Researchers look to nature to develop sustainable polycarbonate

Conventional petroleum-based polycarbonate today is made using use BPA (banned from use in baby bottles) and highly toxic phosgene, used as a chemical weapon in World War One.

Dr Antoine Buchard, Whorrod Research Fellow in the University’s Department of Chemistry, and his team at the Centre for Sustainable Chemical Technologies, have now successfully created a much safer, more sustainable alternative which adds carbon dioxide to the sugar at low pressures and at room temperature.

“Our process uses carbon dioxide instead of the highly toxic chemical phosgene, and produces a plastic that is free from BPA, so not only is the plastic safer, but the manufacture process is cleaner too,” he said.

The resulting plastic has similar physical properties to those derived from petrochemicals, being strong, transparent and scratch-resistant. The crucial difference is that they can be degraded back into carbon dioxide and sugar using the enzymes found in soil bacteria.
The new BPA-free plastic could potentially replace current polycarbonates in items such as baby bottles and food containers, and since the plastic is bio-compatible, it could also be used for medical implants or as scaffolds for growing tissues or organs for transplant.
Taking nature as their inspiration, the researchers hit on the idea of using the sugar found in DNA called thymidine as a building block to make the novel polycarbonate plastic.

PhD student and first author of the articles, Georgina Gregory, explained: “Thymidine is one of the units that makes up DNA. Because it is already present in the body, it means this plastic will be bio-compatible and can be used safely for tissue engineering applications.

“The properties of this new plastic can be fine-tuned by tweaking the chemical structure – for example we can make the plastic positively charged so that cells can stick to it, making it useful as a scaffold for tissue engineering.” Such tissue engineering work has already started in collaboration with Dr Ram Sharma from Chemical Engineering, also part of the CSCT.

The researchers have also looked at using other sugars such as ribose and mannose.
As Dr Buchard pointed out: “Chemists have 100 years’ experience with using petrochemicals as a raw material so we need to start again using renewable feedstocks like sugars as a base for synthetic but sustainable materials. It’s early days, but the future looks promising.”

The Bath research team published their work in a series of articles in the journals Polymer Chemistry and Macromolecules.

This work was supported by Roger and Sue Whorrod (Fellowship to Dr Buchard), EPSRC (Centre for Doctoral Training in Sustainable Chemical Technologies), University of Bath Alumni Fund and a Royal Society research Grant.

Diagram of the process:
The new process converts sugar to plastic using carbon dioxide gas. Credit: Georgina Gregory