‘Living plastic’ can digest itself

US researchers have developed a new form of biodegradable plastic where dormant bacterial spores are prompted to ‘digest’ the material at the end of its lifecycle.

It’s the latest in a growing suite of materials research where the digestive abilities of microbes are being harnessed to combat ever-growing plastic waste.

A recent study showed that for every 1% increase in plastic production, environmental waste grows proportionally.

Developed by the University of California San Diego, the biodegradable polyurethane thermoplastic (used to make items like shoes, pillows, and car parts) contains Bacillus subtilis spores that germinate when exposed to ground nutrients and begin to eat away at its plastic housing. The results are published in the journal Nature Communications.

The dormant spores can survive within the plastic for extended periods until the plastic is added to the compost pile, prompting their awakening. Thanks to a protein ‘shield’ encasing them, the bacterial spores can survive the harshest environmental conditions.

That’s why feeding the spores into a plastic extruder with thermoplastic polyurethane pellets is possible. These two feedstocks are melted together at 135°C, but the shield ensures the bacteria survive and can be activated at the end of the plastic product’s life.

“It’s an inherent property of these bacteria,” says Professor Jon Pokorski, a nanoengineer at UC San Diego. “We took a few strains and evaluated their ability to use TPUs as a sole carbon source, then picked the one that grew the best.”

Once added to compost, the spores germinated and were able to degrade 90% of the plastic within 5 months when exposed to water. This included within a sterile composted environment, showing that other microbes aren’t required to achieve the decomposition.

While efforts are underway to enact a global plastics treaty and reduce the production of plastics overall, the development of a self-digesting polyurethane could be a small but positive step forward, given most materials made from the product are unrecyclable and largely end up in landfill.

“Our material breaks down even without the presence of additional microbes,” said Pokorski.

“Chances are, most of these plastics will likely not end up in microbially rich composting facilities. So this ability to self-degrade in a microbe-free environment makes our technology more versatile.”

Adding bacterial spores to the polyurethane was found to improve the mechanical strength of the final product as well.

The researchers anticipate testing their techniques with other forms of plastic to see whether any strains of bacteria demonstrate similar properties.