2. Contents
• Definition of compression, compaction and consolidation.
• Physics of tablet compression.
• Process of tablet compression.
• Compaction equations.
• Forces involved in compression.
• Effect of friction.
• Distribution of force.
• Compaction profile .
• Solubility enhancement technique.
3.
4. Compression : compression means reduction in bulk volume of a
material as a result of the removal of gaseous phase (air) by applies
pressure .
Consolidation : Consolidation is increase in mechanical strength of
material resulting from particle-particle interaction
Compaction : Compaction of powder is term is used to describe in
which materials are subjected to some level of mechanical force
Compaction = compression+ consolidation
5.
6. Physics of tablet compression
1. Transitional repacking Or Particle rearrangement.
2. Deformation .
3. Fragmentation.
4. Bonding.
5. Deformation of solid body.
6. Ejection .
8. Process of tablet compression :
1.Transitional Repacking Or Particle rearrangement:
• When a particle is compressed initially the particles are rearranged
under low compaction to form a closer packaging structure.
• The finer particle enter the voids between larger one give a closer
packaging structure.
• In this process the energy is evolved as a result of inter particulate
friction and their is an increase in amount of particle surface area
capable of forming inter particulate bonds .
9.
10. 2. Deformation
• When particle of granules are closely packed that no further filing of
voids can occur , a further increase in the compression force cause
deformation at that point of contact.
• Change in shape of material occurs, At certain points the packing
characteristics of the particle reduced space or porosity of inter
particulate friction will prevent further rearrangement of particles.
• At this point further reduction in compact volume results in elastic or
plastic deformation.
11. 3. Fragmentation
• As compression increase deform particles start fragmentation due to
high load, particle breaks into small fragments leading to formation of
new bonding areas.
• The fragments undergo densification with infiltration of small
fragments in voids.
• Some particles undergo structural breakdown called as brittle fracture.
12. 4. Bonding
• Bonding occurs through various mechanisms such as inter particulate
forces like Van der Waals forces, hydrogen bonding, and electrostatic
interactions, as well as through the use of binders or excipients that
facilitate adhesion between particles.
• The process aims to create tablets with sufficient mechanical strength
and integrity for their intended use.
5. Deformation of solid bodies
• In tablet compression, solid bodies undergo deformation due to the
applied pressure.
• This deformation includes elastic deformation, where particles
temporarily change shape but return to their original form once the
pressure is released
13. • Plastic deformation, where particles permanently change shape due
to the applied pressure.
• The degree of deformation affects the tablet’s final properties such as
hardness, thickness, and friability
14. 6. Ejection
• Ejection in tablet compression refers to the process of removing the
formed tablets from the die cavity after compression.
• It’s typically achieved using an ejection mechanism, which can
involve the use of upper and lower punches, as well as specialized
ejector pins or cams within the tablet press.
• Proper ejection is important to ensure the tablets are released
smoothly without damage or sticking to the die cavities,
15. Compaction Equations
1. Heckel Equation: The Heckel equation relates the logarithm of the
relative density (1 – V/Vo, where V is the volume under pressure and
V0 is the initial volume) to the applied pressure in the compaction
process.
It’s expressed as: ln(1/(1 – V/V0)) = K * P
where: ln is the natural logarithm
• V is the volume under pressure
• V0 is the initial volume
• P is the applied pressure
• K is the Heckel constant.
16. 2. Kawakita Equation.
Yield asis of kawakita equation for powder compression is that the
particles are subjected to compressive load in equilibrium at all stages of
compression , so that the product term and volume term is constant .
Pa/C= 1/ab + Pa/a
Where
Pa = applied pressure
a = degree of reduction for bed particles
b = constant inversely proportional to yield strength
C= degree of volume reduction.
17. Forces involved in tablet compression
1. Friction force.
• Inter particulate friction.
• Die wall friction.
2. Distribution force
3. Ejection force
4. Radial force
18. Inter particulate friction :
• Inter particulate friction refers to the resistance encountered
between individual particles within a powder mixture when they
slide or move past each other.
• It’s a result of various factors such as particle shape, size, surface
roughness, and the presence of any lubricants or binders.
• High inter particulate friction can lead to poor powder flow
properties, uneven tablet weight distribution, and difficulty in
achieving the desired tablet hardness during compression.
19. Die wall friction :
• Die-wall friction refers to the resistance encountered by the tablet
formulation as it moves along the walls of the die during the
compression process.
• High die-wall friction can lead to issues such as sticking of the
formulation to the die walls, uneven tablet weight, and variations in
tablet hardness.
