Compression and compaction

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Department of Pharmacy (Pharmaceutics) | Sagar savale
04/21/16 Sagar KiShor Savale

CONTENTS.
Definition.
Inherent properties of powder solids.
Solid air interface.
Angle of repose and flow rates.
Mass volume relationship.
Process of compression.

Die wall lubricant.
Force and volume relationship.
Heckel plot and kawatika equation.
Compaction profile.
Energy expenditure.
Measurement of energy.
 transmission of force.
 force displacement curve.
Strength of tablet and its estimation.
References.

WHAT IS COMPRESSION ?
Compression means reduction of bulk volume of
material as a result of the removal of gaseous
phase (air) by applied pressure
WHAT IS CONSOLIDATION?
Consolidation is an increase in mechanical
strength of material resulting from particle -
particle interactions.

WHAT IS COMPACTION ?
The compression and consolidation of a two
phase (solid + gas) system due to an applied
force, resulting in the formation of a compact
but porous mass of definite geometry.
Compaction =compression + consolidation
of two phases (solid-gas) on
application of force.

Inherent properties of
powder solids
Solid –air interfaces.
Angle of repose.
Fixed funnel and free standing cone method.
Tilting box method.
Revolving cylinder method.
Mass –volume relationships.
Methods to mesure volume of powder.
 Helium pycnometer
 Liquid displacement method (specific gravity
bottle method

7
Angle of repose.
The maximum angle possible
between the surface of pile of
the powder and the horizontal
plane. (also called as Dynamic angle)

8
METHODS TO MEASURE
ANGLE OF REPOSE.
a.Fixed funnel and free standing cone method.
b.Tilting box method.
c.Revolving cylinder method

9
FORMULA FOR MEASURING
ANGLE OF REPOSE
1. θ = Tan-1
(h/r)
here, h =height of pile
r = radius of the base of
the pile
θ = angle of repose.
2. θ = cos-1
D/ (l1+l2)
here, D = diameter of base
l1+l2 = the opposite sides
Angle of
repose
Flow
property of
powder
<25
25-30
Excellent
Good
30-40 Passable
>40 poor

10
CONSOLIDATION
INDEX (Carr, % )
FLOW
5-15 EXCELLENT
12-16 GOOD
18-21 FAIR TO PASSABLE
23-35 POOR
33-38 VERY POOR
>40 VERY VERY POOR

11
MASS-VOLUME RELATIONSHIPS.
TYPE OF VOIDS OR AIR SPACES:
 Open intraparticulate voids-
 Closed intraparticulate voids-
 Interparticulate voids-
11
Fig:- types of voids and air
spaces.

METHODS TO MEASURE
VOLUME OF POWDER.
 Helium pycnometer
 Liquid displacement method (specific gravity bottle
method)
HELIUM PYCNOMETER
Vt = Vc/U1-U2x[U1-Us]
Vt = true volume of sample.
Vc =true volume of stainless steel spheres.
U1=Volume of empty cell.
U1-U2=Volume occupied by the std. sample.
U1-Us = volume occupied by sample.

13
Helium pycnometer.

Liquid displacement method.
Solvent used are ---e.g., ethyl alcohol ,water,
mercury , etc.
Pycnometer or specific gravity bottle used.
True density= w3/(w4-w2) = (w2-w1)/(w4-w2)
w1 = wt. of Pycnometer
w2 = Wt. of Pycnometer +sample or glass
beads
w4 = Wt. ofPycnometerwith powder & filled with
solvent
w3=w2-w1=Wt. of sample
w4-w2=Volume of liquid displaced by the solid

15
specific gravity bottle

Tablet Press Machine

.
17
The process of compression.
17
REMOVAL OF PRESSURE

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

Effects of compression force.
19
INITIALLY
REPACKING
DEFORMATION

Transitional repacking/particle
rearrangement.

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).

22
If, only elastic deformation occurs –
Under nonisostatic conditions-
Uniaxial
relaxation

Ejection.
2323
Portion under strain caps strain > shear strength.

