particle. Degree of deformation is thus particle. Degree of deformation is thus
controlled by applied pressure and controlled by applied pressure and
independent of the time of loading.independent of the time of loading.
Deformation occurs without a change in particle Deformation occurs without a change in particle
volume.volume.
The materials in which – The materials in which –
Shear strength< tensile or breaking strength, Shear strength< tensile or breaking strength,
will show plastic deformation. But when - shear will show plastic deformation. But when - shear
strength> tensile or breaking strength, particles strength> tensile or breaking strength, particles
becomes fractured and fragmented. Then becomes fractured and fragmented. Then
fragmented smaller particles will fill up the fragmented smaller particles will fill up the
adjacent air space and helps the compression adjacent air space and helps the compression
process.process.
Example: ‘Sucrose’ behaves like that way.Example: ‘Sucrose’ behaves like that way.
Cohesion is retained (among the particles)Cohesion is retained (among the particles)
Shear strength< tensile or breaking strength, Shear strength< tensile or breaking strength,
will show plastic deformation. But when - shear will show plastic deformation. But when - shear
strength> tensile or breaking strength, particles strength> tensile or breaking strength, particles
becomes fractured and fragmented. Then becomes fractured and fragmented. Then
fragmented smaller particles will fill up the fragmented smaller particles will fill up the
adjacent air space and helps the compression adjacent air space and helps the compression
process.process.
Example: ‘Sucrose’ behaves like that way.Example: ‘Sucrose’ behaves like that way.
Cohesion is retained (among the particles)Cohesion is retained (among the particles)
Shear strength< tensile or breaking strength, will Shear strength< tensile or breaking strength, will
show plastic deformation.show plastic deformation.
But when - shear strength> tensile or breaking But when - shear strength> tensile or breaking
strength, particles becomes fractured and strength, particles becomes fractured and
fragmented. Then fragmented smaller particles fragmented. Then fragmented smaller particles
will fill up the adjacent air space and helps the will fill up the adjacent air space and helps the
compression process.compression process.
Example: ‘Sucrose’ behaves like that way.Example: ‘Sucrose’ behaves like that way.
Cohesion is retained (among the particles)Cohesion is retained (among the particles)
show plastic deformation.show plastic deformation.
But when - shear strength> tensile or breaking But when - shear strength> tensile or breaking
strength, particles becomes fractured and strength, particles becomes fractured and
fragmented. Then fragmented smaller particles fragmented. Then fragmented smaller particles
will fill up the adjacent air space and helps the will fill up the adjacent air space and helps the
compression process.compression process.
Example: ‘Sucrose’ behaves like that way.Example: ‘Sucrose’ behaves like that way.
Cohesion is retained (among the particles)Cohesion is retained (among the particles)
Irrespective of the behavior of large Irrespective of the behavior of large
particles, of the materials, small particles, of the materials, small
particles may deform plastically, a particles may deform plastically, a
process known as micro-squashing process known as micro-squashing
and the proportion of fine particles and the proportion of fine particles
in a sample may therefore be in a sample may therefore be
significant.significant.
particles, of the materials, small particles, of the materials, small
particles may deform plastically, a particles may deform plastically, a
process known as micro-squashing process known as micro-squashing
and the proportion of fine particles and the proportion of fine particles
in a sample may therefore be in a sample may therefore be
significant.significant.
Mechanism of compression:Mechanism of compression:
An appropriate volume of granules are fed into a An appropriate volume of granules are fed into a
die cavity.die cavity.
↓↓
Granules are compressed between an upper Granules are compressed between an upper
and a lower punchand a lower punch
↓↓
Consolidation of materials / granules into a Consolidation of materials / granules into a
single solid matrixsingle solid matrix
↓↓
Tablets are ejected from the die cavity.Tablets are ejected from the die cavity.
An appropriate volume of granules are fed into a An appropriate volume of granules are fed into a
die cavity.die cavity.
↓↓
Granules are compressed between an upper Granules are compressed between an upper
and a lower punchand a lower punch
↓↓
Consolidation of materials / granules into a Consolidation of materials / granules into a
single solid matrixsingle solid matrix
↓↓
Tablets are ejected from the die cavity.Tablets are ejected from the die cavity.
Process of compression:Process of compression:
Spherical particles undergo less particle Spherical particles undergo less particle
rearrangement than irregular particles, as rearrangement than irregular particles, as
spherical particles undergo a close packing spherical particles undergo a close packing
initially.initially.
* To achieve the fast flow rate for high speed * To achieve the fast flow rate for high speed
compression, granulation is performed to compression, granulation is performed to
produce spherical or oval particles. That’s why; produce spherical or oval particles. That’s why;
particle rearrangement and energy expended in particle rearrangement and energy expended in
rearrangement are minor consideration in the rearrangement are minor consideration in the
total process of compression.total process of compression.
rearrangement than irregular particles, as rearrangement than irregular particles, as
spherical particles undergo a close packing spherical particles undergo a close packing
initially.initially.
* To achieve the fast flow rate for high speed * To achieve the fast flow rate for high speed
compression, granulation is performed to compression, granulation is performed to
produce spherical or oval particles. That’s why; produce spherical or oval particles. That’s why;
particle rearrangement and energy expended in particle rearrangement and energy expended in
rearrangement are minor consideration in the rearrangement are minor consideration in the
total process of compression.total process of compression.
Deformation at points of contact:Deformation at points of contact:
When force is applied to a material, 2 types of When force is applied to a material, 2 types of
deformation occur: deformation occur: Elastic deformation, Plastic Elastic deformation, Plastic
deformation.deformation.
The force required to initiate a plastic deformation is The force required to initiate a plastic deformation is
called yield stress.called yield stress.
When the particles of the granulation are closely packedWhen the particles of the granulation are closely packed
↓ ↓
No further filling of void space can occurNo further filling of void space can occur
↓ ↓
Further ↑ of compressional force causes deformation at Further ↑ of compressional force causes deformation at
the points of contactthe points of contact
When force is applied to a material, 2 types of When force is applied to a material, 2 types of
deformation occur: deformation occur: Elastic deformation, Plastic Elastic deformation, Plastic
deformation.deformation.
The force required to initiate a plastic deformation is The force required to initiate a plastic deformation is
called yield stress.called yield stress.
When the particles of the granulation are closely packedWhen the particles of the granulation are closely packed
↓ ↓
No further filling of void space can occurNo further filling of void space can occur
↓ ↓
Further ↑ of compressional force causes deformation at Further ↑ of compressional force causes deformation at
the points of contactthe points of contact
A = Loose packing B = Close packing, C = A = Loose packing B = Close packing, C =
Elastic deformation D = Plastic Elastic deformation D = Plastic
deformation, E = Brittle fracturedeformation, E = Brittle fracture
Fig: Graphical representation of Fig: Graphical representation of
elastic & plastic deformation.elastic & plastic deformation.
Deformation Deformation ↑es the area of true contact↑es the area of true contact
↑ ↑es the area of potential es the area of potential
bondingbonding
Elastic deformation D = Plastic Elastic deformation D = Plastic
deformation, E = Brittle fracturedeformation, E = Brittle fracture
Fig: Graphical representation of Fig: Graphical representation of
elastic & plastic deformation.elastic & plastic deformation.
Deformation Deformation ↑es the area of true contact↑es the area of true contact
↑ ↑es the area of potential es the area of potential
bondingbonding
Fragmentation & deformation:Fragmentation & deformation:
At higher pressure, fragmentation occurs within At higher pressure, fragmentation occurs within
the particles.the particles. ↓↓
Fragmentation ↑es the number of particles and Fragmentation ↑es the number of particles and
new surface area.new surface area.
↓ ↓
So density of the material further increased.So density of the material further increased.
