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COMPRESSION PHYSICS OF
THE TABLETS

SUBMITTED BY ;
SUBMITTED TO :

Dipak Kumar Gupta
DR. YASMEEN SULTANA

MPharm (Pharmaceutics) Sem I

DEPARTMENT OF PHARMACEUTICS , JAMIA HAMDARD

 

CONTENTS –

• DEFINITIONS

• PROPERTIES OF POWDERS

• FORCE VOLUME RELATIONSHIP

• COMPRESSION CYCLE AND THE EFFECT OF THE FORCES ON IT.

• COMPACTION ANALYSIS.

DEPARTMENT OF PHARMACEUTICS , JAMIA HAMDARD

 

 The simplest process for tableting is direct compression, in which the
drug(s) and excipient(s) are dry mixed and then compacted. For this
process to be successful, the powder mixture requires certain
properties, such as high flowability, low segregation tendency, and
high compactibility.

 Compaction represents one of the most important unit operations in
the pharmaceutical industry because physical and mechanical
properties of the tablets, such as density or strength
(hardness/friability), are determined during this process.

 Dosage form integrity and bioavailability is related to the tablet
compression process.

DEPARTMENT OF PHARMACEUTICS , JAMIA HAMDARD

 

What is compaction ?
Compaction is a important parameter to consider in
phramaceutical industry as it is a essential step in the
manufacturing of the tablets & it is compression and
consolidation of two phases (solid and gas) system due to
applied force and which includes :

 Compression
 Consolidation

 COMPRESSION :
• Compression means reduction volume & particle

rearrangement. Compressibilty is the property of
powder to compress under pressure.

DEPARTMENT OF PHARMACEUTICS , JAMIA HAMDARD.

 

• Compression refers to a reduction in the bulk volume
of materials as a result of
displacement of the gaseous phase.

 CONSOLIDATION

Process of the interparticulate bond formation & it is the
ability of the powder to form strong compact.

• Cold welding

• Fusion bonding

 

• PROPERTIES OF POWDERS –
Volume

1. True Volume
2. Bulk volume
3. Granular volume

• Density
1. True density
2. Bulk density
3. Granular density

• Porosity
• Flow properties

Now we will discuss about these topics.

 

• POROSITY
It is one of the important property of the powder . Here porosity is
denoted by the ‘ E ‘ .

VOID VOLUME = BULK VOLUME – TRUE VOLUME

&

Porosity (E) = VOID VOLUME / BULK VOLUME

Here , as said porosity a important parameter as it plays a important role

in the Rate of Dissolution , Rate of Disintegration & Absorption.

Some other factors also there which has to be considered for
the properties of the powder.

 

• PARTICLE SIZE

Smooth particle size type of granules increases the flow

property.

• DENSITY / POROSITY

The relationship between the density and porosity is
inversely proportional.

i.e higher the density means lesser will be the porosity and
flow would be the good.

• MOISTURE

It plays a important role in the manufacturing of the

 

Pharmaceutical formulation.

 One of the method used to determine the compressibility
of a powder bed is the degree of volume reduction owing
to applied pressure, which is related to porosity and is
assumed to be a first-order reaction .

• FLOW PROPERTIES

i. Good flow property of a pharmaceutical powder is
essential to ensure proper die fill during compression,
especially in direct compaction process.

ii. Angle of repose is commonly used to measure flow of
powders, and is the maximum angle (θ) between the
plane of powder and horizontal surface.

 

ANGLE OF REPOSE

FLOW PROPERTY ANGLE OF REPOSE

Excellent 25-30

Good 31-35

Passable 36-40

Poor 41-45

Very poor 46-55

Very very poor 56-65

The increase in bulk density of a powder is
related to its cohesivity.

 

Indices like Hausner’s Ratio (H) and Carr’s Index (CI) is based
on the bulk density and Tapped density.

 HAUSNER’S RATIO (H) –

It is the ratio of the bulk denstiy and the tapped density & and
varies from about 1.2 for a free-flowing powder to 1.6 for
cohesive powders.

H = TAPPED DENSITY / BULK DENSITY

The percentage compressibility, also called as Carr’s Index is
100 times the ratio of the difference between tapped density
and bulk density to the tapped density.

 

• SCALE OF FLOWABILITY

COMPRESSIBILITY INDEX FLOW CHARACTER HAUSNER
RATIO

10 EXCELLENT 1.00 – 1.11

11-15 GOOD 1.12 – 1.18

16-20 FAIR 1.19 -1.25

21-25 PASSABLE 1.26 – 1.34

26-31 POOR 1.34 – 1.45

32-37 VERY POOR 1.4 – 1.59

>38 VERY VERY POOR >1.60

 

 A Hausner ratio of <1.25 indicates a powder that is free flowing
whereas >1.25 indicates poor flow ability.

