1 Compression and consolidation of powder solids. Presented by
PAYAL H. PATIL (M.pharm 1st yr.)
Dept. of pharmaceutics and Q.A
R.C.Patel Institute of Pharmaceutical Education and Research, Shirpur. 1

Contents :

2 Contents DEFINATIONS
DERIVED PROPERTIES OF POWDERED SOLID
EFFECT OF APPLIED FORCES ON COMPRESSION
GRANULATION
COMPRESSION & CONSOLIDATION UNDER HIGH LOAD
FORCE VOLUME RELATIONSHIP
HECKEL PLOT
KAWAKITA EQUATION
COOPER & EATON EQUATION
DECOMPRESSION
COMPACTION PROFILE
ENERGY OF COMPRESSION
REFERENCES 2

Definitions :

3 Definitions Compression- Compression means
reduction of bulk volume of material as a
result of displacement of gaseous phase.
Consolidation – Consolidation is an increase
in mechanical strength of material from
particle - particle interactions. 3

Derived properties of powdered solids :

4 Derived properties of powdered solids The solid-air interface
Angle of repose
Flow rates
Mass-volume relationships
Density 4

THE SOLID-AIR INTERFACE :

5 THE SOLID-AIR INTERFACE COHESION:
Attraction between like
particle.Experienced by
particles in bulk.
ADHESION:
Attraction between unlike
particle.Experienced
by particles at surface.
Resistance to movement of particles is affected by two factors:-
a) Electrostatic forces.
b)Adsorbed layer of moisture on particles. 5

ANGLE OF REPOSE :

6 ANGLE OF REPOSE DEFINITION:
The maximum angle possible between the surface of pile of the powder and the horizontal plane. 6

METHODS TO MEASURE ANGLE OF REPOSE :

7 METHODS TO MEASURE ANGLE OF REPOSE Fixed funnel and free standing cone method.
Tilting box method.
Revolving cylinder method. Wall is lined by sandpaper 7

Formula for measuring angle of repose. :

8 Formula for measuring angle of repose. 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
of pile Adding glidant,0.2% aerosil may improve flow. 8

FLOW RATES :

9 FLOW RATES Compressibility index (Carr's consolidation index)
I = [1-v/vo]x100
here, V = Tapped Volume
V0 = Volume before
tapping Adding glidant,0.2% aerosil may improve flow. 9

MASS-VOLUME RELATIONSHIPS :

10 MASS-VOLUME RELATIONSHIPS TYPE OF VOIDS OR AIR SPACES:
Open intraparticulate voids
Closed intraparticulate voids
Interparticulate voids 10

TYPES OF VOLUME :

11 TYPES OF VOLUME True volume (Vt)
Granule volume (Vg)
Bulk volume (Vb)
Relative volume (Vr)
Vr = V/ Vt
Vr tends to become unity as all air is eliminated from the mass during the compression process 11

Porosity (E) :

12 Porosity (E) porosity, E = VV/ Vb
here, VV = Void volume
Vb = Bulk volume
now,
Void volume (VV) = Vb –Vt
Therefore,
Porosity (E) =(Vb–Vt)/ Vb
Porosity when expressed as percentage
E =100.[(Vb–Vt)/ Vb] 12

Methods to measure volume of powder. :

13 Methods to measure volume of powder. Helium pycnometer
Liquid displacement method (specific gravity bottle method) 13

Helium pycnometer :

14 Helium pycnometer Vt = Vc/U1-U2x[U1-Us]
Here, 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 14

Slide 15:

15 HELIUM PYCNOMETER

Liquid displacement method :

16 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)
Here , w1 = wt. of Pycnometer
w2 = Wt. of Pycnometer + sample or glass beads
w4 = Wt. of Pycnometer with powder & filled with
solvent
w3 = w2-w1 = Wt. of sample
w4-w2 = Volume of liquid displaced by the solid Specific gravity bottle 16

DENSITY :

17 DENSITY DIFFERENT TYPE OF DENSITY :
True density
ρt=M/vt
Granule density
ρg=M/vg
Bulk density
ρb=M/vb
relative density
ρr= ρ/ ρt Tapped density-tester 17

Slide 18:

18 Effect of applied forces DEFORMATION:
Strain: The relative amount of deformation produced on a solid body due to applied force.
It is dimensionless quantity.
Compressive strain,
Z = ∆H/Ho
Stress(σ):
σ = F/A
here, F is force required to produce
strain in area A 18

Slide 19:

19 a)Tensile strain b)Compressive strain c)Shear strain FIG. Diagram shows changes in geometry (strain) of solid body resulting from various types of applied forces.
*( In fig. dash line is original shape & solid
line is deformed shape) H H0 D D0 19

Slide 20:

20 COMPRESSION:
When external mechanical forces are applied to a powder mass, there is reduction in bulk volume as follows,
1. Repacking 3.Brittle fracture: e.g., sucrose
2.Particle 4.microquashing
deformation
e.g., acetyl salicylic acid, MCC
- when elastic limit or yield point
is reached.
Microsquasing: Irrespective of the behavior
of larger particles smaller particles may
deform plastically. Elastic deformation Plastic deformation 20