• To minimize die-wall friction, tablet manufacturers may use
techniques such as incorporating lubricants into the formulation,
modifying the surface properties of the die.
20. Ejection force:
• Ejection force refers to the force required to eject a formed tablet from
the die cavity once the compression process is complete.
• It’s influenced by factors such as the friction between the tablet and
the die walls, the elasticity of the material, and the design of the tablet
press.
• Controlling ejection force is important to ensure smooth and consistent
tablet ejection without damaging the tablets or the press equipment.
21. Radial force :
• Radial force in tablet compression refers to the force exerted
outwardly by the compressed material against the walls of the die
cavity.
• This force is essential for maintaining the integrity and shape of the
tablet during the compression process.
• Controlling radial force is crucial for achieving uniform tablet weight,
thickness, and hardness.
• It’s influenced by factors such as the properties of the tablet
formulation, the design of the die, and the compression force applied
during the process.
22. Effect of Friction
There are mainly two effects of frictional forces:
1. Effect on Inter particulate friction
2. Effect of die-wall friction
1. Effect on Inter particulate friction forces occur due to particle-
particle contact and it is more significant at low applied load.
These forces are reduced by using glidants.
▪ It is expressed in terms of co-efficient of inter particulate friction.
▪ It is denoted by µ1.
▪ Eg; colloidal silica.
23. 2.Effect of die-wall friction occur from material pressed against die
wall and moved it is dominant at high applied load the particle
rearrangement has ceased and particularly important in tablet
operations.
▪ It is expressed as µw.
▪ Most of the tablet contains the common additive to reduce the die-wall
friction such additives are known as lubricants.
▪ Eg: talc and magnesium stearate.
24. Distribution of forces
• It is carried out on single-station presses or even an isolated punch and
die sets in conjunction with hydraulic press.
▪ When the force is being applied to the top of the cylindric powder
mass. The distribution of the force takes place which is commonly
explained by the basic relationships.
▪ Since there must be an axial (vertical) balance of forces.
▪ Fa= FL + FD.
▪ Where, FA is the force applied to greater punch. ▪ FL proportion
transmitted to lower punch.
▪ FD is a reaction at die wall due to friction at this surface.
25. ▪ Because of this inherent difference between the force applied at the
upper punch and that affecting material close to lower punch, a mean
compaction force, F has been proposed.
Where, FM = FA + FL/2
▪ FM is the friction-independent measure of compaction load.
▪ In single-station presses, where the applied force transmission decays
exponentially.
26. Compaction profile
• Compaction profiles are hysteresis curve that establish the relationship
between the axial pressure and radial pressure.
• In compaction cycle two forces are considered.
• Axial force :
This is vertical component applied by the upper puch during
compression.
• Radial force :
This the horizontal component observed in the die wall, when
powder mass attempt to in the die wall.
27.
28. • Compression phase :
• OA – Repacking of powders or granules
• AB- Represent elastic deformation which continues upto B
• BC – Represent plastic deformation and brittle fracture and point C
indicates maximum compression force.
• Decompression phase:
• CD – Represent elastic recovery.
• DE – Represent recovery from plastic deformation.
• E- Represent residual force, hold compact on die Sides .
• Ejection force must be greater than residual force.
30. Micronization
• In micronization the solubility of drug is often intrinsically related to
drug particle size.
• By reducing the particle size, the increased surface area improves the
dissolution properties of the drug
• Micronization increases the dissolution rate of drugs through increased
surface area, it does not increase equilibrium solubility.
• Micronization of drugs is done by milling techniques using jet mill,
rotor stator colloid mills etc
31. Polymorphs
• It is possible to prepare crystals with different packing arrangement;
such crystals are called polymorphs.
• As a result, polymorphs for the same drug may differ in their
physicochemical properties such as solubility, dissolution rate, melting
point, and stability.
• Most drugs exhibit structural polymorphism and it is preferable to
develop the most thermodynamically stable polymorph of the drug to
assure reproducible bioavailability of the product over its shelf-life
under a variety of real-world storage conditions.
32. Solid solution
• Solid solutions are generally made by the “melt method” or the
“solution method” .
• In the solution method, API and excipients are co-dissolved in a
solvent, which is then removed to form the dosage form.
• Two components crystallize together in a homogeneous one phase
system, because of reduction in particle size to the molecular level
solid solution shows greater aqueous solubility.
• E.g., Griseofulvin from such solid solution dissolves 6-7 times faster
than pure form.
33. Previously asked questions
1. Explain fundamental principle involved in compression and
compaction of material.
2. Describe the various factors affecting the compression of tablet.
3. Explain various solubility enhancement technique.
