Powder flow and compression properties

POWDER FLOW &COMPRESSION

17/09/2016 RAHUL.SAGDE 1

Prepared By: RAHUL.SAGDE M.PHARM(QA) GOVT. PHARMACY COLLEGE AMRAVATI

Prepared By: RAHUL.SAGDE M.PHARM(QA) GOVT. PHARMACY COLLEGE AMRAVATI

OVERVIEW


INTRODUCTION

FLOW PROPERTIES

METHODS

COMPRESSION

DERIVED PROPERTIES

REFERENCES

INTRODUCTION


DEFINATION OF POWDER: Powders are the solid bulk dosage forms.It refer to a chemical or mixture that is solid in physical state.Powder generaly ranging from 0.1 to 10 micron in size.The size of the particle are often expressed as a number which corresponds to the mesh screen size of sieve.The screen size indicates the number of openings in the mesh screen per inch. eg: #40 sieve has 40 opening per inch in the screen mesh

FLOW PROPERTIES


WHY FLOW OF POWDER DETERMINATION NECCESORY:

Irregular flow of the powder from the hopper produces tablet with non uniform weight.As a result, content uniformity and dose precision cannot be achieved in the production of tablet and capsule.

The flow properties depend upon particle size, shape, porosity, and density of the bulk powder


FACTORS

Particle size: If the particle size is small (10um), the powder flow us restricted owing to cohesion of particle by by van der waals, and electrostatic forces. As the particle size increases , the flow of the powder increasesNature of particle: smooth surface of particle improve the flow. surface roughness leads to poor flow due to friction and cohesiveness.Moisture content: the higher the moisture content ,the greater the risk of cohesion and adhesion.

FACTORS


Particle shape: Powders with similar particles sizes but dissimilar shapes can have markedly different flow properties due to differences in interparticle contact area.

Particle density: powders normally flow under the influence of gravity, dense particles are generally less cohesive than less dense particle of the same size and shape.

METHODS TO DETERMINE FLOW PROPERTIeS


ANGLE OF REPOSE

BULK DENSITY

HAUSNER RATIO

CARRS INDEX

GRANULAR DENSITY

ANGLE OF REPOSE


DEFINATION:- Is the maximum angle possible between the surface of a pile of the powder and the horizontal plane. The flow characteristics are measured by angle of repose.Improper flow of powder is due to frictional forces between the particle.


The flow of powder and angle of repose are expressed by following formula

Tan ø = h/r Where: h= height of pile r= radius of the base of pile ø= Angle of repose

TABLE


ANGLE OF REPOSE(degrees) type of flow

<25 Excellent

25-30 Good

30-40 Passable

>40 Very poor

BULK DENSITY


Neumann (1967) develop a simple test to evaluate floability of a powder by comparising the poured density and tapped density.When particles are packed loosely ,lots of gap between particle are observed .Hence bulk volume increases making the powder light.Based on bulk volume , powder are classified as Light and Heavy. It is mathematically expressed as:- Bulk Density(Þ) =

Mass of powder (w)

Bulk volume(Vb)

CARRS INDEX


Carrs (1965) developes this method to measures the flow of powder.

It is mathematically expressed as:-

Carrs index(%) =Tapped density – poured density

Tapped density×100

TABLE

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Carrs index(%) type of flow

5-15 Excellent

12-16 Good

18-21 Fair to Passable

23-35 Poor

33-38 Very poor

HOUSNER RATIO


A index has been defined by HAUSNER (1967).

It is mathematically expressed by:-

Hausner Ration = Tapped density Poured density

Values : less than 1.25 indicates good flow (=20% carrs) greater than 1.25 indicates poor flow(=30% carrs)Between 1.25 and 1.5 added glidant normally improve flow

TABLE


Other methods


1) INDIRECT METHOD:-

Shear cell determination criticle orifice diameter

2) DIRECT METHOD;- Hopper flow rate Recording flow rate

IMPROVEMENT OF POWDER FLOABILITY


Alteration of particle size

Alteration of particle shape or texture

Alteration of surface force

Formulation additive( flow activators)

Alteration of process condition: use of vibration assisted hopper use of force feeder

COMPRESSION PROPERTIES


COMPRESSION


Powders are normally compressed into tablet using a pressure of about 5.0kg/cm2. this process is called compression.

The compression properties of most drug powders are extremely poor and necessitate the addition of compression aids.

When the dose is less than 50mg, tablets can be usually prepared by direct compression with the addition of modern direct compression bases but at higher doses the preferred method would be wet massing.

PROPERTIES


1) ELASTICITY

2) PLASTICITY

3) FRAGMENTABILITY

4) PUNCH FILMING PROPENSITY


PLASTIC MATERIAL:- when material are ductile they deforms by changing shape.Since there is no fracture, no new surface area are generated during compression.

FRAGMENTING MATERIAL:- If a material is predominantly fragmenting, neither mixing time nor dwell time should affect tablet strength.

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ELASTIC MATERIAL:- Some materials,(Paracetamol), are elastic and there is very little permanent change caused by compression.The material rebounds when the compression load is released.When these done then the Capping and Lamination are occurs.

PUNCH FILMINGS:- The surface of the top and the bottom punches should be examined for adhesion of drug.Sticky material can be improved by a change in the salt forms, high excipient ratio, using abrasive inorganic excipient in wet massing.

REFERENCES


C.V.S Subramanyam, Textbook of Physical Pharmaceutics, second edition,2000 Vallabh Prakashan, page no: 221-228

M.E. AULTON, PHARMACEUTICS: The science of dosage form design , 1st edition 1988, International student edition Publication, ISBN-0-433-08-756-7, London, page no: 247-249 , 601-613

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Health & Medicine

Powder flow and compression properties