Powder Mixing and Flow Flashcards
Importance of powder mixing?
content uniformity
- uniformity of weight
- uniformity of dissolution rate
- uniform bioavailability
How can a random mixture be obtained?
- two different free flowing powders of same particles size, shape and density are mixed
- particles are not cohesive
quality of mixture is determined by the mixing time
Effect of reducing the particle size too much?
- increased cohesiveness –> aggregation
- poor mixing
- poor powder flow properties
What is segregation dependent on?
opposite of mixing
- particle size
- particle shape
- particle density
3 types of segregation
percolation
trajectory
elutriation
Percolation segregation
small particles fall through the voids between larger particles
Trajectory
larger particles travel faster and further than smaller
Elutriation
during mixing, small particles are blown into the air and settle as a layer on top of larger particles
may lead to some degradation, poor distribution, poor drug release and patient harm
e.g. in dry powder inhalers, drug and carrier particles sit on top, exposed to moisture, drug instability
When can a separation of powder occur?
- when they powder exhibits different densities even if they are the same size
effect of spherical particles
- good flowability
- easy mixing
- easy segregation
effect of elongated, needle particles
- tendency to interlock –> higher SA
irregular particles
- cohesive effects due to greater surface area increases likelihood of dusting out
