As we know, conventional plastics are very useful and resistant, a fact that has allowed them to be used in a large number of applications, but we are also aware of the great environmental damage that plastics have caused to the planet. That is why several alternatives have been proposed to replace plastics, however, attempts to develop more environmentally friendly substitutes have not been very successful, mainly due to their high production cost and low resistance. So the question arises, can we design a plastic that has good mechanical properties and at the same time can be easily recycled?
The new polyester resembles polyethylene but is recyclable and biodegradable. Source: image elaborated in Powerpoint.
Currently, about 90% of today's plastics are produced from petroleum and are not biodegradable, and bioplastics still have a long way to go before they can be used on a large scale. But solving these plastics issues was the goal of a group of researchers at the University of Konstanz, who have recently published an article in the journal Angewandte Chemie, where they present a new polyester material with attractive properties for the plastics industry that is more environmentally friendly.
Generally speaking, plastics are made up of long chains of several individual basic units called monomers, forming densely packed crystalline structures; and as we have noted, their characteristics include high crystallinity and water repellency, making them very stable and resistant. But while these characteristics make them ideal for various applications, especially for the manufacture of containers and packaging, they also have a great disadvantage, and that is that recycling these plastics is very difficult, since the deconstruction of the material in its basic units consumes a lot of energy and current processes are not very efficient; not to mention that their biodegradation in the environment requires excessively long periods of time.
Representation of a polyethylene molecule. Source: Wikipedia.com
Now, this research team presented a novel polyester material obtained from readily available bio-based 1,18- octadecanedicarboxylic acid and ethylene glycol, which possesses a structure similar to polyethylene. Using the polycondensation method, catalyzed by dibutyltin oxide, polyesters of 1,18-dimethyl octadecanedioate with different α,ω-diols were produced, generating a compound named PE-2,18, which stands out among other synthesized polyesters for its high melting point of Tm=96 °C, besides presenting crystalline properties similar to those of high-density polyethylene.
The new PE-2,18 plastic consists of two basic units, a short diol with two carbon atoms and a dicarboxylic acid with 18 carbon atoms. Due to its structure, this polyester presents both mechanical stability and temperature resistance, similar to high density polyethylene; but with the difference that the first experiments showed an easy recyclability under comparatively mild conditions, recovering the two basic units that make up the material.
Synthesis of PE-2,18. Source: Source: image elaborated in Powerpoint.
The new plastic also showed a very interesting property: despite its crystallinity compared to polyethylene, the new material proved to be easily hydrolyzable by natural enzymes, i.e. it can be completely biodegraded by composting. In a laboratory test, this material was degraded by enzymes within a few days, and was degraded by microorganisms in a composting plant within two months, so this material even meets ISO composting standards.
Although it is not yet possible to translate the laboratory results to environmental conditions, it can be assured that the material is biodegradable and that it is much less persistent in the environment than any other plastic.
Of course, the idea is not to deliberately release it into the environment, but it is good to know that if a plastic of this type unintentionally reaches the environment it can be degraded in a few months and not in dozens of years, as happens with conventional petroleum-derived plastics.
Well friends, let's hope that this research continues to advance and we will soon find a viable solution to replace the commonly used plastics that have polluted the environment so much. See you next time!
Marcel Eck, Simon Timm Schwab, Taylor Frederick Nelson, Katrin Wurst, Steffen Iberl, David Schleheck, Christoph Link, Glauco Battagliarin, Stefan Mecking (2022). Biodegradable high density polyethylene-like material. Angewandte Chemie International Edition.
