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 5.<br />
Characterizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Scaffolds for C<strong>on</strong>nective Tissue Engineering<br />
1.1.4 Discussi<strong>on</strong> <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> Transiti<strong>on</strong>s<br />
<strong>The</strong> parameters <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> observed glass transiti<strong>on</strong> measured by DSC are reported <strong>on</strong> Table 5.5,<br />
determined by <str<strong>on</strong>g>the</str<strong>on</strong>g> DSC technique.<br />
Table 5.5: Glass transiti<strong>on</strong>s parameters <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> various polylactides.<br />
T Onset<br />
(°C)<br />
T Midpoint<br />
(°C)<br />
Polylactide<br />
Cp<br />
(J/g.K)<br />
P L,D LA (PABR L 68) 54.2 55.6 0.421 54.9<br />
g (°C)<br />
(supplier)<br />
P L,DL LA (Resomer ® LR 704) 59.8 60.1 0.347 56−62<br />
PLGA 85:15 (Resomer ® RG 858S) 41.8 42.7 0.388 43<br />
PLGA 85:15 (DL-PLG) 52.2 53.1 0.451 50−55<br />
PLGA 50:50 (PLG 8523) 57.4 59.5 0.465 55−60<br />
PLGA 85:15 (PLG 8531) 56.1 57.4 0.462 55−60<br />
PLGA 85:15 (LG 857 S) 59.3 61.4 0.392 57−63<br />
PLGA 50:50 (Resomer ® RG 504) 47.1 49.2 0.499 46−50<br />
PLGA 50:50 (PDLG 5010) 47.7 49.1 0.524 46−50<br />
Polymer molecules are <str<strong>on</strong>g>of</str<strong>on</strong>g>ten partially crystalline, with crystalline regi<strong>on</strong>s dispersed within<br />
amorphous material. Chain disorder or misalignment, which is comm<strong>on</strong>, leads to amorphous material since<br />
twisting, kinking and coiling prevent strict ordering required in <str<strong>on</strong>g>the</str<strong>on</strong>g> crystalline state. Thus, linear polymers<br />
with small side groups, which are not too l<strong>on</strong>g form crystalline regi<strong>on</strong>s easier than branched, network,<br />
atactic polymers, random copolymers, or polymers with bulky side groups. Crystalline polymers are denser<br />
than amorphous polymers, so <str<strong>on</strong>g>the</str<strong>on</strong>g> degree <str<strong>on</strong>g>of</str<strong>on</strong>g> crystallinity can be obtained from <str<strong>on</strong>g>the</str<strong>on</strong>g> measurement <str<strong>on</strong>g>of</str<strong>on</strong>g> density.<br />
Crystallinity is indicative <str<strong>on</strong>g>of</str<strong>on</strong>g> amount <str<strong>on</strong>g>of</str<strong>on</strong>g> crystalline regi<strong>on</strong> in polymer with respect to amorphous<br />
c<strong>on</strong>tent. Crystallinity influences many <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymer properties such as hardness, modulus, tensile,<br />
stiffness, and melting point. <strong>The</strong> ratio <str<strong>on</strong>g>of</str<strong>on</strong>g> glycolide to lactide at different compositi<strong>on</strong>s allows c<strong>on</strong>trol <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
degree <str<strong>on</strong>g>of</str<strong>on</strong>g> crystallinity <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> polymers [Park et al., 1995; Cohn et al., 1987]. When <str<strong>on</strong>g>the</str<strong>on</strong>g> crystalline PGA is<br />
co-polymerized with PLA, <str<strong>on</strong>g>the</str<strong>on</strong>g> degree <str<strong>on</strong>g>of</str<strong>on</strong>g> crystallinity is reduced and, as a result, this leads to increase in<br />
rates <str<strong>on</strong>g>of</str<strong>on</strong>g> hydrati<strong>on</strong> and hydrolysis. It can <str<strong>on</strong>g>the</str<strong>on</strong>g>refore be c<strong>on</strong>cluded that <str<strong>on</strong>g>the</str<strong>on</strong>g> degradati<strong>on</strong> time <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> copolymer is<br />
related to <str<strong>on</strong>g>the</str<strong>on</strong>g> ratio <str<strong>on</strong>g>of</str<strong>on</strong>g> m<strong>on</strong>omers used in syn<str<strong>on</strong>g>the</str<strong>on</strong>g>sis. In general, <str<strong>on</strong>g>the</str<strong>on</strong>g> higher <str<strong>on</strong>g>the</str<strong>on</strong>g> glycolide c<strong>on</strong>tent, <str<strong>on</strong>g>the</str<strong>on</strong>g> quicker<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> rate <str<strong>on</strong>g>of</str<strong>on</strong>g> degradati<strong>on</strong> has been observed [Park, 1995].<br />
1.1.4.1 Effect <str<strong>on</strong>g>of</str<strong>on</strong>g> L and DL Ratio <strong>on</strong> <strong>The</strong>rmal Property <str<strong>on</strong>g>of</str<strong>on</strong>g> Polylactide Acid<br />
For <str<strong>on</strong>g>the</str<strong>on</strong>g>rmal properties, it can be observed that P L , DL LA copolymers showed T g glass transiti<strong>on</strong><br />
temperature ranging 55−60°C. However, <strong>on</strong>ly P L,D LA copolymers c<strong>on</strong>taining 10 mol % D,LLA showed T g<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> 54°C; similarly <str<strong>on</strong>g>the</str<strong>on</strong>g> T m melting point <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>se two polymers were also at 154 and 143°C, respectively.<br />
<strong>The</strong>se copolymers had lower degree <str<strong>on</strong>g>of</str<strong>on</strong>g> crystallinity than that <str<strong>on</strong>g>of</str<strong>on</strong>g> P L LA homopolymer (~50%). Buchatip et al.<br />
[2008] also produced similar type <str<strong>on</strong>g>of</str<strong>on</strong>g> results explaining that T g glass transiti<strong>on</strong>, T m melting temperature as<br />
well as crystallinity <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> copolymers decreased as mol% <str<strong>on</strong>g>of</str<strong>on</strong>g> D,LLA com<strong>on</strong>omer increased. Melting peak<br />
and crystallinity can not be observed in P D,L LA homopolymer and copolymers with more than 10 mol % <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
D,LLA suggesting <str<strong>on</strong>g>the</str<strong>on</strong>g> amorphous nature <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>se polymers.<br />
Apart from this discussi<strong>on</strong>, it may be noted that <str<strong>on</strong>g>the</str<strong>on</strong>g> different processes used for <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
copolymerizati<strong>on</strong> (polyc<strong>on</strong>densati<strong>on</strong>/open ring polymerizati<strong>on</strong>/copolymerizati<strong>on</strong>) and <str<strong>on</strong>g>the</str<strong>on</strong>g> nature <str<strong>on</strong>g>of</str<strong>on</strong>g> catalyst<br />
used also plays an important role in <str<strong>on</strong>g>the</str<strong>on</strong>g> crystallinity and o<str<strong>on</strong>g>the</str<strong>on</strong>g>r properties <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> final copolymer.<br />
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