Powder + Mixing

Question 1

What is the importance?

Answer 1

All solid dosage forms
Content uniformity
Therapeutic efficacy
Patient saefty

Question 2

What are the challenges?

Answer 2

Homogeneity difficult to achieve
Demixing
Overmixing

Question 3

When is homogeneity especially difficult to achieve?

Answer 3

Mixing small amounts into large bulk

Question 4

What happens in prolonged mixing?

Answer 4

Degrades material properties

Question 5

What are the different types of mixtures?

Answer 5

Positive
Negative
Neutral

Question 6

What is a positive mixture?

Answer 6

Mixes spontaneously

Question 7

What is a negative mixture?

Answer 7

Segregates spontaneously

Question 8

What is a neutral mixture?

Answer 8

Neither mixes nor segregates spontaneously

Question 9

What is a perfect mixture?

Answer 9

Completely homogenous

Question 10

What is a random mixture?

Answer 10

Not completely homogenous BUT “close enough”
Ver low content variability
Practically indistinguishable from perfect mixture

Question 11

What is an ordered mixture?

Answer 11

Small particles adsorbed on to larger particles
Components move inter-dependently

Question 12

What are the mechanisms of mixing?

Answer 12

Connective mixing
Shear mixing
Diffusive mixing

Question 13

What is connective mixing?

Answer 13

Mixing between large groups of particles

Question 14

What is shear mixing?

Answer 14

Mixing at interface between large groups of particles

Question 15

What is diffusive mixing?

Answer 15

Mixing within large groups of particles

Question 16

What are the different types of mixers?

Answer 16

Tumbling mixer
Agitator mixer
Shear mixer
Fluidised bed mixer
Static mixture

Question 17

Describe tumbling mixer

Answer 17

Rotating vessel contains powder

Question 18

What are tumbling mixers mostly?

Answer 18

Shear + diffusive mixing

Question 19

What are tumbling mixers suitable for?

Answer 19

Free-flowing powders

Question 20

What is the performance of tumbling mixers affected by?

Answer 20

Fill vol = not exceed 50-60%
Residence time
Rotation speed
Inclination of angle of mixer

Question 21

Describe shear mixer

Answer 21

High-speed rotating blade split agglomerates

Question 22

What are shear mixers mostly?

Answer 22

Shear + diffusive mixing

Question 23

What are shear mixers unsuitable for?

Answer 23

Friable materials

Question 24

Describe fluidised bed mixer

Answer 24

High speed air stream disperses particles

Question 25

What are fluidised bed mixers suitable for?

Answer 25

Medium density <800 kgm*2
Friable powders

Question 26

Describe static mixer

Answer 26

Particles flowthrough static mixing elements

Question 27

What are static mixers suitable for?

Answer 27

Continuous processing

Question 28

Describe agitator mixer

Answer 28

Low shear rotating paddles move powder

Question 29

What is the Nauta mixer?

Answer 29

Orbital agitator mixer

Question 30

Describe Nauta mixer

Answer 30

Rotating screw in conical vessel
Rotates axially + orbitally

Question 31

What must we ensure practically?

Answer 31

Mixer matches material properties
Appropriate fill vol + mixing mechanism

Question 32

How do you determine appropriate mixing time?

Answer 32

By monitoring mixture at intervals

Question 33

What does static cause?

Answer 33

Clumping + powder adhesion to mixer

Question 34

How do you dissipate statics?

Answer 34

Earthing mixer
Mixing at relative humidity >40%
Geometric pre-blending