Physics of tablet compression

Physics of Tablet compression is very useful during study of the tablet. It contains the mechanism of tablet compression. It also contains the process of tablet compression.

1. Prepared By
Mr. M. D. Birajdar
M. Pharm First Year
Physics Of Tablet Compression
Guided By
Mr. Chate sir
Assistant Professor
School of pharmacy , Srtmu, nanded (mh)

2. CONTENTS
1.Introduction
2.Compression
3.Consolidation
4.Compaction
5.Process of compression
6.Forces involved in Compression
7.References

3. Definitions
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 an increase in the mechanical strength of a material
resulting from particle-particle interactions.
Compaction
Compaction of powders is the general term used to describe the situation in
which these materials are subjected to some level of mechanical force.
The physics of compaction may be simply stated as "the compression and
consolidation of a two-phase (particulate solid-gas) system due to the
applied force."

5. ConsolidationConsolidation
An increase in the mechanical strength of the material resulting from
particle or particle interaction. (Increasing in mechanical strength of the
mass)
Consolidation Process
Cold welding: When the surface of two particles approach each other
closely enough, (e.g. at separation of less than 50nm) their free surface
energies result in strong attractive force, this process known as cold
welding.
Fusion bonding: Contacts of particles at multiple points upon application
of load, produces heat which causes fusion or melting. If this heat is not
dissipated, the local rise in temperature could be sufficient to cause melting
of the contact area of the particles.
Upon removal of load it gets solidified giving rise to fusion bonding &
increase the mechanical strength of mass.

6. .
The process of compression.
REMOVAL OF PRESSURE

7. 
Transitional repacking/particle rearrangement.

8. Deformation
•The force required to initiate a plastic deformation is called as yield stress
or elastic limit.

10. Fragmentation and deformation.
Fragmentation do not occur when applied stress-
 is balanced by a plastic deformation.
change in shape.
sliding of groups of particle (viscoelastic flow).

11. After fragmentation of the particles, as the pressure increases, formation of new
bonds between the particles at the contact area occurs. The hypothesis favouring for
the increasing mechanical strength of a bed of powder when subjected to rising
compressive forces can be explained by the following theory.
Bonding Mechanism
There are three theories about the bonding of particles in the tablet by compression
I.Mechanical theory
II.Intermolecular force theory
III.Liquid-Film surface theory
The mechanical theory
It occurs between irregularly shaped particles.
The mechanical theory proposes that, under pressure the individual particles undergo
Elastic / Plastic deformation and the particle boundaries that the edges of the particle
intermesh forming a mechanical Bond.
Mechanical interlocking is not a major mechanism of bonding in pharmaceutical
tableting.
Bonding Of ParticlesBonding Of Particles

12. The Molecules at the surface of solids have unsatisfied forces which
interact with the other particle in true contact.

According to this theory, under compressional pressure the molecules at
the points of true contact between new clean surfaces of the granules are
close enough so that vanderwaals forces interact to consolidate the
particles.
Material containing plenty OH group may also create hydrogen bond
between molecules. E.g. microcrystalline cellulose is believed to undergo
significant hydrogen bonding during tablet compression
The intermolecular forces theory and the liquid-surface film theory are
believed to be the major bonding mechanisms in tablet compression
Intermolecular force theoryIntermolecular force theory

13. Ejection.
Portion under strain caps strain > shear strength.

14. 
3 stages of force necessary to eject a finished table,
1. Peak force required to initiate ejection.
2. Small force required to push tablet up to die- wall .
3. Decline force as tablet emerge from die.

15. Various Forces involved in CompressionVarious Forces involved in Compression
1. Frictional Forces
2.Distribution Forces
3.Radial Forces
4.Ejection Forces
Frictional Forces: are interparticulate friction & Die wall Friction.
reduced Glidants Lubricants
E.g. Colloidal silica E.g. Mag. 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.

16. References:-
Keith marshall 1987,Compression and consolidation of powderd solids,
Leon lachman, Herbert a.Liberman, & Joseph kanig ,The theory and
practice of industrial pharmacy, third edition varghese publication
house,bombay, pp.66,68,70-88.
Eugene parrott , 2007,Compression,Herbert A.Liberman, Leon
Lachman & Joseph B.Schwartz ,Pharmaceutical dosage forms, tablets,
volume ii,pp.201-241.
Stanforth J.N, Aulton’s pharmaceutics the design and manufacturing
of medicine,third edition, Churchill livingstone elsevier,pp.176,177.
Subrahmanyam C.V. ,Micromeritics, Textbook Of Physical
Pharmaceutics, Second Edition,vallabh prakashan,delhi,Pp-180-234.
Gilbert S. Banker , Christopher T. Rhodes, Modern
Pharmaceutics , Fourth Edition.Pp.408-409.
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