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

Chapter 3.
Analytical Methods and Designs <strong>of</strong> Experiments
Fraunh<strong>of</strong>er’ diffraction assumes that <strong>the</strong> measured particles are opaque and scatter light at narrow
angles. Therefore it is applied only with <strong>the</strong> large particles and gives incorrect results with <strong>the</strong> fine particles
[Kippax, 2005].
4 Sorption Analysis
Sorption analyses have been carried out in order to study <strong>the</strong> amount <strong>of</strong> CO 2 sorbed by <strong>the</strong>
polymers at different pressures. The method used, which is proposed by Berens and Huvard [1989a]
involves <strong>the</strong> sorption <strong>of</strong> CO 2 into <strong>the</strong> polymer pellets, followed by very rapid venting <strong>of</strong> <strong>the</strong> chamber and
transfer <strong>of</strong> <strong>the</strong> pellets to a precision balance for recording <strong>the</strong> weight variation during desorption. Recording
with a video camera gives kinetic data <strong>of</strong> desorption, and since <strong>the</strong> early stages <strong>of</strong> desorption are linear (cf.
Figure 3.11 for example for P = 125 bars), it allows to extrapolate to t = 0 sec (which is <strong>the</strong> end <strong>of</strong> <strong>the</strong>
saturation period). This extrapolation gives <strong>the</strong> total amount <strong>of</strong> CO 2 sorbed by <strong>the</strong> polymer in <strong>the</strong> end <strong>of</strong> <strong>the</strong>
saturation period. Sorption <strong>of</strong> CO 2 is <strong>the</strong>n calculated by:
w w0
s (3.9)
w
where s is <strong>the</strong> sorption (g CO 2 /g polymer), w is <strong>the</strong> extrapolated weight <strong>of</strong> polymer and w 0 is <strong>the</strong>
polymer weight before <strong>the</strong> experiment.
Variation <strong>of</strong> PLGA 50:50
Wt.(gm)
0.178
0.176
0.174
0.172
0.170
0.168
0.166
y = -0.002x + 0.1935
Polymer Weight
Extrapolated Weight <strong>of</strong> Polymer with Time
0 5 10 15 20 25 30
(t) 1/2 (sec) 1/2
Figure 3.11: Desorption <strong>of</strong> CO 2 from PLGA 50:50 with time.
By changing <strong>the</strong> saturation time, kinetics <strong>of</strong> diffusion <strong>of</strong> CO 2 into <strong>the</strong> polymer samples can be
calculated.
5 Microscopic Methods to Analyze Porous Structures
5.1 Methods to Determine Porosity
5.1.1 Geometric Porosity
The porosity <strong>of</strong> a porous medium describes <strong>the</strong> fraction <strong>of</strong> void space in <strong>the</strong> material, where <strong>the</strong>
void may contain, for example, air or water. It is defined by <strong>the</strong> relationship:
V
V
v
(3.10)
T
where V v is <strong>the</strong> volume <strong>of</strong> void-space (such as fluids) and V T is <strong>the</strong> total or bulk volume <strong>of</strong>
material, including <strong>the</strong> solid and void components.
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