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 1.<br />
Polylactide Based Bio-Materials<br />
or lactic acid) are linked toge<str<strong>on</strong>g>the</str<strong>on</strong>g>r in PLGA by ester linkages, thus resulting in linear, aliphatic polyester as a<br />
product [Middlet<strong>on</strong> and Tipt<strong>on</strong>, 1998]. Using <str<strong>on</strong>g>the</str<strong>on</strong>g> polyglycolide and polylactide properties as a starting point,<br />
it is possible to copolymerize <str<strong>on</strong>g>the</str<strong>on</strong>g> two m<strong>on</strong>omers to extend <str<strong>on</strong>g>the</str<strong>on</strong>g> range <str<strong>on</strong>g>of</str<strong>on</strong>g> homopolymer properties.<br />
Copolymers <str<strong>on</strong>g>of</str<strong>on</strong>g> glycolide with both L-lactide and D,L-lactide have been developed for both device and drug<br />
delivery applicati<strong>on</strong>s.<br />
Figure 1.5: Schemaic syn<str<strong>on</strong>g>the</str<strong>on</strong>g>sis <str<strong>on</strong>g>of</str<strong>on</strong>g> poly(lactide-co-glycolide).<br />
[Middlet<strong>on</strong> and Tipt<strong>on</strong>, 1998]<br />
To tailor <str<strong>on</strong>g>the</str<strong>on</strong>g> processability and to enhance biodegradati<strong>on</strong>, <str<strong>on</strong>g>the</str<strong>on</strong>g>se copolymers are fur<str<strong>on</strong>g>the</str<strong>on</strong>g>r modified<br />
by copolymerizing with linear dicarboxylic acids (e.g. adipic acid) and glycol comp<strong>on</strong>ents with more than<br />
four methylene groups (e.g. hexanediol) [Sublett, 1983]. To enhance <str<strong>on</strong>g>the</str<strong>on</strong>g> envir<strong>on</strong>mentally benevolent aspect<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>se materials and to broaden <str<strong>on</strong>g>the</str<strong>on</strong>g> range <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>ir use, aliphatic-aromatic co-polyesters blended with<br />
cellulose esters have been processed into useful fibres, films and moulded objects [Buchanan et al., 1994,<br />
1995].<br />
2.2.2 <strong>Properties</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> PLGA Copolymers<br />
Physical properties <str<strong>on</strong>g>of</str<strong>on</strong>g> poly(glycolic acid), as well as different PLGAs, are ga<str<strong>on</strong>g>the</str<strong>on</strong>g>red in Table 1.3.<br />
Table 1.3: Main physical properties <str<strong>on</strong>g>of</str<strong>on</strong>g> PGA and several PLGAs.<br />
<strong>Properties</strong> Unit PGA P D,L LGA 50:50 P D,L LGA 75:25 P D,L LGA 85:15<br />
Density ρ gm/cm 3 1.5−1.7 1.3−1.4 1.3 1.25<br />
Tensile strength σ MPa 60−99.7 41.4−55.2 41.4−55.2 45−52<br />
Tensile modulus E GPa 6−7 1−4.3 1.4−4.1 2.0*<br />
Ultimate strain ε % 1.5−20 2−10 2.5−10 −<br />
Specific tensile strength S* Nm/g 40−45.1 30.9−41.2 31.8−42.5 −<br />
Specific tensile modulus E* kNm/g 4−4.5 8−2.1 1.1−2.1 −<br />
Glass transiti<strong>on</strong> temperature T g °C 35−40 45−50 50−55 55−55<br />
Melting point T m °C 225−230 amorphous amorphous amorphous<br />
[Van de Velde and Kiekens, 2002]<br />
Polyglycolide has a glass transiti<strong>on</strong> temperature between 35 and 45°C and its melting point is<br />
reported to be in <str<strong>on</strong>g>the</str<strong>on</strong>g> range <str<strong>on</strong>g>of</str<strong>on</strong>g> 225-230°C. PGA also exhibits a higher degree <str<strong>on</strong>g>of</str<strong>on</strong>g> crystallinity than PLA (~ 45-<br />
55 %), thus resulting in better mechanical properties but insolubility in water [Middlet<strong>on</strong> and Tipt<strong>on</strong>, 1998].<br />
<strong>The</strong> solubility <str<strong>on</strong>g>of</str<strong>on</strong>g> this polyester is somewhat unique, in that its high molecular weight form is insoluble in<br />
almost all comm<strong>on</strong> organic solvents (acet<strong>on</strong>e, dichloromethane, chlor<str<strong>on</strong>g>of</str<strong>on</strong>g>orm, ethyl acetate, tetrahydr<str<strong>on</strong>g>of</str<strong>on</strong>g>uran).<br />
<strong>The</strong> excepti<strong>on</strong>s are highly fluorinated organics such as HFIP (hexafluoroisopropanol) while low molecular<br />
weight oligomers sufficiently differ in <str<strong>on</strong>g>the</str<strong>on</strong>g>ir physical properties to be more soluble. Sutures <str<strong>on</strong>g>of</str<strong>on</strong>g> PGA lose<br />
about 50% <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g>ir strength after 2 weeks and 100% at 4 weeks, and are completely absorbed in 4~6 m<strong>on</strong>ths.<br />
Glycolide has been copolymerized with o<str<strong>on</strong>g>the</str<strong>on</strong>g>r m<strong>on</strong>omers to reduce <str<strong>on</strong>g>the</str<strong>on</strong>g> stiffness <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> resulting fibres<br />
[Middlet<strong>on</strong> and Tipt<strong>on</strong>, 1998].<br />
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