3. COMPRESSION
the reduction in the bulk volume of a material as a result of
the removal of the gaseous phase (air) by applied pressure
CONSOLIDATION
Involves an increase in the mechanical strength of a material
resulting from particle-particle interactions.
COMPACTION
The compression and consolidation of a 2 phase (solid +
gas) system due to an applied force.
4. FUNDAMENTALS OF POWDER COMPRESSION
Attractive forces exist between particles vander Waal’s, H-bonding,
Electrostatic consider a number of granules in a die to which a force is
applied
5. DERIVED PARAMATERS
• solid-air interface,
• angle of repose,
• mass volume relationship,
• volume
• density,
• compressibilty
6. Solid-air interface
Cohesion is the attraction between like particle; Experienced by
particles in bulk.
Adhesion is the attraction between unlike particle; Experienced by
particles at surface.
7. Angle of repose
The maximum angle possible between the surface of pile of non-cohesive
(free-flowing) material and the horizontal plane.
Angle of repose is an indication of the flow ability of
the material.
8. Angle of Repose (θ)
θ = tan-1(h/r)
where
h = height of pile
r = radius of the base of the pile
h
Excellent flow ability if θ < 25o
Good flowability if 25o < θ < 30o
Passable flowability if 30o < θ < 40o
Very poor flowability if θ > 40o
r
9. Mass-Volume relationships
VOLUME
1. Open intraparticulate voids-those with in a single
particle but open to the external environment.
2. closed interparticulate voids-those within a single
particle but closed to the external environment.
3. Interparticulate voids-the air spaces between
individual particles.
• True volume (VT)
• Granule volume (VG)
• Bulk volume (VB)
• Relative volume (VR)
VR = VB / VT
VR tends to become unity as all air is eliminated from the mass during the
compression process.
10. DENSITY:
The ratio of mass to volume is known as the density of the material
Types of Density:
• True density (ρT = M / VT )
• Granule density (ρG = M / VG )
• Bulk density (ρB = M / VB)
• Relative density (ρR = M / VR)
M is the mass of powder
11. Compressibility:
The ability of the powder bed to be compressed (under
pressure) and consequently be reduced in volume.
Measuring Compressibility:
Carr’s (Compressibility) Index
= [(VB – VTap) / VB] x 100 ≈ E
where
VB = Freely settled volume of a given mass of powder
VTap = Tapped volume of the same mass of powder ≈ VT
Carr’s (Compressibility) Index
= [(ρTap – ρB) / ρTap] x 100 ≈ E
where
ρB = Freely settled bulk density of the powder
ρTap = Tapped bulk density of the powder ≈ ρT
12. Measuring Compressibility
Excellent flowability if 5 < Carr’s Index < 15
good flowability if 12 < Carr’s Index < 16
Passable flowability if 18 < Carr’s Index < 21
poor flowability if 23 < Carr’s Index < 35
Very poor flowability if 33 < Carr’s Index < 38
Very very poor flowability if Carr’s Index > 40
16. COMPRESSION MACHINES
Components of compression machines
• Hopper for holding and feeding granulation to be compressed
• Dies that define the size and shape of the tablet
• Punches for compressing the granulation within the dies
• Cam tracks for guiding the movement of the punches
• Feeding mechanisms for moving granulation from the
hopper into the dies
20. Reference
Adolfsson, Å., Caramella, C., Nyström, C., 1998. The effect of
milling and addition of dry binder on the interparticulate bonding
mechanisms in sodium chloride tablets. Int.J. Pharm. 160, 187-195.
Adolfsson, Å., Gustafsson, C., Nyström, C., 1999. Use of tablet
tensile strength adjusted for surface area and mean interparticulate
distance to evaluate dominating bonding mechanisms. Drug Dev.
Ind. Pharm. 25, 753-764.
Adolfsson, Å., Nyström, C., 1996. Tablet strength, porosity,
elasticity and solid state structure of tablets compressed at high
loads. Int. J. Pharm. 132, 95-106.