Poly Lactic Acid PLA

PLA is known both as poly(lactic acid) and as polylactide. It is currently the most used packaging plastic that is both biodegradable and biobased. PLA is a member of the polyester family, and is chemically synthesized from lactic acid that is derived from starch by fermentation. PLA has the following structure  

PLA actually can take on two stereochemical forms, as lactic acid has two isomers, D- and L-. Therefore, the resulting PLA can be all one isomer (e.g., PLLA) or a combination of both isomers. The pure PLA made from either isomer is crystalline, but over a wide range of isomer content, the PLA cannot crystallize, so it is amorphous. To have useful properties, PLA needs to be somewhat crystalline, but not too much so, as crystallinity increases brittleness. Since the L-isomer is the one produced predominantly in natural processes (fermentation), commercially available PLA is mostly PLLA modified with some D-. The amount of D-isomer is 

While PLA was invented about 150 years ago, its moisture sensitivity and relatively high cost meant it did not have any packaging applications. Most uses of PLA were for medical applications where cost is not a harrier, and its biocompatibility is extremely important. When PET degrades, it produces lactic acid, which is also produced naturally in the human body (associated with muscle fatigue, for example). The advantages of something that can be implanted in the human body and then will slowly degrade and disappear over time are obvious. 

Use of PLA in packaging applications became possible with the development of new routes for synthesis that were able to produce high molecular weight polymer at much lower cost, as well as control the stereochemistry. Key to this development was a partnership between Cargill, which had the basic technology, and Dow Chemical, which had the polymer production knowledge. This partnership culminated in a full scale production facility in Blair, Nebraska, for production of PLA from corn. Dow later pulled out of the joint venture, which Cargill has now spun off under the NatureWorks name. 

Lactic acid is produced from corn by fermentation. Relatively small PLA polymers are produced next, and then broken down into dimers (lactide). These lactic acid dimers are then polymerized in a ring-opening polymerization process, yielding high molecular weight PLA, as shown in Fig. 4.9. 

Polyflactic acid) (PLA) is synthesized by the cyclic dimer of lactic acid (LA) that exists as two optical isomers d- and L-Iactate are the naturally occurring isomers. 

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Polyester chemistry is the same as studied by Carothers long ago, but polyester synthesis is still a very active field. New polymers have been very recently or will be soon commercially introduced PTT for fiber applications poly(ethylene naph-thalate) (PEN) for packaging and fiber applications and poly(lactic acid) (PLA), a biopolymer synthesized from renewable resources (corn syrup) introduced by Dow-Cargill for large-scale applications in textile industry and solid-state molding resins. Polyesters with unusual hyperbranched architecture also recently appeared and are claimed to find applications as crosstinkers, surfactants, or processing additives. 

Figure 13.1.4 The synthesis of poly(lactic acid) (PLA) by a ring-opening polymerization of the cyclic diester of lactic acid (lactide).

Poly(lactic acid) (PLA) has also been added to poly(SA) via melt polycondensation to produce the triblock copolymers poly(lactic acid-Wock-sebacic acid-Wock-lactic acid) (P(LA-block-SA-block-LA)) by Slivniak and Domb (2002). The PLA (d-, l-, and dl-) was incorporated by acetylation and addition to the PSA synthesis. They showed the formation of stable stereocomplexed particles with increased melting points and reduced solubility, and studied the degradation and drug release characteristics of the same (Slivniak and Domb, 2002). The stereocomplexes self-assemble as a consequence of the chirality in the PLA portions of the chains (Slivniak and Domb, 2002). 

Figure 12.6 Structure of a biodegradable polyester, poly(lactic acid) (PLA), with alternating pendent groups...

The most common synthetic biodegradable polymers for suture material and their corresponding weight loss in aqueous solution are listed in Table 3.10. Of these, poly(glycolic acid), PGA, poly(lactic acid), PLA, and copolymers of these two polyesters are the most widely used for resorbable sutme material. PGA is a tough. 

Kader A, Jalil R. Formulation factors affecting drug release from poly(lactic acid)(PLA) microcapsule tablets. Drug Dev Ind Phann 1999 25(2) 141 151. 

Polyesters, such as poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA), are examples of biomaterials that are degraded by homogeneous bulk erosion. 

Solid lipid poly(lactic acid) (PLA), poly(lactide-co-glycotide) (PLGA), poly(e-caprolactone) (PCL), poly(methyl methacrylate), and poly(alkyl cyanoacrylate) derivatives of cyclodextrin and starch some modified polymers (e.g., PEGylated polymers) also used Mainly glycerides and High-pressure... 

Ruan, G. Feng, S.-S. Preparation and characterization of poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA) microspheres for controlled release of paclitaxel. Biomaterials 2003, 24, 5037-5044. 

One of the most highly developed biopolymers is poly (lactic acid) (PLA). In the USA, PLA is manufactured by NatureWorks at a plant in Nebraska using lactic acid derived from corn. (Lactic acid can also be obtained from other natural sources such as wheat or potatoes.) Poly (lactic acid) is produced by ring opening polymerization of the lactide, as shown in Figure 8.12. 

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