ABSTRACT
Polylactic acid (PLA) is a rigid thermoplastic polymer that can be semi-crystalline or totally amorphous, depending on the stereopurity of the polymer backbone. L(−−)-lactic acid (2-hydroxy propionic acid) is the natural and most common form of the acid, but o(+)-lactic acid can also be produced by microorganisms or through racemization and this “impurity” acts much like comonomers in other polymers such as polyethylene terephthalate (PET) or polyethylene (PE). In PET, diethylene glycol or isophthalic acid is copolymerized into the backbone at low levels (1-10%) to control the rate of crystallization. In the same way, D-lactic acid units are incorporated into L-PLA to optimize the crystallization kinetics for specific fabrication processes and applications.
