Powder flow Flashcards
Why is Powder flow important ?
- Tabletting
- Granulation
- Capusulation
For transfer in the manufacturing process
State 3 types of transfer in the manufacturing process ?
- Pneumatic transfer
- Hydraulic transfer
- Gravity or mechanically assisted feeding
Name 3 methods used for measurement of Powder flow
1) Hausner ratio
2) Carr index
3) Angle repose
State 6 consequences of poor powder flow
1) Uneven mix into food
2) Risk of degradation
3) No-uniformity of dose
4) Problems w/reproducibility of dosage forms (which require powder transfer)
5) Risk of capping and lamination (tabletting specific problem) (due to entrapped air w/in powders)
6) Increase in particle-die-wall friction and risk of dust contamination
What is Adhesion
Clinging of unlike molecules
What is Cohesion
Clinging of like molecules
due to: 1) VDW forces
- dependent on nature of particles
- VDW forces increases as particle size decreases
2) Moisture
(formed b/wn particles when above critical humidity)
Factors affecting powder flow
- Resistance to flow; due to Adhesion/Cohesion
- Particle size;
< 10micrometre particles extremely cohesive
< 50micrometre particles = irregular/no flow due to VDW
> 50micrometre = free flowing
-Density of particles
(dense particles = less cohesive)
- Particle shape
(Spherical particles have less interparticulate contact than uniform/irregular shaped particles) - Particle size distribution
- Particle surface
(Electrostatic forces increases Cohesion) - Particle texture
(Rough surfaces are more cohesive) - Humidity
(Absorbed moisture on particle surface) - Processing conditions
- Powder density
- Powder porosity
Rearrangement of particle packing geometry can lead to 2 changes. Name them
1) Change in bulk volume
2) Change in powder density
Different geometric packing can be achieved with particles of the same shape. TRUE or FALSE
TRUE
What is Bulk density ?
The density of a powder sample
The volume of a powder sample includes ?
Particulate volume and Interparticulate pores
Define ‘Minimum bulk density’
The maximum vol occupied by powder
Define ‘Poured bulk density’ (Do)
Volume of powder measured after pouring into a cylinder
Define ‘Tapped bulk density’ (Df)
The maximum bulk density (in theory) that can be achieved w/out deformation of particles
Relative density (k) is also known as …
Packing fraction or Fractional solids content
What is the equation for bulk density
k = bulk density/true density
What is meant by ‘Porosity of powder bed’ ?
The proportion of powder bed that is occupied by pores
Name 2 things added to powder to improve formulation ?
1) Glidants (added to powder to improve flowability)
2) Anti-adherent properites
Give 3 examples of Anti-adherent properties
1) Magnesium stearate
2) Colloidal silicon dioxide (helps reduce bulk density of powder bed)
3) Sodium bicarbonate (May improve flow of hygroscopic powder)
Name 2 types of powder flow in a hopper
1) Mass flow
2) Core flow
All material is in motion during discharge in Mass flow. TRUE or FALSE
TRUE
In Mass flow, the whole bulk of powder moves downwards. TRUE or FALSE
TRUE
Mass flow has a wall friction angle of about 20 degrees. TRUE or FALSE
TRUE
During Core flow, some powders remain undisturbed. TRUE or FALSE
TRUE
During Core flow, dead space occurs during discharge. TRUE or FALSE
TRUE
State one difference b/wn Mass and Core flow
- MASS flow; all material is in motion during discharge (move downwards)
whereas in CORE flow; some powders remain undisturbed (dead space occurs during discharge)
Core flow has a wall friction angle of about 50 degrees. TRUE or FALSE
TRUE
State 3 problems associated with Core flow
1) Flow from hopper can suddenly stop
2) On the other hand, sudden rapid discharge of powder can occur
3) Segragation of powder
Particles just above
orifice flow freely. TRUE or FALSE
TRUE
A ‘tongue’ is formed
above the orifice. TRUE or FASLE
TRUE
At which angle of repose is powder considered to have ‘good flow’ ?
when angle of repose is <30degrees
At which angle of repose is powder considered to have ‘problematic flow’ ?
when angle of repose is
> 40 degrees
Tapped bulk density / Poured bulk density = ?
Hausner ratio
When value of Hausner ratio is about 1.2, what does this suggest ?
The powder is free flowing
When value of Hausner ratio is greater than 1.6, what does this suggest ?
The powder is Cohesive
What equations can be in bulk density measurement ?
Tapped bulk density / Poured bulk density = Hausner ratio
and CARR INDEX
The smaller the Carr index value, the better the powder flowability. TRUE or FALSE
TRUE
Describe how to measure Tapped density according to the BP
Carry out 10,500 and 1250 taps and read the
corresponding volumes (V10, V500, V1250) to the
nearest mL
