Low temperature pyrolysis of polylactic acid (PLA) and its products

The fact that polylactic acid (PLA) is not biodegradable makes it necessary to find the methods of effective treatment of its waste. A significant method of processing waste PLA can be slow low-temperature pyrolysis, providing mostly oil and energy gas. The PLA pyrolysis provides almost 50 wt.% oil and 21–23 wt.% energy gas with a high carbon monoxide content above 90 vol.% at temperatures up to 420 °C. The temperatures above 420 °C do not give acceptable yields of oil anymore, and at the same time there are higher losses due to the release of low boiling aldehydes and ketones. The obtained oil and gas showed an acceptable calorific value as a basis for their use as substitute fuels. Due to its composition, oil can also be considered as a source of valuable chemicals (tetrahydrofuran, paraldehyde, cyclopentanone and ether) and gas as a source of carbon monoxide for industrial applications and, more recently, for biomedical use. Even plastic waste mixtures with a high proportion of PLA in a 1:1 ratio can be efficiently processed by slow low-temperature pyrolysis. The pyrolyzed mixture showed very similar yields of solid carbonaceous residue and oil (38 wt.% and 35 wt.%). The composition of the solid phase was only minimally different from the low-temperature pyrolysis of PLA. Although the ratio of PLA:LPO components was 1:1, the CO content decreased by ca. 20 vol.% at the expense of CO2 and lighter C2-C5.