A new material with high mechanical stability that can be easily recycled and even composted

Stefan Mecking and his research group at the University of Konstanz in Germany have developed a new biodegradable material – a polyester plastic with high mechanical stability that can be easily recycled and even composted.

Plastics are made of monomers – long chains of one or more basic chemical modules. Commonly used plastics are characterized by high crystallinity and hydrophobicity, and thus high mechanical strength and stability. An example is high-density polyethylene (HDPE), whose basic modules consist of non-polar hydrocarbon molecules. What, on the one hand, may be beneficial for application applications, unfortunately also has negative effects – recycling of such plastics and recovery of basic modules is very energy-intensive and inefficient. In addition, if such plastics get into the environment, the degradation process is extremely long.

To overcome the mismatch between the stability and biodegradability of plastics, Mecking and his team are introducing chemical “breakpoints” into their materials. This greatly improves the recyclability of polyethylene-like plastics, but good biodegradability is not automatically guaranteed. “Plastics often achieve high resilience because they are ordered into densely packed crystalline structures,” Mecking explains. However, this does not apply to the new material developed by scientists.

The new plastic, 2.18-polyester, consists of two basic modules: a short diol unit with two carbon atoms and a dicarboxylic acid with 18 carbon atoms. Both modules are easily sourced from sustainable sources. For example, the starting material for the dicarboxylic acid, which is the main component of the plastic, comes from a renewable source. The properties of polyester resemble those of HDPE due to its crystalline structure, it exhibits both mechanical stability and temperature resistance. At the same time, the first experiments on recyclability showed that under relatively mild conditions, the basic modules of this material can be recovered.

The new material also has another, quite unexpected property: despite its high crystallinity, it is biodegradable, as shown by laboratory experiments with natural enzymes and tests in an industrial composting plant. Within a few days in a laboratory experiment, polyester was broken down by enzymes. The composting plant’s microorganisms took about two months, so this plastic even meets ISO standards for composting. “We were amazed at the rapid degradation,” Mecking says, adding, “Of course we cannot transfer the composting results one-to-one to any possible environmental condition. However, they confirm that the material is indeed biodegradable and indicate that it is much less durable than plastics such as HDPE if accidentally released into the environment.”

Both the recyclability of the new polyester and its biodegradability under varying environmental conditions now need to be further investigated. Mecking sees possible uses for this new material, including in 3D printing or in the production of packaging films. In addition, there are further areas of interest where a combination of crystallinity with recyclability and abrasion particle degradation or similar loss of material is desirable.

Źródło: www.uni-konstanz.de