Synthesis of Lactide, the Dimer of Lactic Acid
Lactic acid (2-hydroxypropanoic acid), the precursor to the lactide is a chiral
molecule. Its optical isomers includes L-(+)-lactic acid ( (S)-lactic acid) and
the its mirror image D-(-)-lactic acid ((R)-lactic acid). In nature, L-(+)-Lactic
acid is the most abundant isomer.
The precursor for the synthesis of lactide, lactic acid is produced through
fermentation of agricultural sugars including corn or beet sugar.
Synthesis of Lactide
Depending on the combination of the lactic acid isomers used, lactide, the cyclic
dimer of lactic acid could exist in three different types; L,L Lactde, D,D, Lactide or
D,L Lactide (Meso Lactide).
The type of lactide used for the production of polylactide has a significant
effect on the final properties of PLA.
Polylactides synthesized from the ring opening polymerization of L, L or D,
D-Lactide exhibit semi-crystalline properties, while PLA produced with their
mixtures, or with small content of meso-lactide results in amorphous polymers.
L-Lactic Acid Structure
D-Lactic Acid Structure
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