Ultrafast Simultaneous and Selective Depolymerization of Heterogeneous Streams of Polyethylene Terephthalate and Polycarbonate: Towards Industrially Feasible Chemical Recycling

Mixed plastic waste-streams are a main obstacle to a more extensive implementation of polymer recycling. Separating mixed-plastic waste streams demands time and effort at collection or in the recycling plant, while many products consist of multiple polymers that cannot be readily separated. Chemical recycling could provide the key to overcome this issue by targeting specific chemical bonds, enabling selective depolymerization of a single polymer class in a mixture. This work explores the depolymerization of polycarbonate (PC) and polyethylene terephthalate (PET) in separate and in mixed streams. Selective depolymerization of mixed streams composed of PET and PC and one-step separation of their constituent monomers are carried out with outstanding energy efficiency through an inexpensive KOH-in-methanol hydrolysis (KMH) process developed for instantaneous PET hydrolysis. The activation energies for depolymerization of PC and PET pellets are 68.6 and 131.4 kJ mol(-1), respectively. Randomly mixed streams are fully depolymerized within 2 min at 120 degrees C using 30 mL of depolymerization solution per gram of polymer. The separation of bisphenol A and terephthalic acid is demonstrated in a one-step separation process, yielding 98 and 97 % purity without any secondary reactions detected. Simultaneous depolymerization and selective one-step separation of monomers are also demonstrated for a PET/PC polymer blend prepared by solution casting, showing that this process also works for intimately mixed PET/PC mixtures.

Automated summary

Mixed plastic waste-streams pose a challenge to polymer recycling, but this study demonstrates the potential of chemical recycling to selectively depolymerize and separate specific polymers such as polycarbonate (PC) and polyethylene terephthalate (PET) with high energy efficiency.