Oxidative degradation of polylactide (PLA) and its effects on physical and mechanical properties

• Oxidative degradation of PLA results in a random chain scission process.
• Chain scission causes chemi-crystallization and a Tg drop.
• Complete embrittlement is observed when Mn drops below 40 kg mol−1.
• Critical molar mass for embrittlement is linked to molar mass between entanglements.

The thermo-oxidative degradation of polylactide (PLA) films was studied between 70 and 150 °C. It was shown that the oxidative degradation of PLA leads to a random chain scission responsible for a reduction of the molar mass. These molar mass changes affect Tg and the degree of crystallinity, and it was found that Tg decreases according to the Fox–Flory theory whereas the degree of crystallinity increases due to a chemicrystallization process. A correlation between molar mass and strain at break during oxidation has been established: PLA displays a brittle behavior when Mn falls below 40 kg mol−1 in agreement with relationships linking the critical value for embrittlement with the molar mass between entanglements.

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