Rheological Characterization of UV and Shear‐Induced Degradation of Poly(Ethylene Terephthalate): Linking Environmental and Processing Histories to Recyclability

ABSTRACT Throughout its lifecycle, poly(ethylene terephthalate) (PET) undergoes significant degradation from long‐term ultraviolet (UV) exposure, moisture, and shear forces, with these effects intensified during mechanical recycling. To characterize molecular degradation, PET samples subjected to UV aging in dry, marine, and freshwater environments, as well as diverse shear rates (90–450 s −1 ) are investigated using rheological analysis. Rheological analysis effectively distinguishes competing PET degradation effects under UV exposure from shear effects, highlighting crosslinking in dry conditions and hydrolytic chain scission under aqueous environments. Under shear, virgin PET shows an upshift in molecular weight ( Mw ) due to crosslinking reactions, while recycled PET experiences a drastic reduction in Mw owing to chain scission. When virgin PET goes through even a single shear‐proces…