UvA chemists develop new type of bio-based plastic: “Strong, recyclable and biodegradable”
Plastics that are only used once are made from materials that will float around in nature for hundreds of years. UvA chemists have now developed a strong, heat-resistant plastic that breaks down in the nature after six months. “It’s a different mindset, but plastics with an expiration date make a lot more sense.”
“The combination of good physical properties such as strength, heat resistance, and biodegradability are what make the plastic so interesting,” chemist Gert-Jan Gruter says of the new plastic PISOX, which he has been developing over the past five years with his research group Industrial Sustainable Chemistry. “Such a material did not yet exist.”
PISOX is one of the unexpected outcomes of the five-year research project RIBIPOL, funded by NWO, chemical company Avantium, and toy manufacturer Lego to develop new pathways for strong, wear-resistant, and recyclable plastics from renewable raw materials such as biomass or CO2.
In Dutch nature, the new plastic breaks down into CO2 within six months. Unlike “ordinary” biodegradable plastics, which only break down when they come into contact with fungi and bacteria, PISOX also breaks down when it comes into contact with water. This does not have to involve a lot of water. Even water contained in the air can initiate that reaction after just a few months.
Researchers can set the shelf life of the plastic by substituting some of the ingredients. PISOX is a polyester, which can be thought of as a long beaded chain composed of alternating oxalic acid and an alcohol (isosorbide). The oxalic acid reacts fairly easily with water, so in general, the more oxalic acid in the plastic, the faster it breaks down with water.
The plastic can also be completely chemically recycled. Unlike mechanical recycling, where plastics are melted down to make a new, often lower-value product, chemical recycling reduces the polymer chain to its original building blocks, from which new polyesters can be made. Says Gruter: “Chemical recycling back to the building blocks is only possible with certain types of plastics, especially polyesters, such as PISOX and PET. With many other plastic families - such as the polyolefins, plastics like polythene (PE), polypropylene (PP) and polyvinyl chloride (PVC) from which all kinds of materials are made from pipes to beer crates and slides - this does not work.”
Mussel banks
PISOX plastic breaks down even faster in the sea, although it still takes several months. This is an advantage, according to Gruter, because most biodegradable plastics do not break down specifically in seawater. That makes the material ideally suited as an attachment point for mussel beds or vegetation on the sea floor or mud flats. Once the mussels have grown, the plastic structure then disappears on its own.
The researchers are also already spinning fibers from the plastic for cloth, which could be used for example to reinforce the seabed for some time against coastal erosion. Coffins, such as the ones the Loop Biotech company makes from mycelium, could also be made from the new plastic. Gruter says: “For all materials with finite applications, the new plastic is very suitable.”
The material could also be used as packaging material. “Packaging with an expiration date requires a different mindset,” says Gruter, “but if you think about it, it’s quite logical. Why would you design a material that will last for two hundred years for an application that we only use for a very short time?”
Unlike most plastics made from fossil fuel products like petroleum, PISOX is produced in part from CO2. In fact, the oxalic acid in PISOX can be made from carbon dioxide, by combining two CO2 molecules using electricity. “This process is interesting for many industrial companies because it can give a company a negative footprint by storing CO2 in a product. In addition to storing it, using CO2 for new products is another way to quickly reduce its levels in the atmosphere.
Lego
Another plastic that could come in handy for toy manufacturer Lego has also emerged from the research project. Unlike PISOX, this plastic is not biodegradable, since the blocks should last for generations. It is, however, recyclable. Lego is optimistic about the new material and wants to explore it further. The first step is to scale up production to 100 kilograms to test more of the properties and processing. The material could also be used for many other sustainable applications, such as reusable water bottles.
Companies from the industry are interested in both new plastics, although Gruter does not yet want to disclose any names. One advantage of scaling up is that production could take place in existing PET production facilities. The plastic is not yet profitable, as production on a scale of 100 kilograms still costs hundreds of euros per kilogram. But on an industrial scale, the plastic could compete with plastics already on the market, such as nylon and ABS, Gruter said.