↓↓
DeformationDeformation
At higher pressure, fragmentation occurs within At higher pressure, fragmentation occurs within
the particles.the particles. ↓↓
Fragmentation ↑es the number of particles and Fragmentation ↑es the number of particles and
new surface area.new surface area.
↓ ↓
So density of the material further increased.So density of the material further increased.
↓↓
DeformationDeformation
Bonding:Bonding:
3 theories of bonding are-:3 theories of bonding are-:
Mechanical theoryMechanical theory
Intermolecular theoryIntermolecular theory
Liquid – surface film theoryLiquid – surface film theory
3 theories of bonding are-:3 theories of bonding are-:
Mechanical theoryMechanical theory
Intermolecular theoryIntermolecular theory
Liquid – surface film theoryLiquid – surface film theory
A. Mechanical theoryA. Mechanical theory
Under pressure, particles undergo elastic Under pressure, particles undergo elastic
deformation, plastic deformation, brittle deformation, plastic deformation, brittle
deformation.deformation.
↓↓
Mechanical bond is formed through the edges of Mechanical bond is formed through the edges of
the particles.the particles.
*If only mechanical bond exists, then-*If only mechanical bond exists, then-
Total energy of compression = deformation energy Total energy of compression = deformation energy
+ heat + energy absorbed by each particle.+ heat + energy absorbed by each particle.
Under pressure, particles undergo elastic Under pressure, particles undergo elastic
deformation, plastic deformation, brittle deformation, plastic deformation, brittle
deformation.deformation.
↓↓
Mechanical bond is formed through the edges of Mechanical bond is formed through the edges of
the particles.the particles.
*If only mechanical bond exists, then-*If only mechanical bond exists, then-
Total energy of compression = deformation energy Total energy of compression = deformation energy
+ heat + energy absorbed by each particle.+ heat + energy absorbed by each particle.
B. Intermolecular force theoryB. Intermolecular force theory
Under pressure, molecules remain at the points Under pressure, molecules remain at the points
of true contact, between the new surfaces of the of true contact, between the new surfaces of the
particles.particles.
Vander waals force is activated.Vander waals force is activated.
↓↓
Consolidations of particles occur.Consolidations of particles occur.
ExampleExample::
Microcrystalline cellulose – “cellulose crystals” Microcrystalline cellulose – “cellulose crystals”
remain in close contact by H-bonding remain in close contact by H-bonding
Under pressure, molecules remain at the points Under pressure, molecules remain at the points
of true contact, between the new surfaces of the of true contact, between the new surfaces of the
particles.particles.
Vander waals force is activated.Vander waals force is activated.
↓↓
Consolidations of particles occur.Consolidations of particles occur.
ExampleExample::
Microcrystalline cellulose – “cellulose crystals” Microcrystalline cellulose – “cellulose crystals”
remain in close contact by H-bonding remain in close contact by H-bonding
C. Liquid – surface film C. Liquid – surface film
theory:theory:
Here bonding occurs through a thin liquid Here bonding occurs through a thin liquid
film (which is the consequence of fusion or film (which is the consequence of fusion or
solution) at the surface of the particle.solution) at the surface of the particle.
The bonding is induced by the energy of The bonding is induced by the energy of
compression.compression.
theory:theory:
Here bonding occurs through a thin liquid Here bonding occurs through a thin liquid
film (which is the consequence of fusion or film (which is the consequence of fusion or
solution) at the surface of the particle.solution) at the surface of the particle.
The bonding is induced by the energy of The bonding is induced by the energy of
compression.compression.
During compression an applied force is During compression an applied force is
exerted on the granules, but locally the exerted on the granules, but locally the
force is applied to a small area of true force is applied to a small area of true
contact and for this a very high pressure contact and for this a very high pressure
exists at the true contact surface. The exists at the true contact surface. The
local effect of the high pressure on the local effect of the high pressure on the
melting point and solubility of a material is melting point and solubility of a material is
essential for bonding.essential for bonding.
exerted on the granules, but locally the exerted on the granules, but locally the
force is applied to a small area of true force is applied to a small area of true
contact and for this a very high pressure contact and for this a very high pressure
exists at the true contact surface. The exists at the true contact surface. The
local effect of the high pressure on the local effect of the high pressure on the
melting point and solubility of a material is melting point and solubility of a material is
essential for bonding.essential for bonding.
*Hot welding:*Hot welding:
Most particles in the powder bed have irregular shape and for this Most particles in the powder bed have irregular shape and for this
they have many points of contact.they have many points of contact.
↓↓
When pressure is applied, it may produce frictional heat.When pressure is applied, it may produce frictional heat.
↓↓
If heat is not dissipated, local rise in temperature may cause the If heat is not dissipated, local rise in temperature may cause the
melting of contact area of the particles.melting of contact area of the particles.
↓↓
Then stress in that particular area is relieved and melt solidities, Then stress in that particular area is relieved and melt solidities,
giving rise to fusion bonding.giving rise to fusion bonding.
↓↓
And at last, the mechanical strength of the mass is ↑ed.And at last, the mechanical strength of the mass is ↑ed.
Most particles in the powder bed have irregular shape and for this Most particles in the powder bed have irregular shape and for this
they have many points of contact.they have many points of contact.
↓↓
When pressure is applied, it may produce frictional heat.When pressure is applied, it may produce frictional heat.
↓↓
If heat is not dissipated, local rise in temperature may cause the If heat is not dissipated, local rise in temperature may cause the
melting of contact area of the particles.melting of contact area of the particles.
↓↓
Then stress in that particular area is relieved and melt solidities, Then stress in that particular area is relieved and melt solidities,
giving rise to fusion bonding.giving rise to fusion bonding.
↓↓
And at last, the mechanical strength of the mass is ↑ed.And at last, the mechanical strength of the mass is ↑ed.
*cold welding: *cold welding:
When the surfaces of two particles When the surfaces of two particles
approach each other closely enough (e. g. approach each other closely enough (e. g.
at a separation of less than 50 nm), their at a separation of less than 50 nm), their
free surface energies result in a strong free surface energies result in a strong
attractive force , a process known as cold attractive force , a process known as cold
welding.welding.
When the surfaces of two particles When the surfaces of two particles
approach each other closely enough (e. g. approach each other closely enough (e. g.
at a separation of less than 50 nm), their at a separation of less than 50 nm), their
free surface energies result in a strong free surface energies result in a strong
attractive force , a process known as cold attractive force , a process known as cold
welding.welding.
solubility ∞ Pressuresolubility ∞ Pressure
Surface of granules during compression, the solubility of Surface of granules during compression, the solubility of
true contact are or is increased with increasing pressure.true contact are or is increased with increasing pressure.
↓↓
When pressure is released, solubility is decreased.When pressure is released, solubility is decreased.
↓↓
Solutes dissolved in the adsorbed water, or present in Solutes dissolved in the adsorbed water, or present in
the solution, crystalline into small crystals between the the solution, crystalline into small crystals between the
particles.particles.
↓↓
So, the mechanical strength of the mass is ↑ed.So, the mechanical strength of the mass is ↑ed.
Surface of granules during compression, the solubility of Surface of granules during compression, the solubility of
true contact are or is increased with increasing pressure.true contact are or is increased with increasing pressure.
↓↓
When pressure is released, solubility is decreased.When pressure is released, solubility is decreased.
↓↓
Solutes dissolved in the adsorbed water, or present in Solutes dissolved in the adsorbed water, or present in
the solution, crystalline into small crystals between the the solution, crystalline into small crystals between the
particles.particles.
↓↓
So, the mechanical strength of the mass is ↑ed.So, the mechanical strength of the mass is ↑ed.
