On the Recycling of a Biodegradable Polymer: Multiple Extrusion of Poly (Lactic Acid)

Poly (lactic acid) (PLA) was submitted up to five cycles of extrusion in order to evaluate the effect of mechanical recycling. The material was evaluated under two conditions, thoroughly dried before processing and without drying. The changes in the molecular weight, acidity, thermal properties and coloring were assessed after each extrusion, and with this information, mechanisms of degradation were purposed. Molecular weight was reduced at a maximum of 30% after the most aggressive condition; five cycles without drying, which caused also an increase in acidity due to hydrolysis. Thermal properties were not significantly altered, which in combination to the molecular weight decrease allow to infer the recyclability of PLA. However, the most degraded samples had developed strong yellowing, particularly for samples without drying, which could be a problem for final products.