1) Tablet compression involves the application of force to reduce the volume of powder materials through three main processes: compression, compaction, and consolidation. Compression removes air, compaction rearranges particles, and consolidation increases strength through bonding. 2) Key forces involved in compression include inter-particulate and die wall friction, which can be reduced by adding glidants and lubricants, respectively. Distribution forces transmit pressure from the punches to the powder bed and die wall. 3) Compaction profiles examine the relationship between axial and radial pressure. They provide information on elastic versus plastic deformation and ejection forces.

1. COMPRESSION
AND
COMPACTION
Mehak Aggarwal
M.Pharm (Pharmaceutics)
Himachal Institute of Pharmacy

2. CONTENT
• Introduction
• Physics ofTablet Compression
• Process ofTablet Compression
• Forces involved in compression
• Effect of friction
• Distribution of Forces
• Compaction profiles
• Solubility
• References
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3. INTRODUCTION
• Tablet is defined as a compressed unit solid dosage form containing medicaments with or without
excipients.
• Compaction represent one of the most important unit operations in the pharmaceutical industry.
• Compaction is the situation in which materials are subjected to some level of mechanical force.
• The physics behind the compaction is stated as the compression and consolidation of the two
phase system due to applied force.
• While considering the compaction and compression of tablets we have to take the properties of
powder into the consideration as they are involved in the process of the compression and
compaction.
• Derived properties of powder are: volume, density, porosity, flow properties, angle of repose etc.
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4. COMPRESSION
Compression means reduction of bulk volume of material as a result of
the removal of gaseous phase (air) by applied pressure.
COMPACTION
Compaction of the powder is the term is used to describe the situation
in which the materials are subjected to some level of mechanical
forces.
CONSOLIDATION
Consolidation is an increase in mechanical strength of material
resulting from particle-particle interactions.
Compaction =compression + consolidation of two phases (solid-
gas) on application of force.
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5. PHYSICS OF TABLET
COMPRESSION
Transitional repacking or particle rearrangement
Deformation at points of contact
Fragmentation
Bonding
Removal of pressure
Deformation of solid body
Ejection
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6. PROCESS OF TABLET COMPRESSION
TRANSITIONAL REPACKING
When a powder is compressed initially the particles are rearranged under low
compaction pressures to form a closer packing structure.
The small particles enter the voids between the larger ones and give a closer packing
arrangement.
In this process, the energy is evolved, as a result of inter particulate friction and there
is an increase in the amount of particle surface area capable of forming inter
particulate bonds.
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7. DEFORMATION
When the particles of granulation are so closely packed that no further filing of voids
can occur, a further increase in the compression force causes deformation at that
point of contact.
Change in shape of material occurs. At certain points the packing characteristics of
the particles reduced space or porosity of inter-particulate friction will prevent any
further rearrangement of particles.
At this point further reduction in the compact volume results in elastic or plastic
deformation.
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8. FRAGMENTATION
As compression force increases deformed particles start fragmentation due to high
load, particles breaks into smaller fragments leading to formation of new bonding
areas.
The fragment undergo densification with infiltration of small fragments into voids.
Some particles undergo structural break down called as brittle fracture.
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9. BONDING
After the fragmentation of the particles, as the pressure increases, formation of new
bonds between the particles at that contact area occurs. The hypothesis favoring for
increase in mechanical strength of bed of powder when subjected rising compressive
forces can be explained by following theories:
a) Liquid surface film theory
b) Intermolecular theory
c) The mechanical theory
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10. • Liquid Surface Theory: This theory attributes bonding to the
presence of a thin liquid film which may be the consequences of
fusion or solution at the surface of the particles. This theory is a
combination of Solid bridge, Hot welding and Cold welding theory.
• Intermolecular Theory: This theory proposes that under
compressional pressure the molecules at the points of true contact
between new clean surfaces of the granules are close enough so
that Vander Waals forces interact to consolidate the particles.
• The Mechanical Theory: It occurs between irregularly shaped
particles and increase number of point of contact between the
particles. This theory proposes that under pressure the individual
particles undergo elastic or plastic deformation and edges of particle
intermesh deforming a mechanical bond.
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11. DEFORMATION OF SOLID BODY
As the applied force /pressure is further increased, the bonded solid is consolidated
towards a limiting density by plastic/ elastic deformation of the tablet within the die.
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EJECTION
The last stage in compression cycle is ejection from die.
The force necessary to eject a tablet involves the distinctive peak force required to
initiate ejection, by breaking of die wall– tablet adhesion. The second stage involves
the force required to push the tablet up the die wall, and the last force is required for
ejection.

