Researchers have taken a critical step toward greatly expanding the range of recyclable plastics.
Scientists have taken a critical step towards greatly expanding the range of recyclable plastics.The research, led by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and including a faculty member in the Oregon State University (OSU) School of Engineering, will be published today (October 13) in the journal science.
This breakthrough is important because plastic waste is a huge problem globally and in the United States. In fact, according to NREL, only about 5% of plastic waste in the United States is recycled.
Packaging materials, containers and other waste are filling landfills and littering at an incredible rate. According to NREL, scientists estimate that by 2050, there will be more plastic in the ocean than fish.
A collaboration led by NREL’s Gregg Beckham and including OSU researcher Lucas Ellis, who served as an NREL postdoctoral fellow during the project, combined chemical and biological processes in a proof-of-concept to “value” mixed plastic waste. Valorize means to increase the value of something.
The research builds on the use of chemical oxidation to break down various plastic types, a method pioneered by chemical industry giant DuPont a decade ago.
“We developed a technique that uses oxygen and a catalyst to break down plastics into smaller, biofriendly chemical building blocks,” said Ellis, assistant professor of chemical engineering. “From there we used a bioengineered soil microorganism capable of consuming these building blocks and ‘pooling’ them into components for biopolymer or advanced nylon production.”
Beckham, a senior fellow at NREL and head of biooptimization technologies for preventing thermoplastics from entering landfills, said the work offers a “potential entry point to address issues that simply cannot be Recycled Plastics” today. “
Beckham explained that current recycling technologies only work effectively if the plastic is put into cleaning and separated by type.
Plastics can be made from different polymers, each with their own unique chemical building blocks. When polymer chemicals are mixed in collection bins, or formulated together in certain products (such as multi-layer packaging), recycling becomes expensive and nearly impossible because polymers often must be separated before recycling.
“Our work resulted in a process that can convert mixed plastics into a single chemical product,” Ellis said. “In other words, it’s a technology that recyclers can use without sorting plastics by type.”
The scientists applied the process to a mixture of three common plastics:[{” attribute=””>polystyrene, used in disposable coffee cups; polyethylene terephthalate, the basis for carpets, polyester clothing and single-use beverage bottles; and high-density polyethylene, used in milk jugs and many other consumer plastics.
The oxidation process broke down the plastics into a mixture of compounds including benzoic acid, terephthalic acid, and dicarboxylic acids that, in the absence of the engineered soil microbe, would require advanced and costly separations to yield pure products.
The researchers engineered the microbe, Pseudomonas putida, to biologically funnel the mixture into one of two products – polyhydroxyalkanoates, an emerging form of biodegradable bioplastics, and beta-ketoadipate, which can be used in the manufacture of performance-advantaged nylon.
Trying the process with other types of plastics including polypropylene and polyvinyl chloride will be the focus of upcoming work, the researchers said.
“The chemical catalysis process we have used is just a way of accelerating a process that occurs naturally, so instead of degrading over several hundred years, you can break down these plastics in hours or minutes,” said co-author Kevin Sullivan, a postdoctoral researcher at NREL.
Reference: “Mixed plastics waste valorization through tandem chemical oxidation and biological funneling” 13 October 2022, Science.
DOI: 10.1126/science.abo4626
Funding was provided by the U.S. Department of Energy’s Advanced Manufacturing Office and Bioenergy Technologies Office, and the work was performed as part of the BOTTLE Consortium.
Scientists from the Massachusetts Institute of Technology (MIT), the University of Wisconsin-Madison, and Oak Ridge National Laboratory also took part in the study.
NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. It is operated for the department by the Alliance for Sustainable Energy, LLC.