Enzymes to make plastic compostable

To date, biodegradable plastic (article in German) is not as environmentally friendly as anticipated. Not even in industrial composting facilities does it decompose sufficiently. Let alone in your household compost. Now, however, a team led by materials scientist Ting Xu of the University of California, Berkeley, claims to have developed a plastic that is truly compostable. This is owed to embedded enzyme particles. As soon as they’re activated, they degrade the plastic almost completely into its components. The team published the results in «Nature» magazine.

Already during production of the plastic, the specially developed enzyme is embedded in the material as tiny nanoparticles. A decisive advance in their development is a protective shell that covers the enzymes and prevents them from decaying prematurely.

The researchers tested their method on two biodegradable types of plastic – polyesters polycaprolactone (PCL) and polylactides (PLA). Heated tap water was enough to destroy them. The water dissolves the protective shell of the enzymes. Once released, they almost completely degrade the PCL within one day at 40 degrees Celsius and the PLA after six days in a 50-degree Celsius water bath. These conditions are also the conditions at professional composting plants. According to first tests in these composting plants, the material disappeared after a comparable period of time. The lactic acid produced by the degradation of PLA could serve as a nutrient for microbes in the compost. The finely dispersed enzyme also ensures that the plastic is completely broken down and doesn’t disintegrate into microplastics.

However, if the plastic is only exposed to low levels of moisture or heat in everyday use, it remains stable. Xu and her team proved that even after three months in 37-degree Celsius water, the plastic had not significantly dissolved. PLA is often used in packaging, It’s also a frequently used material in 3D printers. PCL is used primarily in the medical sector, for example in medicines and dressing materials. In theory, there should be nothing in the way of applying the same technique to other plastics.

The team is currently working on the modification of the protective shells. One goal is to stop plastic degradation at a certain point so that the plastic isn’t completely destroyed, but can be remelted and recycled.

Spektrum der Wissenschaft

We’re a partner of «Spektrum der Wissenschaft» (link in German) and strive to make scientific information better available to you. Follow Spektrum der Wissenschaft if you like the articles.