1. Compression and consolidation of
powder solids
Dr Fauzia rehman
Mphil pharmaceutics
Lecturer
The University of Faisalabad
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2. Definitions
• Compression- Compression means
reduction of bulk volume of material as a
result of displacement of gaseous phase (empty /
air spaces).
• Consolidation – Consolidation is an increase
in mechanical strength of material from
particle - particle interactions.
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4. Derived properties of powdered
solids
1. The solid-air interface
2. Angle of repose
3. Flow rates
4. Mass-volume relationships
5. Density
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5. Solid air interface:-
Atoms or ions within the solids are of two type:-
1.Those situated on the surface of solids.
2. Those situated on the surface or inside the solids.
• Those atoms or ions are or particles which are present within the bulk are
attracted from all side equally. So set force on them is zero,while in case
of those atoms or ions or particles which are present on the surface. So
they are attracted not equally from all sides. This phenomena creates free
surface energy of a solid. The energy due to unsatisfied attractive force is
called surface free energy.
• Surface free energy plays a very important role in the interaction between
the particles and its environment so the important factors of surface free
energy are adsorption,cohesion,adhesion and crystalization etc.
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6. 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.
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7. • Adhesion and cohesion has an important influence on several
operation such as flow from hoppers or feeders, relative
motion in mixers and compressions to produce granules or
tablets.
• These are different types of the particles and interface
techniques before measuring the resistance to the particles
measurements.
1. Angle of repose
2. Flow rate
3. Compressibility index
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8. ANGLE OF REPOSE
• It is a practical technique to
measure the resistance to the
flow of powders.
• DEFINITION:
The maximum angle that
can be obtained between
free standing surface of
the powder heap and the
horizontal plain or plain
of the ground as shown in
fig.
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9. METHODS TO MEASURE
ANGLE OF REPOSE
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a. For example a quantity called angle of repose of a
powder can be determined. This is the angle θ as
defined by equation.
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Tan θ = 2h/d
d=2r
Tan θ= h/r
θ= tan-1 h/r
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ANGLE OF REPOSE
STATIC ANGLE OF
REPOSE
KINETIC/DYNAMIC
ANGLE OF REPOSE
•It is angle of repose
determined by 1st two
methods (a. & b.)
•It is angle of repose
determined by the 3rd
method ( c.)
•It is preferred since
they most closely
mimic the
manufacturing
situation in which
powder is in motion.
12. 1.Pertri dish method:-
Simplest method and in this method the powder is allowed to flow
through the funnel to a petri dish below. The process of powder
dropping is continued until the powder starts sliding from a conical
shape formed in a petridish and measure the height of heap and
diameter of the petri dish. Then determine the angle of repose by
formula
θ=h/r
2. Box method:-
Rectangular box is used for determination of the angle of repose. The
internal surface of the box is lined by the sand paper to present the
slippage or sliding. The box is filled with the powder sample. Then box
is started to raise slowly from one slide till the powder starts falling
from the lower side. Then determine the angle of repose.
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13. 3. Cylinder method:-
In this method, a glass cylinder internally lined with the paper
is half filled with the powder sample then it is slowly rolled
over the smooth surface until powder going to start flow.
Then determine the angle of repose by formula
Angle of repose methods which results in a so called a dynamic
angle are prefered because they most closely copy the
manufacturing situated in which powder is a motion,values of θ
are rarely less than 20˚ and values of upto 40˚ indicated
reasonable flow particle. Above 50˚ the flow only with great
difficulty with dynamic angle of repose measurement can be
replicated(n=3) produce with RSD of the approximately 2%
not more. They are particularly sensitive to changes in particle
size distribution and to moisture content and they provide a
rapid means of monitoring the significant batch to batch
differences in these respect.
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14. Flow rates
• Alternatively, resistance to
movement of particles especially for
granules with little cohesiveness may
be accessed by determining their
flow rate through a circular orifice
(tablet dye) fitted in base of
cylinderic container.
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15. flow rate = quantity of powder (pass)
time
It has been observed that for maximum flow rate ,
there should be optimum proportions of different size
fractions of the same materials but when the
proportion of particle exceed 40% , than there is
dramatic fall in flow rate.
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16. Compressibility index
• It is another practical technique
used to determine the flow ability
of powders. In this technique
powders is filled upto a mark in
graduated cylinder, than it is
subjected to standardized tapping
procedure until volume of particles
is reduced to constant level .
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17. Compressibility index
• Compressibility index
(Carr's consolidation
index)
I = [1-v/vo]x100
here, V = Tapped Volume
V0 = Volume before
tapping
• If value I below
15 % usually give
rise to good flow
properties, but
readings above
25% indicate poor
flowability.
• And between 15-
25% indicate
intermediate
flowing properties17
18. MASS-VOLUME RELATIONSHIPS
1. VOLUME
TYPE OF VOIDS OR AIR
SPACES:
Open intraparticulate voids
Closed intraparticulate voids
Interparticulate voids
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19. 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 such as tableting.
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20. 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]
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21. METHODS TO MEASURE VOLUME
OF POWDER.
Helium pycnometer
Liquid displacement method (specific gravity bottle
method)
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22. HELIUM PYCNOMETER
• In this case He is introduced into
whole compartment then its entrance
is closed. He gas is neutral, non
reacting and non-adsorbing, So used
in this method. He gas will exert
some pressure and frictionless piston
will move and reading is detected on
scale.
