Fostering Bioplastics Circularity through Hydrothermal Treatments: Degradation Behavior and Products

Bioplastics are produced in growing amounts due to their environmental benefits, but their disposal routes remain ambiguous. A hydrothermal treatment (HT) may be a sustainable process to improve the fate of waste bioplastics, but nearly no information is available on how they respond to it. In this work, HT of biodegradable bioplastics was performed, and the resulting solid and liquid products were characterized by elemental analysis, analytical pyrolysis-based techniques, ion chromatography, and gas chromatography coupled with mass spectrometry. We selected tableware based on polylactic acid (PLA), cellulose, and Mater-Bi (MB) and performed HT at 160-200 °C. MB was identified as a mixture of PLA and polybutylene succinate (PBS). Higher treatment temperatures enhanced the solubilization, which was very marked for PLA and MB and minor for cellulose. Characterization of the solid residues revealed that PLA and MB were quantitatively degraded at 180 °C and above, while cellulose could never be fully degraded. The analysis of the aqueous phases from the HT of PLA and MB revealed the presence of an array of oligomers of PLA and PBS at low temperatures and of the corresponding monomers (lactic acid and succinic acid) at high temperatures: their recovery could represent a way to give new life to waste bioplastics.