Quantification of Polyethylene Biodegradation Enabled by Catalytic Methods

• Applicant: Professor Dr. Stefan Mecking
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541017081

Environmental pollution by mismanaged plastic waste is one of the largest problems facing humanity. To this day huge amounts of polyolefins have already been leaked to the environment, and due to their persistency they are found in virtually all habitats throughout the world. A knowledge and understanding of the fate and degradation of polyethylene plastics in the environment is therefore important. Breakdown of polyethylene in the environment occurs by abiotic and biotic steps, the later being a prerequisite for any elimination of environmental polyethylene contamination by ultimate mineralization to CO2. Yet, key fundamental questions on the biodegradation of polyethylene are unanswered: 1) How does mineralization of a polyethylene chain correlate with its length? It has often been argued that below a certain chain length, on the order of a few kDa, hydrocarbons can be assimiliated by microorganisms and eventually are converted to CO2 or biomass. However, the limit of chain length up to which biodegradation actually occurs is not known and positive proof of mineralization has remained elusive. (2) To what extent do functional groups in polyethylene chains promote their mineralization? Oxygenated in-chain or end-groups introduced to the original hydrocarbon chains during the breakdown process can impact the biodegradation. Yet, reliable data on biodegradation rates and whether CO2 is reached as the actual chemical endpoint of degradation are lacking. (3) How does particle size impact polyethylene biodegradation in this context? Originally macroscopic plastic litter is mechanically abraded to microparticles, and can be further broken down to nanoparticles. In the context of points (1) and (2), it is also relevant how any biodegradation is impacted by the polyethylene's particle size. That these important questions remain unanswered is due to a number of methodological problems. The research proposed envisions to resolve these questions through stable isotope labelling. Key is the elaboration of catalytic methods to generate fully 13C polyethylenes with defined chain lengths and extremely narrow molecular weight distributions, as well as defined end-groups or a single functional in-chain group. Access to 13C polyethylene nano- and microparticles is sought via aqueous polymerizations. Soil incubations monitoring the 13CO2 that evolves from the precise 13C polyethylenes' shall provide unambiguous proof of whether biodegradation occurs for a given chain length and composition, and reveal the mineralization rate. In a broader sense, the anticipated insights will enhance the understanding of the environmental behavior and fate of polyolefin litter, and they may serve to design truly sustainable solutions of materials for the future, and rule out unsustainable approaches.

• DFG Programme: Reinhart Koselleck Projects