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1. A SEMINAR ON
COMPRESSION AND COMPACTION
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2. CONTENTS
 COMPRESSION PROPERTIES
 AXIL FORCE AND RADIAL FORCE
 PROCESS OF COMPRESSION
 MEASURMENT OF FORCE
 DISTRIBUTION OF FORCE

3. COMPRESSION PROPERTIES
COMPRESIBILITY:- It is the ability of powder to
decrease in volume under pressure.
COMPACTIBILITY:- It is the ability of a powder to be
compressed into a tablet of a certain strength or
hardness.
1. Plastic material
ex:kaolin, pvp.
1. Elastic material
ex:aspirine, microcrystalline cellulose

5. AXIAL FORCE :
 it is the force required to attempt of material to constrict
vertically.

6. RADIAL FORCE :
 it is the force required to the attempt the material to
expand horizontally

7. PROCESS OF COMPESSION
1. Transitional repacking
2. Deformation at the point of contact
3. Fragmentation
4. Bonding
5. Deformation of solid body
6. Decompression
7. Ejection

8. Transitional repacking or particle
rearrangement.
 Granules to be placed in the hopper of the tablet press.
 Formulation and processing are designed to ensure that
at a fast production rate the weight variation of the final
tablet is minimal.
 The particle size distribution of granulation and the
shape of the granules determine the initial packing as
the granules is delivered in to the die cavity.
 In the initial event the punch and particle movement
occur at low pressure.
 The granule flow with respect to each other, with the
finer particle entering the void between the larger
particle, and the bulk density of the granulation is
increased.

9.  Spherical particle undergo less particle
rearrangement then irregular particle as the
spherical particle tend to assume a close
packing rearrangement initially.
 To achieve a fast flow rate required for high-
speed presses the granulation is generally
processed to produce spherical or oval particles.
 Thus, particle rearrangement and the energy
expended in rearrangement era minor
consideration in the total process of
compression

11. Deformation at point of contact
 When the stress is applied to a material, deformation
(change of forms) occurs.
 If the deformation disappears completely (return to the
original shape) upon release of stress , it is an Elastic
deformation.
 A deformation that dose not completely recover after
release of the stress is known as a Plastic deformation.
 The force required to initiate plastic deformation is
known as the yield stress.
 In the initial event the punch and particle movement
 occur at low pressure.
 the granule flow with respect to each other ,with the
finer particles entering the void between the larger
particle, and the bulk density of granule is increased.

12.  spherical particle under go less particle arrangement
then irregular particles as the spherical particles tend to
assume a close packing arrangement initially.
 To achieve a fast flow rate required for high speed presses
the granulation is generally processed to produce spherical
or oval particles, thus particle rearrangement and the energy
expended in rearrangement are minor considerations in the
process of compression.
 When the particles of a granulation are so closely packed
that no further filing of the void can occur, a further increases
of compressional force cause deformation at he point of
contact.
 Both plastic and elastic deformation may occur although one
type predominates for a given material.
 Deformation increase the area of true contact and the
formation of potential bonding areas.

14. Fragmentation and Deformation
 At higher pressure, fracture occur when the stresses
within the particles become great enough to propagate
cracks.
 fragmentation further densification, with the infiltration of
the smaller fragment in to the void space
 Fragmentation increase the number of particle and form
new, clean surface that are potential bonding area.

16. Bonding
 Several mechanism of bonding in the compression
process have been conceived, but they have not been
useful in in the prediction of the compressional
properties of material.
 Three theory are

 1 . Mechanical theory
 2 . The intermolecular theory.
 3. the liquid surface film theory

17. Mechanical theory:-
 This theory proposes that under pressure the individual
particle undergo elastic, plastic or brittle deformation and
that the edges of the particle intermesh, forming a
mechanical bond.
 If only the mechanical bond exists, the total energy of
compression is equal to the sum of the energy of
deformation, heat and energy adsorb for each
constituent.
 Mechanical inter locking is not a major mechanism of
bonding in pharmaceutical tablets.

18. The inter molecular theory:-
 The molecule (or ions) at the surface of the solid have
unsatisfied intermolecular force, which interacts with
other particles in true contact.
 According to the intermolecular forces theory, under
pressure the molecules at the point of true contact
between new, clean surface of the granules are close
enough so that van der Waals forces interact to
consolidate the particle.

