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 />
Figure 1.3: Ring opening polymerizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> lactide to polylactide.<br />
Lactic acid is obtained by <str<strong>on</strong>g>the</str<strong>on</strong>g> fermentati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> engineered microbes <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> genus Lactobacilli.<br />
<strong>The</strong>se microorganisms are highly efficient sources <str<strong>on</strong>g>of</str<strong>on</strong>g> lactic acid. Lactobacilli can be subdivided into strains<br />
that produce ei<str<strong>on</strong>g>the</str<strong>on</strong>g>r <str<strong>on</strong>g>the</str<strong>on</strong>g> L (+) or <str<strong>on</strong>g>the</str<strong>on</strong>g> D (-) isomer. A variety <str<strong>on</strong>g>of</str<strong>on</strong>g> different sugars is used as carb<strong>on</strong> sources in <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
fermentati<strong>on</strong> process. <strong>The</strong>se sugars are ei<str<strong>on</strong>g>the</str<strong>on</strong>g>r specifically prepared enzymatically from starch for lactic acid<br />
producti<strong>on</strong>, or are by products from fruit processing.<br />
In additi<strong>on</strong>, lactose, a by-product in <str<strong>on</strong>g>the</str<strong>on</strong>g> cheese industry, can also be used as a carb<strong>on</strong> source for<br />
lactic acid producti<strong>on</strong>. In all cases sugars from renewable resources are transformed into a value-added<br />
product by an enzymatic whole-cell catalysis process. <strong>The</strong> subsequent steps in <str<strong>on</strong>g>the</str<strong>on</strong>g> producti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> PLA are<br />
based <strong>on</strong> syn<str<strong>on</strong>g>the</str<strong>on</strong>g>tic chemistry and involve <str<strong>on</strong>g>the</str<strong>on</strong>g> formati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> dimer by a self-c<strong>on</strong>densati<strong>on</strong> reacti<strong>on</strong> that<br />
results in a low molecular weight prepolymer. Depolymerizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> prepolymer gives lactide, which is<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g>n polymerized through ring-opening polymerizati<strong>on</strong>. <strong>The</strong> prepolymer can also be polymerized into high<br />
molecular weight PLA by <str<strong>on</strong>g>the</str<strong>on</strong>g> acti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> chain coupling agents. In c<strong>on</strong>trast to lactic acid, glycolic acid is<br />
produced in an industrial scale by a chemical process. <strong>The</strong> different ways <str<strong>on</strong>g>of</str<strong>on</strong>g> producing PLA are ga<str<strong>on</strong>g>the</str<strong>on</strong>g>red in<br />
Figure 1.4.<br />
Figure 1.4: Different ways <str<strong>on</strong>g>of</str<strong>on</strong>g> producing PLA.<br />
[Garlotta, 2001]<br />
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