Lecture 1- Powder Flow

Question 1

What is flowability?

Answer 1

The ability of a powdered material to flow from a stationary to a moving condition
*free flowing powder= moves consistently and steadily with particles moving independently of one another
*non-free flowing powder= contains cohesive particles moving as agglomerates

Question 2

What is floodability?

Answer 2

Unstable, liquid-like flow of powder
*flooding caused by fluidising a mass of particles by air or other stimuli
*type of flow is uncontrollable and undesirable

Question 3

Producing free-flowing powders

Answer 3

-improves mixing
-uniformity of feed- maintains tablet weight
-reproducible filling of tablet- improves weight uniformity
-uniformity of dose
-reproducibility of the finished product

Question 4

Particle properties

Answer 4

*adhesion
- unlike surfaces; e.g. powder and feed hopper and die wall
-forces of electrostatic attraction
*cohesion
- like surfaces such as component particles of a bulk solid
-short range forces.g. Van der waal’s forces

Question 5

Assessment of powder flow

Answer 5

*direct methods- hopper flow rate or flow meter
*indirect methods- angle of repose, angle of difference, angle of spatula, carr’s consolidation index etc

Question 6

Flow through hopper

Answer 6

-time taken for a known amount of powder to flow through the hopper
Method- page 10

Question 7

Recording flow meter

Answer 7

Similar to flow through hopper method however the powder is allowed to discharge from a hopper onto a balance

*sodium chloride= uniform flow pattern, easy flowing powder
*lactose regular= more cohesive, localised disruption in flow rate and flow pattern is not uniform

Question 8

Indirect methods of measurement

Answer 8

Slides 13, 14, 15, 26
16- equation

Question 9

Angle of fall

Answer 9

-results after disturbing the initial angle of repose heap
-INCREASES flowability and DECREASES angle of fall

Question 10

Angle of difference

Answer 10

Angle of repose- angle of fall= angle of difference

INCREASES angle of difference INCREASES floodability

Question 11

Equations

Answer 11

Carr’s consolidation index=
CCI= tapped identity- initial density/ tapped density x 100

Fluff density=
Powder weight/initial volume

Tap density=
Powder weight/ final volume

Question 12

Physical and environmental factors influencing powder flowability

Answer 12

Physical=
•Particle size distribution
•The presence of fine particles
•Shape of particles
•Friction Coefficient of the particle surface
•Cohesiveness of powder
•Adhesiveness of powder
•Electrostatic charge on particles
•Compressibility of powder
•Moisture content of powder
•Temperature of powder

Environmental=
•Humidity of the atmospheric air
•External pressure
•Vibrations

Question 13

Particles properties- free-flowing powders/ good flowability

Answer 13

oNarrow particle size distribution
oSmall surface area/unit weight
oSpherical shape
oLow cohesiveness
oHigh hardness, not easily deformed
oMinimal induced electrostatic activity
oNon-hygroscopic
oHigh particle density
oLow particle compressibility

Question 14

Particle properties- floodable flow

Answer 14

-Larger available surface area
-Spherical shape
-Uniform size
-Exist as individual particles
-Does not agglomerate
-Low density
-Non hygroscopic

Question 15

Shear strength

Answer 15

Cohesion- stress (force per unit area) necessary to shear a powder bed under condition of zero normal load
-can be determined from the resistance to flow caused by cohesion/friction + can be measured using a shear cell

Question 16

Tensile strength

Answer 16

-Tensile strength of a powder bed is characteristic of the internal friction or cohesion of the particles
-powder bed is caused to fail in tension by splitting rather than failing in shear by sliding
Measurement= using a tilting table method - slide 32

Question 17

Formulation of flow activators

Answer 17

-glidants
-some lubricant and anti-adherent
-reduce adhesion and cohesion
-talc, maize starch and magnesium stearate
-colloidal silicone dioxide - very high specific surface area - low density