The mechanical strength of the mass depends The mechanical strength of the mass depends
on – on –
The amount of material depositedThe amount of material deposited
The rate of crystallizationThe rate of crystallization
*Both hot and cold welding depend on several *Both hot and cold welding depend on several
factors- factors-
The chemical nature of the materialThe chemical nature of the material
The extent of contact areaThe extent of contact area
The presence of surface contaminationsThe presence of surface contaminations
The inter-surface distanceThe inter-surface distance
on – on –
The amount of material depositedThe amount of material deposited
The rate of crystallizationThe rate of crystallization
*Both hot and cold welding depend on several *Both hot and cold welding depend on several
factors- factors-
The chemical nature of the materialThe chemical nature of the material
The extent of contact areaThe extent of contact area
The presence of surface contaminationsThe presence of surface contaminations
The inter-surface distanceThe inter-surface distance
Decompression:Decompression:
In tablet manufacturing, compressional process In tablet manufacturing, compressional process
is applied followed by a decompression stage, is applied followed by a decompression stage,
as the applied pressure is removed.as the applied pressure is removed.
Decompression leads a new set of stresses Decompression leads a new set of stresses
within the tablet as a result of elastic recovery, within the tablet as a result of elastic recovery,
which is augmented by the forces necessary to which is augmented by the forces necessary to
eject the tablet from the die cavity.eject the tablet from the die cavity.
In tablet manufacturing, compressional process In tablet manufacturing, compressional process
is applied followed by a decompression stage, is applied followed by a decompression stage,
as the applied pressure is removed.as the applied pressure is removed.
Decompression leads a new set of stresses Decompression leads a new set of stresses
within the tablet as a result of elastic recovery, within the tablet as a result of elastic recovery,
which is augmented by the forces necessary to which is augmented by the forces necessary to
eject the tablet from the die cavity.eject the tablet from the die cavity.
During decompression, as the upper During decompression, as the upper
punch is withdrawn from the die cavity, the punch is withdrawn from the die cavity, the
tablet is confined in the die by a radial tablet is confined in the die by a radial
pressure. But if only elastic deformation s pressure. But if only elastic deformation s
occurred due to sudden removal of axial occurred due to sudden removal of axial
pressure, then the granules will return to pressure, then the granules will return to
their original form by breaking any bonds their original form by breaking any bonds
that was formed under pressure.that was formed under pressure.
punch is withdrawn from the die cavity, the punch is withdrawn from the die cavity, the
tablet is confined in the die by a radial tablet is confined in the die by a radial
pressure. But if only elastic deformation s pressure. But if only elastic deformation s
occurred due to sudden removal of axial occurred due to sudden removal of axial
pressure, then the granules will return to pressure, then the granules will return to
their original form by breaking any bonds their original form by breaking any bonds
that was formed under pressure.that was formed under pressure.
As the movement of the tablet is restricted by As the movement of the tablet is restricted by
the die wall pressure and the friction with the die the die wall pressure and the friction with the die
wall, the stress from axial elastic recovery and wall, the stress from axial elastic recovery and
radial contraction causes the splitting of the radial contraction causes the splitting of the
tablet unless the shear stress is relieved by tablet unless the shear stress is relieved by
plastic deformation.plastic deformation.
But stress relaxation by plastic deformation is But stress relaxation by plastic deformation is
time dependent. Materials having slow rates of time dependent. Materials having slow rates of
stress relaxation, cracking occur in the die stress relaxation, cracking occur in the die
during compression.during compression.
the die wall pressure and the friction with the die the die wall pressure and the friction with the die
wall, the stress from axial elastic recovery and wall, the stress from axial elastic recovery and
radial contraction causes the splitting of the radial contraction causes the splitting of the
tablet unless the shear stress is relieved by tablet unless the shear stress is relieved by
plastic deformation.plastic deformation.
But stress relaxation by plastic deformation is But stress relaxation by plastic deformation is
time dependent. Materials having slow rates of time dependent. Materials having slow rates of
stress relaxation, cracking occur in the die stress relaxation, cracking occur in the die
during compression.during compression.
Example:Example:
Paracetamol – Rate of stress relieve is Paracetamol – Rate of stress relieve is
slow.slow.
So, cracking occurs while the So, cracking occurs while the
tablet is within the die.tablet is within the die.
Microcrystalline cellulose - Microcrystalline cellulose - Rate of stress Rate of stress
relieve is rapidrelieve is rapid
So, no cracking occurs.So, no cracking occurs.
Paracetamol – Rate of stress relieve is Paracetamol – Rate of stress relieve is
slow.slow.
So, cracking occurs while the So, cracking occurs while the
tablet is within the die.tablet is within the die.
Microcrystalline cellulose - Microcrystalline cellulose - Rate of stress Rate of stress
relieve is rapidrelieve is rapid
So, no cracking occurs.So, no cracking occurs.
Ejection:Ejection:
Ejection is the last stage of tablet Ejection is the last stage of tablet
compression.compression.
As the lower punch rises and pushes the As the lower punch rises and pushes the
tablet upward, there is a continued tablet upward, there is a continued
residual die wall pressure and residual die wall pressure and
considerable energy may be expanded considerable energy may be expanded
due to die wall friction.due to die wall friction.
Ejection is the last stage of tablet Ejection is the last stage of tablet
compression.compression.
As the lower punch rises and pushes the As the lower punch rises and pushes the
tablet upward, there is a continued tablet upward, there is a continued
residual die wall pressure and residual die wall pressure and
considerable energy may be expanded considerable energy may be expanded
due to die wall friction.due to die wall friction.
As the tablet is removed from the die,As the tablet is removed from the die,
Lateral pressure is relivedLateral pressure is relived
Tablet undergoes elastic Tablet undergoes elastic
recoveryrecovery
Radial and longitudinal Radial and longitudinal
relaxation occursrelaxation occurs
`` (2 – 10) % of tablet volume is (2 – 10) % of tablet volume is
↑ed.↑ed.
Lateral pressure is relivedLateral pressure is relived
Tablet undergoes elastic Tablet undergoes elastic
recoveryrecovery
Radial and longitudinal Radial and longitudinal
relaxation occursrelaxation occurs
`` (2 – 10) % of tablet volume is (2 – 10) % of tablet volume is
↑ed.↑ed.
Stages in the compression Stages in the compression
processprocess
Initially, the particles in the die are rearranged Initially, the particles in the die are rearranged
resulting in a closer packing structure.resulting in a closer packing structure.
At a certain load, the packing characteristics of At a certain load, the packing characteristics of
the particles or a high interparticulate friction the particles or a high interparticulate friction
between particles will prevent any further between particles will prevent any further
interparticulate movement.interparticulate movement.
The subsequent reduction of compact volume is The subsequent reduction of compact volume is
therefore accompanied by elastic and plastic therefore accompanied by elastic and plastic
deformation of the initial particles.deformation of the initial particles.
processprocess
Initially, the particles in the die are rearranged Initially, the particles in the die are rearranged
resulting in a closer packing structure.resulting in a closer packing structure.
At a certain load, the packing characteristics of At a certain load, the packing characteristics of
the particles or a high interparticulate friction the particles or a high interparticulate friction
between particles will prevent any further between particles will prevent any further
interparticulate movement.interparticulate movement.
The subsequent reduction of compact volume is The subsequent reduction of compact volume is
therefore accompanied by elastic and plastic therefore accompanied by elastic and plastic
deformation of the initial particles.deformation of the initial particles.
For many materials these particles are For many materials these particles are
then fragmented.then fragmented.
Fragmentation can be defined as a Fragmentation can be defined as a
dividing up of a particle into number of dividing up of a particle into number of
smaller, discrete parts. smaller, discrete parts.
The particle fragment will then normally The particle fragment will then normally
find new positions, which will further find new positions, which will further
decrease the compact volume.decrease the compact volume.
then fragmented.then fragmented.
Fragmentation can be defined as a Fragmentation can be defined as a
dividing up of a particle into number of dividing up of a particle into number of
smaller, discrete parts. smaller, discrete parts.
