Week 10 - Compaction and Tabletting Flashcards
What is compression
Forcefully pressing powder to form a compact tablet
- apply more force = thinner compact
- do NOT over compress (too much force) = tablet won’t disintegrate + dissolve = LAMINATION
- During compression air between powder particles are released
- applying force causes particle deformation = new bonds form to give tablet - Compact tablet needs to be strong enough to withstand packaging, transport etc.
Applying force / stress leads to:
- elastic deformation which can lead to plastic deformation OR breaking of material (depending on particle size)
List the 4 types of deformation behaviours
- Elastic deformation
- Plastic deformation
- Young’s modulus
- Brittle-ductile transition
Explain the deformation behaviour of particles for “elastic deformation”
Deformation is reversible in every single particle
- as stress on material ↑ the strain also ↑
- Apply stress to material causing them to bend
- When stress is removed material bounce back / return to original form
Explain the deformation behaviour of particles for “plastic deformation”
Deformation is irreversible
- NEEDED for tablet formation
- Apply a lot of stress / force to material it changes shape
- ‘Yield strength’ = the stress required for deformation to occur
- higher yield strength = harder to plastically deform
- after this stress value can ↓ stress as molecules begin to flow
- ‘Fracture point’ = max. stress / plastic deformation after this point molecule will snap
- AUC = max. stress we can put into material before it beaks / material’s toughness - When stress is removed it remains in that shape
- remain because new bonds have formed between particles
Explain the deformation behaviour of particles for “brittle-ductile transition (BDT)”
BDT is the particle size where plastic deformation occurs
- Applying stress to large particle = more likely to snap than plastically deform
- material breaking = ↓ particle size
Explain the deformation behaviour of particles for “Young’s modulus”
Young’s modulus value tells us how hard / easy it is to deform our material
- it is a constant (work out by dividing stress by strain)
- High Young’s modulus = material is hard to deform
- more rigid / strong material is = harder to make into tablet - Low Young’s modulus = easy to deform material
- porous material lowers modulus
- more pores = softer material = easy to compress - Diff. excipients have diff. Young’s modulus
- e.g. fillers have high modulus
- e.g. binders have low modulus
Explain Heckel analysis
It allows us to control the plastic deformation of powder mixtures
- observe how porosity changes with applied pressure
ln [1/e] = KP + A
- takes into account yield strength, particle ere-arrangements + plastic deformation
What influences yield strength
‘Yield strength’ = the stress required for plastic deformation to occur
- Particle size of powder mix
- Moisture content
- Lubrication (prevents powder sticking in moulds)
- Punch dimensions (how big tablets are)
What is the process for compression
- Compress / exert force on powder = ↑ tensile strength = particles become harder
- Deformation occurs + new bonds begin to form
- REMAIN in this area - If continue ↑ tensile strength = over-compression = lamination
- tablet becomes too thins + break
compression force profile
What is the difference between direct compression and non-direct compression
Direct:
1. Mix drug + excipients (binder, filler, disintegrant etc.)
2. Add a lubricant + mix again (for 5 min max.)
3. Put powder mix into tablet press = tablet formed
Non-direct:
1. Mix drug + excipients
2. Granulation to form granules
3. Add more excipients + mix
4. Add lubricant + mix
5. Put powder mix into tablet press = tablet formed
What bonds are formed during compression
- Mechanical interlocking
- as particles flow around each other - Binder bridges
- have binder excipient in powder mix = binder is compressed with powder - Liquid bonding
- have liquid layer on top of particles
What excipients are used for immediate release tablets
- Fillers
- lactose, cellulose, microcrystalline cellulose - Binders
- gelatine, cellulose, microcrystalline cellulose - Disintegrants
- ion exchange resins, citric acid - Lubricants
- talc - Glidants
- talc, fumed silica
List the different tableting machines
- Single station tablet press
- Rotary tablet press
Can form single tablets or multi-layer tablets, matrix tablets
- multi-layer = fill 1st layer compress, fill 2nd layer compress etc,
Explain how tableting occurs with a single station tablet press
- Hopper shoe which feeds powder into a die
- lower punch is below die - Upper punch comes down + compresses powder = tablet formed
- Upper punch moves out
- Lower punch moves up to push tablet out + hopper pushes table out of way + fills die again
Explain how tableting occurs with a rotary tablet press
- Hopper shoe which feeds in powder into multiple dies
- As upper rotary moves along the upper punch they will move down + compress powder = tablet formed
- as upper rotary moves of upper punch they will move out - Lower rotary moves along lower punch = tablets are pushed out
