Depolymerization Induced Polymer Separation: A New Strategy for Continuous and Efficient Separation of PP/PET Multilayer Plastic Packaging Waste

Plastic pollution is quickly becoming a global crisis. Despite the various methods published in the literature, mechanical recycling remains the main form of plastic recycling. However, mechanical recycling of mixed plastic waste still represents a challenge due to the need for separation and sorting. This study proposes and demonstrates depolymerization-induced polymer separation (DIPS), a new solventless, continuous twin-screw reactive extrusion process that allows for the separation and recycling of mixed plastic waste. Utilizing a blend of polypropylene (PP) and poly(ethylene terephthalate) (PET), it is shown that through the depolymerization of the PET by reactive extrusion with glycerol, it is possible to separate the PP and oligomeric PET (OPET). Characterization also shows that the recovered PP has a similar performance to the virgin polymer. It is hypothesized that in situ separation occurs due to phase separation and viscosity differences. The process is also successfully tested on postindustrial waste comprising multilayer flexible plastic packaging. This novel process has the potential to be translated to the industrial setting due to the benign conditions used and the prevalence of screw extruders in the plastic industry.