The particle fragment will then normally The particle fragment will then normally
find new positions, which will further find new positions, which will further
decrease the compact volume.decrease the compact volume.
When the applied pressure is further increased, When the applied pressure is further increased,
the smallest particles formed could again the smallest particles formed could again
undergo deformation.undergo deformation.
Thus a single particle may pass through one or Thus a single particle may pass through one or
several of these processes several times during several of these processes several times during
a compression..a compression..
As a consequence of the compression of the As a consequence of the compression of the
powder, particle surfaces are brought into close powder, particle surfaces are brought into close
to each other and interparticulate attraction or to each other and interparticulate attraction or
bonds will be formed.bonds will be formed.
the smallest particles formed could again the smallest particles formed could again
undergo deformation.undergo deformation.
Thus a single particle may pass through one or Thus a single particle may pass through one or
several of these processes several times during several of these processes several times during
a compression..a compression..
As a consequence of the compression of the As a consequence of the compression of the
powder, particle surfaces are brought into close powder, particle surfaces are brought into close
to each other and interparticulate attraction or to each other and interparticulate attraction or
bonds will be formed.bonds will be formed.
In summaryIn summary
1. Particle rearrangement1. Particle rearrangement
2. Elastic deformation2. Elastic deformation
3. Plastic deformation of particles3. Plastic deformation of particles
4. Fragmentation of particles4. Fragmentation of particles
5. Formation of interparticulate 5. Formation of interparticulate
bondsbonds
EjectionEjection
1. Particle rearrangement1. Particle rearrangement
2. Elastic deformation2. Elastic deformation
3. Plastic deformation of particles3. Plastic deformation of particles
4. Fragmentation of particles4. Fragmentation of particles
5. Formation of interparticulate 5. Formation of interparticulate
bondsbonds
EjectionEjection
Examples of materials consolidating by Examples of materials consolidating by
plastic deformation are Sodium Chloride, plastic deformation are Sodium Chloride,
starch. Fragmenting materials are, for starch. Fragmenting materials are, for
example, crystalline lactose, sucrose.example, crystalline lactose, sucrose.
However all materials posses both an However all materials posses both an
elastic and a plastic components.elastic and a plastic components.
plastic deformation are Sodium Chloride, plastic deformation are Sodium Chloride,
starch. Fragmenting materials are, for starch. Fragmenting materials are, for
example, crystalline lactose, sucrose.example, crystalline lactose, sucrose.
However all materials posses both an However all materials posses both an
elastic and a plastic components.elastic and a plastic components.
The volume reduction mechanism which The volume reduction mechanism which
will dominate for a specific material is will dominate for a specific material is
dependent on factors such as temperature dependent on factors such as temperature
and compression rate.and compression rate.
Lower temperatures and faster loading Lower temperatures and faster loading
during compression will generally facilitate during compression will generally facilitate
consolidation by fragmentation.consolidation by fragmentation.
will dominate for a specific material is will dominate for a specific material is
dependent on factors such as temperature dependent on factors such as temperature
and compression rate.and compression rate.
Lower temperatures and faster loading Lower temperatures and faster loading
during compression will generally facilitate during compression will generally facilitate
consolidation by fragmentation.consolidation by fragmentation.
Ejection:Ejection:
Ejection is the last stage of tablet Ejection is the last stage of tablet
compression.compression.
As the lower punch rises and pushes the As the lower punch rises and pushes the
tablet upward, there is a continued tablet upward, there is a continued
residual die wall pressure and residual die wall pressure and
considerable energy may be expanded considerable energy may be expanded
due to die wall friction.due to die wall friction.
Ejection is the last stage of tablet Ejection is the last stage of tablet
compression.compression.
As the lower punch rises and pushes the As the lower punch rises and pushes the
tablet upward, there is a continued tablet upward, there is a continued
residual die wall pressure and residual die wall pressure and
considerable energy may be expanded considerable energy may be expanded
due to die wall friction.due to die wall friction.
As the tablet is removed from the die,As the tablet is removed from the die,
Lateral pressure is relivedLateral pressure is relived
Tablet undergoes elastic Tablet undergoes elastic
recoveryrecovery
Radial and longitudinal Radial and longitudinal
relaxation occursrelaxation occurs
`` (2 – 10) % of tablet volume is (2 – 10) % of tablet volume is
↑ed.↑ed.
Lateral pressure is relivedLateral pressure is relived
Tablet undergoes elastic Tablet undergoes elastic
recoveryrecovery
Radial and longitudinal Radial and longitudinal
relaxation occursrelaxation occurs
`` (2 – 10) % of tablet volume is (2 – 10) % of tablet volume is
↑ed.↑ed.
F′ = Normal force to die wall during ejection.F′ = Normal force to die wall during ejection.
Fe = Maximum lower punch force to initiate ejection.Fe = Maximum lower punch force to initiate ejection.
F′F′
FeFe
Fig: Forces at the start of ejection.Fig: Forces at the start of ejection.
← ← RR →RR →
↑↑LrLr
LpLp
Fig: Elastic recovery dFig: Elastic recovery d
Fe = Maximum lower punch force to initiate ejection.Fe = Maximum lower punch force to initiate ejection.
F′F′
FeFe
Fig: Forces at the start of ejection.Fig: Forces at the start of ejection.
← ← RR →RR →
↑↑LrLr
LpLp
Fig: Elastic recovery dFig: Elastic recovery d
Primary and Secondary factors for tablets Primary and Secondary factors for tablets
strengthstrength
Two factors are regarded as primary factors for Two factors are regarded as primary factors for
the compactability of powder are : a. the compactability of powder are : a. the the
dominating bond mechanism and b. the dominating bond mechanism and b. the
surface area surface area overwhich these bonds are overwhich these bonds are
active.active.
More indirect , secondary factors are normally More indirect , secondary factors are normally
studied and used for correlation with tablet studied and used for correlation with tablet
strength. These are , strength. These are , particle shape, surface particle shape, surface
texture and particle size.texture and particle size.
strengthstrength
Two factors are regarded as primary factors for Two factors are regarded as primary factors for
the compactability of powder are : a. the compactability of powder are : a. the the
dominating bond mechanism and b. the dominating bond mechanism and b. the
surface area surface area overwhich these bonds are overwhich these bonds are
active.active.
More indirect , secondary factors are normally More indirect , secondary factors are normally
studied and used for correlation with tablet studied and used for correlation with tablet
strength. These are , strength. These are , particle shape, surface particle shape, surface
texture and particle size.texture and particle size.
Bonding surface areaBonding surface area
The term bonding surface area is The term bonding surface area is
often defined as the effective often defined as the effective
surface area taking part in the surface area taking part in the
interparticulate attraction.interparticulate attraction.
In case of solid bridges, the term In case of solid bridges, the term
corresponds to the true corresponds to the true
interparticulate contact area, while interparticulate contact area, while
for intermolecular forces the term is for intermolecular forces the term is
difficule to define.difficule to define.
The term bonding surface area is The term bonding surface area is
often defined as the effective often defined as the effective
surface area taking part in the surface area taking part in the
interparticulate attraction.interparticulate attraction.
In case of solid bridges, the term In case of solid bridges, the term
corresponds to the true corresponds to the true
interparticulate contact area, while interparticulate contact area, while
for intermolecular forces the term is for intermolecular forces the term is
difficule to define.difficule to define.
