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Polylactide Degradation
Degradable plastics can be defined as the materials which can go significant chemical
structural changes under specific environmental conditions. Biodegradable materials
degrade under naturally occurring microorganisms including bacteria, fungi, and algae.
Polylactide is a biopolymer and biodegradable. Further,
it can degrade in various other ways including hydrolytic
degradation, photo degradation, and thermal
degradation, to form non toxic byproducts mainly lactic
acid, carbon dioxide and water.

Polylactide has received lot of attention as a commodity
thermoplastic due to its superior mechanical
performance, low toxicity, and the ability to undergo
degradation. It has been tested for the suitability in
various applications including biomedical
pharmaceutical, and commodity products.

Degradation of polylactide in various conditions are
researched by scientists around the world to understand
various factors that affect the degradation including the
environment, additives that could increase/decrease
degradation rate etc.
Enzymatic Degradation of Polylactide

The effect of various enzymes on the degradation of polylactides has been studied
extensively by various researchers. Some of the latest findings are discussed below.
Enzymatic Degradation of PLA: Effect of proteinase K on PLA
degradation

Degradation of Polylactide in the presence of proteinase K was studied by
Numata et al,(1) and reported that the hydrolysis rate is influenced by the
stereochemical structure, molecular weight and the number of branches in PLA.

The hydrolysis rate was higher in PLLA samples with a lower molecular weight,
while for the branched PLLA, the rate was determined by the molecular weight
of the branched segments and not the overall molecular weight of the sample.
Further, the presence of d-lactyl units decreased the hydrolysis rate.

References:
1. Numata et al. Biomacromolecules, 2008, 9 (8), pp 2180-2185
2. Oda et al. Journal of Polymers and the Environment, 8, 1, 2000 , 29-32(4)
3. Soo-Hong et al. Journal of polymer science. Part A. Polymer chemistry. 2001, 39(7), pp. 973-985
Enzymatic Degradation of Polylactide : Effect of commercial Proteases on
PLA degradation

Oda et al (2) studied the degradation of Polylactide by 46 different commercial
Proteases. The study revealed that acid and neutral proteases has very little or no
effect on the degradation of polylactide, while alkaline proteases showed
degrading activity by increasing the amount of lactic acid in the sample.

Thermal and hydrolytic degradation of end-group-functionalized
polylactide

The effect of the end group on the thermal degradation was studied for
polylactide by Soo-Hong et al (3). Polylactides with four different end group
functionalities including OH-, Cl-, NH2-, and COOH- were synthesized and
their thermal degradation was analyzed.

The highest thermal stability was reported to be in Cl-, NH2-, and
COOH-terminated polylactides, while the OH- terminated Polylactides
showed the poorest thermal stability.

When these end group functionalized PLA was exposed to hydrolytic
degradation, the COOH- terminated polylactides showed the highest rate of
degradation, while Cl- and NH2- terminated polylactides were lower.
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