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New Method Uses Engineered Microbes to Convert Waste PET into Nylon

Scientists from the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL) are making progress on a . A collaborative research team is combining chemistry and biology to turn PET into a nylon material with better properties that can be used to create a more versatile range of new products.
Engineered Bacterium for Upcycling Plastics
In conjunction with the BOTTLE Consortium, NREL researchers and partners from Oak Ridge National Laboratory (ORNL) engineered a bacterium to convert deconstructed into building blocks for a superior product. These high-performance monomers can then be recycled into higher-value plastic materials and products, a process known as upcycling.
"This biological conversion step is one important part of the equation that makes PET upcycling possible, creating the opportunity to turn polluting plastic bottles into prized manufacturing materials, ultimately moving us closer to a circular economy at scale," said NREL scientist Allison Werner.
The Chemo-catalytic Process
BOTTLE researchers are exploring how a range of chemical and biological processes can be used to to higher-value, recyclable materials. The recent BOTTLE project deconstructed PET using a chemo-catalytic process and engineered the bacterium Pseudomonas putida KT2440 to convert the PET into the chemical β-ketoadipic acid (βKA), a building block for performance-advantaged nylon.
NREL and ORNL collaborated in engineering the bacterium. ORNL engineered the bacterium to utilize a key intermediate in PET breakdown, which enabled the NREL team to build a complete platform for bioconversion.
Better Properties for Upcycled Nylon
The biological transformations engineered by NREL and ORNL scientists into P. putida, paired with a chemo-catalytic glycolysis process, can create a more valuable product from PET and ultimately incentivize higher reclamation rates—eventually translating into fewer discarded plastic bottles polluting ocean waters and mountain wilderness areas.
The material extracted through this tandem catalytic deconstruction and biological conversion technique offers better properties than the common types of nylon it is intended to replace, including lower water permeability, higher melt temperature, and higher glass-transition temperature. These performance advantages expand the ways the material can be used, including for automotive parts that need to withstand high temperatures. Increased value of the recycled material could incentivize industry to recycle more plastic, leading to plastic recovery on a much larger scale.
Expanded Opportunities for Upcycled PET
While this initial breakthrough already promises to expand opportunities for PET upcycling, researchers continue to refine the approach. In addition to optimizing the chemistry-biology interface, the team is evaluating a wide range of other factors.
Postconsumer PET waste streams can contain additives that P. putida may be unable to catabolize. Characterization of these streams to identify the chemicals present and engineering metabolic pathways to enable consumption of these compounds as well will be needed to maximize efficiency of the bioconversion process, increase yields, and comprehensively deal with the plastic waste.
The future success of any tandem deconstruction and upcycling approach for PET will ultimately be determined by its combined technical feasibility, economic viability, and environmental impact. The NREL team plans to perform techno-economic analysis and life cycle assessment to build a better understanding of the process energy requirements and greenhouse gas emissions.
Various Post Consumer Recycled Nylon Grades

Source: NREL

Publication date: 19/10/2021

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870292.