Bonding MechanismsBonding Mechanisms
Mainly five typesMainly five types
1. Solid bridges (melting, crystallization, 1. Solid bridges (melting, crystallization,
chemical reactions, and hardened chemical reactions, and hardened
binders)binders)
2. Bonding due to movable liquids 2. Bonding due to movable liquids
(capillary and surface tension forces)(capillary and surface tension forces)
3. Non-freely movable binder bridges 3. Non-freely movable binder bridges
(viscous binders and adsorption layers)(viscous binders and adsorption layers)
4. Attraction between particles4. Attraction between particles
5. Shape related bonding (mechanical 5. Shape related bonding (mechanical
interlocking)interlocking)
Mainly five typesMainly five types
1. Solid bridges (melting, crystallization, 1. Solid bridges (melting, crystallization,
chemical reactions, and hardened chemical reactions, and hardened
binders)binders)
2. Bonding due to movable liquids 2. Bonding due to movable liquids
(capillary and surface tension forces)(capillary and surface tension forces)
3. Non-freely movable binder bridges 3. Non-freely movable binder bridges
(viscous binders and adsorption layers)(viscous binders and adsorption layers)
4. Attraction between particles4. Attraction between particles
5. Shape related bonding (mechanical 5. Shape related bonding (mechanical
interlocking)interlocking)
However, the dominating bonds However, the dominating bonds
types adhering particles together in types adhering particles together in
compression of dry powder could compression of dry powder could
for simplicity be limited to three for simplicity be limited to three
types.types.
1. Solid brides (due to e. g. melting)1. Solid brides (due to e. g. melting)
2. Distance attraction 2. Distance attraction
(intermolecular forces)(intermolecular forces)
3. Mechanical interlocking (between 3. Mechanical interlocking (between
irregularly shaped particle)irregularly shaped particle)
types adhering particles together in types adhering particles together in
compression of dry powder could compression of dry powder could
for simplicity be limited to three for simplicity be limited to three
types.types.
1. Solid brides (due to e. g. melting)1. Solid brides (due to e. g. melting)
2. Distance attraction 2. Distance attraction
(intermolecular forces)(intermolecular forces)
3. Mechanical interlocking (between 3. Mechanical interlocking (between
irregularly shaped particle)irregularly shaped particle)
The term intermolecular forces includes The term intermolecular forces includes
van der Waals forces, electrostatic forces, van der Waals forces, electrostatic forces,
and hydrogen bonding.and hydrogen bonding.
The dominant interaction force between The dominant interaction force between
solid surfaces is the van der Waals force solid surfaces is the van der Waals force
of attraction.of attraction.
This forces operates in vacuum, gas, and This forces operates in vacuum, gas, and
liquid environment up to a distance of 100-liquid environment up to a distance of 100-
10000 A. 10000 A.
van der Waals forces, electrostatic forces, van der Waals forces, electrostatic forces,
and hydrogen bonding.and hydrogen bonding.
The dominant interaction force between The dominant interaction force between
solid surfaces is the van der Waals force solid surfaces is the van der Waals force
of attraction.of attraction.
This forces operates in vacuum, gas, and This forces operates in vacuum, gas, and
liquid environment up to a distance of 100-liquid environment up to a distance of 100-
10000 A. 10000 A.
Hydrogen bonding is predominantly an Hydrogen bonding is predominantly an
electrostatic interaction and may occur electrostatic interaction and may occur
either intermolecularly or intramolecularly either intermolecularly or intramolecularly
and mainly important for many direct and mainly important for many direct
compressible binders such as Avicel.compressible binders such as Avicel.
Electrostatic forces arise during mixing Electrostatic forces arise during mixing
and compaction due to triboelectric and compaction due to triboelectric
charging. It is neutralized with time by charging. It is neutralized with time by
electrostatic discharging.electrostatic discharging.
electrostatic interaction and may occur electrostatic interaction and may occur
either intermolecularly or intramolecularly either intermolecularly or intramolecularly
and mainly important for many direct and mainly important for many direct
compressible binders such as Avicel.compressible binders such as Avicel.
Electrostatic forces arise during mixing Electrostatic forces arise during mixing
and compaction due to triboelectric and compaction due to triboelectric
charging. It is neutralized with time by charging. It is neutralized with time by
electrostatic discharging.electrostatic discharging.
Solid bridges that contribute to the overall Solid bridges that contribute to the overall
compact strength can be defined as areas of compact strength can be defined as areas of
real contact i. e. contact at an atomic level real contact i. e. contact at an atomic level
between adjacent surfaces in the compact. between adjacent surfaces in the compact.
Different types of solid bridges are: Different types of solid bridges are: solid bridges solid bridges
due to melting, self diffusion of atoms between due to melting, self diffusion of atoms between
surfaces, recrystallization of soluble materials in surfaces, recrystallization of soluble materials in
the compacts.the compacts.
It can be measured by electrical resistivity It can be measured by electrical resistivity
measurementmeasurement
compact strength can be defined as areas of compact strength can be defined as areas of
real contact i. e. contact at an atomic level real contact i. e. contact at an atomic level
between adjacent surfaces in the compact. between adjacent surfaces in the compact.
Different types of solid bridges are: Different types of solid bridges are: solid bridges solid bridges
due to melting, self diffusion of atoms between due to melting, self diffusion of atoms between
surfaces, recrystallization of soluble materials in surfaces, recrystallization of soluble materials in
the compacts.the compacts.
It can be measured by electrical resistivity It can be measured by electrical resistivity
measurementmeasurement
*Hot welding:*Hot welding:
Most particles in the powder bed have irregular shape Most particles in the powder bed have irregular shape
and for this they have many points of contact.and for this they have many points of contact.
↓↓
When pressure is applied, it may produce frictional When pressure is applied, it may produce frictional
heat.heat.
↓↓
If heat is not dissipated, local rise in temperature may If heat is not dissipated, local rise in temperature may
cause the melting of contact area of the particles.cause the melting of contact area of the particles.
↓↓
Then stress in that particular area is relieved and melt Then stress in that particular area is relieved and melt
solidities, giving rise to fusion bonding.solidities, giving rise to fusion bonding.
↓↓
And at last, the mechanical strength of the mass is And at last, the mechanical strength of the mass is
↑ed.↑ed.
Most particles in the powder bed have irregular shape Most particles in the powder bed have irregular shape
and for this they have many points of contact.and for this they have many points of contact.
↓↓
When pressure is applied, it may produce frictional When pressure is applied, it may produce frictional
heat.heat.
↓↓
If heat is not dissipated, local rise in temperature may If heat is not dissipated, local rise in temperature may
cause the melting of contact area of the particles.cause the melting of contact area of the particles.
↓↓
Then stress in that particular area is relieved and melt Then stress in that particular area is relieved and melt
solidities, giving rise to fusion bonding.solidities, giving rise to fusion bonding.
↓↓
And at last, the mechanical strength of the mass is And at last, the mechanical strength of the mass is
↑ed.↑ed.
*cold welding: *cold welding:
When the surfaces of two particles approach each other closely When the surfaces of two particles approach each other closely
enough (e. g. at a separation of less than 50 nm), their free enough (e. g. at a separation of less than 50 nm), their free
surface energies result in a strong attractive force , a process surface energies result in a strong attractive force , a process
known as cold welding.known as cold welding.
solubility ∞ Pressuresolubility ∞ Pressure
Surface of granules during compression, the solubility of true Surface of granules during compression, the solubility of true
contact area or is increased with increasing pressure.contact area or is increased with increasing pressure.
↓↓
When pressure is released, solubility is decreased.When pressure is released, solubility is decreased.
↓↓
Solutes dissolved in the adsorbed water, or present in the Solutes dissolved in the adsorbed water, or present in the
solution, crystalline into small crystals between the particles.solution, crystalline into small crystals between the particles.
↓↓
So, the mechanical strength of the mass is ↑ed.So, the mechanical strength of the mass is ↑ed.