19.  A microcrystalline cellulose tablet has been described as
a cellulose fibril in which the crystals are compressed
close enough together so that hydrogen bonding
between them occurs.
 It appear that very little deformation or fusion occur in the
compression of microcrystalline cellulose.
 Aspirin crystals under go slight deformation and
fragmentation at low pressure, it appear that hydrogen
bonding has strongly bonded the tablet, because the
granules retain their integrity with further increase in
pressure .

20. The liquid surface film theory:-
 The liquid surface film theory attributes bonding to the
presence of a thin liquid film, at the surface of the
particle induced by the energy of compression.
 During the compression an applied force is exerted on
the granules; however, locally the force applied to a
small area of true contact so that a very high pressure
exists at the true contact surface.
 The local effect of the high pressure on the melting point
and solubility of a material is essential to bonding.
 The relation of pressure and melting point (clapeyron)
 dT T(V1-Vs) T-temperature
 dP H
 By analogous reasoning , the pressure distribution in
compression is such that the solubility is increased with
increasing pressure.

21.  With an increase in solubility at the point of true contact,
solution usually occur in the film of adsorb moisture on the
surface of the granule.
 When the applied pressure is released and the solubility
decrease, the solute dissolve in the adsorbed water
crystallizes in small crystals between the particles.
 the strength of the bridge depend on the amount of material
deposited and rate of crystallization.
 At higher rates of crystallization, a finer crystalline structure
and a greater strength are obtained.

22.  The poor compressibility of most water insoluble material
and the relative ease of compression of water soluble
materials suggest that pressure induced solubility is
important in tableting.
 The moisture may be present as that retain from the
granulating solution after drying or that adsorb from the
atmosphere.
 Granulation that are absolutely dry have poor
compressional characteristics.

24. Decompression:-
 After the compression and consolidation of the powder
in the die, the formed compact must be capable of
 withstanding the stresses encountered during
decompression and tablet ejection.
 The rate at which the force is removed (dependent on
the compression roller diameter and the machine speed)
can have a significant effect on tablet quality.
 The same deformation characteristics that come into
play during compression, play a role during
decompression.
 After application of the maximum compression force, the
tablet undergoes elastic recovery.

25.  While the tablet is constrained in the die, elastic recovery
occurs only in the axial direction. If the rate and degree
of elastic recovery are high, the tablet may cap or
laminate in the die due to rapid expansion in the radial
direction only.
 Tablets that do not cap or laminate are able to relieve
the developed stresses by plastic deformation.
 Since plastic deformation is time-dependent, stress
relaxation is also time-dependent.
 Formulations which contain significant concentrations of
microcrystalline cellulose typically form good compacts
due to its plastic deformation properties.
 However, if the machine speed and the rate of tablet
compression are significantly increased, these
formulations exhibit capping and lamination tendencies.

26.  The rate of decompression can also have an effect on
the ability of the compacts to consolidate (form bonds).
 Based on the liquid-surface film theory, the rate of
crystallization or solidification should have an effect on
the strength of the bonded surfaces. The rate of
crystallization is affected by the pressure (and the rate at
which the pressure is removed).
 High decompression rates should result in high rates of
crystallization. Typically, slower crystallization rates
result in stronger crystals.
 Therefore, if bonding occurs by these mechanisms,
lower machine speeds should result in stronger tablets.
 The rate of stress relieve is slow for acetaminophen so
cracking occurs while the tablet is within the die. with
microcrystalline cellulose the rare of stress relieve is
rapid, and intact tablets result.

27. Ejection
 As the lower punch rises and pushes the tablet upward
there is a continued residual die wall pressure and
considerable energy may be expanded due to the die
wall friction.
 As the tablet removed from the die, the lateral pressure
is relieved, and the tablet undergoes elastic recovery
with an increase (2 to 10%) in the volume of that portion
of the tablet removed from the die.
 During ejection that portion of the tablet within the die is
under strain, and if this strain exceeds the sheer strength
of tablet the tablet break as elastic recovery.