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

Compression and consolidation
under high loads.
2525
Thin layer is abrasion resistant but it –
Retards air escape during compression.
Retards the ingress of liquid media during dissolution.
punch
Die wall
tablet

Die-wall lubrication
• Best lubricant has low shear strength & strong
cohesive tendencies.
• Lubricant forms a film of low shear strength at
the interface between tabletting mass & die-wall.
2626
LUBRICANT SHEAR
STRENGTH
(M pa)
Stearic acid 1.32
Calcium stearate 1.47
Magnesium
stearate
1.96
Boric acid 7.16
graphite 7.35

Force volume relationship.
2727
FIG. Decreasing porosity with increasing
compressional force
for single ended pressing
i) initial repacking
ii) Elastic deformation
iii) Plastic deformation
iv) compression
End of compressional process is when
bulk volume = tapped volume.
porosity (E)= 0
 Decrease in porosity is due to two process:
1. Filling of large spaces by Interparticulate
Slippage.
2. Filling of small voids by deformation or
fragmentation at high loads.
 A more complex sequence of events
during compression process involves four
stage as shown in fig.,

Heckel plot.
• It follows 1st
order
The pore in the mass are the reactant.
log 1/E = KyP + Kr
E = porosity
P = Applied pressure
Ky= material dependent constant
Ky inversely proportional to it’s yield strength (S)
(Ky = 1/3S)
Kr = related to repacking stage &
hence E0
For cylindrical tablet,
P = 4F / ∏×D2
here, P = applied pressure
D = tablet diameter
F = applied compressional force

2929
E = 100×[1 – 4w/ρt ×∏×D2×H]
here, w = weight of tabletting mass.
ρt = true density.
H = thickness of tablet.
•Type a : Soft material(e.g., NaCl)
• Type b: Hard material(e.g., lactose)
• Crushing strength of tablet
is directly proportional to Ky.
APPLICATION OF HECKEL PLOT:
•Used to check lubricant efficacy.
• For interpretation of consolidation
mechanisms.
•Duberg & nystom distinguish between
plastic and elastic deformation
characteristics of a material.

Kawakita Equation.
C = Vi – Vp/ Vt = abPa / 1+ bPa
C = degree of volume reduction,
Vi = initial apparent volume,
Vp =powder volume under applied pressure Pa,
Vt = true volume,
a & b = constants.
 LIMITATION: Compaction process can be
described upto certain pressure, above which the
equation is no longer linear.

Cooper and Eaton Equation.
Vi – Vp/ Vi– Vt = C2 exp (-K2/Pa ) + C3 exp (-K3/Pa)
C2,C3, K2,K3 = constants.
 LIMITATION : Applies only to single
component analysis.

Energy expenditure.

Crushing strength.
Compression force applied diametrically to tablet.
Measured by-
o Monsanto tester.
o Pfizer tester.
o Erweka tester.
o Schleuniger tester.
o Strongcobb tester.
Fracture across granule – size of granule influence
strength
3333
Fig:- pfizer tester.

Friability.
3434
• Measures the resistance for abrasion.
Parameter indicating tablet weight loss.
F = 100 x (1 – wo/w)
0.8% -1.0% upper limit for acceptance .
Fig:- Roche
friabilater

Lamination and Capping.
Laminating-
Separation of tablet into two
or more distinct layer.
Capping –
Partial or complete separation of
top and bottom crowns of tablet
from the main body.

3636
REASONS FOR CAPPING AND
LAMINATING.

Minimizing capping and lamination.
 use of flat punch.
 use of tungsten carbide insert.
 proper set up of press.
 addition .
 use of binders.

References:-
 Keith marshall 1987,Compression and consolidation of powderd solids,
Leon lachman, Herbert a.Liberman, & Joseph kanig ,The theory and
practice of industrial pharmacy, third edition varghese publication
house,bombay, pp.66,68,70-88.
 Eugene parrott , 2007,Compression,Herbert A.Liberman, Leon Lachman &
Joseph B.Schwartz ,Pharmaceutical dosage forms, tablets, volume
ii,pp.201-241.
 Stanforth J.N,Aulton’s pharmaceutics the design and manufacturing of
medicine,third edition,Churchill livingstone elsevier,pp.176,177.
 Subrahmanyam C.V. ,Micromeritics, Textbook Of Physical
Pharmaceutics, Second Edition,vallabh prakashan,delhi,Pp-180-234.
 Gilbert S. Banker , Christopher T. Rhodes, Modern
Pharmaceutics , Fourth Edition.Pp.408-409.
 encyclopedia of pharmaceutical Technology, Second Edition,volume-
3.Pp.303-305

Thank YouThank You

Compression and compaction

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