When the surfaces of two particles approach each other closely When the surfaces of two particles approach each other closely
enough (e. g. at a separation of less than 50 nm), their free enough (e. g. at a separation of less than 50 nm), their free
surface energies result in a strong attractive force , a process surface energies result in a strong attractive force , a process
known as cold welding.known as cold welding.
solubility ∞ Pressuresolubility ∞ Pressure
Surface of granules during compression, the solubility of true Surface of granules during compression, the solubility of true
contact area or is increased with increasing pressure.contact area or is increased with increasing pressure.
↓↓
When pressure is released, solubility is decreased.When pressure is released, solubility is decreased.
↓↓
Solutes dissolved in the adsorbed water, or present in the Solutes dissolved in the adsorbed water, or present in the
solution, crystalline into small crystals between the particles.solution, crystalline into small crystals between the particles.
↓↓
So, the mechanical strength of the mass is ↑ed.So, the mechanical strength of the mass is ↑ed.
The term mechanical interlocking is used to The term mechanical interlocking is used to
describe the hooking and twisting together of describe the hooking and twisting together of
the packed materials. the packed materials.
It has been claimed that materials bonding It has been claimed that materials bonding
predominantly by this mechanisms require high predominantly by this mechanisms require high
compression forces and have an extremely long compression forces and have an extremely long
disintegration time.disintegration time.
It is dependent on the shape and surface It is dependent on the shape and surface
structure of the particles.structure of the particles.
describe the hooking and twisting together of describe the hooking and twisting together of
the packed materials. the packed materials.
It has been claimed that materials bonding It has been claimed that materials bonding
predominantly by this mechanisms require high predominantly by this mechanisms require high
compression forces and have an extremely long compression forces and have an extremely long
disintegration time.disintegration time.
It is dependent on the shape and surface It is dependent on the shape and surface
structure of the particles.structure of the particles.
Role of moisture in tablet preparation:Role of moisture in tablet preparation:
At least some moisture is present in all tablet At least some moisture is present in all tablet
formulas, coming from the granulating solution formulas, coming from the granulating solution
after drying out or adsorbed from the after drying out or adsorbed from the
atmosphere. Granulations that are dry have poor atmosphere. Granulations that are dry have poor
compressional properties. compressional properties.
Water or saturated solutions of the material may Water or saturated solutions of the material may
form a film that acts as lubricant which removes form a film that acts as lubricant which removes
particles friction. particles friction.
So due to the presence of moisture, it is easy to So due to the presence of moisture, it is easy to
compress the tablet granules and stronger intact compress the tablet granules and stronger intact
tablet is formed through various bond formation. tablet is formed through various bond formation.
And less force is required to eject the tablet.And less force is required to eject the tablet.
At least some moisture is present in all tablet At least some moisture is present in all tablet
formulas, coming from the granulating solution formulas, coming from the granulating solution
after drying out or adsorbed from the after drying out or adsorbed from the
atmosphere. Granulations that are dry have poor atmosphere. Granulations that are dry have poor
compressional properties. compressional properties.
Water or saturated solutions of the material may Water or saturated solutions of the material may
form a film that acts as lubricant which removes form a film that acts as lubricant which removes
particles friction. particles friction.
So due to the presence of moisture, it is easy to So due to the presence of moisture, it is easy to
compress the tablet granules and stronger intact compress the tablet granules and stronger intact
tablet is formed through various bond formation. tablet is formed through various bond formation.
And less force is required to eject the tablet.And less force is required to eject the tablet.
Example:Example:
Optimum moisture content of lactose is 12%Optimum moisture content of lactose is 12%
Optimum moisture content of phenacetin is Optimum moisture content of phenacetin is
3%3%
From graph we can say-From graph we can say-
0.02% moisture can affect the proportion of 0.02% moisture can affect the proportion of
applied pressure transmitted to lower punch, applied pressure transmitted to lower punch,
where as –where as –
0.55% or 10 % moisture, the behavior is just 0.55% or 10 % moisture, the behavior is just
opposite as that for full dry material.opposite as that for full dry material.
Optimum moisture content of lactose is 12%Optimum moisture content of lactose is 12%
Optimum moisture content of phenacetin is Optimum moisture content of phenacetin is
3%3%
From graph we can say-From graph we can say-
0.02% moisture can affect the proportion of 0.02% moisture can affect the proportion of
applied pressure transmitted to lower punch, applied pressure transmitted to lower punch,
where as –where as –
0.55% or 10 % moisture, the behavior is just 0.55% or 10 % moisture, the behavior is just
opposite as that for full dry material.opposite as that for full dry material.
Role of moisture in granulation:Role of moisture in granulation:
Moisture is also important in moist Moisture is also important in moist
granulation process. Optimum moisture granulation process. Optimum moisture
content is required for maximum bonding. content is required for maximum bonding.
Moisture is also important in moist Moisture is also important in moist
granulation process. Optimum moisture granulation process. Optimum moisture
content is required for maximum bonding. content is required for maximum bonding.
A. Pendular state:A. Pendular state:
Powder particles are wetted during the initial Powder particles are wetted during the initial
stage of granulation.stage of granulation.
Liquid films are formed on the powder surface Liquid films are formed on the powder surface
and combine to form discrete liquid bridge at and combine to form discrete liquid bridge at
point of contacts.point of contacts.
The aggregation has – Dry surfaceThe aggregation has – Dry surface
Low densityLow density
Non-spherical (in use)Non-spherical (in use)
Powder particles are wetted during the initial Powder particles are wetted during the initial
stage of granulation.stage of granulation.
Liquid films are formed on the powder surface Liquid films are formed on the powder surface
and combine to form discrete liquid bridge at and combine to form discrete liquid bridge at
point of contacts.point of contacts.
The aggregation has – Dry surfaceThe aggregation has – Dry surface
Low densityLow density
Non-spherical (in use)Non-spherical (in use)
B. Funicular state:B. Funicular state:
As liquid content increases, several As liquid content increases, several
bridges may coalesce to give stronger bridges may coalesce to give stronger
bridge.bridge.
The aggregation has – Dry surfaceThe aggregation has – Dry surface
Denser than ‘A’Denser than ‘A’
Non-spherical / (nearly Non-spherical / (nearly
spherical)spherical)
As liquid content increases, several As liquid content increases, several
bridges may coalesce to give stronger bridges may coalesce to give stronger
bridge.bridge.
The aggregation has – Dry surfaceThe aggregation has – Dry surface
Denser than ‘A’Denser than ‘A’
Non-spherical / (nearly Non-spherical / (nearly
spherical)spherical)
C. Capillary state:C. Capillary state:
As more liquid is added, void space is As more liquid is added, void space is
eliminated and more stronger bridge is eliminated and more stronger bridge is
formed.formed.
The aggregation has – wetted surfaceThe aggregation has – wetted surface
Denser than “B”Denser than “B”
Nearly spherical.Nearly spherical.
As more liquid is added, void space is As more liquid is added, void space is
eliminated and more stronger bridge is eliminated and more stronger bridge is
formed.formed.
The aggregation has – wetted surfaceThe aggregation has – wetted surface
Denser than “B”Denser than “B”
Nearly spherical.Nearly spherical.
D. Droplet state:D. Droplet state:
Further addition of liquid causes droplet Further addition of liquid causes droplet
formation, where particles are still held together formation, where particles are still held together
by surface tensionby surface tension
The aggregation has – more wetted surface The aggregation has – more wetted surface
Maximum densityMaximum density
Maximum consistencyMaximum consistency
Spherical.Spherical.
Further addition of liquid causes droplet Further addition of liquid causes droplet
formation, where particles are still held together formation, where particles are still held together
by surface tensionby surface tension
The aggregation has – more wetted surface The aggregation has – more wetted surface
Maximum densityMaximum density
Maximum consistencyMaximum consistency
Spherical.Spherical.
