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Kirstys Flashcards > MDM: Powders & Granulation > Flashcards

MDM: Powders & Granulation Flashcards

1
Q

What is a powder?

A

A solid substance in the form of tiny loose particles.

Drug powder normally mixed with powder excipents to produce final product

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2
Q

What are oral an external powders called?

A

Oral and dusting powders

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3
Q

What are the techniques used to derermine powder properties?

A
  • Angle of response
  • Bulk Density
  • Flow through an orifice
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4
Q
  1. What is angle of response?
  2. What effects angle of response?
  3. What does angle of response tell you?
  4. State the calculation used to determine it
A
  1. Angle of repose – maximum angle to the horizontal made by a static heap of powder.
  2. Angle increased by smaller particle size, increased surface roughness and increased moisture content of the powder.
  3. inter-particulate cohesion
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5
Q
  1. What is bulk density?
  2. What is bed porosity? How does BD effect this?
  3. What does BD tell you?
A
  1. Bulk density – density of a powder taking into account its packing fraction (k).
  2. Percentage of the volume which is taken up by air is known as the bed porosity. An increase in bulk density and a consequent decrease in bed porosity is an indicator of how well the powder flows.
  3. friction and percentage compressibility
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6
Q

What calculations are used to determine BD?

A

Calculations using bulk density (BD) measurements:

  • Hausner’s ratio = Tapped bulk density/poured bulk density.

Values close to 1 indicated non-cohesive powder with good flow characteristics; > 1.5 indicates a cohesive powder with poor flow.

  • Carr’s compression ratio =((Tapped BD - poured BD)/ tapped BD) x 100

CCI of < 10 indicates excellent flow , whereas > 20 indicates poor flow.

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7
Q

What is Critical orifice diameter? What does it tell you?

A

Flow through an orifice – flow rate

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8
Q

What is a granule

A

A larger particle consisting of aggregated powder particles

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9
Q

Explain what happens to granules as you mix

A
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10
Q

Why do we require granulation products?

A
  • To prevent segregation
  • Improve flow properties
  • To improve compaction properties
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11
Q

What are methods used to make granulations?

A
  • Dry granulations:

Powders mixed and compressed to form a ‘slug’. Slugs are milled and sieved. Used for APIs that don’t compress well after wet granulation or are sensitive to granulation fluid

  • Wet granulations:

Powder mixed and a granulation fluid added. Wet granules screened, sieved and dried

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12
Q

What forced are used to bind powder particles in granules together?

A
  • Adhesive and Cohesive forces
  • Interfacial forces
  • Solid bridges
  • Attractive Forces
  • Mechanical interlocking
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13
Q

Describe adhesive and Cohesive forces in the immobile liquid films

A

If sufficent liquid in a powder is present, it will from a thin immobile layer. This decreases interparticular distance and increases contact area between particles. Bond strenght between particles will be increased as van der waals force of atraction are proportional to interparticular distance

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14
Q

Describe interfacial forces

A

During wet granulation a granulation fluid is added. Enough liquid is added to produce a mobile film between particles. There are three states of water distrubtution between particles:

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15
Q

Describe solid bridges

A

These can be formed by:

  • Partial melting
  • Hardening binders
  • crystilisation of dissolved substances

Size of crystals determined by rate of drying: slower drying - larger

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16
Q

Describe attractive forces

A

If no granulating fluid there are 2 forces which opperate:

  • Van der waals
  • Electrostatic
17
Q

Describe mechanical interlocking

A

Particle size and shape determine degree of interlocking

18
Q

What are granulation equipment?

A
  • Shear granulator
  • High speed mixer
  • Fluidised- bed granulator
19
Q

Describe a shear granulator

A

Powder placed in a planetary mixer and granulation fluid added during aggitation

20
Q

Describe high speed mixer

A

Powder mixed in bowl by impller while granulation fluid added. When moist mass formed a chopper is switched on to break it up into granule

21
Q

Describe a fluidised bed granulator

A

Heated air blown up through powder to produce a fluidised bed. Granulation is sprayed onto bed to produce granules that are subsequently dried in the hot air

22
Q

What is a common application of wet granules?

A

Multiparticulates- pellets

23
Q

What are multiparticulates and there properties?

A
  • Small
  • Spherical
  • narrow particle size distribution
  • low friability reduces dust
  • Distributed through GI tract
  • High SA/ volume ratio: ideal surface for coating, maximises drug dissolution
24
Q

How are multiparticulates/ pellets formed?

A

Dry blend —> Wet granulation —> extrusion (forms uniform rods) —-> spheronization (forms spherical particles) —> drying —> screening (narrow size distribution) —> coating = tablets / capsule filling

25
Q

What are advantages of pellets in the GI tract?

A
  • Less irregular passage through GI tract
  • Less chance of ulceration
  • Failure of individual pellets will not result in dose dumping
  • Can contain high levels of API wihtough large particle
26
Q

What are advantages of pellets?

A
  • immediate/ controlled release
  • can be filled into hard gelatine capsules of compacted into tablets
  • Can contain 2 or more API
  • Incompatabilities can be manufcatured as pellets seperated
  • Can be coated at different coat weights
27
Q

Advantages of pellets in processing

A
  • Increased BD
  • Improved flow properties
  • Reduced dust production
  • Increased strength
  • Smooth surface for coating
  • Regular shape for packaging
28
Q

Disadvantages of pellets in processing

A

More energy/ labour required than other granulation methods especially due to high levels of solvent required

29
Q

Factors effecting pellet quality

A
  • Water content:

Too less: dust formation

More: agglomeration of pellets (larger spheres)

  • Composition:
  • Different grades of same excipent
  • solubility of drug and excipents
  • particle size of starting material
  • amount/ type pf granulation fluid
30
Q

What are examples of extrusion types?

A
  • Screw extruder
  • roller extruder
31
Q

Factors effecting pellet quality (Extruders)

A
  • Speed - surface roughness, shark skinning with increased speeds
  • Type: different densities
  • Temperature: increased temperature causes evaporation of granulation fluid
  • Extrion screen: diametre of perforstions effect pellet size
32
Q

What are process variables effecting pellets

A
  • Feed of wet mass
  • Dianeter of die and length of die - effects final pellet size
  • water content
33
Q

Factors effecting pellet size (spheronisation)

A
  • Speed - particle size of pellets, pellet hardness, bulk
  • Time and load - no correlation
34
Q

Discuss the critical nature of the absolute amount of water used in terms of the rheological properties of the wet granulation and the effect of extrudate quality

A

If too dry, the cohesive and adhesive forces will be weak and formation of extrudate impossible from the partially wetted powders. The granulation will not exhibit the plastic flow necessary for successful extrusion and densification. Spheronisation will result in a fragmented powder. If too wet, extrusion will be easy but spheronisation will produce large spheres.

35
Q

Following spheronisation, the water content of the spheronised pellets is measured at 30 %(w/w) and the total quantity of pellets is 250 g prior to drying.

(a) Give a reason for the reduced amount of water measured in the spheronised pellets compared with the wet granulation prior to extrusion

A

Frictional processes during extrusion and spheronisation produce heat which causes granulating fluid to evaporate and exposure to the environment causes further desorption of water.

Kirstys Flashcards (116 decks)

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