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New plastic 'turns into compost as quickly as a banana peel'

These bioplastics are made from powdered blue-green cyanobacteria cells, otherwise known as spirulina
UW materials science and engineering doctoral student Mallory Parker works with the new bioplastic. (Mark Stone/University of Washington)

A new bioplastic turns into compost as quickly as a banana peel, and leaves no microplastic behind.

The new bioplastic deals with a problem of bio-based plastics, which usually have to be processed in commercial composting facilities, say the University of Washington (UW) researchers.

The new plastics look and feel like single-use plastics derived from petroleum – in other words, like the plastic we use today.

The new bioplastics are made entirely from powdered blue-green cyanobacteria cells, otherwise known as spirulina.

The team used heat and pressure to form the spirulina powder into various shapes, the same processing technique used to create normal plastics.

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Senior author Eleftheria Roumeli, UW assistant professor of materials science and engineering said, "We were motivated to create bioplastics that are both bio-derived and biodegradable in our backyards, while also being processable, scalable and recyclable," said.

"The bioplastics we have developed, using only spirulina, not only have a degradation profile similar to organic waste, but also are on average 10 times stronger and stiffer than previously reported spirulina bioplastics.

"These properties open up new possibilities for the practical application of spirulina-based plastics in various industries, including disposable food packaging or household plastics, such as bottles or trays."

Spirulina can easily be cultivated on large scales because people already use it for various foods and cosmetics.

In addition, spirulina cells sequester carbon dioxide as they grow, making this biomass a carbon-neutral, or potentially carbon-negative, feedstock for plastics.

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Lead author Hareesh Iyer, a UW materials science and engineering doctoral student, said, "Spirulina also has unique fire-resistant properties.

"When exposed to fire, it instantly self-extinguishes, unlike many traditional plastics that either combust or melt. This fire-resistant characteristic makes spirulina-based plastics advantageous for applications where traditional plastics may not be suitable due to their flammability.

"One example could be plastic racks in data centres because the systems that are used to keep the servers cool can get very hot."

Creating plastic products often involves a process that uses heat and pressure to shape the plastic into a desired shape. The UW team took a similar approach with their bioplastics.

These bioplastics are not quite ready to be scaled up for industrial usage. For example, while these materials are strong, they are still fairly brittle. Another challenge is that they are sensitive to water.

The newly developed materials are also recyclable.

"Biodegradation is not our preferred end-of-life scenario," Roumeli said. "Our spirulina bioplastics are recyclable through mechanical recycling, which is very accessible.

"People don't often recycle plastics, however, so it's an added bonus that our bioplastics do degrade quickly in the environment"

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