PET packaging—used for non-transparent soft drinks bottles—has so far bypassed the returnables systems and refuse bins because it has been time-consuming and expensive to recycle it. Photo: Jesse Wagstaff/Flickr

New method can break down PET plastic with microwaves

Monday 30 Apr 18

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Ioannis V Skiadas
Associate Professor
DTU Chemical Engineering
+45 45 25 27 29

What is PET?

PET stands for polyethylene terephthalate, which is a thermoplastic polymer resin in the polyester family.


The melting point is between 235-260°C.


The material is easily recyclable. PET bottles are used for, for example, soft drinks and water.

In a large-scale project, researchers will reproduce PET packaging using sustainable microwave technology.

Large volumes of PET packaging—used for, for example, non-transparent soft drinks bottles—bypass the returnables systems and refuse bins, and end up in nature.

So far, recycling the hard plastic type has been a time-consuming and expensive process because the plastic contains many chemicals. However, the Swiss company GR3N has developed a new microwave technology which can break down PET plastic quickly and inexpensively. This may pave the way for a circular economy in plastics to the benefit of the environment. The method is now to be tested in a project in which DTU is among the participants.

“The problem with PET plastic is that it can only be reused a certain number of times before it wears down. And the current method used for destroying it has a highly detrimental impact on the environment because it is either burnt or discarded in nature,” says Ioannis V. Skiadas, Associate Professor and researcher at DTU Chemical Engineering, and project manager for the Danish part of the so-called DEMETO project, in which the new technology will be tested in a test facility.

The only way in which you can reproduce the hard plastic is to break down the so-called polymers in a depolymerization process. This process is the pivot in the DEMETO project:

“By mixing new microwave technology with a well-known chemical reaction, a unique process has been created that makes it possible to reuse PET in an cost-effective manner and apply the recycling method industrially,” says Ioannis V. Skiadas.

"By mixing new microwave technology with a well-known chemical reaction, a unique process has been created."
Ioannis V Skiadas

In the process, the plastic is returned to its original constituent parts and can be relaunched as a brand-new raw material, which, for example, NEOGROUP—another partner in the DEMETO project—purchases and uses to make new PET.

Complicated purification process
The DEMETO project—which commenced in September and runs over the next three years—is financed by the EU’s Horizon 2020 programme. At DTU Chemical Engineering, researchers are still conducting the basic testing before they start the actual testing of the technology in a test facility:

“We’ll receive hydrolyzed PET, which is the thick mass produced in the microwave process. Our job is then to separate from the mass the ingredients which can be used to make new PET. This is done using a complicated purification process. In order for us to achieve this, there is much that needs to be tested. We must, for example, examine how we can optimize the steps between the individual processes, minimize energy consumption, and find out how we can reuse the chemicals,” says Ioannis V. Skiadas.

The environment is the big winner
When asked about the biggest benefit of DEMETO, Ioannis V. Skiadas answers:

“The big winner is definitely the environment. By reusing PET bottles and reproducing the chemicals used for PET production, nature will potentially be spared millions of tonnes of plastic, because there is now the necessary financial incentive to collect and reuse old PET. We have the industry in our corner because the recycling process can be performed cost-effectively. It’s a win-win situation.”

Not only non-transparent PET bottles are recyclable. All PET packaging—including polyester in clothing—can be reused. Fashion giant H&M is therefore also among the partners in the project.


Partners in the DEMETO consortium

The partners in DEMETO—which stands for DEpolymerization by MicrowavE TechnolOgy—are GR3N, NEOGROUP, DTU Chemical Engineering, H&M Hennes & Mauritz AB, Synesis, PETCIA, Processi Innovativi (project coordinators), 3V Tech, ACTOR, Fricke and Mallah GmbH, EuPC, SUPSI-DTI, European Outdoor Group.


The project has received funding from the European Union’s Horizon 2020 research and innovation programme.

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