Compression : It is reduction in bulk volume of the material as a result of displacement of gaseous phase (entrapped air). When external force is applied to powder mass there is reduction in bulk volume. The onset of loading is associated with closed repacking of a powder mass followed by deformation.

1. PHYSICS OF TABLET
COMPRESSION
Dr. V. S. Kashikar
Asso. Prof., Head, Dept. of Pharmaceutics
PES Modern College of Pharmacy ( for ladies), Moshi Pune 412 105

2. Compression : It is reduction in bulk
volume of the material as a result of
displacement of gaseous phase
(entrapped air). When external force is
applied to powder mass there is
reduction in bulk volume. The onset of
loading is associated with closed

3. Physics of tablet compression, machines
and equipments
When external mechanical forces applied
to a powder mass there is reduction in
bulk volume as follows
– Repacking
– Particles deformation
• Elastic deformation-e.g. acetyl salicylic acid, MCC
• Plastic deformation-at yield point of elastic.
– Brittle fracture – e.g. sucrose
– Microquashing-irrespective of larger particles,
smaller particles may deform plastically.

4. Repacking : With the application of
external force (load) particle rearrange
themselves in a void spaces and
repacked, leads to volume reduction. As
the pressure increases rearrange became
difficult causing particle deformation.

5. Deformation : When powdered mass is subjected to
pressure, there is finite change in geometry
depend upon intensive operation.
 Elastic Deformation : If on removal of load the
powdered mass spontaneously reversed back to
its original form then it is called elastic
deformation.
Plastic Deformation : After exceeding the elastic
limit of material (yield value) the deformation may
become plastic.
Brittle Fracture : Upon exceeding the plastic limit,
particle undergoes brittle fracture if the shear
strength is greater than the tensile / breaking
strength here, large particle broken into smaller
particles with filled void spaces.
Micro-Squashing : Irrespective of behavior of

6. A] Effect of compression force on the
properties of tablet compressed: The
force exerted by the top punch affect
physical properties of compressed tablet,
so hardness, disintegration time, apparent
density increases with the increase in
compression force.

7. Generally, internal surface area increases
with increasing compression force. This
initial increase is due to fragmentation of
granules at relatively low compression
force. When compression force is further
increase; rebonding takes leads to
decrease in free internal surface.

8. B] Effect of lubricant on transmission of forces: If we
used water to fill a dye, then the force exerted by the top
punches will be transmitted unchanged to the bottom punch,
as fluid exerts equal pressure in all directions.
When granules / powder are compressed in a dye there is an
attenuation of transmitted force largely due to friction among
granules and dye wall. Lower punch experiences reduced
pressure. Dye wall friction can be minimized by adding
lubricants. The perfect lubricant, which equalizes top and
bottom punch force do not exist. So R value is used to
measure lubricant efficiency.
R = Lower punch force/Upper punch force.

9. C] Pressure distribution within the
granule/ powdered mass: Generally high
pressure areas exist near top and centre
of the component. High pressures near the
tops sometime result in elastic
compression. Low pressure areas exist at
the bottom and sides of compact. Highly
compressed core, near the centre of the

10. REFERENCES
Cooper and Gunn’s Tutorial pharmacy