Slide 21:

21 INITIALLY
REPACKING
DEFORMATION FIG.EFFECT OF COMPRESSION FORCE ON BED OF POWDER 21

Slide 22:

22 CONSOLIDATION:
Mechanism,
1.Cold welding (particle distance <50nm)
2.Fusion welding (caused due to frictional
heat)
3.Recrystallization
Consolidation process is influenced by,
- Chemical Nature of materials
- Extent of available surface
- presence of surface contaminants
- Intersurface distance 22

Slide 23:

23 Effect of increasing compressional force on specific surface area of powder mass,
Increased surface area (from O to A), initial
particle fracture due to increased compression
point A ,Particle rebonding predominates & then
surface area decreases (from A to B). Compressional force 23

Granulation :

24 Granulation Addition of granulating liquid to mass of powder mass leads to following stages, Or droplet 24

Slide 25:

25 FIG. Plot of change in torque of mixer shaft during addition of granulating fluid. point F indicates exact end point to wet massing Granulation equipment can be instrument with the torque measuring devices, which senses the change in agitator power.
METHOD TO DETERMINE
STRENGTH OF GRANULE:
Compressive strength or
crushing strength.
Abrasion tests 25

Compression and consolidation under high load :

26 Compression and consolidation under high load Relationship between upper punch FA & lower
punch forces FL:
FL = FA × e-KH/D
here, K = constant,
H & D = height & diameter of
tablet
Effects of friction:
1.Interparticulate friction(μi ): Glidants used e.g.,
colloidal silica
2.Die-wall friction(μw ): lubricants used e.g.,
magnesium stearate 26

Slide 27:

27 Force distribution
-Axial balance of forces in
punches is given by,
FA = FL+FD
-Mean compaction force (FM),
FM = FA+FL/ 2
here, FA = upper punch force,
FL =lower punch force,
FD =axial friction force. 27 FIG. Cross section of a typical simple punch & die assembly used for compaction studies

Slide 28:

28 Development of radial force:
- Radial force (FR) develops perpendicular to die-wall
surface.
Poisson ratio , λ = ∆D / ∆H
here, ∆D =change in horizontal direction,
∆H=change in height.
According to classic friction theory,
FD = μw × FR
here, FD =axial friction force.
μw = Die-wall friction - Coefficient of Lubricant efficiency (R),
R = max. FL
min. FA 28

Slide 29:

29 Ejection forces
- 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. 29

Slide 30:

30 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. 30

Slide 31:

31 End of compressional process is when
bulk volume = tapped volume & porosity = 0
Decrease in porosity is due to two process:
filling of large spaces by Interparticulate
slippage
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., FIG. Decreasing porosity with increasing compressional force
for single ended pressing
i) initial repacking
ii)Elastic deformation
iii)Plastic deformation
iv)compression Force volume relationship 31

Slide 32:

32 Heckel plot It follows 1st order
The pore in the mass are the reactant.
log 1/E = KyP + Kr
here, 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 32

Slide 33:

33 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. 33 FIG. Example of heckel plot.

Slide 34:

34 Kawakita Equation C = Vi – Vp/ Vt = abPa / 1+ bPa
here, 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. Vi – Vp/ Vi – Vt = C2 exp (-K2/Pa ) + C3 exp (-K3/Pa )
here, C2,C3, K2,K3 = constants
LIMITATION : Applies only to single component
system. Cooper and Eaton Equation 34

Slide 35:

35 Decompression Occurs on removal of applied force after compression.
Tablet must mechanically strong to withstand stresses
produce during decompression.
Plastoelasticity(γ),
γ = [Ho / Hm - (Hr-Hm) / Ho - Hm]
here, Ho ,Hm, Hr = thickness of tablet mass at onset of
loading, at max. applied pressure & on ejection from die
γ > 9 produce tablets that are laminated or capped. 35

Slide 36:

36 Compaction profile Monitoring of applied pressure transmitted radially to die-wall gives compaction profile as follow, 36

Slide 37:

37 Energy involved in compaction Tablet machine, roll compactor, extruder requires high
input of mechanical work
Work involve in various phases of compaction are,
1.To overcome interparticulate friction
2.To overcome friction between machine parts and particles
3.To induce deformation
4.For brittle fracture
5.Mechanical operation of various machine parts
Lubrication reduce energy expenditure by 75%. 37

Slide 38:

38 REFERENCES Leon Lachman, Herbert A.Liberman, & Joseph kanig ,THE THEORY AND PRACTICE OF INDUSTRIAL PHARMACY, third edition.
Herbert A.Liberman, Leon Lachman & Joseph B. Schwartz ,PHARMACEUTICAL DOSAGE FORMS, TABLETS, volume II.
ENCYCLOPEDIA OF PHARMACEUTICAL
TECHNOLOGY, second edition,volume-3.
C.V.Subrahmanyam ,TEXTBOOK OF PHYSICAL PHARMACEUTICS, second edition.
Gilbert S. Banker , Christopher T. Rhodes, Modern
Pharmaceutics , Fourth Edition. 38

Slide 39:

39 THANK YOU 39

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