Pellets + Extrusion

Question 1

What are pellets + granules commonly filled in?

Answer 1

Capsules or pressed into tablets

Question 2

What are the advantages of spherical pellets compared to granules?

Answer 2

Greater density
Better flow properties
Lower friability
Narrower particle size distribution
More uniform packing
Smoother surface

Question 3

What are the advantages of spherical pellets because of?

Answer 3

Smoother, more spherical morphology
Compression + densification during pellet formation

Question 4

What are the steps involved in pellet formation?

Answer 4

Agglomeration = granules agglomerated into larger particle
Extrusion = form extrudate
Pelletisation
Spheronisation = spherical dense pellets

Question 5

What is extrusion?

Answer 5

Pushing semi-solid material through a screen

Question 6

What does extrusion produce?

Answer 6

Elongated, cylindrical, rod-shaped extrudate

Question 7

Describe screw extruder

Answer 7

Contains Archimedes screw
= compresses material
= moves material through cylinder

Question 8

What are the 2 types of screw extruder?

Answer 8

Axial screw extruder = screen at end of cylinder
Radial = screen in cylinder wall

Question 9

Describe sieve + basket extruder

Answer 9

Material pushed through screen by rotating device
Sieve = screen at bottom
Basket = screen in wall

Question 10

Describe roll extruder

Answer 10

Material passes through screen using rollers
Extrudate within perforated rollers

Question 11

Describe ram extruder

Answer 11

Material compressed + forced through screen by moving piston

Question 12

What could happen if extruder speed too fast?

Answer 12

Shark-skinning = effects quality

Question 13

What could happen if the extruder temperature is not right?

Answer 13

May affect flow behaviour + stability of thermolabile formulation

Question 14

Describe spheronisation

Answer 14

Uses spheroniser
Particles placed on rotating friction plate, broken into smaller particles + rounded through collision
= spherical pellets

Question 15

Describe friction plate

Answer 15

Crosshatch = most common
Radial = gentler BUT unsuitable for large disc diameters

Question 16

Describe rope movement in spheroniser

Answer 16

Particles thrown outwards by centrifugal force
Particles rebound inwards upon impact of spheroniser wall

Question 17

What are the different mechanisms for spheronisation?

Answer 17

Plastic deformation
Dumbbell break up
Attrition-agglomeration

Question 18

What is plastic deformation?

Answer 18

Edges are rounded + don’t break up

Question 19

What is dumbbell break up?

Answer 19

Dumbbell shape then break up to separate particles then rounded

Question 20

What is attrition-agglomeration?

Answer 20

Particles rounded (fine) then stick together

Question 21

What are the parameters for spheronisation?

Answer 21

Friction plate rotational speed
Charge vol or mass
Retention time

Question 22

Why is friction plate rotational speed parameter for spheronisation?

Answer 22

Smaller plate = higher speed

Question 23

Why is charge vol or mass parameter for spheronisation?

Answer 23

Amount of particle loaded
Overloading = hamper particle interactions with wall + plate
Underloading = hamper particle-particle interactions

Question 24

Why is retention time parameter for spheronisation?

Answer 24

Duration which particles move
3-8mins
Prolonged = increase sphericity + narrower particle size distribution BUT overall larger particle size