Comminution lecture 18

Question 1

How does smaller particle size affect bioavailability?

Answer 1

the smaller the particle, the faster the dissolution and the higher the bioavailability
however, v small particles can result in a v rapid absorption/clearance

Question 2

what are the different particle size ranges?

Answer 2

coarse: >350um
medium/fine powder: 100 - 350um
fine powder: 50 - 100um
very fine powder: 10 - 50um
micronised powder: <10um

Question 3

what is the particle size of inhaled powders?

Answer 3

0.5-1um

Question 4

What is the ‘equivalent sphere’ for?

Answer 4

to reduce the 3D nature to a single number so easier to know particle size

Question 5

determining equivalent sphere is based on what?

Answer 5

surface, volume, sieve aperture, sedimentation charecteristics

Question 6

What is the difference between circumscribed and inscribed circle?

Answer 6

circumscribed - absolute outside of circle/rough edges
inscribed - the biggest ‘full’ circle inside
(see image better explanation lol)

Question 7

what are the different methods used to analyse particle size?

Answer 7

sieve, microscope, sedimentation, laser diffraction

Question 8

Why is the mean better than mode/median?

Answer 8

as it’s determined when size distribution is complete and determines upper and lower size limits

Question 9

define comminution:

Answer 9

the reduction of solid materials from a bigger mean particle size to a smaller mean particle size

Question 10

what is the difference between milling and prolonged milling?

Answer 10

milling = normal –> fine particles (bimodal)

prolonged milling = finer –> finer particles (unimodal)

Question 11

what are the size reduction method particle sizes ranges?

Answer 11

cutting: 100um-100mm
compression: 10um - 100mm
impact: 1um - 10mm
attrition: 1um - 100um
combination of impact and attrition: 1um - 10mm

Question 12

what needs to be considered when particle size is reduced to 1-5um?

Answer 12

• that particle to particle forces will be the main comminution stress
• particle agglomeration might happen

Question 13

Describe the cutting method:

Answer 13

knives/blades on a rotor, causing fracture of particles.
A screen retains the material larger than a specified size (so it’s a self classifying method)
- coarse degree of size reduction in dried granules is due to high shear rates

Question 14

Describe the compression method:

Answer 14

material is compressed by frictional forces between rollers. one roller is mechanically driven, the other is rotated by force
there can be a series of rollers to get smaller sizes

Question 15

What are the 2 impact methods?

Answer 15

• conventional ball mill (filled to 80% porcelain/steel balls)
• vibrational ball mill (filled with 50-70% porcelain/steel balls) BETTER than conventional

Question 16

What are the different sieving methods?

Answer 16

1. agitation
2. brushing
3. centrifugation

Question 17

define separation efficiency:

Answer 17

the effectiveness of a given process in separating particles into oversize and undersize fractions

Question 18

What are the different size separation methods?

Answer 18

sieving (wet is better than dry)
sedimentation
elutriation
cyclone