Granules Formation and Properties

Granules are aggregations of fine particles of powders inGranules are aggregations of fine particles of powders in
a mass of about spherical shapea mass of about spherical shape..

Why we prepare granules when we have powders?Why we prepare granules when we have powders?
1.1. To avoid powder segregation,To avoid powder segregation,
if the powder is composed of particles with differentif the powder is composed of particles with different
dimensions & different densities, a separationdimensions & different densities, a separation
between these particles will occur.between these particles will occur.
2.2. To enhance the flow of powder,To enhance the flow of powder,
Higher flowability gives better filling of the dies orHigher flowability gives better filling of the dies or
containers, during a volumetric dosage.containers, during a volumetric dosage.

3.3. Granules have higher porosity than powders,Granules have higher porosity than powders,
4.4. To improve the compressibility of powders.To improve the compressibility of powders.
5.5. The granulation of toxic materials will reduce theThe granulation of toxic materials will reduce the
hazard of generation of toxic dust, which may arisehazard of generation of toxic dust, which may arise
during the handling of the powders.during the handling of the powders.
6.6. Materials, which are slightly hygroscope, may adhereMaterials, which are slightly hygroscope, may adhere
& form a cake if stored as a powder.& form a cake if stored as a powder.

 Technologically, granules are used according to twoTechnologically, granules are used according to two
visions:visions:
1.1. As a true & proper pharmaceutical dosage form form,As a true & proper pharmaceutical dosage form form,
These granules are used to prepare an instant solution orThese granules are used to prepare an instant solution or
suspension.suspension.
Granules, can be packaged as:Granules, can be packaged as:
 Bulk granules (Multi-dosage containers),Bulk granules (Multi-dosage containers),
 Divided granules (Mono-dosage containers ).Divided granules (Mono-dosage containers ).

2.2. Semi-finished products for the preparation of tabletsSemi-finished products for the preparation of tablets
or other dosage forms.or other dosage forms.
Usually, granules have an excellent compressibility,Usually, granules have an excellent compressibility,

Methods of GranulationMethods of Granulation
 Some of the available methods in the industrial fieldSome of the available methods in the industrial field
for the preparation of granules:for the preparation of granules:
1.1. Wet Granulation.Wet Granulation.
2.2. Dry granulation methods.Dry granulation methods.
3.3. Granulation by Crystallization.Granulation by Crystallization.
I.I. Granulation by Crystallization.Granulation by Crystallization.
 This method exploits theThis method exploits the presence of crystallizationpresence of crystallization
water in the active materialwater in the active material; this method is rarely; this method is rarely
used.used.

II.II. Dry Granulation.Dry Granulation.
Pharmaceutical powders that were mixed homogeneouslyPharmaceutical powders that were mixed homogeneously
together are compressed to obtain large tablets.together are compressed to obtain large tablets.
The high compression forces are obtained by using one ofThe high compression forces are obtained by using one of
the following procedures:the following procedures:
1.1. Tabling machines (see industrial pharmacy).Tabling machines (see industrial pharmacy).
These machines are provided with dies of 2-3 cm diametersThese machines are provided with dies of 2-3 cm diameters
(the fine powders have low flowability)(the fine powders have low flowability)
So,So,
large dies are easily filled in this case, the dies travellarge dies are easily filled in this case, the dies travel
between two punches, which press the powder formingbetween two punches, which press the powder forming
large tablets, with 2-3 cm of diameters.large tablets, with 2-3 cm of diameters.

2.2. Roller compaction (see industrial pharmacy).Roller compaction (see industrial pharmacy).
The powder mixture flow between two rollers to form aThe powder mixture flow between two rollers to form a
compressed sheet.compressed sheet.
These large tablets or sheets are milled.These large tablets or sheets are milled.
The milled sheets are sieved.The milled sheets are sieved.

The sieving process gives three fractions of granules :The sieving process gives three fractions of granules :
1.1. Very coarse granules, which return back to the millingVery coarse granules, which return back to the milling
process.process.
2.2. Very fine fraction, which return back to theVery fine fraction, which return back to the
compaction.compaction.
3.3. Fraction with optimal dimensions for followingFraction with optimal dimensions for following
manufacturing steps.manufacturing steps.

