Comparing Parallel Plastic-to-X Pathways and Their Role in a Circular Economy for PET Bottles

Abstract

The United States generates the most plastic waste of any country and is a top contributor to global plastic pollution. Multiple end-of-life strategies must be implemented to minimize environmental impacts and retain valuable plastic material, but it is challenging to compare options that generate products with different lifetimes and utilities. Herein, they present a material flow model equipped with consequential life cycle assessment, cost analysis, and a plastic circularity indicator that considers product quality and lifetime. The model is used to estimate the greenhouse gas (GHG) emissions, circularity, and cost of polyethylene terephthalate (PET) bottle mechanical downcycling to lower-quality resin, closed-loop glycolysis to food-grade PET, upcycling to glass fiber-reinforced plastic, and conversion to non-plastic products (electricity, oil) on a United States economy-wide basis for the year 2020. A brute force algorithm suggests that a combination of 68% glycolysis, 11% mechanical recycling, 6% upcycling, 9% landfilling, and 5% incineration can minimize the cost and GHG emissions and maximize the circularity of the current PET economy. However, uncertainty around transportation distances, materials recovery facility efficiencies, and recycling yields can result in different “optimal” pathway mixes. This flexible framework enables informed decision-making to move toward a cost- and environment-conscious circular economy for plastic.