Influence of the Processes Parameters on the Properties of The ...

Chapter 4.
Experimental Procedures and Protocols for Analyses
3 Protocols for Analysis
3.1 Granulometry
Experiments have been performed at <strong>the</strong> "Laboratoire de Génie Chimique de Toulouse"
The s<strong>of</strong>tware proposed by Malvern with <strong>the</strong> granulometer Mastersizer 2000 uses <strong>the</strong> Mie
<strong>the</strong>ory and permits to limit artefacts at small sizes <strong>of</strong> <strong>the</strong> size distributions. Experimentally, <strong>the</strong> particles pass
through <strong>the</strong> Scirocco composed <strong>of</strong> a vibrating hopper where particles are placed. A compressed air supply
is out <strong>of</strong> <strong>the</strong> hopper and creates depression causing <strong>the</strong> particles to <strong>the</strong> sensor. Vacuum allows <strong>the</strong> recovery
<strong>of</strong> particles at <strong>the</strong> end <strong>of</strong> <strong>the</strong> circuit. The particles diffract light at an angle. A lens Fourier can be reduced
into a single optical diffracting each source. Image result <strong>of</strong> diffraction <strong>of</strong> a light beam is a set <strong>of</strong> concentric
rings. The value <strong>of</strong> <strong>the</strong> deflection angle and <strong>the</strong> amount <strong>of</strong> light can be accessed respectively to particle size
and quantity. The deflection angle <strong>of</strong> all smaller particles is large. The light diffracted by <strong>the</strong> sample is
recorded which can be traced back to <strong>the</strong> size distribution, and <strong>the</strong> percentage volume in each size class. The
size range available is between 0.05 and 2000 microns.
Approximately a mass <strong>of</strong> 200 to 300 mg <strong>of</strong> powder material is placed inside <strong>the</strong> inlet pan. It tracks
<strong>the</strong> evolution <strong>of</strong> total grain size during milling. The parameters that affect <strong>the</strong> measure are <strong>the</strong> amplitude <strong>of</strong>
vibration <strong>of</strong> <strong>the</strong> hopper that controls <strong>the</strong> flow <strong>of</strong> particles introduced into <strong>the</strong> measuring cell and <strong>the</strong> pressure
<strong>of</strong> compressed air that plays on <strong>the</strong> velocity <strong>of</strong> passage <strong>of</strong> particles to <strong>the</strong> laser beam. After various trials for
analysis, we found better reproducibility <strong>of</strong> measurements for 70% <strong>of</strong> <strong>the</strong> maximum amplitude <strong>of</strong> vibration
<strong>of</strong> <strong>the</strong> hopper and a pressure <strong>of</strong> 2 bars. Its measure range in dry dispersion is 0.1 to 2 000 microns. Typical
measurement time is 5 seconds.
The size distributions <strong>of</strong> <strong>the</strong> polymer powders after pre-treatment (just sieving or grinding in <strong>the</strong>
knife mill and sieving) are presented in Figure 4.17. Most <strong>of</strong> <strong>the</strong> particles <strong>of</strong> different materials used have
mean diameter between 100 and 175m. The mean diameter (d 50 ) <strong>of</strong> a grinded polymer is 89.54 m.
The median diameter (d 50 ) is a very important characteristic <strong>of</strong> this distribution because it
represents a cummulative frequency <strong>of</strong> 50%, which divides <strong>the</strong> size distribution into two parts <strong>of</strong> equal area.
This parameter permits to follow easily <strong>the</strong> evolution <strong>of</strong> particle size during a treatment <strong>of</strong> a powder. As an
illustration, Figure 4.18 presents <strong>the</strong> variation <strong>of</strong> <strong>the</strong> median size <strong>of</strong> P L,D LA particles submitted to a grinding
treatment in a tumbling ball mill.
12
10
400
Particle Diameter Variation with Grinding time
Volume (%)
8
6
4
2
Poly (Lactide-co-glycolide) : Granulometry
d 50 (m)
300
200
100
0
0.01 0.1 1 10 100 1000 10000
Particle Size(m)
0
0 1000 2000 3000 4000 5000
Grinding Time (min)
Figure 4.17: Size distribution <strong>of</strong> P L,D LA particle
after 30 minutes <strong>of</strong> grinding.
Figure 4.18: Variation <strong>of</strong> particle diameter with
grinding time for P L,D LA
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