 The smaller the Carr’s Index the better the flow properties. For example
5-10 indicates excellent, 11-15 good, 16-20 fair and > 23 poor flow.

COMPACTION

• Compaction can be defined as the compression and consolidation of a
particulate solid–gas system as a result of an applied force.

• Compression involves a reduction in bulk volume as a result of reduced
gaseous phase

 

• A closer packing of the powder particles as a result of
rearrangement is the main mechanism for initial volume reduction.

• As the force is further increased, rearrangement becomes difficult
and particle deformation occurs.

 CONSOLIDATION

• Consolidation, a simultaneous occurring process, involves increase in
the mechanical strength resulting from particle-particle interactions.

• As the particles move into closer to each other during the volume
reduction process, bonds are established between the particles, the
nature of which depends upon the nature of the bond in the
molecular structure of the interior of the particles

 

• It should be noted that consolidation is the major reason for increase in
mechanical strength of a powder bed, when subjected to rising
compressive forces.

 

STEPS INVOLVED IN COMPACTION OF
POWDER UNDER APPLIED FORCE

1. Particle Rearrangement and Volume Reduction.

1. Deformation of Particles.

2. Time Dependence of Compaction Process.

 

PARTICLE REARRANGEMENT
AND VOLUME REDUCTION

• The compression of powder or granular material to
produce a compact is a complex process, arising from the
numerous internal processes that lead to consolidation.

• When a powder is compressed initially the particles are
rearranged under low compaction pressures to form a
closer packing structure.

• The finer particles enter the voids between the larger
ones and give a closer packing arrangement.

 

• In this process, the energy is evolved, as a result of
interparticulate friction and there is an increase in the
amount of particle surface area capable of forming
interparticulate bonds.

• As the pressure increases, further rearrangement is
prevented and subsequent volume reduction is
accomplished by plastic and elastic deformation and/or
fragmentation of the particles.

 “ Elastic deformation is a reversible process and
plastic deformation results in a permanent change
in the particle shape.”

 

 DEFORMATION OF PARTICLES

• As the upper punch penetrates the die containing the powder
bed, initially there are essentially only points of contact
between the particles. The application of the external forces
to the bed results in force being transmitted in through these
interparticulate points of contact, leading to development of
stress and local deformation of the particles.

• Energy is lost at this stage as a result of interparticulate and
the die-wall friction, as well as deformation.

Although, under the influence of an applied pressure,
the particles not only deform plastically or elastically, but also
fragment to form smaller particles (termed as brittle fracture).

 

 TIME DEPENDENCE OF COMPACTION
PROCESS

• Successful formation of a pharmaceutical tablet by the
compression of solid particulate matter depends on
interparticulate bonding across particle-particle interfaces.

• Some deformation processes (e.g., plastic deformation) are
time dependent and occur at various rates during the
compaction sequence . This means that the rate at which
load is applied and removed may be a critical factor.

“ Speed of the process (dwell time) can have marked effect on
compactibility and on tendencies such as lamination, capping,
and picking, which can occur during and/or after ejection ”

 

 COMPRESSION CYCLE
The compression cycle on a rotary tablet press includes –

• Precompression
• Main compression
• Decompression
• Ejection phases

 Precompression is the stage where the tablets are
partially formed and the precompression roller is
usually smaller than the compression roller, so that the
applied force is smaller in precompression stage.

 

 During main compression, the applied energy is
transformed into formation of interparticulate bonds.
When a force is applied in a die, the particles firstly
undergo rearrangement to form a less porous structure
at very low forces. Afterwards, the particles reach a
state where further relative movement is impossible, and
an increase in the applied force induces either particle
fragmentation or deformation (or both).

 

COMPACTION ANALYSIS
Compaction is analyzed by Compaction stimulators,
which are attached to punching machine.

 

COMPACTION PROFILE –
 Force – time Profile

 Force – displacement profile

 Die wall force profile

 

Force – time profile is categories in 3 parts :

a) Compression phase

b) Dwell phase :

a) Decompression/Relaxation phase

 

Compression event is divided in the series of the
time periods :

 Consolidation time : Time period to reach maximum force

 Dwell time : Time at the max. force & time between the compression
& decompression

 Contact time : Time for compression & decompression

 Ejection time : Time during which the ejection occurs.

 Residence time : Time during which the formed tablets are in the die