Chemical recycling of poly(lactic acid) by water-ethanol solutions

Abstract

The chemical recycling of PLA by hydrolysis in water-ethanol solutions at moderate temperatures was investigated and the kinetic parameters of the hydrolysis, rate constant and activation energy (Ea) were assessed. Hydrolysis experiments of PLA in 50% ethanol at 40, 60, 70 and 80 °C were performed. Analyses of the molecular weight distribution (MWD) of PLA were performed by conducting a deconvolution of the MWD distribution since the MWD at the latter stages of the hydrolysis experiments was not normally distributed. Conducting this analysis allowed us to identify the more likely possible hydrolysis reactions and to estimate the prevalent rate of hydrolysis. A reparameterization of the Arrhenius equation was conducted for a better estimation of the Ea with a low correlation coefficient between the parameters. No dependence of the hydrolysis rate with the change in pH for 50% ethanol was detected. For a better understanding of the effect of temperature on the hydrolytic degradation of PLA in water, hydrolysis experiments were also performed at 60, 70, 80 and 90 °C. The final Ea values for the hydrolytic degradation of PLA in 50% ethanol and in water were 9.627 × 104 and 10.474 × 104 J/mol, respectively, that are within the same range of values reported in literature. The Ea was 9% higher when PLA was hydrolyzed in water than in 50% ethanol. This study presents an alternative method for PLA chemical recycling using 50% ethanol.