Description of compression process:Description of compression process:
The process of compression can be described in terms of the The process of compression can be described in terms of the
relative volume (ratio of the volume of compressed mass to the relative volume (ratio of the volume of compressed mass to the
volume of the mass of zero void) and applied pressure which is volume of the mass of zero void) and applied pressure which is
given bellow.given bellow. ------ ------
appliedapplied
pressurepressure
A A
HH
GG B B
CC
FF
EE
DD
AA
EE
Relative volume →Relative volume → P →P →
Fig:Fig: Events of tablet compression process in times of applied pressure Vs relative volume.Events of tablet compression process in times of applied pressure Vs relative volume.
The process of compression can be described in terms of the The process of compression can be described in terms of the
relative volume (ratio of the volume of compressed mass to the relative volume (ratio of the volume of compressed mass to the
volume of the mass of zero void) and applied pressure which is volume of the mass of zero void) and applied pressure which is
given bellow.given bellow. ------ ------
appliedapplied
pressurepressure
A A
HH
GG B B
CC
FF
EE
DD
AA
EE
Relative volume →Relative volume → P →P →
Fig:Fig: Events of tablet compression process in times of applied pressure Vs relative volume.Events of tablet compression process in times of applied pressure Vs relative volume.
AEAE → transitional repacking stage, where → transitional repacking stage, where
granules are packed in such a way that particles granules are packed in such a way that particles
are immobile and no. of inter granular points of are immobile and no. of inter granular points of
contact is ↑ed and relative volume is ↓ed.contact is ↑ed and relative volume is ↓ed.
EFEF → with further increase in pressure, particles → with further increase in pressure, particles
become close contact and deformation at points become close contact and deformation at points
of contact occurs.of contact occurs.
FGFG → fragmentation and/ or plastic deformation → fragmentation and/ or plastic deformation
GH GH → at some higher pressure, bonding and → at some higher pressure, bonding and
consolidation of the solid occur to some extent consolidation of the solid occur to some extent
and relative volume is decreased.and relative volume is decreased.
granules are packed in such a way that particles granules are packed in such a way that particles
are immobile and no. of inter granular points of are immobile and no. of inter granular points of
contact is ↑ed and relative volume is ↓ed.contact is ↑ed and relative volume is ↓ed.
EFEF → with further increase in pressure, particles → with further increase in pressure, particles
become close contact and deformation at points become close contact and deformation at points
of contact occurs.of contact occurs.
FGFG → fragmentation and/ or plastic deformation → fragmentation and/ or plastic deformation
GH GH → at some higher pressure, bonding and → at some higher pressure, bonding and
consolidation of the solid occur to some extent consolidation of the solid occur to some extent
and relative volume is decreased.and relative volume is decreased.
Heckel equation:Heckel equation:
For compressional process, “Heckel” proposed an For compressional process, “Heckel” proposed an
equation based on 1st–order reaction-equation based on 1st–order reaction-
V V○V V○
Lu —— = Kp + ————Lu —— = Kp + ————
V-V∞ V○-V∞V-V∞ V○-V∞
Where,Where,
V = Volume of pressure P.V = Volume of pressure P.
V∞ = Volume of the solid. V∞ = Volume of the solid.
K = Constant related to yield value (Heckel constant).K = Constant related to yield value (Heckel constant).
P = Pressure (applied).P = Pressure (applied).
V○ = Original volume of powder including vo V○ = Original volume of powder including vo
For compressional process, “Heckel” proposed an For compressional process, “Heckel” proposed an
equation based on 1st–order reaction-equation based on 1st–order reaction-
V V○V V○
Lu —— = Kp + ————Lu —— = Kp + ————
V-V∞ V○-V∞V-V∞ V○-V∞
Where,Where,
V = Volume of pressure P.V = Volume of pressure P.
V∞ = Volume of the solid. V∞ = Volume of the solid.
K = Constant related to yield value (Heckel constant).K = Constant related to yield value (Heckel constant).
P = Pressure (applied).P = Pressure (applied).
V○ = Original volume of powder including vo V○ = Original volume of powder including vo
Porosity and Pressure functionPorosity and Pressure function
Porosity is a function of the void in a powder Porosity is a function of the void in a powder
column, and in general represent all pore space column, and in general represent all pore space
is considered, including both inter- and is considered, including both inter- and
intraparticulate voids.intraparticulate voids.
For porosity measurement, the dimensions and For porosity measurement, the dimensions and
weight of a powder column (i.e.apparent density) weight of a powder column (i.e.apparent density)
and the particle density (referred to often as true and the particle density (referred to often as true
density) of the solid materials should be known. density) of the solid materials should be known.
The porosity, ε can be expressed by the The porosity, ε can be expressed by the
equation equation
Porosity is a function of the void in a powder Porosity is a function of the void in a powder
column, and in general represent all pore space column, and in general represent all pore space
is considered, including both inter- and is considered, including both inter- and
intraparticulate voids.intraparticulate voids.
For porosity measurement, the dimensions and For porosity measurement, the dimensions and
weight of a powder column (i.e.apparent density) weight of a powder column (i.e.apparent density)
and the particle density (referred to often as true and the particle density (referred to often as true
density) of the solid materials should be known. density) of the solid materials should be known.
The porosity, ε can be expressed by the The porosity, ε can be expressed by the
equation equation
ε = 1 – ρA / ρrε = 1 – ρA / ρr
Where, ρA, is the apparent density of a Where, ρA, is the apparent density of a
powder column and ρpowder column and ρ
rr
is the particle is the particle
density of the compressed material. The density of the compressed material. The
value of ρA / ρr, also referred as D, is value of ρA / ρr, also referred as D, is
regarded as the relative density or the regarded as the relative density or the
packing fraction, which describes the solid packing fraction, which describes the solid
fraction of a porous powder column.fraction of a porous powder column.
Where, ρA, is the apparent density of a Where, ρA, is the apparent density of a
powder column and ρpowder column and ρ
rr
is the particle is the particle
density of the compressed material. The density of the compressed material. The
value of ρA / ρr, also referred as D, is value of ρA / ρr, also referred as D, is
regarded as the relative density or the regarded as the relative density or the
packing fraction, which describes the solid packing fraction, which describes the solid
fraction of a porous powder column.fraction of a porous powder column.
Porosity and Pressure EquationsPorosity and Pressure Equations
Three equations describing the change of Three equations describing the change of
relative density in a powder column as a relative density in a powder column as a
function of the applied pressure have function of the applied pressure have
been widely applied to pharmaceutical been widely applied to pharmaceutical
purposes, namelypurposes, namely
a. Heckel Equation (also called as Athy-a. Heckel Equation (also called as Athy-
Heckell), Heckell),
b. Kawakita and b. Kawakita and
c. Cooper – Eatonc. Cooper – Eaton
Three equations describing the change of Three equations describing the change of
relative density in a powder column as a relative density in a powder column as a
function of the applied pressure have function of the applied pressure have
been widely applied to pharmaceutical been widely applied to pharmaceutical
purposes, namelypurposes, namely
a. Heckel Equation (also called as Athy-a. Heckel Equation (also called as Athy-
Heckell), Heckell),
b. Kawakita and b. Kawakita and
c. Cooper – Eatonc. Cooper – Eaton
A. Heckel equation.A. Heckel equation.
Heckel introduced an equation for the Heckel introduced an equation for the
densification phenomenon following the first-densification phenomenon following the first-
order kinetics. The equation is order kinetics. The equation is
Ln 1 / 1-D = k P + A (1)Ln 1 / 1-D = k P + A (1)
Where k, and A are constants obtained from the Where k, and A are constants obtained from the
slope and intercept of the plot ln (1 / ( 1 – D)) slope and intercept of the plot ln (1 / ( 1 – D))
versus P, respectively, D is the relative density versus P, respectively, D is the relative density
of a powder column at the pressure P. of a powder column at the pressure P.
