PLLA Depolimerization Kinetics: A Preliminary Study

Poly(L-lactide) (PLLA) which is produced from renewable plant resources, is recently increasingly utilized as an alternative to petroleum-based polymers in order to reduce their impact on the environments. The monomer of PLLA is mainly produced from corn, which can also be utilized for food or to produce bioethanol or biofuels. Because of these reasons, the recycling of PLLA after its utilization, like other plastic material (PE, PP, or PET), must be carried out. For plastic material it is possible to carry out both a mechanical and chemical recycling: in the first case, the material is mechanically processed to obtain polymer pellets, while, in the second case, it is possible to obtain the monomer directly from the material depolymerization in order to reduce the consumption of renewable resources for the monomer synthesis. One of the most important processes used to produce lactic acid (LA) from PLLA is based on hydro-depolymerization of PLLA at high temperature and under pressure. In the present paper the hydrolytic depolymerization of pellets of PLLA in batch reactor at temperature near the melting temperature of the solid PLLA has been investigated and some preliminary experimental data are presented. Considering a residence time lesser than 120 minutes, a yield of lactic acid higher than 95% has been obtained at temperature equal to about 170-180 degrees C, at pressure equal to water vapour pressure and with a water/PLLA ratio equal to about 20