Tablets: Compression and Compaction Flashcards
What characteristics should a diluent have?
- inert
- hydrophilic
- non-hygroscopic
- biocompatible
- cost effective
- good flow properties
What are the three steps for direct compressed tablets?
- particle size reduction
- mixing
- tablet press
What are the excipients used in compressed tablets?
- filler
- binder
- disintegrant
- glidant
- antiadherent
- lubricant - added as close to tabletting process otherwise it will coat other excipients
- flavour, sweetener and colouring agent
Why would disintegration be faster for direct compression?
no granules
tablet to fine powder particles
What is there an increased risk of in compressed tablets?
segregation caused by wide size distribution
What is compression and compaction?
compression: reduction of bulk volume under applied force
compaction: formation of a solid with defined geometry and strength
What does compression and compaction consist of?
- re-arrangement: less porosity
- deformation: moderate pressure causes deformation and densification and high pressure causes fragmentation
- bonding: formation of interparticular bonds
What is the yield point of powders and what is it effected by?
the point inbetween region of elastic deformation and plastic deformation
- polymorphism
- salt form
- moisture content
- particle size
- compression rate
What happens to granules during rearrangement and deformation?
rearrangement: limited impact for granules
deformation: densification ; loss of intragranular pores
What is more likely in granules attrition/erosion or fragmentation?
attrition/erosion
What can compressibility be assessed by?
- look at properties of ejected tablets
- look at compression/decompression events
What does bonding result from in dry powders?
- solid bridges
- mixing at interface between solid, creates continuous solid phase
- more likely for tablets with a low porosity
- adsorption bonding
- result of reduced inter-particular distances
- mechanical interlocking
- interparticular locking of irregularly shaped rough particles
What does high compactability lead to?
tablets that have
- high resistance to fracture
- low tendency to cap (fracture of bottom or top layer) or laminate (separated into two layers in the middle)
How does compression affect compactability in solid particles?
- fragmentation and plastic deformation are associated to increased tablet strength
- fragmentation lead to formation of smaller particles and decreased porosity - interparticular bonds formed
- plastic deform: increased contact between particles - interparticular bonds formed
- elastic deformation leads to low tablet strength
- higher capping/lamination propensity
- impact of size; smaller tablets lead to increased tablet strength
How does compression affect compactability in granules?
- impact of granulation process
- shape, size porosity, strength
- impact of properties of primary powder particle
- impact on granule composition
- presence of a binder
- binders help bond strength = improved compactability = imporoved tablet strength
