Physics of compaction & compression

1. PHYSICS OF TABLET
COMPRESSION
Presented By:
Mahewash A Pathan

2. Contents:
 Introduction
 Compaction
 Compression
 Consolidation
 Stages of compression
 Forces involved in compression
 Compaction profiles
 Compaction equations
 Conclusion
 references
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3. INTRODUCTION
 Tablets constitutes about 70-80% of all pharmaceutical dosage
forms.
 Processes:
1. wet granulation
2. Dry granulation
3. Direct compression
 Compaction represents one of the most important unit operations
in the pharmaceutical industry.
 compaction is the situation in which the materials are subjected
to some level of mechanical forces.
 The physics of compaction may be stated as the compression &
consolidation of two phase system due to the applied force.
 Invention of tabletting machine : in 1843 by William Brockedon.
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4. Properties of powders:
a) Surface properties
b) Porosity
c) Flow properties:
i. Angle of repose
ii. Carr’s index
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5.  Compression:
Compression means a reduction in the bulk
volume of a material as a result of the removal of the
gaseous phase(air) by applied pressure.
 Consolidation:
Consolidation is defined as an increase in
the mechanical strength of a material resulting from
particle-particle interactions.
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6.  Compaction:
Compaction of powders is the term used to
describe the situation in which the materials are
subjected to some level of mechanical forces.
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7. Compression
 When some external forces applied on the powder reduction in the
bulk volume of the powder.
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8.  Stages involved are:
1. Transitional repacking/ Particle rearrangement
2. Deformation at points of contact
3. Fragmentation
4. Bonding
5. Removal of pressure
6. Deformation of solid bonding
7. Decompression
8. ejection
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9. 1.Particle Rearrangement
 Particles are rearranged under compaction pressure to
form a closer packing structure. The finer particles enter
the voids between the larger ones & give a closer packing
arrangement.
 The energy is evolved as a result of interparticulate
friction & there is an increase in amount of particle
surface area capable of forming interparticulate bonds.
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10. 2.Deformation:
3.Fragmentation:
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11. 4. Bonding:
 After fragmentation of particles, as the pressure
increases, formation of new bonds between the
particles at the contact area occurs.
 There are 3 theories about bonding of particles in the
tablet by compression
1) Mechanical theory
2) Intermolecular force theory
3) Liquid surface film theory
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12. 5. Deformation:
 Change in geometry of solid body. Deformation
produced by force of Tensile strain, Compressive
strain ,Shear strain.Two types of deformations :
1. Elastic deformation
Ex:- Acetyl salicylic acid, MCC.
2. Plastic deformation
Ex:- sucrose
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13. 6. Decompression:
 The success & failure of intact tablet depends on
stress induced by elastic rebound & the associated
deformation produced during compression &
ejection.
 As the upper punch is withdrawn from the die the
tablet is confined in die cavity by radial pressure
consequently any radial change during
decompression must occur in axial direction.
 Thus capping is due to unaxial relaxation in die
cavity at the point where punch pressure is
released & some may occur at ejection.
 If decompression occurs in all directions
simultaneously capping is reduced.
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14. 7. Ejection
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15. Forces involved in compression
1. Frictional forces
a. Interparticulate friction; reduced by adding glidants.
b. Die wall friction; reduced by adding lubricants.
2. Radial forces
3. Ejection force; the force necessary to eject a finished
tablet.
4. Distribution forces
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16. Consolidation:
 Increase in mechanical strength of the mass.
 Consolidation process-
Cold welding: When surface of two particles approach each
other (<50 nm), their free surface energies result in a strong
attractive forces.
Fusion bonding: contacts of particles at multiple points upon
application of load, produces heat which causes fusion or
melting. Upon removal of load it gets solidified giving rise to
fusion bonding & increase in mechanical strength.
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17. Compaction profiles
1. Force-Time profile:
 Compression phase,
 dwell phase,
 decompression phase.
 Consolidation time
 Dwell time
 Contact time
 Peak offset time (toff)
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18. 2. Force-displacement profile:
NWC = GWC – WER
GWC = Wf + Wp + We
Work of elastic relaxation=WER
net work of compaction=WOC
Wf=work of fragmentation
Wp=work of plastic deformation
We= work of elastic deformation
GWC= gross work of compaction
WER= work of elastic relaxation
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19. Compaction equations
1. Kawatika equation:
 particles are subjected to compressive load is equilibrium at
all stages of compression, so that the product of pressure
term and volume term is constant. The Kawatika equation is-
P/C = P/a + 1/ab
Where,
P = Applied pressure
C= degree of volume reduction of a powder compact.
a = total volume reduction for the powder bed ( Carr’s index)
b = constant that is inversely related to the yield strength of the
particles.
This equation holds best for soft fluffy pharmaceutical powders,
and is best used for low pressures and high porosity
situations
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20. 2. Heckel equation:
 based on the assumption that
densification of the bulk powder
under force follows first-order
kinetics.
 The Heckel equation is expressed
as
ln [1/1–D] = KP + A
where,
D = relative density of the powder
P = applied pressure
k = constant, measure of the
plasticity of a compressed material
A = constant, die filling & particle
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21.  In 1961, Heckel proposed a relationship between the
constant K and the yield strength for a range of metal
powders.
K = 1/3 σ
where, σ is the yield strength of the material. K is
inversely related to the ability of the material to deform
plastically.
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22. 3. Walker Equation:
 The Walker equation is based on the assumption that the
rate of change of pressure with respect to volume is
proportional to the pressure, thus giving a differential
equation
Log P = –L x V′ / V0 + C1
 where, V0 is the volume at zero porosity.
The relative volume is V′/V0 = V =1/D,
C1 is constant.
The coefficient L is referred to as the pressing
modulus.
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23. Conclusion
 Compression & consolidation are important in
tableting of materials.
 The importance of each will largely depend on the
type of compact required whether soft or hard & on
the brittle properties of the materials.
 Various mathematical equations have been used to
describe the compaction process.
 The particular value of heckel plot arises from their
ability to identify the predominant form of
deformation in a given sample.
 Kawakita equation is modified form of heckel’s
equation.
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24. References:
 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.
 www.wikipedia.com
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