Compaction andconsolidation parameters of tablet

1. COMPRESSION AND COMPACTION
Mr. Gaurav Shriram Patil
M PHARM PHARMACEUTICS
H R PATEL INSTIUTE OF PHARMACEUTICAL EDUCATION AND RESEARCH, SHIRPUR
DEPARTMENT OF PHARMACEUTICS / HRPIPER
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2. Contents
• Introduction
• Physics of Tablet Compression
• Process of Tablet Compression
• Compaction Equation
• Forces involve in compression
• Effect of friction
• Distribution of Forces
• Compaction profiles
• Solubility
• Conclusion
• References
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3. Introduction
• Tablets constitutes of almost 70-80% of the all dosage forms.
• Tablets are generally manufactured by 3 main processes.
• 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 had to taken the
properties of powder into the consideration as they are involve in the process of
the compression and compaction.
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4. • Derived properties of powder: Volume, density, porosity, Flow properties, angle of repose etc., help
in quantification of important variables.
• Definitions:
• What is Compression:
• Compression means reduction of bulk volume of material as a result of the removal of gaseous
phase (air) by applied pressure.
• What is Consolidation:
• Consolidation is an increase in mechanical strength of material resulting from particle-particle
interactions.
• What is 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.
• Compaction =compression + consolidation of two phases (solid-gas) on application of force.
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5. Physics of Tablet Compression:
• Steps involved in the compression of Tablet.
1. Transitional repacking or particle rearrangement.
2. Deformation
3. Fragmentation
4. Bonding (here removal of process)
5. Deformation of solid body
6. Ejection.
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6. Chart showing the steps and process behind the tablet compression
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7. Process of Tablet Compression:
1. Transitional Repacking or Particle rearrangement:
• When a powder is compressed initially the particles are rearranged under low compaction pressures
to form a closer packing structure.
• The finer 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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8. 2. 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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9. 3.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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10. 4.Bonding of Particles:
• 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.
• 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.
• The Mechanical Theory: It occurs between irregularly shape particles and increase no
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. 5. Deformation of the 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.
6. 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.
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12. Compaction Equations:
1.Heckel equation: The Heckel equation is based on the assumption that
densification of the bulk powder under force follows first-order kinetics.
• The Heckel equation is expressed as; In [1/1-D] = KP +A
• Where, D is the relative density of the tablet (the ratio of tablet density to true
density of powder) at applied pressure P, and K is the slope of straight line
portion of the Heckel plot.
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13. 2.Kawakita equation: The basis for Kawakita equation for powder compression is
that the particles are subjected to compressive load in equilibrium at all stages of
compression, so that the product of pressure term and volume term is constant.
• Pa/C = 1/ab +Pa/a
Where,
Pa= Applied pressure,
a= degree of volume of reduction for bed particles.
b= Constant inversely proportional to yield strength.
C= Degree of Volume of reduction.
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14. 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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15. 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. Eg. Waxes, Stearic acid, PEG.
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16. Distribution of Forces
• Distribution Force:
• The fundamentals of tableting have been carried out on single station
press or even on isolated punch or punch with hydraulic press.
• When the force is being applied to top of cylindrical powder mass, the
following basic relationship is applies, since there must be an axial
balance of forces.
• FA=FL+FD Where,
• FA= Force applied to upper punch and FD= force transmitted to lower
punch & FD= Reaction at die wall due friction at surface.
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17. 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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18. • Compression phase:
• OA- Repacking of powder or granules.
• AB- Represent elastic deformation which continues upto B
• BC- It represent plastic deformation and brittle fracture and point C indicates maximum
compression force.
• Decompression Phase:
• CD- Represent elastic recovery.
• DE- Represent recovery from plastic deformation.
• E- Represent residual force, hold compact in die sides.
• Ejection force must be greater than residual force.
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19. • How they are measured:
• It is analysed by the compaction simulators, these are attached to the
which collect or measure the data from the forces on punches,
displacement of punches, die wall friction, ejection force, and temp
change.
• Types of compaction profiles:
1. Force- time profile
2. Force displacement profile
3. Die wall force profile
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20. Applications of compaction profiles
• These can be used to monitor the compaction cycle.
• Provide information regarding the radial transmission of applied force
to the die wall.
• Helps in calculating ejection force and lubricant requirements.
• Compaction profiles give good assessment of elastic component of the
powder.
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21. 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 is depends on bioavailability of the drug and
hence it ultimately depends on the solubility.
• Imp to achieve desired concentration of drug molecule into the systemic
circulation.
• Important in respect to the preformulation studies.
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22. Conclusion
• Compaction and compression are an integral processes for the
manufacture of tablets, and it is pertinent to understand the underlying
physics of compaction.
• Complete understanding of compaction physics still eludes us, many
variables such as inherent deformation behaviour of drugs/excipients,
solid state properties, and process parameters are known to affect the
final attributes of tablets.
• Various mathematical equations have been used to describe the
process of compaction are played integral role in overall process.
• Check out this short and simple video of tablet compression here
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23. References
• 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.
• Images an Video: Source Google and Wikipedia.
• Textbook of the theory and practice of industrial pharmacy by
Lachman.
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