Degradation Behavior of Aliphatic–Aromatic Polyesters: from Microplastic-free Composting to Enzyme-Driven Recycling Possibility

To develop a polymer that leaves no microplastic traces in compost and is recyclable, this study investigates the degradation behavior of custom-designed synthetic aliphatic–aromatic polyesters. These polyesters, synthesized via melt polycondensation from 1,4-benzenedimethanol and aliphatic diacids of varying chain lengths, underwent comprehensive degradation experiments in alkaline solutions, industrial compost, sludge water, and with five enzymes: commercially obtained Hi-Cutinase (HiC), Esterase EL-01, and in-house-produced Ideonella sakaiensis PETase (IsPETase), Cryptosporangium aurantiacum PETase variant M9(CaPETase), and metagenomic leaf-branch compost cutinase variant ICCG (LCCICCG). The degradation behavior was correlated with polymer properties, including chemical structure, melting point, hydrophobicity, and crystallinity. Spiking and compost extraction experiments confirmed complete degradation of all polyesters under study within 12 weeks in industrial compost, leaving no detectable plastic residues. Enzymatic studies identified HiC as the most effective enzyme for these polyesters at 30 °C, while odd-carbon-containing polyesters served as good substrates for Esterase EL-01, HiC, and IsPETase. In contrast, aromatic PET, even with low crystallinity, showed no enzymatic specificity with these enzymes.