This system produces granules with:This system produces granules with:
 irregular shape,irregular shape,
 low rate of dissolution due to thelow rate of dissolution due to the high compression forcehigh compression force
used to aggregate the powders.used to aggregate the powders.
These granules are poorlyThese granules are poorly water-permeablewater-permeable due to the lowdue to the low
porosity.porosity.
So, water canSo, water can’’t permeate them easily in order to disintegratet permeate them easily in order to disintegrate
& dissolve them.& dissolve them.
This will extremely reduce the velocity of dissolution & soThis will extremely reduce the velocity of dissolution & so
the bioavailability of the active material.the bioavailability of the active material.

 Vice versa if the granules have high porosity theVice versa if the granules have high porosity the
molecules of water can penetrate easily into the pores,molecules of water can penetrate easily into the pores,
& disintegrate the granules.& disintegrate the granules.
 High Porosity means high specific surface area,High Porosity means high specific surface area,
leading to an increasing in the dissolution velocity ofleading to an increasing in the dissolution velocity of
the granules, & thus their bioavailability.the granules, & thus their bioavailability.
 Thus, we can say that the dry granulation method isThus, we can say that the dry granulation method is
used only for those powders, which cannot beused only for those powders, which cannot be
granulated with the wet granulation method.granulated with the wet granulation method.

Wet GranulationWet Granulation
 This is the most used method to prepareThis is the most used method to prepare
granules.granules.
 The main disadvantage of this method is theThe main disadvantage of this method is the
higher number of steps present in this processhigher number of steps present in this process
when compared with the other two methods.when compared with the other two methods.

Steps of Wet Granulation:Steps of Wet Granulation:
1.1. The 1The 1stst
step is the wetting of the powder with a liquid orstep is the wetting of the powder with a liquid or
solution to form a paste.solution to form a paste.
Characteristics of the granulating liquid:Characteristics of the granulating liquid:
 It should have all required characteristics of pharmaceuticalIt should have all required characteristics of pharmaceutical
excipient, &excipient, &
 It should dissolve the powder only within a certain limitIt should dissolve the powder only within a certain limit
(mild solvent):(mild solvent):
If the powder is soluble in the solvent, a solution or suspensionIf the powder is soluble in the solvent, a solution or suspension
will be obtained instead of the paste.will be obtained instead of the paste.

 From another side, if the solvent cannot absolutelyFrom another side, if the solvent cannot absolutely
dissolve the powder, we cannot obtain the liquiddissolve the powder, we cannot obtain the liquid
forces, which stick together the powder particles.forces, which stick together the powder particles.
 The fraction of powder, which dissolves in theThe fraction of powder, which dissolves in the
solvent, & then re-crystallizes, after the drying, willsolvent, & then re-crystallizes, after the drying, will
form bridges between the particles of the powder.form bridges between the particles of the powder.

 When two particles become in contact between eachWhen two particles become in contact between each
other by certain forces, they institute:other by certain forces, they institute:
 forces of electrostatic nature (week forces) &forces of electrostatic nature (week forces) &
 forces of viscous or/and adhesive natures (which areforces of viscous or/and adhesive natures (which are
the most important) so the particles remain attachedthe most important) so the particles remain attached
to each others.to each others.
 Thus the used liquid in the wet granulation must beThus the used liquid in the wet granulation must be
mild solvent for the powder.mild solvent for the powder.

 There is a few number of solvents available forThere is a few number of solvents available for
pharmaceutical granulation.pharmaceutical granulation.
 This is because we canThis is because we can’’t totally eliminate the solvent,t totally eliminate the solvent,
so if traces of the solvent remain in the formula atso if traces of the solvent remain in the formula at
the end of the manufacturing, these traces must bethe end of the manufacturing, these traces must be
non toxic for the patient.non toxic for the patient.

 The most used solvents in wet granulation :The most used solvents in wet granulation :
1.1. Water.Water.
2.2. Ethanol.Ethanol.
3.3. Isopropanol.Isopropanol.
 If we want to use water for granulation, the powder must be:If we want to use water for granulation, the powder must be:
 fairly or discreetly soluble in the water, &fairly or discreetly soluble in the water, &
 compatible with it.compatible with it.
 If the powder is very soluble in water, we can use anotherIf the powder is very soluble in water, we can use another
liquid or the following arrangements:liquid or the following arrangements:
4.4. Water Solutions.Water Solutions.

