Nanoplastics in Depolymerization Products from Hydrolysis of Poly(Ethylene Terephthalate) in the Solid State

Circularity in plastic waste management through depolymerization to monomer is a promising route to address inefficiencies in the current recycling ecosystem, especially for poly(ethylene terephthalate) (PET). Hydrolysis provides a green solvent to promote the depolymerization of PET, but lifecycle analyses have driven extensive efforts to lower the reaction temperature to minimize greenhouse gas emissions. However, recent work (Nat. Commun., 2025, 16, 3051) has indicated that hydrolysis at temperatures near the normal boiling point of water can generate nanoplastics. Here, we demonstrate that PET hydrolysis at temperatures less than 180°C leads to nanoplastics as determined from dynamic light scattering (DLS) and differential scanning calorimetry (DSC). Clear evidence of plastic nanoparticles is observed after hydrolysis at 150°C for three of the four PET sources examined. DSC thermograms of hydrolysis products on heating exhibit a broad peak with a depressed melting point that is consistent with small PET crystals. Hydrolysis at higher temperatures leads to smaller particles with DSC thermograms that are indicative of small molecules and oligomers. These results illustrate the potential for unintended consequences from efforts to reduce GHG emissions with chemical recycling to generate nanoplastics in the product stream that may be difficult to readily differentiate from expected products.