Kinetics of Hydrolytic Degradation of PLA

The chemical recycling of poly(lactic acid) (PLA) to its monomer is crucial to reduce both the consumption of renewable resources for the monomer synthesis and the environmental impact related to its production and disposal. In particular, the production of lactic acid from PLA wastes, rather than from virgin raw materials, it is also possible to achieve considerable primary energy savings. The focus of this work is to analyse deeply the PLA hydrolytic decomposition by means of a kinetic model based on two reactions mechanism. To this end, new experimental data have been gathered in order to investigate a wider temperature range (from 140 to 180 °C) and to extend the water/PLA ratio up to 50 % of PLA by weight. The reported results clearly highlight that more than 95 % of PLA is hydrolyzed to water-soluble lactic acid within 120 min, when it is hydrolyzed within 160–180 °C. Furthermore, the kinetic constant is highly influenced by reaction temperature. The proposed “two reactions” kinetic mechanism complies satisfactorily with the experimental data under analysis.