• Electric circuit detect the pressure
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23. HELIUM PYCNOMETER
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Vt = Vc/U1-U2x[U1-Us]
Here, Vt = true volume of sample
Vc=true volume of standard
U1=Volume of empty cell
U2 = reading on scale when known sample is
placed. (standard)
Us = reading on scale when test sample is
placed.
U1-U2=Volume occupied by the std.
sample
U1-Us = volume occupied by sample
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25. LIQUID DISPLACEMENT METHOD/
SPECIFIC GRAVITY METHOD
• In this method specific gravity bottle is
used. First of all powder is placed in
specific gravity bottle, then bottle is
filled with some kind of solvent which is
insoluble and even the liquid does not wet
the solid e.g; mercury. Then quantity of
liquid required to filled the bottle upto the
mark is noted and volume of sample
determined by following formula
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26. LIQUID DISPLACEMENT METHOD/
SPECIFIC GRAVITY 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 26
Specific gravity bottle
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27. 2. DENSITY
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Ratio of mass/volume known as 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
During compressional processes, relative density
increases to a maximum of unity when all air
spaces have been eliminated.
Tapped density-tester
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28. CONSOLIDATION:
Increase in mechanical strength of solids by the application of compression
force.
Three Mechanisms involved which increase the mechanical strength of
solid powder,
1.Cold welding (particle distance <50nm)
2.Fusion welding (caused due to frictional heat)
3.Recrystallization
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33. 3. Recrystallization
• For the satisfactory compression of granules some residual
amount of moisture is necessary. This moisture is present in
the form of thin film on solid surface. So when force is
applied the solubilty of the soluble component of formation
increases but when the force is relived then results in
recrystallization of the soluble components and this
recrystallization forms a solid bridge between the particles
and whose strength would particularly depend on the rate of
recrystallization and this bridge formation then increase
the mechanical strength of solids.
• So, this Finding comes in the cases of some out dried
mixture in which moisture residue are extremely low and
produce inferior tableting qualities.
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34. Granulation
• Process of formation of granules from
powder sample known as granulation.
• When a binding agent or granulating liquid
is added to a mass of powders then
depending upon the quantity of binding
agent it passes through a series of stages
which are describes.
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35. Preparation of granules
• 1. Dry method
i. direct compression
ii. compression granulation
a). Slugging method
b). Roller compaction
2. Wet method
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37. Direct compression
• In this method active ingredient and
exceipients if required are weighed,
mixed and than compressed directly
into tableting machine. A number of
materials are available which are
directly compressed and serve as
diluent e.g; microcrystalline cellulose,
dicalcium phosphate and dextrose
solution
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38. Advantages
• It is more economical in terms of
time, labour and equipment because
very few steps are involved.
• Bioavilibilty of drugs is high due to
absence of binders or adhesive
agents.
• As no moisture is involved so many
stability problems are prevented.
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39. Disadvantages
• If the active ingredient and
exceipienthave different densties
and particle sizes there may be
chances of segregation.
• Only few componds can be
compressed directly.
• It may also generate a lot of dust.
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40. Compressional
granulation
• A). Slugging
• This technique is used for substances who cannot
be directly compressed, or which are sensitive to
the presence of moisture and heat e.g; aspirin
tablets .
• In this process of slugging the powder mass is
compressed in tableting machine using large plate
punches to form large tablets termed as slugs and
process called slugging.
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41. • Pressure used for slugging is 15 tons.
• Slugs are pass through mill to reduce them
to required size. After sizing the
lubricants and glidants are mixed and
other excipients if required. The resulting
mass is compressed into tablet form. The
process used to produce uniform particle
size and improve consolidation property.
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42. Roller compaction
• On large scale compression, granulation also performed on
specially design machines known as roller compactor and
chilsonator.
• Powder to be compressed is placed in lower hopper and than
sucked to upper hopper. Then powder pass through rolls.
Pressure is applied about 10 tons.
• After passing through roller the compact mass resembles
thin, white, ribbon sheet. This sheet broken into large
pieces or slugs in pre break mill and broken into smaller
granules via mill and finally required size granules pass
through screen while undersized or over sized granules are
passed to hopper again and recycled.
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52. Friability
• Friability is defined as the % of weight loss by
tablets due to mechanical action during the
test. Tablets are weighing before and after
testing and friability is expressed as a
percentage loss on pre test tablet weight.
• Friability refers the ability of the compressed
tablet to avoid fracture and breaking during
transport
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53. Friabilty
• Appratus: Roche fribilator
• Causitive factors
• Friction
• Shock
• So, when cylindrical section of fribilator rotates
than tablet undergoes self collosions this will lead
to friction of tablets.
• when tablets drops from 6 inches. This is called
shock to tablets.
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54. Procedure
• A number of tablets (20 Nos.) are weighed and
placed in the apparatus where they are exposed to
rolling and repeated shocks as they fall 6 inches in
each turn within the apparatus. After 4 minutes of
this treatment or 100 revolutions the tablets are
weighed and the weight compared with initial weight.
The loss due to abrasion is a measure of tablet
friability. The value is expressed in percentage.
• Limit: less than 0.8%-1% w/w
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55. • Limitation:
• If during friability operation the
tablets breaks than broken tablets
not consider for measure of
friability.
• On long storage tablets may loose
H2O and moisture and become more
friable this phenomenon called aging
of tablets.
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56. • Significance: friability is inversely
proportional to hardness, so friability
is non-official test.
• So, this test is performed to
evaluate the ability of tablet to
withstand mechanical shock during
manufacture packing and
transportation.
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