Is sustainable recycling of plastics possible?
University of Konstanz
In order to offer novel solutions, chemists developed a more sustainable method for chemically recycling polyethylene-like plastics. The researchers use 'breaking-points' on a molecular level to disassemble the plastic back to its molecular components.
The new method works without
extremely high temperatures, is therefore more energy-efficient and has a
significantly higher recovery rate (approx. 96 per cent of the starting
material) than established processes. These findings will be published on 17
February 2021 in the scientific journal Nature.
Mechanical recycling vs. chemical recycling
"The direct re-utilization of
plastics is often hampered by the fact that, in practice, mechanical recycling
only functions to a limited degree -- because the plastics are contaminated and
mixed with additives, which impairs the properties of the recycled
materials," Stefan Mecking explains.
"Chemical recycling" is an
alternative: Via a chemical process, used plastic is broken down into its
molecular building blocks, which can then be converted into new plastic.
Limitations of chemical recycling of
polyethylene
Specifically in the case of
polyethylene -- the most widely used plastic -- chemical recycling is
difficult. On a molecular level, plastics are made up of long molecular chains.
"Polymer chains of polyethylene are very stable and not easily reversed
back into small molecules," Stefan Mecking explains. Temperatures
exceeding 600° Celsius are required, making the procedure energy-consuming. At
the same time, the recovery rate is limited (in some cases less than ten per
cent of the starting material).
How chemical recycling of
polyethylene can be made more sustainable
Stefan Mecking and his team report on a method that makes a more energy-efficient chemical recycling of polyethylene-like plastics possible, coupled with a very high recovery rate of around 96 per cent of the starting materials. To do so, the chemists used "breaking-points" on a molecular level enabling a deconstruction of the chain into smaller molecular building blocks.
"Key for our method are
polymers with a low density of predetermined breaking-points in the
polyethylene chain, so that the crystalline structure and material properties
are not compromised," Stefan Mecking explains and adds: "This type of
materials is also very suitable for 3D printing."
Stefan Mecking´s research team demonstrated this chemical recycling on polyethylene-like plastics based on plant oil. The recycling stage requires temperatures of only about 120 degrees. Furthermore, the chemists also performed this recycling method on mixed plastics as they occur in waste streams.
The properties of the recycled
materials are on a par with those of the starting material. "Recyclability
is an important aspect for future technologies based on plastics. Re-utilizing
such valuable materials as efficiently as possible makes sense. With our
research we want to contribute to making chemical recycling of plastics more
sustainable and effective," Stefan Mecking resumes.