31.  A large value of the heckel constant indicate the onset of
plastic deformation at relatively low pressure.
 A heckel plot permits an interpretation of the mechanism
of bonding.
 For dibasic calcium phosphate dihydrate, which
undergoes fragmentation during compression, the heckel
plot is nonlinear and has small value for its slope (a
small heckel constant).
 As dibasic calcium phosphate dihydrate fragments, the
tablet strength is essentially independent of particle size.
 For sodium chloride a heckel plot is linear indicating that
sodium chloride undergoes plastic deformation during
compression. no fragmentation occur.

32. Effect of friction
 At least two major component to the frictional force can
be distinguished
 Interparticulate friction :- this arises at particle /particle
contacts and can be expressed in term of a coefficient of
interparticulate friction m1. it is more significant at low
applied loads.
 Material that reduce this effect are referred to as
glidants.
 Ex:- colloidal silica, talc, corn starch
 Die-wall friction :-this result from material being pressed
against the die wall and moved down it ; it is expressed
as mw, the coefficient of die wall friction.

33.  This effect become dominant at high applied forces
when particle rearrangement has ceased and is
particularly important in tabletting operations.
 Most tablets contain a small amount of an additive
design to reduce die wall friction; such additives are
called lubricants.
 Ex:-magnesium stearate, talc, PEG, waxes, stearic acid
Force distribution
FA
HO
H
FR FD
D
FL
 Diagram of a cross section of a typical simple punch and die assembly

34.  This investigation carried on single station press.
 Force being applied to the top of a cylindric power mass
and the following basic relationships apply.
 FA=FL+FD
 Where, FA =is the force applied to upper punch
 FL =is that proportion of it transmitted to the lower punch
 FD =is a reaction at the die wall due to friction at this
surface
 Because of this difference between the force applied at
the upper punch and that affecting material closed to the
lower punch, a mean compaction force, FM where,
FM=FA+FL/2
 A recent report confirm that FM offer a practical friction-
independent measure of compaction load, which is
generally more relevant then FA.

35.  In single station presses, where the applied force
transmission decay exponentially, a more appropriate
geometric mean force FG, might be
 0.5
 FG=(FA . FL)
 Use of this force parameters are probably more
appropriate then use of FA when determining
relationships between compressional force and such
tablet properties as tablet strength.

36.  Development of radial force
 As the compressional force increased and any repacking
of the tabletting mass is completed, the material may be
regarded to some extent as a single solid body.
 Then as with all other solid, compressive force applied in
one direction (e.g. vertical) result in decrease in H in
the height, i.e. a compressive stress.
 In the case of an unconfined solid body, this would be
accompanied solid body, this would be accompanied by
an expansion in the horizontal direction of D
 The ratio of these two dimensional changes is known as
poisson ratio of the material, defined as:
 Poisson ratio = D/H
 The poisson ratio is a characteristic constant for each
solid and may influence the tabletting process in
following way.

37.  Under the condition illustrated in figure , the material in
not free to expand in horizontal plane because it is
confined in the die.
 Consequently, a radial die wall force FR develops
perpendicular to the die wall surface, material with larger
poisson ratios giving rise to higher value of FR.
 Classic friction theory can then be applied to deduce that
the axial frictional force FD is related to FR by the
expression:
 FD = mw.FR
 Where mw is the coefficient of die wall friction.
 Note that FR is reduced when material of small poisson
ratio are used, and that in such cases, axial force
transmission is optimum.

38. Die wall lubrication
 Most pharmaceutical tablet formulation require the
addition of a lubricant to reduce friction at the die wall .
 Die wall lubricant function by interposing a film of low
shear strength at the interface between the tabletting
mass and the die wall.
 Preferably, there is some chemical bonding between this
boundary lubricant and the surface of the die wall as well
as the edge of the tablet.
 The best lubricant are those with low shear strength but
strong cohesive tendencies in direction at right angles to
the plane of shear.

39. Ejection forces
 Radial die wall forces and die wall friction also effect the
ease with which the compressed tablet can be removed
from the die.
 The force necessary to eject a finished tablet follows a
distinctive pattern of three stage.
 The first stage involves the distinctive peak force
required to initiate ejection, by braking of tablet/die wall
adhesions.
 A smaller force usually follows, namely that required to
push the tablet up the die wall.
 The final stage is marked by declining force of ejection
as the tablet emerges from the die.

