physics of tablet compression by Avinash Hamre

Physics of Tablet Compression

Presented By , Avinash Shankarrao Hamre

B . Pharm VII semSudhakarrao Naik Institute Of Pharmacy , Pusad

INTRODUCTION

COMPRESSION : Compression of Powder means

reduction in bulk volume of a material as a result of

displacement of a gaseous phase under pressure.

COMPACTION : it is defined as the Transformation of

power into coherent specimen caused by applied pressure.

MECHANISM OF TABLET COMPRESSION The process of tablet compression involves the following identifiable phases ,

1. Transsional repacking or particle rearrangement

2. Deformation .

3. Fragmentation.

4. Bonding.

5. Deformation of the solid body.

6. Ejection.

1. PARTICLE REARRANGEMENT

generally it occures at low pressures.

It depends on particle size of distribution and shape.

Reduction in relative volume of powder bed into closure

packing structures.

the granules flow with respect to each other with the finer

particles entering the void between the larger particles and the

bulk density of the granulation is increased.

As pressure increases , relative particle movement becomes

imposible , inducing deformation.

2. DEFORMATION

When the particles of the granulation are so closely packed that

no further fillings of the voids can occur , a further increase of

compression force causes deformation at the point of contact.

change in the shape of material occurs.

At a certain point , 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

result in elastic , plastic or viscoelastic deformation of

particles .

3. FRAGMENTATION

Under high pressure the deformed particles may fragment resulting in new clean surfaces that have potential bonding areas.

Fragmentation leads to further densification with the infiltration of the smaller particles in the voids.

The mechanism of fragmentation and plastic deformation are not independent because both the phenomena modify particle size distribution.

with some materials fragmentation doesn’t occurs because the stresses are released by plastic deformation.

4. BONDING OF PARTICLES :

Governed by several theories as follows -

The Mechanical Theory

The Intermolecular Theory

THE MECHANICAL THEORY:

It occures between irregularly shaped particles .

Also Increases the number of contact points Between the particles

The mechanical theory proposes that under pressure the individual particles undergo Elastic / Plastic Deformation & that the Edges of the particle intermesh deforming a mechanical Bond.

Mechanical interlocking is not a major mechanism of bonding in pharmaceutical tableting.

INTERMOLECULAR THEORY

The Molecules at surface at the surface of solids have

unsatisfied forces which interact with the other particle in

true contact

Under Pressure Molecules in true contact between new

clean surface of the granule are close enough so that

vanderwal forces interact to consolidate the particles.

Material containing plenty OH group may also creat

hydrogen bond between molecule.

5. DEFORMATION OF THE SOLID BODY

On further increases of the pressure , the non- bonded Solid is consolidated towards a limiting density by plastic/elastic deformation.

6. EJECTION

Finally as the lower punch rises and pushes the tablet upward, there is continued residual wall pressure and considerable energy May be expanded due to the die wall Friction.