Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
Influence of the Processes Parameters on the Properties of The ...
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Chapter 3.<br />
Analytical Methods and Designs <str<strong>on</strong>g>of</str<strong>on</strong>g> Experiments<br />
<strong>The</strong> T m value depends <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> molecular weight <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer. So, lower grades will have lower<br />
melting points (cf. Figure 3.2). <strong>The</strong> crystallinity ratio <str<strong>on</strong>g>of</str<strong>on</strong>g> a polymer can also be found using DSC from <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
following equati<strong>on</strong>:<br />
C = (H m −H c )/H m<br />
<br />
(3.1)<br />
where H m is <str<strong>on</strong>g>the</str<strong>on</strong>g> melting enthalpy, H c is <str<strong>on</strong>g>the</str<strong>on</strong>g> crystallizati<strong>on</strong> enthalpy and H m <str<strong>on</strong>g>the</str<strong>on</strong>g> melting<br />
enthalpy <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> totally crystallised PLA sample.<br />
According to Fischer et al. [1973], H m = 93 J.g -1 but according to Miyata and Masuko [1998]<br />
H m = 135 J.g -1 . It can be found from <str<strong>on</strong>g>the</str<strong>on</strong>g> crystallizati<strong>on</strong> peak from <str<strong>on</strong>g>the</str<strong>on</strong>g> DSC graph since <str<strong>on</strong>g>the</str<strong>on</strong>g> heat <str<strong>on</strong>g>of</str<strong>on</strong>g> melting<br />
can be calculated from <str<strong>on</strong>g>the</str<strong>on</strong>g> area under an absorpti<strong>on</strong> peak as shown <strong>on</strong> Figure 3.2. Ahmed et al. [2008] and<br />
Wunderlich [2005] observed that both P L LA exhibits an endo<str<strong>on</strong>g>the</str<strong>on</strong>g>rmic melting peak during <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal run. P L LA<br />
samples exhibit crystallinity. However, for low molecular mass (M n < 1500) crystallizati<strong>on</strong> occurs during<br />
negative scan and for higher molecular mass, it is observed during positive run.<br />
1.3 Sec<strong>on</strong>d Order Transiti<strong>on</strong><br />
(A)<br />
(B)<br />
Figure 3.2: <strong>The</strong>rmograms <str<strong>on</strong>g>of</str<strong>on</strong>g> two P L LAs <str<strong>on</strong>g>of</str<strong>on</strong>g> different Mw.<br />
[Ahmed et al., 2008]<br />
<strong>The</strong> glass transiti<strong>on</strong> is a much more subtle transiti<strong>on</strong> than melting or evaporati<strong>on</strong>: glass transiti<strong>on</strong><br />
is a<str<strong>on</strong>g>the</str<strong>on</strong>g>rmic. In Figure 3.3, <str<strong>on</strong>g>the</str<strong>on</strong>g> change in heat capacity <strong>on</strong> going through <str<strong>on</strong>g>the</str<strong>on</strong>g> glass transiti<strong>on</strong> temperature is<br />
drawn for a typical semi-crystalline PLGA polymer. <strong>The</strong>re is <strong>on</strong>ly a jump in <str<strong>on</strong>g>the</str<strong>on</strong>g> heat capacity in <str<strong>on</strong>g>the</str<strong>on</strong>g> range<br />
20 to 190 °C.<br />
<strong>The</strong> increase in heat capacity, Cp, generally occurs over a temperature range <str<strong>on</strong>g>of</str<strong>on</strong>g> 5 to 20 K, and<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> jump is <str<strong>on</strong>g>of</str<strong>on</strong>g>ten 11 J.K -1 .mol -1 for mobile units in <str<strong>on</strong>g>the</str<strong>on</strong>g> liquid. This means that <str<strong>on</strong>g>the</str<strong>on</strong>g> decrease in heat capacity<br />
at <str<strong>on</strong>g>the</str<strong>on</strong>g> glass transiti<strong>on</strong> is 11 J.K -1 .mol -1 , for a m<strong>on</strong>atomic liquid.<br />
Figure 3.3: Characteristic variati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> glass transiti<strong>on</strong> in PLGA.<br />
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