Question

explain how PLA is biodegradable?

Answer 1

PLA (Polylactic acid) is a polymer of high levels polylactic acid molecules which is thermoplastic aliphatic polyester that are derived from corn starch, tapioca products etc.

For degradation of PLA abiotically usually three mechanisms are followed as below :.

a) Hydrolytic reaction : In this hydrolysis reactions the ester group of polylactic acid molecule main chain break down and reduces molecular weight.

   -COO- + H₂O -----> -COOH + OH^-

   Ester    water    carboxylic acid hydroxyl

b) Using heat (thermal degradation) : In this process heavy complex PLA molecules are degraded to lighter molecules with reduced molar mass and lactide molecule in presence of high temperatures.

c) Using light (Photo degradation) : In this process Ultraviolet light is used for the degradation of PLA molecule

Biotically PLA is degraded (Biodegradation) : The digested PLA molecules to oligomers and monomers in present of UV light or heat or moisture gets assimilated and biodegraded using microorganisms.

a) PLA decomposes into water and carbon dioxide in 47 to 90 days by hydrolytic reactions using minimum essential medium (MEM that contain Calcium chloride, sodium chloride along with the supplementation of foetal bovine serum where submersion takes place. After 30 days it is decomposed to PLLA (Poly-L-Lactide) lose its 20% weight.

b) Degradation using microorganisms (Composting): Microorganisms like Amycolatopsis and Saccharothrix contain PLA depolymerase that degrade PLA.

Microorganism like Tritirachium album contain enzyme called Pronase, proteinase K that also involve in degradation of PLA.