Preformulation - compaction Flashcards
What is the difference between compression and compaction?
Compression = Particles forced into close proximity,
reducing powder porosity and volume, whereas, compaction = particles cohere to form a solid specimen (compact/tablet) of defined geometry
How well a powder blend is compressed affects what?
The tablet hardness and friability which in turn is related to dosage form integrity and bioavailability.
State the 4 phases of the compression cycle.
a. Filling
b. Packing and initial compression (precompression)
c. Main compression
d. Decompression
e. Ejection - final tablet
Describe the bonds between particles during compaction.
- Bonds establishes as particles move closer together during the volume reduction process
- These particle-particle interactions increase the mechanical strength of the powder bed
Describe the process of particle rearrangement.
- Particles rearranged under low compaction pressure to form a closely packed structure
- Smaller particles fill the void between the larger particles to give a closer packing arrangement
- As compression force increases the energy is evolved in the form of heat because of inter particulate friction
- increase in particle surface area further increases the possibility of forming inter particulate bonds
What does the extension of volume reduction of powder bed depend on?
The mechanical properties of the powder.
- Brittle materials generally undergo extensive fragmentation which results in tablets of relatively high porosity due to large number of bonding points which prevent further volume reduction
- Ductile material form tablets of low porosity as the high degree of plastic deformation enables the particle to move close to each other
What happens when compression force is applied to the powder bed?
It causes development of stress and local deformation of the particles can occur:
Stress applied - deformation - removal of stress - original state regain (elastic deformation) OR original state lost (plastic deformation)
What is compression pressure?
An external force which occurs when a physical force is pressed inward on the solid surface of an object, deforming it either permanently or temporarily
What does the magnitude of compression force determine?
- Whether a compact tablet forms
- Tablet volume, porosity and density
- Tablet tensile strength
What can compression pressure influence?
Mechanical strength and release properties of tablets.
State the heckel equation.
ln 1/e = ln KP + A
e = porosity
P = applied compression pressure
K = constant relating to particle deformation
A = Constant relating to particle rearrangement and fragmentation
Describe the three regions of a typical Heckel plot
Region I: curvature is due to particle
rearrangement and fragmentation
Region II: particle deformation, either plastic or elastic, is controlling the mechanism of powder
compression
Region III: elastic deformation of the compact
control the process
State the particle properties.
Plasticity - deformation increases contact area; plastic deformation prevents elastic recovery
Crystallinity - amorphous more compactable than crystalline
Morphology - Needle-like less compatible than equidimensional
Hydrates - More compactable than anhydrous
What is the tensile strength the result of?
Inter-particle bonding within tablet
Determined using diametric compression test
The greater the tensile strength the more resistant the tablet is to crushing
Give reasons for capping and lamination.
- Too dry granules
- High speed compression
- Rapid decompression
- Air entrapment
