Powder + Mixing Flashcards
What is the importance?
All solid dosage forms
Content uniformity
Therapeutic efficacy
Patient saefty
What are the challenges?
Homogeneity difficult to achieve
Demixing
Overmixing
When is homogeneity especially difficult to achieve?
Mixing small amounts into large bulk
What happens in prolonged mixing?
Degrades material properties
What are the different types of mixtures?
Positive
Negative
Neutral
What is a positive mixture?
Mixes spontaneously
What is a negative mixture?
Segregates spontaneously
What is a neutral mixture?
Neither mixes nor segregates spontaneously
What is a perfect mixture?
Completely homogenous
What is a random mixture?
Not completely homogenous BUT “close enough”
Ver low content variability
Practically indistinguishable from perfect mixture
What is an ordered mixture?
Small particles adsorbed on to larger particles
Components move inter-dependently
What are the mechanisms of mixing?
Connective mixing
Shear mixing
Diffusive mixing
What is connective mixing?
Mixing between large groups of particles
What is shear mixing?
Mixing at interface between large groups of particles
What is diffusive mixing?
Mixing within large groups of particles
What are the different types of mixers?
Tumbling mixer
Agitator mixer
Shear mixer
Fluidised bed mixer
Static mixture
Describe tumbling mixer
Rotating vessel contains powder
What are tumbling mixers mostly?
Shear + diffusive mixing
What are tumbling mixers suitable for?
Free-flowing powders
What is the performance of tumbling mixers affected by?
Fill vol = not exceed 50-60%
Residence time
Rotation speed
Inclination of angle of mixer
Describe shear mixer
High-speed rotating blade split agglomerates
What are shear mixers mostly?
Shear + diffusive mixing
What are shear mixers unsuitable for?
Friable materials
Describe fluidised bed mixer
High speed air stream disperses particles
What are fluidised bed mixers suitable for?
Medium density <800 kgm*2
Friable powders
Describe static mixer
Particles flowthrough static mixing elements
What are static mixers suitable for?
Continuous processing
Describe agitator mixer
Low shear rotating paddles move powder
What is the Nauta mixer?
Orbital agitator mixer
Describe Nauta mixer
Rotating screw in conical vessel
Rotates axially + orbitally
What must we ensure practically?
Mixer matches material properties
Appropriate fill vol + mixing mechanism
How do you determine appropriate mixing time?
By monitoring mixture at intervals
What does static cause?
Clumping + powder adhesion to mixer
How do you dissipate statics?
Earthing mixer
Mixing at relative humidity >40%
Geometric pre-blending