12. Forces involves in the
Compression
1. Frictional forces
• Inter-particulate friction
• Die wall friction
2. Distribution force
3. Ejection Force: The force necessary to eject the finished the
tablets.
4. Radial Force.
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13. • Frictional Forces: Interparticulate friction & Die wall Friction.
E.g. Colloidal silica E.g. Magnesium
Stearate
• Distribution Forces: Most investigational of fundamental of tableting
have been carried out on single punch presses with hydraulic
press.
• Ejection Forces: Radial die wall forces & die wall friction also
affects ejection of the compressed tablet from die. The force
necessary to eject a finished tablet is known as Ejection Force.
Variation also occurs in ejection force when lubrication is
inadequate.
• Radial Force: It is the force required by material to expand
horizontally.
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Reduced by adding
glidants
Reduced by
adding lubricants

14. EFFECT OF FRICTION
Two major component to the frictional force.
1. Inter-particulate friction
• Occur due to particle-particle contact and more significant due at low applied load.
• These frictional effect is reduced by addition of glidants like colloidal silica or corn
starch.
2. Die wall friction.
• Die wall friction occurs from material pressed against die wall and moved it down.
• It is expressed as ‘mw’ the coefficient of die wall friction.
• This effect is reduced by the addition of lubricants. E.g. Waxes, Stearic acid, PEG.
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15. DISTRIBUTION OF FORCES
The force distribution when compaction takes place is a single station press and is
given by-
FA=FL+FD
Where,
FA= Force applied to upper punch
FL= force transmitted to lower punch &
FD= Reaction at die wall due friction at surface.
• Mean compaction force is given by-
FM=FA+FL
2
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16. COMPACTION PROFILES
Compaction profiles are hysteresis curve that establish the
relationship between the axial pressure and radial pressure.
In compaction cycle two forces are considered:
• Axial Force:This is the vertical component applied by upper
punch during the compression.
• Radial force:This is the horizontal component observed in die
wall , when powder mass attempt to in the die wall.
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COMPACTION PROFILE OF A MATERIAL

18. Compression Phase:
• OA - Represents repacking of granules or powders.
• AB - Represents elastic deformation which continues up to B (elastic limit)
• BC - Represents plastic deformation and brittle fracture. Point C indicates the
maximum compression force.
Decompression phase:
• CD - Represents elastic recovery on the removal of applied force.
• DE - Represents recovery from plastic deformation
• E - Represents residual force, which holds the compact in the sides of the die.
Ejection force must be greater than residual force.
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19. • How they are measured?
It is analyzed by compaction simulators, these are attached to
punching machines which collect or measure the data from forces
on punches, displacement of punches, die wall friction, ejection
force and temperature change.
• Types of compaction profiles
1. Force-time profile
2. Force-displacement profile
3. Die wall force profile
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20. Force-Time Profile
It is used to characterize the compression behavior
of the active ingredients, excipients and
formulations with respect to their plastic and elastic
deformation.
a) Compression phase: Compression is the
process in which maximum force is applied on
powdered bed in order to reduce its volume.
b) Dwell phase: When compression force reaches
a maximum value, this maximum force is
maintained for prolonged period before
decompression. The time period b/w the
compression phase and decompression phase
is known as dwell time.
c) Decompression phase: Removal of applied
force on powder bed i.e., both punches moving
away from upper and lower surfaces.
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21. Force-Displacement Profile
Assessment of the compaction behavior of
materials is done by force-displacement profile.
Force-displacement profile can be used to
determine the behavior of plastic and elastic
materials.
Stress relaxation is observed to be minimal in
case of plastic deformation; where as materials
that undergoes elastic deformation tend to
relax to a greater extent during and/or after
compression.
At a given fmax the displacement area of plastic
deformation is more when compared to the
displacement area of elastic deformation.
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22. Die Wall Force Profile
During tableting, friction arises b/w the material and the die wall which is called Die
wall force friction.
The die wall force reaches maximum just after the maximum upper and lower force,
and a constant residual value after upper and lower forces become zero.
The high die wall force during ejection is a sign of adhesion of powders to the die.
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23. Applications
• These can be used to monitor compaction cycle.
• Compaction profiles give a good assessment of the elastic
component of the powder.
• Provides information regarding the radial transmission of applied
force to the die wall.
• Helps in calculating possible ejection force and lubricant
requirements.
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24. SOLUBILITY
• Solubility can be defined as spontaneous interactions of two or more substances
to form homogenous molecular dispersion.
Or
• Concentration of Solute in a saturated solution at constant temperature.
 Importance of Solubility:
• Therapeutic effectiveness of the drug depends on bioavailability of the drug and
hence it ultimately depends on the solubility.
• Important to achieve desired concentration of drug molecule into the systemic
circulation.
• Important in respect to the preformulation studies.
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25. REFRENCES
• Sarsvat Patel and Arvind Bansal Compression Physics in the Formulation Development of Tablets,
Critical Reviews in Therapeutic Drug Carrier Systems, February 2006.
• Lachman, L. liberman, H. A. and kanig, Compression and Consolidation, The Theory and Practice of
industrial Pharmacy, J.L.;2009; Page No. 66- 99.
• CVS Subramanyam, Textbook of Physical pharmaceutics, Page No. 224- 227.
• Michael E. Aulton, Aulton’s Pharmaceutics The design and manufacture of medicines, Third Edition
Page No. 478,443,468-473,355-358.
• Banker GS, Anderson NR. Tablets, In: Lachman L, Liberman HA, Kanig JL, editors. The Theory and
Practice of Industrial Pharmacy, 3rd ed., Bombay, Varghese Publishing, 1976.
• Marshall K. Compression and consolidation of powdered solids, In: Lachman L, Lieberman HA, Kanig
JL, editors. The Theory and Practice of Industrial Pharmacy, 3rd ed. Bombay, Varghese Publishing,
1987.
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