Compaction Flashcards
What is compression ?
- particles forced into close proximity, reducing powder porosity and volume
What is compaction ?
- Particles cohere to form a solid specimen (compact/tablet) of defined geometry
What does compaction require ?
- requires compression
What is the relationship between powder blend compression and tablet hardness?
- a well-compressed blend results in a stronger tablet with better integrity
- influences its bioavailability by ensuring proper dissolution and absorption in the body.
What are the 4 phases of the tablet compression cycle?
- Filling
- Packing and initial compression(precompression)
- Main compression
- Decompression and ejection (final tablet)
How does compaction affect the mechanical strength of a powder bed?
- during compaction, as particles move closer together during volume reduction, bonds are established between them
- these particle-particle interactions increase the mechanical strength of the powder bed, contributing to a stronger tablet.
What happens to porosity, bulk volume, and bulk density during particle rearrangement?
- Porosity and bulk volume decrease
- while bulk density increases.
What is the result of particle deformation during compression?
- the contact surface area and cohesion increase
What are the two possible outcomes after the compressive force is removed?
- Elastic recovery (low cohesion, no compaction) and - plastic deformation (high cohesion, compaction)
What happens to particles under low compaction pressure?
- Particles are rearranged to form a closely packed structure.
How do smaller particles affect the packing arrangement in a powder?
- smaller particles fill the voids between larger particles, resulting in a closer packing arrangement
What happens when the compression force increases?
- energy is evolved in the form of heat due to interparticulate friction
How does an increase in particle surface area affect interparticulate bonds?
- It increases the possibility of forming interparticulate bonds.
What powder characteristics affect the formation of inter- or intraparticulate bonds?
- Particle size, particle size distribution, density, surface properties, and interparticulate voids.
What does the extent of volume reduction in a powder bed depend on ?
- the mechanical properties of the powder.
What happens when brittle materials undergo volume reduction?
- they fragment extensively, resulting in tablets with high porosity due to many bonding points that prevent further volume reduction.
How do ductile materials behave during volume reduction?
- form tablets with low porosity because plastic deformation allows particles to move very close to each other
How do different crystal morphologies affect packing structure?
- Different crystal morphologies, such as spherical, cubical, and acicular, have different tendencies to pack into a close structure
What happens when compression force is applied to a powder bed?
- causes the development of stress, leading to local deformation of the particles
What is elastic deformation?
- elastic deformation occurs when the material regains its original state after the stress is removed.
What is elastic deformation?
- elastic deformation occurs when the material regains its original state after the stress is removed
- resume original shape instantaneously
What is plastic deformation?
- happens when the material loses its original state and does not return to it after the stress is removed
- results are permanent
What factors influence the type of deformation a material undergoes?
- depends on the material’s physical properties, as well as the rate, magnitude, and duration of the applied force and induced stress.
What is compression pressure?
- an external force applied inward on the solid surface of an object
- deforming it either permanently or temporarily, depending on the material and force magnitude.
What does the magnitude of compression force determine?
- it determines whether a compact (tablet) forms
- well as the tablet’s volume, porosity, density
- tablet tensile strength.
What does the Heckel equation describe in relation to pharmaceutical powders?
- describes the compaction properties of pharmaceutical powders, relating porosity and compression pressure.
What is the Heckel equation ?
- look online
What does a typical Heckel plot represent?
- a typical Heckel plot represents three different powder compression regions during tablet formation.
What happens in Region I of a Heckel plot?
- the curvature is due to particle rearrangement and fragmentation.
What occurs in Region II of a Heckel plot?
- In Region II, particle deformation, either plastic or elastic, controls the mechanism of powder compression
What is observed in Region III of a Heckel plot?
- elastic deformation of the compact controls the powder compression process.
How does plasticity affect particle deformation?
- plasticity increases the contact area between particles
- plastic deformation prevents elastic recovery.
How does plasticity affect particle deformation?
- plasticity increases the contact area between particles
- plastic deformation prevents elastic recovery.
How does crystallinity affect compactability?
- amorphous particles are more compactable than crystalline particles
How does particle morphology influence compactability?
- Needle-like particles are less compactable than equidimensional particles.
How do hydrates compare to anhydrous particles in terms of compactability?
- Hydrates are more compactable than anhydrous particles because the water of hydration can act as a plasticizer.
What happens in Region 1 of tensile strength during compression?
- compression occurs, but no compact (tablet) is formed.
What occurs in Region 2 in terms of tablet tensile strength?
- a higher compression pressure results in a greater tablet tensile strength
What is observed in Region 3 regarding tensile strength?
- the maximum tensile strength is achieved.
What is tensile strength in tablets the result of?
- the result of inter-particle bonding within the tablet.
How is tensile strength typically determined?
- determined using a diametric compression test.
What does greater tablet tensile strength indicate?
- greater the tablet tensile strength, the more resistant the tablet is to crushing.
What assumption is made when measuring tensile strength?
- It assumes simple tensile failure
What is the tensile strength equation
- σt = 2F/ pi x d x h
Tensile strength of tablets depends on: - F Tablet fracture force or crushing strength (in
Newtons) - d Tablet diameter
- h Tablet thickness
How does the shape of a tablet affect its tensile strength?
- Tablets with extreme shapes
- such as flat faces or deep convex shapes, are inherently weaker and have lower tensile strength.
Reasons for capping and lamination
- Too dry granules
- High speed compression
- Rapid decompression
- Air entrapment
