Poly lactic acid -based bioplastics

1 (Palade et al, 2001). The stereo-isomeric l/d ratio of the lactate unit association influenced PLA properties (Tsuji and Ikata, 1992). There are three types of PLAs because there are two stereoisomeric forms of lactic acid, poly (levo-lactic acid) and poly (dextro-lactic acid), which are both semi-crystalline and have identical chemical and physical properties. Poly (D,L-lactic acid) or poly (meso-lactic acid), a racemic polymer obtained from an equimolar mixture of D- and L- lactic acid, is amorphous, with weak mechanical properties. The 

1 Chemical structure of poly(lactic acid) (PLA) and its constituent monomers (Palade etal., 2001). 

Loshaek, 1955)), the rheological properties at any other temperatures and molecular weights can be determined for the entire PLA system. Once the relation of temperature and molecular weight is known it can be applied in modeling applications. For instance, in screw extrusion and general flow simulations. 

The scaling of the zero-shear viscosity with molecular weight is presented in Fig. 10.2 for a wide variety of optical compositions. There is no systematic trend of the melt viscosity with changing composition. Dynamic and steady rheological tests found diat the molecular weight between entanglement in PLA melt is close to 10 x 10. This value corresponds to a characteristic ratio of Coo (a fundamental chain property defined as the ratio of the chain dimensions under 6 conditions to the size of a random walk) = 12, implying that PLA chains 

3 Effect of molecular weight on zero-shear viscosity and elasticity coefficient for poly(L-lactic acid) (PLLA) at 200 C (Cooper-White and Mackay, 1999). 

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Zhang J.F., Sun X., Poly(lactic acid)based bioplastics, in Biodegradable polymers for industrial applications, Ed. Smith R., CRC, 2005, Woodhead Publishing Limited, Cambridge -England, 2005, pp. 251-288, Chapter 10. 

Zhang, J-F., Sun, X. Poly(lactic acid)-Based Bioplastics, Biodegradeable Polymers for Industrial Applications. Smith, R. ed. CRC Press LLC, Boca Raton, FL, (2005)... 

The global demand for bioplastics was estimated at 0.36 million tonnes, which is equivalent to 0.2 % of the annual petrochemical plastic production (Thompson et al. 2009). PHA accounted for about 10 % of the bioplastic market which is currently dominated by poly(lactic acid) and other starch-based biopolymers (Barker et al. 2009). Based on the statistics, in order to fulfill the PHA market demand... 

Poly(lactic acid) (PL A) is a renewable resource-based bioplastic with many advantages, compared to other synthetic polymers. PL A is eco-friendly, because, apart from being derived from renewable resources such as corn, wheat, or rice, it is recyclable and compostable [1, 2]. PLA is biocompatible, as it has been approved by the Food and Drug Administration (FDA) for direct contact with biological fluids [3] and has better thermal processability compared to other biopolymers such as poly(hydroxy alkanoate)s (PHAs), poly(ethylene glycol) (PEG), or poly(e-caprolactone) (PCL) [4]. Moreover, PLA requires 25-55% less energy to be produced than petroleum-based polymers, and estimations show that this can be further reduced by 10% [5]. 

Today the bioplastics available in the market at different levels of development are mainly carbohydrate-based materials. Starch can be either physically modified and used alone or in combination with other polymers, or it can be used as a substrate for fermentation for the production of polyhydroxyalkanoates or lactic acid, transformed into poly lactic acid (PLA) through standard polymerisation processes. Also vegetable oil based polymers are under development. 

Polymerization of a-hydroxycarboxylic acids, glycerol, 1,3-propanediol, and amino acids, either individually or as copol)oners, can generate commercially viable polymers [2]. Other researchers have shown that renewable-resource polymers, such as poly(lactic acid) and others, can be viably produced and these materials are currently on the market for biomedical and packaging apphcations [4,5]. Our goal is to develop low-cost bioplastics with comparable or even enhanced physical and chemical properties versus petroleum-based conunodity plastics. 

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