Coupling of chemical deconstruction and pyrolysis to upcycle metallized multilayer plastic films

Multilayer metallized plastic films are popular packaging materials that are not currently recycled due to their complex multi-material make-up. In this study, a sequential pathway combining chemical, thermal and biological techniques was introduced to recycle military multilayer packaging made up of Polyethylene Terephthalate (PET), Polyethylene (PE), and aluminum. Chemical deconstruction using 10 wt% aqueous ammonia was able to selectively depolymerize the PET layer at a conversion close to 100 %. Aluminum and other metals were not detected in the deconstructed PET product, which contained Terephthalic Acid (TPA), terephthalic acid monoamide, terephthalamide, and ethylene glycol monomers that serve as the substrate for biological conversion. A natural microbial community was able to grow on the deconstructed multilayer at monomer concentrations of 5 g/L, producing a single cell protein product that could be used for food or animal feeds. The polyethylene and aluminum layers, which are inert during chemical deconstruction, were then pyrolyzed to breakdown the residual polyethylene into oil and wax hydrocarbons, leaving the aluminum unreacted. Elemental and gas chromatography-mass spectrometry analyses confirmed that the chemical deconstruction pretreatment step significantly improved the pyrolysis product quality by removing oxygen. The presented proof-of-concept technology represents an intriguing method to control contamination when processing complex waste plastic.