Polylactic Acid (PLA), The Magic Of Turning Crops Into Plastic

Polylactic acid is an aliphatic polyester material derived from biomass, which has good biocompatibility and biodegradability, and has the advantages of high mechanical strength, good transparency, easy processing and molding, and is the largest synthetic degradable plastic in industrialization.
Polylactic acid can be prepared by direct dehydration polycondensation of lactic acid and ring-opening polymerization of lactide (cyclic dimer of lactic acid).
PLA is an aliphatic polyester formed from lactic acid through oligomerization, cyclization, polymerization and other processes. The transformation process of PLA is as follows: chemists can efficiently make LA from starch extracted from crops such as corn through hydrolysis and microbial fermentation, and further convert it into PLA by means of condensation polymerization or ring-opening polymerization, realizing the "magic" of turning crops into plastics.

Since LA monomer contains both hydroxyl (-OH) and carboxyl groups, it can condense with the carboxyl and hydroxyl groups of another LA monomer, respectively. In this way, the LA monomers react alternately to obtain a high molecular weight PLA material.

At present, the main commercial polylactic acid is poly-L-lactic acid (PLLA). Lactic acid is a chiral molecule containing two isomers, L-lactic acid (L-lactate) and D-lactic acid (D-lactate). In the production process of polylactic acid, the L-lactic acid unit is transformed into D-lactic acid unit due to the influence of high temperature, catalyst and other factors, which ultimately leads to the increase of D-lactic acid unit and the decrease of its theoretical optical rotation value in PLLA.