 Simple SyrupSimple Syrup
This syrup has less dissolving capacity than the pure water,This syrup has less dissolving capacity than the pure water,
because the majority of water molecules are involved in thebecause the majority of water molecules are involved in the
hydration & dissolving of the sugar molecules instead of thehydration & dissolving of the sugar molecules instead of the
powder molecules.powder molecules.
 But if the powder is water insoluble,But if the powder is water insoluble,
5.5. A co-solvent is recommended.A co-solvent is recommended.
This is aThis is a mixturemixture between water & another water-solublebetween water & another water-soluble
pharmaceutical solvent with high dissolving capacity towardpharmaceutical solvent with high dissolving capacity toward
the powder.the powder.
6.6. We can also use a water solution of polymers,We can also use a water solution of polymers,
The evaporation of water can determine the adhesion betweenThe evaporation of water can determine the adhesion between
the particles of the powder.the particles of the powder.

 Polymers solutions that can be used in the wet granulation:Polymers solutions that can be used in the wet granulation:
1.1. Gelatin solution at 5-10%.Gelatin solution at 5-10%.
Such viscose solutions determine the adhesion of the particles ofSuch viscose solutions determine the adhesion of the particles of
the powders,the powders,
When water evaporates the gelatin solidifies between the twoWhen water evaporates the gelatin solidifies between the two
particles of powder and maintain them stuck together.particles of powder and maintain them stuck together.
2.2. Starch past 5 -10%.Starch past 5 -10%.
Pre-gelatinized starch, which has the characteristic to swell in aPre-gelatinized starch, which has the characteristic to swell in a
cold water.cold water.
3.3. Semi-synthetic polymers like CMC, MC.Semi-synthetic polymers like CMC, MC.
4.4. Synthetic polymers like P.V.P.Synthetic polymers like P.V.P.

Some of these compounds can be used in organicSome of these compounds can be used in organic
solvent like ethanol,solvent like ethanol,
 This is useful in case of thermo-sensitive compounds,This is useful in case of thermo-sensitive compounds,
&&
 To reduce the cost of production.To reduce the cost of production.
The granules obtained in this way are called agglutinatedThe granules obtained in this way are called agglutinated
granules.granules.

2.2. The 2The 2ndnd
step is the granulation or the formation ofstep is the granulation or the formation of
granules starting from the paste.granules starting from the paste.
To achieve this, many granulators are available (seeTo achieve this, many granulators are available (see
industrial pharmacy):industrial pharmacy):
1.1. Rotative granulator,Rotative granulator,
2.2. Oscillating granulator,Oscillating granulator,
3.3. High speed mixer granulator,High speed mixer granulator,
4.4. Fluidized bed granulator,Fluidized bed granulator,
5.5. Freund granulator,Freund granulator,
6.6. Roller compaction granulator.Roller compaction granulator.

 The quality of the granules depends on the:The quality of the granules depends on the:
1.1. Granulation solvent,Granulation solvent,
2.2. Type of granulator,Type of granulator,
3.3. Powder nature.Powder nature.
 The paste that we have to obtain mustnThe paste that we have to obtain mustn’’t drains betweent drains between
the fingers of the hand, which means that must remainthe fingers of the hand, which means that must remain
aggregated & easily crumbled.aggregated & easily crumbled.
 This is a very coarse reference, but nowadays there is theThis is a very coarse reference, but nowadays there is the
possibility to have a qualitative evaluation.possibility to have a qualitative evaluation.

 we can measure the energy that we must provide towe can measure the energy that we must provide to
the system in which we carry out the wetting process.the system in which we carry out the wetting process.
How?How?
1.1. Put the powder for granulation in the granulator,Put the powder for granulation in the granulator,
2.2. Add gradually the granulating liquid,Add gradually the granulating liquid,
3.3. Then mix by the use of electrical motorThen mix by the use of electrical motor
This motor measures the absorbed power in function ofThis motor measures the absorbed power in function of
the time & so in function of the putted liquid.the time & so in function of the putted liquid.

How can we calculate the exact volume of granulatingHow can we calculate the exact volume of granulating
liquid for powder kneading?liquid for powder kneading?
 We can evaluate the liquid quantity for the kneadingWe can evaluate the liquid quantity for the kneading
process by measuring continuously the absorbedprocess by measuring continuously the absorbed
power during the addition of the granulating liquid.power during the addition of the granulating liquid.
 The increase in the required power is connected withThe increase in the required power is connected with
the increase of the viscosity of the dough mass, due tothe increase of the viscosity of the dough mass, due to
the formation of the liquid bonds (adhesive & viscousthe formation of the liquid bonds (adhesive & viscous
types).types).
 Generally, all instruments are able to form a curve, asGenerally, all instruments are able to form a curve, as
in the following figure:in the following figure:

4.4. Perform the curve by putting the absorbed power in Y-Perform the curve by putting the absorbed power in Y-
axis, & the volume of the granulating liquid in X- axis.axis, & the volume of the granulating liquid in X- axis.
5.5. Interpretation of the obtained curve:Interpretation of the obtained curve:
 Initially, the addition of the granulating liquid doesnInitially, the addition of the granulating liquid doesn’’tt
produce a significant change in the absorbed power,produce a significant change in the absorbed power,
 At point 2 we fined that any added quantity of theAt point 2 we fined that any added quantity of the
granulating liquid, increases proportionally the absorbedgranulating liquid, increases proportionally the absorbed
power.power.

