Physics of tablet compression (compression & compaction)

compression & compaction

1. PHYSICS OF TABLET COMPRESSION Presented By- ROHIT R.K.S.D college of pharmacy, Kaithal ( Hry ) M.Pharma 1 st year (Pharmaceutics)

2. C O N TE N T S Introduction Compression Consolidation Compaction Process of compression Forces involved in Compression 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 C o nsoli d a ti o n i s a n i n c r e a s e i n th e m e ch a n i ca l s tr e n gth of a m a t e ri a l 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."

4. Consolidation 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.

5. . The process of compression. REMOVAL OF PRESSURE

6.  Transitional repacking/particle rearrangement .

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

8.  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).

9. 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 Mechanical theory 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 Particles

10. 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 theory

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

12.  3 stages of force necessary to eject a finished table, Peak force required to initiate ejection. Small force required to push tablet up to die- wall . Decline force as tablet emerge from die.

13. Various Forces involved in Compression Frictional Forces Distribution Forces Radial Forces 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.