40.  Variation on this pattern are sometimes found, especially
when lubrication is inadequate and/or “slip-stick”
condition occur between the tablet and the die wall,
owing to continuing formation and breakage of tablet die
wall adhesion.
 A direct connection is to be expected between die wall
frictional forces and the force required to eject the tablet
from the die, FE.
 For e.g. well lubricated systems have been shown to
lead to smaller FE values.
 Compection profiles
 Monitoring of that proportion of the applied pressure
transmitted radially to the die wall has been reported by
several groups of workers.
 For many pharmaceutical materials, such investigation
lead to characteristic hysteresis curves , which have
been termed compaction profiles.

41.  The radial die wall forces arises as a result of tabletting
mass attempting to expand in the horizontal plane in
response to the vertical compression.
 The ratio of this two dimensional changes, the Poisson
ratio, is an important material dependent property
affecting the compressional process.
 When the elastic limit of the material is high, elastic
deformation may make major contribution, and on
removal of the applied load, the extent of the elastic
relaxation depend upon the value of the materials
modulus of elasticity (young’s modulus).
 If this value is low, there is considerable recovery, and
unless a strong structure has been formed, there is the
danger of structural failure.
 If the modulus of elasticity is high, there is small
dimensional change on decompression and less risk of
failure.

42. C
D
radial
pressure
E B
c’ A
O axial pressure

43.  The area of the hysteresis loop (OABC’) indicate the
extent of departure from ideal elastic behavior, science
for perfectly elastic body, line BC’ would coincide with
AB.
 In many tabletting operation the applied force exceed the
elastic limit (point B), and brittle fracture and/or plastic
deformation is then a major mechanism.
 For example, if the material readily undergoes plastic
deformation with a constant yield stress as the material
is sheared, then the region B to C should obey the
equation.
 PR = PA – 2S
 Where S is the yield stress of the material
 The slope of this plot is unity, so that mark deviation from
this value may indicate a more complex behavior.

44.  Deviation could also be due to the fact that the material
is still significantly porous.
 For e.g. since point C represent the situation at the
maximum compressional force level, the region CD is
therefore the initial relaxation response as the applied
lode is removed.
 In practice, many compaction profiles exhibit a marked
change in the slope of this line during decompression,
and a second yield point D has been reported.

 Perhaps the residual redial pressure (intercept EO),
when all the compressional force has been removed, is
more significant, since this pressure is an indication of
the force being transmitted by the die wall to the tablet.

45.  As such, it provide a measure of possible ejection force
level and likely lubricant requirements, it suggests a
strong tablet capable of at least withstanding such a
compressive pressure.
 A low value of residual redial pressure, or more
significantly, a sharp change in slop (DE) is sometime
indicative of at least incipient failure of the tablet
structure.
 In practical term this may mean introducing a plastically
deforming component (e.g.pvp as binder).

46. Energy involve in compaction
 Tablet machines, roller compactors, and similar types of
equipment required a high input of mechanical work.
 The work involve in various phase of tablets operation
includes,
 That necessary to overcome friction between particles,
 That necessary to overcome friction between the
particles and machine parts,
 That required to induce elastic and/or plastic deformation
of the materials,
 That required to cause brittle fracture within the
materials, and
 That associated with the mechanical operation of various
machine parts.

47.  Nelson and associate, who compared the energy
expenditure in lubricated and unlubricated sulfathiazole
granules.
 Lubrication reduce energy expenditure by 70%, chiefly
because of a lessening of the major component, namely
energy utilized during ejection of the finished tablet.
 Lubricant has no apparent effect on the actual amount of
energy required to compress the material.
Compression Energy expended(joules)
process Unlubricated Lubricated
Compression 6.28 6.28
Overcoming die wall friction 3.35 --
Upper punch withdrawal 5.02 --
Tablet ejection 21.35 2.09
Total 36.00 8.37

48.  By assuming that only energy expended in the process
of forming the tablet cause a temperature rise, Higuchi
estimated the temperature rise to be approximately 5 c.
 For a single punch machine operating at 100 tablets per
min, and approximately 43 kcal/hr were required for
unlubricated granules.
 Wurster and creekmore by use of an internal
temperature probe found a 2 to 5 c rise in the
temperature of tablet compressed from microcrystal
cellulose, calcium carbonate, starch and sulfathiazole
 The temperature of compressed tablet is affected by the
pressure and speed of tablet machine.

