Flashcards in Compaction Deck (29)
How are tablets made?
How can tableting be done?
by compaction on a tablet press
What types of tablet presses are there? (2)
single-station tablet press
- suited for small scale manufacture
multi-station (rotary) tablet press
What is compression?
Particles are forced into close proximity, reduced porosity and volume of powder.
What is compressibility?
Amenability to compression
What is compaction?
Particles cohering to form a solid specimen
What is compatibility?
Susceptibility to compaction.
Compression may not necessarily result in...
compaction and compression are two different things.
How can particle cohesion be modified?
What is the compaction cycle? (3)
how tablets are formed.
1) filling step
- the lower punch is partially inserted from the bottom into the dicavity - where the powder is filled inside. pusher comes in and sweeps off any excess.
2) compression step
- upper punch comes from the top and inserts into the dicavity. both upper punch and lower move to compress the powder. the powder is squeezed into a smaller and smaller space.
3) ejection step
- both upper and lower punches move up and tablet is lifted up and collected by a pusher into a vesicle.
Sometimes there is an additional step, what is it and what does it do?
same punch movement as compression but gentler and slower.
the aim to expel the majority of air from the powder in the dicavity.
What determines whether a powder compacts?
- plastic deformation: the change in shape - this is permanent. It helps the particle to stick.
How does Plasticity affect compactibility?
Where deformation increases contact area, plastic deformation prevents elastic recovery.
How does Crystallinity affect compatibility?
Amorphous more compatible than crystalline.
How does Polymorphism affect compactibility?
More stable polymorph is less compactable.
How do Morphology affect compactibility?
Needle-like less compactable than equidimensional.
How do Hydrates affect compactibility?
Hydrates more compactable than anhydrous as the water of hydration can act as a plasticiser.
What does the compression force affect?
determines whether it compacts but also the tablet volume, porosity, density and tensile strength
a measure of empty spaces in a material.
The lower the porosity ...
the denser the tablet.
What happens as you increase the compression pressure?
region 1 - particles rearrange and fragment
region 2 - particles deform plastically
no more room to rearrange
region 3- compact deforms elastically
In (1/e) = KP + A
e - porosity
P - compression pressure
K - constant relating to particle deformation
A - constant relating to particle rearrangement and fragmentation
What is the tensile strength?
A measure of how strongly particles stick to each other.
Measure of how much force it takes to break a tablet too - resistance to crushing.
What happens if tensile strength is too low and too high?
too low - tablets may crumble before patient even uses correctly
too high - won't dissolve when patient takes it.
How can tensile strength be determined?
a diametric compression test.
a compression force is applied until tablet breaks.
How to determine tensile strength for a disc shaped, flat faced tablet:
Ot = 2F / pi dh
Ot = tensile strength
F = tablet fracture force
d = tablet diameter
h = tablet thickness
If you want a tablet with the optimum tensile strength..
avoid making them flat or overly round.