EFRI E3P: Supercritical Extraction for the Elimination of End-of-Life Plastics (SCE3P)

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Multilayer plastic packaging is critical to keeping a wide range of food products, including meats, juice pouches, cheeses, and prepared foods, safe during transportation and storage. To function, multiple materials are used together to meet requirements that individual materials cannot. However, most multilayer food packaging winds up in landfills because current recycling processes cannot separate the various components. In this project, researchers will use high pressure and high temperature to turn gases into supercritical fluids that enable separating the materials used in typical multilayer food packaging. The higher value of the resulting purer material streams will improve the economics of recycling multilayer structures. The process will be designed to allow straightforward implementation on equipment commonly found at existing recycling plants. The work will include a thorough assessment of both the economic and environmental impacts of increased recycling rates for multilayer packaging. If successful, the project will result in new technology that increases the recyclability of plastic waste, reduces the amount of plastic waste entering landfills, and limits the environmental impact of food packaging. The project will also enhance education, diversity, and workforce development by combining efforts from a large four-year university, a historically black university, and a two-year community college in a highly interdisciplinary approach to addressing the research questions. Graduate and undergraduate students participating in the research will cross-train at the partner institutions and develop community outreach activities on polymers, recycling, and related science for use at open houses and area classrooms.This project aims to valorize the multilayer polymer waste stream through a process designed to reclaim high-value barrier polymers from multilayer food packaging and simultaneously recycle the polyolefins. The investigators hypothesize: 1) supercritical CO2, in combination with cosolvents, will improve the extraction of ethylene vinyl alcohol (EVOH) and polyxylylene adipamide (MXD6) from multilayer systems by increasing the polymer concentration in the solvent phase and enhancing the solvent's ability to penetrate the multilayer structure via plasticization, 2) modifying extrusion equipment to use supercritical fluids offers several advantages including enhanced layer separation and dissolution kinetics and reduced costs including overall recycling energy and recycling facility retrofitting expenses, 3) the materials reclaimed by this process will be suitable for use in closed-loop recycling, and 4) the proposed technology will increase overall recycling rates, having a net positive environmental impact. The work will increase our thermodynamic and kinetic understanding of the phase behavior of commercially important plastics and their mixtures in supercritical CO2 with cosolvents. Fundamental understanding of how solvent choice, processing conditions (e.g., temperature and pressure), and extruder screw design impact partition coefficients and polymer extraction kinetics will be gained. A combination of techno-economic analysis, life-cycle assessment, and economic and environmental impact analysis will be used to establish the potential impact of recycling multilayer food packaging on the environment and determine the need for policy instruments to promote the recycling of these materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.