W21 Powder technology Flashcards
two systems/powders
- monocrystalline
- systems with defined habits/shaps - polycrystalline
- systems composed of aggregates of smaller particles (microcrystals)
Particle size
Coarse >350um
Medium 100-350um
Fine 50-100
Very fine 10-50
Micronised 10 >
Coarse, medium, fine - tablet/ capsule
very fine - suspension
Micronised - aerosol
ideal vs real powder
ideal: mono-sized / mono-dispersed
real: poly-dispersed
how to measure size of non-spherical particles
aspect ratio = length / width (breath)
how to change roughness of particle
by changing processing factors and control parameters
1)electrospraying: works by ionising solution of drug and creating spray of droplets. As solvents of droplets evaporate, particles with different morphology produced
2) can use different solvents
==> change morphology/size/surface roughness of particles, how they aggregate, how they flow
who has high cohesion
small particles = high contact area
tangent of angle in angle of repose represent
coefficient of internal friction
tapped density
more (. ) powder = more (. ) = (. ) difference in (. ) and tapped density
cohesive
air trapped
larger
bulk
two formulas to represent tapped density
- Hausner ratio
volume (i) /volume (f) = density (f)/density (i)
- good flow: < 1.2
- bad flow: >1.4 - Carr’s compressibility index
(tapped density - bulk density) / tapped density x 100
- good flow: 5-15
- bad flow: 25 <
different mechanisms of mixing
- convective mixing
- move large portion of powder from one area to another
- no mvm within that individual portion - Shear mixing
- one layer of powder flows over another layer - Diffusive mixing
- particles to tumble over each other
what is a good mix
- Random mix
- probability of finding a type of particle is proportional to the number of them in overall mix - Ordered mix - only for aerosol formulation, not solid dose forms
- when small drug particles stick on larger excipient carrier particles
Types of mixers
- Tumble mixer / roller mixer
- Agitator mixers
Tumble mixer / roller mixer details
mix how
- diffusive, shear mixing
- runs at low speed
Good for
- free flowing powders
- direct compression mixtures for tableting
- lubrication
not good for
- very low drug loading
- mixing odd shaped particles
- wet granulation
Examples
1) V-blender
2) Double-cone mixer
- low shear, not good for very fine particles
- but good that it doesn’t have any dead spots mixisng, easy to clean
3) Rotating cube blender - corner가 있어서 안 쫗음
Agitator mixers details
characterstics
- for shear, convective mixing
- higher shear (quick)
- blade configuration is impt
GOod for
- more cohesive powders
- mixing odd-shapeed particles
- wet granulation
- very low drug loading
considerations for mixing
- endpoint detection
- mixing speeds
- mixing time
- sampling
- blade configuration - if agitator mixer
- Powder quantities
- particle morphology