Self-healing plastic becomes biodegradable
Konstanz chemists develop mineral plastics with numerous positive properties from sustainable basic building blocks and, together with biologists, demonstrate the material's excellent microbiological degradability.
Imagine a plastic like this: harder than common plastics, non-flammable, and even with self-healing properties. But that is not all! It can be produced at room temperature in water, which is very energy-efficient and does not require toxic solvents. Before hardening, you can shape the plastic in any way you want – like chewing gum. By adding water, it can also be converted back to its "chewing gum" form at any time, reshaped and thus recycled as often as desired.
Is that impossible? No, it is not! In 2016, the research team around Konstanz chemist Helmut Cölfen presented just such a material – a mineral plastic. However, even though the plastic, with its novel manufacturing process and outstanding material properties, has since attracted great interest from industry, it still had a crucial shortcoming from the Konstanz chemists' point of view: due to its chemical composition, it was difficult to biodegrade.
A new ingredient for greater environmental compatibility
"Previously, we used polyacrylic acid to produce our mineral plastic. Chemically, this acid has the same backbone as polyethylene, which is known to cause major problems in the environment because it is hardly biodegradable", explains Cölfen. The research team led by Cölfen and Ilesha Avasthi, a postdoc in Cölfen's lab, therefore set to work looking for an alternative basic building block to develop an environmentally compatible mineral plastic that retains the intriguing properties of the original material. And they found what they were looking for.
In their current publication in the journal Small Methods, the Konstanz chemists present the next generation of their mineral plastic. Instead of petroleum-based ingredients such as polyacrylic acid, they now use polyglutamic acid. This natural biopolymer is readily available in large quantities and can even be obtained sustainably, for example from biotechnological production using microorganisms. A variety of microorganisms that already exist in the environment can degrade polyglutamic acid.
"Our new mineral plastic has the same positive properties as the previous one, but has the decisive advantage that its basic building block – polyglutamic acid – can be produced with the help of microorganisms and is completely biodegradable", says Helmut Cölfen.
Support from biologists
In order to prove that this biodegradability also applies to the new mineral plastic itself and not just to its individual components, the chemists enlisted the support of David Schleheck and postdoc Harry Lerner from the Department of Biology at the University of Konstanz. "Helmut Cölfen has created a new type of mineral plastic in his laboratory, and our task now was to make it disappear again with the help of microorganisms", says Schleheck with a smile.
In degradation experiments, the biologists were able to show that microorganisms found in forest soils, for example, began metabolizing the mineral plastic after just a few days. After only 32 days, the microorganisms had completely degraded the plastic. So the researchers have actually succeeded in making the mineral plastic with all its positive material properties now also sustainable and biodegradable.
Key facts:
- Original publication: I. Avasthi, H. Lerner, J. Grings, C. Gräber, D. Schleheck & H. Cölfen (2023) Biodegradable Mineral Plastics. Small Methods; doi: 10.1002/smtd.202300575
- Konstanz study presents sustainable and biodegradable mineral plastic
- Mineral plastic is harder than common plastics, non-flammable and self-healing
- Collaboration project of the Departments of Chemistry and Biology at the University of Konstanz
- Funding: Carl Zeiss Foundation (INPEW project)
Note to editors:
You can download images here:
Link: https://www.uni-konstanz.de/fileadmin/pi/fileserver/2023/selbstheilender_kunststoff_sem1.jpg
Caption: Scanning electron microscope image of the new mineral plastic.
Image: © Avasthi et al.; https://doi.org/10.1002/smtd.202300575; licence: CC BY 4.0
Link: https://www.uni-konstanz.de/fileadmin/pi/fileserver/2023/selbstheilender_kunststoff_Interactions.jpg
Caption: Schematic image of the interactions in mineral plastic. The curved black line corresponds to the polyglutamic acid backbone of the mineral plastic.
Image: © Avasthi et al.; https://doi.org/10.1002/smtd.202300575; licence: CC BY 4.0
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JOURNAL
Small Methods
ARTICLE TITLE
Biodegradable Mineral Plastics
ARTICLE PUBLICATION DATE
Polystyrene upcycling
Recovering valuable chemical building blocks from polystyrene waste
Peer-Reviewed PublicationPolystyrene, the main material in plastic tableware and insulating materials, is a widely used polymer but is currently difficult to recycle. Reporting in the journal Angewandte Chemie, a team of US researchers have now developed a thermochemical approach, making it possible to recover valuable chemicals from polystyrene waste in a simple two-step process. This new approach could enable the recycling of insulating and packaging materials for a truly circular plastics economy.
The newly developed “Degradation Upcycling” (Deg-Up for short) makes it possible to produce a wide array of highly valuable aromatic chemicals to be produced from polystyrene waste, as explained by Guoliang Liu and co-authors from Virginia Tech in Blacksburg, USA, explain. The process involves a two-step cascade: in a first step, polystyrene is broken down to give benzene as main degradation product, and in a second step this benzene product is chemically modified in the same reactor. The process gives rise to benzene derivatives, covering many important substances for the cosmetics and pharmaceuticals industries.
Methods for breaking down polystyrene into benzene usually require expensive catalysts, are energy-intensive, or produce a complex mixture of products. Liu and colleagues’ new thermochemical method uses inexpensive aluminum chloride catalysts and can be performed in reactors at a moderate 80 °C (ca. 180 °F). Another advantage of their method is the clever use of the solvent, benzene. “Only the amount of benzene recovered from the polymer is converted into the desired chemical. Unused solvent can be recycled to process more polymer feed,” Liu says.
As a proof of concept, the team dissolved various types of polystyrene waste, such as packing peanuts and plastic utensils, in benzene, and heated the mixture in a reactor under air-free conditions with aluminum chloride as the only reagent. The liquid product, consisting primarily of benzene, could be used directly to obtain the desired value-added chemicals in high yield and with high selectivity.
For example, by adding the reagent acetyl chloride, the team obtained acetophenone, an important chemical in the cosmetics and pharmaceuticals industries. By adding the related reagent oxalyl chloride, the team obtained benzophenone, a common ingredient in sunscreen products and plastic additives. In addition, sulfur-containing aromatics, some of which are used as high-performance solvents in the polymer industry, were produced with a high degree of selectivity from polystyrene waste.
The goal of this new chemical upcycling method is to recycle large volumes of polystyrene waste into value-added chemicals for other industrial processes. Having a low density, polystyrene insulating materials are not well-suited to mechanical recycling, i.e., the process of sorting, shredding, and transportation of materials for the profitable manufacture of new products. The Deg-Up process described here, on the other hand, is robust, tolerant of contamination, and suitable as a platform for chemical upcycling of large-volume polystyrene waste.
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About the Author
Guolinang (Greg) Liu is an Associate Professor at the Department of Chemistry, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, VA, USA. His research group envisions that smartly designed organic polymers and inorganic nanomaterials can be integrated to create novel materials with unique collective emergent properties, with huge implications for sustainable energy and environmental science and technology.
JOURNAL
Angewandte Chemie International Edition
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
A Generic Platform for Upcycling Polystyrene to Aryl Ketones and Organosulfur Compounds
COI STATEMENT
The authors have filed a patent based upon this work.
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