Compression and compaction

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Department of Pharmacy (Pharmaceutics) | Sagar savale

05/01/23 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 solidsSolid –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


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


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METHODS TO MEASURE ANGLE OF REPOSE.

a.Fixed funnel and free standing cone method.b.Tilting box method.c.Revolving cylinder method


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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 of pile

Angle of repose

Flow property of powder

<25

25-30

Excellent

Good 30-40 Passable

>40 poor


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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


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MASS-VOLUME RELATIONSHIPS.TYPE OF VOIDS OR AIR SPACES:

Open intraparticulate voids-

Closed intraparticulate voids-

Interparticulate voids-

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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.


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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. of Pycnometer with powder & filled

with solvent w3 = w2-w1 = Wt. of sample w4-w2 = Volume of liquid displaced by the

solid141405/01/23 Sagar Kishor Savale

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specific gravity bottle


Tablet Press Machine


.

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The process of compression.

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REMOVAL OF PRESSURE


Deformation

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


Effects of compression force.

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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).


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If, only elastic deformation occurs –

Under nonisostatic conditions-

Uniaxial relaxation


Ejection.

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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.

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Thin layer is abrasion resistant but it –Retards air escape during compression.Retards the ingress of liquid media during dissolution.

punc

h

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.

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LUBRICANT SHEAR STRENGTH(M pa)

Stearic acid 1.32

Calcium stearate 1.47

Magnesium stearate

1.96

Boric acid 7.16

graphite 7.3505/01/23 Sagar Kishor Savale

Force volume relationship.

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FIG. Decreasing porosity with increasing compressional force for single ended pressing i) initial repackingii) Elastic deformationiii) Plastic deformationiv) 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 orderThe 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


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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

strength3333

Fig:- pfizer tester.


Friability.

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• 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.


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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




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Compression and compaction