Ohmic Heating as a Strategy for Upcycling PET Plastic Waste for New Supramolecular Structures

The massive accumulation of poly(ethylene terephthalate) (PET) plastic waste poses a significant global environmental challenge, requiring the development of more sustainable upcycling strategies. This study investigated the alkaline hydrolysis of PET flakes to recover terephthalic acid (TPA) using ohmic heating and compared its performance with conventional and microwave heating methods. The sequential PET loading in the same reaction medium, as well as the use of opaque white and opaque colored PET feedstocks, was also evaluated. The spectroscopic characterization by ¹H NMR and powder X-ray diffraction (PXRD) confirmed the successful recovery of TPA from different PET sources. This recovered TPA was subsequently co-crystallized with 4-(dimethylamino)pyridine (DMAP) and 4-aminopyridine (AP) in low-temperature methanol to synthesize new supramolecular structures 1 and 2, respectively. Both compounds were characterized by scanning electron microscopy (SEM) and PXRD. Single-crystal X-ray diffraction analysis of compound 1 revealed a three-dimensional supramolecular network stabilized by ionic/hydrogen bonding interactions between the TPA and DMAP units. Overall, ohmic heating emerged as a potentially energy-efficient and sustainable approach for PET hydrolysis. Furthermore, the successful synthesis of these supramolecular architectures demonstrates that recycled TPA can serve as a valuable building block for advanced functional materials, highlighting a promising route for the high-value upcycling of PET waste.