Pharmaceutics: Powder Mixing Flashcards
What is the aim of powder mixing?
To distribute drug and excipient particles uniformly among one another (homogeneity of contents)
Effect of powder mixing in the long run?
Affects
- content uniformity in final pharmaceutical product
- the therapeutic efficacy
- patient safety.
Out of gases, solids and liquids, which is more difficult to obtain homogeneity with?
Solids because they don’t flow as freely as fluids (gases and liquids)
What are the challenges faces when mixing powders?
1) difficulty obtaining homogeneity when mixing a small amount into a large bulk
2) segregation of particles
3) over-mixing which degrades particles hen affecting their properties.
Types of powder mixtures?
1) positive - mix spontaneously
2) neutral - don’t mix/segregate spontaneously
3) negative - segregate spontaneously
Types of mixtures that can be achieved?
1) perfect - completely homogeneous (unattainable with powders)
2) random - close to complete homogeneity with free-flowing particles of similar size and density.
3) ordered - small particles adsorbed onto larger ones and move inter-independently. Cohesive particles of different sizes.
What type of mixtures are powders and what type of mixtures do they achieve?
Powders are neutral mixtures and when they form homogeneous mixtures, it is random type of mixture.
How do you asses the homogeneity of random mixtures?
doing statistical calculations and sampling small amounts from different parts of the mixture and analysing their composition.
How can you reduce variances when sampling?
Take larger samples
What are 5 essential performance characteristics of equipment’s used to mix powders?
1) homogeneity without degradation
2) short mixing time
3) reproducible
4) high yield
5) cleanable
7 desirable features when choosing equipment’s to mix powders?
1) versatile - able to mix wide range of materials efficiently
2) Scalable—small to large batches.
3) Integrates with upstream/downstream processes to facilitate automation and continuous processing.
4) Small footprint.
5) Cost and energy efficient.
6) In-line monitoring.
7) Environmental controls, e.g. temperature, vacuum.
What is the basic principle of powder mixing operation?
splitting up groups of particles (agglomerates) and rearranging them spatially.
Three mechanisms of mixing:
1) Convective mixing - between large groups of particles
2) Shear Mixing - mixing at an interface between large groups of particles
3) Diffusive mixing - mixing within large groups of particles.
How does a tumbling mixer work?
- uses mainly shear and diffusing mixing mechanisms.
- suitable for free-flowing particles.
- rotation of mixing vessel mixes the powders together
How does a shear mixer work?
- uses high velocity rotating blades to create a high shear force to break up agglomerates.
- uses mainly shear and diffusing mixing mechanisms.