 At this point we have initial formation of:At this point we have initial formation of:
1.1. Electrostatic bonds (less important),Electrostatic bonds (less important),
2.2. Liquid bonds (more important).Liquid bonds (more important).
 These bonds start to bind together the powderThese bonds start to bind together the powder
particles & to form the granules.particles & to form the granules.
 Therefore the equipment meet higher resistance toTherefore the equipment meet higher resistance to
maintain constant the number of rounds/minute.maintain constant the number of rounds/minute.

 Then continuing in the liquid addition, we note that theThen continuing in the liquid addition, we note that the
absorbed power will be stabilized on a certain value (intervalabsorbed power will be stabilized on a certain value (interval
between 3-4), this means that the system was reached anbetween 3-4), this means that the system was reached an
equilibrium state.equilibrium state.
 At points 3-4, we have an excellent adhesion between theAt points 3-4, we have an excellent adhesion between the
various particles of powder &various particles of powder &
 The granule shape depends on the type of the usedThe granule shape depends on the type of the used
granulator.granulator.

 The addition of further liquid, will give phase 5 whereThe addition of further liquid, will give phase 5 where
we note a sharp drop in the absorbed power,we note a sharp drop in the absorbed power, becausebecause
the granulate will be transformed in a suspensionthe granulate will be transformed in a suspension..
In this manner we have an idea about the percentageIn this manner we have an idea about the percentage
quantity of the granulating liquid, which we have toquantity of the granulating liquid, which we have to
add, by evaluating the curve.add, by evaluating the curve.

This curve can subdivide the granulators in:This curve can subdivide the granulators in:
1.1. Slow granulator (fluidized bed granulator and dryer).Slow granulator (fluidized bed granulator and dryer).
2.2. Speed granulators (e.g. plates and rotate granulatorsSpeed granulators (e.g. plates and rotate granulators……etc, seeetc, see
industrial pharmacy).industrial pharmacy).
III.III. The 3The 3rdrd
step is thestep is the Drying ProcessDrying Process..
Water is more difficult to be eliminated than the organicWater is more difficult to be eliminated than the organic
solvents, therefore the water gives some problems:solvents, therefore the water gives some problems:
1.1. When the powder is thermosensitive the heating for longWhen the powder is thermosensitive the heating for long
period of time can alter the stability of the powder,period of time can alter the stability of the powder,
2.2. The consumption of energy is higher than the organicThe consumption of energy is higher than the organic
solvents.solvents.

 We have three kinds of water in the granulate mass:We have three kinds of water in the granulate mass:
1.1. Water of Crystallization,Water of Crystallization,
It is very difficult to be eliminated without causing theIt is very difficult to be eliminated without causing the
decomposition of the product or variation of its crystallinedecomposition of the product or variation of its crystalline
form.form.
2.2. Adsorped water,Adsorped water,
The amount of water, which was absorbed by a drug present inThe amount of water, which was absorbed by a drug present in
a moist air, this amount depends on the nature of the drug &a moist air, this amount depends on the nature of the drug &
the relative humidity of the air.the relative humidity of the air.
3.3. Imbibition of water,Imbibition of water,
The amount of water, which impregnates the granules, thisThe amount of water, which impregnates the granules, this
water is easy to be eliminated by simple evaporation.water is easy to be eliminated by simple evaporation.

According to the used dryer, we can eliminate the totalAccording to the used dryer, we can eliminate the total
amount ofamount of imbibition’s water & a portion of theimbibition’s water & a portion of the
adsorpted wateradsorpted water..
 The elimination of the total amount of the adsorbedThe elimination of the total amount of the adsorbed
water is not advisable.water is not advisable.
 For example the elimination of the total amount ofFor example the elimination of the total amount of
the adsorbed water, may create electrostatic charges,the adsorbed water, may create electrostatic charges,
 This lead to the attraction or repulsion of the granulesThis lead to the attraction or repulsion of the granules
between themselves & the walls of the equipment,between themselves & the walls of the equipment,
 This type of granules are very difficult to be managed.This type of granules are very difficult to be managed.

