Concurrent solvent induced crystallization and hydrolytic degradation of PLA by water-ethanol solutions

Abstract

Poly(lactic acid) (PLA) films were immersed in pure water, 50% and 95% ethanol solutions for up to 180 days. The change in molecular weight, sorption of water, sorption of ethanol, and lactic acid released were monitored. Glass transition temperature and percent crystallinity as a function of ethanol content were also measured. PLA experienced faster hydrolytic degradation in contact with 50% than with 95% ethanol or pure water. NMR methodologies were developed to measure sorption of deuterated water and ethanol in PLA. More water was sorbed in 50% ethanol, explaining the higher hydrolysis. During exposure, PLA experienced solvent induced crystallization. Higher percent crystallinity was found in films exposed to 50% ethanol with the formation of α-form crystals. The hydrolysis of PLA was correlated with the release of lactic acid during exposure. Mathematical models are proposed to explain the concurrent solvent induced crystallization and hydrolytic degradation of PLA.

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