Life Cycle Assessment of Chemical Upcycling of Postconsumer Polyethylene Terephthalate to Kevlar Polymer

Abstract

Due to its low cost and chemical stability, poly(ethylene terephthalate) (PET) is widely used in single-use items, such as plastic bottles and packaging materials. The high demand has resulted in a significant amount of discarded PET waste, underscoring the need for effective recycling strategies. One promising approach is PET chemical upcycling, but it requires evaluation of the environmental impact of the entire process, from waste collection to polymer synthesis. This study, for the first time, uses life cycle assessment (LCA) to assess the environmental impact of chemical upcycling of postconsumer PET to Kevlar polymer. The study models the life cycle inventory of chemical upcycling via PET ammonolysis and hydrolysis, developing scenarios based on the environmental hotspots of each chemical process for future optimization. The results show that upcycled Kevlar (15.22 kg CO2 eq/kg Kevlar) has lower impacts than virgin Kevlar polymer production, with a 15% reduction in global warming potential (GWP), 30% in cumulative energy demand (CED), 1% in ecotoxicity, and 40% in fossil fuel depletion. Hotspot analysis identifies monomer preparation as the most impactful process, particularly due to the use of solvents such as chloroform and diethyl ether. Chloroform, used in the p-phenylenediamine (PPD) preparation process, is one of the largest contributors, accounting for approximately 20.8% of GWP and 12.1% of ecotoxicity. The best-case scenario, which replaces potassium hydroxide with sodium hydroxide and reduces solvent consumption for purifying and extracting monomers, results in a 19.9% decrease in GWP and a 21.1% reduction in costs compared to those of the baseline. These results highlight that upcycled Kevlar has the potential to reduce the environmental burden of Kevlar production by utilizing PET waste. However, achieving adoption on an industrial scale requires targeted process optimization, addressing process hotspots, and replacing conventional solvents with greener alternatives.