milling

1. Industrial pharmacy I
Lec 4:
milling
Pharmacist
Hussein kadhim alkufi
MSc in pharmaceutics
Collage of thi-qar
University of pharmacy

2. Milling
As process for reducing of particle size of solid,
sometimes we have other terms crushing,
disintegration, dispersion, grinding and
pulverization.
all these terms can be used some times instead
of milling term depending on
1. Product
2. Equipment
3. Process

3. Milling
The most commonly classification used for the
milling equipment is depend on particle size
so will coarse, intermediate and fine.
Size is conventionally expressed in terms of
mesh( number of opening per linear inch of a
screen).

4. So for coarse milling this produce particle larger than
20 mesh or 840 µm
So intermediate milling this produce particle with
range 200 – 20 mesh or in other words 74 – 840 µm
Fine milling this produce particle with size less than
200 mesh or 74 µm
Note: Some mills (equipment for milling process) can
be used to give more than one type of particle size
into different successive processing like ?????????

5. Pharmaceutical application of milling
1. The milling can be used for increase the
therapeutic effect of some poorly H2O
soluble drugs by at the particle size reduction
and increase surface area
Ex: Griseofulvin prepared as micronized powder
2. By controlling the particle size, specific SA
influences the duration of adequate serum
concentration, rheology, product
syringeability of suspension or some types of
drugs used IM
EX: Penicillin G procaine IM

6. 3. In extraction of some material from plant or
animal origin
4. Milling process help in drying of wet masses
5. Help in the mixing process, by decrease
particle size sometime decrease variation of
particle size
6. Milling can affect the efficiency of some
equipment used in some manufacturing tab,
cap
Ex: Increase efficiency of lubricant by decrease
the particle size

7. 7. Milling can affect the smooth texture or
appearance of semisolid products like oint,
cream, paste
8. Can effect the deposition and absorption of
powder particles or liquid droplets in
aerosols

8. Size distribution and measurement

10. For irregular shape particles the size considered in
term of an equivalent sphere
For particle size measurement
1. Optical microscopy
2. Sieving
3. Sedimentation
4. Light scattering method and other method
For each method we must know
1. The range of particles
2. The sample preparation
3. Mechanism of measurement and type

11. Microscopy

13. Two type for microscopy Scanning electron
microscopy(SEM) and transition electron
microscopy(TEM)
SEM we can get particles size reach to 0.001µm

14. Mechanism of measurement

15. Mechanism of measurement
So by this method we take each particle alone to
obtain diameter
The number of particle taken by this method
being 620 particles

16. Disadvantage of this method
1. slow (prolong time) for measurement because in
involve counting procedure
2. there is considerable variation among operatous
using the microscopy technique.
Photomicrographs, projections, and automatic
scanners have been used to lessen operator
fatigue.
3. this type of measurement give two types of
dimensional (there is no depth) only length and
weigth

17. Sieving method

18. We have two types of sieves in US
1_tyler standard scale sieve
2_ US standard scale
For tyler depend on 200 mesh
US depend on 18 mesh

19. Mechanism of measurement

20. Factors affecting sieving method
1. Type of motion
2. Sieve loading
3. Time of sieving

21. Sedimentation

23. For this method the samples of powder particles to be
measured disperse in suitable solvent in
concentration 1% or not more than 2% “to get settle
for the particles independent of one another.
This sample is put in a pipette fixed within graduated
cylinder called andreasen pipette method withdraw
sample from specified depth without disturbing the
suspension, and they are dried so that the residue
may be weighted.

24. Note
1. If we have hydrophobic powder, this powder
disperse it with H2O in presence of dispersing
agent.
2. If we hydrophilic powder we late non aqueous
solvent
3. By means of stokes equation, the particle
diameter corresponding to each interval of time is
calculated.

25. Other method
Light scattering method and X- ray
scattering method
Range of particle: 0.2-500 µm
Sample prepare: sample disperse in liquid or gas passes
through a sensory zone
Laser scattering method
0.02 - 2000µm

26. Coulter counter “electrical stream
sensing zone method”
• For this method the sample of particles is dispense
in electrolyte like “Nacl” to form suspension
• Which is usually suspected to ultrasonic dispersion
for a period of time to break up any aggregates of
particles
• Dispersing agent may be adding
• Range similar to the laser
Adsorption and electrical method