**2. Synthesis**

The monomer of PLA is lactic acid. Although this monomer can synthesize from petroleum, almost all lactic acid available on the market is produced by fermentation. During fermentation a suitable carbohydrate is converted to lactic acid by microorganisms without the presence of oxygen, hence, under anaerobic conditions. Fermentation of sour whey resulted in the discovery of lactic acid in 1780, when it was isolated by C. W. Scheele [5].

Lactic acid is the simplest α‐hydroxyacid that contains a chiral carbon atom and exists in the following two enantiomeric forms: L‐lactic acid and D‐lactic acid. Monomer forms a stable cycled dimer, that is, lactide. Consequently, dimer presents three different structures, namely L‐lactide, D‐lactide and DL‐lactide. Isotactic, optically active and crystalline homopolymers are obtained if either L‐ or D‐lactide dimers are polymerized. However, DL‐lactide or copoly‐ mers of L‐ and D‐dimers polymerize obtain atactic, nonactive optically and amorphous polymers [6].

Polymerization of this lactic acid is carried out by polycondensation [7], instead of polymeri‐ zation of the dimer that occurs by ring opening polymerization [8]. Polymerization started from lactide dimer allows to obtain high level of molecular mass due to a chain polymerization mechanism and this is the mechanism that is normally used for production.
