COMPRESSION AND CONSOLIDATION

by

Namile.Shyam Prasad

M.pharm(pharmaceutics)

CONTENTS

INTRODUCTION

FUNDAMENTALS OF POWDER COMPRESSION

METHODS

COMPRESSION MACHINES

CONCLUSION

REFERENCES

DERIVED PARA METERS

COMPRESSIONthe reduction in the bulk volume of a material as a result of

the removal of the gaseous phase (air) by applied pressure

CONSOLIDATIONInvolves an increase in the mechanical strength of a material

resulting from particle-particle interactions.

COMPACTIONThe compression and consolidation of a 2 phase (solid +

gas) system due to an applied force.

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

DERIVED PARAMATERS

• solid-air interface,

• angle of repose,

• mass volume relationship,

• volume

• density,

• compressibilty

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.

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.

Angle of Repose (θ)

θ = tan-1(h/r)

where

h = height of pile

r = radius of the base of the pile

Excellent flow ability if θ < 25o

Good flowability if 25o

< θ < 30o

Passable flowability if 30o

< θ < 40o

Very poor flowability if θ > 40o

h

r

• 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.

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.

Mass-Volume relationships

• True density (ρT = M / VT )

• Granule density (ρG = M / VG )

• Bulk density (ρB = M / VB)

• Relative density (ρR = M / VR)

Types of Density:

M is the mass of powder

DENSITY:

The ratio of mass to volume is known as the density of the material

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

Measuring Compressibility:

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

Compressibility:The ability of the powder bed to be compressed (under

pressure) and consequently be reduced in volume.

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

METHODS

Direct Compression

Dry Granulation

Wet Granulation

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

Components of compression machines

Single Punch Machine

Multistation tablet press

CONCLUSION

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.

Reference