(700c) Recycling of Multilayer Plastic Packaging Materials By Solvent-Targeted Recovery and Precipitation
Many plastic packaging materials manufactured today are composites made of distinct polymer layers (i.e., multilayer films). Billions of pounds of these multilayer films are produced annually, but no technologies exist to recycle them back into their pure resins without breaking the films down into their original monomers. Herein, we demonstrate a new strategy we call Solvent-Targeted Recovery And Precipitation (STRAP) to deconstruct multilayer films into their constituent resins using a series of solvent washes that are guided by thermodynamic calculations of solvent-polymer solubility. We show that the STRAP process is able to separate three representative polymer resins (polyethylene, ethylene vinyl alcohol, and polyethylene terephthalate) from a post-industrial multilayer film with near 100% material efficiency. In this process a single polymer layer was selectively dissolved in a solvent system to be later separated from the insoluble layers and then precipitated by the addition of an antisolvent and/or decreasing the solvent temperature. The process was repeated for each of the polymer layers in the multilayer film and 100% recovery was obtained for each. This resulted in segregated streams of chemically pure dry polymers that can be much more efficiently recycled. The FTIR spectra of the separated polymer fractions were comparable to the virgin resins and less than 1100-ppm residual solvent was detected with head-space GC-FID. The glass transition temperatures for the PET and EVOH fractions were similar to the virgin materials. The solvent selection and process conditions for STRAP were based on quantifying polymer and solvent thermodynamic properties using three computational methods: Hansen Solubility Parameters (HSPs), molecular dynamics (MD) simulations, and COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS). An economic analysis was performed to assess the feasibility of STRAP at a larger scale. The total capital investment for this technology was estimated to be 13.92 million dollars with a minimum selling price (MSP) of $1.34/kg when the feed rate was assumed to be 3,000 ton/year of multilayer films.