Heckel introduced an equation for the Heckel introduced an equation for the
densification phenomenon following the first-densification phenomenon following the first-
order kinetics. The equation is order kinetics. The equation is
Ln 1 / 1-D = k P + A (1)Ln 1 / 1-D = k P + A (1)
Where k, and A are constants obtained from the Where k, and A are constants obtained from the
slope and intercept of the plot ln (1 / ( 1 – D)) slope and intercept of the plot ln (1 / ( 1 – D))
versus P, respectively, D is the relative density versus P, respectively, D is the relative density
of a powder column at the pressure P. of a powder column at the pressure P.
AA is an intercept which is extrapolated from the is an intercept which is extrapolated from the
linear part of the Heckel plot. As the plots were linear part of the Heckel plot. As the plots were
curved at low pressures,curved at low pressures,
Heckel related the constant Heckel related the constant AA to process of to process of
volume reduction which have taken place by (1) volume reduction which have taken place by (1)
die filling and (2) particle rearrangement before die filling and (2) particle rearrangement before
deformation and bonding of the discrete deformation and bonding of the discrete
particles, (2) particles, (2)
linear part of the Heckel plot. As the plots were linear part of the Heckel plot. As the plots were
curved at low pressures,curved at low pressures,
Heckel related the constant Heckel related the constant AA to process of to process of
volume reduction which have taken place by (1) volume reduction which have taken place by (1)
die filling and (2) particle rearrangement before die filling and (2) particle rearrangement before
deformation and bonding of the discrete deformation and bonding of the discrete
particles, (2) particles, (2)
Densification of a powder by die filling can Densification of a powder by die filling can
be expressed as be expressed as
ln 1 / 1-D0ln 1 / 1-D0
Where D0 is the relative density of a Where D0 is the relative density of a
powder column at resting pressure, and powder column at resting pressure, and
usually derived from the bulk density. usually derived from the bulk density.
be expressed as be expressed as
ln 1 / 1-D0ln 1 / 1-D0
Where D0 is the relative density of a Where D0 is the relative density of a
powder column at resting pressure, and powder column at resting pressure, and
usually derived from the bulk density. usually derived from the bulk density.
The combined effect of die filling and particle The combined effect of die filling and particle
rearrangement at low pressures can be rearrangement at low pressures can be
described by the equationdescribed by the equation
A = ln 1 / 1 – D0 + BA = ln 1 / 1 – D0 + B
Where B describes a volume reduction Where B describes a volume reduction
purely by particle rearrangement. purely by particle rearrangement.
Relative densities corresponding the Relative densities corresponding the
processes above are DA, which includes processes above are DA, which includes
both die filling and particle both die filling and particle
rearrangement, and DB, which describes rearrangement, and DB, which describes
only the extent of particle rearrangementonly the extent of particle rearrangement
rearrangement at low pressures can be rearrangement at low pressures can be
described by the equationdescribed by the equation
A = ln 1 / 1 – D0 + BA = ln 1 / 1 – D0 + B
Where B describes a volume reduction Where B describes a volume reduction
purely by particle rearrangement. purely by particle rearrangement.
Relative densities corresponding the Relative densities corresponding the
processes above are DA, which includes processes above are DA, which includes
both die filling and particle both die filling and particle
rearrangement, and DB, which describes rearrangement, and DB, which describes
only the extent of particle rearrangementonly the extent of particle rearrangement
In his original work Heckel studied the In his original work Heckel studied the
densification o metal powder . densification o metal powder .
The slope k, of the Heckel plot was The slope k, of the Heckel plot was
intended to give a measure of the intended to give a measure of the
plasticity of a compressed material. plasticity of a compressed material.
Consequently , greater slopes indicated a Consequently , greater slopes indicated a
greater degree of plasticity of materialgreater degree of plasticity of material
densification o metal powder . densification o metal powder .
The slope k, of the Heckel plot was The slope k, of the Heckel plot was
intended to give a measure of the intended to give a measure of the
plasticity of a compressed material. plasticity of a compressed material.
Consequently , greater slopes indicated a Consequently , greater slopes indicated a
greater degree of plasticity of materialgreater degree of plasticity of material
Significance of Heckel equation / plotsSignificance of Heckel equation / plots
11. . Three types of volumes reduction mechanisms of Three types of volumes reduction mechanisms of
pharmaceutical powders have been distinguished by pharmaceutical powders have been distinguished by
using the Heckel equation. The types are referred as using the Heckel equation. The types are referred as
A, B, and C (Fig 2)A, B, and C (Fig 2)
In type A, size fractions had different initial packing In type A, size fractions had different initial packing
fraction and the plot remained parallel as the fraction and the plot remained parallel as the
compression pressure was increased.compression pressure was increased.
In type B, the plot were sightly curved at the initial In type B, the plot were sightly curved at the initial
stages of compaction and later became coincidental.stages of compaction and later became coincidental.
In type C, the plot had an initial steep linear part after In type C, the plot had an initial steep linear part after
which they became coincidental with only trivial which they became coincidental with only trivial
volume reduction.volume reduction.
11. . Three types of volumes reduction mechanisms of Three types of volumes reduction mechanisms of
pharmaceutical powders have been distinguished by pharmaceutical powders have been distinguished by
using the Heckel equation. The types are referred as using the Heckel equation. The types are referred as
A, B, and C (Fig 2)A, B, and C (Fig 2)
In type A, size fractions had different initial packing In type A, size fractions had different initial packing
fraction and the plot remained parallel as the fraction and the plot remained parallel as the
compression pressure was increased.compression pressure was increased.
In type B, the plot were sightly curved at the initial In type B, the plot were sightly curved at the initial
stages of compaction and later became coincidental.stages of compaction and later became coincidental.
In type C, the plot had an initial steep linear part after In type C, the plot had an initial steep linear part after
which they became coincidental with only trivial which they became coincidental with only trivial
volume reduction.volume reduction.
Generally type A, behavior was related to Generally type A, behavior was related to
the densification by plastic flow, preceded the densification by plastic flow, preceded
by particle rearrangement.by particle rearrangement.
In type B, powder densification occurs by In type B, powder densification occurs by
fragmentation of the particlesfragmentation of the particles
Type C densification occurs by plastic flow Type C densification occurs by plastic flow
but no initial particle rearrangement is but no initial particle rearrangement is
observed.observed.
the densification by plastic flow, preceded the densification by plastic flow, preceded
by particle rearrangement.by particle rearrangement.
In type B, powder densification occurs by In type B, powder densification occurs by
fragmentation of the particlesfragmentation of the particles
Type C densification occurs by plastic flow Type C densification occurs by plastic flow
but no initial particle rearrangement is but no initial particle rearrangement is
observed.observed.
2. The crushing strength of tablet is related to 2. The crushing strength of tablet is related to
the value of K. Larger value of K indicates the value of K. Larger value of K indicates
harder tablets. So this relation can be used in harder tablets. So this relation can be used in
binder selection for tablet formationbinder selection for tablet formation
Hardness ∞K∞ Crushing strength.Hardness ∞K∞ Crushing strength.
3. Larger value of Heckel constant (K) indicates 3. Larger value of Heckel constant (K) indicates
the one set of plastic deformation of low the one set of plastic deformation of low
pressure. pressure.
Plastic deformation ∞ KPlastic deformation ∞ K
the value of K. Larger value of K indicates the value of K. Larger value of K indicates
harder tablets. So this relation can be used in harder tablets. So this relation can be used in
binder selection for tablet formationbinder selection for tablet formation
Hardness ∞K∞ Crushing strength.Hardness ∞K∞ Crushing strength.
3. Larger value of Heckel constant (K) indicates 3. Larger value of Heckel constant (K) indicates
the one set of plastic deformation of low the one set of plastic deformation of low
pressure. pressure.
Plastic deformation ∞ KPlastic deformation ∞ K
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