Fragmentation and Mineralization of a Compostable Aromatic–Aliphatic Polyester during Industrial Composting

Compostable plastics support the separate collection of organic waste. However, there are concerns that the fragments generated during disintegration might not fully biodegrade and leave persistent microplastic in compost. We spiked particles of an aromatic–aliphatic polyester containing polylactide into compost and then tracked disintegration under industrial composting conditions. We compared the yields against polyethylene. The validity of the extraction protocol and complementary microscopic methods (μ-Raman and fluorescence) was assessed by blank controls, spike controls, and prelabeled plastics. Fragments of 25–75 μm size represented the most pronounced peak of interim fragmentation, which was reached already after 1 week of industrial composting. Larger sizes peaked earlier, while smaller sizes peaked later and remained less frequent. For particles of all sizes, count and mass decreased to blank level when 90% of the polymer carbon were transformed into CO2. Gel permeation chromatography (GPC) analysis suggested depolymerization as the main driving force for disintegration. A transient shift of the particle composition to a lower percentage of polylactide was observed. Plastic fragmentation during biodegradation is the expected route for decomposing, but no accumulation of particulate fragments of any size was observed.