Researchers examine the environment’s degradation of polyethylene

Nearly one-third of all plastic waste worldwide is made from polyethylene, a cheap and simple plastic. A multidisciplinary team from the University of Bayreuth investigated the environmental degradation of polyethylene for the first time.

Although the process of degradation results in fragmentation into smaller particles, isolated nanoplastic particles rarely are found in the environment. This is because such decay products don’t like to be left alone and instead attach rapidly to larger colloidal system that naturally occur in the environment. The journal has published the findings of the researchers. Science of the Total Environment.

Polyethylene is a plastic with many molecular structures. Because of its high demand, low-density plasticethylene (LDPE), is a widely used material for packaging everyday consumer goods such as food. It has been difficult to estimate how this widely used plastic will break down after it is released into the atmosphere as waste. This question has been systematically investigated by a research team at the Collaborative Research Centre Microplastics at the University of Bayreuth. This was possible thanks to a new, technically advanced experimental setup.

This allows us to simulate in our laboratory two well-known, but also environmentally related, processes of plastic degrading: 1. photo-oxidation is when long polyethylene chains are gradually broken down into smaller, more water-soluble molecules by exposure to light. Increased fragmentation due to mechanical stresses This allowed us to gain detailed insight into the complex physical as well as chemical processes involved in LDPE degrading.

For studies addressing the potential environmental impacts of polyethylene, the final stage in LDPE degradation is particularly important. Researchers discovered that the degradation of LDPE packaging material does not stop with its release into the environment. This leaves behind many micro- and nanoplastic pieces, which have high levels of crystallinity. These tiny particles have a strong tendency of aggregating: they attach quickly to larger colloidal system made up of organic and inorganic molecules.

Clay minerals, polysaccharides and humic acid are all examples of colloidal systems. “This is because individual nanoparticles made by polyethylene degrading are prevented from being freely accessible in the environment and from interfacing with animals or plants. This is not an all-clear signal. Living organisms often ingest larger aggregates that are part of the material cycle in the environment. This is how nanoplastics can eventually get into the food chain,” Teresa Menzel, one the lead authors of the new study and a doctoral researcher in the field polymer materials, said.

To identify the degradation products formed when polyethylene decomposes, the researchers employed a method that has not been widely used in microplastics research: multi-cross-polarization in solid-state NMR spectroscopy. “This method even allows for us to quantify the degradation products produced by photooxidation,” said co-author Anika Maurel, a doctoral researcher and inorganic chemical chemist.

Bayreuth’s researchers also discovered that polyethylene is also degraded and broken down, which leads to the formation peroxides. “Peroxides have been known to be cytotoxic, meaning that they can cause damage to living cells. Another way in which LDPE degrading poses a threat is through the use of cytotoxic substances. These interrelationships must be studied more in the future,” Nora Meides, co-author and a doctoral researcher specialized in macromolecular chemical chemistry, says.

Without the University of Bayreuth’s interdisciplinary network and coordinated use of state of the art research technologies, it would have been impossible to analyze the chemical and physical processes that lead to the degradation of polyethylene. These include scanning electron microscope (SEM), energy-dispersive Xray spectroscopy(EDS), Xray diffractions (XRD), NMR spectroscopy. Fourier transform infrared spectroscopy is (FTIR) and differential scanning calorimetry is (DSC).