They developed a three-step process to make PU. First, the yellow-coloured fish oil derived from Atlantic salmon waste is epoxidised using hydrogen peroxide. The epoxides are then reacted with carbon dioxide, and subsequently reacted with an amine, producing a non-isocyanate polyurethane.
‘We thought that if we used an amine from a biological source, we could make the process more sustainable,’ Kerton said. By using commercially available phenalkamines derived from cashew nut shell waste, the result was a red-coloured PU film. The process also works successfully with amino acids, including asparagine.
The new material’s biodegradability was also studied. Electron microscope images show that the surface of the polymer is smooth, but if they are placed in water, they swell and holes start to appear on the surface. Bacteria and fungi start to grow on it, too. Adding a lipase enzyme accelerated the process. ‘The material appears to be more degradable [than regular polyurethane], and we are excited about the opportunities,’ Kerton said.
Its practical applications are as yet unclear. ‘A colleague suggested that the red colour from the cashew shell amine might make them good for filters for different light tones,’ she said. ‘It would be interesting to see whether, even if they are not 100% compatible with water, would they be good for food packaging and wound dressings?’ She has also been asked whether they might be useful for mopping up oil from seawater.
They are still in the early stages of characterising its mechanical properties, and investigating its biodegradability further. ‘The largest piece we have made so far is a film 2 or 3 cm square, and we haven’t yet tried to use it in a specific application,’ Kerton said. ‘We are excited to share our technology with others who have great ideas for applications.’
The work was presented at the online Spring 2021 American Chemical Society meeting.