Semi crystalline PLA

Mihai M, Huneault MA, Favis BD, Li H. Extrusion foaming of semi-crystalline PLA and PLA/ thermoplastic starch blends. Macromol Biosci 2007 7 907-20. 

PLA is a semi-crystalline polyester. A typical DSC signal of PLLA is shown in Figure 8.5. 

The mechanical properties of PLA, which have been extensively studied, are dependent on the production process and the amorphous or semi-crystalline state of the sample. Amorphous PLA presents a tensile modulus between 2.05... 

Like other semi-crystalline polymers, the glass transition of PLA is influenced by physical aging [150], crystallinity, morphology, and impurities [151, 152]. Other properties of PLA such as the mechanical strength also depend on the morphology, crystallinity, and orientation. It was found by Wong et al. [153] that the orientation of the crystalline phase was always higher than that of the amorphous phase. 

In an attempt to gain an element of control over the mechanical, physical and degradation properties of PLA, large-scale efforts are currently underway to chemically and physically modify PLA throng copolymerization and physical blending with prudently chosen secondary constituents. Without immediate consideration for the issue of financial accessibility of PLA-based products, a logical, con lementary conqx)nent to PLA is poly(8-caprolactone)[PCL]. PCL is a flexible, semi-crystalline(Tg -60°C, Tm 60°C) aliphatic polyester with unique biodegradation characteristics and superior thermal and hydrolytic stabihty. ... 

The properties of PLA, as indeed those of other polymers, depend on its molecular characteristics, as well as on the presence of ordered structures, such as crystalline thickness, crystallinity, spherulite size, morphology and degree of chain orientation. The physical properties of polylactide are related to the enantiomeric purity of the lactic acid stereo-copolymers. Homo-PLA is a linear macromolecule with a molecular architecture that is determined by its stereochemical composition. PLA can be produced in a totally amorphous or with up to 40 per cent crystalline. PLA resins containing more than 93 per cent of L-lactic acid are semi-crystalline, but, when it contains 50-93 per cent of it, it is entirely amorphous. Both meso- and D-lactides induce twists in the very regular PLLA architecture. Macromolecular imperfections are responsible for the decrease in both the rate and the extent of PLLA crystallization. In practise, most PLAs are made up of L-and D,L-lactide copolymers, since the reaction media often contain some meso-lactide iir turities. 

Figure 2.6 Weight loss changes of initially amorphous PLAiqoa and semi-crystalline PLAiqqc during in vitro degradation. PLA, poly(lactic acid).

Poly(D-Lactide) (D-PLA) Purasorb PD PURAC Semi-crystalline... 

Poly(L-Lactide) (L-PLA) Purasorb PL Lac tel L-PLA Medisorb lOOL PURAC Birmingham Polymers Inc. (BPI) Alkermes Inc Semi-crystalline 173-178 °C Tg 60-65 °C Soluble in MeClj CHCl MW >100,000 Tensile strength 55-82 MPa % Elongation 5-10 Modulus 2.8-4.1 GPa... 

According to Limt, PLA polymers range from amorphous glassy polymers with a Tg of 60 "C to semi-crystalline/highly crystalline products with crystalline melting points of 130-180 "C [36]. Many of the basic properties of PLA lie between those of crystal... 

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