The new environmentally friendly plastic.
The University of Konstanz presents a new material: a polyester plastic with great mechanical stability, easily recyclable and compostable.
How can plastics be designed so that they retain their desirable properties, but at the same time can be recycled more effectively? This and other questions regarding the environmental friendliness of plastics are the focus of chemist Stefan Mecking and his research team from the University of Konstanz (Germany). In the latest work published in the international edition of Angewandte Chemie, the team presents a new polyester that exhibits properties that are interesting for industry and at the same time environmentally friendly. Plastics are made up of long chains of one or more modules of monomers. Plastics, characterized by high crystallinity and water repellency, therefore mechanically very resistant and stable, are widely used. A well-known example is high-density polyethylene (HDPE), the basic modules of which are made up of non-polar hydrocarbon molecules. What on the one hand can be advantageous properties for applications, on the other can have negative effects: recycling of these plastics and the recovery of the basic modules are very expensive in terms of energy and inefficient. Furthermore, if these plastics are dispersed in the environment, the degradation process is extremely long. To overcome this alleged incompatibility between the stability and biodegradability of plastics, Mecking and his group have inserted “breaking points” chemicals in their materials. They have already shown that this significantly improves the recyclability of polyethylene-like plastics. “Plastics often have a high resilience because they are ordered in densely packed crystalline structures,” Mecking explains: “Crystallinity, in combination with water repellency, usually slows down the biodegradation process greatly, as it hinders the access of microorganisms at breaking points. However, this does not apply to the researchers’ new plastic.
Crystal clear and compostable
The new plastic, polyester-2,18 , consists of two basic modules: a unit with two carbon atoms and a dicarboxylic acid with 18 carbon atoms. Both modules can easily be obtained from sustainable sources . For example, the starting material for dicarboxylic acid, which is the main component of plastics, comes from a renewable source. Polyester thanks to its crystalline structure, for example, has mechanical stability and resistance to temperature. At the same time, the first recyclability experiments have shown that, under relatively mild conditions, the basic modules of this material can be recovered.
The new plastic also has another completely unexpected property: despite its high crystallinity, it is biodegradable , as laboratory experiments with natural enzymes and tests in an industrial composting plant have shown. Within days, in a laboratory experiment, polyester was degraded by enzymes. The microorganisms from the composting plant took about two months; hence, this plastic also meets ISO standards for composting. “Even we were amazed by this rapid degradation,” says Mecking, who adds: “Of course we cannot transfer the results of the composting plant one by one under any imaginable environmental condition. But they confirm that this material is indeed biodegradable and indicate that it is much less persistent than plastics such as HDPE (high-density polyethylene), should it be unintentionally released into the environment.”
Both the recyclability of this polyester and its biodegradability under varying environmental conditions will now be the subject of further study. Mecking sees possible applications for this new material, for example in 3D printing or the production of packaging foils.
