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Degradable commodity plastics from metallosupramolecular polymers

Periodic Reporting for period 1 - DECOMPOSE (Degradable commodity plastics from metallosupramolecular polymers)

Reporting period: 2020-06-15 to 2022-06-14

Plastic pollution, including tiny fragments known as microplastics, can adversely affect the environment, wildlife and humans. Only a very small percentage of commodity plastics are recycled. Much of the rest is incinerated, sits in landfills or is abandoned in the environment. Biodegradable plastics can ease this problem, especially if these are made from renewable resources. The combination of biodegradability and renewability allows to reduce the use of fossil fuel resources, decrease the material's carbon footprint, and lead to a faster decomposition in the environment. One of the main challenges for the end-of-life of polymers, i.e. what happens to them after their use by the consumer, is the difference in speed of degradation depending on the environment they are in. While most biodegradable polymers degrade readily within composting conditions, marine environments lead to a much slower degradation as a result of the different environmental conditions, namely temperature. One of the slowest step in plastic degradation is the decomposition of plastic materials from the macroscopic (cm to m scale) to the microscopic level (µm to nm). Once at the nanometer level, the polymers are much more exposed to microorganisms and other degradative processes in the environment, speeding up their degradation. This EU-funded project with the name “Degradable Commodity Plastics from Metallosupramolecular Polymers” (DECOMPOSE), provides a solution to this issue by installing water-extractable units within the polymer which massively accelerate the polymer degradation in the presence of water or in marine environments. While this project only showed a proof-of-concept for a certain type of polymeric material, it can be expanded to other types of material. In principle this coul provide another way of controlling the end-of-life of polymers in addition to recycling (chemical or mechanical), burning, and reuse.
The research performed so far has been focused on the first two work packages (WG1 and 2) investigating i) the proof-of-concept that metallosupramolecular polymers can be degraded by a simple extraction process with water, and ii) the synthesis of novel polyester-based building blocks suitable analogous to commodity polymers. WG1 used metallosupramolecular polymers already available in the host lab to establish the degradation of such polymers in water. The first tests were in liquid-liquid extractions in which the polymer was dissolved in a suitable solvent and then extracted with water, base, acid, or salt water. The degradation was followed by standard characterisation techniques, such as mechanical properties analyses.
At the same time, a novel polyester-based metallosupramolecular polymer was developed and fully characterised in terms of structure, and thermal and mechanical properties. This polymer was then also investigated for its ability to degrade in the dissolved and solid phase. Similar results to the previously tested polymer were obtained. Further investigations into other types of metallosupramolecular polymers highlighted that this degradative behaviour is universally applicable. Furthermore, the special polymers used have properties very similar to the commercial equivalents and could thus be a drop-in replacement.
The concept developed within this project, although simple, goes well beyond what is currently known about the degradation of (metallosupramolecular) polymers. In addition, this concept can be easily implemented into all types of polymer backbones, degradation by extraction of metal salts is a useful tool within the macromolecular toolbox to install degradability into commodity polymers. It is therefore a meaningful addition to the general discussion on plastic waste, reuse, recycling, and degradation. These types of scientific insights and discoveries are needed in order to advance and eliminate the issue of plastic waste as a whole. The publication of the results results from this project will contribute to the advancement of the field and their publication in a broad-interest peer reviewed journal is currently underway.
Degradation mechanism of metallosupramolecular polymers