 If we use a hydrophilic polymer solution, as aIf we use a hydrophilic polymer solution, as a
granulating liquid, & we proceed for long time in thegranulating liquid, & we proceed for long time in the
drying process, the hydrophilic polymer will assume adrying process, the hydrophilic polymer will assume a
glassy consistency.glassy consistency.
 These glassy characteristics cause the fragmentation ofThese glassy characteristics cause the fragmentation of
the granules during the following manufacturingthe granules during the following manufacturing
processes.processes.
 Thus, a certain quantity of moisture is useful toThus, a certain quantity of moisture is useful to
improve the manipulation of the granules.improve the manipulation of the granules.

 The dryers are (see industrial pharmacy):The dryers are (see industrial pharmacy):
1.1. Static Oven,Static Oven,
2.2. Rotary Drier,Rotary Drier,
3.3. Fluidized Bed Drier,Fluidized Bed Drier,
4.4. Vacuum Oven,Vacuum Oven,
5.5. Microwave Drier,Microwave Drier,
6.6. Spray Drier,Spray Drier,
7.7. Rotary Atomizer,Rotary Atomizer,
8.8. I.R Drier.I.R Drier.

IV.IV. The 4The 4thth
step is the Classification of the granules.step is the Classification of the granules.
The last step is the classification according to particlesThe last step is the classification according to particles
dimension:dimension:
1.1. Coarse granules, which must be milled,Coarse granules, which must be milled,
2.2. Fine granules, which must be re-granulated.Fine granules, which must be re-granulated.
3.3. Optimum granules with optimum dimensions,Optimum granules with optimum dimensions,
which are ready for use.which are ready for use.

We have two problems correlated to the size of granules:We have two problems correlated to the size of granules:
1.1. Concerning the filling of big volume (i.e. sachets or bottles).Concerning the filling of big volume (i.e. sachets or bottles).
If we have big granules we can use big measuring tool, while ifIf we have big granules we can use big measuring tool, while if
the granules have small size, we can use small measuring tool.the granules have small size, we can use small measuring tool.
The most critical problem is :The most critical problem is :
2.2. when we must to fill the die of the tableting machine in orderwhen we must to fill the die of the tableting machine in order
to prepare the tablet.to prepare the tablet.
In this case:In this case:
it is not only important to have granules with equal dimensionsit is not only important to have granules with equal dimensions,,
butbut
it is also important that the size of these granules are within ait is also important that the size of these granules are within a
certain range, which is in function with the diameter of thecertain range, which is in function with the diameter of the
die.die.

 The essential concept when producing tablets, is thatThe essential concept when producing tablets, is that
the granules which we want to fill the die with, mustthe granules which we want to fill the die with, must
bebe more fine as the diemore fine as the die becomesbecomes smaller.smaller.
 In fact there are well-defined relations between theIn fact there are well-defined relations between the
size of the granules & the diameters of the die, insize of the granules & the diameters of the die, in
order to have a filling uniformity of the die, &order to have a filling uniformity of the die, &
so to obtain tablets, which remain within the limits ofso to obtain tablets, which remain within the limits of
the weight uniformity.the weight uniformity.

For example:For example:
 If we have a die with diameter of 3/16 of inch, weIf we have a die with diameter of 3/16 of inch, we
should prepare granules, which pass through a sieveshould prepare granules, which pass through a sieve
with mesh 20 (20 mesh /1 linear inch).with mesh 20 (20 mesh /1 linear inch).
 If we have a die with diameters of 7/16 inch, we haveIf we have a die with diameters of 7/16 inch, we have
to have granules with dimensions that pass through ato have granules with dimensions that pass through a
sieve of mesh 12.sieve of mesh 12.

Quality ControlsQuality Controls
1.1. Weight uniformity test.Weight uniformity test.
2.2. Dissolution profile.Dissolution profile.
3.3. Friability test.Friability test.
The granules must be:The granules must be:
packaged in order to be used as final pharmaceutical dosagepackaged in order to be used as final pharmaceutical dosage
form, orform, or
added to other substances for example to prepare the tablets,added to other substances for example to prepare the tablets,
So, we must avoid the transformation of the granules intoSo, we must avoid the transformation of the granules into
powder during the manipulation processes.powder during the manipulation processes.

Friability testerFriability tester

Some Particular Granules:Some Particular Granules:
1.1. Sustained release granules.Sustained release granules.
2.2. Enteric coated granules.Enteric coated granules.
3.3. Effervescent granules.Effervescent granules.

Granules Formation and Properties

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