Heavy petting: technique upcycles single-use plastics
Mixing PET plastics with biomass produces stronger and more valuable recycled results. Nick Carne reports.
US researchers have found a way to turn unwanted plastic into materials that may well be better than the original.
Their recycling process combines polyethylene terephthalate (the ubiquitous PET plastic) with renewable sources such as waste plant biomass to create a type of fibre-reinforced plastic (FRP) that is longer lasting, more versatile and more valuable.
And it is more energy-efficient to produce than recycled PET or conventional FRPs.
It’s still early days, with scalability one of the inevitable challenges, but the research team from the Department of Energy's National Renewable Energy Laboratory (NREL) in Denver, Colorado, is confident its approach can overcome one of the big stumbling block to mass recycling – the economics.
“Standard PET recycling today is essentially 'downcycling,'” says researcher Gregg Beckham. “The process we came up with is a way to 'upcycle' PET into long-lifetime, high-value composite materials like those that would be used in car parts, wind turbine blades, surfboards or snowboards.”
The world loves PET because it is strong, light, shatterproof and resistant to water. Global production hits 26 million tonnes of it a year – most of which ends up in landfill or the ocean.
The will to recycle is diminished by the business reality that the resultant product is lower in quality and thus in value – about 30% less, the researchers suggest. That’s largely because of contamination in the recycling process.
“The idea is to develop technologies that would incentivise the economics of PET reclamation,” explains Beckham.
“That's the real hope: to develop second-life upcycling technologies that make single-use waste plastic valuable to reclaim.”
In this case, Beckham and colleagues have tried to do that by moving the recycling process from the purely mechanical to the chemical. They essentially deconstruct the plastic and create something new, which also allows them to deal with any potential contamination.
The “strengths” of the original PET are retained, and the addition of bio-based monomers provides additional functionality or properties because of their different chemistry.
This isn’t the first study to explore a chemical approach, but it has produced some impressive results.
In a paper published in the journal Joule, the researchers report that by combining PET with sustainably sourced, bio-based molecules they produced two types of FRPs that are two to three times more valuable than the original PET.
And, they add, analysis suggests these composite products would require 57% less energy to produce than standard reclaimed PET, using the current recycling process, and would emit 40% fewer greenhouse gases than current petroleum-based FRPs.
“Supply chain energy calculations reveal that this strategy for plastics upcycling could save significant total manufacture energy, mainly from savings in associated energy from petroleum feedstocks, and could also reduce greenhouse gas emissions,” they write.
“Overall, this approach provides an economic incentive for plastics recycling and renewable feedstock use through the creation of long-lifetime, performance-advantaged materials.”
The next step is to produce materials that can themselves be recycled. The current composites can last years, even decades, but are not necessarily recyclable in the end.