Regranulate - plastic ground into smaller pieces. Photo by Christian Ove Carlsson.

How can we make plastic more sustainable?

Wednesday 21 Oct 20
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by Morten Andersen

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Anders Egede Daugaard
Associate Professor
DTU Chemical Engineering
+45 23 65 21 52
All stages of plastics use, from processing to initial product and after-life will need to be taken into account for design of tomorrow’s plastic materials and to increase their value for society.

The optimal sustainable polymer would be made from biological feedstock and be fully recyclable. However, we cannot get to this ideal scenario in one go, as Anders E. Daugaard, Associate Professor with the Danish Polymer Centre (DPC) at DTU Chemical Engineering, explains:

“We still see more bio-based polymers with satisfactory technical properties being developed. This is good news for climate change mitigation. We need alternative sources of raw materials, and production of bio-based polymers does emit less CO2 than production of polymers from fossil raw materials. However, these bio-polymers do not recycle well so far. I would argue that a fossil polymer, such as our current commodity plastics, which can be recycled many times, is in fact more sustainable than a bio-based polymer that can only be used once.”

Further, Anders E. Daugaard wants us to think polymer sustainability in a broader context:

“We should not only be concerned about the source of raw material or the fate of the polymer itself, but also include its function. Without polymer wrapping, food like fish, meat, and fruit would quickly go bad. We would have to return to the situation 50 years ago, where people had to do most of their shopping at a daily basis. And we would waste a lot more food than we currently do. This would hardly be sustainable.”

Multi-layer foils challenge recycling

Most consumers don’t know that as they pick up a random tray with fresh meat at the supermarket, the product is protected not by one, but typically 5-7 different layers of foil. The middle layer will have excellent barrier properties—stopping meat juice from getting out, and oxygen from getting in—while the other layers add other technical properties.

“The result is unique protection, and we can thus see food products last for several weeks rather than maybe a couple of days. However, from a recycling perspective this is really problematic. It is just not possible to separate these 5-7 different layers after collection. At the very best, you may be able to tolerate these polymers in a blended form in granulated re-used polymer, which could be utilized for making, say, an outdoor bench. Nevertheless, you will never be able to restore the excellent barrier properties and re-use these high-value polymers for the original purpose,” says Anders E. Daugaard.

Solving this problem will require a combination of technical research and a change of attitude, Anders E. Daugaard argues:

“Efforts in many research groups, including ours, aim at developing novel polymers which as one-layer foils have satisfactory barrier and other properties. This will enable recycling for the original purpose. We have shown that a significant improvement can be achieved using various composite systems. Such solutions are able to meet requirements in some areas of packaging. However, even though a lot of progress is made, it is still very difficult to meet the excellent barrier properties of the best multi-layer foils.”

Through a recently granted Innovation Fund Denmark Grand solutions project, DPC will collaborate with industrial partners covering all the elements of processing and preparation of industrial solutions to reduce the need for muli-layer foils for packaging applications.

Getting value out of plastic waste at all stages of the process

Reducing plastic consumption during processing by direct recirculation, when possible, or through industrial recycling is currently being done. However, for some materials, such as multi-layer foils or thermosets, this is particularly difficult, since these cannot just be re-grinded and recirculated into the production. In these cases, companies will not even be able to recycle waste created in-house.

“We’re talking about significant quantities here, and it should be possible to utilize this resource. Multi-layer foils are one such example, but also thermoset materials or heavily degraded materials that have been in circulation, are fractions that will need to be handled,” says Anders E. Daugaard.

If a quantum of newly produced polymer has some kind of flaw, it will often have to be incinerated. In addition to waste from production, also thermoset materials as well as heavily degraded or mixed plastics need to be recycled to a much greater extent to generate higher value from these types of materials.

Through an internal collaboration at the Department, we combine gasification technology from the CHEC research group with our expertise on plastics, together with industrial and academic partners in an Innovation Fund Denmark Grand Solutions project, to extract higher value products from such complicated waste fractions. Particularly, the possibility to be able to produce new pristine polymers from these raw materials holds a great potential for increasing the value of these waste fractions.

“By considering all the stages of plastics use, from processing to initial product and after-life, we believe it will be possible to both reduce the amount of waste as well as to increase the value of the waste products that we as a society will inevitably create. All of these aspects are critical in the development of a more sustainable use of plastics,” Anders E. Daugaard concludes.

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