49.  In non instrumented single punch tablet machine set at
minimum pressure, the compression of 0.7 g of sodium
chloride caused a temperature increase of 1.5 c ;
when the machine was set near maximum pressure , the
temp. increase was 11.1 c .
 When the machine was operating at 26 and 140 rpm the
increase in temp. was 2.7 and 7.1 respectively.
 When the machine was operating at 26 and 140 rpm to
compress 0.5 g of calcium carbonate, the increase in
temp. was 16.3 and 22.2 c respectively.

50. Properties of tablet influence by compression
 Higuchi and train were the first pharmaceutical scientists
to study the effect of compression on tablet
characteristics.
 The relationship between applied pressure and weight,
thickness, density, and the force of ejection are relatively
independent of the material being compressed
 Density and porosity
 Hardness and tensile strength
 Specific surface
 Disintegration
 Dissolution

51. 1.5
1.4
Density
g/cm 3 1.3 sulphathiazole tablet
1.2
1.1 500 1000 2000 4000
logarithm applied pressure, kg/cm 2

52. 30
Lactose
porosity 20
% lactose-aspirin
10 aspirin
500 1000 2000 4000
applied pressure, kg/cm 2
 The effect of applied pressure on the porosity of
various tablet with 10% of starch. Porosity and density
inversely proportional to each other.

53. 30
Lactose
hardness 20 lactose-aspirin
s.c unit
10 aspirin
500 1000 2000 4000
applied pressure, kg/cm 2

54. 80 radial
tensile 60
strength
kg/cm 2 40
20 axial
200 4000 6000 8000
applied pressure, kg/cm 2
The effect of applied pressure on tensile strengths of tablet of
dibasic calcium phosphate granulated with 1.2% starch.

55. DISTRIBUTION OF FORCE :
Fm = Fa + Fd
2
Fa = Fl +Fd
Fa =force applied to upper punch.
Fl =force transmitted to lower punch.
Fd =is the reaction at the die wall due
to friction at the surface.
Fm = mean force

56. Relation between applied and transmitted
force
 The relation between applied & transmitted
forces Fa, Fl practically linear
 In case of single punch the force exerted by
upper punch ↓ exponentially as depth ↑
 The relation between Fa, Fl written as
Fl = Fl٠ Fl e KH / D
 Rearranging the above equation
Fa = Fl ٠ eKH / D

57. COMPACTION PROFILE
Radial pressure is due to the
attempt of material to expand
horizontally.
Axial pressure is due to the
attempt of material to constrict
vertically.
OA =Shows Early repacking
AB = elastic deformation
BC = plastic deformation
CD = elastic recovery
DE = plastic recovery

58. MEASURMENT OF FORCES
1) STRAIN GAUGE :
 A coil of high resistant with length width ratio 2:1 &
resistant 100 ohm is suitable
 During compression the applied force causes a small elastic
deformation of two punches
 Strain gauge are connected to punch as close to the
compression site. it is deformed as the punch deformed
 With the deformation, the length of resistance wire ↓ & its
diameter is ↑.
 The resulting decrease in resistance is measured by wheat
stone bridge as a recording devise.
 Care must be taken to use low voltage so that heating effect
do not interfere with the strain measurement.

59. DIAGRAMETIC REPRASENTATION OF
STRAIN GAUGES

60. 2)PIEZO-ELECTRIC LOAD CELLS:
 Certain crystals like quartz may be used. When subjected to
external force these develop an electrical charge proportional to
the force.
 This transducer is connected to amplifier which converts the
charge in to dc voltage.
 The small piezo-electrical transducer are connected to upper &
lower punch holder of single station press.
 The disadvantage is the dissipation of charge with time, hence
nit suitable for static measurement.

61. DIAGRAMATIC REPRASENTATION OF
PIEZO-ELECTRIC CELLS

62. REFRENCES
1. The theory & practice of industrial
pharmacy By: Lachman
2. The science of dosage form design
edited by: Michael E. Aulton
3. Text book of physical pharmacy by Alfred
Martin, James Swarbric.
4. By internet source.