Thermoanalytical approach to assess riverine PET litter and its recycling potential

In this proof-of-concept study, a thermoanalytical method based on differential scanning calorimetry (DSC) is proposed to quantitatively link the crystallisation dynamics of bottle-grade poly(ethylene-terephthalate) (PET) with its degradation state. The study uniquely simulates long-term sunlight exposure through controlled artificial ageing of PET bottles in a Xenon chamber, with degradation levels accurately determined via intrinsic viscosity (IV) measurements. Following degradation, DSC analysis was conducted, and the complex melting endotherms observed during the post-isothermal crystallisation heating phase were deconvoluted into sub-peaks using the Fraser-Suzuki function. A novel discovery was made: a specific sub-peak exhibited a melting temperature with a strong, linear relationship to the molecular chain length of PET, providing a precise indicator of polymer degradation. This correlation represents a significant advancement in the field, as it was successfully applied to PET litter samples collected from floodplains in Hungary within the catchment area of the Tisza River, enabling accurate estimation of environmental degradation levels. Moreover, based on the determined IV ranges of the riverine PET bottles, we propose targeted recycling strategies for this pervasive pollutant, with a comprehensive evaluation of reprocessing outcomes. These findings open new avenues for assessing polymer degradation in environmental and industrial contexts, highlighting the method's potential for broader applications in waste management and material science.